Kazuo Tanaka

This paper presents the aggregation-induced emission (AIE) properties of o-carborane derivatives and proposes a potential strategy for constructing AIE-active organoboron complexes via the enhancement of freedom of intramolecular mobility. Initially, the optical properties of o-carborane derivatives with or without the fused ring structure at the C–C bond in o-carborane in which elongation should be induced by photo-excitation according to theoretical calculations were compared. Accordingly, it was shown that large mobility at the C–C bond in o-carborane should be responsible for the annihilation of emission in solution, leading to the AIE property. From this result, it was presumed that by enhancing the freedom of intramolecular mobility in conventional luminescent organoboron complexes, the deactivation of the excited state in solution and emission recovery in the aggregate can be induced. Based on this idea, we have performed several studies and introduce two representative results. Firstly, the decrease in luminescent properties of boron dipyrromethene (BODIPY) in solution by introducing a movable functional group is explained. Next, the AIE behaviors of boron ketoiminates and the potential mechanism concerning conformational changes for the deactivation of the excited state in the solution state are illustrated. It is proposed that enhancement of the freedom of mobility in the excited state of luminescent organoboron complexes could be a potential strategy for realizing AIE behaviors.

Design of bond-cleavage-induced intramolecular charge transfer emission with dibenzoboroles and their application to ratiometric sensors for discriminating chain lengths of alkanes

Co-reporter:Takuya Matsumoto;Hirofumi Takamine;Yoshiki Chujo

Materials Chemistry Frontiers 2017 vol. 1(Issue 11) pp:2368-2375

Publication Date(Web):2017/10/26

DOI:10.1039/C7QM00350A

Dibenzoborole derivatives containing four-coordinated boron were designed to realize emission from the bond-cleavage-induced intramolecular charge transfer (BICT) transition. A series of electron-donating and accepting groups were introduced into dibenzoborole through regioselective bromination and Suzuki–Miyaura coupling reaction in high yields. The synthesized dibenzoboroles showed dual-emissive properties composed of emission from the π–π* transition with four-coordinated boron and the BICT transition with a three-coordinated state. The influence of the substituents on the optical properties was experimentally and theoretically analyzed. Next, on the basis of the dual-emissive properties, it was demonstrated that dibenzoborole was feasible as a ratiometric fluorescent sensor for discriminating the viscosity of solvent alkanes including the length of alkane chains with a wide detection range. Finally, it was demonstrated that this detection system with a ratiometric output was applicable for evaluating viscosity with mixture samples and various kinds of natural oils.

Control of aggregation-induced emission versus fluorescence aggregation-caused quenching by bond existence at a single site in boron pyridinoiminate complexes

Co-reporter:Madoka Yamaguchi;Shunichiro Ito;Amane Hirose;Yoshiki Chujo

Materials Chemistry Frontiers 2017 vol. 1(Issue 8) pp:1573-1579

Publication Date(Web):2017/07/27

DOI:10.1039/C7QM00076F

This manuscript reports the control of the luminescence properties of organoboron complexes between fluorescence aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE) with or without a chemical bond at a single site in the pyridinoiminate skeleton. Novel boron complexes with (FBPI) and without (BPI) the fused structure in the ligand moiety were designed and synthesized. From the optical measurements, it was demonstrated that their solution- and solid-state emission behaviors oppositely varied with the presence of the fused structures. FBPI showed critical ACQ in a poor solvent. In contrast, BPI presented AIE behaviors. Additionally, from further evaluation of the solid-state emissive properties, it was shown that both boron complexes had crystallization-induced emission enhancement (CIEE) properties. Finally, it was demonstrated that reversible regulation of the emission intensity by external stimuli such as heating and solvent vapor fuming was accomplished with BPI based on the CIEE properties.

Construction and properties of a light-harvesting antenna system for phosphorescent materials based on oligofluorene-tethered Pt–porphyrins

Co-reporter:Hyeonuk Yeo;Yoshiki Chujo

RSC Advances (2011-Present) 2017 vol. 7(Issue 18) pp:10869-10874

Publication Date(Web):2017/02/07

DOI:10.1039/C6RA28735B

Tetramerous molecular assemblies composed of four oligofluorenes as a light-harvesting antenna (LHA) and a Pt–porphyrin core as a phosphorescent chromophore were designed and synthesized for obtaining efficient phosphorescent materials. The resulting molecules showed good solubility in common organic solvents and high film-formability. From the series of optical measurements, it was shown that bright phosphorescence was observed from the LHA molecules. Efficient energy transfer through the cardo structure was confirmed from the oligofluorene units to the Pt–porphyrin core. Additionally, it was shown that aggregation-caused quenching (ACQ) and oxygen-deactivation of phosphorescence can be inhibited in the film state because of steric hinderance of bulky rings on the cardo structure. Finally, film materials with oxygen-resistant solid-state phosphorescence were obtained. Our material design is feasible not only for constructing highly-emissive solid-state phosphorescent materials but also for enhancing environment resistance to emissive materials by a unique structural unit.

Development of emissive aminopentaazaphenalene derivatives employing a design strategy for obtaining luminescent conjugated molecules by modulating the symmetry of molecular orbitals with substituent effects

Co-reporter:Hiroyuki Watanabe;Masataka Hirose;Yoshiki Chujo

Chemical Communications 2017 vol. 53(Issue 36) pp:5036-5039

Publication Date(Web):2017/05/02

DOI:10.1039/C7CC01287J

This communication describes the transformation of a non-emissive heterocycle into a luminophore via modulation of molecular orbitals by employing a dialkylamine-substituted pentaazaphenalene (A5AP) skeleton. It was presumed that the introduction of the amine group changed the symmetry-forbidden HOMO–LUMO (H–L) transition to an allowed one. According to optical measurements and theoretical calculations, the H–L transition was turned into the symmetry-allowed one because of the lone pair on the nitrogen atom in the dialkylamine substituent. Finally, the A5AP derivatives presented significant emission from the H–L transition.

Development of the optical sensor for discriminating isomers of fatty acids based on emissive network polymers composed of polyhedral oligomeric silsesquioxane

Co-reporter:Hayato Narikiyo, Takahiro Kakuta, Hiroki Matsuyama, Masayuki Gon, Kazuo Tanaka, Yoshiki Chujo

Bioorganic & Medicinal Chemistry 2017 Volume 25, Issue 13(Issue 13) pp:

Publication Date(Web):1 July 2017

DOI:10.1016/j.bmc.2017.04.029

It was shown that water-soluble network polymers composed of polyhedral oligomeric silsesquioxane (POSS) had hydrophobic spaces inside the network because of strong hydrophobicity of the cubic silica cage. In this study, the water-soluble POSS network polymers connected with triphenylamine derivatives (TPA-POSS) were synthesized, and their functions as a sensor for discriminating the geometric isomers of fatty acids were investigated. Accordingly, in the photoluminescence spectra, different time-courses of intensity and peak wavelengths of the emission bands were detected from the TPA-POSS-containing solution in the presence of cis- or trans-fatty acids during incubation. Furthermore, variable time-dependent changes were obtained by changing coexisting ratios between two geometric isomers. From the mechanistic investigation, it was implied that these changes could be originated from the difference in the degree of interaction between the POSS networks and each fatty acid. Our data could be applicable for constructing a sensing material for generation and proportion of trans-fatty acids in the oil.Download high-res image (62KB)Download full-size image

POSS-based molecular fillers for simultaneously enhancing thermal and viscoelasticity of poly(methyl methacrylate) films

Co-reporter:Kazuo Tanaka, Hiroto Kozuka, Kazunari Ueda, Jong-Hwan Jeon, Yoshiki Chujo

Materials Letters 2017 Volume 203(Volume 203) pp:

Publication Date(Web):15 September 2017

DOI:10.1016/j.matlet.2017.05.127

•Proof of concept for improving viscoelastic parameters by fillers is demonstrated.•Mechanical and thermal properties of PMMA were reinforced by the designed fillers.•Syntheses of the novel POSSs were accomplished.It was previously shown that polyhedral oligomeric silsesquioxane (POSS)-based molecular fillers can enhance the mechanical properties of polymer matrices as a viscoelastic material. However, POSS fillers hardly affected the initial pyrolysis step. Therefore, it was still challenging to reinforce thermal durability of polymers. This manuscript demonstrates development of molecular fillers for simultaneously enhancing decomposition temperature and both storage (E′) and loss (E″) moduli. The series of molecular fillers based on POSS having various functional groups to make an interaction with poly(methyl methacrylate) (PMMA) matrices were designed and synthesized. Initially, the single and multiple reactive units as methacrylate ester to form covalent bonds with PMMA were introduced into octaisobutyl POSS (iBu-POSS). It was proposed that cross-linking reactions with polymer chains proceeded after annealing at 65 °C. Then, significant enhancements of both E′ and E″ were observed. To obtain further enhancements especially for thermal stability, the POSS fillers of second generation having amine and 1,2-diol groups, which were expected to make strong interaction with the side chains in PMMA, were designed and loaded into polymer matrices. From the series of measurements with the homogeneous film samples containing POSS fillers, it was presented that all modified POSS derivatives can greatly improve thermal stability and mechanical properties as we expected.Download high-res image (85KB)Download full-size image

Synthesis of furan-substituted aza-BODIPYs having near-infrared emission

Co-reporter:Honami Yamane, Shunsuke Ohtani, Kazuo Tanaka, Yoshiki Chujo

Tetrahedron Letters 2017 Volume 58, Issue 30(Issue 30) pp:

Publication Date(Web):26 July 2017

DOI:10.1016/j.tetlet.2017.06.054

•Novel BODIPY derivatives having furan rings were synthesized.•The synthesized BODIPYs showed bright emission in the NIR region.•We clarified that introduction of furan rings should enhance molecular planarity.Development of near-infrared-emissive aza-boron dipyrromethene (aza-BODIPY) derivatives having furanyl groups is reported. From the optical measurements, it was clearly indicated that the emission bands were presented in the longer wavelength region than those of the conventional aza-BODIPYs. The emission bands with the peaks at 730 nm and 758 nm were observed from the bis- and tetra-substituted furanyl aza-BODIPYs with similar extents of emission efficiencies, respectively. According to the computer calculations, it was proposed that molecular planarity could be enhanced in the case of the furan groups. As a result, band-gap energy could be lowered comparing to those of the conventional benzene and thiophene-substituted aza-BODIPYs.Download high-res image (95KB)Download full-size image

Design and Luminescence Chromism of Fused Boron Complexes Having Constant Emission Efficiencies in Solution and in the Amorphous and Crystalline States

Co-reporter:Kazumasa Suenaga;Yoshiki Chujo

European Journal of Organic Chemistry 2017 Volume 2017(Issue 35) pp:5191-5196

Publication Date(Web):2017/09/25

DOI:10.1002/ejoc.201700704

Mechanochromic luminescent molecules often suffer from critical loss of luminescence intensity during phase transitions in the solid state. In this study, we present mechanochromic luminescent molecules that can provide clear color changes with constant emission intensity during phase transitions. It was reported that the class of aggregation-induced emission (AIE)-active boron complexes can present intense emission by freezing intramolecular motions. According to this mechanism, we designed a complex with a fused ligand to preserve the enhanced emission in the aggregated state in the AIE during phase transitions between the solution, amorphous, and crystalline states. From optical measurements, it was shown that the synthesized boron complexes present bright emission in various phases. In particular, as we expected, the luminescence color was clearly altered during phase transition, whereas the emission intensity changed only slightly. Finally, we also found that diverse luminescence colors were obtained from each polymorph and for various substituents as induced by the substituent effect. The results in the series of mechanistic studies show that electronic interactions and π–π interactions can modulate the electronic conjugation system of the complexes without causing loss of emission efficiency.

Front Cover: Design and Luminescence Chromism of Fused Boron Complexes Having Constant Emission Efficiencies in Solution and in the Amorphous and Crystalline States (Eur. J. Org. Chem. 35/2017)

Co-reporter:Kazumasa Suenaga;Yoshiki Chujo

European Journal of Organic Chemistry 2017 Volume 2017(Issue 35) pp:5178-5178

Publication Date(Web):2017/09/25

DOI:10.1002/ejoc.201701191

The Front Cover shows novel boron complexes that can provide clear color changes with constant emission intensity during phase transitions. The ligand structures for boron complexes were designed according to previous aggregation-induced emission-active boron complexes. Finally, it was shown that the complexes provided emission color changes during phase transitions between solution, crystal, aggregation, and ground powders without significant changes in the luminescent properties. More information can be found in the Full Paper by K. Suenaga, K. Tanaka, and Y. Chujo.

Modulation of sensitivity to mechanical stimulus in mechanofluorochromic properties by altering substituent positions in solid-state emissive diiodo boron diiminates

Co-reporter:Madoka Yamaguchi, Shunichiro Ito, Amane Hirose, Kazuo Tanaka and Yoshiki Chujo

Journal of Materials Chemistry A 2016 vol. 4(Issue 23) pp:5314-5319

Publication Date(Web):12 May 2016

DOI:10.1039/C6TC01111J

This manuscript describes modulation of the sensitivity to mechanical forces in diiodo boron diiminates by altering the substituent position of iodine groups. A series of modified complexes were prepared, and their solid-state luminescence properties based on aggregation and crystallization-induced emission mechanisms were observed. By adding mechanical forces to the crystalline samples of each complex, changes in the optical properties were monitored. Interestingly, peak shift degree of the emission bands was varied. From X-ray crystallographic analyses, it was shown that molecular distributions in the crystal packing significantly depended on the positions of the iodine groups in the complex. In particular, it was found that by increasing the dihedral angles between the phenyl substituents and the boron-containing six-membered ring, a larger peak shift width was obtained. Finally, the most planar conformation of the complexes was detected from the complex insensitive to mechanical forces. It was suggested that intramolecular electronic conjugation in the initial crystalline state could be responsible for the degree of peak shift. This is the first example, to the best of our knowledge, to offer regulation of sensitivity to mechanical forces in a series of structural isomers with the same chemical component.

Size-discrimination of volatile organic compounds utilizing gallium diiminate by luminescent chromism of crystallization-induced emission via encapsulation-triggered crystal–crystal transition

Co-reporter:Shunichiro Ito, Amane Hirose, Madoka Yamaguchi, Kazuo Tanaka and Yoshiki Chujo

Journal of Materials Chemistry A 2016 vol. 4(Issue 24) pp:5564-5571

Publication Date(Web):24 May 2016

DOI:10.1039/C6TC01819J

This manuscript describes the role of multi-functional gallium diiminate in photochemistry, crystal structural transition and molecular recognition. Discrimination of volatile organic compounds (VOCs) is a key technology to develop chemical sensors and probes such as for the detection of hazardous chemicals as well as for the assessment of air pollution. So far, there are several optical materials which can selectively capture some kinds of VOCs and present the alteration of optical properties. However, it is still rare to distinguish for only the size of VOCs by luminescent chromism regardless of chemical components of VOCs or functional groups in VOCs. This manuscript demonstrates that the size-dependent inclusion of the fumed VOCs into the solid-state emissive crystals of gallium diiminate can occur with the luminescent chromism of its crystallization-induced emission (CIE). In particular, it was shown that the degree of luminescent chromism was critically dependent not on the chemical components of the captured VOCs but on their radius of gyration (rg). Finally, it was also demonstrated that from the changes in the thermal and physical properties monitored through powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and diffuse reflectance profiles, the precise discrimination of the molecular sizes of VOCs by 0.1 Å was accomplished. From the structural analyses before and after fuming VOCs to the crystalline samples of gallium diiminate, it was revealed that the crystal–crystal structural transition was induced.

Development of Solid-State Emissive Materials Based on Multifunctional o-Carborane–Pyrene Dyads

Co-reporter:Kenta Nishino, Hideki Yamamoto, Kazuo Tanaka, and Yoshiki Chujo

Organic Letters 2016 Volume 18(Issue 16) pp:4064-4067

Publication Date(Web):July 29, 2016

DOI:10.1021/acs.orglett.6b01920

The molecular design based on o-carborane dyads is described for preparing multifunctional luminescent molecules such as dual emissions, aggregation and crystallization-induced emission enhancements, and luminescent color changes. The pyrene-substituted o-carborane dyads were synthesized via the insertion reaction between decaborane and 1-ethynylpyrene in the presence of Lewis base in a good yield. Finally, extremely bright luminescent compounds with solid-state emission properties (ΦPL > 0.99) were obtained.

Color tuning of alternating conjugated polymers composed of pentaazaphenalene by modulating their unique electronic structures involving isolated-LUMOs

Co-reporter:Hiroyuki Watanabe, Masataka Hirose, Kazuyoshi Tanaka, Kazuo Tanaka and Yoshiki Chujo

Polymer Chemistry 2016 vol. 7(Issue 22) pp:3674-3680

Publication Date(Web):13 May 2016

DOI:10.1039/C6PY00685J

Synthesis of a series of alternating copolymers composed of pentaazaphenalene (5AP) with several kinds of comonomer units was performed via Suzuki–Miyaura coupling reactions. Systematic absorption shift was introduced in a successful manner by changing the electron-donating and electron-accepting abilities of the comonomer units, leading to remarkable color change of the polymer solution. In order to elucidate the electronic structures of these polymers, electrochemical measurement and theoretical analysis were performed. In particular, it was suggested that the highest occupied molecular orbital (HOMO) conjugated throughout the polymer chain and the lowest unoccupied MO (LUMO), or its equivalent, localized at the 5AP fragment, play an important role in absorption in the visible region. To the best of our knowledge, this is the first report on the unique electronic structures of polymer main-chains having simultaneously various conjugation motifs.

Preservation of main-chain conjugation through BODIPY-containing alternating polymers from electronic interactions with side-chain substituents by cardo boron structures

Co-reporter:Honami Yamane, Shunichiro Ito, Kazuo Tanaka and Yoshiki Chujo

Polymer Chemistry 2016 vol. 7(Issue 16) pp:2799-2807

Publication Date(Web):01 Apr 2016

DOI:10.1039/C6PY00377J

This manuscript describes the synthesis and electronic structures of the modified boron dipyrromethene derivatives containing cardo boron. By using organometallic reagents, the replacement of fluorine groups to aryl substituents with electron-donating groups and/or electron-withdrawing groups was accomplished, resulting in the formation of cardo boron. From the theoretical calculations and optical measurements, electronic structures in the main-chain conjugation were evaluated. In summary, it was clearly shown that cardo boron can efficiently isolate the main-chain conjugation from the electronic interaction with the side chains since the optical properties were highly preserved from the introduction of the side-chain substituents. Our findings should be fundamentally significant for the application of cardo boron-containing conjugated polymers as a scaffold to construct a multi-functional unit by the assembly of functional units.

Controllable intramolecular interaction of 3D arranged π-conjugated luminophores based on a POSS scaffold, leading to highly thermally-stable and emissive materials

Co-reporter:Masayuki Gon, Keita Sato, Kazuo Tanaka and Yoshiki Chujo

RSC Advances 2016 vol. 6(Issue 82) pp:78652-78660

Publication Date(Web):18 Aug 2016

DOI:10.1039/C6RA14971E

This manuscript describes the inorganic cubic core as an advantageous scaffold for realizing solid-state emissive materials with high thermal stability. Polyhedral oligomeric silsesquinoxane (POSS) materials having π-conjugated luminophores connected to eight vertices of the POSS core were prepared. In a dilute solution, the π-conjugated luminophores around the POSS scaffold interacted with the neighboring π-conjugated luminophores, resulting in excimer formation. By introducing bulky alkyl chains into the luminophores, the intrinsic luminescent property of the monomer was recovered. In the solid state, interestingly, the π-conjugated luminophores linked to the POSS scaffold exhibited similar optical properties regardless of the existence of the bulky substituents. Emission bands with almost the same shapes in the spectra were obtained from the POSS materials. In addition, high thermal stabilities of the π-conjugated luminophores were detected. Finally, it was demonstrated that the POSS materials presented bright blue emission even beyond 200 °C in the open air. High thermal stabilities and solid-state emissive properties were realized owing to the cubic structure of the POSS core. A new versatile molecular scaffold for thermally-durable optical materials is offered.

Sponge-Type Emissive Chemosensors for the Protein Detection Based on Boron Ketoiminate-Modifying Hydrogels with Aggregation-Induced Blueshift Emission Property

Co-reporter:Kazumasa Suenaga;Ryousuke Yoshii;Yoshiki Chujo

Macromolecular Chemistry and Physics 2016 Volume 217( Issue 3) pp:414-421

Publication Date(Web):

DOI:10.1002/macp.201500276

Tunable Optical Property between Pure Red Luminescence and Dual Emission Depended on the Length of Light-Harvesting Antennae in the Dyads Containing the Cardo Structure of BODIPY and Oligofluorene

Co-reporter:Hyeonuk Yeo, Kazuo Tanaka, and Yoshiki Chujo

Macromolecules 2016 Volume 49(Issue 23) pp:8899-8904

Publication Date(Web):November 17, 2016

DOI:10.1021/acs.macromol.6b02169

The design and synthesis of light-harvesting antenna (LHA) and alternative properties between pure red luminescence and dual emission are demonstrated. The dyads composed of size-defined oligofluorenes including trimer (O3), pentamer (O5), and heptamer (O7) as a light absorber and red-emissive boron dipyrromethene (BODIPY) derivative linked via the cardo carbon were prepared. As we expected, amplified emission via the LHA process in the red region was obtained (Φ > 0.78). By increasing the number of fluorene repeats from 3-mer to 7-mer, the light absorption ability increased, leading to large LHA efficiency. Especially, owing to the steric distribution of the conjugation components on the basis of the cardo carbon, electronic interaction was suppressed in the dyad. Then, intrinsic emission properties such as sharp and intense spectra can be preserved. Interestingly, it was observed that O7 showed dual emission from both oligofluorene and BODIPY units. From the mechanistic analyses, it was revealed that energy transfer was suppressed only in O7 (O3, O5: >0.95, O7: <0.70). It was implied that the effective exciton diffusion length on the oligofluorene might be from 5 to 7 fluorene units. In O7, the exciton could be localized in the part of the oligofluorene unit. Therefore, some percentage of the exciton could show emission in the oligofluorene unit before energy transfer.

Recent progress of optical functional nanomaterials based on organoboron complexes with β-diketonate, ketoiminate and diiminate

Co-reporter:Kazuo Tanaka and Yoshiki Chujo

NPG Asia Materials 2015 7(11) pp:e223

Publication Date(Web):2015-11-01

DOI:10.1038/am.2015.118

The synthesis and application of organoboron complexes are a highly relevant topic owng to their unique characteristics. Based on their emissive properties, these complexes have been used to make novel optical materials and devices; boron β-diketonate is a simple and robust organoboron complex. From a series of recent studies, unique and versatile optical properties have been reported. In this review, we introduce the results of primarily recent studies on boron diketonate and related compounds containing polymers and particularly explain their optical properties. Initially, the multi-emission of boron diketonate derivatives and its application to biotechnology are explained. Next, the formation of nanostructures and its emission properties are demonstrated. The modulation of optical properties by mechanical stress is also presented. Finally, recent progress in the development of solid-emissive materials are shown with boron diketonates and their derivatives, which have aggregation-induced emission properties. The versatility of boron diketonates as a building block for the preparation of functional optical materials is the focus of this review.

POSS ionic liquid crystals

Co-reporter:Kazuo Tanaka, Fumiyasu Ishiguro, Jong-Hwan Jeon, Tatsuhiro Hiraoka and Yoshiki Chujo

NPG Asia Materials 2015 7(4) pp:e174

Publication Date(Web):2015-04-01

DOI:10.1038/am.2015.28

Here we report the use of unique organic−inorganic hybrid materials composed of octa-substituted polyhedral oligomeric silsesquioxane (POSS) cores as ionic liquid (IL) crystals. These materials have a wide temperature range in which they exist in liquid crystal (LC) phase because of the stabilizing effect of the POSS core. We synthesized ion pairs composed of alkyl chain-substituted imidazolium and carboxylates of various lengths that were or were not connected to the POSS core; then the thermal properties of these materials were investigated. It was found that both ion salts and the octadecyl-substituted imidazolium ion pairs with or without connection to POSS could form LCs. Interestingly, the LC phase of the POSS-tethered ion salts was maintained until decomposition. In contrast, the octadecyl-substituted imidazolium ion salts that were not tethered to the POSS core showed a clearance point during heating. The highly symmetric structure of POSS contributes not only to the suppression of the molecular motion of the ion salts, but also results in the formation of regular structures, leading to thermally stable, thermotropic IL crystals.

Synthesis of emissive water-soluble network polymers based on polyhedral oligomeric silsesquioxane and their application as optical sensors for discriminating the particle size

Co-reporter:Takahiro Kakuta, Kazuo Tanaka and Yoshiki Chujo

Journal of Materials Chemistry A 2015 vol. 3(Issue 48) pp:12539-12545

Publication Date(Web):28 Oct 2015

DOI:10.1039/C5TC03139G

We report organic–inorganic hybrid gels composed of polyhedral oligomeric silsesquioxane (POSS)-based network polymers and their variable emission properties depending on the size of coexisting silica particles (SPs). The POSS networks were constructed from octaammonium POSS by connecting with bithiophene dicarboxylic acid. By modulating the feed ratio of the bithiophene linker, a series of POSS networks were obtained with various cross-linking ratios among the POSS units. The POSS networks showed good water-solubility and emissions originating from the bithiophene linkers in water. Initially, it was observed that the POSS networks with relatively low cross-linking ratio showed higher affinity to SPs. An increase of the affinity was observed from all POSS networks to small-sized SPs. Interestingly, it was found that the emission properties were varied simply by adding silica particles into the sample. In the presence of nanoparticles dispersed in the sample, the red-shifted emission of the POSS network was induced. On the other hand, the blue-shifted emission was observed from the samples containing microparticles. These peak shifts depending on the size of coexisting particles should originate from the polarity changes around the bithiophene cross-linkers induced by the adsorption of the POSS networks onto the particle surfaces. These emission characteristics could be applicable for developing a facile optical chemosensor for discriminating the size of nanomaterials.

Synthesis of Air- and Moisture-Stable Dibenzogallepins: Control of Planarity of Seven-Membered Rings in Solid States by Coordination to Gallium Atoms

Co-reporter:Takuya Matsumoto, Hirofumi Takamine, Kazuo Tanaka, and Yoshiki Chujo

Organic Letters 2015 Volume 17(Issue 6) pp:1593-1596

Publication Date(Web):March 4, 2015

DOI:10.1021/acs.orglett.5b00489

Air- and moisture-stable dibenzo[b,f]gallepins with planar seven-membered rings have been designed and synthesized. From X-ray single-crystal analyses, the effects of the coordination numbers were evaluated at the gallium atom on the planarity of the seven-membered rings with a series of the synthesized complexes. Accordingly, it was shown that the seven-membered ring of dibenzogallepin involving a three-coordinated gallium atom presented the highest planarity compared to other dibenzogallepins with four- or five-coordinated gallium atoms. In addition, from theoretical calculations, it was proposed that the electronic states of the gallium atom in the complexes contributed to the energy levels of LUMOs+1.

Synthesis of a Platinum Diketonate-Containing Polymer Showing Oxygen-Resistant Phosphorescence

Co-reporter:Kazuo Tanaka;Amane Hirose;Kenji Tamashima ;Yoshiki Chujo

Macromolecular Rapid Communications 2015 Volume 36( Issue 7) pp:684-688

Publication Date(Web):

DOI:10.1002/marc.201500104

Synthesis and characterization of heterofluorenes containing four-coordinated group 13 elements: theoretical and experimental analyses and comparison of structures, optical properties and electronic states

Co-reporter:Takuya Matsumoto, Kazuo Tanaka, Kazuyoshi Tanaka and Yoshiki Chujo

Dalton Transactions 2015 vol. 44(Issue 18) pp:8697-8707

Publication Date(Web):09 Apr 2015

DOI:10.1039/C5DT00718F

Herein, we report the syntheses of dibenzoheteroles, namely, heterofluorenes, containing four-coordinated group 13 elements (boron Bf; aluminum Alf; gallium Gaf; indium Inf) and the relationship between their structures and optical properties. The electronic states of the compounds were considered theoretically by the density functional theory (DFT) calculation. In particular, we focused on their emission behaviors and electronic structures in the excited states. Initially, we confirmed that Bf and Gaf showed high stability in water and air, while Alf and Inf were sensitive. The structures of heterofluorenes, involving the heavier elements in the 13th group, tend to form trigonal planar structures even in the presence of coordination by nitrogen. Next, in their emissions, larger contribution from the triplet excited states was observed in the heterofluorenes with heavier elements. The major emission of Inf at 77 K was attributed to phosphorescence. These phosphorescence properties can be explained by the heavy atom effect. In Gaf and Inf, their excited states were deactivated by vibrational relaxation in their triplet excited states at room temperature. In Bf, Alf and Gaf when adding B(C6F5)3, the emissions oriented from the triplet exciplex were observed. Time-dependent DFT (TD-DFT) calculations revealed that the optimized structure of Bf in the excited S1 state has a considerably different geometry from those of Alf and Gaf. Finally, we obtained the data that the B–N bond could be cleaved in the excited S1 of Bf according to the B–N bond length and bond order. As a result, the lower intensity of the emission of Bf was comparable to that of Alf. This bond cleavage could be caused by an increase of the anti-bonding property in the B–N bond in the Franck–Condon (FC) S1 state and by weak electrostatic interaction between boron and nitrogen atoms. In Alf and Gaf, although the anti-bonding character of the M–N bonds (M = Al or Ga) in the FC S1 states also increases, the M–N bonds survive because of their stronger electrostatic interaction. The subsequent stronger emission in Alf and Gaf could be observed by suppressing the molecular motion in the excited states.

Integration of benzo[h]quinoline and π-extended dibenzo[b,f]silepins on pentacoordinate silicon

Co-reporter:Yuichiro Tokoro, Kazuo Tanaka and Yoshiki Chujo

RSC Advances 2015 vol. 5(Issue 30) pp:23331-23339

Publication Date(Web):02 Mar 2015

DOI:10.1039/C5RA00418G

We investigated the relationship between the chemical structure involving the pentacoordinate silicon and the electronic properties of the molecules. The substituent effects on the electronic structures of dibenzo[b,f]silepins containing pentacoordinate silicon were evaluated with two series of position isomers with electron–donor and/or electron–acceptor groups by NMR, UV-vis absorption and photoluminescence spectroscopies. It was found that the electronic structures of the complexes were strongly influenced by the type of substituent on the silicon center. In contrast, the substituents at the dibenzosilepin moiety showed only slight electronic perturbation. In 2,8-diaryl substituted compounds, the electron-donating group induced the emission peak to shift to longer wavelength regions than those observed with an electron-withdrawing group. In 3,7-diaryl substituted dibenzo[b,f]silepins, the introduction of both the fluorine group at the silicon center and the methoxy group on the dibenzosilepin moiety also led to bathochromic shifts in the absorption spectra. This is the first study, to the best of our knowledge, to offer systematic information on the substituent effects on the electronic structure of the pentacoordinate complex.

High HOMO levels and narrow energy band gaps of dithienogalloles

Co-reporter:Takuya Matsumoto, Kazuo Tanaka and Yoshiki Chujo

RSC Advances 2015 vol. 5(Issue 68) pp:55406-55410

Publication Date(Web):24 Jun 2015

DOI:10.1039/C5RA08584E

We synthesized dithieno[3,2-b:2′,3′-d]galloles containing four-coordinated gallium atoms. It was found that dithienogalloles had high stability to air and moisture and showed narrower energy-band gaps than dithienosiloles which are commodity materials in organic opto and/or electronic devices. In addition, relatively-higher HOMO levels were observed from dithienogalloles than those of other dithienoheteroles from electrochemical measurements. We experimentally and theoretically demonstrated the electron-donating properties and resonance effects of gallium atoms of dithienogalloles.

Synthesis and color tuning of boron diiminate conjugated polymers with aggregation-induced scintillation properties

Co-reporter:Kazuo Tanaka, Takayuki Yanagida, Amane Hirose, Honami Yamane, Ryousuke Yoshii and Yoshiki Chujo

RSC Advances 2015 vol. 5(Issue 117) pp:96653-96659

Publication Date(Web):10 Nov 2015

DOI:10.1039/C5RA20459C

We report film-type scintillators based on conjugated polymers with aggregation-induced emission (AIE) properties and the modulation of their scintillation abilities by chemical modification. Alternating copolymers containing a series of boron diiminates with various substituents and comonomers were synthesized via the palladium-catalyzed cross-coupling reaction. The synthesized polymers showed AIE properties. In addition, the corresponding emission colors to photoluminescence were also obtained with X-ray excitation. These data suggest that the AIE-active polymers should be a promising platform for developing a function-tunable plastic scintillator.

Energy transfer through heterogeneous dyes-substituted fluorene-containing alternating copolymers and their dual-emission properties in the films

Co-reporter:Hyeonuk Yeo;Yoshiki Chujo

Journal of Polymer Science Part A: Polymer Chemistry 2015 Volume 53( Issue 17) pp:2026-2035

Publication Date(Web):

DOI:10.1002/pola.27652

ABSTRACT

We report synthesis of the modified fluorene polymers tethered to the heterogeneous types of the fluorescent dyes at the cardo carbon for obtaining the dual-emissive solid materials. A series of the alternating fluorene copolymers modified with pyrene or 9,10-diphenylanthracene and BODIPY at the cardo carbon based on the red-emissive donor–acceptor structure were prepared, and their characteristics were examined. From the measurements of the optical properties, the energy transfer efficiencies were evaluated. In summary, variable energy transfer efficiencies were observed between the side chains and from the side chain to the main chain. It was indicated that the energy transfer efficiencies were strongly depended on the types of the energy donor and the detection conditions as such in the solution or film. Furthermore, it was found that the cardo fluorene units can contribute to the suppression of the energy transfer in the condensed state. Finally, the dual-emissive polymers were obtained in the film states. This is the first example, to the best of our knowledge, not only to offer systematic information on the energy transfer between the dye molecules and the polymer main-chains via the cardo structure but also to demonstrate the polymer-based optical materials with the dual-emission properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2026–2035

Synthesis and Characterization of Gallafluorene-Containing Conjugated Polymers: Control of Emission Colors and Electronic Effects of Gallafluorene Units on π-Conjugation System

Co-reporter:Takuya Matsumoto, Kazuo Tanaka, and Yoshiki Chujo

Macromolecules 2015 Volume 48(Issue 5) pp:1343-1351

Publication Date(Web):February 17, 2015

DOI:10.1021/ma502592c

We present synthesis and characteristics of the conjugated polymers involving organogallium complexes. A series of alternating copolymers composed of gallafluorene were prepared with diverse comonomers through various types of cross-coupling reactions such as Suzuki–Miyaura, Sonogashira–Hagihara, and Stille reactions. It was confirmed that the synthesized polymers possess solubility in common organic solvents and stability toward air and moisture. Significantly, optical properties originating from the electronic interaction between gallafluorene and various comonomers were observed. For example, vivid color emissions were demonstrated in the blue, green, yellow, orange, and red regions depending on the chemical structures of the comonomer units. In addition, it was eventually found that the benzotriazole-containing polymer showed significant optical properties originating from aggregation in the film state. From the electrochemical measurements, it was indicated that the energy levels of their frontier orbitals were varied by the comonomer units. Indeed, it is supported that the gallafluorene polymers have higher energy levels of HOMOs (highest occupied molecular orbitals) than those of the fluorene-based conjugated polymers instead of gallafluorene. Finally, it is suggested that the gallafluorene unit could work as an electron-donating group in the polymer main chain.

Liquid scintillators with near infrared emission based on organoboron conjugated polymers

Co-reporter:Kazuo Tanaka, Takayuki Yanagida, Honami Yamane, Amane Hirose, Ryousuke Yoshii, Yoshiki Chujo

Bioorganic & Medicinal Chemistry Letters 2015 25(22) pp: 5331-5334

Publication Date(Web):

DOI:10.1016/j.bmcl.2015.09.037

Mechanofluorochromic Materials Based on Aggregation-Induced Emission-Active Boron Ketoiminates: Regulation of the Direction of the Emission Color Changes

Co-reporter:Dr. Ryousuke Yoshii;Kazumasa Suenaga;Dr. Kazuo Tanaka; Yoshiki Chujo

Chemistry - A European Journal 2015 Volume 21( Issue 19) pp:7231-7237

Publication Date(Web):

DOI:10.1002/chem.201500033

Abstract

We report a series of mechanofluorochromic (MFC) compounds based on organoboron complexes with aggregation-induced emission (AIE) characteristics. We synthesized a variety of boron ketoiminates and investigated the effect of the substituents on the optical properties by altering the end groups in the compounds. The synthesized boron ketoiminates showed AIE properties and MFC behavior. Interestingly, the hypsochromic and bathochromic shifts of the emission bands individually observed for boron ketoiminates depended on the chemical structures of the end groups. From the X-ray diffraction and differential scanning calorimetry analyses, it was confirmed that the MFC property of boron ketoiminates should be derived from a phase transition between crystalline and amorphous states. In addition, the direction of the peak shifts of the emission bands was controlled by the degree of steric hindrance of the end group.

Arsonic acid-presenting superparamagnetic iron oxide for pH-responsive aggregation under slightly acidic conditions

Co-reporter:Hiroki Minehara, Kensuke Naka, Kazuo Tanaka, Asako Narita, Yoshiki Chujo

Bioorganic & Medicinal Chemistry 2011 Volume 19(Issue 7) pp:2282-2286

Publication Date(Web):1 April 2011

DOI:10.1016/j.bmc.2011.02.027

We report the synthesis and characterization of the arsonic acid-presenting superparamagnetic iron oxide (SPIO). We used arsonoacetic acid as the ligand for SPIOs in aqueous media. The surface modification of the SPIOs was accomplished via the ligand exchange from undecanoic acid to the carboxyl moiety of arsonoacetic acid. Consequently, the well-dispersed arsonic acid-presenting SPIOs in water were obtained. We found that the dispersion state of the arsonic acid-presenting SPIOs can be sharply regulated by pH changes in the biological significant region. The well dispersion state of the arsonic acid-presenting SPIOs can be maintained at the neutral pH region. In contrast, the arsonic acid-presenting SPIOs can sensitively form the aggregation below pH 6.1. Moreover, these dispersion states can be controlled reversibly by the pH alteration in the narrow region.

Development of highly-sensitive detection system in 19F NMR for bioactive compounds based on the assembly of paramagnetic complexes with fluorinated cubic silsesquioxanes

Co-reporter:Takahiro Kakuta, Hayato Narikiyo, Jong-Hwan Jeon, Kazuo Tanaka, Yoshiki Chujo

Bioorganic & Medicinal Chemistry (15 February 2017) Volume 25(Issue 4) pp:

Publication Date(Web):15 February 2017

DOI:10.1016/j.bmc.2016.12.044

This manuscript reports the detection system with 19F NMR probes for bioactive amine compounds at sub-micro molar concentrations. Water-soluble fluorinated polyhedral oligomeric silsesquioxane (POSS) derivatives were prepared, and the paramagnetic Ni-porphyrin (NiPor) with the fluorinated POSS (F-POSS) was adsorbed in the buffer. By adding the series of amine derivatives to the homogeneous dispersion containing the POSS-NiPor complexes, the changes in the signal intensity were evaluated. It was clearly observed from homogeneous dispersions that the signal intensity of 19F NMR decreased especially in the presence of ethanediamine and hexylamine. From the dynamic light scattering measurements, it was revealed that the assembly of the F-POSS complexes was dramatically induced by the amine compounds when the signal intensity decreased. According to these data, it is proposed that the signal reduction of 19F NMR from the POSS-NiPor complexes could be induced via the strong paramagnetic relaxation enhancement from NiPor in the assembly. Finally, based on the signal reduction by the assembly, we can detect the amine derivatives under 1 μM concentration which is similar sensitivity to the conventional fluorescence probes. Our system is valid to monitor the distribution of the bio-active molecules at cellular concentrations.

Modulation of sensitivity to mechanical stimulus in mechanofluorochromic properties by altering substituent positions in solid-state emissive diiodo boron diiminates

Co-reporter:Madoka Yamaguchi, Shunichiro Ito, Amane Hirose, Kazuo Tanaka and Yoshiki Chujo

Journal of Materials Chemistry A 2016 - vol. 4(Issue 23) pp:NaN5319-5319

Publication Date(Web):2016/05/12

DOI:10.1039/C6TC01111J

Co-reporter:Hiroyuki Watanabe, Masataka Hirose, Kazuo Tanaka and Yoshiki Chujo

Chemical Communications 2017 - vol. 53(Issue 36) pp:NaN5039-5039

Publication Date(Web):2017/04/21

DOI:10.1039/C7CC01287J

Control of aggregation-induced emission versus fluorescence aggregation-caused quenching by bond existence at a single site in boron pyridinoiminate complexes

Co-reporter:Madoka Yamaguchi, Shunichiro Ito, Amane Hirose, Kazuo Tanaka and Yoshiki Chujo

Inorganic Chemistry Frontiers 2017 - vol. 1(Issue 8) pp:NaN1579-1579