Co-reporter:Mingshan Zhu, Sooyeon Kim, Liang Mao, Mamoru Fujitsuka, Junying Zhang, Xinchen Wang, and Tetsuro Majima
Journal of the American Chemical Society September 20, 2017 Volume 139(Issue 37) pp:13234-13234
Publication Date(Web):August 31, 2017
DOI:10.1021/jacs.7b08416
In the drive toward green and sustainable chemistry, exploring efficient and stable metal-free photocatalysts with broadband solar absorption from the UV to near-infrared region for the photoreduction of water to H2 remains a big challenge. To this end, a binary nanohybrid (BP/CN) of two-dimensional (2D) black phosphorus (BP) and graphitic carbon nitride (CN) was designed and used as a metal-free photocatalyst for the first time. During irradiation of BP/CN in water with >420 and >780 nm light, solid H2 gas was generated, respectively. Owing to the interfacial interaction between BP and CN, efficient charge transfer occurred, thereby enhancing the photocatalytic performance. The efficient charge-trapping and transfer processes were thoroughly investigated with time-resolved diffuse reflectance spectroscopic measurement. The present results show that BP/CN is a metal-free photocatalyst for artificial photosynthesis and renewable energy conversion.
Co-reporter:Ossama Elbanna, Mamoru Fujitsuka, and Tetsuro Majima
ACS Applied Materials & Interfaces October 11, 2017 Volume 9(Issue 40) pp:34844-34844
Publication Date(Web):September 15, 2017
DOI:10.1021/acsami.7b08548
The photocatalytic performance of graphitic carbon nitride (g-C3N4) has been limited to low efficiency due to fast charge recombination. Here, we constructed g-C3N4 nanosheets/TiO2 mesocrystals metal-free composite (g-C3N4 NS/TMC) to promote the efficiency of charge separation. The photocatalytic H2 evolution experiments indicate that coupling g-C3N4 NS with TMC increases photogenerated charge carriers in g-C3N4 NS/TMC composite due to efficient charge separation. g-C3N4 NS (31 wt %)/TMC shows the highest photocatalytic activity and the corresponding H2 evolution rate is 3.6 μ mol h–1. This value is 20 times larger than that of g-C3N4 NS without any noble metal cocatalyst under visible-light irradiation (λ > 420 nm). The photocatalytic activity of g-C3N4 NS/TMC (3.6 μmol h–1) is 7 times higher than that of g-C3N4 NS/P25 (0.5 μ mol h–1), confirming the importance of strong interface interaction between two-dimensional g-C3N4 NS and plate-shape TMC. Femtosecond time-resolved diffuse reflectance (fs-TDR) was employed to study the fundamental photophysical processes of bulk g-C3N4, g-C3N4 NS, and g-C3N4/TMC composite which are essential to explain the photocatalytic activity. Using fs-TDR, we demonstrate that the photocatalytic activity depends on the increased driving force for photoinduced electron transfer and a higher percentage of photogenerated charges.Keywords: charge carriers dynamics; femtosecond time-resolved diffuse reflectance; graphitic carbon nitride; hydrogen evolution; TiO2 mesocystals; visible-light photocatalysis;
Co-reporter:Mamoru Fujitsuka, Sachiko Tojo, Toru Amaya, Toshikazu Hirao, and Tetsuro Majima
The Journal of Physical Chemistry A July 6, 2017 Volume 121(Issue 26) pp:4902-4902
Publication Date(Web):June 14, 2017
DOI:10.1021/acs.jpca.7b03700
Strained polyaromatic carbon molecules exhibit interesting properties owing to enhanced interactions between p orbitals of sp2 carbons; sumanene (SUM) is one of these bowl-shaped π-conjugated molecules (π-bowls). In the present study, the radical cation and radical anion of SUM were characterized by radiation chemical methods, that is, pulse radiolysis and γ-ray radiolysis. Absorption spectra of the SUM radical cation and radical anion in a wide spectral region ranging from the visible to near-IR were successfully obtained. Absorption spectra of the SUM radical cation and radical anion are similar in shape to those of the corresponding species of triphenylene (TP), which possesses a planar structure and the same π-electron system as SUM. However, the SUM radical anion showed lower peak shifts than the TP radical anion. Theoretical calculations revealed that the MOs responsible for the electronic transitions of the SUM radical anion are different from those of the TP radical anion, in contrast to the radical cations. These results demonstrate that the strains in the molecular geometries affect the electronic transitions of radical ions.
Co-reporter:Zaizhu Lou;Mamoru Fujitsuka
The Journal of Physical Chemistry Letters February 16, 2017 Volume 8(Issue 4) pp:844-849
Publication Date(Web):February 3, 2017
DOI:10.1021/acs.jpclett.6b03045
Two-dimensional Au-nanoprism/reduced graphene oxide (rGO)/Pt-nanoframe was synthesized as plasmonic photocatalyt, exhibiting activity of photocatalytic hydrogen generation greater than those of Au-nanorod/rGO/Pt-nanoframe and metallic plasmonic photocatalyst Pt–Au. The single-particle plasmonic photoluminescence study demonstrated that Au-nanorod has only a longitudinal plasmon resonance mode for hot electron transfer to rGO, while Au-nanoprism has in-plane dipole and multipole surface plasmon resonance modes for hot electron transfer, leading to highly efficient charge separation for hydrogen generation.
Co-reporter:Zaizhu Lou, Sooyeon Kim, Peng Zhang, Xiaowei Shi, Mamoru FujitsukaTetsuro Majima
ACS Nano 2017 Volume 11(Issue 1) pp:
Publication Date(Web):December 22, 2016
DOI:10.1021/acsnano.6b07581
In situ etching of single Au triangular nanoprism (TNP) was successfully monitored by the plasmonic photoluminescence (PL) spectra using single-particle microscopy, which provides clear results to understand the geometric and anisotropic dependence of surface plasmon resonance in Au nanostructures. Various Au nanostructures (TNP, obtuse TNP (O-TNP) and nanodisk) were obtained to synthesize anisotropic Pt–Au as plasmonic photocatalyts for hydrogen generation. Single-particle PL spectra and finite-difference time-domain simulations demonstrate that the Pt-edged Au O-TNP has larger tip area and higher plasmon enhanced electrical field for hot electron transfer and charge separation, leading to more efficient photocatalytic hydrogen generation.Keywords: Au triangular nanoprism; hydrogen generation; in situ reaction; plasmonic photocatalysis; single-particle spectroscopy;
Co-reporter:Chao Lu, Mamoru FujitsukaTetsuro Majima
The Journal of Physical Chemistry C 2017 Volume 121(Issue 1) pp:
Publication Date(Web):December 13, 2016
DOI:10.1021/acs.jpcc.6b07904
A new series of mesitylene-linked oligothiophenes (nT, n is the number of thiophene units), including 2T-M, 3T-M, 4T-M, 4T-M-2T, and 4T-M-3T, was prepared to investigate the intramolecular hole transfer (HT) from the excited radical cation for the first time. The results of spectroscopic and theoretical studies indicated that mesitylene acts as a spacer minimizing the perturbation to the thiophene π-conjugation and increasing the stability of nT radical cations (nT•+). Femtosecond laser flash photolysis was applied to the FeCl3-oxidized 4T•+-M, 4T•+-M-2T, and 4T•+-M-3T. Upon 670 nm laser excitation, the transient absorption spectra of 4T•+-M showed the existence of two species as the D1 and D0hot states. The intramolecular HT processes from excited 4T•+ with the time constants of 1.6 and 0.8 ps were observed upon excitation of 4T•+-M-2T and 4T•+-M-3T, respectively. This is the first capture of such ultrafast processes with the subsequent back HT from the ground-state 2T•+ or 3T•+ in nT assemblies. The current findings indicated an accelerated migration of photocarriers (polarons) in thiophene-based p-type semiconductor materials upon irradiation and provided a fresh viewpoint to understand the successive HT in polythiophenes for various organic molecular devices.
Co-reporter:Dr. Peng Zhang;Tomoya Ochi; Mamoru Fujitsuka; Yasuhiro Kobori; Tetsuro Majima; Takashi Tachikawa
Angewandte Chemie International Edition 2017 Volume 56(Issue 19) pp:5299-5303
Publication Date(Web):2017/05/02
DOI:10.1002/anie.201702223
AbstractThe higher-order structures of semiconductor-based photocatalysts play crucial roles in their physicochemical properties for efficient light-to-energy conversion. A novel perovskite SrTiO3 mesocrystal superstructure with well-defined orientation of assembled cubic nanocrystals was synthesized by topotactic epitaxy from TiO2 mesocrystals through a facile hydrothermal treatment. The SrTiO3 mesocrystal exhibits three times the efficiency for the hydrogen evolution of conventional disordered systems in alkaline aqueous solution. It also exhibits a high quantum yield of 6.7 % at 360 nm in overall water splitting and even good durability up to 1 day. Temporal and spatial spectroscopic observations revealed that the synergy of the efficient electron flow along the internal nanocube network and efficient collection at the larger external cubes produces remarkably long-lived charges for enhanced photocatalysis.
Co-reporter:Peng Zhang;Sooyeon Kim;Mamoru Fujitsuka
Chemical Communications 2017 vol. 53(Issue 38) pp:5306-5309
Publication Date(Web):2017/05/09
DOI:10.1039/C7CC01894K
Herein, we investigated that sheet-like TiO2 mesocrystals with controllable nanothorns on the {101} facet during the topotactic transformation exhibit facet-induced charge separation and anisotropic electron flow, realizing the superior facet-dependent photocatalysis in solar energy conversion.
Co-reporter:Chao Lu, Mamoru FujitsukaAkira Sugimoto, Tetsuro Majima
The Journal of Physical Chemistry C 2017 Volume 121(Issue 8) pp:
Publication Date(Web):February 7, 2017
DOI:10.1021/acs.jpcc.7b00970
Intramolecular electron transfer (ET) processes in the excited aromatic diimide bis(radical anion)s (ADI•–*–ADI′•–) were systematically investigated by applying femtosecond laser flash photolysis to bis(radical anion)s of naphthalenediimide (NDI) and perylenediimide (PDI), including NDI•––m-NDI•–, NDI•––p-NDI•–, PDI•––m-PDI•–, and NDI•––m-PDI•– (m and p indicate the substitution positions). The excitation of NDI•––m-NDI•– and NDI•––p-NDI•– initiated disproportionation reactions generating NDI and NDI2– with different ET rate constants. For the first time, the dual characteristics of ADI•–* were confirmed upon selective excitation of NDI•––m-PDI•–: NDI•–* was unambiguously demonstrated to function as an electron donor in NDI•–*–m-PDI•–, whereas PDI•–* acted as an electron acceptor in NDI•––m-PDI•–* because of the energetically preferable production of NDI–m-PDI2–. The relationship between the ET rate constants and driving forces in ADI•–*–ADI′•– can be reasonably analyzed by using the Marcus theory. The current findings provide a new viewpoint regarding the bipolaron-generating nature of ADI•–*–ADI′•– and facilitate simulating various types of photocarrier migration in the densely charged regions of homo- and heterogeneous n-type semiconductor materials upon irradiation.
Co-reporter:Xiaoyan Cai, Junying Zhang, Mamoru Fujitsuka, Tetsuro Majima
Applied Catalysis B: Environmental 2017 Volume 202(Volume 202) pp:
Publication Date(Web):1 March 2017
DOI:10.1016/j.apcatb.2016.09.021
•Doping perovskite structured LTO with nitrogen through facile hydrothermal method.•Hybridization of two kinds of 2D layered materials (NLTO and g-C3N4 nanosheets) with enhanced the visible-light-driven photocatalytic activity.•Formation of large scale of type II heterojunction by large interfacial area between 2D layered g-C3N4/NLTO composite with efficient charge transfer.•Formation of ultrathin g-C3N4/NLTO heterostructure with shortened charge transport distance.•Exploration of charge transfer dynamics on g-C3N4/NLTO composite using the femtosecond time-resolved diffused reflectance measurement.Perovskite-type La2Ti2O7 (LTO), having a layered structure and the separated H2 and O2 evolution sites, is attractive as an efficient photocatalyst. However, the photocatalytic activity is often limited by the poor electron mobility. This problem can be conquered by hybridization with materials having efficient properties for the visible light absorption and charge carrier transport. Here, we report a two-dimensional (2D) layered composite hybridized by approximately 2 nm thick graphitic C3N4 nanosheets (g-C3N4) and 7 nm thick nitrogen doped LTO nanosheets (NLTO) (g-C3N4/NLTO), in which g-C3N4 and NLTO act as hole receptor and electron conductor, respectively. g-C3N4/NLTO exhibited high photocatalytic activities for H2 production via water splitting and dye degradation under the UV and visible light irradiation, due to the interfacial charge transfer between g-C3N4 and NLTO. The electrochemical measurement showed the type II band alignment with favorable charge transfer from g-C3N4 to NLTO. The 2D architecture with a maximized interfacial area allows efficient charge separation with a short interfacial distance. This efficient interfacial charge transfer is further elucidated from monitoring of charge separation and trapping processes using the femtosecond time-resolved diffused reflectance (TDR) measurement.Download high-res image (169KB)Download full-size imageThe large interfacial area of 2D layered g-C3N4/NLTO composite results in sufficient interface for efficient charge transfer to generate an excellent type II heterojunction.
Co-reporter:Mingshan Zhu, Yasuko Osakada, Sooyeon Kim, Mamoru Fujitsuka, Tetsuro Majima
Applied Catalysis B: Environmental 2017 Volume 217(Volume 217) pp:
Publication Date(Web):15 November 2017
DOI:10.1016/j.apcatb.2017.06.002
•2D black phosphorus (BP) nanoflakes with a broad spectrum are synthesized.•BP/Pt/RGO nanoflakes harness visible and NIR light for photocatalytic H2 evolution.•AQEs are as high as 8.7% at 420 nm (visible) and 1.5% at 780 nm (NIR).•BP/Pt/RGO acts as visible and NIR-driven photocatalyst in solar energy conversion.The search for active photocatalysts that directly split water to hydrogen (H2) under visible and near-infrared (NIR) light irradiation remains one of the most challenging tasks for solar energy utilization. Here we report that two dimensional (2D) black phosphorus (BP) nanoflakes can harness visible and NIR light for H2 evolution. In the presence of reduced graphene oxide and Pt nanoparticles, ca. 5.13 and 1.26 μmol H2 were obtained after excited BP nanoflakes under >420 nm and >780 nm irradiation for 4 h, respectively. The apparent quantum efficiencies (AQEs) were as high as approximately 8.7% at 420 ± 5 nm (visible) and 1.5% at 780 ± 5 nm (NIR), respectively. These results indicate that 2D BP can be used as visible- and NIR-activated elemental photocatalyst in artificial photosynthesis and renewable energy conversion.Download high-res image (278KB)Download full-size image
Co-reporter:Ossama Elbanna, Sooyeon Kim, Mamoru Fujitsuka, Tetsuro Majima
Nano Energy 2017 Volume 35(Volume 35) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.nanoen.2017.03.014
•Au NRs/TMC with tunable light harvesting in visible-NIR region has been prepared.•Au NRs/TMC show high photocatalytic activity for H2 production.•Single-particle PL and femtosecond TDR confirm hot electron transfer.•H2 production is due to LSPR of Au NRs inducing efficient charge separation.TiO2 mesocrystals (TMC) have efficient charge transport properties and long-lived charges which cause high photoconductivity and photocatalytic activity. However, TMC have no absorption in the region of visible and near-Infrared (NIR) light. The optical resonance of Au nanorods (NRs) depending mainly on their length and width (aspect ratio) can be used to design panchromatic absorbers, covering most of the useful solar spectrum. Therefore, in this article, Au NRs and TMC composites were prepared by the ligand exchange method to show highly efficient H2 production (924 µmol h−1 g−1) under visible-NIR light irradiation. The efficient H2 production is explained by surface plasmon resonance (SPR) of Au NRs, electron injection to TMC, efficient charge transport in TMC due to the superstructure of TMC and water reduction on TMC. Single-particle confocal fluorescence microscopy and time-resolved diffuse reflectance measurements confirmed the efficient hot electron injection and charge separation from Au NRs with strong SPR to the superstructure of TMC.TiO2 mesocrystals composited with gold nanorods for highly efficient visible-NIR-photocatalytic hydrogen production.Download high-res image (192KB)Download full-size image
Co-reporter:Peng Zhang;Mamoru Fujitsuka
Nanoscale (2009-Present) 2017 vol. 9(Issue 4) pp:1520-1526
Publication Date(Web):2017/01/26
DOI:10.1039/C6NR07740D
Plasmonic nanostructures attracting particular interest in plasmon-induced highly energetic electrons, also known as hot electrons, play a fundamental role in photocatalysis for solar energy conversion. Plasmon-induced hot electron excitation, relaxation, transport, and injection to two-dimensional semiconductors are necessary to clearly understand the efficient plasmon-induced chemical reaction. Herein, we use a plasmonic photocatalyst composed of anisotropic gold nanostructures as the electron donor assembled on two-dimensional molybdenum dichalcogenide, monolayer MoS2, as the electron acceptor in order to unveil the plasmon-induced interfacial hot electron transfer for the hydrogen evolution reaction (HER). Single-particle confocal fluorescence microscopy, computational calculation of finite-difference-time-domain (FDTD) simulation, and time-resolved transient absorption measurements revealed that anisotropic gold nanostructures with strong plasmon resonance exhibit interfacial hot electron transfer to monolayer MoS2, giving the charge separated state with a long lifetime of 800 ps which is responsible for efficient HER. This is the first example to show the plasmon-induced interfacial hot electron transfer from anisotropic Au nanostructures to two-dimensional materials.
Co-reporter:Xiaowei Shi;Mamoru Fujitsuka;Zaizhu Lou;Peng Zhang
Journal of Materials Chemistry A 2017 vol. 5(Issue 20) pp:9671-9681
Publication Date(Web):2017/05/23
DOI:10.1039/C7TA01888F
Visible-light-driven water splitting process is highly attractive for alternative energy utilization, while developing efficient, earth-abundant, and environmentally friendly photocatalysts for hydrogen evolution reaction has remained a major challenge. Herein, heterostructured photocatalysts composed of hollow N-doped TiO2 and g-C3N4 (N-TiO2/g-C3N4) were developed by an in situ impregnation calcination method. N-TiO2 and N-TiO2/g-C3N4 heterostructures with different ratios of N-TiO2 and g-C3N4 were synthesized by simply varying the amount of cyanamide (CY) as the g-C3N4 precursor. Using N-TiO2/g-C3N4 as a H2 evolution photocatalyst, the largest rate of 296.4 μmol g−1 h−1 was obtained under visible light irradiation (λ ≥ 420 nm) without any noble metal co-catalyst, which is 25.8 times larger than that of pure g-C3N4 (11.5 μmol g−1 h−1). Femtosecond time-resolved diffuse reflectance spectroscopy was used to evaluate the lifetime of photogenerated electrons and electron transfer dynamics in N-TiO2/g-C3N4. It is suggested that an additional decay pathway exists for the photogenerated electrons in N-TiO2/g-C3N4, in which N-TiO2 acts as an electron trapping site, leading to higher photocatalytic H2 evolution activity than pure g-C3N4. The present work not only provides a facile method for preparing doped materials and heterostructures with efficient photocatalytic activity, but also deepens the understanding of charge transfer dynamics in heterostructured photocatalysts.
Co-reporter:Xiaoyan Cai;Liang Mao;Junying Zhang;Mingshan Zhu;Mamoru Fujitsuka
Journal of Materials Chemistry A 2017 vol. 5(Issue 21) pp:10442-10449
Publication Date(Web):2017/05/30
DOI:10.1039/C7TA02379K
Formation of surface heterojunctions in photocatalysts through tailoring the exposed crystal facets is an efficient strategy to boost charge separation. In this work, successive surface heterojunctions with large space-charge separation were achieved in a nanostep structured La2Ti2O7 (LTO NSP) single crystal exposed periodically with (010) and (012) facets. The three-dimensional (3D) nanosteps were found to enhance the photocatalytic hydrogen generation performance 35 and 74 times, compared with LTO nanosheets and nanoparticles with the same surface area, respectively. The ultrahigh superficial charge accumulation in LTO NSP verified by surface photovoltage (SPV) measurements suggested the efficient migration of photogenerated charge carriers to the surface. Femtosecond time-resolved diffuse reflectance (TDR) spectroscopy provided direct evidence that the electrons generated from the excited sites of LTO NSP were effectively delivered to the high energy (012) facets and temporarily stored there for further reduction reactions, originating from the successive (010) and (012) surface heterojunctions.
Co-reporter:Mamoru Fujitsuka
Chemical Science (2010-Present) 2017 vol. 8(Issue 3) pp:1752-1762
Publication Date(Web):2017/02/28
DOI:10.1039/C6SC03428D
In the past few decades, charge transfer in DNA has attracted considerable attention from researchers in a wide variety of fields, including bioscience, physical chemistry, and nanotechnology. Charge transfer in DNA has been investigated using various techniques. Among them, time-resolved spectroscopic methods have yielded valuable information on charge transfer dynamics in DNA, providing an important basis for numerical practical applications such as development of new therapy applications and nanomaterials. In DNA, holes and excess electrons act as positive and negative charge carriers, respectively. Although hole transfer dynamics have been investigated in detail, the dynamics of excess electron transfer have only become clearer relatively recently. In the present paper, we summarize studies on the dynamics of hole and excess electron transfer conducted by several groups including our own.
Co-reporter:Xiaowei Shi, Zaizhu Lou, Peng Zhang, Mamoru Fujitsuka, and Tetsuro Majima
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 46) pp:31738
Publication Date(Web):November 2, 2016
DOI:10.1021/acsami.6b12940
Nowadays, how to convert solar energy efficiently to other energies, such as chemical energy, is an important subject. In the present work, gold nanosphere (AuNS) monoencapsulated in TiO2 hollow nanosphere (Au–TiO2) and three-dimensional assembled array of Au–TiO2 (3D-array) were fabricated to carefully explore the multiscattering effect on the photocatalytic activity of H2 generation under simulated solar light and visible light irradiation, respectively. Au–TiO2 with the inner cavity diameter of 176 nm was uniformly synthesized via SiO2 protection method and then was used as building blocks for construction of 3D-array. The 3D-array exhibited a much higher photocatalytic activity of H2 generation (3.5 folds under visible light irradiation, 1.4 folds under solar light irradiation) than Au–TiO2. Single-particle plasmonic photoluminescence measurement and computational simulation of finite difference time domain (FDTD) were performed to elucidate the detailed mechanisms of photocatalysis. It was suggested that the hot electrons generated by AuNS under visible light irradiation play a significant role during the photocatalysis process. The higher activity of 3D-array is due to the elongation of light path length because of the multiscattering in-between Au-TiO2 and the reflection inside of the TiO2 shell. Therefore, the AuNS has more opportunity to absorb light and more hot electrons are expected to be generated through the electron transfer from AuNS to TiO2 shell, leading to an increment in the H2 generation. This result gives us a new perspective of constructing structures for efficient light utilization.Keywords: 3D-assemble array; Au-TiO2; multiscattering; photocatalysis; yolk−shell
Co-reporter:Masaaki Abe, Hiroaki Yamada, Toru Okawara, Mamoru Fujitsuka, Tetsuro Majima, and Yoshio Hisaeda
Inorganic Chemistry 2016 Volume 55(Issue 1) pp:7-9
Publication Date(Web):December 17, 2015
DOI:10.1021/acs.inorgchem.5b02078
Two new porphycenes functionalized with ferrocenyl pendants have been synthesized and characterized spectroscopically and structurally. The porphycene-based emission in porphycene–ferrocene dyads was switched on and off by the reversible control of the ferrocenyl pendant redox states. Transient absorption spectroscopy with a femtosecond laser-pulsed technique has successfully detected the picosecond charge-separated excited state of the dyad upon Q-band excitation of the porphycene ring.
Co-reporter:Sooyeon Kim, Mamoru Fujitsuka, Mikiji Miyata and Tetsuro Majima
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 3) pp:2097-2103
Publication Date(Web):27 Nov 2015
DOI:10.1039/C5CP06541K
Since it was first reported in 2008, great attention has been paid to Si–rhodamine (SiR) because of its far-red to near-infrared (NIR) absorption/fluorescence and suitability for high-resolution in vivo imaging. However, properties of SiR in the excited state have not been reported, even though they are directly related to its fluorescence. In the present study, the properties of SiR monomers in the excited states are thoroughly characterized for the first time. Moreover, by replacing a phenyl moiety of SiR with a 4-(9-anthryl)phenylene group (SiR–An), we prepared H- and J-aggregates of SiR in the aqueous solution, and succeeded in monitoring exciton formation and annihilation in the aggregates. Interestingly, the relative exciton population in the SiR J-aggregate increases as the excitation power becomes stronger, which is unusual considering that the substantial exciton–exciton annihilation process occurs as more excitons are generated. The results obtained in the present study suggest high versatility of SiR not only as a red fluorophore in the cutting-edge microscopic techniques but also as a NIR absorber in the light harvesting system.
Co-reporter:Peng Zhang; Takashi Tachikawa; Mamoru Fujitsuka
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 7) pp:1173-1179
Publication Date(Web):March 10, 2016
DOI:10.1021/acs.jpclett.6b00227
Ti3+ self-doped TiO2 nanocrystals (TNCs) confined with controllable atomic layer deposition (ALD) amorphous layers were developed to provide a novel model of metal–insulator–semiconductor (MIS) photocatalysts for hydrogen generation in the ultraviolet to near-infrared region. Photoexcitation of optimized MIS nanostructures consisting of a metal cocatalyst (Pt), electron tunneling layer (ALD TiO2), and photoactive nonstoichiometric core (Ti3+-doped TNC) exhibited efficient hydrogen generation (52 μmol h–1·g–1), good reusability (16 h), and long-term stability (>7 d). The charge-transfer dynamics were examined using transient absorption spectroscopy to clarify the relationship between the photocatalytic activity and the tunneling effect. Our strategies highlight defect engineering in fabricating MIS photocatalysts with improved charge separation and tailored solar energy conversion properties.
Co-reporter:Shih-Hsun Lin, Mamoru Fujitsuka, and Tetsuro Majima
The Journal of Physical Chemistry B 2016 Volume 120(Issue 4) pp:660-666
Publication Date(Web):January 7, 2016
DOI:10.1021/acs.jpcb.5b10857
The dynamics of excess-electron transfer in DNA has attracted the attention of scientists from all kinds of research fields because of its importance in biological processes. To date, several studies on excess-electron transfer in consecutive adenine (A):thymine (T) sequences in donor–DNA–acceptor systems have been published. However, the reported excess-electron transfer rate constants for consecutive T’s are in the range of 1010–1011 s–1 depending on the photosensitizing electron donor, which provides various driving forces for excess-electron injection into DNA. In this study, we employed a strongly electron-donating photosensitizer, a dimer of 3,4-ethylenedioxythiophene (2E), and an electron acceptor, diphenylacetylene (DPA), to synthesize a series of modified DNA oligomers (2-Tn, n = 3–6) in order to investigate the excess-electron transfer dynamics in these donor–DNA–acceptor systems using femtosecond laser flash photolysis. The relation between the free energy change for charge injection and the excess-electron transfer rate among consecutive T’s provided an intrinsic excess-electron hopping rate constant of (3.8 ± 1.5) × 1010 s–1 in the DNA, which is consistent with the fluctuation frequency of the DNA sugar backbone and bases (3.3 × 1010 s–1). Thus, we discuss the effect of structural fluctuations on the excess-electron hopping in DNA.
Co-reporter:Jungkweon Choi, Cheolhee Yang, Mamoru Fujitsuka, Sachiko Tojo, Hyotcherl Ihee, and Tetsuro Majima
The Journal of Physical Chemistry B 2016 Volume 120(Issue 11) pp:2987-2989
Publication Date(Web):March 1, 2016
DOI:10.1021/acs.jpcb.6b00713
Co-reporter:Dr. Zhaoke Zheng ;Dr. Tetsuro Majima
Angewandte Chemie International Edition 2016 Volume 55( Issue 8) pp:2879-2883
Publication Date(Web):
DOI:10.1002/anie.201511764
Abstract
Surface plasmon resonances of metal nanoparticles have shown significant promise for the use of solar energy to drive catalytic chemical reactions. More importantly, understanding and monitoring such catalytic reactions at single-nanoparticle level is crucial for the study of local reaction processes. Herein, using plasmonic photoluminescence (PL) spectroscopy, we describe a novel sensing method for catalytic ethanol oxidation reactions at the single-nanoparticle level. The Au nanorod monitors the interfacial interaction with ethanol during the catalytic reaction through the PL intensity changes in the single-particle PL spectra. The analysis of energy relaxation of excited electron–hole pairs indicates the relationship between the PL quenching and ethanol oxidation reaction on the single Au nanorod.
Co-reporter:Dr. Zhaoke Zheng ;Dr. Tetsuro Majima
Angewandte Chemie 2016 Volume 128( Issue 8) pp:2929-2933
Publication Date(Web):
DOI:10.1002/ange.201511764
Abstract
Surface plasmon resonances of metal nanoparticles have shown significant promise for the use of solar energy to drive catalytic chemical reactions. More importantly, understanding and monitoring such catalytic reactions at single-nanoparticle level is crucial for the study of local reaction processes. Herein, using plasmonic photoluminescence (PL) spectroscopy, we describe a novel sensing method for catalytic ethanol oxidation reactions at the single-nanoparticle level. The Au nanorod monitors the interfacial interaction with ethanol during the catalytic reaction through the PL intensity changes in the single-particle PL spectra. The analysis of energy relaxation of excited electron–hole pairs indicates the relationship between the PL quenching and ethanol oxidation reaction on the single Au nanorod.
Co-reporter:Chao Lu
The Journal of Physical Chemistry C 2016 Volume 120(Issue 23) pp:12734-12741
Publication Date(Web):May 23, 2016
DOI:10.1021/acs.jpcc.6b02454
Radical anions in the excited states can be treated as stronger reductants than those in the ground states. In this study, the intramolecular electron transfer (ET) processes from the excited perylene-3,4,9,10-tetracarboxydiimide radical anion (PDI•–*) were examined for the first time by applying the femtosecond laser flash photolysis to the dyads of PDI and acceptors (PDI-A). Efficient intramolecular ET from PDI•–* was detected upon the excitation of PDI•–-pyromellitimide (PI) and PDI•–-naphthalenediimide (NDI) because of the sufficient driving forces. In particular, unprecedented ET processes were confirmed in a PDI-PDI dimer. Excitation of PDI•–-PDI gave the shortest PDI•–* lifetime due to the fastest intramolecular ET. Surprisingly, an intramolecular disproportionation reaction generating the dianion of PDI and neutral PDI was confirmed upon the excitation of PDI•–-PDI•–. These processes successfully simulated the photocarrier (polaron and bipolaron) generations in PDI-based n-type semiconducting materials for various organic molecular devices. Comparing the NDI-A and PDI-A dyad systems, the significant difference found in the intramolecular ET rate constants can be explained by the energy required to form the reduced spacer and the distances between the electron donors and acceptors.
Co-reporter:Mamoru Fujitsuka, Takaaki Miyazaki, Chao Lu, Teruo Shinmyozu, and Tetsuro Majima
The Journal of Physical Chemistry A 2016 Volume 120(Issue 8) pp:1184-1189
Publication Date(Web):February 8, 2016
DOI:10.1021/acs.jpca.5b11766
Paracyclophanes (PCPs), which exhibit interesting properties due to their transannular interactions, have been employed as a spacer in various electron transfer (ET) systems. In the present work, we investigated ET processes in dyads and triads containing [2.2]PCP or [3.3]PCP as donors to study their properties in multistep ET processes. The dyad molecules of PCP and 1,8-naphthalimide (NI) as a photosensitizing electron acceptor exhibited charge separation (CS) upon excitation of NI. In addition, triads of NI, PCP, and carbazole showed charge shift after an initial CS, thus confirming multistep ET. In this study, we demonstrated that use of [3.3]PCP in place of [2.2]PCP enhanced the initial CS rate. Lower oxidation potentials and a smaller reorganization energy for [3.3]PCP are shown to be key factors for this enhanced CS rate. Both of these properties are closely related to the strained structure of PCP; hence, the present results demonstrate the importance of strain in ET chemistry.
Co-reporter:Zaizhu Lou, Mamoru Fujitsuka, and Tetsuro Majima
ACS Nano 2016 Volume 10(Issue 6) pp:6299
Publication Date(Web):May 22, 2016
DOI:10.1021/acsnano.6b02494
Three anisotropic Pt-covered, Pt-edged, and Pt-tipped Au triangular nanoprisms (TNPs) were prepared by controlling the overgrowth of Pt as photocatalysts for H2 generation. With strong electric field and more interface for the hot electrons transfer, the H2 generation rate of Pt-edged Au TNPs was 3 and 5 times higher than those of Pt-tipped and Pt-covered Au TNPs. Single-particle photoluminescence (PL) spectra and finite-difference-time-domain (FDTD) simulations demonstrated that dipole surface plasmon resonance (DSPR) of Au TNPs enhanced the hot electrons transfer from Au to Pt leading to H2 generation. SPR bands of Au TNPs depending on the size play an important role on the photocatalytic activity of Pt-edged Au TNPs.Keywords: dipole plasmon resonance; hydrogen generation; plasmonic photocatalysis; Pt−Au triangular nanoprism; single-particle spectroscopy
Co-reporter:Mamoru Fujitsuka, Kamani Satyanarayana, Tien-Yau Luh, Tetsuro Majima
Journal of Photochemistry and Photobiology A: Chemistry 2016 Volume 331() pp:56-59
Publication Date(Web):1 December 2016
DOI:10.1016/j.jphotochem.2015.10.011
•Migration processes of the S1 and T1 states in porphyrin polymers were investigated.•Migration of the S1 was characterized by the time-dependent annihilation model.•Polymers with high Z/E ratio showed fast S–S annihilation.•Fluorescence decay of porphyrin polymers was regulated by the S–T annihilation.In the present paper, we investigated migration processes of the S1 and T1 states in polycyclobutene bearing zinc porphyrin as a pendant group. Transient absorption spectra during femtosecond laser flash photolysis showed a fast decaying component, which can be attributed to singlet–singlet (S–S) annihilation resulted from migration of the S1 state among the porphyrin units. Decay kinetics of the S1 state were well characterized by the time-dependent annihilation model, indicating interaction between the excited states. In addition, polymers with high Z/E ratio showed fast annihilation, demonstrating importance of the ordered structure. On the other hand, in low temperature glassy matrix, fluorescence decay profiles of all polymers showed a enhanced fast decaying component, when laser fluence and/or repetition became higher, indicating the quenching of the S1 state by accumulated T1 state (S–T annihilation). Similar annihilation rates were found with three kinds of polymers, indicating the structural change due to low temperature. The present study demonstrated importance of the stacked structure both in the S1 and T1 migration processes.
Co-reporter:Zhaoke Zheng, Takashi Tachikawa and Tetsuro Majima
Chemical Communications 2015 vol. 51(Issue 76) pp:14373-14376
Publication Date(Web):04 Aug 2015
DOI:10.1039/C5CC05898H
We employed single-particle photoluminescence (PL) measurements to investigate the interfacial electron transfer between single Au nanorods (NRs) and TiO2 coated by ALD. Analyzing the energy relaxation path of plasmon-generated hot electrons as well as the PL intensities allowed for the detection and study of the interfacial electron transfer process spatially.
Co-reporter:Sooyeon Kim, Mamoru Fujitsuka, Norimitsu Tohnai, Takashi Tachikawa, Ichiro Hisaki, Mikiji Miyata and Tetsuro Majima
Chemical Communications 2015 vol. 51(Issue 58) pp:11580-11583
Publication Date(Web):10 Jun 2015
DOI:10.1039/C5CC03969J
We report a substitution of 9-phenylanthracenyl group into rhodamine derivatives that can induce the J-aggregate formation of rhodamine moieties in the aqueous solution upon the addition of a halide ion. From X-ray crystallographic analysis, the dramatic red-shift in the absorption band (i.e. app. 100 nm) originates from the cooperative slipped-stacking of rhodamine and anthracene molecules.
Co-reporter:Peng Zhang, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
Chemical Communications 2015 vol. 51(Issue 33) pp:7187-7190
Publication Date(Web):20 Mar 2015
DOI:10.1039/C5CC01753J
Here we demonstrated that 3D architectures of TiO2 mesocrystals uniformly packed with a chemically exfoliated MoS2 shell exhibit promising reactive efficiency and good stability in synergetic hydrogen evolution. The efficient interfacial electron transfer from the excited TiO2 moieties to the decorated ultrathin MoS2 shell was effectively monitored.
Co-reporter:Mamoru Fujitsuka, Tatsuya Ohsaka and Tetsuro Majima
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 46) pp:31030-31038
Publication Date(Web):26 Oct 2015
DOI:10.1039/C5CP05254H
In the present study, electron transfer (ET) processes from excited radical anions have been investigated using dyad molecules including C60. The deactivation process of excited C60˙−, including the internal conversion from the D1 to the D0 state and the cooling process of the vibrationally hot ground state (Dhot0), was observed spectroscopically for the first time. These processes could be unambiguously distinguished by the observation of the stimulated emission from the D1 state. The intramolecular ET processes from the excited C60˙− were confirmed by the transient absorption spectra. Clearly, both D1 and Dhot0 states acted as precursors for the ET, i.e., dual ET pathways were confirmed. The driving force dependence of the ET rates was well characterized by the Marcus theory, which revealed that the forward ET processes are located at the top region of the Marcus parabola. In addition, the ET from the excited imide radical anion to C60 and that from the ground state C60˙− to imide were examined. The ET rate from the excited imide radical anion and that from ground state C60˙− did not follow the Marcus parabola estimated for the ET from the excited C60˙−. The observed difference can be attributed to the difference in the energy required to form the reduced spacer (Δ) in the superexchange mechanism. Because the Δ value tends to become smaller for ET processes from excited radical ions, fast and efficient ET processes are expected from these states as demonstrated in the present study.
Co-reporter:Jungkweon Choi, Dae Won Cho, Sachiko Tojo, Mamoru Fujitsuka and Tetsuro Majima
Molecular BioSystems 2015 vol. 11(Issue 1) pp:218-222
Publication Date(Web):22 Oct 2014
DOI:10.1039/C4MB00551A
Although the folding kinetics of cytochrome c (Cyt-c), ferric or ferrous Cyt-c, has been extensively investigated as a paradigm for a protein folding reaction using various time-resolved spectroscopic techniques, the configurational change of heme associated with the folding reaction from a ferric Cyt-c to a ferrous Cyt-c induced by one-electron reduction has not been elucidated. To address this issue, we investigated the configurational change of heme in the Cyt-c folding process induced by one-electron reduction using a combination of time-resolved resonance Raman spectroscopy and pulse radiolysis. The results presented herein reveal that the reduction of ferric Cyt-c and the ligation of Met80 occur simultaneously within a timescale of approximately 2 μs, and that the ligand binding and exchange of heme depend on the initial configuration of the heme. The rapid ligation of Met80 observed in this study may be attributed to the intramolecular diffusion of Met80 into ferrous Cyt-c with a 5-coordinated high-spin configuration. Conversely, the ligand exchange of a ferrous Cyt-c with a 6-coordinated low-spin configuration was significantly slower.
Co-reporter:Jungkweon Choi, Dae Won Cho, Sachiko Tojo, Mamoru Fujitsuka, and Tetsuro Majima
The Journal of Physical Chemistry A 2015 Volume 119(Issue 5) pp:851-856
Publication Date(Web):January 10, 2015
DOI:10.1021/jp511229t
The structures of various para-substituted biphenyls (Bp-X; X = −OH, −OCH3, −CH3, −H, −CONH2, −COOH, and −CN) and their radical anions (Bp-X•–) were investigated by time-resolved resonance Raman spectroscopy combined with pulse radiolysis. The inter-ring C1–C1′ stretching modes (ν6) of Bp-X were observed at ∼1285 cm–1, whereas the ν6 modes of Bp-X•– with an electron-donating or -withdrawing substituent were significantly up-shifted. The difference (Δf) between the ν6 frequencies of Bp-X and Bp-X•– showed a significant dependence on the electron affinity of the substituent and exhibited a correlation with the Hammett substituent constants (σp). In contrast to Bp-H•– with a planar geometry, the theoretical and experimental results reveal that all Bp-X•– with an electron-donating or -withdrawing substituent have a slightly twisted structure. The twisted structure of Bp-X•– is due to the localization of the unpaired electron and negative charge density on one phenyl moiety in Bp-X•–.
Co-reporter:Mamoru Fujitsuka, Dae Won Cho, Jungkweon Choi, Sachiko Tojo, and Tetsuro Majima
The Journal of Physical Chemistry A 2015 Volume 119(Issue 26) pp:6816-6822
Publication Date(Web):June 8, 2015
DOI:10.1021/acs.jpca.5b04127
Stilbene (St) derivatives have been investigated for many years because of their interesting photochemical reactions such as cis–trans isomerization in the excited states and charged states and their relation to poly(p-phenylenevinylene)s. To clarify their charged state properties, structural information is indispensable. In the present study, radical cations and radical anions of St derivatives were investigated by radiation chemical methods. Absorption spectra of radical ion states were obtained by transient absorption measurements during pulse radiolysis; theoretical calculations that included the solvent effect afforded reasonable assignments. The variation in the peak position was explained by using HOMO and LUMO energy levels. Structural changes upon one-electron oxidation and reduction were detected by time-resolved resonance Raman measurements during pulse radiolysis. Significant downshifts were observed with the CC stretching mode of the ethylenic groups, indicative of the decrease in the bonding order. It was confirmed that the downshifts observed with reduction were larger than those with oxidation. On the other hand, the downshift caused by oxidation depends significantly on the electron-donating or electron-withdrawing nature of the substituents.
Co-reporter:Sachiko Tojo;Dr. Mamoru Fujitsuka;Dr. Akihiko Ouchi;Dr. Tetsuro Majima
ChemPlusChem 2015 Volume 80( Issue 1) pp:68-73
Publication Date(Web):
DOI:10.1002/cplu.201402300
Abstract
A seleniumselenium σ-bond (SeSe) cleavage of a diaryl diselenide radical anion (ArSeSeAr.−) was investigated by absorption measurements during the γ radiolysis and pulse radiolysis in 2-methyltetrahydrofuran. A di-α-naphthyl diselenide radical anion (αNpSeSeαNp.−) in which an unpaired electron is localized in the SeSe σ* orbital between both Se atoms with an elongated SeSe bond showed an absorption band at 440 nm at 77 K. Upon increasing temperature, the absorption band at 440 nm shifted to 540 nm, thus suggesting that an unpaired electron is delocalized over two naphthalene rings and the SeSe bond. The disappearance of the absorption band at 540 nm and formation of absorption bands at 420, 620, and 690 nm assigned to the α-naphthylselenyl radical were observed during the pulse radiolysis of αNpSeSeαNp, thus indicating that the SeSe bond cleavage occurred in αNpSeSeαNp.−. The relationship between the SeSe bond cleavage and delocalization of the unpaired electron in ArSeSeAr.− is discussed.
Co-reporter:Sachiko Tojo;Dr. Mamoru Fujitsuka;Dr. Akihiko Ouchi;Dr. Tetsuro Majima
ChemPlusChem 2015 Volume 80( Issue 1) pp:
Publication Date(Web):
DOI:10.1002/cplu.201402376
Abstract
Invited for this month’s cover are collaborators from the Institute of Scientific and Industrial Research (SANKEN), Osaka University and the National Institute of Advanced Industrial Science and Technology (AIST), Japan. The cover picture shows selenium–selenium σ-bond cleavage of the di-α-naphthyl diselenide radical anion elucidated by transient absorption measurements during pulse radiolysis using the L-band linear accelerator (background picture). Read the full text of the article at 10.1002/cplu.201402300.
Co-reporter:Sachiko Tojo;Dr. Mamoru Fujitsuka;Dr. Akihiko Ouchi;Dr. Tetsuro Majima
ChemPlusChem 2015 Volume 80( Issue 1) pp:
Publication Date(Web):
DOI:10.1002/cplu.201402375
Co-reporter:Minoru Yamaji, Sachiko Tojo, Mamoru Fujitsuka, Akira Sugimoto, and Tetsuro Majima
The Journal of Organic Chemistry 2015 Volume 80(Issue 16) pp:7890-7895
Publication Date(Web):July 28, 2015
DOI:10.1021/acs.joc.5b00660
The mesolysis mechanisms for eight aromatic thioether radical anions (ArCH2SAr′•–) generated during radiolysis in 2-methyltetrahydrofuran were studied by spectroscopic measurements and DFT calculation. Seven of ArCH2SAr′•– underwent mesolysis via dissociation of the σ-bond between the benzylic carbon and sulfur atoms, forming the corresponding radical and anion with the stepwise mechanism or concerted mechanism. Conversely, no mesolysis in the benzyl β-naphthyl sulfide radical anion was found. From the Arrhenius analysis of the mesolysis with the stepwise mechanism, apparent activation energies (ΔEexp) were determined and compared with those (ΔEcal) estimated by the DFT calculations. Two types of C–S bond dissociation are possible to give the C radical and S anion (ArCH2•/Ar′S–) and the C anion and S radical (ArCH2–/Ar′S•). The dissociation energies (BDE(ArCH2•/Ar′S–) and BDE(ArCH2–/Ar′S•)) were estimated by the DFT calculations, and BDE(ArCH2•/Ar′S–) were found to be smaller than BDE(ArCH2–/Ar′S•). The formation of ArCH2•/Ar′S– was observed on the mesolysis of five ArCH2SAr′•–, while one ArCH2SAr′•– provided ArCH2–/Ar′S•. Chemical properties governing the mesolysis mechanisms of ArCH2SAr′•– are discussed.
Co-reporter:Chao Lu
The Journal of Physical Chemistry C 2015 Volume 119(Issue 31) pp:17818-17824
Publication Date(Web):July 10, 2015
DOI:10.1021/acs.jpcc.5b04823
As a new series of compounds designed for organic light-emitting diodes and organic photovoltaics, dihydro-indenoindenes (DI) substituted by bis(diarylamino) groups (R-DI) including bis(diphenylamino)dihydro-indenoindene, bis(ditolylamino)dihydro-indenoindene, and bis(carbazolyl)dihydro-indenoindene were studied during the pulse radiolysis in solvents to measure the transient absorptions of the corresponding radical cations (R-DI•+), radical anions (R-DI•–), and R-DI in the triplet excited states (3R-DI*). It was clearly indicated that the origin of the electronic transitions in the visible region of DI•+, DI•–, and 3DI* is mainly attributed to the trans-stilbene skeleton of DI. With increasing the electron-donating ability of the diarylamino substituents, the absorption peaks of R-DI•+, R-DI•–, and 3R-DI* showed a red shift. The observed spectra and theoretical calculations suggested that the positive charge is mainly localized on the triphenylamine moiety of R-DI•+, whereas the negative charge is localized on the trans-stilbene moiety of R-DI•–. All R-DI showed emissions during the pulse radiolysis in benzene. It was found that the fluorescence quantum yields and the difference between annihilation enthalpy changes and singlet excited-state energies are responsible for the relative emission intensity obtained during the pulse radiolysis. Moreover, on the basis of the observed spectra and thermodynamic calculations, the emissions are suggested to be originated from R-DI in the singlet excited states, which are generated from the charge recombination between the corresponding R-DI•+ and R-DI•–.
Co-reporter:Mamoru Fujitsuka, Sung Sik Kim, Chao Lu, Sachiko Tojo, and Tetsuro Majima
The Journal of Physical Chemistry B 2015 Volume 119(Issue 24) pp:7275-7282
Publication Date(Web):November 14, 2014
DOI:10.1021/jp510850z
Excited radical ions are interesting reactive intermediates owing to powerful redox reactivities, which are applicable to various reactions. Although their reactivities have been examined for many years, their dynamics are not well-defined. In this study, we examined intermolecular and intramolecular electron transfer (ET) processes from excited radical anions of naphthalene-1,4,5,8-tetracarboxydiimide (NDI•–*). Intermolecular ET processes between NDI•–* and various electron acceptors were confirmed by transient absorption measurements during laser flash photolysis of NDI•– generated by pulse radiolysis. Although three different imide compounds were employed as acceptors for NDI•–*, the bimolecular ET rate constants were similar in each acceptor, indicating that ET is not the rate-determining step. Intramolecular ET processes were examined by applying femtosecond laser flash photolysis to two series of dyad compounds, where NDI was selectively reduced chemically. The distance dependence of the ET rate constants was described by a β value of 0.3 Å–1, which is similar or slightly smaller than the reported values for donor–acceptor dyads with phenylene spacers. Furthermore, by applying the Marcus theory to the driving force dependence of the ET rate constants, the electronic coupling for the present ET processes was determined.
Co-reporter:Shih-Hsun Lin, Mamoru Fujitsuka, and Tetsuro Majima
The Journal of Physical Chemistry B 2015 Volume 119(Issue 25) pp:7994-8000
Publication Date(Web):June 4, 2015
DOI:10.1021/acs.jpcb.5b03494
Charge transfer and proton transfer in DNA have attracted wide attention due to their relevance in biological processes and so on. Especially, excess-electron transfer (EET) in DNA has strong relation to DNA repair. However, our understanding on EET in DNA still remains limited. Herein, by using a strongly electron-donating photosensitizer, trimer of 3,4-ethylenedioxythiophene (3E), and an electron acceptor, diphenylacetylene (DPA), two series of functionalized DNA oligomers were synthesized for investigation of EET dynamics in DNA. The transient absorption measurements during femtosecond laser flash photolysis showed that guanine:cytosine (G:C) base pair affects EET dynamics in DNA by two possible mechanisms: the excess-electron quenching by proton transfer with the complementary G after formation of C•– and the EET hindrance by inserting a G:C base pair as a potential barrier in consecutive thymines (T’s). In the present paper, we provided useful information based on the direct kinetic measurements, which allowed us to discuss EET through oligonucleotides for the investigation of DNA damage/repair.
Co-reporter:Mamoru Fujitsuka, Sachiko Tojo, Takahiro Iwamoto, Eiichi Kayahara, Shigeru Yamago, and Tetsuro Majima
The Journal of Physical Chemistry A 2015 Volume 119(Issue 18) pp:4136-4141
Publication Date(Web):April 13, 2015
DOI:10.1021/acs.jpca.5b01189
Hoop-shaped π-conjugated molecules have attracted much attention. In this study, the radical ions of [4]cyclo-2,7-pyrenylene ([4]CPY), a cyclic tetramer of pyrene, and [4]cyclo-4,5,9,10-tetrahydro-2,7-pyrenylene ([4]CHPY) were investigated using radiation chemical methods, namely, γ-ray radiolysis and pulse radiolysis. The absorption spectra of the radical ions of [4]CPY and [4]CHPY showed clear peaks in the near-IR and UV–vis regions similar to those of [8]cycloparaphenylene ([8]CPP). Theoretical calculations using time-dependent density functional theory provided reasonable assignments of the observed absorption bands. It was indicated that the C4–C5 and C9–C10 ethylene bonds of [4]CHPY do not contribute to the electronic transitions, resulting in absorption spectra similar to those of [8]CPP. On the other hand, it was confirmed that the allowed electronic transitions of the radical ions of [4]CPY are different from those of the radical ions of [4]CHPY and [8]CPP.
Co-reporter:Jungkweon Choi; Cheolhee Yang; Mamoru Fujitsuka; Sachiko Tojo; Hyocherl Ihee
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 24) pp:5045-5050
Publication Date(Web):December 3, 2015
DOI:10.1021/acs.jpclett.5b02313
The oxidation of guanine (G) is studied by using transient absorption and time-resolved resonance Raman spectroscopies combined with pulse radiolysis. The transient absorption spectral change demonstrates that the neutral radical of G (G•(−H+)), generated by the deprotonation of G radical cation (G•+), is rapidly converted to other G radical species. The formation of this species shows the pH dependence, suggesting that it is the G radical cation (G•+)′ formed from the protonation at the N7 of G•(−H+). On one hand, most Raman bands of (G•+)′ are up-shifted relative to those of G, indicating the increase in the bonding order of pyrimidine (Pyr) and imidazole rings. The (G•+)′ exhibits the characteristic CO stretching mode at ∼1266 cm–1 corresponding to a C–O single bond, indicating that the unpaired electron in (G•+)′ is localized on the oxygen of the Pyr ring.
Co-reporter:Zhaoke Zheng ; Takashi Tachikawa
Journal of the American Chemical Society 2014 Volume 136(Issue 19) pp:6870-6873
Publication Date(Web):April 29, 2014
DOI:10.1021/ja502704n
Pt-modified Au nanorods (NRs) synthesized by anisotropic overgrowth were used for producing H2 under visible and near-infrared light irradiation. The Pt-tipped sample exhibited much higher activity compared with fully covered samples. Using single-particle spectroscopies combined with transmission electron microscopy, we observed obvious quenching phenomena for photoluminescence and light scattering from individual Pt-tipped NRs. The analysis of energy relaxation of plasmon-generated hot electrons indicates the electron transfer from the excited Au to Pt.
Co-reporter:Zhaoke Zheng; Takashi Tachikawa
Journal of the American Chemical Society 2014 Volume 137(Issue 2) pp:948-957
Publication Date(Web):December 26, 2014
DOI:10.1021/ja511719g
Plasmonic bimetal nanostructures can be used to drive the conventional catalytic reactions efficiently at low temperature with the utilization of solar energy. This work developed Pd-modified Au nanorods, which work as the light absorber and the catalytically active site simultaneously, and exhibit efficient plasmon-enhanced catalytic formic acid dehydrogenation even when below room temperature (5 °C). Plasmon-induced interface interaction and photoreaction dynamics of individual nanorods were investigated by single-particle photoluminescence measurement, and a complete quenching phenomenon at the LSPR region was observed for the first time. More importantly, the spatial distribution of the SPR-induced enhancement, analyzed by the finite difference time domain (FDTD) simulation, shows that only tip-coated Pd can be affected for the occurrence of plasmon resonance energy transfer. This finding provides a route to decrease the amount of Pd species by the selective deposition only at the field-enhanced sites.
Co-reporter:Sooyeon Kim ; Takashi Tachikawa ; Mamoru Fujitsuka
Journal of the American Chemical Society 2014 Volume 136(Issue 33) pp:11707-11715
Publication Date(Web):July 30, 2014
DOI:10.1021/ja504279r
Singlet oxygen (1O2), molecular oxygen in the lowest excited state, has a critical role in the cell-killing mechanism of photodynamic therapy (PDT). Although 1O2 phosphorescence measurement has been mainly used to monitor 1O2 formation during PDT, its intensity is far insufficient to obtain two-dimensional images of intracellular 1O2 with the subcellular spatial resolution using the currently available near-IR detector. Here, we propose a new far-red fluorescence probe of 1O2, namely, Si-DMA, composed of silicon-containing rhodamine and anthracene moieties as a chromophore and a 1O2 reactive site, respectively. In the presence of 1O2, fluorescence of Si-DMA increases 17 times due to endoperoxide formation at the anthracene moiety. With the advantage of negligible self-oxidation by photoirradiation (ΦΔ < 0.02) and selective mitochondrial localization, Si-DMA is particularly suitable for imaging 1O2 during PDT. Among three different intracellular photosensitizers (Sens), Si-DMA could selectively detect the 1O2 that is generated by 5-aminolevulinic acid-derived protoporphyrin IX, colocalized with Si-DMA in mitochondria. On the other hand, mitochondria-targeted KillerRed and lysosomal porphyrins could not induce fluorescence change of Si-DMA. This surprising selectivity of Si-DMA response depending on the Sens localization and photosensitization mechanism is caused by a limited intracellular 1O2 diffusion distance (∼300 nm) and negligible generation of 1O2 by type-I Sens, respectively. For the first time, we successfully visualized 1O2 generated during PDT with a spatial resolution of a single mitochondrial tubule.
Co-reporter:Takashi Tachikawa and Tetsuro Majima
NPG Asia Materials 2014 6(5) pp:e100
Publication Date(Web):2014-05-01
DOI:10.1038/am.2014.21
Mesocrystals (MCs) are superstructures with a crystallographically ordered alignment of nanoparticles. Owing to their organized structures, MCs posses some unique characteristics such as a high surface area, pore accessibility, and good electronic conductivity and thermal stability; thus, MCs could be beneficial for many areas of research and application. This review begins with a description of the common synthesis strategies for, and characterization and fundamental properties of metal oxide MCs. Newly developed analytical methods (that is, photoconductive atomic force microscopy and single-molecule, single-particle fluorescence microscopy) for unraveling the charge transport and photocatalytic properties of individual MCs are then introduced. Further, recent developments in the applications of various metal oxide MCs, especially in the fields of energy conversion and storage, are also reviewed. Finally, several perspectives in terms of future research on MCs are highlighted.
Co-reporter:Takashi Tachikawa, Peng Zhang, Zhenfeng Bian and Tetsuro Majima
Journal of Materials Chemistry A 2014 vol. 2(Issue 10) pp:3381-3388
Publication Date(Web):17 Dec 2013
DOI:10.1039/C3TA14319H
Development of efficient photocatalysts based on semiconductor materials for organic synthesis, fuel generation, and environmental purification is a central theme in current research and various industries. In this study, we propose a novel strategy for improving the photooxidation activity of photocatalysts by combining metal oxide superstructures and oxygen/hydrogen-evolving co-catalysts. Cobalt phosphate (CoPi) and Pt nanoparticles were selected as model co-catalysts and photochemically deposited on anatase TiO2 mesocrystals. The structures and reaction dynamics of the composites were thoroughly studied by ensemble-averaged and single-particle spectro-microscopies. Time-resolved diffuse reflectance and electron spin resonance spectroscopy measurements revealed that photogenerated holes in TiO2 are transferred to the Co species in CoPi upon UV light irradiation. The photooxidation properties of the composites were tested using fluorescence dye probes. It was found that CoPi-loaded TiO2 mesocrystals had higher activity than standard TiO2 photocatalysts, and their activity was further enhanced by introducing Pt nanoparticles on specific surfaces. In situ fluorescence imaging on a single crystal provides information on the location of reactive sites and the diffusion of product molecules. Consequently, the site-specific modification of co-catalysts tailored by anisotropic electron flow in the mesocrystal superstructures significantly retarded the charge recombination between the holes and electrons, thereby resulting in enhanced (up to approximately 300 times) photooxidation activity.
Co-reporter:Kiyohiko Kawai, Takeshi Koshimo, Atsushi Maruyama and Tetsuro Majima
Chemical Communications 2014 vol. 50(Issue 72) pp:10478-10481
Publication Date(Web):22 Jul 2014
DOI:10.1039/C4CC00377B
The more a fluorescent molecule is exposed to a solvent, the faster its triplet excited state is quenched by molecular oxygen. The changes in the solvent accessibility of a fluorescent molecule were probed by measuring the duration of the off time during the blinking of the fluorescence, which enabled analysis of the function of a molecular beacon-type probe.
Co-reporter:Atsushi Tanaka, Jungkweon Choi and Tetsuro Majima
RSC Advances 2014 vol. 4(Issue 103) pp:59071-59077
Publication Date(Web):20 Oct 2014
DOI:10.1039/C4RA08053J
The structure and stability of a G-quadruplex formed by a long human telomeric sequence containing five or more TTAGGG repeats are not clear yet. Using the guanine-to-inosine (G-to-I) substitution, we conducted thermodynamic studies on the structural polymorphisms of G-quadruplexes formed by the long telomeric sequences, 37htel and five G-to-I substituted sequences (I-1/2, I-1/6, I-4/5, I-4/6, and I-5/6), and investigated their folding dynamics at single-molecule level. The thermodynamic study reveals that a G-quadruplex formed from I-1/2 has a higher Tm and a larger ΔG298K than those formed by other G-to-I substituted sequences, suggesting that a long telomeric sequence preferentially forms a thermodynamically stable G-quadruplex at the 3′ end. In addition, from changes in the hydrodynamic radius by the formation of a G-quadruplex at single-molecule level, we found that the folding reaction of 37htel may proceed through a two-state mechanism without any detectable intermediate and that the global structure, which leads to the change in molecular size, is still occurring even after the formation of a secondary structure (G-quadruplex).
Co-reporter:Shih-Hsun Lin, Mamoru Fujitsuka, Mayuka Ishikawa, and Tetsuro Majima
The Journal of Physical Chemistry B 2014 Volume 118(Issue 42) pp:12186-12191
Publication Date(Web):September 29, 2014
DOI:10.1021/jp509691f
Charge transfer in DNA has attracted great attention of scientists because of its importance in biological processes. However, our knowledge on excess-electron transfer in DNA still remains limited in comparison to numerous studies of hole transfer in DNA. To clarify the dynamics of excess-electron transfer in DNA by photochemical techniques, new electron-donating photosensitizers should be developed. Herein, a terthiophene and two 3,4-ethylenedioxythiophene oligomers were used as photosensitizers in dyads including natural nucleobases as electron acceptors. The charge separation and recombination processes in the dyads were investigated by femtosecond laser flash photolysis, and the driving force dependence of these rate constants was discussed on the basis of the Marcus theory. From this study, the conformation effect on charge recombination process was found. We expect that 3,4-ethylenedioxythiophene oligomers are useful in investigation of excess-electron-transfer dynamics in DNA.
Co-reporter:Mamoru Fujitsuka, Chao Lu, Takahiro Iwamoto, Eiichi Kayahara, Shigeru Yamago, and Tetsuro Majima
The Journal of Physical Chemistry A 2014 Volume 118(Issue 25) pp:4527-4532
Publication Date(Web):June 10, 2014
DOI:10.1021/jp504689q
Cycloparaphenylenes (CPPs), a class of hoop-shaped conjugated macrocycles, have attracted the attention of researchers in various fields because of their interesting properties. Although their properties in the singlet-excited state have been reported, there is no systematic information on the triplet-excited state. In the present study, the properties of triplet-excited [n]CPP (n = 8–12, where n denotes the number of phenyl rings) were comprehensively investigated. The phosphorescence peak shifted to the shorter-wavelength side with increasing ring size of the CPPs, indicating smaller triplet energy for smaller CPPs. It was found that the triplet energy of a smaller CPP is even smaller than those of poly(p-phenylene)s, indicating that small hoop-shaped conjugated macrocycles are effective in realizing low-band gap materials. By applying laser flash photolysis, the Tn–T1 absorption spectra of CPPs were obtained, from which the size-dependence of energy levels of higher triplet states were also determined. Generation of singlet oxygen by the energy transfer from a triplet-excited CPP was confirmed. The generation yield became smaller with increasing size of the CPP in accordance with the triplet yield. From these observations, the size-dependence of the deactivation pathways is explained.
Co-reporter:Mamoru Fujitsuka, Tsutomu Shiragami, Dae Won Cho, Sachiko Tojo, Masahide Yasuda, and Tetsuro Majima
The Journal of Physical Chemistry A 2014 Volume 118(Issue 22) pp:3926-3933
Publication Date(Web):May 12, 2014
DOI:10.1021/jp502153x
Electron and energy transfer processes from higher excited states are attractive for efficient photoenergy utilization because energy dissipating internal conversion processes can be avoided. In the present study, charge separation processes in meso-substituted Sb- and Ge tetraphenylporphyrins (TPPs) were investigated by means of laser spectroscopy. For both Sb- and GeTPPs, S2- and S1-fluorescence emissions were confirmed. Sb- and GeTPPs containing a meso-substituent with a higher electron donor-ability exhibited charge separation from the S2 state, and this was confirmed by transient absorption spectroscopy and a fluorescence up-conversion method. Charge separation was faster for SbTPP with a donor at the meso position than for SbTPP bearing a donor as an axial ligand. The faster charge separation of the present TPPs was attributed to a larger electronic coupling due to a larger HOMO electron density at the meso-carbon of the porphyrin ring. In addition, the charge separation processes in the present meso-substituted TPPs occurred under the adiabatic condition. Contribution of the intramolecular exciplex to the relaxation process was also indicated for the S1 state of GeTPPs.
Co-reporter:Mamoru Fujitsuka, Dae Won Cho, Sachiko Tojo, Jungkweon Choi, Hsin-Hau Huang, Jye-Shane Yang, and Tetsuro Majima
The Journal of Physical Chemistry A 2014 Volume 118(Issue 12) pp:2307-2315
Publication Date(Web):March 5, 2014
DOI:10.1021/jp412744p
Because of their excellent optical and electronic properties, oligofluorenes and polyfluorenes have been investigated for years. Recently developed star-shaped oligomers bearing a truxene or isotruxene core are interesting two-dimensional oligomers. Since employment of a condensed ring system will be effective in further extension of π-conjugation system, we studied electronic and vibrational properties of radical cation of CITFn, star-shaped condensed oligomer with isotruxene core and fluorene unit, by means of the radiation chemical methods. Absorption spectra of radical cation of CITFn were measured in the wide spectral range, which revealed extended π-conjugation of CITFn. Furthermore, time-resolved resonance Raman spectra during pulse radiolysis revealed that the oxidation of CITFn induced structural change to enhance quinoidal character. The Raman data and theoretical calculation indicated that the rigid framework of the present star-shaped oligomer which makes the oligomer a planar structure is quite important in extension of the conjugation pathway.
Co-reporter:Mamoru Fujitsuka, Sachiko Tojo, Takahiro Iwamoto, Eiichi Kayahara, Shigeru Yamago, and Tetsuro Majima
The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 13) pp:2302-2305
Publication Date(Web):June 18, 2014
DOI:10.1021/jz5009054
Cycloparaphenylenes (CPPs) have attracted wide attention because of their interesting properties owing to distorted and strained aromatic systems and radially oriented p orbitals. For application of CPPs, information on their charged states (radical cation and radical anion) is essential. Here, we measured absorption spectra of the radical cations and the radical anions of CPPs with various ring sizes over a wide spectral region by means of radiation chemical methods. The peak position of the near-IR bands for both the radical cation and the radical anion shifted to lower energies with an increase in the ring size. This trend is contrary to what is observed for transitions between the HOMO and LUMO of the neutral CPP. The observed spectra of the CPP radical ions were reasonably assigned based on time-dependent density functional theory. These results indicate that the next HOMO and the next LUMO levels are important in the electronic transitions of radical ions.Keywords: density functional theory; hoop-shaped macrocycle; pulse radiolysis; radiation chemistry; γ-ray irradiation;
Co-reporter:Kiyohiko Kawai and Tetsuro Majima
Accounts of Chemical Research 2013 Volume 46(Issue 11) pp:2616
Publication Date(Web):June 27, 2013
DOI:10.1021/ar400079s
Not long after the discovery of the double-helical structure of DNA in 1952, researchers proposed that charge transfer along a one-dimensional π-array of nucleobases might be possible. At the end of the 1990s researchers discovered that a positive charge (a hole) generated in DNA migrates more than 200 Å along the structure, a discovery that ignited interest in the charge-transfer process in DNA. As a result, DNA became an interesting potential bottom-up material for constructing nanoelectronic sensors and devices because DNA can form various complex two-dimensional and three-dimensional structures, such as smiley faces and cubes. From the fundamental aspects of the hole transfer process, DNA is one of the most well-studied organic molecules with many reports on the synthesis of artificial nucleobase analogues. Thus, DNA offers a unique system to study how factors such as the HOMO energy and molecular flexibility affect hole transfer kinetics.Understanding the hole transfer mechanism requires a discussion of the hole transfer rate constants (kHT). This Account reviews the kHT values determined by our group and by Lewis and Wasielewski’s group, obtained by a combination of the synthesis of modified DNA and time-resolved spectroscopy. DNA consists of G/C and A/T base pairs; the HOMO localizes on the purine bases G and A, and G has a lower oxidation potential and a higher energy HOMO. Typically, long-range hole transfer proceeded via sequential hole transfer between G/C’s. The kinetics of this process in DNA sequences, including those with mismatches, is reproducible via kinetic modeling using the determined kHT for each hole transfer step between G/C’s. We also determined the distance dependence parameter (β), which describes the steepness of the exponential decrease of kHT. Because of this value, >0.6 Å–1 for hole transfer in DNA, DNA itself does not serve as a molecular wire. Interestingly, hole transfer proceeded exceptionally fast for some sequences in which G/C’s are located close to each other, an observation that we cannot explain by a simple sequential hole transfer between G/C’s but rather through hole delocalization over the nucleobases.To further investigate and refine the factors that affect kHT, we examined various artificial nucleobases. We clearly demonstrated that kHT depends strongly on the HOMO energy gap between the bases (ΔHOMO), and that kHT can be increased with decreasing ΔHOMO. We reduced ΔHOMO between the two type of base pairs by replacing adenines (A’s) with deazaadenines (zA’s) or diaminopurines (D’s) and showed that the hole transfer rate through the G/C and A/T mix sequence increased by more than 3 orders of magnitude. We also investigated how DNA flexibility affects kHT. Locked nucleic acid (LNA) modification, which makes DNA more rigid, lowered kHT by more than 2 orders of magnitude. On the other hand, 5-Me-2′-deoxyzebularine (B) modification, which increases DNA flexibility, increased kHT by more than 1 order of magnitude. These new insights in hole transfer kinetics obtained from modified DNAs may aid in the design of new molecular-scale conducting materials.
Co-reporter:Zhenfeng Bian ; Takashi Tachikawa ; Peng Zhang ; Mamoru Fujitsuka
Journal of the American Chemical Society 2013 Volume 136(Issue 1) pp:458-465
Publication Date(Web):December 5, 2013
DOI:10.1021/ja410994f
Plasmonic photocatalysts were successfully synthesized by the modification of TiO2 mesocrystals with Au nanoparticles (NPs) by a simple impregnation method. The Au NP sensitizers show a strong photoelectrochemical response in the visible-light region (400–800 nm) due to their surface plasmon resonance (SPR). The diffuse reflectance spectroscopy measurements on a wide range of time scales (from picoseconds to minutes) demonstrate that a substantial part of electrons, injected from the Au NPs to the TiO2 mesocrystals through the SPR excitation, directionally migrate from the basal surfaces to the edges of the plate-like mesocrystals through the TiO2 nanocrystal networks and are temporally stored there for further reactions. This anisotropic electron flow significantly retarded the charge recombination of these electrons with the holes in the Au NPs, thereby improving the visible-light-photocatalytic activity (for organic-pollutant degradation) by more than an order of magnitude, as compared to that of conventional Au/TiO2 NP systems.
Co-reporter:Mamoru Fujitsuka, Sachiko Tojo, Jye-Shane Yang, Tetsuro Majima
Chemical Physics 2013 Volume 419() pp:118-123
Publication Date(Web):20 June 2013
DOI:10.1016/j.chemphys.2012.12.035
Abstract
Poly- and oligofluorenes have been intensively studied for years, because of their excellent properties as photo- and electro-functional materials. Especially, star-shaped oligofluorenes as two-dimensional oligomers are interesting materials for wide researchers. To understand their electronic properties in charged states, absorption spectra of radical cation and radical anion of star-shaped oligomers with varied size were investigated by means of γ-ray radiolysis. The absorption spectra of their radical ions ranged from the visible to near-IR regions were successfully obtained. By using the theoretical calculation, the observed peaks were assigned. It is indicated that the transition between HOMO and LUMO of the original neutral state plays a significant role in the visible region. Furthermore, it is indicated that the star-shaped oligofluorenes tend to take a planar structure upon oxidation and reduction.
Co-reporter:Jungkweon Choi
Photochemistry and Photobiology 2013 Volume 89( Issue 3) pp:513-522
Publication Date(Web):
DOI:10.1111/php.12042
Abstract
Non-B DNAs, which can form unique structures other than double helix of B-DNA, have attracted considerable attention from scientists in various fields including biology, chemistry and physics etc. Among them, i-motif DNA, which is formed from cytosine (C)-rich sequences found in telomeric DNA and the promoter region of oncogenes, has been extensively investigated as a signpost and controller for the oncogene expression at the transcription level and as a promising material in nanotechnology. Fluorescence techniques such as fluorescence resonance energy transfer (FRET) and the fluorescence quenching are important for studying DNA and in particular for the visualization of reversible conformational switching of i-motif DNA that is triggered by the protonation. Here, we review the latest studies on the conformational dynamics of i-motif DNA as well as the application of FRET and fluorescence quenching techniques to the visualization of reversible conformational switching of i-motif DNA in nano-biotechnology.
Co-reporter:Dr. Jungkweon Choi;Atsushi Tanaka;Dr. Dae Won Cho;Dr. Mamoru Fujitsuka;Dr. Tetsuro Majima
Angewandte Chemie International Edition 2013 Volume 52( Issue 49) pp:12937-12941
Publication Date(Web):
DOI:10.1002/anie.201306017
Co-reporter:Sooyeon Kim, Mamoru Fujitsuka, and Tetsuro Majima
The Journal of Physical Chemistry B 2013 Volume 117(Issue 45) pp:13985-13992
Publication Date(Web):October 10, 2013
DOI:10.1021/jp406638g
To detect singlet oxygen (1O2), the commercially available fluorescent sensor named Singlet Oxygen Sensor Green (SOSG) has been the most widely used from material studies to medical applications, for example, photodynamic therapy. In light of the previous studies, SOSG is a dyad composed of fluorescein and anthracene moieties. In the present study, we carried out quantitative studies on photochemical dynamics of SOSG for the first time, such as the occurrence of intramolecular photoinduced electron transfer (PET), 1O2 generation, and two-photon ionization. It was revealed that these relaxation pathways strongly depend on the irradiation conditions. The visible-light excitation (ex. 532 nm) of SOSG induced intramolecular PET as a major deactivation process (kPET = 9.7 × 1011 s–1), resulting in fluorescence quenching. In addition, intersystem crossing occurred as a minor deactivation process that gave rise to 1O2 generation via the bimolecular triplet–triplet energy transfer (kq = 1.2 × 109 M–1 s–1). Meanwhile, ultraviolet-light excitation (355 nm) of SOSG caused the two-photon ionization to give a SOSG cation (Φion = 0.003 at 24 mJ cm–2), leading to SOSG decomposition to the final products. Our results clearly demonstrate the problems of SOSG, such as photodecomposition and 1O2 generation. In fact, these are not special for SOSG but common drawbacks for most of the fluorescein-based sensors.
Co-reporter:Sachiko Tojo, Mamoru Fujitsuka, and Tetsuro Majima
The Journal of Organic Chemistry 2013 Volume 78(Issue 5) pp:1887-1893
Publication Date(Web):November 27, 2012
DOI:10.1021/jo301853g
A central carbon–carbon (C–C) σ bond dissociation of polyphenylethane radical anions (PhnE•-, n = 3–6), mesolysis, was investigated by the transient absorption measurement during pulse radiolysis of PhnE in 2-methyltetrahydrofuran. The charge resonance (CR) band of 1,1,2,2-tetraphenylethane radical anion (1,1,2,2-Ph4E•-) was observed in the near-infrared region immediately after an electron pulse to be attributed to the intramolecular dimer radical anion. The CR band disappeared with simultaneous formation of two absorption bands at 330 and 460 nm corresponding to diphenylmethyl radical and diphenylmethyl anion, respectively, indicating the occurrence of the mesolysis in 1,1,2,2-Ph4E•-. During pulse radiolysis of 1,1,1,2,2,2-hexaphenylethane (Ph6E), an absorption band of triphenylmethyl radical was observed at 340 nm immediately after an electron pulse. It is suggested that one electron attachment to Ph6E is followed by the subsequent rapid C–C σ bond dissociation. Formation of intramolecular dimer radical anions in PhnE•- such as 1,1,2-triphenylethane (Ph3E), 1,1,1,2-tetraphenylethane (1,1,1,2-Ph4E), and 1,1,1,2,2-pentaphenylethane (Ph5E) was also studied together with the subsequent mesolysis. The mesolysis of PhnE•- is discussed in terms of charge delocalization in the intramolecular dimer radical anions and the central C–C σ bond as well as bond dissociation energy of the central C–C σ bond of PhnE•-.
Co-reporter:Takashi Tachikawa, Tatsuya Ohsaka, Zhenfeng Bian, and Tetsuro Majima
The Journal of Physical Chemistry C 2013 Volume 117(Issue 21) pp:11219-11228
Publication Date(Web):May 7, 2013
DOI:10.1021/jp402144h
Nanoscale mapping of adsorption sites for molecules or ions at solid–liquid interfaces has not been explored in detail because of the difficulty in probing both stochastic adsorption/desorption events and heterogeneous surface structures. We report here the application of single-molecule-based super-resolution fluorescence microscopy using a catechol-modified boron–dipyrromethene dye (CA-BODIPY), which serves as a fluorescent reporter, to identify the locations of effective adsorption sites on metal oxide surfaces. Upon adsorption on a TiO2 nanoparticle, individual CA-BODIPY molecules exhibited detectable fluorescence because of the formation of chelating complexes between the catechol moiety and the surface Ti sites. Interestingly, a significant effect of the crystal face on the adsorption preference for CA-BODIPY was found in the case of anatase TiO2 microcrystals in neutral water: {101} > {001} ≈ {100}. In an aprotic solvent such as acetonitrile, however, the opposite crystal face effect was observed; this implies a significant contribution of solvent molecules to the adsorption of organic compounds on specific surfaces. From the quantitative analysis of the formation rate of fluorescent complexes per unit area, it was found that nanometer-sized TiO2 crystals have superior adsorptivity over micrometer-sized TiO2 crystals and an atomically flat TiO2 surface. This observation is consistent with the higher density of surface defects on the nanoparticles. Furthermore, it was revealed that CA-BODIPY molecules are preferentially adsorbed on the top branches of α-Fe2O3 micropines, where a high density of exposed Fe cations is expected. Our methodology and findings yield new insights into the mechanisms underlying the synthesis and (photo)catalytic activity of metal oxide particles with different sizes and shapes.
Co-reporter:Dr. Mamoru Fujitsuka;Takahiro Iwamoto;Dr. Eiichi Kayahara; Shigeru Yamago; Tetsuro Majima
ChemPhysChem 2013 Volume 14( Issue 8) pp:1570-1572
Publication Date(Web):
DOI:10.1002/cphc.201300144
Co-reporter:Takashi Tachikawa, Tomoyuki Yonezawa, and Tetsuro Majima
ACS Nano 2013 Volume 7(Issue 1) pp:263
Publication Date(Web):December 5, 2012
DOI:10.1021/nn303964v
Interfacial charge transfer at the heterogeneous surface of semiconductor nanoparticles is a fundamental process that is relevant to many important applications, such as photocatalysis, solar cells, and sensors. In this study, we developed new water-soluble fluorogenic probes for interfacial electron transfer reactions on semiconductor nanoparticles. The synthesized boron-dipyrromethene-based fluorescence dyes have one or two sulfonate groups, which confer solubility in aqueous media, and a dinitrophenyl group as a redox reaction site. These probes produce the corresponding fluorescent products via multiple interfacial electron transfer processes, allowing us to investigate the photoinduced redox reactions over individual pristine and Au-nanoparticle-deposited TiO2 nanoparticles at the single-particle, single-molecule levels. The minimum probe concentration to detect single-product molecules on a single TiO2 nanoparticle was found to be in the nanomolar range (<10 nM) in acidic solution. Furthermore, super-resolution mapping of the reaction sites revealed that visible-light-induced reduction reactions preferentially occurred on the TiO2 surface within a distance of a few tens of nanometers around the deposited Au nanoparticles. This result was qualitatively interpreted on the basis of plasmon-induced electron and/or energy transfer mechanisms. Overall, this study provides a great deal of valuable information related to solar-energy-conversion processes that is impossible or difficult to obtain from ensemble-averaged experiments.Keywords: electron transfer; fluorogenic probe; single-molecule fluorescence spectroscopy; surface plasmon resonance; TiO2 nanoparticle
Co-reporter:Dr. Jungkweon Choi;Jongjin Park;Atsushi Tanaka;Dr. Man Jae Park;Dr. Yoon Jung Jang;Dr. Mamoru Fujitsuka;Dr. Seog K. Kim;Dr. Tetsuro Majima
Angewandte Chemie International Edition 2013 Volume 52( Issue 4) pp:1134-1138
Publication Date(Web):
DOI:10.1002/anie.201208149
Co-reporter:Atsushi Tanaka, Jungkweon Choi, Seog K. Kim, and Tetsuro Majima
The Journal of Physical Chemistry B 2013 Volume 117(Issue 22) pp:6711-6717
Publication Date(Web):May 10, 2013
DOI:10.1021/jp4036277
As in the human genome there are numerous repeat DNA sequences to adopt into non-B DNA structures such as hairpin, triplex, Z-DNA, G-quadruplex, and so on, an understanding of the interaction between DNA repair proteins and a non-B DNA forming sequence is very important. In this regard, the interaction between RecA protein and human telomeric 5′-TAGGG-(TTAGGG)3-TT-3′ sequence and the G-quadruplex formed from this sequence has been investigated in bulk phase and at the single-molecule level. The RecA@ssDNA filament, which is formed by the interaction between RecA protein and a G-rich sequence, was dissociated by the addition of K+ ions, and the dissociated G-rich sequence was quickly folded to a G-quadruplex structure, indicating that the G-quadruplex structure is more favorable than the RecA@ssDNA filament in the presence of K+ ions. In addition, we demonstrate that the conformation of the G-quadruplex, which is heterogeneous in the absence of RecA, converged to the specific G-quadruplex with one double-chain-reversal loop upon association of RecA protein.
Co-reporter:Jungkweon Choi ; Mamoru Fujitsuka ; Sachiko Tojo
Journal of the American Chemical Society 2012 Volume 134(Issue 32) pp:13430-13435
Publication Date(Web):July 19, 2012
DOI:10.1021/ja304904p
Pulse radiolysis is a powerful method to realize real-time observation of various redox processes, which induces various structural and functional changes occurring in biological systems. However, its application has been mainly limited to studies of the redox reactions of rather smaller biological systems such as DNA because of an undesired reaction due to various free radicals generated by pulse radiolysis. For application of pulse radiolysis to generate plenty of redox reactions of biological systems, selective redox reactions induced by electron pulses have to be developed. In this study, we report that in the presence of the high concentration of the denaturant, guanidine HCl (GdHCl), the selective reduction of the oxidized cytochrome c (Cyt c) takes place in time scales of a few microseconds by the electron transfer from the guanidine radical that is formed by the fast reaction of eaq– with GdHCl, consequently leading to folding kinetics of Cyt c. By providing insight into the folding dynamics of Cyt c, we show that the pulse radiolysis technique can be used to track the folding dynamics of various biomolecules in the presence of a denaturant including GdHCl.
Co-reporter:Kiyohiko Kawai ; Mitsuo Hayashi
Journal of the American Chemical Society 2012 Volume 134(Issue 22) pp:9406-9409
Publication Date(Web):May 16, 2012
DOI:10.1021/ja302641e
We report the measurement of hole-transfer rate constants (kht) in locked nucleic acid (LNA) and 5-Me-2′-deoxyzebularine (B)-modified DNA. LNA modification, which makes DNA more rigid, caused a decrease of more than 2 orders of magnitude in kht, whereas B modification, which increases DNA flexibility, increased kht by more than 20-fold. The present results clearly showed that hole-transfer efficiency in DNA can be increased by increasing DNA flexibility.
Co-reporter:Zhenfeng Bian, Takashi Tachikawa, Shi-Cong Cui, Mamoru Fujitsuka and Tetsuro Majima
Chemical Science 2012 vol. 3(Issue 2) pp:370-379
Publication Date(Web):11 Oct 2011
DOI:10.1039/C1SC00552A
In this study, we investigated interfacial charge transfer dynamics in water-soluble perylenediimide (WS-PDI) dye sensitized p-type semiconductor NiO nanoparticle films to better understand how molecular interactions influence photoconversion processes involved in solar cells by means of ensemble-averaged and single-molecule spectroscopies. Transient absorption data showed that strong and weak electronic couplings coexist between WS-PDI molecules and NiO nanoparticles, resulting in fast (within several picoseconds) and slow (requiring tens of picoseconds to nanoseconds) hole transfer from the excited dye to NiO, followed by charge recombination occurring at pico- to microsecond time scales. The correlated analyses of single-molecule fluorescence intensity, lifetime, blinking, and anisotropy revealed the intrinsic distribution and temporal fluctuation of interfacial charge transfer reactivity, which are closely related to site-specific molecular interactions and dynamics. It was also found that a suitable insulating Al2O3 layer can weaken the electronic interaction between WS-PDI and NiO, thereby retarding charge recombination and significantly enhancing photoelectric conversion efficiency. The results presented here will provide a reliable basis for design of highly efficient p-type solar cells and other molecule/semiconductor systems for their use in optoelectronic and solar energy applications.
Co-reporter:Man Jae Park, Mamoru Fujitsuka, Haruhiro Nishitera, Kiyohiko Kawai and Tetsuro Majima
Chemical Communications 2012 vol. 48(Issue 89) pp:11008-11010
Publication Date(Web):24 Sep 2012
DOI:10.1039/C2CC36054C
Excess electron transfer dynamics in DNA hairpins was investigated by femtosecond laser flash photolysis of a donor–DNA–acceptor system using N,N-dimethylaminopyrene and diphenylacetylene as an electron donor and acceptor, respectively. It was revealed that the excess electron hopping rate between T's is faster than that of the hole.
Co-reporter:Takashi Tachikawa and Tetsuro Majima
Chemical Communications 2012 vol. 48(Issue 27) pp:3300-3302
Publication Date(Web):10 Feb 2012
DOI:10.1039/C2CC30597F
We report a single-particle approach for studying the photocatalytic oxidation reaction on individual anatase TiO2 particles. Single-particle kinetic and imaging analyses of the chemiluminescence (CL) emitted from the probe dye molecules revealed that the oxidation reactivity is not significantly dependent on the crystal faces.
Co-reporter:Mamoru Fujitsuka, Dae Won Cho, Takahiro Iwamoto, Shigeru Yamago and Tetsuro Majima
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 42) pp:14585-14588
Publication Date(Web):06 Sep 2012
DOI:10.1039/C2CP42712E
Hoop-shaped π-conjugated molecules such as cycloparaphenylene (CPP) have attracted the attention of many chemists because they exhibit interesting properties due to the distorted π-electron system. To gain a systematic understanding of the properties that result from distorted π-electron systems, it is important to know precisely how these properties depend on the hoop size. In the present study, we have investigated the size dependence of the fluorescence properties of CPPs. The fluorescence spectra of smaller CPPs showed red-shifted fluorescence peaks, smaller fluorescence quantum yields, and longer lifetimes, when compared to those of larger ones. One of the important factors that gave rise to these fluorescence properties of smaller CPPs was greater structural relaxation from the Franck–Condon state, which is a postulation supported by theoretical calculations. The structural relaxation in the picosecond domain was experimentally detected by the fluorescence upconversion method. The present results are an important example that confirms steric factors strongly governing the fluorescence properties of a molecule.
Co-reporter:Takashi Tachikawa, Shi-Cong Cui, Mamoru Fujitsuka and Tetsuro Majima
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 12) pp:4244-4249
Publication Date(Web):02 Feb 2012
DOI:10.1039/C2CP23317G
Graphene oxide (GO) nanosheets have received a great deal of attention for a wide range of applications from optoelectronic devices to biological sensors. We now report a mechanistic study of the interfacial electron transfer (ET) processes between organic dye molecule, 9-phenyl-2,3,7-trihydroxy-6-fluorone (PF), and nanometre-sized GO sheets using ensemble-averaged and single-molecule spectroscopies. The ET dynamics was characterized by the direct observation of the PF radical cation during the laser flash photolysis, and its reaction rate was determined to be ∼1011 s−1. The single-molecule fluorescence spectroscopy was utilized to clarify the heterogeneous nature of the interfacial ET within individual composites. Their fluorescence lifetimes and spectra were found to vary from composite to composite, possibly due to the different local structures and molecular interactions. The autocorrelation analysis of fluorescence intensity trajectories also revealed the temporal fluctuation of the ET reactivity.
Co-reporter:Zhenfeng Bian, Takashi Tachikawa, and Tetsuro Majima
The Journal of Physical Chemistry Letters 2012 Volume 3(Issue 11) pp:1422-1427
Publication Date(Web):May 10, 2012
DOI:10.1021/jz3005128
Materials with intricate nanostructures display fascinating properties, which have inspired extensive research on the synthesis of materials with controlled structures. In this study, we investigated the properties of superstructures of TiO2 to understand the inter-relationship between structural ordering and photocatalytic performance. The nanoplate anatase TiO2 mesocrystals were chosen as the typical investigation objects, which were newly synthesized by a topotactic structural transformation. The TiO2 mesocrystals displayed the superstructure of crystallographically ordered alignment of anatase TiO2 nanocrystals with high surface area and large high-energy surface {001} planes exposed. The photoconductive atomic force microscopy and time-resolved diffuse reflectance spectroscopy were utilized to determine the charge transport properties of TiO2 mesocrystals, and their features were highlighted by a comparison with reference TiO2 samples, for example, anatase TiO2 nanocrystals with similar surface area and single crystal structure. Consequently, it was found for the first time that such a superstructure of TiO2 could largely enhance charge separation and had remarkably long-lived charges, thereby exhibiting greatly increased photoconductivity and photocatalytic activity.Keywords: conductive atomic force microscopy; electron transfer; mesocrystal; superstructure; TiO2 photocatalysis;
Co-reporter:Zhenfeng Bian ; Takashi Tachikawa ; Wooyul Kim ; Wonyong Choi
The Journal of Physical Chemistry C 2012 Volume 116(Issue 48) pp:25444-25453
Publication Date(Web):November 13, 2012
DOI:10.1021/jp309683f
Metal–semiconductor nanocomposites have been widely employed for designing efficient optoelectronic devices and catalysts. The performance of such nanocomposites is significantly influenced by both the method of preparation and the electronic and morphological structures of metals and semiconductors. Here, we have synthesized novel nanocomposites containing plate-like anatase TiO2 mesocrystal superstructures and noble metal (Au, Pt) nanoparticles. These metal nanoparticles were preferentially photodeposited on the edge of TiO2 mesocrystals. The electron transport and photocatalytic properties of the novel nanocomposites were subsequently studied. Single-molecule fluorescence spectroscopy measurements on a single particle directly revealed that most of the photogenerated electrons could migrate from the dominant surface to the edge of the TiO2 mesocrystal with the reduction reactions mainly occurring at its lateral surfaces containing {101} facets. The loading of metal nanoparticles on the superstructure of TiO2 was found to greatly improve the photogenerated charge separation efficiency allowing significant (more than 1 order of magnitude) enhancement of the photocatalytic reaction rate in organic degradation reactions. These outstanding features allowed significantly reduced consumption (ca. 10% of that of typical TiO2 nanocrystal samples) of the Au or Pt loading on the TiO2 mesocrystal while maintaining the same photocatalytic activity.
Co-reporter:Takashi Tachikawa and Tetsuro Majima
Langmuir 2012 Volume 28(Issue 24) pp:8933-8943
Publication Date(Web):February 10, 2012
DOI:10.1021/la300177h
In this Article, we focus on the in situ observation of photochemical reactions on individual nanoobjects of solid catalysts using single-molecule, single-particle fluorescence spectroscopy. The use of high-resolution imaging techniques with suitable fluorogenic probes enables us to determine the location of the catalytically active sites that are related to the structural heterogeneities on the surface of the solid catalyst and the temporal fluctuation of photochemical reactivity. Furthermore, we present the real-time observation of metastable gold nanoclusters in polymer matrices at the single-cluster level. This Article encourages readers to explore the nanoworld in terms of practical applications in many fields such as fundamental physics and chemistry.
Co-reporter:Dr. Yasuko Osakada;Dr. Kiyohiko Kawai;Dr. Takashi Tachikawa;Dr. Mamoru Fujitsuka;Dr. Kazuki Tainaka; Shozo Tero-Kubota; Tetsuro Majima
Chemistry - A European Journal 2012 Volume 18( Issue 4) pp:1060-1063
Publication Date(Web):
DOI:10.1002/chem.201101964
Co-reporter:Man Jae Park;Dr. Mamoru Fujitsuka;Dr. Kiyohiko Kawai ;Dr. Tetsuro Majima
Chemistry - A European Journal 2012 Volume 18( Issue 7) pp:2056-2062
Publication Date(Web):
DOI:10.1002/chem.201103663
Abstract
Excess-electron transfer (EET) in DNA has attracted wide attention owing to its close relation to DNA repair and nanowires. To clarify the dynamics of EET in DNA, a photosensitizing electron donor that can donate an excess electron to a variety of DNA sequences has to be developed. Herein, a terthiophene (3T) derivative was used as the photosensitizing electron donor. From the dyad systems in which 3T was connected to a single nucleobase, it was revealed that 13T* donates an excess electron efficiently to thymine, cytosine, and adenine, despite adenine being a well-known hole conductor. The free-energy dependence of the electron-transfer rate was explained on the basis of the Marcus theory. From the DNA hairpins, it became clear that 13T* can donate an excess electron not only to the adjacent nucleobase but also to the neighbor one nucleobase further along and so on. From the charge-injection rate, the possibilities of smaller β value and/or charge delocalization were discussed. In addition, EET through consecutive cytosine nucleobases was suggested.
Co-reporter:Dr. Mamoru Fujitsuka;Dr. Shingo Samori;Sachiko Tojo;Dr. Michael M. Haley;Dr. Tetsuro Majima
ChemPlusChem 2012 Volume 77( Issue 8) pp:682-687
Publication Date(Web):
DOI:10.1002/cplu.201200110
Abstract
Dimerization of a series of regioisomeric 1,4-, 1,3-, and 1,2-bis(phenylethynyl)benzene radical anions (bPEBs.−) substituted by various electron-donor and/or electron-acceptor groups was studied during the pulse radiolysis in N,N-dimethylformamide (DMF). The transient absorption of bPEB.− decayed with the formation of new bands attributed to the dimer radical anion of bPEB.− and bPEB (bPEB2.−). From the dependence of decay and formation rates on the concentration of bPEB, the bimolecular rate constants of kb=(1.2±0.1)×107 to (3.2±0.2)×108 M−1 s−1 were estimated. It is suggested that bPEB.− dimerizes with bPEB through the formation of a CC bond between two sp carbon atoms, to give σ-type dimer radical anion (σ-(bPEB)2.−) with a diene-type structure. The kb values of bPEB.− with bPEB changed with the substitution pattern of the phenylacetylene group on the central benzene ring and the various kinds of donor and/or acceptor group.
Co-reporter:Sachiko Tojo, Mamoru Fujitsuka, and Tetsuro Majima
The Journal of Organic Chemistry 2012 Volume 77(Issue 11) pp:4932-4938
Publication Date(Web):April 19, 2012
DOI:10.1021/jo300144r
Intramolecular dimer radical anions of di-, tri-, tetra-, and pentaphenylalkanes were investigated on the basis of absorption spectral measurements during γ-radiolysis in 2-methyltetrahydrofuran (MTHF) glassy matrix at 77 K and theoretical calculations. The absorption spectrum of 1,1,2,2-tetraphenylethane (1,1,2,2-Ph4E) radical anion showed two bands in the near-infrared (NIR) region (900–2600 nm). One band observed at shorter wavelength than 2000 nm is assigned to the intramolecular charge resonance (CR) band between two phenyl groups of the 1,1-diphenylmethyl chromophore (1,1-dimer radical anion). The intramolecular CR band of the 1,1-dimer radical anion was observed for various alkanes having 1,1-diphenylmethyl chromophore such as 1,1,1-triphenylmethane (1,1,1-Ph3M), 1,1,1,1-tetraphenylmethane (1,1,1,1-Ph4M), and so on. The other intramolecular CR band observed at longer wavelength than 2200 nm is assigned to intramolecular dimer radical anion between two phenyl groups of the 1,2-diphenylethyl chromophore (1,2-dimer radical anion). The intramolecular CR band of the 1,2-dimer radical anion was observed for various alkanes having a 1,2-diphenylethyl chromophore, such as 1,1,2-triphenylethane (1,1,2-Ph3E), 1,1,2,2-Ph4E, and 1,1,1,2,2-pentaphenylethane (1,1,1,2,2-Ph5E) and so on. No dimer radical anion was observed for 1,n-diphenylalkanes (n > 2) without 1,1-diphenylmethyl chromophore. The relationship between the structure and negative charge delocalization over two phenyl groups connected by an sp3 carbon is discussed.
Co-reporter:Jungkweon Choi and Tetsuro Majima
Chemical Society Reviews 2011 vol. 40(Issue 12) pp:5893-5909
Publication Date(Web):07 Sep 2011
DOI:10.1039/C1CS15153C
In contrast to B-DNA that has a right-handed double helical structure with Watson–Crick base pairing under the ordinary physiological conditions, repetitive DNA sequences under certain conditions have the potential to fold into non-B DNA structures such as hairpin, triplex, cruciform, left-handed Z-form, tetraplex, A-motif, etc. Since the non-B DNA-forming sequences induce the genetic instability and consequently can cause human diseases, the molecular mechanism for their genetic instability has been extensively investigated. On the contrary, non-B DNA can be widely used for application in biotechnology because many DNA breakage hotspots are mapped in or near the sequences that have the potential to adopt non-B DNA structures. In addition, they are regarded as a fascinating material for the nanotechnology using non-B DNAs because they do not produce any toxic byproducts and are robust enough for the repetitive working cycle. This being the case, an understanding on the mechanism and dynamics of their structural changes is important. In this critical review, we describe the latest studies on the conformational dynamics of non-B DNAs, with a focus on G-quadruplex, i-motif, Z-DNA, A-motif, hairpin and triplex (189 references).
Co-reporter:Kiyohiko Kawai ; Eri Matsutani ; Atsushi Maruyama
Journal of the American Chemical Society 2011 Volume 133(Issue 39) pp:15568-15577
Publication Date(Web):August 29, 2011
DOI:10.1021/ja206325m
Photoinduced charge-transfer fluorescence quenching of a fluorescent dye produces the nonemissive charge-separated state, and subsequent charge recombination makes the reaction reversible. While the information available from the photoinduced charge-transfer process provides the basis for monitoring the microenvironment around the fluorescent dyes and such monitoring is particularly important in live-cell imaging and DNA diagnosis, the information obtainable from the charge recombination process is usually overlooked. When looking at fluorescence emitted from each single fluorescent dye, photoinduced charge-transfer, charge-migration, and charge recombination cause a “blinking” of the fluorescence, in which the charge-recombination rate or the lifetime of the charge-separated state (τ) is supposed to be reflected in the duration of the off time during the single-molecule-level fluorescence measurement. Herein, based on our recently developed method for the direct observation of charge migration in DNA, we utilized DNA as a platform for spectroscopic investigations of charge-recombination dynamics for several fluorescent dyes: TAMRA, ATTO 655, and Alexa 532, which are used in single-molecule fluorescence measurements. Charge recombination dynamics were observed by transient absorption measurements, demonstrating that these fluorescent dyes can be used to monitor the charge-separation and charge-recombination events. Fluorescence correlation spectroscopy (FCS) of ATTO 655 modified DNA allowed the successful measurement of the charge-recombination dynamics in DNA at the single-molecule level. Utilizing the injected charge just like a pulse of sound, such as a “ping” in active sonar systems, information about the DNA sequence surrounding the fluorescent dye was read out by measuring the time it takes for the charge to return.
Co-reporter:Man Jae Park ; Mamoru Fujitsuka ; Kiyohiko Kawai
Journal of the American Chemical Society 2011 Volume 133(Issue 39) pp:15320-15323
Publication Date(Web):September 2, 2011
DOI:10.1021/ja2068017
Charge transfer in DNA is an essential process in biological systems because of its close relation to DNA damage and repair. DNA is also an important material used in nanotechnology for wiring and constructing various nanomaterials. Although hole transfer in DNA has been investigated by various researchers and the dynamic properties of this process have been well established, the dynamics of a negative charge, that is, excess electron, in DNA have not been revealed until now. In the present paper, we directly measured the rate of excess electron transfer (EET) through a consecutive thymine (T) sequence in nicked-dumbbell DNAs conjugated with a tetrathiophene derivative (4T) as an electron donor and diphenylacetylene (DPA) as an electron acceptor at both ends. The selective excitation of 4T by a femtosecond laser pulse caused the excess electron injection into DNA, and led to EET in DNA by a consecutive T-hopping mechanism, which eventually formed the DPA radical anion (DPA•–). The rate constant for the process of EET through consecutive T was determined to be (4.4 ± 0.3) × 1010 s–1 from an analysis of the kinetic traces of the ΔO.D. during the laser flash photolysis. It should be emphasized that the EET rate constant for T-hopping is faster than the rate constants for oxidative hole transfers in DNA (104 to 1010 s–1 for A- and G-hopping).
Co-reporter:Nan Wang, Takashi Tachikawa and Tetsuro Majima
Chemical Science 2011 vol. 2(Issue 5) pp:891-900
Publication Date(Web):04 Mar 2011
DOI:10.1039/C0SC00648C
Electronic communication between the building blocks of nanocomposites is an important property that affects their functionality with regard to many optoelectronic and catalytic applications. Herein, we report a single-molecule, single-particle approach for elucidating the inherent photocatalytic activity of individual Au nanoparticle-loaded TiO2 particles using a novel redox-responsive fluorescent dye. A single-particle kinetic analysis of the fluorescence bursts emitted from the products revealed that the photocatalytic activity leading to reduction of the probe molecules is controlled by not only the substrate concentration and excitation intensity but also the Au particle size, and that these factors are intricately interrelated. Furthermore, we discovered that the stochastic photocatalytic events around the millisecond-to-second time scale showed considerable temporal and spatial heterogeneity during photoirradiation, and that they actually originate from the charging/discharging of Au nanoparticles on TiO2. Our findings represent a significant contribution to the scientific understanding of the interfacial electron transfer dynamics in composite systems, and more fundamentally, in heterogeneous (photo)chemical processes.
Co-reporter:Jungkweon Choi, Sooyeon Kim, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 13) pp:5651-5658
Publication Date(Web):09 Feb 2011
DOI:10.1039/C0CP02689A
Denaturant-induced conformational change of yeast iso-1-cytochrome c (Cytc) has been comprehensively investigated in the single-molecule and bulk phases. By fluorescence-quenching experiments with dye-labelled heme-protein (Alexa 488-labelled Cytc, Cytc-A488), we clearly show that the fluorescence quenching observed from folded Cytc-A488 is due mainly to photoinduced electron transfer (PET) between electron-donating amino acids such as tryptophan and the dye attached to the protein. In addition, the unfolding process of Cytc-A488 observed in the single-molecule and bulk phases can be explained well in terms of a three-state model: Cytc unfolds through an intermediate with a native-like compactness. By quantitative analysis of fluorescence correlation spectroscopy (FCS) data, we were able to observe a relaxation time of ∼1.5 μs corresponding to segmental motion and fast folding dynamics of 55 μs in the unfolded state of Cytc. The results presented here also suggest that a combination of single-molecule and ensemble-averaged spectroscopy is necessary to provide convincing and comprehensive assignments of protein kinetics.
Co-reporter:Mamoru Fujitsuka, Sachiko Tojo, Masahiko Shibahara, Motonori Watanabe, Teruo Shinmyozu, and Tetsuro Majima
The Journal of Physical Chemistry A 2011 Volume 115(Issue 5) pp:741-746
Publication Date(Web):December 31, 2010
DOI:10.1021/jp110916m
In the present study, delocalization of a positive charge in π-stacked multi-benzene rings in multilayered para- and meta-cyclophanes, in which benzene rings are connected by propyl chains to form a chromophore array with the face-to-face structure, was investigated by means of transient absorption spectroscopy during the pulse radiolysis using dichloroethane as a solvent. The local excitation and charge resonance (CR) bands were successfully observed. It was revealed that the CR band shifted to the longer wavelength side with the number of the benzene rings. The stabilization energy estimated from the peak position of the CR band showed the efficient charge delocalization over the cyclophanes. Furthermore, the CR bands showed the slight spectral change attributable to the change in distribution of the conformers. The substantially long lifetime of the CR band can be explained on the basis of the smaller charge distribution on the outer layers of the multilayered cyclophanes.
Co-reporter:Shi-Cong Cui ; Takashi Tachikawa ; Mamoru Fujitsuka
The Journal of Physical Chemistry C 2011 Volume 115(Issue 5) pp:1824-1830
Publication Date(Web):January 7, 2011
DOI:10.1021/jp1110828
Interfacial electron transfer (ET) to and from semiconductor quantum dots (QDs) is of intense interest because of its important roles in many applications, including biosensors, light-emitting diodes, and solar cells. In this work, we have investigated the photoinduced ET between water-soluble CdTe QDs and nitrobenzene amine (NBzA) through specific cucurbit[6]uril host−guest complex interactions. The modification of cucurbit[6]uril on the QD surface with thiol linker groups significantly improved the physical and chemical stability of QDs. The steady-state and time-resolved fluorescence and absorption spectroscopies were combined to clarify the process of ET from the excited QDs to the guest NBzA molecules in the cucurbit[6]uril cavity. Furthermore, single-particle fluorescence correlation spectroscopy (FCS) experiments revealed that the blinking phenomenon in the microsecond time scale was attributed to the charge separation between the QD and the NBzA molecule.
Co-reporter:Mamoru Fujitsuka, Dae Won Cho, Hsin-Hau Huang, Jye-Shane Yang, and Tetsuro Majima
The Journal of Physical Chemistry B 2011 Volume 115(Issue 46) pp:13502-13507
Publication Date(Web):October 10, 2011
DOI:10.1021/jp2074336
Oligofluorenes attract wide attention due to their excellent fluorescent properties. For the detailed understanding of the excited state properties, ultrafast processes have to be clarified. Here, we have investigated the structural relaxation in the singlet excited state of star-shaped oligofluorenes with a truxene or isotruxene core, to which oligofluorenes (n = 1–4) were attached. The transient absorption peak showed red-shift with time upon excitation. The fluorescence decay profiles in the picosecond domain showed the fast component in addition to the component corresponding to the singlet excited state lifetime. These ultrafast phenomena can be attributed to the structural relaxation, i.e., planarization, in the singlet excited state. The planarization process was supported by the theoretical calculation based on the time-dependent density functional theory. Furthermore, dependence of two-photon absorption cross section on the core of the star-shaped oligofluorene has been elucidated.
Co-reporter:Sooyeon Kim, Jungkweon Choi, and Tetsuro Majima
The Journal of Physical Chemistry B 2011 Volume 115(Issue 51) pp:15399-15405
Publication Date(Web):November 15, 2011
DOI:10.1021/jp208911t
The investigation on the self-assembly of polydeoxyadenylic acid (poly(dA)) is highly important to fully understand its biological function and for its application in the field of nanotechnology. Using the fluorescence resonance energy transfer (FRET) technique, we report investigations for the self-assembly of adenine oligomers induced by pH and coralyne binding at the single-molecule level and in the bulk phase. Results presented here show that A-motif 1 (Alexa488-5′-(dA)20-3′-Cy5-5′-(dA)20-3′-Alexa488) forms the wire-type duplex at acidic pH, whereas the same conformation of A-motif 2 (Alexa488-5′-(dA)20-3′-Cy5-3′-(dA)20-5′-Alexa488) is induced by coralyne binding at neutral pH. These results indicate that poly(dA) at acidic pH forms a right-handed helical duplex with parallel-mannered chains, whereas the coralyne–poly(dA) binding induces a stable antiparallel duplex. Furthermore, we found that the antiparallel duplex of poly(dA) formed by coralyne binding has a rather extended and less twisted structure as compared to the parallel duplex of poly(dA) formed at acidic pH. On the other hand, from dilution experiments, we found that the parallel duplex formed at acidic pH is converted to “S-form”, which has the single-stranded structure with short intramolecular double-stranded regions formed by intramolecular A:A base pairing, while the A-motif–coralyne assembly is dissociated into single strands below a certain concentration. The formation of S-form with a short intramolecular double-stranded region formed at acidic pH and very low concentration is confirmed by the quantitative analysis of FCS curve to measure the hydrodynamic radius of a molecule.
Co-reporter:Mamoru Fujitsuka and Tetsuro Majima
The Journal of Physical Chemistry Letters 2011 Volume 2(Issue 23) pp:2965-2971
Publication Date(Web):November 8, 2011
DOI:10.1021/jz201274j
In the present Perspective, a recent approach in radiation chemistry is summarized. By employing radiation chemical methods, such as γ-ray radiolysis and pulse radiolysis, powerful oxidative and reductive species can be generated to initiate various reactions. Thus, radiation chemical methods are applicable to various systems in a wide variety of fields and are not restricted to basic radical or radical ion chemistry. For example, our research group has employed radiation chemical methods to elucidate the mechanisms of various phenomena. Here, radiation chemical investigations on the charge delocalization process, excited radical ions, photocatalytic systems, emitting devices, and biological systems are introduced as examples of the wide applicability of radiation chemistry. Radiation chemical methods should be useful for a wide variety of researchers in the future as well.
Co-reporter:Mamoru Fujitsuka, Hisashi Shimakoshi, Yoshio Hisaeda, Tetsuro Majima
Journal of Photochemistry and Photobiology A: Chemistry 2011 Volume 217(Issue 1) pp:242-248
Publication Date(Web):1 January 2011
DOI:10.1016/j.jphotochem.2010.10.016
The internal reorganization energy (λV) of photoinduced electron transfer (ET) in the supramolecular donor–acceptor dyads of 2,3,7,8,12,13,17,18-octaethylporphinatozinc(II) (ZnOEP) and electron acceptor ligands was compared with those of structural isomers, 2,3,7,8,11,12,17,18-octaethylhemiporphycenatozinc(II) (ZnHPc) and 2,3,6,7,12,13,16,17-octaethylporphycenatozinc(II) (ZnPcn). First, ET process of the supramolecular donor–acceptor dyads of ZnOEP was investigated by means of the transient absorption spectroscopy mainly. The formation of supramolecular dyads was confirmed by absorption spectral change, from which the association constant was estimated. The ET process was confirmed by the observation of radical cation of ZnOEP during the laser flash photolysis. The ET rates of these dyads are in the order of ZnOEP > ZnHPc > ZnPcn, when the driving forces for ET are similar to each other. From the free energy dependence of ET rates, the λV values of OEP and its isomers were estimated. The estimated λV value was in the order of ZnOEP < ZnHPc < ZnPcn. This tendency was reproduced by calculation at B3LYP/6-31G(d) and BHandHLYP/6-31G(d) levels. The origin of this tendency was discussed on the basis of the structural change during the ET process.
Co-reporter:Takashi Tachikawa and Tetsuro Majima
Chemical Society Reviews 2010 vol. 39(Issue 12) pp:4802-4819
Publication Date(Web):07 Sep 2010
DOI:10.1039/B919698F
Nanostructured metal oxide semiconductors, such as TiO2 and ZnO, have attracted great attention as the promising material for photovoltaic devices, photocatalysts for water splitting and environmental purification, sensors, batteries, etc. In this critical review, we have focused on the on-site observation of interfacial chemical reactions involving charge carriers and reactive oxygen species (ROS), such as singlet oxygen and the hydroxyl radical, generated by the photoexcitation of TiO2 nanoparticles using single-molecule, single-particle fluorescence spectroscopy. Advanced fluorescence imaging techniques enable us to determine the location of the photocatalytically active sites that are closely related to the defects heterogeneously distributed on the surface. Consequently, this review provides a great opportunity to understand the temporal and spatial heterogeneities within an individual catalyst particle, allowing for the potential use of single-molecule, single-particle approaches in the analysis of photocatalytic reactions (189 references).
Co-reporter:Kiyohiko Kawai ; Haruka Kodera
Journal of the American Chemical Society 2010 Volume 132(Issue 40) pp:14216-14220
Publication Date(Web):September 22, 2010
DOI:10.1021/ja105850d
By decreasing the HOMO energy gap between the base-pairs to increase the charge conductivity of DNA, the positive charge photochemically generated in DNA can be made to migrate along the π-way of DNA over long distances to form a long-lived charge-separated state. By fine-tuning the kinetics of the charge-transfer reactions, we designed a functionalized DNA system in which absorbed photon energy is converted into chemical energy to form I−I covalent bonds, where more than 100 I2 molecules were produced per functionalized DNA. Utilizing the fact that charge-transfer kinetics through DNA is sensitive to the presence of a single mismatch that causes the perturbation of the π-stacks, single nucleotide polymorphisms (SNPs) in genomic sequences were detected by measuring the photon energy conversion efficiency in DNA by a conventional starch iodine method.
Co-reporter:Jungkweon Choi, Takashi Tachikawa, Youngmin Kim, Mamoru Fujitsuka, Hyotcherl Ihee and Tetsuro Majima
Chemical Communications 2010 vol. 46(Issue 48) pp:9155-9157
Publication Date(Web):01 Nov 2010
DOI:10.1039/C0CC03056B
The study of the structural reorganization and photophysical properties of Zn–Cytc using the single-molecule and ensemble-averaged spectroscopy shows that the photoblinking behaviors of single-Zn–Cytc depend on the folded and unfolded structures, whereas the fluorescence dynamics of Zn–Cytc observed in the bulk phase are hardly affected by the conformational change of a protein.
Co-reporter:Kiyohiko Kawai, Eri Matsutani and Tetsuro Majima
Chemical Communications 2010 vol. 46(Issue 19) pp:3277-3279
Publication Date(Web):29 Mar 2010
DOI:10.1039/C002810J
The kinetics and efficiency of oxidative degradation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo) in DNA during the photosensitized one-electron oxidation of DNA was investigated. The presence of 8-oxodGuo was shown to increase the lifetime of the charge-separated state in DNA by serving as a “hole sink” resulting in efficient and exclusive degradation.
Co-reporter:Masanori Sakamoto, Sung Sik Kim, Hirotoshi Furusho and Tetsuro Majima
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 2) pp:365-372
Publication Date(Web):11 Nov 2009
DOI:10.1039/B917981J
Photochemical synthesis of metal nanostructures through photosensitized reduction of metal sources is a powerful method in a wide variety of environments, because light can selectively promote the desired reaction without damaging the surrounding environment. A drawback of the method is that most organic photosensitizers are disposable and consumed during the photochemical reactions and as a consequence a much larger amount of photosensitizer than that of the metal source is usually required, and therefore, the photosensitized reduction method is wasteful in terms of the sensitizer. In the present work, we propose a new photochemical synthetic method using a recyclable photosensitizer and applied it to fabricate Ag nanostructures at the solid–liquid interface. The photosensitized reduction of Ag ion at the solid–liquid interface resulted in the formation of unique Ag nanostructures (nanowires or plates) without the use of templates or stabilizing agents. The relation between the morphology and several external contributing factors, such as solvent polarity and interaction between the substrate and crystal phase, was discussed.
Co-reporter:Mamoru Fujitsuka, Takeshi Nakatani, Masanori Sakamoto, Akira Sugimoto, and Tetsuro Majima
The Journal of Physical Chemistry A 2010 Volume 114(Issue 40) pp:10789-10794
Publication Date(Web):September 20, 2010
DOI:10.1021/jp106056e
In the present paper, we have investigated the inter- and intramolecular electron transfer processes from the higher triplet excited state (Tn) of oligothiophenes (3T and 4T). In the case of the intermolecular systems, two-color two-laser flash photolysis using nanosecond lasers was applied to the solution including benzophenone, oligothiophene, and halogenated benzene as a photosensitizer, an electron donor, and an electron acceptor, respectively. The first laser light irradiation generated the lowest triplet excited state (T1) of oligothiophene via energy transfer from benzophenone. Upon the second laser light irradiation, the absorption band of the radical cation of oligothiophene appeared with the simultaneous bleaching of the absorption band of the T1 state, indicating the electron transfer from the T2 state of the oligothiophene to the electron acceptor. The observed electron transfer rate dependent on the free energy change was explained on the basis of the Marcus theory. The intramolecular electron transfer in the dyad molecule of oligothiophene and acceptor was investigated using the two-color two-laser flash photolysis employing femtosecond laser. Upon the second laser light irradiation, which generates the Tn state, the kinetic trace of the absorption band of T1 state showed the bleaching and recovery, the rate of which depends on the driving force for the charge separation from the T2 state of the oligothiophene. This observation suggests the existence of charge separation process from the T2 state, and the observation of the charge-separated state was difficult probably due to the low charge separation yield and fast charge recombination.
Co-reporter:Jun Rye Choi, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
The Journal of Physical Chemistry Letters 2010 Volume 1(Issue 7) pp:1101-1106
Publication Date(Web):March 15, 2010
DOI:10.1021/jz100243u
We report in situ observations of molecular interactions and photodynamics for the polarity-sensitive fluorescence dye 4-dimethylamino-4′-nitrostilbene (DNS) when encapsulated inside of metal−organic frameworks (MOFs) by utilizing single-molecule, single-particle fluorescence spectroscopy. While the fluorescence intensity from DNS molecules adsorbed onto the surface of MOF-177 particles exhibited a strong solvent polarity dependence toward external solvent exchanges, the intensity from molecules encapsulated inside of well-defined MOF-177 particles slightly changed when the solvent was switched from toluene to chloroform. Furthermore, the photostability of the DNS molecules was significantly enhanced by incorporation into the MOF host. These observations strongly suggest that guest molecules encapsulated in MOFs should be protected from external solvent and gas molecules. The photoblinking behavior of encapsulated single DNS molecules was also observed and analyzed in terms of the probability density.Keywords (keywords): host−guest; metal−organic framework; polarity-sensitive probe; single-molecule fluorescence spectroscopy;
Co-reporter:Kazuki Tainaka, Mamoru Fujitsuka, Tadao Takada, Kiyohiko Kawai, and Tetsuro Majima
The Journal of Physical Chemistry B 2010 Volume 114(Issue 45) pp:14657-14663
Publication Date(Web):May 28, 2010
DOI:10.1021/jp1024685
DNA-mediated charge transfer has recently received a substantial attention because of its biological relevance in the DNA damage and DNA repair as well as the potential applications to nanoscale electronic devices. In contrast to the numerous mechanistic studies on oxidative hole transfer (HT) through DNA, our understanding of reductive electron transfer process still remains limited. In this article, we demonstrate the results of direct observation of the excess electron transfer (EET) through DNA, which conjugated with aminopyrene (APy) and diphenylacetylene (DPA) as a photosensitizing donor and an acceptor of excess electron, respectively. By inserting dihydrothymine as a spacer between APy and T or C, the yield of electron arrival to DPA was improved. It was indicated that EET through DNA completed within a few or a few tens nanosecond time scale even for EET over 34 Å for both consecutive T and C sequences. The various factors such as mismatch sequence and DNA length on the yield of electron arrival to DPA were examined.
Co-reporter:Kiyohiko Kawai, Yasuko Osakada, Eri Matsutani and Tetsuro Majima
The Journal of Physical Chemistry B 2010 Volume 114(Issue 31) pp:10195-10199
Publication Date(Web):July 16, 2010
DOI:10.1021/jp102483k
Charge-separation and charge-recombination dynamics and oxidative DNA degradation were investigated for DNA modified with a photosensitizer (Sens) naphthalimide (NI), naphthaldiimide (ND), or anthraquinone (AQ). In all three Sens-modified DNA systems, the formation of long-lived charge-separated states was observed in which the lifetime increased with increasing numbers of A-T base pairs between Sens and the neighboring G-C base pair. The lifetime of the charge-separated state correlated well with the DNA damage yield, indicating that the charge-separated state provides time for the irreversible DNA oxidative damage to occur. The quantum yield of DNA damage was the lowest for ND-modified DNA due to the slow reaction of ND radical anion with molecular oxygen; the process needed to preclude charge recombination. The AQ-modified DNA resulted in the highest charge separation and subsequent DNA damage yield, which would be partly explained by the formation of the spin-forbidden triplet radical ion pairs during charge separation.
Co-reporter:Sachiko Tojo, Mamoru Fujitsuka and Tetsuro Majima
The Journal of Organic Chemistry 2010 Volume 75(Issue 11) pp:3618-3625
Publication Date(Web):May 7, 2010
DOI:10.1021/jo1003949
An acyclic 1,4-distonic dimer radical cation (DAE2•+) was generated from the dimerization of 1,1-bis(4-methoxyphenyl)ethylene radical cation (DAE•+) with the neutral molecule (DAE) in solution. The absorption spectrum of DAE2•+ shows bimodal absorption bands with peaks at 350 and 500 nm corresponding to the 1,1-bis(4-methoxyphenyl)ethyl radical (An2C•CH3) and 1,1-bis(4-methoxyphenyl)ethyl cation (An2C+CH3), respectively. Therefore, DAE2•+ in the ground state has the spin and positive charge localized on the 1- and 4-positions, respectively. The bimodal characteristic emissions by the site-selective excitation of radical and cation sites of DAE2•+ were observed at 77 K, showing that the excitation energy is localized on the radical or cation site of DAE2•+ in the excited state. The interaction between radical and cation sites of DAE2•+ in the ground and excited states are discussed on the basis of the steady-state spectroscopic and transient absorption measurements, as well as theoretical calculations.
Co-reporter:Takashi Tachikawa Dr.;Soichiro Yamashita Dr.
Angewandte Chemie International Edition 2010 Volume 49( Issue 2) pp:432-435
Publication Date(Web):
DOI:10.1002/anie.200904876
Co-reporter:Dr. Takashi Tachikawa;Nan Wang ;Soichiro Yamashita;Shi-Cong Cui;Dr. Tetsuro Majima
Angewandte Chemie International Edition 2010 Volume 49( Issue 46) pp:8593-8597
Publication Date(Web):
DOI:10.1002/anie.201004976
Co-reporter:Mamoru Fujitsuka, Hisashi Shimakoshi, Sachiko Tojo, Lingli Cheng, Daisuke Maeda, Yoshio Hisaeda and Tetsuro Majima
The Journal of Physical Chemistry A 2010 Volume 114(Issue 12) pp:4156-4162
Publication Date(Web):March 3, 2010
DOI:10.1021/jp9119342
In the present study, photoinduced electron transfer (ET) processes of supramolecular donor−acceptor dyads of Zn 2,3,7,8,11,12,17,18-octaethylhemiporphycene (ZnHPc) and axial ligands were investigated by using various spectroscopic methods. The formation of 1:1 dyads was confirmed by absorption spectral change during titration of axial ligand. The association constants were determined from the spectral change. Quenching of the fluorescence intensity was observed when electron acceptor ability of the axial ligand increased. The driving forces for ET were estimated based on the estimated redox potentials and structural parameters. It became clear that various ZnHPc dyads showed ET because of slightly higher donor-ability and larger excitation energy of ZnHPc when compared to the corresponding dyads of Zn porphycene (ZnPcn). The transient absorption spectra during the sub-picosecond laser flash photolysis showed the formation of charge separated state, that is, radical cation of ZnHPc and radical anion of axial ligand, from the singlet excited ZnHPc. The observed ET rates were compared with the previously reported values for Zn porphyrins and ZnPcn. The ET rates of ZnHPc were located between those observed with porphyrins and ZnPcn supramolecular dyads, even when the −ΔG values were similar to each other. This observation was explained on the basis of the variation in reorganization energy and electronic coupling (V) values. Furthermore, distribution of HOMO electron density gave a plausible explanation for the variation in V values of these dyads.
Co-reporter:Shi-Cong Cui, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
The Journal of Physical Chemistry C 2010 Volume 114(Issue 2) pp:1217-1225
Publication Date(Web):November 10, 2009
DOI:10.1021/jp909579j
Photoinduced electron transfer (ET) to and from semiconductor quantum dots (QDs) is of intense interest because of its important roles in QD-based devices, such as detectors, light-emitting diodes, and solar cells. In this study, we have investigated the solvent dependence of the interfacial ET between ZnS-capped CdSe (CdSe/ZnS) QDs and pyromellitimide (PI) at the ensemble and single-particle levels. The steady-state and time-resolved photoluminescence (PL) and absorption measurements revealed that the rates of ET from the excited CdSe/ZnS to the adsorbed PI-CA molecules in nonpolar solvents, such as octane and toluene, are higher than aprotic polar solvents, such as benzonitrile. Furthermore, it was found that two pathways are included in the ET processes between CdSe/ZnS and PI, that is, ET from the excited CdSe core to PI-CA molecules adsorbed on the surface of the CdSe or ZnS. The former process proceeds on the picosecond time scale, while the latter proceeds on the nanosecond time scale. The interfacial ET dynamics in individual CdSe/ZnS-PI conjugates in different solvents were next examined. The PL intermittency or blinking kinetics of single QDs were analyzed by adapting a diffusion-controlled electron transfer (DCET) theory for the probability distribution of the “on” events. The results, which are qualitatively consistent with that obtained from the bulk experiments, clearly showed that the probability of the ET events increases with the decreasing solvent polarity. Consequently, our findings provide new insight into the mechanism of the interfacial ET reactions on the semiconductor nanoparticles and potentially contribute to the development of the design of QD-based devices.
Co-reporter:Jun Rye Choi, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
Langmuir 2010 Volume 26(Issue 13) pp:10437-10443
Publication Date(Web):June 1, 2010
DOI:10.1021/la101770h
Lanthanide-based metal−organic frameworks (Ln-MOFs) are fascinating because of their versatile coordination geometry, unique luminescent and magnetic properties, and possible high framework stability to water. We synthesized nanosized europium-based MOF (Eu-MOF) particles and investigated the photoinduced electron transfer between the excited Eu-MOF nanoparticles and various organic compounds, such as aromatic sulfides and amines. From the time-resolved emission measurements, the bimolecular quenching rate constants of luminescence from the Eu3+ ions in the MOF framework by electron donors were determined and explained in terms of the Marcus theory of electron-transfer reactions. Furthermore, spatially resolved emission quenching images obtained by confocal fluorescence microscopy revealed that small (large) quencher molecules quickly (slowly) and homogeneously (inhomogeneously) penetrate microsized Eu-MOF crystals. These observations led us confidently to assume the possibility that Eu-MOFs work as a size-selective photocatalyst for the one-electron oxidation of organic compounds.
Co-reporter:Yi Wei ; Shingo Samori ; Sachiko Tojo ; Mamoru Fujitsuka ; Jin-Sheng Lin ; Chien-Tien Chen
Journal of the American Chemical Society 2009 Volume 131(Issue 19) pp:6698-6707
Publication Date(Web):April 22, 2009
DOI:10.1021/ja8090005
A series of bipolar OLED materials were subjected to pulsed radiolysis experiments to determine their transient absorption and lifetime profiles of the independently in situ generated radical cations and anions in solutions. Moreover, their emission behaviors from the charge recombination of their radical ions were also determined by the pulse radiolysis method. It was found the absorption bands in doubly ortho-linked quinoxaline/diphenylfluorene hybrids 1a−e are red-shifted progressively with increasing electron-donating nature at the C5 and C8 positions of the quinoxaline template. The incipient radical anions in 1a−e are mainly localized on the quinoxaline heterocyclic moiety, whereas the incipient radical cations are mainly distributed onto the attached electron-donating groups at the C5 and C8 positions of the quinoxaline template. For other doubly ortho-linked cis-stilbene derivatives 3d, 3f, and 4f, the radical anions are mainly localized on the cis-stilbene central moiety and the radical cation is mainly distributed onto both para substituents of the cis-stilbene templates. It was also shown that there is a correlation between their optoelectronic emission efficiencies and the radiolysis induced emission intensities. In addition, the charge transporting behaviors within an OLED device were found to show the relationship with transient absorption half-lives (τ1/2) of the radical ions. Charge recombination mechanisms in both the OLED and pulsed radiolysis experiments were proposed to rationalize these observations, allowing us to establish some guidelines for an ultimate molecular design of ideal bipolar optoelectronic materials with a judicious choice of local charge appendages in the optoelectronic templates.
Co-reporter:Tadao Takada ; Yuichiro Takeda ; Mamoru Fujitsuka
Journal of the American Chemical Society 2009 Volume 131(Issue 19) pp:6656-6657
Publication Date(Web):April 23, 2009
DOI:10.1021/ja9009919
The DNA base stack provides unique features for the efficient long-range charge transfer. For the purpose of investigating the hole transfer process of individual DNA and the optical readout of DNA information at the single molecule level, we performed single-molecule detection of DNA hole transfer (DNA HT) using single-molecule fluorescence spectroscopy. We have established the single-molecule detection of DNA HT at the single molecule level based on the fluorescence generation by combining the oxidative reaction of the quencher molecule through DNA HT and the cancelation of FRET. This “signal-on” detection system makes it possible to detect DNA HT in individual DNA and the base-pair mismatch in the target DNA with high sensitivity and accuracy.
Co-reporter:Kiyohiko Kawai ; Haruka Kodera
Journal of the American Chemical Society 2009 Volume 132(Issue 2) pp:627-630
Publication Date(Web):December 16, 2009
DOI:10.1021/ja907409z
A positive charge migrates along DNA mainly via a series of short-range charge transfer (CT) processes between G-C base pairs, which have relatively high HOMO levels. As such, the CT efficiency sharply decreases with the insertion of A-T base pairs between the G-C base pairs. We have previously demonstrated that the CT efficiency through DNA can be dramatically increased by using deazaadenine (Z), an analogue of A, to adjust the HOMO levels of the A-T base pairs closer to those of the G-C base pairs (Nat. Chem. 2009, 1, 156). In the present study, we have expanded this approach to show that the CT efficiency can also be increased by replacing A bases with diaminopurine (D).
Co-reporter:Takashi Tachikawa
Journal of the American Chemical Society 2009 Volume 131(Issue 24) pp:8485-8495
Publication Date(Web):May 29, 2009
DOI:10.1021/ja900194m
One-dimensional nanostructures of metal oxide semiconductors have both potential and demonstrated applications for use in light waveguides, photodetectors, solar energy conversion, photocatalysis, etc. We investigated the transport and reaction dynamics of the photogenerated charge carriers in individual titania nanowires using single-particle photoluminescence (PL) spectroscopy. Examination of the spectral and kinetic characteristics revealed that the photoluminescence bands originating from defects in the bulk and/or on the surface appeared in the visible region with numerous photon bursts by photoirradiation using a 405-nm laser under an Ar atmosphere. From the single-molecule kinetic analysis of the bursts, it was found that the quenching reaction of trapped electrons by molecular oxygen follows a Langmuir−Hinshelwood mechanism. In addition, a novel spectroscopic method, i.e., single-molecule spectroelectrochemistry, was utilized to explore the nature of the defect states inherent in the wires. The spatially resolved PL imaging techniques thus enable us to ascertain the location of the luminescent active sites that are related to the heterogeneously distributed defects and to present experimental evidence of the long-distance transport of charge carriers in the wire. Consequently, this study provides a great opportunity to understand the role of defects in the behavior of charge carriers in TiO2 nanomaterials with various morphologies.
Co-reporter:Mamoru Fujitsuka, Sachiko Tojo, Teruo Shinmyozu and Tetsuro Majima
Chemical Communications 2009 (Issue 12) pp:1553-1555
Publication Date(Web):20 Feb 2009
DOI:10.1039/B810122A
Intramolecular dimer radical anions of [3n]cyclophanes generated by γ-ray irradiation in low-temperature glassy matrices showed an absorption band attributable to charge resonance around 936–1210 nm, from which the stabilization energy of the dimer radical anions were analyzed on the basis of π-electron delocalization over two benzene rings and the damping factor (β) was estimated to be 0.35 Å−1, which is smaller than that of the intramolecular dimer radical cation of [3n]cyclophanes, indicating a effective charge delocalization of the dimer radical anions.
Co-reporter:Kiyohiko Kawai Dr.;Yasuko Osakada Dr.
ChemPhysChem 2009 Volume 10( Issue 11) pp:1766-1769
Publication Date(Web):
DOI:10.1002/cphc.200900148
Co-reporter:Masanori Sakamoto, Mamoru Fujistuka, Tetsuro Majima
Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2009 Volume 10(Issue 1) pp:33-56
Publication Date(Web):March 2009
DOI:10.1016/j.jphotochemrev.2008.11.002
The photo-induced synthesis of metal nanoparticles (NPs) was reviewed with a closer look at those based on photochemistry. Recent developments in metal NPs research, photochemistry, and photoprocessing techniques have allowed researchers to devise various photo-induced synthetic strategies to obtain metal NPs under a variety of conditions. We begin by outlining the classical method. The photochemical synthesis of metal NPs including direct photoreduction and photosensitization has been developed to achieve decent yields. We focused on stabilization and functionalization method of NPs in photochemical synthesis, which has enabled us to fabricate a variety of metal nanostructures and composite materials. In addition, we mention an alternative approach, that is, laser ablation at the solid–liquid interface. Some of the most innovative studies dealing with the three-dimensional fabrication of metal NPs are highlighted, together with new directions such as potential applications for a light-driven actuator, bioimaging, and three-dimensional processing. This review is concluded with the future perspectives for the photo-induced synthesis of metal NPs.
Co-reporter:Shingo Samori, Sachiko Tojo, Mamoru Fujitsuka, Tetsuro Majima
Journal of Photochemistry and Photobiology A: Chemistry 2009 Volume 205(2–3) pp:179-185
Publication Date(Web):25 June 2009
DOI:10.1016/j.jphotochem.2009.05.003
Emission from charge recombination between radical cation and anion of various aromatic hydrocarbons (AHs) was observed in the time scales of nanosecond to microsecond during the pulse radiolysis of AH in benzene (Bz). Based on the time-dependent emission study, it is suggested that AH in the excited singlet state (1AH*) is generated in the nanosecond to microsecond time scale mainly from the charge recombination between AH radical cation (AH+) and AH radical anion (AH−). This mechanism is reasonably explained by the relationship between the annihilation enthalpy change (−ΔH°) for the charge recombination and excitation energies of 1AH* (ES1). It is found that the rate constant of the charge recombination (krec) between AH+ and AH− increases with the increase of energy differences between −ΔH° and ES1 of AH (−ΔH° − ES1), indicating that the intensity of the radiolysis-induced emission from AH (I) depends on (−ΔH° − ES1). The effect of (−ΔH° − ES1) on I value was also examined during the pulse radiolysis of mixtures of two AHs in Bz. Consequently, it is suggested that not only the fluorescence quantum yield (Φfl) of 1AH* but also (−ΔH° − ES1) is important factor for the formation yield of 1AH* during the pulse radiolysis of AH in Bz.
Co-reporter:Masanori Sakamoto, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
Langmuir 2009 Volume 25(Issue 24) pp:13888-13893
Publication Date(Web):July 2, 2009
DOI:10.1021/la901552f
Noble metal clusters of sizes comparable to the Fermi wavelength are known to exhibit molecule-like transitions owing to the discretion of the density of states. In the present article, the important factors influencing the reactivity of excited gold (Au) clusters are examined from the viewpoint of molecular photochemistry. The investigation of the differently sized Au clusters embedded in a polymer film using single-molecule fluorescence spectroscopy facilitates the further understanding of their size-dependent photoreactivity. In addition, it was discovered that the spin multiplicity of the excited state (i.e., singlet or triplet excited state) governs the photoreactivity.
Co-reporter:Mamoru Fujitsuka, Hisashi Shimakoshi, Sachiko Tojo, Lingli Cheng, Daisuke Maeda, Yoshio Hisaeda and Tetsuro Majima
The Journal of Physical Chemistry A 2009 Volume 113(Issue 14) pp:3330-3335
Publication Date(Web):March 12, 2009
DOI:10.1021/jp810617a
The electron transfer processes of Zn octaethylporphycene (ZnPcn), a structural isomer of Zn octaethylporphyrin, have been investigated mainly using transient absorption spectroscopy. To form a supramolecular donor−acceptor dyad, imide compounds bearing a pyridine group at the N position of the imides have been used as an acceptor. The N atom of the pyridine ring can coordinate to the central Zn ion of ZnPcn. Formation of a supramolecular donor−acceptor dyad, that is, pentacoordinated ZnPcn, was confirmed by steady-state absorption spectroscopy using toluene as a solvent. Charge separation upon excitation of ZnPcn was indicated by efficient fluorescence quenching, especially when pyromellitic diimide was used as the acceptor. Electron transfer processes were confirmed by subpicosecond transient absorption spectroscopy, in which generation of a radical anion of the acceptor and a radical cation of ZnPcn, which was identified by means of γ-ray radiolysis, was confirmed. It became clear that the charge separation rate was smaller than that of the corresponding supramolecular dyads of Zn tetraphenylporphyrin and Zn octaethylporphyrin despite a similar driving force. This observation indicates a larger internal reorganization energy and a smaller coupling element of the ZnPcn dyad.
Co-reporter:Minoru Yamaji, Xichen Cai, Masanori Sakamoto, Mamoru Fujitsuka and Tetsuro Majima
The Journal of Physical Chemistry A 2009 Volume 113(Issue 9) pp:1696-1703
Publication Date(Web):February 4, 2009
DOI:10.1021/jp8098208
Photochemical properties in the lowest singlet and triplet excited states (S1 and T1) and in the higher triplet excited states (Tn) of p-phenylbenzoyl derivatives (PB-X) having C−O and C−S bonds were investigated in solution using a stepwise two-color two-laser flash photolysis technique. PB-Xs (X = OPh and SPh as a leaving group) undergo α-bond dissociation in the S1 state, while the C−O bonds in PB-OH and -OMe were stable upon the 266-nm laser flash photolysis. The T1(π,π*) states of PB-X were efficiently produced during the 355-nm laser flash photolysis of PB-X in the presence of benzophenone as a triplet sensitizer. The T1(π,π*) states of PB-Xs deactivate to the ground-state without producing any intermediates. However, when PB-Xs (X = OPh and SPh) in the T1 states (PB-X(T1)) were excited upon the 430-nm laser flash photolysis, their disappearance was observed. These observations indicate that PB-X(T1) (X = OPh and SPh) is excited to PB-Xs in the Tn states which decompose through the C−X bond cleavage. From the transient absorption measurements, quantum yields (Φdec) of the disappearance of PB-X(T1) were determined while bond dissociation energies (BDE) of the C−X bonds of PB-X were calculated by computations. On the basis of the Φdec and the BDE values, it was shown that the rates of the decomposition process of PB-X in the Tn states were expressed in an energy gap low form as a function of BDE. Features of the C−X bond cleavage of PB-X in the Tn states were discussed.
Co-reporter:Shingo Samori, Sachiko Tojo, Mamoru Fujitsuka, Torben Ryhding, Aaron G. Fix, Brittany M. Armstrong, Michael M. Haley and Tetsuro Majima
The Journal of Organic Chemistry 2009 Volume 74(Issue 10) pp:3776-3782
Publication Date(Web):April 14, 2009
DOI:10.1021/jo900494j
Emission from charge recombination between radical cations and anions of a series of regioisomeric 1,4-, 1,3-, and 1,2-bis(phenylethynyl)benzenes (bPEBs) substituted by various electron donor and/or acceptor groups was measured during pulse radiolysis in benzene (Bz). The formation of bPEB in the excited singlet state (1bPEB*) can be attributed to the charge recombination between bPEB• + and bPEB• −, which are initially generated from the radiolytic reaction. This mechanism is reasonably explained by the relationship between the annihilation enthalpy change (−ΔH°) for the charge recombination of bPEB• + and bPEB• − and excitation energy of 1bPEB*. Since the degree of the π-conjugation in the S1 state and HOMO−LUMO levels of bPEB change with the substitution pattern of phenylacetylene groups on the central benzene ring and the various kinds of donor and/or acceptor group, the fine-tuning of the emission color and intensity of bPEB can be easily carried out during pulse radiolysis in Bz. For donor-acceptor-substituted bPEB, it was found that the difference in the charge transfer conjugated pathways between donor and acceptor substituents (linear-, cross-, and “bent”-conjugated pathways) strongly influenced the HOMO−LUMO energy gap.
Co-reporter:Takashi Tachikawa and Tetsuro Majima
Langmuir 2009 Volume 25(Issue 14) pp:7791-7802
Publication Date(Web):April 29, 2009
DOI:10.1021/la900790f
Heterogeneous photocatalysts have both potential and demonstrated applications for use in the water-splitting reaction that produces hydrogen, the degradation of organic pollutants, the surface wettability conversion, etc. In this feature article, we have focused on the in-site observation of various reactive oxygen species (ROS), such as singlet oxygen (1O2) and the hydroxyl radical (•OH), generated by the photoexcitation of TiO2 nanomaterials using single-molecule fluorescence spectroscopy. The spatially resolved photoluminescence (PL) imaging techniques enable us to determine the location of the (photo)catalytically active sites that are related to the heterogeneously distributed defects on the surface. We also present the results that revealed the formation and reaction dynamics of the photogenerated charge carriers in individual TiO2 nanoparticles. Furthermore, we introduce the single-molecule single-mismatch detection of the nucleotide sequence upon the photoexcitation of a novel nanoconjugate consisting of TiO2 and DNA on the basis of the mechanistic aspects. Notably, the present conjugates can recognize the difference in a single nucleotide. Consequently, this article provides a significant opportunity to understand the temporal and spatial distributions of ROS generated during the photoirradiation of TiO2 nanomaterials and directly explore the microscopic world in many fields ranging from fundamental physics and chemistry to practical applications.
Co-reporter:Masanori Sakamoto;Takashi Tachikawa;Mamoru Fujitsuka
Advanced Materials 2008 Volume 20( Issue 18) pp:3427-3432
Publication Date(Web):
DOI:10.1002/adma.200800404
Co-reporter:Masanori Sakamoto, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
Chemistry of Materials 2008 Volume 20(Issue 6) pp:2060
Publication Date(Web):February 22, 2008
DOI:10.1021/cm702170h
Co-reporter:Yasuko Osakada, Kiyohiko Kawai, Mamoru Fujitsuka and Tetsuro Majima
Chemical Communications 2008 (Issue 23) pp:2656-2658
Publication Date(Web):08 May 2008
DOI:10.1039/B801876F
Transient absorption measurements of charge transfer (CT) demonstrated that the CT in the DNA assembly constructed by simply mixing DNAs with sticky ends occurs over 200 Å selectively to the complementary sticky end sequences.
Co-reporter:Takashi Tachikawa Dr.;Takamasa Ishigaki Dr.;Ji-Guang Li Dr.;Mamoru Fujitsuka Dr. Dr.
Angewandte Chemie 2008 Volume 120( Issue 29) pp:5428-5432
Publication Date(Web):
DOI:10.1002/ange.200800528
Co-reporter:Koji Nakayama, Takashi Tachikawa and Tetsuro Majima
Langmuir 2008 Volume 24(Issue 13) pp:6425-6428
Publication Date(Web):May 29, 2008
DOI:10.1021/la801028m
Protein adsorption and dissociation on cell membrane surfaces is a topic of important study to reveal biological processes including signal transduction and protein trafficking. We demonstrated here the establishment of a mimic model system for the spatial control of protein adsorption/elimination on a lipid bimembrane using a photochemical technique. The novel photoeliminative linker that we synthesized here consists of three distinct components: a substrate (biotin), a photoeliminative group (4-(4-(1-hydroxyethyl)-2-methoxy-5-nitrophenoxy)butanoic acid), and a lipid bimembrane-adsorbent group (farnesyl). The photoeliminative linker was inserted on the entire surface of the lipid bimembrane and two-dimensionally eliminated by spatial UV irradiation onto the membrane to create a biotin pattern. A target protein, streptavidin was selectively immobilized on the patterned biotin, although it was almost not attached on the nonirradiated region. The streptavidin array was selectively dissociated by UV irradiation onto the entire membrane.
Co-reporter:Takashi Tachikawa Dr.;Takamasa Ishigaki Dr.;Ji-Guang Li Dr.;Mamoru Fujitsuka Dr. Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 29) pp:5348-5352
Publication Date(Web):
DOI:10.1002/anie.200800528
Co-reporter:Sachiko Tojo ; Takashi Tachikawa ; Mamoru Fujitsuka
The Journal of Physical Chemistry C 2008 Volume 112(Issue 38) pp:14948-14954
Publication Date(Web):August 30, 2008
DOI:10.1021/jp804985f
Iodine-doped TiO2 powders (I-TiO2) prepared via hydrothermal treatment have absorption in the region of ultraviolet (UV) and visible light, and were used as a photocatalyst with irradiation of UV or visible light. The I-TiO2 powders were characterized by XRD, TEM, EDS, XPS, FTIR, and steady-state UV−vis diffuse reflectance spectra (DRS), and their photocatalytic activities were investigated based on the photodegradation of 4-chlorophenol (4-CP) in water. A higher photodegradation efficiency of 4-CP was observed for I-TiO2 under UV- and visible-light irradiation, when compared to the undoped TiO2. The transient behavior of the photogenerated charge carriers, such as trapped electrons (e−) and holes (h+), and the one-electron oxidation dynamics of substrates during UV or visible laser flash photolysis of undoped TiO2 and I-TiO2 powders were investigated using time-resolved diffuse reflectance (TDR) spectroscopy. The time evolution of transient signals indicated that the long-lived photogenerated h+ were formed upon the laser excitation of I-TiO2 powders, while no trapped e− were observed. From the experimental results, it is suggested that the recombination of e−−h+ pairs is inhibited because the doping I sites act as trapping site to capture the e− during the I-TiO2 photocaltalytic reaction. Furthermore, the trapped h+ generated in I-TiO2 have no significant oxidation reactivity toward substrates, such as aliphatic and aromatic compounds, adsorbed on the surface under both UV- and visible-light irradiation.
Co-reporter:Shi-Cong Cui, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
The Journal of Physical Chemistry C 2008 Volume 112(Issue 49) pp:19625-19634
Publication Date(Web):November 14, 2008
DOI:10.1021/jp807591d
Charge transfer to and from semiconductor quantum dots (QDs) is of intense interest because of its important roles in QD-based devices, such as light emitting diodes and solar cells. We now report a mechanistic study of the electron transfer (ET) processes between CdTe QDs and a pyromellitimide derivative with a carboxylic acid (PI-CA) using ensemble and single-particle spectroscopies. First, to confirm whether the photochemical reactions occur by excitation of the QDs, the quenching of the QD emission by PI-CA as well as control substrates was examined using steady-state and time-resolved emission spectroscopies. It was found that the PI-CA molecules are strongly bound to the surface of the QDs and significantly quench the photoluminescence (PL) band near 675 nm. Nanosecond transient absorption measurements also revealed that PI•- was formed during the laser flash photolysis of the conjugates between CdTe QD and PI-CA in chloroform solution. The single-particle PL spectroscopy was utilized to clarify the interfacial ET processes within individual CdTe/PI-CA conjugates modified on the glass surface via thiol linkers. The influences of the modified PI-CA molecules on the luminescence intermittency, the so-called blinking phenomenon, of single QDs were discussed in terms of a diffusion-controlled electron transfer (DCET) theory for the probability distributions of the “on” or “off” events. Finally, on the basis of the experimental and analytical results, it was concluded that the blinking characteristics observed for individual CdTe/PI-CA conjugates are due to the energy diffusions away from and back to a resonance condition fulfilled by the energy of the acceptor states resulting in the intermittent changes in the interfacial ET redox turnover rates.
Co-reporter:Takashi Tachikawa Dr.;Yoshiaki Asanoi;Kiyohiko Kawai Dr.;Sachiko Tojo;Akira Sugimoto Dr.;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2008 Volume 14( Issue 5) pp:1492-1498
Publication Date(Web):
DOI:10.1002/chem.200701030
Abstract
TiO2/DNA nanoconjugates were successfully fabricated by using the catechol moiety as a binding functional group, which was confirmed by steady-state absorption and fluorescence spectroscopies. Upon UV irradiation, the photocatalytic cleavage of the TiO2/DNA nanoconjugates was observed at the single-molecule level by using wide-field fluorescence microscopy. The decrease in the number of conjugates, which was estimated from the luminescent spots due to semiconductor quantum dots modified at the DNA strand, was significantly inhibited by a single A/C mismatch in the DNA sequences. This result strongly suggests that the migration of holes, which are injected from the photoexcited TiO2 into the DNA, through the DNA bases plays an important role in the photocatalytic cleavage of the conjugates. The influences of the photogenerated reactive oxygen species (ROS) on the cleavage efficiency were also examined. According to the experimental results, it was concluded that oxidation of the catechol moiety and/or the DNA damage are key reactions in this process.
Co-reporter:Mamoru Fujitsuka, Ken Harada, Akira Sugimoto and Tetsuro Majima
The Journal of Physical Chemistry A 2008 Volume 112(Issue 41) pp:10193-10199
Publication Date(Web):September 13, 2008
DOI:10.1021/jp805350d
In the present paper, photoinduced processes in the dyad molecules of pentathiophene (5T) and perylene-3,4:9,10-bis(dicarboximide) (PDI) with a flexible alkyl linker (propyl or hexyl) were investigated by using femtosecond laser flash spectroscopy in various solvents. Since absorption of 5T covers the wavelength region where absorption of PDI has minima and fluorescence of 5T overlaps with absorption of PDI, combination of 5T and PDI is favorable to achieve light energy harvesting as well as efficient electron transfer. When the sample was excited at the PDI moiety of the dyad, charge separation occurred almost quantitatively even in nonpolar solvent as well as in polar solvents. When the 5T moiety of the dyad was excited, efficient energy transfer to the PDI moiety from which charge separation occurred was confirmed, indicating that 5T acts as an antenna of the charge separation system, like a photosynthesis system of a plant. On the basis of Förster and Marcus theories and the estimated energy and electron-transfer rates, it was indicated that these dyads tend to take a folded structure in all solvents investigated.
Co-reporter:Shingo Samori, Mamoru Fujitsuka and Tetsuro Majima
The Journal of Physical Chemistry A 2008 Volume 112(Issue 45) pp:11312-11318
Publication Date(Web):October 17, 2008
DOI:10.1021/jp804369e
Excited-state properties of radical cations of substituted oligothiophenes (nT•+, n denotes the number of thiophene rings, n = 3, 4, 5) in solution were investigated by using various laser flash photolysis techniques including two-color two-laser flash photolysis. nT•+ generated by photoinduced electron transfer to p-chloranil or resonant two-photon ionization (RTPI) by using the first 355-nm ns laser irradiation was selectively excited with the second picosecond laser (532 nm). Bleaching of the absorption of nT•+ together with growth of a new absorption was observed during the second laser irradiation, indicating the generation of nT•+ in the excited state (nT•+*). The D1 state lifetime was estimated to be 34 ± 4, 24 ± 2, and 18 ± 1 ps for 3T•+, 4T•+, and 5T•+, respectively. In the presence of hole acceptor (Q), bleaching of nT•+ and growth of Q•+ were observed upon selective excitation of nT•+ during the nanosecond−nanosecond two-color two-laser flash photolysis, indicating the hole transfer from nT•+(D1) to Q. Recovery of nT•+ was also observed together with decay of Q•+ because of regeneration of nT•+ by hole transfer from Q•+ to nT at the diffusion-limiting rate. It was suggested that the hole transfer rate (kHT) from nT•+(D1) to Q depended on the free-energy change for hole transfer (−ΔG = 1.41−0.46 eV). The estimated kHT faster than the diffusion-limiting rate can be explained by the contribution of the static quenching for the excited species in the presence of high concentration of Q (0.1−1.0 M).
Co-reporter:Minoru Yamaji, Xichen Cai, Masanori Sakamoto, Mamoru Fujitsuka and Tetsuro Majima
The Journal of Physical Chemistry A 2008 Volume 112(Issue 45) pp:11306-11311
Publication Date(Web):October 15, 2008
DOI:10.1021/jp805593m
Photochemical properties of p-phenylphenacyl derivatives (PP-X) having C−halide, C−S, and C−O bonds in the lowest (T1) and higher (Tn) triplet excited states were investigated in solution by using single-color and stepwise two-color two-laser flash photolysis techniques. PP-Xs (X = Br, SH, and SPh) undergo β-bond dissociation in the lowest singlet excited states (S1) while the C−X bonds of other PP-Xs are stable upon 266-nm laser photolysis. The T1(π,π*) states of PP-X were efficiently produced during 355-nm laser photolysis of benzophenone as a triplet sensitizer. Triplet PP-Xs deactivate to the ground state without photochemical reactions. Upon 430-nm laser photolysis of the T1 states of PP-X (X = Br, Cl, SH, SPh, OH, OMe, and OPh), decomposition of PP-X in the Tn states was found. On the basis of the changes in the transient absorption, quantum yields (Φdec) of the decomposition of PP-X in the Tn states were determined, while bond dissociation energies (BDE) of the C−X bonds were calculated by computations. According to the relationship between the Φdec and BDE values, it was shown that the decomposition of PP-X in the Tn state is due to β-cleavage of the corresponding C−X bond, and that the state energy of the reactive Tn for the C−O bond cleavage differs from that for the C−halide and C−S bond cleavage. The reaction profiles of the C−X bond cleavage of PP-X in the Tn states were discussed.
Co-reporter:Takashi Tachikawa, Jun Rye Choi, Mamoru Fujitsuka and Tetsuro Majima
The Journal of Physical Chemistry C 2008 Volume 112(Issue 36) pp:14090-14101
Publication Date(Web):2017-2-22
DOI:10.1021/jp803620v
Metal-organic frameworks (MOFs), which exhibit large surface area and porosity retention upon solvent removal, have attracted considerable attention due to their elegant topology and potential applications in separation, gas storage, nonlinear optics, and catalysis. We report herein comprehensive studies on the nature of luminescence transitions in MOF-5 nanoparticles, which are referred to as MOF-5_n, and the interfacial charge transfer from the photoexcited MOF-5_n to various organic compounds. The time-resolved diffuse reflectance (TDR) and fluorescence spectroscopies were combined in order to clarify the photoinduced one-electron oxidation processes of organic compounds on the MOF-5_n. First, to identify the nature of the luminescence transitions in MOF-5, the temperature dependences of the spectral characteristics were elucidated and compared with those of ZnO nanoparticles. The quenching of MOF-5 emission by several substrates (S), such as aromatic sulfides and amines, was then investigated using steady-state and time-resolved fluorescence spectroscopies. The one-electron oxidation reaction of S during the 355 nm laser flash photolysis of MOF-5_n in acetonitrile was directly examined using TDR spectroscopy, and it was revealed that MOF-5 has a much higher oxidation reaction efficiency than that of P-25 TiO2 powder, which is the most common photocatalyst. The experimental data were rationalized in terms of the Marcus theory on the electron transfer reactions. Moreover, the influence of adsorbed water on the reaction processes was examined because the MOF crystal morphology is affected by exposure to water during synthesis or after evacuation. Consequently, the present study provides an excellent opportunity to understand the difference in the photoinduced charge-transfer processes between MOFs and semiconductors.
Co-reporter:M. Sakamoto;T. Tachikawa;M. Fujitsuka;T. Majima
Advanced Functional Materials 2007 Volume 17(Issue 6) pp:857-862
Publication Date(Web):1 FEB 2007
DOI:10.1002/adfm.200600700
Metal nanoparticle (NP)–polymer nanocomposite thin films are attractive for applications in various devices. Since bimetallic NPs provide additional opportunities for tuning the physical properties of the NP components, the development of bimetallic NP nanocomposite thin films should lead to further enhancements of various applications. Au/Cu bimetallic NPs are fabricated in a poly(vinyl alcohol) (PVA) film using a photochemical process. Interestingly, different sizes and shapes of Au/Cu bimetallic NPs are formed in the PVA film, resulting in a uniquely patterned nanocomposite structure. It is determined that the different formation and growth mechanisms of NPs inside and outside the UV-light irradiation spot leads to the differences in size and shape.
Co-reporter:Xichen Cai, Minoru Yamaji, Masanori Sakamoto, Mamoru Fujitsuka, Tetsuro Majima
Chemical Physics Letters 2007 Volume 443(4–6) pp:248-252
Publication Date(Web):6 August 2007
DOI:10.1016/j.cplett.2007.06.062
Abstract
C–O bond dissociation of naphthoxymethyl compounds NpO–CH2R (Np = α- or β-naphthalene moiety, R = Ph or Me) in the higher triplet excited state (Tn, n ⩾ 2) was investigated using two-color two-laser flash photolysis. The C–O bond dissociation was found to occur with quantum yields (Φ) of 0.06 and 0.07 for α- and β-NpO–CH2Ph(Tn), respectively. With the use of reported data on C–O bond cleavage in NpCH2–OPh(Tn) and NpCH2–OMe(Tn), it was concluded that Φ is related to the Tn-state lifetime and the energy barrier between the Tn state and dissociative potential surfaces.
Co-reporter:Koji Nakayama, Masayuki Endo, Mamoru Fujitsuka and Tetsuro Majima
Photochemical & Photobiological Sciences 2007 vol. 6(Issue 8) pp:836-841
Publication Date(Web):28 Jun 2007
DOI:10.1039/B705049F
The local change in the three different structures of restriction enzymeBamHI, which include DNA-free dimer and non-specific and specific complexes with DNA, were detected by the fluorescence from a site-selectively introduced solvatochromic fluorophore Nβ-L-alanyl-5-(N,N-dimethylamino)naphthalene-1-sulfonamide (DanAla). According to the crystal structure, α-helices of the non-specific complex containing Ile82, Glu86 and Trp206 residues are converted into random coil by the formation of specific complex with a substrate. To understand the microenvironmental change caused by the structural transition around these positions, the DanAla probe was site-specifically introduced into the positions, and steady-state and time-resolved fluorescence was observed. The steady-state fluorescence gave us information that the rigidity of the polypeptide chains would be enhanced by the formation of the specific complex. The time-resolved fluorescence supported that the change in a water molecule-accessible space was induced by DNA binding. We revealed that the change in rigidity and solvation around the specific positions was detected by the characteristic fluorescence using the combination of steady-state and time-resolved fluorescence techniques.
Co-reporter:Tadao Takada Dr.;Chunyan Lin
Angewandte Chemie 2007 Volume 119(Issue 35) pp:
Publication Date(Web):30 JUL 2007
DOI:10.1002/ange.200701525
Welche Bedeutung hat die Beziehung zwischen Ladungsrekombination und Ladungstransfer beim Erzeugen eines Photostroms durch DNA-Filme? Mit photoelektrochemischen Messungen an einer Au-Elektrode wurde die Effizienz des Photostroms für DNA-Filme untersucht, in denen die Geschwindigkeiten von Ladungstransfer und -rekombination durch Verändern der Sequenz moduliert wurden.
Co-reporter:Masayuki Endo Dr.;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2007 Volume 13(Issue 31) pp:
Publication Date(Web):12 SEP 2007
DOI:10.1002/chem.200700895
We have demonstrated the construction of multiple porphyrin arrays in the tobacco mosaic virus (TMV) supramolecular structures by self-assembly of recombinant TMV coat protein (TMVCP) monomers, in which Zn-coordinated porphyrin (ZnP) and free-base porphyrin (FbP) were site-selectively incorporated. The photophysical properties of porphyrin moieties incorporated in the TMV assemblies were also characterized. TMV–porphyrin conjugates employed as building blocks self-assembled into unique disk and rod structures under the proper conditions as similar to native TMV assemblies. The mixture of a ZnP donor and an FbP acceptor was packed in the TMV assembly and showed energy transfer and light-harvesting activity. The detailed photophysical properties of the arrayed porphyrins in the TMV assemblies were examined by time-resolved fluorescence spectroscopy, and the energy transfer rates were determined to be 3.1–6.4×109 s−1. The results indicate that the porphyrins are placed at the expected positions in the TMV assemblies.
Co-reporter:Mamoru Fujitsuka, Dae Won Cho, Nathalie Solladié, Vincent Troiani, Hongjin Qiu, Tetsuro Majima
Journal of Photochemistry and Photobiology A: Chemistry 2007 Volume 188(2–3) pp:346-350
Publication Date(Web):20 May 2007
DOI:10.1016/j.jphotochem.2006.12.034
S2- and S1-states properties of zinc porphyrin polypeptides were investigated using various fast spectroscopic techniques. The B band of zinc porphyrin polypeptides showed broadening and shift to the longer wavelength side with the polymerization degree, indicating the interaction between the porphyrin units. The lifetime of S2-fluorescence became shorter with increasing the polymerization degree. This phenomenon can be explained by applying the energy gap law to the S2–S1 internal conversion. From the picosecond transient absorption measurements, singlet–singlet annihilation was confirmed, indicating the intrachain singlet energy migration in the polypeptides. The annihilation rate became faster with the polymerization degree because of the shorter distance between the zinc porphyrin units of longer polypeptides.
Co-reporter:Dae Won Cho, Mamoru Fujitsuka, Ung Chan Yoon, Tetsuro Majima
Journal of Photochemistry and Photobiology A: Chemistry 2007 Volume 190(Issue 1) pp:101-109
Publication Date(Web):5 July 2007
DOI:10.1016/j.jphotochem.2007.03.018
Co-reporter:Tadao Takada;Mamoru Fujitsuka;
Proceedings of the National Academy of Sciences 2007 104(27) pp:11179-11183
Publication Date(Web):June 25, 2007
DOI:10.1073/pnas.0700795104
DNA charge transfer highly depends on the electronic interaction between base pairs and reflects the difference in the base
composition and sequence. For the purpose of investigating the charge transfer process of individual DNA molecules and the
optical readout of DNA information at the single-molecule level, we performed single-molecule observation of the DNA charge
transfer process by using single-molecule fluorescence spectroscopy. The DNA charge transfer process, leading to the oxidation
of the fluorescent dye, was explored by monitoring the on–off signal of the dye after the charge injection by the excitation
of a photosensitizer. The photobleaching efficiency of the dyes by the DNA charge transfer specifically depended on the base
sequence and mismatch base pair, demonstrating the discrimination of the individual DNA information. Based on this approach,
the optical readout of a single-base mismatch contained in a target DNA was performed at the single-molecule level.
Co-reporter:Masanori Sakamoto Dr.;Takashi Tachikawa Dr.;Sung Sik Kim Dr.;Mamoru Fujitsuka Dr. Dr.
ChemPhysChem 2007 Volume 8(Issue 11) pp:1701-1706
Publication Date(Web):5 JUL 2007
DOI:10.1002/cphc.200700328
The association behavior of the dyes 5(6)-carboxyfluorescein and nitrilotriacetic acid (NTA)-modified 5(6)-carboxyfluorescein (F-NTA) in a poly(vinyl alcohol) (PVA) film and in a PVA film containing metal nanoparticles is investigated. Well-dispersed gold nanoparticles (AuNps) and Ni(II)-adsorbed AuNps are formed in the PVA film using in situ photochemical fabrication method. 5(6)-carboxyfluorescein and F-NTA are doped into the films. The F-NTA forms an H-aggregate in the PVA film containing Ni(II)-adsorbed AuNps. It is suggested that the interaction between NTA and Ni(II) adsorbed on the AuNps promotes the formation of the H-aggregate.
Co-reporter:Tadao Takada Dr.;Chunyan Lin
Angewandte Chemie International Edition 2007 Volume 46(Issue 35) pp:
Publication Date(Web):30 JUL 2007
DOI:10.1002/anie.200701525
Got a light? The importance of the relationship between the charge recombination and charge transfer during photocurrent generation through DNA films is described. The photocurrent efficiency for DNA films, in which the charge-transfer and recombination rates were modulated by changing the sequence, was investigated by using the photoelectrochemical measurements on an Au electrode.
Co-reporter:Kiyohiko Kawai Dr.;Yasuko Osakada;Akira Sugimoto Dr.;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2007 Volume 13(Issue 8) pp:
Publication Date(Web):13 DEC 2006
DOI:10.1002/chem.200601210
The hole transfer rates in the DNA/DNA B-form duplex and DNA/2′-OMeRNA A-form duplex were measured which occurred in the time range of ≈100 μs. The hole transfer rates in the A-form duplexes were slower and more strongly dependent on the temperature compared to those in the B-form duplexes, suggesting that the A-form is more rigid than the B-form duplex in this time scale.
Co-reporter:Xichen Cai Dr.;Masanori Sakamoto;Minoru Yamaji Dr.;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2007 Volume 13(Issue 11) pp:
Publication Date(Web):10 JAN 2007
DOI:10.1002/chem.200600822
A CO-bond cleavage of esters having a naphthyl group, NpCO-OR and RCO-ONp (Np=α- and β-naphthyl (αNp and βNp, respectively), R=Ph and Me), was found during the two-color two-laser flash photolysis in acetonitrile. The CO-bond cleavage occurred when NpCO-OR and RCO-ONp were excited to the singlet excited states (S1). On the other hand, no reaction occurred from the lowest triplet excited states (T1). When NpCO-OR(T1) and RCO-ONp(T1) were excited to the higher triplet excited states (Tn) using the second laser during the two-color two-laser flash photolysis, the CO-bond cleavage occurred. The CO-bond cleavage quantum yield (Φ) was estimated from the plots of the T1-state esters disappeared within a laser flash versus the second laser intensities. The CO-bond cleavage in βNpCO-OPh(Tn) occurred more efficiently than in αNpCO-OPh(Tn) and that in PhCO-OβNp(Tn) occurred more efficiently than in PhCO-OαNp(Tn). The Φ value for ester with Ph and β-Np groups was larger than that for ester with Ph and α-Np groups. The Φ value for MeCO-OαNp(Tn) was similar to those for PhCO-ONp(Tn), while that for MeCO-OβNp(Tn) was much smaller than those for PhCO-ONp(Tn) and MeCO-OαNp(Tn). On the other hand, no CO-bond cleavage was observed in NpCO-OMe(Tn). The Φ value depended on the characters of the groups (Np, Ph, and Me) on the ester. Whether R is Ph or Me with or without π electron, respectively, is important for the CO-bond cleavage. In other words, electronic delocalization of the Tn state including Np and ester groups is necessary for the occurrence of the CO-bond cleavage in NpCO-OR(Tn) and RCO-ONp(Tn).
Co-reporter:Kiyohiko Kawai, Yasuko Osakada, Mamoru Fujitsuka and Tetsuro Majima
Chemical Communications 2006 (Issue 37) pp:3918-3920
Publication Date(Web):07 Aug 2006
DOI:10.1039/B608027H
Based on the synthesis of DNA modified with photosensitizers, direct spectroscopic measurements of the hole transfer in DNA, and quantification of the yield of the DNA oxidative damage, the reaction rate of the radical anion of the photosensitizer was demonstrated to be critically important in determining the efficiency of photosensitized DNA damage.
Co-reporter:Masayuki Endo and Tetsuro Majima
Chemical Communications 2006 (Issue 22) pp:2329-2331
Publication Date(Web):19 Apr 2006
DOI:10.1039/B601372D
Complexes consisting of a branched DNA with full-matched and mismatched DNA strands were prepared, and the cross-linking of the DNA strands and their diastereochemistry affected the stability of the complexes and the thermodynamics of the complex formation.
Co-reporter:Takumi Kimura, Kiyohiko Kawai and Tetsuro Majima
Chemical Communications 2006 (Issue 14) pp:1542-1544
Publication Date(Web):28 Feb 2006
DOI:10.1039/B600026F
The environment-sensitive fluorophore dan (6-dimethylamino-2-acyl-naphthalene)- modified dC or dG bases were introduced into the Z-DNA forming sequence. It was demonstrated that both grooves of Z-DNA are more hydrated than those of B-DNA. Dan will be useful for probing the microenvironments in the grooves among the DNA polymorphs.
Co-reporter:Takumi Kimura, Kiyohiko Kawai, Mamoru Fujitsuka and Tetsuro Majima
Chemical Communications 2006 (Issue 4) pp:401-402
Publication Date(Web):08 Dec 2005
DOI:10.1039/B514526K
2-Aminopurine (Ap) modified human telomere sequences were used to monitor the specific complex formation of the G-quadruplex and 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4).
Co-reporter:Shinro Yasui, Sachiko Tojo and Tetsuro Majima
Organic & Biomolecular Chemistry 2006 vol. 4(Issue 15) pp:2969-2973
Publication Date(Web):30 Jun 2006
DOI:10.1039/B606857J
In a previous report (S. Yasui, S. Tojo and T. Majima, J. Org. Chem., 2005, 70, 1276), we presented the results from the laser flash photolysis (LFP) and product analysis of the 9,10-dicyanoanthracene (DCA)-photosensitized oxidation of triarylphosphine (Ar3P) in acetonitrile under air, which showed that the photoreaction results in the oxidation of Ar3P to give the corresponding phosphine oxide (Ar3PO) in a nearly quantitative yield, and that the reaction is initiated by the electron transfer (ET) from Ar3P to DCA in the singlet excited state (1DCA*), producing the triarylphosphine radical cation Ar3P˙+. This radical cation decays through radical coupling with O2 to afford the peroxy radical cation Ar3P+–O–O˙, which we proposed to be the intermediate leading to the product Ar3PO. We now examined this photoreaction in more detail using ten kinds of Ar3P with various electronic and steric characteristics. The decay rate of Ar3P˙+ measured by the LFP was only slightly affected by the substituents on the aryl groups of Ar3P. During the photolysis of trimesitylphosphine (Mes3P), the peroxy radical cation intermediate (Mes3P+–O–O˙) had a lifetime long enough to be spectrophotometrically detected. The quantum yields of Ar3PO increased with either electron-withdrawing or -releasing substituents on the aryl groups, suggesting that a radical center is developed on the phosphorus atom during the step when the quantum yield is determined. In addition, the o-methyl substituents in Ar3P decreased the quantum yield. These results clearly indicated that Ar3P+–O–O˙ undergoes radical attack upon the parent phosphine Ar3P that eventually produces the final product, Ar3PO.
Co-reporter:Masayuki Endo Dr.;Hangxiang Wang;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2006 Volume 12(Issue 14) pp:
Publication Date(Web):28 FEB 2006
DOI:10.1002/chem.200501309
The effect of pyrenes introduced into a tobacco mosaic virus (TMV) coat protein monomer on the formation and stability of the TMV assembly was investigated. The possible arrangement of the pyrenes in the inner cavity of the TMV rod was also estimated. The pyrene derivative was introduced to four specific amino acids in the cavity of the TMV rod structure. Rod-structure formation was examined by atomic force microscopy (AFM). Two pyrene-attached mutants (positions 99 and 100) assembled to increase the length of the rod structures by 2.5 μm at pH 5.5. The interaction of the pyrene moieties in the TMV cavity was investigated by steady-state and time-resolved spectroscopic analysis. Strong excimer emission with significantly short wavelength (465 nm) was observed from the two mutants mentioned above. Excitation and UV-visible spectra indicate that the pyrene moieties form π-stacked structures in the TMV cavity. Details of the pyrene interaction were investigated by analyzing the fluorescence lifetime of the excimer. Results suggest that the pyrenes formed preassociated rigid structures with partially overlapped geometry in the restricted space of the TMV cavity. The pyrenes effectively stabilize the TMV rod through a π-stacking interaction in a well-ordered way, and the single pyrene moiety introduced into the monomer affects the overall formation of the TMV rod structure.
Co-reporter:Xichen Cai Dr.;Peter Cygon Dr.;Bernd Goldfuss Dr.;Axel G. Griesbeck Dr.;Heike Heckroth Dr.;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2006 Volume 12(Issue 17) pp:
Publication Date(Web):24 MAR 2006
DOI:10.1002/chem.200600011
Triplet 1,4-biradicals were generated by Norrish-Type-II hydrogen transfer from α-heteroatom-substituted β-branched butyrophenones 1–6 and detected by laser flash absorption measurements. For three oxy-substituted compounds 2–4 (Rα=OH, OCOMe, OCOOEt) comparable lifetimes were determined in acetonitrile (roughly 1.5 μs). In benzene, divergent trends were observed: for the hydroxy compound 2 a lower lifetime of 790 ns was determined, whereas for 3 and 4 the lifetimes increased to 4.9 μs. Photolyses of the α-amino-substituted compounds 1 and 6 resulted in transient species with significant lower lifetimes (for 1 160 ns in benzene and 450 ns in acetonitrile; for 6 <100 ns in both solvents). The mesyloxy substrate 5 undergoes rapid CO bond cleavage upon photolysis and no transient triplet species were detected. Computational (UB3 LYP/6–31G* and natural don orbital (NBO) analyses) results supported the assumption of a negative hyperconjugative interaction strongly stabilizing α-oxy-substituted over α-amino-substituted radicals.
Co-reporter:Takashi Tachikawa Dr.;Sachiko Tojo;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2006 Volume 12(Issue 11) pp:
Publication Date(Web):16 DEC 2005
DOI:10.1002/chem.200501077
The one-electron redox processes of several compounds during polyoxometalate (POM)-mediated photocatalytic reactions of TiO2 were investigated using the two-color two-laser flash-photolysis technique. The efficiency of the one-electron oxidation of aromatic sulfides by the trapped hole (htr+) or the surface-bound OH radical (OHs.) is found to be significantly enhanced due to electron transfer from the conduction band (CB) of TiO2 to the POM. The efficiency of the electron transfer from the CB of TiO2 to the POM decreases in the order H2W12O406− < SiW12O404− < PW12O403−, that is, it depends on the reduction potential (Ered) of the POMs. Electron injection from PW12O404− in the excited state (PW12O404−*) to the CB of TiO2 was clearly observed using the two-color two-laser flash-photolysis technique. Storage of electrons in the TiO2/PW12O403−/methyl viologen (MV2+) ternary system was also achieved upon two-color two-laser irradiation.
Co-reporter:Tadao Takada;Kiyohiko Kawai;Mamoru Fujitsuka
Angewandte Chemie 2006 Volume 118(Issue 1) pp:
Publication Date(Web):21 NOV 2005
DOI:10.1002/ange.200502568
Kästchenhüpfen: Ein langlebiger ladungsgetrennter Zustand wurde in hoher Ausbeute in einer mit einem Diphenylacetylenderivat (DPA) modifizierten DNA durch Hüpfen über Adenin(A)-Basen erzeugt (siehe Diagramm). Durch Modulation der Redoxeigenschaften des Photosensibilisators und der Brückenbasen (z. B. Verwendung von bromiertem Adenin (BrA)) lässt sich die Ausbeute an ladungsgetrenntem Zustand erhöhen.
Co-reporter:Takashi Tachikawa Dr.;Sachiko Tojo;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2006 Volume 12(Issue 29) pp:
Publication Date(Web):6 JUL 2006
DOI:10.1002/chem.200600097
The photocatalytic one-electron oxidation reactions of aromatic sulfides using the carboxymethyl-β-cyclodextrin (CM-β-CD)-modified TiO2 nanoparticles (TiO2/CM-β-CD) were investigated by using nano- and femtosecond transient absorption spectroscopies. The one-electron oxidation processes of the substrate (S) by the valence band hole (hVB+) at the TiO2 surface and the trapped hole at the adsorption site of the CM-β-CD (hCD+) were examined. The transient absorption spectra and time traces observed for the charge carriers and the radical cation of S (S.+) revealed that the one-electron oxidation reaction of S during the nano- and femtosecond laser flash photolyses of TiO2/CM-β-CD is significantly enhanced relative to bare TiO2. The kinetics of the decay and the dimerization processes between S.+s are discussed on the basis of the results obtained by the pulse radiolysis technique.
Co-reporter:Masanori Sakamoto;Xichen Cai Dr.;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2006 Volume 12(Issue 6) pp:
Publication Date(Web):28 NOV 2005
DOI:10.1002/chem.200500409
The properties of benzophenone ketyl radical analogues with large aromatic ring systems, such as naphthylphenylketone (2), 4-benzoylbiphenyl (3), and bis(biphenyl-4-yl)methanone (4), were investigated in the excited state by using nanosecond–picosecond two-color two-laser flash photolysis. Fluorescence and transient absorption spectra of ketyl radicals of 2–4 in the excited state were observed for the first time. The fluorescence and properties of the excited ketyl radicals were significantly affected by the size and electronic properties of the aromatic ring systems. The reactivity of the ketyl radicals in the excited state with several quenchers was examined and they were found to show reactivity toward N,N-diethylaniline. In addition, for the benzophenone ketyl radical, a unique quenching process of the radical in the excited state by the ground-state parent molecule was found. The factors regulating the fluorescence lifetime of the ketyl radicals in the excited state are discussed quantitatively.
Co-reporter:Tadao Takada, Kiyohiko Kawai, Mamoru Fujitsuka,Tetsuro Majima
Angewandte Chemie International Edition 2006 45(1) pp:120-122
Publication Date(Web):
DOI:10.1002/anie.200502568
Co-reporter:Shingo Samori, Michihiro Hara, Sachiko Tojo, Mamoru Fujitsuka, Tetsuro Majima
Journal of Photochemistry and Photobiology A: Chemistry 2006 Volume 179(1–2) pp:115-124
Publication Date(Web):1 April 2006
DOI:10.1016/j.jphotochem.2005.08.005
The resonant two-photon ionization (TPI) of trans-stilbene and substituted trans-stilbenes (S) in acetonitrile was studied by laser flash photolysis using a Nd3+:YAG laser (266- or 355-nm). The transient absorption spectra of S radical cations (S+) with a peak around 450–540 nm were observed. Formation of S+ can be explained by two-step two-photon excitation from the ground state (S0) to the lowest singlet excited state (S1) and from the S1 to the higher singlet excited state (Sn), from which ionization occurs. The formation quantum yield of S+ (ϕion) was 0.005–0.11. Little or no relation between ϕion and Eox was observed for non-substituted (1), mono-p-substituted (2–7) and di-p-substituted (8–11), methoxy-substituted (12–16), and donor–acceptor-p-substituted trans-stilbenes (17–21). On the other hand, ϕion increased with the increase of the fluorescence lifetime (τf) for all S. Interestingly, relatively large ϕion was observed for 17–21 even though they have relatively short τf among those of S. It is suggested that the CT electronic character of the S1 state and, therefore, the large molar absorption coefficient are responsible for the efficient TPI of 17–21.
Co-reporter:Mamoru Fujitsuka;Kiyohiko Kawai;Yasuko Osakada
PNAS 2006 Volume 103 (Issue 48 ) pp:18072-18076
Publication Date(Web):2006-11-28
DOI:10.1073/pnas.0607148103
DNA nanostructures based on programmable DNA molecular recognition have been developed, but the nanoelectronics of using DNA
is still challenging. A more rapid charge-transfer (CT) process through the DNA nanoassembly is required for further development
of programmable DNA nanoelectronics. In this article, we present direct absorption measurements of the long-range CT over
a 140-Å DNA assembly based on a GC repetitive sequence constructed by simply mixing DNA building blocks. We show that a CT
through DNA nanoscale assembly is possible and programmable with the designed DNA sequence.
Co-reporter:Kiyohiko Kawai, Mamoru Fujitsuka and Tetsuro Majima
Chemical Communications 2005 (Issue 11) pp:1476-1477
Publication Date(Web):21 Jan 2005
DOI:10.1039/B418000C
The combination of the transient absorption measurement and DNA damage quantification by HPLC clearly demonstrated the preferential excitation of guanine and its decomposition in quadruplex DNA by UVB-irradiation.
Co-reporter:Masayuki Endo and Tetsuro Majima
Organic & Biomolecular Chemistry 2005 vol. 3(Issue 19) pp:3476-3478
Publication Date(Web):02 Sep 2005
DOI:10.1039/B507126G
Self-complementary cross-linked oligonucleotides with a disulfide linkage were designed and synthesized. Double helix and hairpin structures were controlled using the different diastereochemistry of phosphoramidate where the cross-linker was introduced. The structures of the strained cross-linked DNAs were estimated by gel mobility, circular dichroism spectra, and melting profiles.
Co-reporter:Xichen Cai, Masanori Sakamoto, Michihiro Hara, Susumu Inomata, Minoru Yamaji, Sachiko Tojo, Kiyohiko Kawai, Masayuki Endo, Mamoru Fujitsuka, Tetsuro Majima
Chemical Physics Letters 2005 Volume 407(4–6) pp:402-406
Publication Date(Web):27 May 2005
DOI:10.1016/j.cplett.2005.03.127
Abstract
C–Si bond cleavage of p-trimethylsilylmethylacetophenone(1) occurred in a higher triplet excited state (Tn), giving mainly p-acetylbenzyl radical with the transient absorption in the region of 295–360 nm, with a quantum yield of 0.046 ± 0.008 using the two-color two-laser photolysis techniques. In contrast, the C–Si bond cleavage of p-trimethylsilylmethylbenzophenone(2) was absent in the Tn state whose energy is larger than the C–Si bond cleavage energy. The results can explain existence of a bond cleavage crossing between potential surfaces of the Tn state and a dissociative state of the C–Si bond for 1, but not for 2.
Co-reporter:Masayuki Endo, Nadrian C. Seeman,Tetsuro Majima
Angewandte Chemie International Edition 2005 44(37) pp:6074-6077
Publication Date(Web):
DOI:10.1002/anie.200501034
Co-reporter:Masayuki Endo Dr.;Nadrian C. Seeman Dr. Dr.
Angewandte Chemie 2005 Volume 117(Issue 37) pp:
Publication Date(Web):26 AUG 2005
DOI:10.1002/ange.200501034
Eine Röhre aus Fliesen: Ein neuartiges Verfahren zur Synthese von DNA-Röhren ausgehend von DNA-Fliesen und einem vierfach verzweigten DNA-Porphyrin-Verbindungsstück wird vorgestellt (siehe schematische Darstellung). Zur genauen Analyse der DNA-Strukturen diente die Kraftmikroskopie.
Co-reporter:Xichen Cai Dr.;Masanori Sakamoto;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2005 Volume 11(Issue 22) pp:
Publication Date(Web):3 AUG 2005
DOI:10.1002/chem.200500463
The lifetimes of benzophenone in the higher triplet excited state (BP(Tn)) and several BP derivatives in the Tn states were measured directly to be τTn=37±7 ps and 20–33 ps, respectively, by using the nanosecond–picosecond (ns–ps) two-color/two-laser flash photolysis method. Based on the direct measurements of τTn of BP(Tn), the triplet energy transfer (TET) from BP(Tn) to quenchers (Q), such as carbon tetrachloride (CCl4), benzene (Bz), and p-dichlorbenzene (DCB), was investigated. The fast TET from BP(Tn) to Q can be attributed to the lifetime-dependent quenching process, according to the Ware theoretical model of the bimolecular energy transfer reaction. The contribution of the lifetime-dependent term on kTET was 27, 60, and 86 % for CCl4, Bz, and DCB as the Q of BP(Tn), respectively, indicating that the TET from BP(Tn) to Q is influenced not only by τTn, but also by the size of Q.
Co-reporter:Tadao Takada Dr.;Kiyohiko Kawai Dr.;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2005 Volume 11(Issue 13) pp:
Publication Date(Web):14 APR 2005
DOI:10.1002/chem.200500052
A kinetic study of the single-step hole transfer in DNA was performed by measuring time-resolved transient absorption. DNA molecules with various sequences were designed and conjugated with naphthalimide (NI) and phenothiazine (PTZ) to investigate the sequence and distance dependence of the single-step hole transfer between guanines (Gs). Hole injection into DNA was accomplished by excitation of the NI site with a 355 nm laser pulse, and the kinetics of the hole-transfer process were investigated by monitoring the transient absorption of the PTZ radical cation (PTZ.+). Kinetic analysis of the time profile of PTZ.+ based on the kinetic model showed that the distance dependence of the hole-transfer process was significantly influenced by the DNA sequence. Results of temperature- and isotope-effect experiments demonstrated that the activation energy increased as the number of bridge bases separating the Gs increased. This is because of the distance-dependent reorganization energy and contribution of the proton-transfer process to the hole transfer in DNA.
Co-reporter:Takumi Kimura, Kiyohiko Kawai and Tetsuro Majima
Chemical Communications 2004 (Issue 3) pp:268-269
Publication Date(Web):18 Dec 2003
DOI:10.1039/B313043F
The electron transfer quenching of 2-aminopurine by guanine and 7-deazaguanine was investigated in B- and Z-DNA, and an increase in the fluorescence intensity of 2-aminopurine upon B- to Z-DNA transition was demonstrated.
Co-reporter:Koji Nakayama, Masayuki Endo and Tetsuro Majima
Chemical Communications 2004 (Issue 21) pp:2386-2387
Publication Date(Web):20 Sep 2004
DOI:10.1039/B409844G
Endonuclease BamHI mutants having an azophenylalanine residue in the dimer interface (azoAla-BamHI) were synthesized; while the activity was almost suppressed using trans-azoAla-BamHI, the cis-isomer generated with photoirradiation recovered its intrinsic activity.
Co-reporter:Takumi Kimura, Kiyohiko Kawai, Mamoru Fujitsuka and Tetsuro Majima
Chemical Communications 2004 (Issue 12) pp:1438-1439
Publication Date(Web):19 May 2004
DOI:10.1039/B403913K
The substitution of 2-aminopurine (Ap) for A7 in the human telomeric sequence d[AGGG(TTAGGG)3] resulted in a significant increase in the fluorescence intensity of Ap for the conformational change from duplex to quadruplex.
Co-reporter:Michihiro Hara, Sachiko Tojo, Kiyohiko Kawai and Tetsuro Majima
Physical Chemistry Chemical Physics 2004 vol. 6(Issue 13) pp:3215-3220
Publication Date(Web):29 Apr 2004
DOI:10.1039/B403409K
Formation and decay of pyrene radical cation and pyrene dimer radical cation during resonant two-photon ionizations (TPI) of pyrene (Py) and sodium 1-pyrene sulfonate (NaPySA) in the absence and presence of cyclodextrins were studied with visible and near IR transient absorption measurement using 355-nm laser flash photolysis technique. Ionization of Py and 1-pyrene sulfonate anion (PySA−) occurred within the laser flash (5 ns) to give Py radical cation (Py˙+) and PySA− radical cation (Py˙+SA−) having Py˙+ chromophore. Dimerizations of Py˙+ and Py and of Py˙+SA− and PySA− were observed to give the dimer radical cations (Py2˙+ and Py2˙+(SA−)2) based on time-resolved measurements of the charge resonance (CR) band. The TPI of PySA− was also examined in the presence of β- and γ-cyclodextrins (βCD and γCD, respectively). Py2˙+(SA−)2 in the cavity of two γCDs having fully overlapped structure showed the CR band around 1700 nm, while Py2˙+(SA−)2 in the cavity of two βCD having partially and fully overlapped structures indicated the CR bands around 1500 or 1700 nm, respectively. On the basis of formation and decay rates of Py2˙+(SA−)2, bimolecular formation of Py2˙+(SA−)2 and the neutralization are inhibited in the cavities of CDs. Selective formation of the fully overlapped structure of Py2˙+(SA−)2 in the cavity of two γCDs within a laser flash is explained by direct TPI of two PySA−s with the parallel structure of two Py chromophores in two PySA−s in the cavity of two γCDs.
Co-reporter:Xichen Cai, Masanori Sakamoto, Michihiro Hara, Sachiko Tojo, Kiyohiko Kawai, Masayuki Endo, Mamoru Fujitsuka and Tetsuro Majima
Physical Chemistry Chemical Physics 2004 vol. 6(Issue 8) pp:1735-1741
Publication Date(Web):03 Mar 2004
DOI:10.1039/B400128A
Quenching processes of several aromatic hydrocarbons (AH) such as naphthalene (NAP), dibenz[a,h]anthracene (DBA), and chrysene (CHR) in the higher triplet excited states (T2) by different quenchers (Q) such as p-dichlorobenzene, o-dicyanobenzene aromatic compounds, and chloroalkanes (RCl), have been investigated by the two-color two-laser excitation method. AH in the higher triplet excited states (AH(Tn, n≥2)) initially generated by the excitation of AH(T1) at the wavelength tuned to the absorption of AH(T1). AH(Tn) decays to a AH(T2) with the longest lifetime among AH(Tn) through the fast internal conversion. In the presence of Q, the competition of triplet energy transfer (TENT) and electron transfer (ELT) reactions between AH(T2) and Q are expected. However, no AH radical cation was observed, especially when the quenchers were chloroalkanes such as carbon tetrachloride (CCl4), methylene dichloride (CH2Cl2), 1,2-dichloroethane, which are good electron acceptors. It is suggested that the TENT is important during the quenching of AH(Tn) by Q. The lifetimes of NAP(T2), DBA(T2), and CHR(T2) were calculated from the TENT quenching experiments. It was found that the lifetimes of AH(T2) increase in the order of NAP(T2)
(4.5 ps)<DBA(T2)
(16 ps)<CHR(T2)
(60 ps), which is consistent very well with the energy gap law for the transition from AH(T2) to AH(T1).
Co-reporter:Sachiko Tojo, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
Physical Chemistry Chemical Physics 2004 vol. 6(Issue 5) pp:960-964
Publication Date(Web):05 Feb 2004
DOI:10.1039/B314062H
A laser flash photolysis technique has been employed to clarify the oxidation reaction processes of 4-methylthiophenylmethanol (MTPM) and 2-phenylthioethanol (PTE) in a colloidal TiO2 aqueous solution. The transient absorption spectra attributed to the radical cations of the substrates were observed during the 355 nm laser irradiation of the colloidal TiO2 aqueous solution in the presence of the substrates. The oxidation process on the TiO2 surface and the free OH radical mediated oxidation process were found to depend on the substrate concentration. The oxidation reaction rate constants (kox) determined at low substrate concentrations in the colloidal TiO2 aqueous solution were quite consistent with those obtained in the bulk solution. The significant variations in the spectral shape and formation rates of the radical cation clearly suggest two oxidation processes with the valence band and/or surface-bound OH radicals and the free OH radicals.
Co-reporter:Masayuki Endo Dr.;Koji Nakayama;Yuka Kaida Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 42) pp:
Publication Date(Web):20 OCT 2004
DOI:10.1002/anie.200460889
The selective cleavage achieved by activated caspase-8 has been mimicked by using a photofunctionalized caspase-3 having 2-nitrophenylglycine (Npg) at a specific position of the peptide chain (see picture). The study shows that the activity of caspase-3 has been clearly expressed by photoirradiation and that autocleavage of caspase-3 has been suppressed by the site-selective incorporation of the Npg residue.
Co-reporter:Kiyohiko Kawai Dr.;Xichen Cai Dr.;Akira Sugimoto Dr.;Sachiko Tojo;Mamoru Fujitsuka Dr. Dr.
Angewandte Chemie 2004 Volume 116(Issue 18) pp:
Publication Date(Web):22 APR 2004
DOI:10.1002/ange.200353318
Eine Kombination von Zweifarben-Doppelpulsen bewirkt eine hoch effiziente DNA-Schädigung. Der erste Laserpuls erzeugt Sens.− (Sens=Photosensibilisator) und DNA.+, der zweite löst die Emission eines Elektrons aus Sens.− aus und macht damit die Reaktion irreversibel.
Co-reporter:Masayuki Endo Dr.;Koji Nakayama;Yuka Kaida Dr.
Angewandte Chemie 2004 Volume 116(Issue 42) pp:
Publication Date(Web):20 OCT 2004
DOI:10.1002/ange.200460889
Die selektive Spaltung von aktivierter Caspase-8 wurde durch eine photofunktionalisierte Caspase-3 imitiert, die an bestimmten Positionen der Peptidkette 2-Nitrophenylglycin(Npg)-Reste trägt (siehe Bild). Die Aktivität dieser Caspase-3 wurde durch Bestrahlung mit sichtbarem Licht induziert, die selbständige Spaltung von Caspase-3 durch den positionsspezifischen Einbau von Npg hingegen supprimiert.
Co-reporter:Michihiro Hara, Takeyoshi Sunagawa, Yosuke Oseki, Tetsuro Majima
Journal of Photochemistry and Photobiology A: Chemistry 2004 Volume 163(1–2) pp:153-158
Publication Date(Web):15 April 2004
DOI:10.1016/S1010-6030(03)00441-6
The photochemistry of p-halogenated anilines (H2NC6H4X-p (XA)) such as p-chloroaniline (CA; X=Cl), p-bromoaniline (BA; X=Br), and p-iodoaniline (IA; X=I) in benzene has been studied by the time-variation of microwave dielectric absorption (MWDA) method with respect to the transient behavior of the excited states and intermediates with independent dipole moments. The formation and the transient behavior of CA in the triplet excited state () having the ion pair character of [p-aminophenyl cation/Cl−], an ion pair of [p-aminophenyl cation/Br−], and a p-aminophenyl radical were observed in benzene from the time profiles of the MWDA signals immediately after the laser flash during 308-nm laser irradiation of CA, BA, and IA. The yields of the cleavage of the CX bond were in the order of CABA>IA. Decay of having the character of [p-aminophenyl cation/Cl−] was observed with a lifetime of 3.8 μs. The homolytic cleavage of the CBr bond in occurs to give a radical pair [p-aminophenyl radical/Br] which sequentially gives an ion pair [p-aminophenyl cation/Br−] through electron transfer between radicals. The dissociation of the [p-aminophenyl cation/Br−] to the p-aminophenyl cation and Br− was observed to occur on a 20 μs time scale. On the other hand, homolytic cleavage of the CI bond in occurs efficiently to give the p-aminophenyl radical and I. Bimolecular reactions of having the character of the [p-aminophenyl cation/Cl−] with oxygen and a p-aminophenyl radical with oxygen were found to occur at rate constants of 8.3×107 and 108–109 M−1 s−1, respectively.
Co-reporter:Mamoru Fujitsuka;Tadao Takada;Kiyohiko Kawai
PNAS 2004 Volume 101 (Issue 39 ) pp:14002-14006
Publication Date(Web):2004-09-28
DOI:10.1073/pnas.0402756101
Mechanism of photo-induced electron transfer and the subsequent hole transfer in DNA has been studied extensively, but so
far we are not aware of any reliable report of the observation of the long-distance hole-transfer process. In this article,
we demonstrate the results of direct observation for the long-distance hole transfer in double-helical DNA over 100 Å with
time-resolved transient absorption measurements. DNA conjugated with naphthalimide (NI) and phenothiazine (PTZ) (which worked
as electron-acceptor and donor molecules, respectively) at both 5′ ends was synthesized to observe the hole-transfer process.
Site-selective charge injection into G by means of the adenine-hopping process was accomplished by excitation of NI with a
355-nm laser flash. Transient absorption around 400 nm, which was assigned to the NI radical anion, was observed immediately
after the irradiation of a laser flash, indicating that the charge separation between NI and the nearest G occurred. Then,
the transient absorption of the PTZ radical cation (PTZ•+) at 520 nm was emerged, which was attributed to the hole transfer through DNA to the PTZ site. By monitoring the time profiles
of the transient absorption of PTZ•+ for NI-A6-(GA)n-PTZ and NI-A6-(GT)n-PTZ (n = 2, 3, 4, 6, 8, 12) (base sequences correspond to those for DNA modified with NI), the long-distance hole-transfer process
from G to PTZ, which occurred in the time scale of microsecond to millisecond, was observed directly. By assuming an average
distance of 3.4 Å between base-pairs, total distance reaches 100 Å for n = 12 sequences. Our results clearly show the direct observation of the long-distance hole transfer over 100 Å.
Co-reporter:Michihiro Hara, Sachiko Tojo, Tetsuro Majima
Journal of Photochemistry and Photobiology A: Chemistry 2004 Volume 162(Issue 1) pp:121-128
Publication Date(Web):20 February 2004
DOI:10.1016/S1010-6030(03)00321-6
Formation efficiency of radical cations of trans-stilbene and the methoxy-substituted stilbenes () during the resonant two-photon ionization (RTPI) in acetonitrile has been studied by laser flash photolysis with a XeCl excimer laser (308 nm, 25 ns). The transient absorption spectra of S radical cations (S+) were observed with a peak around 450–540 nm. The formation quantum yield of S+ (Φion) was 0.06–2.1%. No relation between Φion and Eox of S was observed, although Φion increased with the increasing lifetime of S in the lowest excited singlet state (S1). These results are coincident with a two-step two-photon excitation from the ground state (S0) to S1 and from S1 to higher excited singlet state (Sn), and ionization from Sn. Considerably large Φion was obtained for the RTPI of 3,5-dimethoxystilbene (5) with relatively high oxidation potential and a long S1 lifetime among S. This is explained by the intermediacy of the internal charge-transfer excited state for the RTPI of 5 based on the fluorescence lifetime measurement, solvatochromic measurement, and the dipole moment calculation. The concentration of S+ increased with the increasing laser fluence (F). The log–log plot of [S+] versus F gave a linear line with a slope of approximately 2 for the RTPI of 1–4, while approximately 1 for the RTPI of 5 and 6. The slope of 2 indicates clearly two-photon excitation during the RTPI. The slope of 1 is explained by the photostationary state among S0, S1, and Sn states attained during the laser pulse, particularly for the RTPI of S with a long S1 lifetime.
Co-reporter:Takashi Tachikawa Dr.;Akihiro Yoshida;Sachiko Tojo;Akira Sugimoto Dr.;Mamoru Fujitsuka Dr. Dr.
Chemistry - A European Journal 2004 Volume 10(Issue 21) pp:
Publication Date(Web):23 SEP 2004
DOI:10.1002/chem.200400516
The TiO2 photocatalytic one-electron oxidation mechanism of aromatic sulfides with a methylene bridging group (-(CH2)n-, n=0–4) between the 4-(methylthio)phenyl chromophore and the carboxylate binding group on the surface of a TiO2 powder slurried in acetonitrile (MeCN) has been investigated by time-resolved diffuse reflectance (TDR) spectroscopy. The electronic coupling element (HDA) between the hole donor and acceptor, which was estimated from the spectroscopic characteristics of the charge transfer (CT) complexes of the substrates (S) and the TiO2 surface, exhibited an exponential decline with the increasing of the methylene number of S. The determined decay factor (β) of 9 nm−1 also supports the fact that the 4-(methylthio)phenyl chromophore is separated from the TiO2 surface. The efficiency of the one-electron oxidation of S adsorbed on the TiO2 surface, which was determined from the relationship between the amount of adsorbates and the concentration of the generated radical cations, significantly depended on the HDA value, but not on the oxidation potential of S determined in homogeneous solution.
Co-reporter:Kiyohiko Kawai Dr.;Xichen Cai Dr.;Akira Sugimoto Dr.;Sachiko Tojo;Mamoru Fujitsuka Dr. Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 18) pp:
Publication Date(Web):22 APR 2004
DOI:10.1002/anie.200353318
A combination of two-color pulses allows a high DNA-damaging efficiency. The first laser pulse is applied to produce Sens.− and DNA.+, and the second laser pulse causes the ejection of an electron from Sens.−, thus making the reaction irreversible. Sens=photosensitizer.
Co-reporter:Kiyohiko Kawai, Aya Yokoohji, Sachiko Tojo and Tetsuro Majima
Chemical Communications 2003 (Issue 22) pp:2840-2841
Publication Date(Web):11 Oct 2003
DOI:10.1039/B310579B
Using nucleoside derivatives, which are soluble in dichloromethane, we have experimentally demonstrated that the reduction potential of cytosine is lowered by base pairing with guanine.
Co-reporter:Xichen Cai, Masanori Sakamoto, Michihiro Hara, Sachiko Tojo, Mamoru Fujitsuka, Akihiko Ouchi and Tetsuro Majima
Chemical Communications 2003 (Issue 20) pp:2604-2605
Publication Date(Web):18 Sep 2003
DOI:10.1039/B308577E
Rapid cleavage of the naphthylmethyl–oxygen bond of 1- and 2-[(4-benzoylphenoxy)methyl]naphthalenes in higher triplet excited states occurred within a laser flash of 5 ns to give 1- and 2-naphthylmethyl radicals with formation quantum yields of 0.042 ± 0.004 and 0.020 ± 0.002, respectively, during two-colour two-laser flash photolysis.
Co-reporter:Xichen Cai, Michihiro Hara, Kiyohiko Kawai, Sachiko Tojo and Tetsuro Majima
Chemical Communications 2003 (Issue 2) pp:222-223
Publication Date(Web):09 Dec 2002
DOI:10.1039/B210118A
Naphthalene in the higher triplet excited state Np(Tn) was generated from the two-step excitation method using two-colour two-laser flash photolysis technique and the lifetime of Np(Tn) was estimated to be 4.5 ps from the triplet energy quenching by quenchers such as p-dichlorobenzene, o-dicyanobenzene and carbon tetrachloride.
Co-reporter:Xichen Cai, Masanori Sakamoto, Michihiro Hara, Akira Sugimoto, Sachiko Tojo, Kiyohiko Kawai, Masayuki Endo, Mamoru Fujitsuka and Tetsuro Majima
Photochemical & Photobiological Sciences 2003 vol. 2(Issue 11) pp:1209-1214
Publication Date(Web):01 Oct 2003
DOI:10.1039/B307443A
Transient phenomena of benzophenone (BP) in the higher triplet excited state (Tn) have been investigated by the two-colour two-laser excitation method. Triplet energy transfer from BP(Tn) to quenchers (Q) occurred within the duration of a laser pulse (5 ns) to give Q(T1) with higher triplet energy than that of BP(T1). The quantum yield of the triplet energy-transfer quenching of BP(Tn) by CCl4 was found to be 0.0023 ± 0.0002 from the bleaching of the transient absorption of BP(T1) and the absorbed photon number. It appears that internal conversion from BP(Tn) to BP(T1) is the predominant process. The lifetimes (τTn) of BP(Tn) and several substituted benzophenones (BPs) in the higher triplet excited state [BPs(Tn)] were estimated from the dependence of the Q concentration on the efficiency of the triplet energy-transfer quenching of BP(Tn) by Q, and found to be 110–450 ps, depending on the nature of the substituents on the BPs. The effect of the substituents on τTn may be explained by the energy gap between the Tn and T1 states, because the main deactivation pathway for BPs(Tn) is the internal conversion process. In contrast, the substituent effect on the lifetimes of BPs(T1) cannot be explained by the energy gap law. The transient behaviour of Q(T1) depends on the properties of the quencher. Sequential triplet energy transfer from Q(T1) to BP occurred for p-dichlorobenzene and tert-butylbenzene as quenchers, while Q(T1) reacted partly with Q to form triplet excimers (3Q2*) for benzene, chlorobenzene, and o-dichlorobenzene as quenchers. When CCl4 was used as the quencher, the homolytic cleavage of a C–Cl bond of CCl4(T1) occurred to give Cl˙ and Cl3C˙ radicals.
Co-reporter:Masayuki Endo Dr. Dr.
Angewandte Chemie 2003 Volume 115(Issue 46) pp:
Publication Date(Web):25 NOV 2003
DOI:10.1002/ange.200352546
Stabförmige DNA-Mikrostrukturen wurden durch einstufige molekulare Aggregation mithilfe vernetzter Oligonucleotide mit Bismaleimid-Linkern und anschließender DNA-Ligation synthetisiert (siehe Schema). Kraftmikroskopische Analysen weisen auf eine verminderte Flexibilität der DNA-Strukturen in der parallelen Doppelhelix hin.
Co-reporter:Masayuki Endo Dr. Dr.
Angewandte Chemie International Edition 2003 Volume 42(Issue 46) pp:
Publication Date(Web):25 NOV 2003
DOI:10.1002/anie.200352546
Micrometer-scale rodlike DNA architectures can be synthesized by one-step molecular assembly using cross-linked oligonucleotides with bismaleimide linkers and subsequent DNA ligation (see scheme). Atomic force microscopy studies have shown that the flexibility of the DNA structures in the parallel double-helix structure is reduced.
Co-reporter:Kiyohiko Kawai, Tetsuro Majima
Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2002 Volume 3(Issue 1) pp:53-66
Publication Date(Web):21 June 2002
DOI:10.1016/S1389-5567(02)00005-9
The one-electron oxidation of DNA has been extensively studied as it leads to the formation of oxidative lesions that cause carcinogenesis and aging. In this paper, experimental results specifically addressing the effect of hydrogen bonding on the one-electron oxidation rate of nucleosides are presented. To separate the hydrogen bonding from the π-stacking effect, experiments were performed in dichloromethane, in which base-pair formation is possible at the monomer level. The effect of base pairing of guanine with cytosine on the rate constant of the electron transfer from guanine to electron acceptor molecules in the triplet excited state was investigated, and a selective enhancement of the electron transfer was observed for the guanine:cytosine base pair. By introducing a methyl or bromo group to the C5 position of cytosine, acceleration or suppression, respectively, of the one-electron oxidation relative to the guanine:cytosine base pair was observed. The results demonstrate that the one-electron oxidation rate of guanine in DNA can be regulated by introducing a substituent on the base-pairing cytosine.
Co-reporter:Kiyohiko Kawai Dr.;Yasuharu Wata;Nobuyuki Ichinose
Angewandte Chemie 2000 Volume 112(Issue 23) pp:
Publication Date(Web):30 NOV 2000
DOI:10.1002/1521-3757(20001201)112:23<4497::AID-ANGE4497>3.0.CO;2-2
Co-reporter:Peng Zhang, Mamoru Fujitsuka, Tetsuro Majima
Applied Catalysis B: Environmental (15 May 2016) Volume 185() pp:181-188
Publication Date(Web):15 May 2016
DOI:10.1016/j.apcatb.2015.12.022
Co-reporter:Yue Feng, Duan Bin, Bo Yan, Yukou Du, Tetsuro Majima, Weiqiang Zhou
Journal of Colloid and Interface Science (1 May 2017) Volume 493() pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.jcis.2017.01.035
Porous bimetallic PdNi catalysts were fabricated by a novel method, namely, reduction of Pd and Ni oxides prepared via calcining the complex chelate of PdNi-dimethylglyoxime (PdNi-dmg). The morphology and composition of the as-prepared PdNi were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Furthermore, the electrochemical properties of PdNi catalysts towards ethanol electrooxidation were also studied by electrochemical impedance spectrometry (EIS), cyclic voltammetry (CV) and chronoamperometry (CA) measurement. In comparison with porous Pd and commercial Pd/C catalysts, porous structural PdNi catalysts showed higher electrocatalytic activity and durability for ethanol electrooxidation, which may be ascribed to Pd and Ni property, large electroactive surface area and high electron transfer property. The Ni exist in the catalyst in the form of the nickel hydroxides (Ni(OH)2 and NiOOH) which have a high electron and proton conductivity enhances the catalytic activity of the catalysts. All results highlight the great potential application of the calcination-reduction method for synthesizing high active porous PdNi catalysts in direct ethanol fuel cells.
Co-reporter:Xiaoyan Cai, Liang Mao, Junying Zhang, Mingshan Zhu, Mamoru Fujitsuka and Tetsuro Majima
Journal of Materials Chemistry A 2017 - vol. 5(Issue 21) pp:NaN10449-10449
Publication Date(Web):2017/04/24
DOI:10.1039/C7TA02379K
Formation of surface heterojunctions in photocatalysts through tailoring the exposed crystal facets is an efficient strategy to boost charge separation. In this work, successive surface heterojunctions with large space-charge separation were achieved in a nanostep structured La2Ti2O7 (LTO NSP) single crystal exposed periodically with (010) and (012) facets. The three-dimensional (3D) nanosteps were found to enhance the photocatalytic hydrogen generation performance 35 and 74 times, compared with LTO nanosheets and nanoparticles with the same surface area, respectively. The ultrahigh superficial charge accumulation in LTO NSP verified by surface photovoltage (SPV) measurements suggested the efficient migration of photogenerated charge carriers to the surface. Femtosecond time-resolved diffuse reflectance (TDR) spectroscopy provided direct evidence that the electrons generated from the excited sites of LTO NSP were effectively delivered to the high energy (012) facets and temporarily stored there for further reduction reactions, originating from the successive (010) and (012) surface heterojunctions.
Co-reporter:Xiaowei Shi, Mamoru Fujitsuka, Zaizhu Lou, Peng Zhang and Tetsuro Majima
Journal of Materials Chemistry A 2017 - vol. 5(Issue 20) pp:NaN9681-9681
Publication Date(Web):2017/04/19
DOI:10.1039/C7TA01888F
Visible-light-driven water splitting process is highly attractive for alternative energy utilization, while developing efficient, earth-abundant, and environmentally friendly photocatalysts for hydrogen evolution reaction has remained a major challenge. Herein, heterostructured photocatalysts composed of hollow N-doped TiO2 and g-C3N4 (N-TiO2/g-C3N4) were developed by an in situ impregnation calcination method. N-TiO2 and N-TiO2/g-C3N4 heterostructures with different ratios of N-TiO2 and g-C3N4 were synthesized by simply varying the amount of cyanamide (CY) as the g-C3N4 precursor. Using N-TiO2/g-C3N4 as a H2 evolution photocatalyst, the largest rate of 296.4 μmol g−1 h−1 was obtained under visible light irradiation (λ ≥ 420 nm) without any noble metal co-catalyst, which is 25.8 times larger than that of pure g-C3N4 (11.5 μmol g−1 h−1). Femtosecond time-resolved diffuse reflectance spectroscopy was used to evaluate the lifetime of photogenerated electrons and electron transfer dynamics in N-TiO2/g-C3N4. It is suggested that an additional decay pathway exists for the photogenerated electrons in N-TiO2/g-C3N4, in which N-TiO2 acts as an electron trapping site, leading to higher photocatalytic H2 evolution activity than pure g-C3N4. The present work not only provides a facile method for preparing doped materials and heterostructures with efficient photocatalytic activity, but also deepens the understanding of charge transfer dynamics in heterostructured photocatalysts.
Co-reporter:Peng Zhang, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
Chemical Communications 2015 - vol. 51(Issue 33) pp:NaN7190-7190
Publication Date(Web):2015/03/20
DOI:10.1039/C5CC01753J
Here we demonstrated that 3D architectures of TiO2 mesocrystals uniformly packed with a chemically exfoliated MoS2 shell exhibit promising reactive efficiency and good stability in synergetic hydrogen evolution. The efficient interfacial electron transfer from the excited TiO2 moieties to the decorated ultrathin MoS2 shell was effectively monitored.
Co-reporter:Sooyeon Kim, Mamoru Fujitsuka, Norimitsu Tohnai, Takashi Tachikawa, Ichiro Hisaki, Mikiji Miyata and Tetsuro Majima
Chemical Communications 2015 - vol. 51(Issue 58) pp:NaN11583-11583
Publication Date(Web):2015/06/10
DOI:10.1039/C5CC03969J
We report a substitution of 9-phenylanthracenyl group into rhodamine derivatives that can induce the J-aggregate formation of rhodamine moieties in the aqueous solution upon the addition of a halide ion. From X-ray crystallographic analysis, the dramatic red-shift in the absorption band (i.e. app. 100 nm) originates from the cooperative slipped-stacking of rhodamine and anthracene molecules.
Co-reporter:Zhaoke Zheng, Takashi Tachikawa and Tetsuro Majima
Chemical Communications 2015 - vol. 51(Issue 76) pp:NaN14376-14376
Publication Date(Web):2015/08/04
DOI:10.1039/C5CC05898H
We employed single-particle photoluminescence (PL) measurements to investigate the interfacial electron transfer between single Au nanorods (NRs) and TiO2 coated by ALD. Analyzing the energy relaxation path of plasmon-generated hot electrons as well as the PL intensities allowed for the detection and study of the interfacial electron transfer process spatially.
Co-reporter:Kiyohiko Kawai, Takeshi Koshimo, Atsushi Maruyama and Tetsuro Majima
Chemical Communications 2014 - vol. 50(Issue 72) pp:NaN10481-10481
Publication Date(Web):2014/07/22
DOI:10.1039/C4CC00377B
The more a fluorescent molecule is exposed to a solvent, the faster its triplet excited state is quenched by molecular oxygen. The changes in the solvent accessibility of a fluorescent molecule were probed by measuring the duration of the off time during the blinking of the fluorescence, which enabled analysis of the function of a molecular beacon-type probe.
Co-reporter:Man Jae Park, Mamoru Fujitsuka, Haruhiro Nishitera, Kiyohiko Kawai and Tetsuro Majima
Chemical Communications 2012 - vol. 48(Issue 89) pp:NaN11010-11010
Publication Date(Web):2012/09/24
DOI:10.1039/C2CC36054C
Excess electron transfer dynamics in DNA hairpins was investigated by femtosecond laser flash photolysis of a donor–DNA–acceptor system using N,N-dimethylaminopyrene and diphenylacetylene as an electron donor and acceptor, respectively. It was revealed that the excess electron hopping rate between T's is faster than that of the hole.
Co-reporter:Kiyohiko Kawai, Eri Matsutani and Tetsuro Majima
Chemical Communications 2010 - vol. 46(Issue 19) pp:NaN3279-3279
Publication Date(Web):2010/03/29
DOI:10.1039/C002810J
The kinetics and efficiency of oxidative degradation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo) in DNA during the photosensitized one-electron oxidation of DNA was investigated. The presence of 8-oxodGuo was shown to increase the lifetime of the charge-separated state in DNA by serving as a “hole sink” resulting in efficient and exclusive degradation.
Co-reporter:Mamoru Fujitsuka, Sachiko Tojo, Teruo Shinmyozu and Tetsuro Majima
Chemical Communications 2009(Issue 12) pp:NaN1555-1555
Publication Date(Web):2009/02/20
DOI:10.1039/B810122A
Intramolecular dimer radical anions of [3n]cyclophanes generated by γ-ray irradiation in low-temperature glassy matrices showed an absorption band attributable to charge resonance around 936–1210 nm, from which the stabilization energy of the dimer radical anions were analyzed on the basis of π-electron delocalization over two benzene rings and the damping factor (β) was estimated to be 0.35 Å−1, which is smaller than that of the intramolecular dimer radical cation of [3n]cyclophanes, indicating a effective charge delocalization of the dimer radical anions.
Co-reporter:Nan Wang, Takashi Tachikawa and Tetsuro Majima
Chemical Science (2010-Present) 2011 - vol. 2(Issue 5) pp:NaN900-900
Publication Date(Web):2011/03/04
DOI:10.1039/C0SC00648C
Electronic communication between the building blocks of nanocomposites is an important property that affects their functionality with regard to many optoelectronic and catalytic applications. Herein, we report a single-molecule, single-particle approach for elucidating the inherent photocatalytic activity of individual Au nanoparticle-loaded TiO2 particles using a novel redox-responsive fluorescent dye. A single-particle kinetic analysis of the fluorescence bursts emitted from the products revealed that the photocatalytic activity leading to reduction of the probe molecules is controlled by not only the substrate concentration and excitation intensity but also the Au particle size, and that these factors are intricately interrelated. Furthermore, we discovered that the stochastic photocatalytic events around the millisecond-to-second time scale showed considerable temporal and spatial heterogeneity during photoirradiation, and that they actually originate from the charging/discharging of Au nanoparticles on TiO2. Our findings represent a significant contribution to the scientific understanding of the interfacial electron transfer dynamics in composite systems, and more fundamentally, in heterogeneous (photo)chemical processes.
Co-reporter:Masanori Sakamoto, Sung Sik Kim, Hirotoshi Furusho and Tetsuro Majima
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 2) pp:NaN372-372
Publication Date(Web):2009/11/11
DOI:10.1039/B917981J
Photochemical synthesis of metal nanostructures through photosensitized reduction of metal sources is a powerful method in a wide variety of environments, because light can selectively promote the desired reaction without damaging the surrounding environment. A drawback of the method is that most organic photosensitizers are disposable and consumed during the photochemical reactions and as a consequence a much larger amount of photosensitizer than that of the metal source is usually required, and therefore, the photosensitized reduction method is wasteful in terms of the sensitizer. In the present work, we propose a new photochemical synthetic method using a recyclable photosensitizer and applied it to fabricate Ag nanostructures at the solid–liquid interface. The photosensitized reduction of Ag ion at the solid–liquid interface resulted in the formation of unique Ag nanostructures (nanowires or plates) without the use of templates or stabilizing agents. The relation between the morphology and several external contributing factors, such as solvent polarity and interaction between the substrate and crystal phase, was discussed.
Co-reporter:Jungkweon Choi, Sooyeon Kim, Takashi Tachikawa, Mamoru Fujitsuka and Tetsuro Majima
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 13) pp:NaN5658-5658
Publication Date(Web):2011/02/09
DOI:10.1039/C0CP02689A
Denaturant-induced conformational change of yeast iso-1-cytochrome c (Cytc) has been comprehensively investigated in the single-molecule and bulk phases. By fluorescence-quenching experiments with dye-labelled heme-protein (Alexa 488-labelled Cytc, Cytc-A488), we clearly show that the fluorescence quenching observed from folded Cytc-A488 is due mainly to photoinduced electron transfer (PET) between electron-donating amino acids such as tryptophan and the dye attached to the protein. In addition, the unfolding process of Cytc-A488 observed in the single-molecule and bulk phases can be explained well in terms of a three-state model: Cytc unfolds through an intermediate with a native-like compactness. By quantitative analysis of fluorescence correlation spectroscopy (FCS) data, we were able to observe a relaxation time of ∼1.5 μs corresponding to segmental motion and fast folding dynamics of 55 μs in the unfolded state of Cytc. The results presented here also suggest that a combination of single-molecule and ensemble-averaged spectroscopy is necessary to provide convincing and comprehensive assignments of protein kinetics.
Co-reporter:Mamoru Fujitsuka, Dae Won Cho, Takahiro Iwamoto, Shigeru Yamago and Tetsuro Majima
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 42) pp:NaN14588-14588
Publication Date(Web):2012/09/06
DOI:10.1039/C2CP42712E
Hoop-shaped π-conjugated molecules such as cycloparaphenylene (CPP) have attracted the attention of many chemists because they exhibit interesting properties due to the distorted π-electron system. To gain a systematic understanding of the properties that result from distorted π-electron systems, it is important to know precisely how these properties depend on the hoop size. In the present study, we have investigated the size dependence of the fluorescence properties of CPPs. The fluorescence spectra of smaller CPPs showed red-shifted fluorescence peaks, smaller fluorescence quantum yields, and longer lifetimes, when compared to those of larger ones. One of the important factors that gave rise to these fluorescence properties of smaller CPPs was greater structural relaxation from the Franck–Condon state, which is a postulation supported by theoretical calculations. The structural relaxation in the picosecond domain was experimentally detected by the fluorescence upconversion method. The present results are an important example that confirms steric factors strongly governing the fluorescence properties of a molecule.
Co-reporter:Takashi Tachikawa, Shi-Cong Cui, Mamoru Fujitsuka and Tetsuro Majima
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 12) pp:NaN4249-4249
Publication Date(Web):2012/02/02
DOI:10.1039/C2CP23317G
Graphene oxide (GO) nanosheets have received a great deal of attention for a wide range of applications from optoelectronic devices to biological sensors. We now report a mechanistic study of the interfacial electron transfer (ET) processes between organic dye molecule, 9-phenyl-2,3,7-trihydroxy-6-fluorone (PF), and nanometre-sized GO sheets using ensemble-averaged and single-molecule spectroscopies. The ET dynamics was characterized by the direct observation of the PF radical cation during the laser flash photolysis, and its reaction rate was determined to be ∼1011 s−1. The single-molecule fluorescence spectroscopy was utilized to clarify the heterogeneous nature of the interfacial ET within individual composites. Their fluorescence lifetimes and spectra were found to vary from composite to composite, possibly due to the different local structures and molecular interactions. The autocorrelation analysis of fluorescence intensity trajectories also revealed the temporal fluctuation of the ET reactivity.
Co-reporter:Mamoru Fujitsuka, Tatsuya Ohsaka and Tetsuro Majima
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 46) pp:NaN31038-31038
Publication Date(Web):2015/10/26
DOI:10.1039/C5CP05254H
In the present study, electron transfer (ET) processes from excited radical anions have been investigated using dyad molecules including C60. The deactivation process of excited C60˙−, including the internal conversion from the D1 to the D0 state and the cooling process of the vibrationally hot ground state (Dhot0), was observed spectroscopically for the first time. These processes could be unambiguously distinguished by the observation of the stimulated emission from the D1 state. The intramolecular ET processes from the excited C60˙− were confirmed by the transient absorption spectra. Clearly, both D1 and Dhot0 states acted as precursors for the ET, i.e., dual ET pathways were confirmed. The driving force dependence of the ET rates was well characterized by the Marcus theory, which revealed that the forward ET processes are located at the top region of the Marcus parabola. In addition, the ET from the excited imide radical anion to C60 and that from the ground state C60˙− to imide were examined. The ET rate from the excited imide radical anion and that from ground state C60˙− did not follow the Marcus parabola estimated for the ET from the excited C60˙−. The observed difference can be attributed to the difference in the energy required to form the reduced spacer (Δ) in the superexchange mechanism. Because the Δ value tends to become smaller for ET processes from excited radical ions, fast and efficient ET processes are expected from these states as demonstrated in the present study.
Co-reporter:Sooyeon Kim, Mamoru Fujitsuka, Mikiji Miyata and Tetsuro Majima
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 3) pp:NaN2103-2103
Publication Date(Web):2015/11/27
DOI:10.1039/C5CP06541K
Since it was first reported in 2008, great attention has been paid to Si–rhodamine (SiR) because of its far-red to near-infrared (NIR) absorption/fluorescence and suitability for high-resolution in vivo imaging. However, properties of SiR in the excited state have not been reported, even though they are directly related to its fluorescence. In the present study, the properties of SiR monomers in the excited states are thoroughly characterized for the first time. Moreover, by replacing a phenyl moiety of SiR with a 4-(9-anthryl)phenylene group (SiR–An), we prepared H- and J-aggregates of SiR in the aqueous solution, and succeeded in monitoring exciton formation and annihilation in the aggregates. Interestingly, the relative exciton population in the SiR J-aggregate increases as the excitation power becomes stronger, which is unusual considering that the substantial exciton–exciton annihilation process occurs as more excitons are generated. The results obtained in the present study suggest high versatility of SiR not only as a red fluorophore in the cutting-edge microscopic techniques but also as a NIR absorber in the light harvesting system.
Co-reporter:Takashi Tachikawa, Peng Zhang, Zhenfeng Bian and Tetsuro Majima
Journal of Materials Chemistry A 2014 - vol. 2(Issue 10) pp:NaN3388-3388
Publication Date(Web):2013/12/17
DOI:10.1039/C3TA14319H
Development of efficient photocatalysts based on semiconductor materials for organic synthesis, fuel generation, and environmental purification is a central theme in current research and various industries. In this study, we propose a novel strategy for improving the photooxidation activity of photocatalysts by combining metal oxide superstructures and oxygen/hydrogen-evolving co-catalysts. Cobalt phosphate (CoPi) and Pt nanoparticles were selected as model co-catalysts and photochemically deposited on anatase TiO2 mesocrystals. The structures and reaction dynamics of the composites were thoroughly studied by ensemble-averaged and single-particle spectro-microscopies. Time-resolved diffuse reflectance and electron spin resonance spectroscopy measurements revealed that photogenerated holes in TiO2 are transferred to the Co species in CoPi upon UV light irradiation. The photooxidation properties of the composites were tested using fluorescence dye probes. It was found that CoPi-loaded TiO2 mesocrystals had higher activity than standard TiO2 photocatalysts, and their activity was further enhanced by introducing Pt nanoparticles on specific surfaces. In situ fluorescence imaging on a single crystal provides information on the location of reactive sites and the diffusion of product molecules. Consequently, the site-specific modification of co-catalysts tailored by anisotropic electron flow in the mesocrystal superstructures significantly retarded the charge recombination between the holes and electrons, thereby resulting in enhanced (up to approximately 300 times) photooxidation activity.
Co-reporter:Jungkweon Choi and Tetsuro Majima
Chemical Society Reviews 2011 - vol. 40(Issue 12) pp:NaN5909-5909
Publication Date(Web):2011/09/07
DOI:10.1039/C1CS15153C
In contrast to B-DNA that has a right-handed double helical structure with Watson–Crick base pairing under the ordinary physiological conditions, repetitive DNA sequences under certain conditions have the potential to fold into non-B DNA structures such as hairpin, triplex, cruciform, left-handed Z-form, tetraplex, A-motif, etc. Since the non-B DNA-forming sequences induce the genetic instability and consequently can cause human diseases, the molecular mechanism for their genetic instability has been extensively investigated. On the contrary, non-B DNA can be widely used for application in biotechnology because many DNA breakage hotspots are mapped in or near the sequences that have the potential to adopt non-B DNA structures. In addition, they are regarded as a fascinating material for the nanotechnology using non-B DNAs because they do not produce any toxic byproducts and are robust enough for the repetitive working cycle. This being the case, an understanding on the mechanism and dynamics of their structural changes is important. In this critical review, we describe the latest studies on the conformational dynamics of non-B DNAs, with a focus on G-quadruplex, i-motif, Z-DNA, A-motif, hairpin and triplex (189 references).
Co-reporter:Takashi Tachikawa and Tetsuro Majima
Chemical Society Reviews 2010 - vol. 39(Issue 12) pp:NaN4819-4819
Publication Date(Web):2010/09/07
DOI:10.1039/B919698F
Nanostructured metal oxide semiconductors, such as TiO2 and ZnO, have attracted great attention as the promising material for photovoltaic devices, photocatalysts for water splitting and environmental purification, sensors, batteries, etc. In this critical review, we have focused on the on-site observation of interfacial chemical reactions involving charge carriers and reactive oxygen species (ROS), such as singlet oxygen and the hydroxyl radical, generated by the photoexcitation of TiO2 nanoparticles using single-molecule, single-particle fluorescence spectroscopy. Advanced fluorescence imaging techniques enable us to determine the location of the photocatalytically active sites that are closely related to the defects heterogeneously distributed on the surface. Consequently, this review provides a great opportunity to understand the temporal and spatial heterogeneities within an individual catalyst particle, allowing for the potential use of single-molecule, single-particle approaches in the analysis of photocatalytic reactions (189 references).
Co-reporter:Zhenfeng Bian, Takashi Tachikawa, Shi-Cong Cui, Mamoru Fujitsuka and Tetsuro Majima
Chemical Science (2010-Present) 2012 - vol. 3(Issue 2) pp:NaN379-379
Publication Date(Web):2011/10/11
DOI:10.1039/C1SC00552A
In this study, we investigated interfacial charge transfer dynamics in water-soluble perylenediimide (WS-PDI) dye sensitized p-type semiconductor NiO nanoparticle films to better understand how molecular interactions influence photoconversion processes involved in solar cells by means of ensemble-averaged and single-molecule spectroscopies. Transient absorption data showed that strong and weak electronic couplings coexist between WS-PDI molecules and NiO nanoparticles, resulting in fast (within several picoseconds) and slow (requiring tens of picoseconds to nanoseconds) hole transfer from the excited dye to NiO, followed by charge recombination occurring at pico- to microsecond time scales. The correlated analyses of single-molecule fluorescence intensity, lifetime, blinking, and anisotropy revealed the intrinsic distribution and temporal fluctuation of interfacial charge transfer reactivity, which are closely related to site-specific molecular interactions and dynamics. It was also found that a suitable insulating Al2O3 layer can weaken the electronic interaction between WS-PDI and NiO, thereby retarding charge recombination and significantly enhancing photoelectric conversion efficiency. The results presented here will provide a reliable basis for design of highly efficient p-type solar cells and other molecule/semiconductor systems for their use in optoelectronic and solar energy applications.
Co-reporter:Yasuko Osakada, Kiyohiko Kawai, Mamoru Fujitsuka and Tetsuro Majima
Chemical Communications 2008(Issue 23) pp:NaN2658-2658
Publication Date(Web):2008/05/08
DOI:10.1039/B801876F
Transient absorption measurements of charge transfer (CT) demonstrated that the CT in the DNA assembly constructed by simply mixing DNAs with sticky ends occurs over 200 Å selectively to the complementary sticky end sequences.
Co-reporter:Jungkweon Choi, Takashi Tachikawa, Youngmin Kim, Mamoru Fujitsuka, Hyotcherl Ihee and Tetsuro Majima
Chemical Communications 2010 - vol. 46(Issue 48) pp:NaN9157-9157
Publication Date(Web):2010/11/01
DOI:10.1039/C0CC03056B
The study of the structural reorganization and photophysical properties of Zn–Cytc using the single-molecule and ensemble-averaged spectroscopy shows that the photoblinking behaviors of single-Zn–Cytc depend on the folded and unfolded structures, whereas the fluorescence dynamics of Zn–Cytc observed in the bulk phase are hardly affected by the conformational change of a protein.
Co-reporter:Takashi Tachikawa and Tetsuro Majima
Chemical Communications 2012 - vol. 48(Issue 27) pp:NaN3302-3302
Publication Date(Web):2012/02/10
DOI:10.1039/C2CC30597F
We report a single-particle approach for studying the photocatalytic oxidation reaction on individual anatase TiO2 particles. Single-particle kinetic and imaging analyses of the chemiluminescence (CL) emitted from the probe dye molecules revealed that the oxidation reactivity is not significantly dependent on the crystal faces.
Co-reporter:Mamoru Fujitsuka and Tetsuro Majima
Chemical Science (2010-Present) 2017 - vol. 8(Issue 3) pp:NaN1762-1762
Publication Date(Web):2016/12/13
DOI:10.1039/C6SC03428D
In the past few decades, charge transfer in DNA has attracted considerable attention from researchers in a wide variety of fields, including bioscience, physical chemistry, and nanotechnology. Charge transfer in DNA has been investigated using various techniques. Among them, time-resolved spectroscopic methods have yielded valuable information on charge transfer dynamics in DNA, providing an important basis for numerical practical applications such as development of new therapy applications and nanomaterials. In DNA, holes and excess electrons act as positive and negative charge carriers, respectively. Although hole transfer dynamics have been investigated in detail, the dynamics of excess electron transfer have only become clearer relatively recently. In the present paper, we summarize studies on the dynamics of hole and excess electron transfer conducted by several groups including our own.
Co-reporter:Peng Zhang, Sooyeon Kim, Mamoru Fujitsuka and Tetsuro Majima
Chemical Communications 2017 - vol. 53(Issue 38) pp:NaN5309-5309
Publication Date(Web):2017/04/12
DOI:10.1039/C7CC01894K
Herein, we investigated that sheet-like TiO2 mesocrystals with controllable nanothorns on the {101} facet during the topotactic transformation exhibit facet-induced charge separation and anisotropic electron flow, realizing the superior facet-dependent photocatalysis in solar energy conversion.
![Decacyclo[32.2.2.22,5.26,9.210,13.214,17.218,21.222,25.226,29.230,33]tetrapentaconta-1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,53-heptacosaene](/data/chemimg/3742200/1092522-74-1.png)
![Decacyclo[32.2.2.22,5.26,9.210,13.214,17.218,21.222,25.226,29.230,33]tetrapentaconta-1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,53-heptacosaene](/data/chemimg/3742200/1092522-74-1_b.png)
![Stannane, tributyl(3,3'''-dihexyl[2,2':5',2'':5'',2'''-quaterthiophen]-5-yl)-](http://img.cochemist.com/ccimg/384900/384820-76-2.png)
![Stannane, tributyl(3,3'''-dihexyl[2,2':5',2'':5'',2'''-quaterthiophen]-5-yl)-](http://img.cochemist.com/ccimg/384900/384820-76-2_b.png)
![9H-TRIBENZO[A,F,L]TRINDENE, 9,9,14,14,15,15-HEXAETHYL-14,15-DIHYDRO-](http://img.cochemist.com/ccimg/916600/916597-79-0.png)
![9H-TRIBENZO[A,F,L]TRINDENE, 9,9,14,14,15,15-HEXAETHYL-14,15-DIHYDRO-](http://img.cochemist.com/ccimg/916600/916597-79-0_b.png)
![Benzoic acid, 2-[6-(4-hydroxyphenoxy)-3-oxo-3H-xanthen-9-yl]-](http://img.cochemist.com/ccimg/686800/686773-84-2.png)
![Benzoic acid, 2-[6-(4-hydroxyphenoxy)-3-oxo-3H-xanthen-9-yl]-](http://img.cochemist.com/ccimg/686800/686773-84-2_b.png)
![5,7-Diiodo-2,3-dihydrothieno[3,4-b][1,4]dioxine](http://img.cochemist.com/ccimg/640800/640737-72-0.png)
![5,7-Diiodo-2,3-dihydrothieno[3,4-b][1,4]dioxine](http://img.cochemist.com/ccimg/640800/640737-72-0_b.png)
![2,2',3,3'-Tetrahydro-5,5'-bithieno[3,4-b][1,4]dioxine](http://img.cochemist.com/ccimg/195700/195602-17-6.png)
![2,2',3,3'-Tetrahydro-5,5'-bithieno[3,4-b][1,4]dioxine](http://img.cochemist.com/ccimg/195700/195602-17-6_b.png)
![Heptacyclo[20.2.2.22,5.26,9.210,13.214,17.218,21]hexatriaconta-1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35-octadecaene](/data/chemimg/3742600/156980-13-1.png)
![Heptacyclo[20.2.2.22,5.26,9.210,13.214,17.218,21]hexatriaconta-1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35-octadecaene](/data/chemimg/3742600/156980-13-1_b.png)
![2,9-Di(tridecan-7-yl)anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone](/data/chemimg/339200/110590-84-6.png)
![2,9-Di(tridecan-7-yl)anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone](/data/chemimg/339200/110590-84-6_b.png)
![21,22,23,24-Tetraazapentacyclo[16.2.1.12,5.18,11.112,15]tetracosa-1(21),2,4,6,8(23),9,11,13,15,17,19-undecaene](http://img.cochemist.com/ccimg/100600/100572-96-1.png)
![21,22,23,24-Tetraazapentacyclo[16.2.1.12,5.18,11.112,15]tetracosa-1(21),2,4,6,8(23),9,11,13,15,17,19-undecaene](http://img.cochemist.com/ccimg/100600/100572-96-1_b.png)
![Indeno[2,1-a]indene, 5,10-dihydro-5,5,10,10-tetraphenyl-](http://img.cochemist.com/ccimg/91900/91861-70-0.png)
![Indeno[2,1-a]indene, 5,10-dihydro-5,5,10,10-tetraphenyl-](http://img.cochemist.com/ccimg/91900/91861-70-0_b.png)
![2,6-bis(2-ethylhexyl)pyrrolo[3,4-f]isoindole-1,3,5,7-tetrone](http://img.cochemist.com/ccimg/6700/6626-74-0.png)
![2,6-bis(2-ethylhexyl)pyrrolo[3,4-f]isoindole-1,3,5,7-tetrone](http://img.cochemist.com/ccimg/6700/6626-74-0_b.png)
![3',6'-Dihydroxy-3H-spiro[isobenzofuran-1,9'-xanthen]-3-one](http://img.cochemist.com/ccimg/2400/2321-07-5.png)
![3',6'-Dihydroxy-3H-spiro[isobenzofuran-1,9'-xanthen]-3-one](http://img.cochemist.com/ccimg/2400/2321-07-5_b.png)
![Nonacyclo[28.2.2.22,5.26,9.210,13.214,17.218,21.222,25.226,29]octatetraconta-1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47-tetracosaene](/data/chemimg/3742600/1217269-85-6.png)
![Nonacyclo[28.2.2.22,5.26,9.210,13.214,17.218,21.222,25.226,29]octatetraconta-1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47-tetracosaene](/data/chemimg/3742600/1217269-85-6_b.png)
![1H-BENZ[DE]ISOQUINOLINE-1,3(2H)-DIONE, 2-(3-AMINOPHENYL)-](http://img.cochemist.com/ccimg/57100/57037-90-8.png)
![1H-BENZ[DE]ISOQUINOLINE-1,3(2H)-DIONE, 2-(3-AMINOPHENYL)-](http://img.cochemist.com/ccimg/57100/57037-90-8_b.png)
![1H-2-Benzopyrano[6,5,4-def]isoquinoline-1,3,6,8(7H)-tetrone, 7-(2-ethylhexyl)-](/data/chemimg/3759400/282094-08-0.png)
![1H-2-Benzopyrano[6,5,4-def]isoquinoline-1,3,6,8(7H)-tetrone, 7-(2-ethylhexyl)-](/data/chemimg/3759400/282094-08-0_b.png)
![1H-FURO[3,4-F]ISOINDOLE-1,3,5,7(6H)-TETRONE, 6-(2-ETHYLHEXYL)-](http://img.cochemist.com/ccimg/59100/59045-90-8.png)
![1H-FURO[3,4-F]ISOINDOLE-1,3,5,7(6H)-TETRONE, 6-(2-ETHYLHEXYL)-](http://img.cochemist.com/ccimg/59100/59045-90-8_b.png)
![Ferrate(2-), [7,12-diethenyl-3,8,13,17-tetramethyl-21H,23H-porphine-2,18-dipropanoato(4-)-κN21,κN22,κN23,κN24]-, hydrogen (1:2), (SP-4-2)-](/data/chemimg/522800/14875-96-8.png)
![Ferrate(2-), [7,12-diethenyl-3,8,13,17-tetramethyl-21H,23H-porphine-2,18-dipropanoato(4-)-κN21,κN22,κN23,κN24]-, hydrogen (1:2), (SP-4-2)-](/data/chemimg/522800/14875-96-8_b.png)