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Shotaro Hayashi

Bio: Shotaro Hayashi is an academic researcher from Kochi University of Technology. The author has contributed to research in topics: Conjugated system & Chemistry. The author has an hindex of 17, co-authored 62 publications receiving 1009 citations. Previous affiliations of Shotaro Hayashi include Tokyo Institute of Technology & National Defence Academy.


Papers
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TL;DR: An elastic organic crystal of a π-conjugated molecule has been fabricated and it was found to be a remarkably elastic crystalline material.
Abstract: An elastic organic crystal of a π-conjugated molecule has been fabricated. A large fluorescent single crystal of 1,4-bis[2-(4-methylthienyl)]-2,3,5,6-tetrafluorobenzene (over 1 cm long) exhibited a fibril lamella morphology based on slip-stacked molecular wires, and it was found to be a remarkably elastic crystalline material. The straight crystal was capable of bending more than 180° under applied stress and then quickly reverted to its original shape upon relaxation. In addition, the fluorescence quantum yield of the crystal was about twice that of the compound in THF solution. Mechanical bending-relaxation resulted in reversible change of the morphology and fluorescence. This research offers a more general approach to flexible crystals as a promising new family of organic semiconducting materials.

170 citations

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TL;DR: Two fluorescent and highly flexible organic crystals (1 and 2) which could bend under an applied stress are reported on, which showed a unique bending mechanofluorochromism.
Abstract: To create low band-gap, fluorescent, and elastic organic crystal emitters, we focused on an extended π-conjugated system based on: a) a planar conformation,b) a rigid structure, and c) controlled intermolecular interactions. Herein, we report on two fluorescent and highly flexible organic crystals (1 and 2) which could bend under an applied stress. The bent crystals rapidly recover their straight shape upon release of the stress. Crystal 1 with a tetrafluoropyridyl terminal unit and a lower band-gap energy (orange emission, λem =573 nm, ΦF =0.50), showed no bending mechanofluorochromism and had superior performance as an optical waveguide with reddish orange emission. The waveguide performance of the crystal did not decrease under bending stress. For crystal 2 with a pentafluorophenyl terminal unit (green emission, λem =500 nm, ΦF =0.38), the original waveguide performance decreased under an applied bending stress; however, this crystal showed a unique bending mechanofluorochromism.

139 citations

Journal ArticleDOI
TL;DR: A versatile synthetic means for cyclic diblock copolymers has been developed by the combination of atom transfer radical polymerization (ATRP) and ring-closing metathesis (RCM) techniques as mentioned in this paper.
Abstract: A versatile synthetic means for cyclic diblock copolymers has been developed by the combination of atom transfer radical polymerization (ATRP) and ring-closing metathesis (RCM) techniques. Thus, first, an A−B type allyl-telechelic diblock copolymer comprised of two different acrylate ester segments, i.e., poly(methyl acrylate)-b-poly(n-butyl acrylate), poly(MA)-b-poly(BA), was prepared via the ATRP of MA, followed by the addition of the second monomer, BA, with allyl bromide as an initiator and with allyltributylstannane as an end-capping reagent, respectively. Alternatively, an A−B−A type allyl-telechelic triblock copolymer comprised of poly(BA) and poly(ethylene oxide), poly(EO), segments was prepared via the ATRP of BA using a poly(EO) macroinitiator having 2-bromoisobutyryl end groups, followed by the end-capping reaction with allyltributylstannane. The subsequent RCM of the allyl-telechelic block copolymers under dilution in the presence of Grubbs catalyst could afford the corresponding A−B type cycl...

69 citations

Journal ArticleDOI
TL;DR: Fluorescent single crystals of 9,10-dibromoanthracene are elastically bendable and stretchable, which allows a detailed investigation of the deformation behavior.
Abstract: Elastic organic crystals have attracted considerable attention as next-generation flexible smart materials. However, the detailed information on both molecular packing change and macroscopic mechanical crystal deformations upon applied stress is still insufficient. Herein, we report that fluorescent single crystals of 9,10-dibromoanthracene are elastically bendable and stretchable, which allows a detailed investigation of the deformation behavior. We clearly observed a Poisson effect for the crystal, where the short axes (b and c-axes) of the crystal are contracted upon elongation along the long axis (a-axis). Moreover, we found that the Poisson's ratios along the b-axis and c-axis are largely different. Theoretical molecular simulation suggests that the tilting motion of the anthracene may be responsible for the large deformation along the c-axis. Spatially resolved photoluminescence (PL) measurement of the bent elastic crystals reveals that the PL spectra at the outer (elongated), central (neutral), and inner (contracted) sides are different from each other.

61 citations

Journal ArticleDOI
TL;DR: Focusing on fluorescent organic single crystals based on thiophene-tetrafluorobenzene-thiophene derivatives resulted in reversible change of the morphology and fluorescence (mechanofluorochromism), which would lead to the next generation solid-state fluorescent and/or semiconducting materials.
Abstract: Organic single crystals with elastic bending flexibility are rare because they are generally brittle. We report here fluorescent organic single crystals based on thiophene-tetrafluorobenzene-thiophene derivatives, mainly 1,4-bis(thien-2-yl)-2,3,5,6-tetrafluorobenzene. Three derivatives were synthesized by Pd-catalyzed cross-coupling reactions (Stille or direct arylation pathways). The crystallization of the derivatives gave large (mm- or cm-scale) crystals. Two crystals of 1,4-bis(thien-2-yl)-2,3,5,6-tetrafluorobenzene, 1, and 1,4-bis(4-methylthien-2-yl)-2,3,5,6-tetrafluorobenzene, 3, bent under applied stress and quickly recovered its original shape upon relaxation. The other crystal of 1,4-bis(5-methylthien-2-yl)-2,3,5,6-tetrafluorobenzene, 2, showed brittle breakage under applied stress (normal behavior). Fibril lamella crystal structure based on criss-cross packed slip-stacked molecular wires and its structural integrity are important factors for the design and production of next generation crystal materials with elastic bending flexibility. Furthermore, mechanical bending-relaxation resulted in reversible change of the morphology and fluorescence (mechanofluorochromism). Such bendable crystals would lead to the next generation solid-state fluorescent and/or semiconducting materials.

58 citations


Cited by
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TL;DR: The current status and future perspectives in atom transfer radical polymerization (ATRP) are presented in this paper, with a special emphasis on mechanistic understanding of ATRP, recent synthetic and process development, and new controlled polymer architectures enabled by ATRP.
Abstract: Current status and future perspectives in atom transfer radical polymerization (ATRP) are presented. Special emphasis is placed on mechanistic understanding of ATRP, recent synthetic and process development, and new controlled polymer architectures enabled by ATRP. New hybrid materials based on organic/inorganic systems and natural/synthetic polymers are presented. Some current and forthcoming applications are described.

2,188 citations

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TL;DR: This review discusses advances in synthetic organic electrochemistry since 2000 with enabling methods and synthetic applications analyzed alongside innate advantages as well as future challenges of electroorganic chemistry.
Abstract: Electrochemistry represents one of the most intimate ways of interacting with molecules. This review discusses advances in synthetic organic electrochemistry since 2000. Enabling methods and synthetic applications are analyzed alongside innate advantages as well as future challenges of electroorganic chemistry.

1,930 citations

Journal ArticleDOI
TL;DR: This review provides an overview on the use of anodic electrochemical methods for expediting the development of carbon-hydrogen functionalization and carbon-nitrogen bond formation strategies and aims to provide inspiration for future synthetic applications in the field of electrosynthesis.
Abstract: Conventional methods for carrying out carbon–hydrogen functionalization and carbon–nitrogen bond formation are typically conducted at elevated temperatures, and rely on expensive catalysts as well as the use of stoichiometric, and perhaps toxic, oxidants. In this regard, electrochemical synthesis has recently been recognized as a sustainable and scalable strategy for the construction of challenging carbon–carbon and carbon–heteroatom bonds. Here, electrosynthesis has proven to be an environmentally benign, highly effective and versatile platform for achieving a wide range of nonclassical bond disconnections via generation of radical intermediates under mild reaction conditions. This review provides an overview on the use of anodic electrochemical methods for expediting the development of carbon–hydrogen functionalization and carbon–nitrogen bond formation strategies. Emphasis is placed on methodology development and mechanistic insight and aims to provide inspiration for future synthetic applications in the field of electrosynthesis.

626 citations

Journal ArticleDOI
TL;DR: The progress of CMP research since its beginnings is reviewed and an outlook for where these materials might be headed in the future is offered.
Abstract: Conjugated microporous polymers (CMPs) are a unique class of materials that combine extended π-conjugation with a permanently microporous skeleton. Since their discovery in 2007, CMPs have become established as an important subclass of porous materials. A wide range of synthetic building blocks and network-forming reactions offers an enormous variety of CMPs with different properties and structures. This has allowed CMPs to be developed for gas adsorption and separations, chemical adsorption and encapsulation, heterogeneous catalysis, photoredox catalysis, light emittance, sensing, energy storage, biological applications, and solar fuels production. Here we review the progress of CMP research since its beginnings and offer an outlook for where these materials might be headed in the future. We also compare the prospect for CMPs against the growing range of conjugated crystalline covalent organic frameworks (COFs).

620 citations

Journal ArticleDOI
TL;DR: The electrochemical formation of the aryl-substrate bond is discussed for aromatic substrates, heterocycles, other multiple bond systems, and even at saturated carbon substrates.
Abstract: Arylated products are found in various fields of chemistry and represent essential entities for many applications. Therefore, the formation of this structural feature represents a central issue of contemporary organic synthesis. By the action of electricity the necessity of leaving groups, metal catalysts, stoichiometric oxidizers, or reducing agents can be omitted in part or even completely. The replacement of conventional reagents by sustainable electricity not only will be environmentally benign but also allows significant short cuts in electrochemical synthesis. In addition, this methodology can be considered as inherently safe. The current survey is organized in cathodic and anodic conversions as well as by the number of leaving groups being involved. In some electroconversions the reagents used are regenerated at the electrode, whereas in other electrotransformations free radical sequences are exploited to afford a highly sustainable process. The electrochemical formation of the aryl–substrate bond ...

510 citations