Gen-ichi Konishi - Cochemist

The K-Region in Pyrenes as a Key Position to Activate Aggregation-Induced Emission: Effects of Introducing Highly Twisted N,N-Dimethylamines

Co-reporter:Shunsuke Sasaki, Satoshi Suzuki, Kazunobu Igawa, Keiji Morokuma, and Gen-ichi Konishi

The Journal of Organic Chemistry July 7, 2017 Volume 82(Issue 13) pp:6865-6865

Publication Date(Web):June 28, 2017

DOI:10.1021/acs.joc.7b00996

A new design strategy to activate aggregation-induced emission (AIE) in pyrene chromophores is reported. In a previous report, we demonstrated that highly twisted N,N-dialkylamines of anthracene and naphthalene induce drastic AIE when these donors are introduced at appropriate positions to stabilize the S1/S0 minimum energy conical intersection (MECI). In the present study, this design strategy was applied to pyrene: the introduction of N,N-dimethylamine substituents at the 4,5-positions of pyrene, the so-called K-region, are likely to stabilize MECIs. To examine this hypothesis, four novel pyrene derivatives, which contain highly twisted N,N-dimethylamino groups at the 4- (4-Py), 4,5- (4,5-Py), 1- (1-Py), or 1,6-positions (1,6-Py) were tested. The nonradiative transitions of 4,5-Py are highly efficient (knr = 57.1 × 107 s–1), so that its fluorescence quantum yield in acetonitrile decreases to Φfl = 0.04. The solid-state fluorescence of 4,5-Py is efficient (Φfl = 0.49). In contrast, 1,6-Py features strong fluorescence (Φfl = 0.48) with a slow nonradiative transition (knr = 11.0 × 107 s–1) that is subject to severe quenching (Φfl = 0.03) in the solid state. These results underline that the chemistry of the pyrene K-region is intriguing, both from a photophysical perspective and with respect to materials science.

Thermo-responsive fluorescence of AIE-active poly(N-isopropylacrylamides) labeled with highly twisted bis(N,N-dialkylamino)arenes

Co-reporter:Shunsuke Sasaki

RSC Advances (2011-Present) 2017 vol. 7(Issue 28) pp:17403-17416

Publication Date(Web):2017/03/17

DOI:10.1039/C7RA01212H

Highly twisted bis(N,N-dialkylamino)arenes, which represent a new class of viscosity-sensitive fluorophores with aggregation-induced emission (AIE) luminogens, were introduced as co-monomers and cross-linkers into poly(N-isopropylacrylamides) (PNIPAMs). Despite the excellent performance of these bis(N,N-dialkylamino)arenes as fluorophores that are sensitive to the steric environment, synthetic methods to endow them with other reactive groups have not yet been reported. This study presents short synthetic pathways to 9,10-bis(N,N-dialkylamino)anthracenes (BDAAs) and 1,4-bis(N,N-dialkylamino)-2,3-dimethylnaphthalenes (DMe-BDANs) with hydroxyl groups at their alkyl chains. These hydroxyl groups were acylated to afford methacrylate moieties, which were subsequently used for the co-polymerization with N-isopropylacrylamide. At T = 20 °C, the resulting BDAA-containing PNIPAMs exhibited faint fluorescence (Φfl ≈ 0.05) in THF, whereas DMe-BDAN-containing PNIPAMs showed substantially stronger fluorescence in THF (Φfl ≈ 0.32) and water (Φfl ≈ 0.55) relative to the corresponding monomers. Moreover, BDAA-containing PNIPAMs featured a sharp increase of fluorescence intensity and quantum yield at T = 27–35 °C, while DMe-BDAN-containing PNIPAMs exhibited a continuous decrease of fluorescence intensity and Φfl with increasing temperature.

Highly Twisted N,N-Dialkylamines as a Design Strategy to Tune Simple Aromatic Hydrocarbons as Steric Environment-Sensitive Fluorophores

Co-reporter:Shunsuke Sasaki; Satoshi Suzuki; W. M. C. Sameera; Kazunobu Igawa; Keiji Morokuma

Journal of the American Chemical Society 2016 Volume 138(Issue 26) pp:8194-8206

Publication Date(Web):June 14, 2016

DOI:10.1021/jacs.6b03749

The steric-environment sensitivity of fluorescence of 9,10-bis(N,N-dialkylamino)anthracenes (BDAAs) was studied experimentally and theoretically. A new design strategy to tune simple aromatic hydrocarbons as efficient aggregation-induced emission (AIE) luminogens and molecular rotors is proposed. For a variety of BDAAs, prominent Stokes shifts and efficient solid-state fluorescence were observed. Calculations on BDAA-methyl suggested that in the ground state (S0) conformations, the pyramidal amine groups are highly twisted, so that their lone-pair orbitals cannot conjugate with the anthracene π orbitals. Fluorescence takes place from the S1 minima, in which one or both amine groups are planarized. The stability of the S1 excited state minima as well as destabilization of the S0 state is the origin of large Stokes shift. Experimental measurement of the nonadiabatic transition rate suggests that para disubstitution by dialkylamino (or strongly electron-donating) groups is a key for fast internal conversion. Minimum energy conical intersection (MECI) between S1 and S0 states was found to have a Dewar-benzene like structure. Although this can be reached efficiently in liquid phase for fast internal conversion, a large amplitude motion is required to reach this MECI, which is prohibited in the solid state and caused efficient AIE. This strategy is used to find experimentally that naphthalene analogues are also efficient AIE luminogens. The flexibility of alkyl chains on amino groups is also found to be important for allowed charge-transfer transition. Thus, three points [(1) highly twisted N,N-dialkylamines, (2) substitution at the para positions, (3) with flexible alkyl groups] were proposed for activation of small aromatic hydrocarbons.

Amphiphilic gels of solvatochromic fluorescent poly(2-oxazoline)s containing D–π–A pyrenes

Co-reporter:Chia-Hsiu Chen, Yosuke Niko and Gen-ichi Konishi

RSC Advances 2016 vol. 6(Issue 49) pp:42962-42970

Publication Date(Web):26 Apr 2016

DOI:10.1039/C6RA06251B

Herein, we report amphiphilic, fluorescent, solvatochromic poly(2-methyl-2-oxazoline) (POZO-py) and poly(2-ethyl-2-oxazoline) (PEtOZO-py), which contain D–π–A pyrene dye units in their side chains. These new fluorescent polymers display solvatochromism and bright fluorescence in a variety of solvents, ranging from toluene (475 nm) to methanol (515 nm) and water (535 nm). Furthermore, amphiphilic gels (amphigels) of POZO-py and PEtOZO-py were synthesized by cross-linking the amine sites of partially hydrolyzed POZO-py and PEtOZO-py. Amphigels were formed rapidly when bridging ethyleneimine moieties were used for POZO-py and PEtOZO-py. These amphigels swell in various solvents, resulting in a solvatochromic shifts of the fluorescence emission. We furthermore determined the relationship between the swelling process, the solvatochromic properties, and the polymer structure of the POZO-py and PEtOZO-py gels. The different swelling properties led to different amphigel structures in water and hence, to different maximum fluorescence wavelengths. For example, a POZO-py amphigel with 10% ethyleneimine bridging exhibited the same solvatochromic behavior as POZO-py in solution. These results are significant in order to evaluate the solvatochromic properties of pyrene chromophores in polymers and to investigate gel structures and functional group interactions in gels.

Development of novel bistolane-based liquid crystalline molecules with an alkylsulfanyl group for highly birefringent materials

Co-reporter:Yuki Arakawa, Sungmin Kang, Hideto Tsuji, Junji Watanabe and Gen-ichi Konishi

RSC Advances 2016 vol. 6(Issue 20) pp:16568-16574

Publication Date(Web):29 Jan 2016

DOI:10.1039/C5RA25122B

In order to generate high-birefringence liquid crystal (LC) materials, the introduction of highly polarisable groups into the terminal positions of the mesogen represents one of the most important design strategies. Even though the alkylsulfanyl group is a potentially interesting option for this purpose, it has so far been very difficult to obtain enantiotropic mesophases for LCs containing this group. Herein, we report novel high-birefringence LC molecules based on 1,4-bis(2-phenylethynyl)benzene (bistolane) with alkylsulfanyl groups in the terminal positions. The incorporation of a fluorine atom into the central benzene ring of an alkylsulfanyl-substituted bistolane led to the formation of a well-defined enantiotropic nematic phase. In contrast, the nonfluorinated analogue with alkylsulfanyl groups did not exhibit a mesophase. In comparison with an alkoxy-substituted derivative, the birefringence of the alkylsulfanyl-substituted analog was substantially higher (Δn = 0.42 at 550 nm). Furthermore, the birefringence properties of the alkylsulfanyl-substituted derivative were observed to be proportional to the order parameter and largely temperature-dependent over the entire temperature range. These results thus provide not only fundamental insights into structure–reactivity relations, but also furnish practical design principles for the synthesis of new sulfur-containing, rod-shaped LC materials with optical applications.

The effect of regioisomerism on the solid-state fluorescence of bis(piperidyl)anthracenes: structurally simple but bright AIE luminogens

Co-reporter:Shunsuke Sasaki, Kazunobu Igawa and Gen-ichi Konishi

Journal of Materials Chemistry A 2015 vol. 3(Issue 23) pp:5940-5950

Publication Date(Web):11 May 2015

DOI:10.1039/C5TC00946D

A series of regioisomers of piperidylanthracenes (PA) and bis(piperidyl)anthracenes (BPA) were synthesized and their photophysical properties examined in solution, suspension, and the solid state. Aggregation-induced emission (AIE) was observed only for 1,4-BPA and 9,10-BPA, in which two piperidyl groups are substituted at the anthracene moiety in the para-position with respect to each other. Compared to previously reported AIE luminogens, these easily obtainable para-substituted BPAs, exhibited several unique and beneficial features, such as simple structures, bright solid-state fluorescence (Φfl = 0.49 and 0.86 for 1,4-BPA and 9,10-BPA, respectively), tunable fluorescence emission, and large Stokes shifts. Results from diffuse-reflectance and fluorescence lifetime measurements demonstrated that PAs and BPAs intrinsically possess an efficient non-radiative transition pathway in the solid state, and that 1,4-BPA and 9,10-BPA may overcome this pathway. The X-ray crystallographic analysis of 1,4-BPA revealed that undesirable interchromophoric interactions can be minimised, while TD-DFT calculations suggested that the enhanced Stokes shift of 1,4-BPA arises from severe electronic repulsion between neighbouring piperidyl moieties, which presumably results in the absence of self-absorption.

A novel pyrene-based two-photon active fluorescent dye efficiently excited and emitting in the ‘tissue optical window (650–1100 nm)’

Co-reporter:Yosuke Niko, Hiroki Moritomo, Hiroyuki Sugihara, Yasutaka Suzuki, Jun Kawamata and Gen-ichi Konishi

Journal of Materials Chemistry A 2015 vol. 3(Issue 2) pp:184-190

Publication Date(Web):17 Oct 2014

DOI:10.1039/C4TB01404A

The development of two-photon (TP) active fluorophores remains an important issue. Dyes that can be excited and fluoresce efficiently in the ‘tissue optical window’ (650–1100 nm) are especially in demand to maximize the underlying performance of two-photon fluorescence microscopy (TPFM) as an advanced optical technique. Ideally, such dyes would be compatible with the 1050 nm femtosecond fibre laser, which has recently been developed as an inexpensive excitation source to make the TPFM technique universal. In this work, we designed and synthesized a novel pyrene-based acceptor–π–acceptor (A–π–A) dye, PY, which exhibited outstanding properties such as bright fluorescence (λem = 650 nm and ΦFL = 0.80) and a large two-photon absorption cross-section (1100 GM (1 GM = 10−50 cm4 per photon per molecule) at 950 nm and 380 GM at 1050 nm) in the tissue optical window. In living mitochondria, PY provided more sensitive microscopic images than current dyes and showed great potential to be a building block of TP active fluorescent probes for the 1050 nm fibre laser. We believe that the exceptional properties of PY will be extended to other fluorescent probes through further chemical modification.

Assembly of thioether-containing rod-like liquid crystalline materials assisted by hydrogen-bonding terminal carboxyl groups

Co-reporter:Yuki Arakawa, Sungmin Kang, Junji Watanabe and Gen-ichi Konishi

RSC Advances 2015 vol. 5(Issue 11) pp:8056-8062

Publication Date(Web):23 Dec 2014

DOI:10.1039/C4RA15300F

We designed a hydrogen-bonding tolane-based molecule with terminal carboxyl and alkylsulfanyl groups in an effort to realize thioether-containing rod-like liquid crystalline materials. The molecule successfully exhibits a stable enantiotropic mesophase, in contrast to non-hydrogen bonding derivatives, including tolane and diphenyldiacetylene. In addition, it shows two remarkable characteristics compared to analogues with alkyl or alkoxy groups. First, the mesophase of the alkylsulfanyl derivative shows strong long-range correlation. Second, the birefringence of the alkylsulfanyl derivative is highly temperature-dependent, achieving a maximum value of 0.36. These remarkable characteristics are believed to be due to the high polarisability of sulfur atoms and S–S contacts. These findings will be helpful for the design of novel sulfur-containing rod-like liquid crystalline materials.

1-, 3-, 6-, and 8-Tetrasubstituted Asymmetric Pyrene Derivatives with Electron Donors and Acceptors: High Photostability and Regioisomer-Specific Photophysical Properties

Co-reporter:Yosuke Niko, Shunsuke Sasaki, Kaishi Narushima, Dharmendar Kumar Sharma, Martin Vacha, and Gen-ichi Konishi

The Journal of Organic Chemistry 2015 Volume 80(Issue 21) pp:10794-10805

Publication Date(Web):October 15, 2015

DOI:10.1021/acs.joc.5b01987

The systematic synthesis of five 1-, 3-, 6-, and 8-tetrasubstituted asymmetric pyrenes with electron donor and acceptor moieties is presented, together with an examination of their photophysical properties. Pyrene derivative PA1, containing one formyl and three piperidyl groups, showed bright solvatochromic fluorescence from green (λem = 557 nm, ΦFL = 0.94 in hexane) to red (λem = 648 nm, ΦFL = 0.50 in methanol), suggesting potential applications for PA1 as an environmentally responsive probe. Although the synthesis of simple 1- and 3-disubstituted pyrene derivatives is considered difficult, PA13, with two formyl groups at the 1- and 3-positions and two piperidyl groups at the 6- and 8-positions, could be synthesized successfully. PA13 exhibited less pronounced solvatochromism, but displayed a narrow fluorescent band with high ΦFL in all solvents (ΦFL > 0.75). Moreover, its absorption band displayed an exceptional bathochromic shift compared to the other derivatives (e.g., λabs = 480 and 522 nm in ethanol for PA1 and PA13, respectively), suggesting that such modifications of pyrene may be quite important for the modulation of its energy gap. Additionally, all compounds exhibited exceptionally high photostability, which highlights the advantage of these new dyes and provides new insights on the design of photostable fluorophores.

Highly birefringent side-chain LC polymethacrylate with a dinaphthyl-acetylene mesogenic unit

Co-reporter:Sungmin Kang, Shunpei Nakajima, Yuki Arakawa, Masatoshi Tokita, Junji Watanabe and Gen-ichi Konishi

Polymer Chemistry 2014 vol. 5(Issue 7) pp:2253-2258

Publication Date(Web):14 Jan 2014

DOI:10.1039/C3PY01528A

We synthesised a highly birefringent liquid crystalline (LC) side-chain polymer based on polymethacrylate with a dinaphthyl-acetylene mesogenic unit in the side chain. Three polymer types with different carbon numbers in the terminal alkoxy chain (m = 1, 3 and 6) were prepared, and their optical properties as well as phase sequential behaviours were investigated. All polymers formed a nematic phase with a wide temperature range, and a smectic C phase was detected between the nematic and crystal phases when m was extended to 6. Notably, for homologous m = 1, we successfully obtained a nematic glassy-state LC film with high optical performance under ambient temperature conditions. The optical properties of this LC film were shown to be consistent with those of a highly birefringent, low molar mass LC material, with birefringence, extraordinary and ordinary refractive indices of 0.36, 1.82 and 1.46, respectively at 550 nm.

Pyrene-based D–π–A dyes that exhibit solvatochromism and high fluorescence brightness in apolar solvents and water

Co-reporter:Yosuke Niko, Yokan Cho, Susumu Kawauchi and Gen-ichi Konishi

RSC Advances 2014 vol. 4(Issue 69) pp:36480-36484

Publication Date(Web):07 Aug 2014

DOI:10.1039/C4RA06282E

A novel pyrene-based D–π–A dye consisting of piperidine (D) and a secondary N-alkyl carboxamide (A) was prepared. This dye showed solvatochromism and bright fluorescence in solvents with a wide range of polarities, including water. Such emission properties are derived from the role of the secondary N-alkyl carboxamide group as both a weak acceptor and a stabilizer of the n electrons on the carbonyl group.

Aggregation-induced emission active D-π-A binaphthyl luminophore with dual-mode fluorescence

Co-reporter:Shunsuke Sasaki, Yosuke Niko, Kazunobu Igawa and Gen-ichi Konishi

RSC Advances 2014 vol. 4(Issue 63) pp:33474-33477

Publication Date(Web):23 Jul 2014

DOI:10.1039/C4RA05871B

A novel aggregation-induced emission active dye consisting of a simple and highly solvatochromic D-π-A type 1,1′-binaphthyl chromophore was synthesised. The new dye exhibited dual-mode fluorescence in response to different types of restriction of intramolecular rotation; aggregation induces green emission, and blue emission is observed in a glassy matrix.

Design of donor–acceptor geometry for tuning excited-state polarization: fluorescence solvatochromism of push–pull biphenyls with various torsional restrictions on their aryl–aryl bonds

Co-reporter:Shunsuke Sasaki, Yosuke Niko, Andrey S. Klymchenko, Gen-ichi Konishi

Tetrahedron 2014 70(41) pp: 7551-7559

Publication Date(Web):

DOI:10.1016/j.tet.2014.08.002

Design of Weak-Donor Alkyl-Functionalized PushPull Pyrene Dyes Exhibiting Enhanced Fluorescence Quantum Yields and Unique On/Off Switching Properties

Co-reporter:Yosuke Niko;Shunsuke Sasaki;Dr. Susumu Kawauchi;Dr. Katsumi Tokumaru;Dr. Gen-ichi Konishi

Chemistry – An Asian Journal 2014 Volume 9( Issue 7) pp:1797-1807

Publication Date(Web):

DOI:10.1002/asia.201402088

Abstract

We designed, synthesized, and evaluated environmentally responsive solvatochromic fluorescent dyes by incorporating weak push–pull moieties. The quantum yields of the push (alkyl)–pull (formyl) pyrene dyes were dramatically enhanced by the introduction of alkyl groups into formylpyrene (1-formylpyrene: Φ_F=0.10; 3,6,8-tri-n-butyl-1-formylpyrene: Φ_F=0.90; in MeOH). The new dyes exhibited unique sensitivity to solvent polarity and hydrogen-bond donor ability, and specific fluorescence turn-on/off properties (e.g., 3,6,8-tri-n-butyl-1-formylpyrene: Φ_F=0.004, 0.80, 0.37, and 0.90 in hexane, chloroform, DMSO, and MeOH, respectively). Here, the alkyl groups act as weak donors to suppress intersystem crossing by destabilizing the HOMOs of 1-formylpyrene while maintaining weak intramolecular charge-transfer properties. By using alkyl groups as weak donors, environmentally responsive, and in particular, pH-responsive fluorescent materials may be developed in the future.

Large extraordinary refractive index in highly birefringent nematic liquid crystals of dinaphthyldiacetylene-based materials

Co-reporter:Sungmin Kang, Shunpei Nakajima, Yuki Arakawa, Gen-ichi Konishi and Junji Watanabe

Journal of Materials Chemistry A 2013 vol. 1(Issue 27) pp:4222-4226

Publication Date(Web):30 May 2013

DOI:10.1039/C3TC30640B

The extraordinary and ordinary refractive indices in highly birefringent dinaphthyldiacetylene-based nematic liquid crystals with different alkoxy tails were accurately measured by the multiple-beam interference method. The high birefringence in the nematic liquid crystals was attributed to the high value of the extraordinary refractive index, ne. The value of ne increased from 1.8 to 2.1 as the number of carbon atoms in the alkoxy tail decreased from 12 to 3, whereas the ordinary index, no, remained at approximately 1.6.

Diphenyltriacetylenes: novel nematic liquid crystal materials and analysis of their nematic phase-transition and birefringence behaviours

Co-reporter:Yuki Arakawa, Sungmin Kang, Shunpei Nakajima, Koichi Sakajiri, Yokan Cho, Susumu Kawauchi, Junji Watanabe and Gen-ichi Konishi

Journal of Materials Chemistry A 2013 vol. 1(Issue 48) pp:8094-8102

Publication Date(Web):16 Oct 2013

DOI:10.1039/C3TC31658K

Improvements in birefringence properties of LC materials are actively being pursued because of the increase in their applications in optical devices. 1,6-Diphenyl-1,3,5-hexatriyne, i.e., diphenyltriacetylenes (DPTAs; number of acetylene units, n = 3) are expected to have wide nematic mesophases and exhibit extremely high birefringence properties because of the high aspect ratio of their conjugated structures. Therefore, we synthesised DPTA derivatives as novel, highly birefringent nematic liquid crystal materials. The derivatives exhibit stable enantiotropic nematic phases with longer alkoxy carbon chain lengths (i.e., with dodecyloxy groups, m = 12). High birefringence values of Δn = 0.46 at 550 nm and 140 °C and a high extraordinary refractive index (ne) of over 2.0 were exhibited for triyne DPTA–OC6. Furthermore, we investigated the effect of the acetylene bond on the nematic transition behaviours and refractive index parameters of the conjugated oligoyne or polyyne compounds with two terminal aromatic rings. An increasing number of acetylene units (n = 1–3), i.e., extended conjugation, led to wider nematic phases and higher birefringence; the increment in Δn per acetylene unit was estimated to be approximately 0.14.

A three-dimensional assembly of pyrene dye on a tetraphenylethane scaffold enhances fluorescence quantum yield

Co-reporter:Kentaro Sumi, Yosuke Niko, Katsumi Tokumaru and Gen-ichi Konishi

Chemical Communications 2013 vol. 49(Issue 37) pp:3893-3895

Publication Date(Web):21 Mar 2013

DOI:10.1039/C3CC41312H

A three-dimensional pyrene assembly on a tetraphenylethane skeleton enhanced the fluorescence quantum yield compared to the yield obtained when using monomeric species, without changing the shape of the emission spectrum. The unique spacing of the pyrene units may prevent intramolecular fluorescence quenching or non-radiative decay.

Synthesis of high refractive index and low-birefringence acrylate polymers with a tetraphenylethane skeleton in the side chain

Co-reporter:Yusuke Tojo, Yuki Arakwa, Junji Watanabe and Gen-ichi Konishi

Polymer Chemistry 2013 vol. 4(Issue 13) pp:3807-3812

Publication Date(Web):26 Apr 2013

DOI:10.1039/C3PY00377A

We propose a new acrylate monomer that exhibits attractive optical properties, such as good transparency, high refractive index, low birefringence, desirable optical properties, and high thermal stability. Tetraphenylethane has four aromatic rings that bind without anisotropy. A polymer with this tetraarylethane structure is expected to exhibit a high refractive index and low birefringence. In this study, we synthesized two acrylate-based polymers via radical polymerization of the acrylate monomer and methacrylate derived from 1,1′,2,2′-tetrakis(4-hydroxyphenyl)ethane. We prepared transparent coatings of the polymers on a synthetic quartz plate via spin coating and measured their refractive indices using a prism coupler. Both of the polymers exhibited a high refractive index (1.60) as compared with common PMMA (1.49) and a low birefringence, which indicated that a tetraarylethane skeleton is the preferred candidate for suppressing the birefringence of a material.

Environment-responsive multicolor fluorescent dyes based on nitrophenyl or nitrophenylethynyl oligothiophene derivatives: correlation between fluorescence and π-conjugation length

Co-reporter:Sojiro Hachiya, Kengo Asai, Gen-ichi Konishi

Tetrahedron Letters 2013 Volume 54(Issue 26) pp:3317-3320

Publication Date(Web):26 June 2013

DOI:10.1016/j.tetlet.2013.03.054

We report the unique environment-responsive fluorescence of nitrophenyl or nitrophenylethynyl oligothiophene derivatives with different numbers of thiophene rings. With an increase in the number of thiophene rings, the maximum fluorescence quantum yield (ΦF) was obtained even in low-polarity solvents. For 5,5″-bis(4-nitrophenyl)-2,2′-bithiophene (BNP2T), a nitro-group-containing fluorescent dye without a strong donor moiety, the maximum ΦF of 0.43 was observed in CHCl3, which is a large value, and multicolor fluorescence with a moderate quantum yield was observed in various solvents. Thus, we can design functional nitrophenyl-based fluorescent dyes that would find applications as bioimaging probes, polarity sensors, etc.

Phenoxide-mediated Sonogashira coupling of trimethylsilylalkynes and aryliodides: practical synthesis of phenolic-hydroxy-substituted diarylethynes and 1,4-diarylbutadiynes

Co-reporter:Masayuki Shigeta, Junji Watanabe, Gen-ichi Konishi

Tetrahedron Letters 2013 Volume 54(Issue 13) pp:1761-1764

Publication Date(Web):27 March 2013

DOI:10.1016/j.tetlet.2013.01.091

We successfully synthesized phenolic-hydroxy-substituted diarylethynes and 1,4-diarylbutadiynes from trimethylsilylalkynes and aryliodides via silyl-group-migration-induced deprotection of alkynes and the usual Sonogashira coupling. The phenol moiety, which works as a desilylating agent, can be attached to any position in the coupling partner. This improvement for Sonogashira coupling would be highly effective, especially when the coupling partner has a phenol moiety. Additionally, the stability of the migrated silyl moiety on the ethynylation of 2-iodophenol is discussed.

Unique solvent-dependent fluorescence of nitro-group-containing naphthalene derivatives with weak donor–strong acceptor system

Co-reporter:Sojiro Hachiya, Kengo Asai, Gen-ichi Konishi

Tetrahedron Letters 2013 Volume 54(Issue 14) pp:1839-1841

Publication Date(Web):3 April 2013

DOI:10.1016/j.tetlet.2013.01.096

We synthesized nitro-group-containing π-conjugated naphthalene derivatives with a weak donor–strong acceptor system and investigated their photophysical properties. The nitro group was introduced into naphthalene through the phenyl or phenylethynyl moiety at the C2 and C7 positions as the strong acceptor moiety, and a methoxy group was introduced into naphthalene directly at the position opposite to the nitro group, as a weak donor moiety. While 2-(4-nitrophenyl)naphthalene did not show fluorescence in various solvents, 2-methoxy-6-(4-nitrophenyl)naphthalene showed fluorescence in weakly polar solvents (ΦF = 0.11 in CH2Cl2), with a large Stokes shift (Δν = 12,000 cm−1). Additionally, 2-methoxy-6-(4-nitrophenyl)naphthalene did not show fluorescence in polar solvents (acetonitrile) and non-polar solvents (toluene). This unique solvent-dependent fluorescence is remarkable for environmental fluorescence sensor applications.

Synthesis of highly soluble fluorescent π-extended 2-(2-thienyl)benzothiazole derivatives via oxidative cyclization of 2-thienylthioanilide as the key step

Co-reporter:Sanghoon Ji, Masayuki Shigeta, Yosuke Niko, Junji Watanabe, Gen-ichi Konishi

Tetrahedron Letters 2013 Volume 54(Issue 52) pp:7103-7106

Publication Date(Web):25 December 2013

DOI:10.1016/j.tetlet.2013.10.071

In this Letter, we synthesize highly soluble push–pull type fluorescent 2-(2-thienyl)benzothiazole dyes and evaluate their photophysical properties. The key step is the synthesis of 2-(5′-bromothien-2′-yl)-6-alkoxybenzothiazole (2) via oxidative cyclization of 2-thienylthioanilide using PhI(OAc)2 as the oxidant. The target dyes could be easily synthesized by the Suzuki–Miyaura cross-coupling reaction of 2 and an appropriate π-donor. The photophysical properties of the 2-thienylbenzothiazole chromophore were controlled by the π-donor moiety. It was found that 2 exhibited large Stokes shifts (5345 cm−1) and a high quantum efficiency for fluorescence (ΦF = 0.94 in CH2Cl2). Therefore, it can be expected to be a useful photofunctional material in liquid crystal laser dyes and nonlinear optical materials.We report the synthesis of highly soluble push–pull type fluorescent 2-(2-thienyl)benzothiazole dyes and the evaluation of their photophysical properties. The key step is the synthesis of the 2-(5′-bromothien-2′-yl)-6-alkoxybenzothiazole via oxidative cyclization of 2-thienylcarbothioamide using PhI(OAc)2 as an oxidant.

Fluorescence Enhancement of Pyrene Chromophores Induced by Alkyl Groups through σ–π Conjugation: Systematic Synthesis of Primary, Secondary, and Tertiary Alkylated Pyrenes at the 1, 3, 6, and 8 Positions and Their Photophysical Properties

Co-reporter:Yosuke Niko, Susumu Kawauchi, Shun Otsu, Katsumi Tokumaru, and Gen-ichi Konishi

The Journal of Organic Chemistry 2013 Volume 78(Issue 7) pp:3196-3207

Publication Date(Web):February 20, 2013

DOI:10.1021/jo400128c

We have systematically synthesized 1-, 3-, 6-, and 8-alkyl-substituted pyrene derivatives using the latest synthesis methods and investigated the effects of alkyl substitution on the photophysical properties of the pyrene chromophore. Like the trimethylsilyl group, which is known to enhance the fluorescence properties of some chromophores through σ*−π* conjugation, alkyl groups (primary, secondary, and tertiary) enhanced the fluorescence quantum yield of the pyrene chromophore through σ–π conjugation in most cases. While these enhancements in the fluorescence quantum yield were beyond expectations, the results were supported by absolute measurements. These results also indicate that ubiquitous alkyl groups can be used to tune the photophysical properties of the pyrene chromophore, as well as to improve the solubility or prevent aggregation. In other words, they can be used to develop new photofunctional materials.

Synthesis of a new poly(dinaphthylacetylene) and evaluation of its solution conformation

Co-reporter:Yuki Arakawa;Hidemine Furuya

Polymer Bulletin 2013 Volume 70( Issue 1) pp:47-57

Publication Date(Web):2013 January

DOI:10.1007/s00289-012-0819-6

We report the synthesis of various substituted polyacetylenes including a novel poly(dinaphthylacetylene), poly{2-(2-ethylhexyloxy)-6-[2-(6-methoxynaphthyl-2-yl)ethynyl]naphthalene}, by the use of a WCl6–Ph4Sn catalyst system, and systematically investigate their solution properties. It is found that poly(diarylacetylene)s such as poly(dinaphthylacetylene)s and poly(diphenylacetylene)s exhibit a solution morphology between rod-like and semi-flexible, whereas the less bulky poly(phenylacetylene)s, poly(silylacetylene)s, and poly(tert-butylacetylene) exhibit a random coil morphology.

Solvatochromic Pyrene Analogues of Prodan Exhibiting Extremely High Fluorescence Quantum Yields in Apolar and Polar Solvents

Co-reporter:Yosuke Niko;Dr. Susumu Kawauchi;Dr. Gen-ichi Konishi

Chemistry - A European Journal 2013 Volume 19( Issue 30) pp:9760-9765

Publication Date(Web):

DOI:10.1002/chem.201301020

Synthesis of diphenyl-diacetylene-based nematic liquid crystals and their high birefringence properties

Co-reporter:Yuki Arakawa, Shunpei Nakajima, Ryohei Ishige, Makoto Uchimura, Sungmin Kang, Gen-ichi Konishi and Junji Watanabe

Journal of Materials Chemistry A 2012 vol. 22(Issue 17) pp:8394-8398

Publication Date(Web):15 Mar 2012

DOI:10.1039/C2JM16002A

We synthesized two series of diphenyl-diacetylene (DPDA)-based materials with alkoxy and alkyl tails of length m (DPDA–OCm and DPDA–Cm, respectively), and measured their nematic-phase birefringence (Δn) as a function of wavelength and temperature. We found that Δn decreases with an increase in m, possibly by a dilution effect of the low-Δn alkyl tail. Further, of the two series, Δn was found to be relatively higher in the DPDA–OCm materials, with the highest value of 0.4 obtained for DPDA–OC1 at 550 nm at 10 °C below the isotropic-to-nematic transition temperature. Further, we observed the temperature dependence for Δn, which is proportional to the order parameter (s). From extrapolation to s = 1 (the perfect orientation state), it is speculated that the DPDA–O moiety has the potential to afford a very large Δn of 0.9.

Synthesis and evaluation of high-birefringence polymethacrylate having a diphenyl-diacetylene LC moiety in the side chain

Co-reporter:Yuki Arakawa, Shunpei Nakajima, Sungmin Kang, Gen-ichi Konishi and Junji Watanabe

Journal of Materials Chemistry A 2012 vol. 22(Issue 29) pp:14346-14348

Publication Date(Web):25 May 2012

DOI:10.1039/C2JM32489J

We synthesized polymethacrylate with a diphenyl-diacetylene moiety in the side chain. It formed a nematic LC, which appears in the wide temperature region and vitrified at room temperature. The polymer exhibited a high-birefringence of ∼0.3 at 550 nm at room temperature.

Design of an extremely high birefringence nematic liquid crystal based on a dinaphthyl-diacetylene mesogen

Co-reporter:Yuki Arakawa, Shunpei Nakajima, Sungmin Kang, Masayuki Shigeta, Gen-ichi Konishi and Junji Watanabe

Journal of Materials Chemistry A 2012 vol. 22(Issue 28) pp:13908-13910

Publication Date(Web):24 May 2012

DOI:10.1039/C2JM32448B

We designed dinaphthyl-diacetylene-based nematic liquid crystals with alkoxy tails (DNDA–OCm) and evaluated their birefringence (Δn). Actual measurements of pure target compounds showed that DNDA–OC2 had the highest value of 0.62 at 550 nm at Tc + 10 °C.

Synthesis of a branched poly(phenylene ethylene) with bromomethyl groups as an organosoluble and functional parylene

Co-reporter:Ataru Kobayashi;Kentaro Sumi

Journal of Applied Polymer Science 2012 Volume 123( Issue 5) pp:2775-2780

Publication Date(Web):

DOI:10.1002/app.34652

Abstract

We synthesized a branched poly(phenylene ethylene) (BPPE) with bromomethyl groups from 1,3,5-tris(bromomethyl)benzene derivatives via the Wurtz coupling reaction. In the case of 1,3,5-tris(bromomethyl)-2,4,6-trimethoxybenzene as a monomer, the obtained polymer (M_n = 6100, M_w/M_n = 1.9) had bromomethyl groups. The ¹HNMR analysis showed that a very large number of unreacted bromomethyl groups (Ph-CH₂Br) remained in the BPPE; the reaction of this polymer with phenolic hydroxyl groups proceeded quantitatively. This suggested that BPPEs can be functionalized using unreacted bromomethyl groups, making them a very attractive starting point for the creation of functionalized BPPEs with further enhanced processability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Functionalization of lignin: Synthesis of lignophenol-graft-poly(2-ethyl-2-oxazoline) and its application to polymer blends with commodity polymers

Co-reporter:Tadamasa Nemoto;Yusuke Tojo;Youn Chul An;Masamitsu Funaoka

Journal of Applied Polymer Science 2012 Volume 123( Issue 5) pp:2636-2642

Publication Date(Web):

DOI:10.1002/app.34623

Abstract

Lignophenol (LP)-graft-poly(2-ethyl-2-oxazoline) (POZO) was prepared to reuse lignin, an industrial waste material, and to produce novel LP-based polymer blends with poly(vinyl chloride) (PVC), poly(bisphenol A carbonate) (PC), polyvinylpyrrolidone (PVP), and polystyrene (PSt) as commodity polymers. The resulting graft polymer was soluble in various types of organic solvents such as chloroform, THF, acetone, and methanol, unlike LP. The miscibility of LP-graft-POZO with commodity polymers was measured by differential scanning calorimetry (DSC) to determine the glass transition temperatures (T_g). In the cases of the blends of LP-graft-POZO with PVC, PC, and PVP, the T_g values decreased during the second scan. Moreover, in the cases of the blends with PVC and PVP, the T_g values were not detected during the third scan. Therefore, it was inferred that LP-graft-POZO was miscible with PVC, PC, and PVP while forming single phases; in particular, the blends of LP-graft-POZO with PVC and PVP exhibited a secondary miscibility because the T_g values were not detected. Furthermore, the blend of LP-graft-POZO with PC exhibited better thermostability than LP and LP-graft-POZO. These results indicated that LP blended with POZO could be used as a polymer additive and as an adhesive to combine different polymers, organic–inorganic polymers, etc. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Facile synthesis of high refractive index thiophene-containing polystyrenes

Co-reporter:Young Chul An

Journal of Applied Polymer Science 2012 Volume 124( Issue 1) pp:789-795

Publication Date(Web):

DOI:10.1002/app.35077

Abstract

High refractive index polymer films have been extensively investigated because of their wide application potentials. We now designed thiophene-containing polystyrene as colorless and transparent high-refractive-index thin film. The copolystyrenes were synthesized by general radical polymerization with controlled mole ratios 0 : 10, 1 : 9, 3 : 7, 5 : 5, 7 : 3, 9 : 1, 10 : 0 (styrene : p-bromostyrene), respectively. Next, the thiophene-containing polystyrenes were synthesized by Suzuki-Miyaura coupling reaction. The chemical structures of synthesized thiophene-containing polystyrene in accordance with ratios were confirmed by using ¹H-NMR, ¹³C-NMR, and FTIR. The effect of the thiophene units on refractive index according to copolymer ratios were confirmed by using prism coupler. The thiophene-containing polystyrene showed improved refractive index ranging from 1.58 to 1.67 and birefringence in the range of 0.0001–0.0019. The thermal stability and thermal behaviors of thiophene-containing polystyrene also can be confirmed by TGA and DSC. The polymers have high glass transition temperature in the range of 108°C–177°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Fundamental photoluminescence properties of pyrene carbonyl compounds through absolute fluorescence quantum yield measurement and density functional theory

Co-reporter:Yosuke Niko, Yuki Hiroshige, Susumu Kawauchi, Gen-ichi Konishi

Tetrahedron 2012 68(31) pp: 6177-6185

Publication Date(Web):

DOI:10.1016/j.tet.2012.05.072

Polymer-Chain-Induced Tunable Luminescence Properties: Amphiphilic Poly(2-oxazoline)s Possessing a N,N-Dialkylpyrene-1-carboxamide Chromophore in the Side Chain

Co-reporter:Yosuke Niko and Gen-ichi Konishi

Macromolecules 2012 Volume 45(Issue 5) pp:2327-2337

Publication Date(Web):February 27, 2012

DOI:10.1021/ma3001252

We report a polymer-chain-induced tunable luminescence system based on a newly synthesized fluorescent polymer, N,N-dialkylpyrene-1-carboxamide-modified poly(2-methyl-2-oxazoline) (POZO-py) at various ratios of pyrene induction. Photoluminescence and thermal properties of the POZO-py were analyzed in detail. Differential scanning calorimetry (DSC) measurements revealed that the glass-transition temperature (Tg) of POZO-py was above room temperature, which implies that POZO-py is in the glassy state at room temperature. POZO-py-(0.73) (i.e., pyrene content of 0.73%, Mn = 2270, Tg = 40 °C), having the lowest pyrene induction ratio, showed higher fluorescence quantum yields in several solvents, e.g., water, or in the thin film state than did N,N-diethylpyrene-1-carboxamide (a model compound, PA), because the polymer chain prevented the molecular mobilities of the pyrene moieties. In particular, POZO-py showed strong emission (Φfl = 0.52) in glycerin, which is a highly viscous solvent. Highly modified POZO-py-(2.9) (i.e., with a pyrene content of 2.9%, Mn = 2450, Tg = 48 °C) and POZO-py-(9.1) (Mn = 2640, Tg = 57 °C) exhibited both monomer and excimer emissions. These excimers consisted of a static excimer and a dynamic excimer. These results were not obtained for the low-molecular PA. Thus, POZO can induce improved and tunable photoluminescence properties of N,N-dialkylpyrene-1-carboxamide. The synthesis and photoluminescence properties of N,N-dialkylpyrene-1-carboxamide-modified poly(2-ethyl-2-oxazoline)-gel (PEtOZO-py-gel) were also determined.

Additional Insights into Luminescence Process of Polycyclic Aromatic Hydrocarbons with Carbonyl Groups: Photophysical Properties of Secondary N-Alkyl and Tertiary N,N-Dialkyl Carboxamides of Naphthalene, Anthracene, and Pyrene

Co-reporter:Yosuke Niko, Yuki Hiroshige, Susumu Kawauchi, and Gen-ichi Konishi

The Journal of Organic Chemistry 2012 Volume 77(Issue 8) pp:3986-3996

Publication Date(Web):March 29, 2012

DOI:10.1021/jo300317r

Here we report the substitution effects of N-alkyl and N,N-dialkyl carboxamide groups on the fluorescence properties of polycyclic aromatic hydrocarbon chromophores, so as to control their fluorescence properties. The fluorescence properties of compounds obtained using solvents with different polarities showed very little change, indicating that the modified compounds do not form charge transfer states. TD-DFT calculations and measurements performed at low temperature (78 K) and in viscous solvents revealed that the N-alkyl and N,N-dialkyl carboxamide groups tend to reduce the contributions from intersystem crossing and increase those from internal conversion. Considering that the fluorescence mechanism of low-fluorescence carbonyl compounds such as aldehyde and ketone is dominated by intersystem crossing and that of high-luminescence carbonyl compounds such as carboxylic acid and ester is dominated by a radiative process, it can be said that the photophysical process of N-alkyl and N,N-dialkyl carboxamides is novel. In addition, the calculation results for excited states indicated that such contributions can be controlled by selecting the appropriate polycyclic aromatic hydrocarbon or amide structure, in addition to solvent viscosity and temperature.

Synthesis, luminescence properties, and theoretical insights of N-alkyl- or N,N-dialkyl-pyrene-1-carboxamide

Co-reporter:Yosuke Niko, Susumu Kawauchi, Gen-ichi Konishi

Tetrahedron Letters 2011 Volume 52(Issue 38) pp:4843-4847

Publication Date(Web):21 September 2011

DOI:10.1016/j.tetlet.2011.07.020

We report the synthesis and photophysical properties of N-alkyl- or N,N-dialkyl-pyrene-1-carboxamide. These derivatives, as well as pyrene, exhibited blue emission. N-Alkyl-type derivatives exhibited strong fluorescence emission (Φfl = 0.61 in EtOH) in both nonpolar and polar solvents. On the other hand, N,N-dialkyl-type derivatives showed weak fluorescence emission (Φfl <0.01) due to vibrational deactivation. However, in highly viscous solvents such as glycerin, the quantum efficiencies of N-alkyl-type (Φfl = 0.91) and N,N-dialkyl-type (Φfl = 0.082) derivatives were increased. We also investigated the fluorescence mechanism of these compounds using time-dependent density-functional theory (TD-DFT). From these results, we find that highly fluorescent pyrene-1-carboxamide derivatives can be designed by introducing an appropriate functional group at the nitrogen atom of the amide. Thus, N,N-dialkyl-type pyrene-1-carboxamide has considerable potential for use in applications such as environmental response sensors and probes.N-Alkyl-pyrene-1-carboxamide derivatives exhibited bright blue emission in all solvents (for example, glycerin: Φfl = 0.91). While N,N-dialkyl-pyrene-1-carboxamide did not emit in most media studied (EtOH: Φfl <0.01), it showed relatively strong emission in viscous media (glycerin: Φfl = 0.082).

Erratum to “Enhanced absorption and fluorescence efficiency of silylethynyl-functionalized oligothiophenes and thieno[3,2–b]thiophene” [J. Organomet. Chem. 696 (2011) 1266–1271]

Co-reporter:Kengo Asai, Gen-ichi Konishi, Yumiko Nakajima, Susumu Kawauchi, Fumiyuki Ozawa, Kazuhiko Mizuno

Journal of Organometallic Chemistry 2011 696(8) pp: 1701

Publication Date(Web):

DOI:10.1016/j.jorganchem.2011.03.016

Erratum to “Synthesis of silyl-functionalized oligothiophene-based polymers with bright blue light-emission and high refractive index” [J. Organomet. Chem. 696 (2011) 1236–1243]

Co-reporter:Kengo Asai, Gen-Ichi Konishi, Kentaro Sumi, Kazuhiko Mizuno

Journal of Organometallic Chemistry 2011 696(8) pp: 1702

Publication Date(Web):

DOI:10.1016/j.jorganchem.2011.03.017

Enhanced absorption and fluorescence efficiency of silylethynyl-functionalized oligothiophenes and thieno[3,2–b]thiopahene

Co-reporter:Kengo Asai, Gen-ichi Konishi, Yumiko Nakajima, Susumu Kawauchi, Fumiyuki Ozawa, Kazuhiko Mizuno

Journal of Organometallic Chemistry 2011 696(6) pp: 1266-1271

Publication Date(Web):

DOI:10.1016/j.jorganchem.2010.10.044

Synthesis of silyl-functionalized oligothiophene-based polymers with bright blue light-emission and high refractive index

Co-reporter:Kengo Asai, Gen-Ichi Konishi, Kentaro Sumi, Kazuhiko Mizuno

Journal of Organometallic Chemistry 2011 696(6) pp: 1236-1243

Publication Date(Web):

DOI:10.1016/j.jorganchem.2010.11.013

Synthesis of optically active green fluorescent π-conjugated fluorene polymers having chiral Schiff bases in the side chain

Co-reporter:Kengo Asai, Gen-ichi Konishi, Kentaro Sumi and Susumu Kawauchi

Polymer Chemistry 2010 vol. 1(Issue 3) pp:321-325

Publication Date(Web):21 Dec 2009

DOI:10.1039/B9PY00268E

The synthesis of optically active poly(fluorene-alt-chiral iminofluorene)s using 1-phenylethylamine as a chiral auxiliary is described. Optically active polyfluorenes were synthesized by the palladium-catalyzed Suzuki–Miyaura coupling polymerization of 9,9′-dioctylfluorene-2,7-bis(trimethyleneborate) with a chiral Schiff base monomer (imino group modified-fluorene). The obtained polymers showed intense green emission with high quantum efficiency. Analysis of the circular dichroism data of the optically active polymers indicates that the polymers exhibit various highly-ordered regular structures in solution.

Synthesis and evaluation of high-molecular weight diphenyl oxide and diphenyl sulfide novolacs

Co-reporter:Gen-Ichi Konishi;Yamato Nojiri;Toshiki Matsuo;Tadamasa Nemoto;Kengo Asai;Kentaro Sumi;Yoshiaki Nakamoto

Journal of Applied Polymer Science 2010 Volume 118( Issue 3) pp:1651-1657

Publication Date(Web):

DOI:10.1002/app.32561

Abstract

The preparation and characterization of high-molecular weight diphenyl oxide- and diphenyl sulfide-novolacs are described. The polymerization of diphenyl oxide with 2 equivalence of formaldehyde proceeded to give the corresponding polymer (2) (M_n: 160,000, M_w/M_n: 29.1) in good yield. Further, an ultra high-molecular weight fraction (M_w > 1,000,000) was observed in the GPC trace of 2. The developed polymers can be considered as a new class of aromatic polymers that exhibit both novolac-like and engineering plastic properties and are thus promising compounds for material-engineering applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Synthesis and photoluminescence properties of π-extended fluorene derivatives: the first example of a fluorescent solvatochromic nitro-group-containing dye with a high fluorescence quantum yield

Co-reporter:Hidehiro Kotaka, Gen-ichi Konishi, Kazuhiko Mizuno

Tetrahedron Letters 2010 Volume 51(Issue 1) pp:181-184

Publication Date(Web):6 January 2010

DOI:10.1016/j.tetlet.2009.10.118

Functional π-extended fluorene derivatives, 2,7-di(p-substituted-phenyl)fluorenes containing different functional groups such as hydrogen, trimethylsilyl (TMS), methoxycarbonyl, cyano, and nitro groups, were synthesized. Except for the nitro group, the resulting compounds exhibited extremely high fluorescence quantum yields (ΦF >0.85 in chloroform). The diphenylfluorene containing nitro groups have higher fluorescence quantum yield (ΦF = 0.31 in N,N’-dimethyl-formamide) than other nitro-group-containing fluorophores which were previously reported (ΦF <0.1). Furthermore, this compound exhibited large Stokes’ shift with green to orange emission and unique on–off behavior of the emission by solvents.2,7-Di(p-nitrophenyl)fluorene has high fluorescence quantum yield (ΦF = 0.31 in N,N′-dimethyl-formamide) and exhibits large Stokes’ shift with green to orange emission and unique on–off behavior of the emission governed by solvents.

Direct synthesis of functional novolacs and their polymer reactions

Co-reporter:Gen-ichi Konishi, Takatsugu Tajima, Tsuyoshi Kimura, Yusuke Tojo, Kazuhiko Mizuno and Yoshiaki Nakamoto

Polymer Journal 2010 42(6) pp:443-449

Publication Date(Web):April 14, 2010

DOI:10.1038/pj.2010.26

We report the direct synthesis of new functional novolacs having allyl ether (4) or bromoalkyl groups (5 and 6) in the side chain by the addition-condensation of allyl phenyl ether (1), 1-bromo-2-phenoxyethane (2) or 1-bromo-4-phenoxybutane (3) with formaldehyde. The structure of these novolacs was confirmed by Fourier transform infrared, 1H NMR and 13C NMR spectra. The number-average molecular weights (Mn) of the obtained polymers were found to be ~1000–3000. In the case of the polymerization of 1 with formaldehyde using hydrated sulfuric acid as a catalyst, Claisen condensation did not occur with the polymerization; therefore, pure allylated novolac (4) without a phenol moiety was obtained. Thus, in this process, phenol–formaldehyde condensation proceeded under such conditions that the functional group was not affected. These polymers (4–6) have considerable potential as reactive polymers in the field of materials science. Their applications are as follows: (i) a key reaction of a latent curing system: thermal stimuli-induced Claisen rearrangement of allylated novolac to generate phenolic hydroxyl groups; (ii) vinyl ether-modified novolac (7) prepared by 1-bromoethoxy-group-modified novolac; and (iii) an amphiphilic graft-shaped polymer prepared by bromoalkyl-group-modified novolac-initiated ring-opening polymerization of 2-methyl-2-oxazoline.

Synthesis of Alkoxylated Phenolic Resins Containing an Acetyl Group and Their Functionalization by Grignard Reaction

Co-reporter:Tadamasa Nemoto, Isamu Amir and Gen-ichi Konishi

Polymer Journal 2009 41(5) pp:395-401

Publication Date(Web):March 11, 2003

DOI:10.1295/polymj.PJ2008321

We successfully synthesized acetyl group-containing phenolic resins as novel reactive polymers. The addition-condensation of 2,4,6-trimethoxyacetophenone (1) with an equimolar amount of formaldehyde catalyzed by 12mol/L HCl aq. proceeded homogeneously without side reactions to give polymer 3 (Mn 4800, Mw/Mn 1.3) in 32% yield. The FT-IR, 1H NMR and 13C NMR spectra of 3 revealed that it had arylene-methylene units on the polymer backbones. The terpolymerization from 1, 1,3,5-trimethoxybenzene (2) and formaldehyde was also carried out. When the feed ratio of 1 to 2 was 1:1, the content of 1 in the obtained polymer, 4, was found to be 25% by the 1H NMR spectrum; hence, the reactivity of 1 was lower than that of 2. The reactions of 4 with Grignard reagents were carried out to evaluate the reactivity of acetyl groups in the obtained polymers. Their reactions proceeded at some parts of acetyl groups, so 4 can be applied as novel reactive phenolic resins. From thermogravimetric analyses, thermal stabilities of the functionalized polymers (6a-6d) are similar to that of 4, so it is expected that 4 have characters not only of the phenolic resins but also of the reactive polymers.

Synthesis of a Formyl Group-Containing Reactive Novolac

Co-reporter:Tadamasa Nemoto, Isamu Amir and Gen-ichi Konishi

Polymer Journal 2009 41(5) pp:389-394

Publication Date(Web):March 11, 2009

DOI:10.1295/polymj.PJ2008316

We report the preparation of a new novolac having formyl groups by the addition-condensation of 2,4,6-trimethoxy-benzaldehyde (1) and 1,3,5-trimethoxybenzene (2) with formaldehyde. In the case of the polymerization of 1 and formaldehyde, polymerization did not occur; however, the polymerization of 1, 2 and formaldehyde proceeded to give polymer 3 (Mn 4200, Mw/Mn 1.2). The FT-IR, 1H NMR and 13C NMR spectra of 3 showed that it had phenylene-methylene units on the polymer backbone and the formyl groups of 1 remained without side reactions. To evaluate its ability as a reactive polymer, the imination of 3 with 1,5-diaminopentane was carried out to obtain an organo-insoluble gel (5), which had the network structure of 3 and a pentamethylene unit via the imine moiety. The temperature at 5% loss in weight (Td5, 335 °C) of 5 slightly decreased compared to that of 3 (351 °C). This result indicates that polymer 3 can be utilized as a reactive polymer, and form a thermostable gel via the imine moiety.

Synthesis and properties of new novolacs based on heteroatom-bridged phenol derivatives

Co-reporter:Tadamasa Nemoto

Journal of Applied Polymer Science 2009 Volume 113( Issue 4) pp:2719-2726

Publication Date(Web):

DOI:10.1002/app.30200

Abstract

We describe the synthesis and properties of new novolacs prepared by addition-condensation of heteroatom-bridged phenol derivatives and formaldehyde. The trifluoroacetic acid-catalyzed polymerization of equimolar amounts of bis(4-methoxyphenyl) ether (1a) and formaldehyde proceeded homogeneously to afford the polymer (2a) in 49% yield (M_n 2600, M_w/M_n 1.8). From the FTIR, ¹H-NMR, and ¹³C-NMR spectra of 2a, it was evident that the polymer had methylene moieties-bridged repeating units in the polymer backbone. A higher molecular weight novolac (2a′) (yield 99%, M_n 16,600, M_w/M_n 12.9) could be prepared by using an excess of formaldehyde. Bis(4-methoxyphenyl) sulfone novolac (2b) (M_n 1300, M_w/M_n 1.2) and bis(4-methoxyphenyl) sulfide novolac (2d) (M_n 1200, M_w/M_n 1.9) were also prepared. However, the polymerization of bis(4-hydroxyphenyl) sulfone (1c) did not proceed, even when it was attempted under various reaction conditions. From TGA, the temperatures at 10% loss in weight (T₁₀) for 2a, 2a′, and 2b were found to be 413, 430 and 393°C, respectively. These results suggested that heteroatom-bridged novolacs based on phenol derivatives have good thermal stability than other organosoluble polymers; moreover, these novolacs could be expected to function as processable materials, polymer blends for engineering plastics, etc. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Synthesis and Properties of New Organosoluble Alkoxylated Naphthalene-Based Novolacs Preparaed by Addition-Condensation of Mono- or Di-alkoxynaphthalene with Formaldehyde

Co-reporter:Tadamasa Nemoto and Gen-ichi Konishi

Polymer Journal 2008 40(7) pp:651-656

Publication Date(Web):June 4, 2008

DOI:10.1295/polymj.PJ2008035

The preparation of new alkoxylated naphthalene-based novolacs [poly(naphthylenemethylene)s] by acid-catalyzed addition-condensation of mono- or di-methoxynaphthalene with formaldehyde is described in this paper. The polymerization of 2-methoxynaphthelene (1) with an equimolar amount of formaldehyde proceeded homogeneously to give the polymer 2 (Mn 3100, Mw/Mn 1.7) in good yield. The FT-IR, 1H NMR and 13C NMR spectra suggest that 2 might have a naphthylene-methylene unit and approximately linear polymer backbones. In contrast, in the case of 1,5-dimethoxynaphthalene (3a) as a monomer, the obtained polymer (4a) (Mn 1900, Mw/Mn 2.3) was a branched polymer. From TGA, T10 (temperature at 10% loss in weight) indexes of the polymers 2 and 4a were estimated to be 402 and 359 °C, respectively. These results indicate that the alkoxylated naphthalene-based novolacs have good thermal stability.

Synthesis and Properties of Fluorine-Containing Poly(arylenemethylene)s as New Heat Resistant Denatured Phenolic Resins

Co-reporter:Tadamasa Nemoto, Gen-ichi Konishi, Takayuki Arai and Toshikazu Takata

Polymer Journal 2008 40(7) pp:622-628

Publication Date(Web):May 14, 2008

DOI:10.1295/polymj.PJ2008044

We report the synthesis of fluorine-containing poly(arylenemethylene)s as a new heat-resistant denatured phenolic resin by addition-condensation or Friedel-Crafts polymerization. In the case of polymerization of 2,2-bis(4-methoxyphenyl)hexafluoropropane (1a) with an equimolar amount of formaldehyde, the polymerization proceeded homogeneously to give the polymer 2a (Mn 8,200, Mw/Mn 2.1) in 71% yield. The FT-IR, 1H NMR and 13C NMR spectra of 2a revealed that it had arylene-methylene units on the polymer backbone. The polymerizations of 3-(trifluoromethoxy)benzyl bromide (1b) or 4-(trifluoromethoxy)benzyl bromide (1c) via the Friedel-Crafts polymerization using aluminum chloride as a catalyst produced the polymer 2b and 2c in 38% and 16% yield, respectively. From the TGA, the temperatures at 10% loss in weight (T10) of 2a and 2c were found to be 425 and 298 °C, respectively. As compared to the non-fluorinated poly(arylenemethylene) derived from 2,2-bis(4-methoxyphenyl)propane-formaldehyde polymer (2d) (T10=397 °C), 2a showed high thermostability in terms of the temperature of T10. The results indicated that the thermal stability of poly(arylenemethylene)s was enhanced by the introduction of fluorine moieties in the polymer.

Large extraordinary refractive index in highly birefringent nematic liquid crystals of dinaphthyldiacetylene-based materials

Co-reporter:Sungmin Kang, Shunpei Nakajima, Yuki Arakawa, Gen-ichi Konishi and Junji Watanabe

Journal of Materials Chemistry A 2013 - vol. 1(Issue 27) pp:NaN4226-4226

Publication Date(Web):2013/05/30

DOI:10.1039/C3TC30640B

The extraordinary and ordinary refractive indices in highly birefringent dinaphthyldiacetylene-based nematic liquid crystals with different alkoxy tails were accurately measured by the multiple-beam interference method. The high birefringence in the nematic liquid crystals was attributed to the high value of the extraordinary refractive index, ne. The value of ne increased from 1.8 to 2.1 as the number of carbon atoms in the alkoxy tail decreased from 12 to 3, whereas the ordinary index, no, remained at approximately 1.6.

Design of an extremely high birefringence nematic liquid crystal based on a dinaphthyl-diacetylene mesogen

Co-reporter:Yuki Arakawa, Shunpei Nakajima, Sungmin Kang, Masayuki Shigeta, Gen-ichi Konishi and Junji Watanabe

Journal of Materials Chemistry A 2012 - vol. 22(Issue 28) pp:NaN13910-13910

Publication Date(Web):2012/05/24

DOI:10.1039/C2JM32448B

We designed dinaphthyl-diacetylene-based nematic liquid crystals with alkoxy tails (DNDA–OCm) and evaluated their birefringence (Δn). Actual measurements of pure target compounds showed that DNDA–OC2 had the highest value of 0.62 at 550 nm at Tc + 10 °C.

Diphenyltriacetylenes: novel nematic liquid crystal materials and analysis of their nematic phase-transition and birefringence behaviours

Co-reporter:Yuki Arakawa, Sungmin Kang, Shunpei Nakajima, Koichi Sakajiri, Yokan Cho, Susumu Kawauchi, Junji Watanabe and Gen-ichi Konishi

Journal of Materials Chemistry A 2013 - vol. 1(Issue 48) pp:NaN8102-8102

Publication Date(Web):2013/10/16

DOI:10.1039/C3TC31658K

Improvements in birefringence properties of LC materials are actively being pursued because of the increase in their applications in optical devices. 1,6-Diphenyl-1,3,5-hexatriyne, i.e., diphenyltriacetylenes (DPTAs; number of acetylene units, n = 3) are expected to have wide nematic mesophases and exhibit extremely high birefringence properties because of the high aspect ratio of their conjugated structures. Therefore, we synthesised DPTA derivatives as novel, highly birefringent nematic liquid crystal materials. The derivatives exhibit stable enantiotropic nematic phases with longer alkoxy carbon chain lengths (i.e., with dodecyloxy groups, m = 12). High birefringence values of Δn = 0.46 at 550 nm and 140 °C and a high extraordinary refractive index (ne) of over 2.0 were exhibited for triyne DPTA–OC6. Furthermore, we investigated the effect of the acetylene bond on the nematic transition behaviours and refractive index parameters of the conjugated oligoyne or polyyne compounds with two terminal aromatic rings. An increasing number of acetylene units (n = 1–3), i.e., extended conjugation, led to wider nematic phases and higher birefringence; the increment in Δn per acetylene unit was estimated to be approximately 0.14.

The effect of regioisomerism on the solid-state fluorescence of bis(piperidyl)anthracenes: structurally simple but bright AIE luminogens

Co-reporter:Shunsuke Sasaki, Kazunobu Igawa and Gen-ichi Konishi

Journal of Materials Chemistry A 2015 - vol. 3(Issue 23) pp:NaN5950-5950

Publication Date(Web):2015/05/11

DOI:10.1039/C5TC00946D

A series of regioisomers of piperidylanthracenes (PA) and bis(piperidyl)anthracenes (BPA) were synthesized and their photophysical properties examined in solution, suspension, and the solid state. Aggregation-induced emission (AIE) was observed only for 1,4-BPA and 9,10-BPA, in which two piperidyl groups are substituted at the anthracene moiety in the para-position with respect to each other. Compared to previously reported AIE luminogens, these easily obtainable para-substituted BPAs, exhibited several unique and beneficial features, such as simple structures, bright solid-state fluorescence (Φfl = 0.49 and 0.86 for 1,4-BPA and 9,10-BPA, respectively), tunable fluorescence emission, and large Stokes shifts. Results from diffuse-reflectance and fluorescence lifetime measurements demonstrated that PAs and BPAs intrinsically possess an efficient non-radiative transition pathway in the solid state, and that 1,4-BPA and 9,10-BPA may overcome this pathway. The X-ray crystallographic analysis of 1,4-BPA revealed that undesirable interchromophoric interactions can be minimised, while TD-DFT calculations suggested that the enhanced Stokes shift of 1,4-BPA arises from severe electronic repulsion between neighbouring piperidyl moieties, which presumably results in the absence of self-absorption.

Synthesis and evaluation of high-birefringence polymethacrylate having a diphenyl-diacetylene LC moiety in the side chain

Co-reporter:Yuki Arakawa, Shunpei Nakajima, Sungmin Kang, Gen-ichi Konishi and Junji Watanabe

Journal of Materials Chemistry A 2012 - vol. 22(Issue 29) pp:NaN14348-14348

Publication Date(Web):2012/05/25

DOI:10.1039/C2JM32489J

We synthesized polymethacrylate with a diphenyl-diacetylene moiety in the side chain. It formed a nematic LC, which appears in the wide temperature region and vitrified at room temperature. The polymer exhibited a high-birefringence of ∼0.3 at 550 nm at room temperature.

Synthesis of diphenyl-diacetylene-based nematic liquid crystals and their high birefringence properties

Co-reporter:Yuki Arakawa, Shunpei Nakajima, Ryohei Ishige, Makoto Uchimura, Sungmin Kang, Gen-ichi Konishi and Junji Watanabe

Journal of Materials Chemistry A 2012 - vol. 22(Issue 17) pp:NaN8398-8398

Publication Date(Web):2012/03/15

DOI:10.1039/C2JM16002A

We synthesized two series of diphenyl-diacetylene (DPDA)-based materials with alkoxy and alkyl tails of length m (DPDA–OCm and DPDA–Cm, respectively), and measured their nematic-phase birefringence (Δn) as a function of wavelength and temperature. We found that Δn decreases with an increase in m, possibly by a dilution effect of the low-Δn alkyl tail. Further, of the two series, Δn was found to be relatively higher in the DPDA–OCm materials, with the highest value of 0.4 obtained for DPDA–OC1 at 550 nm at 10 °C below the isotropic-to-nematic transition temperature. Further, we observed the temperature dependence for Δn, which is proportional to the order parameter (s). From extrapolation to s = 1 (the perfect orientation state), it is speculated that the DPDA–O moiety has the potential to afford a very large Δn of 0.9.

A three-dimensional assembly of pyrene dye on a tetraphenylethane scaffold enhances fluorescence quantum yield

Co-reporter:Kentaro Sumi, Yosuke Niko, Katsumi Tokumaru and Gen-ichi Konishi

Chemical Communications 2013 - vol. 49(Issue 37) pp:NaN3895-3895

Publication Date(Web):2013/03/21

DOI:10.1039/C3CC41312H

A three-dimensional pyrene assembly on a tetraphenylethane skeleton enhanced the fluorescence quantum yield compared to the yield obtained when using monomeric species, without changing the shape of the emission spectrum. The unique spacing of the pyrene units may prevent intramolecular fluorescence quenching or non-radiative decay.

A novel pyrene-based two-photon active fluorescent dye efficiently excited and emitting in the ‘tissue optical window (650–1100 nm)’

Co-reporter:Yosuke Niko, Hiroki Moritomo, Hiroyuki Sugihara, Yasutaka Suzuki, Jun Kawamata and Gen-ichi Konishi

Journal of Materials Chemistry A 2015 - vol. 3(Issue 2) pp:NaN190-190

Publication Date(Web):2014/10/17

DOI:10.1039/C4TB01404A

The development of two-photon (TP) active fluorophores remains an important issue. Dyes that can be excited and fluoresce efficiently in the ‘tissue optical window’ (650–1100 nm) are especially in demand to maximize the underlying performance of two-photon fluorescence microscopy (TPFM) as an advanced optical technique. Ideally, such dyes would be compatible with the 1050 nm femtosecond fibre laser, which has recently been developed as an inexpensive excitation source to make the TPFM technique universal. In this work, we designed and synthesized a novel pyrene-based acceptor–π–acceptor (A–π–A) dye, PY, which exhibited outstanding properties such as bright fluorescence (λem = 650 nm and ΦFL = 0.80) and a large two-photon absorption cross-section (1100 GM (1 GM = 10−50 cm4 per photon per molecule) at 950 nm and 380 GM at 1050 nm) in the tissue optical window. In living mitochondria, PY provided more sensitive microscopic images than current dyes and showed great potential to be a building block of TP active fluorescent probes for the 1050 nm fibre laser. We believe that the exceptional properties of PY will be extended to other fluorescent probes through further chemical modification.