Faculty Profiles - YAMAGUCHI, Shigehiro

Papers - YAMAGUCHI, Shigehiro

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ESIPT-active organic compounds with white luminescence based on crystallization-induced keto emission (CIKE)

Huapeng Liu, Xiao Cheng, Houyu Zhang, Yue Wang, Hongyu Zhang, Shigehiro Yamaguchi

CHEMICAL COMMUNICATIONS Vol. 53 ( 55 ) page： 7832 - 7835 2017.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Structurally simple pyrazole derivatives that exhibit excited-state intramolecular proton transfer (ESIPT) were synthesized. While these compounds displayed deep violet fluorescence in solution, in the crystalline state they showed white emission from the enol and keto forms.

DOI： 10.1039/c7cc03758a

Structures and Physical Properties of Chemically Reduced Diindenosiloles and Their pi-Extended Derivatives

Ryo Takano, Ryo Shintani, Aiko Fukazawa, Shigehiro Yamaguchi, Koji Nakabayashi, Shin-ichi Ohkoshi, Kyoko Nozaki

ORGANOMETALLICS Vol. 36 ( 14 ) page： 2646 - 2653 2017.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Diindenosilole Si1, a silicon-bridged fulvalene derivative, was successfully reduced to its dianions using various alkali metals, and the structures were characterized by X-ray crystallographic analysis. Radical anions of Si1 as well as dianions of pi-extended Si3 could also be synthesized, and the structural and physical properties were systematically compared. It was also found that the NMR spectra of dianions Si1(2-) and Si3(2-) show countercation and temperature dependency for their signal broadness, indicating the possible existence of thermal interconversion between closed-shell singlet states and open-shell triplet states.

DOI： 10.1021/acs.organomet.7b00260

A Near-Infrared Dye That Undergoes Multiple Interconversions through Acid-Base Equilibrium and Reversible Redox Processes Reviewed

Kengo Asai, Aiko Fukazawa, Shigehiro Yamaguchi

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Vol. 56 ( 24 ) page： 6848 - 6852 2017.6

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

A near-infrared (NIR) polymethine dye (1), consisting of a cyclohepta[1,2-b; 4,3-b'] dithiophene and two phenol moieties, was synthesized. This dye exhibited pH-responsive changes in its photophysical properties due to a two-step acid-base equilibrium that produced a protonated cation (1H(+)) and an anion (1(-)). While 1H(+) showed an intense fluorescence in the red region of the visible spectrum, 1(-) exhibited a strong absorption in the NIR region. The tropylium ion character in 1H(+) induces high pK(a1) and pK(a2) values for 1. Moreover, a stable radical (1(center dot)) was prepared, which showed a NIR absorption band with a maximum at circa 1600 nm. The cyclic voltammogram of 1(center dot) revealed a two-step reversible redox process that produced 1(-) and the cation 1(+), which is different from 1H(+). These redox processes accompany drastic electrochromic changes in the vis-NIR region. Overall, 1 is susceptible to multiple interconversions between five forms, due to the multifaceted character of the cycloheptadithiophene skeleton.

DOI： 10.1002/anie.201702140

Flapping viscosity probe that shows polarity-independent ratiometric fluorescence

Ryota Kotani, Hikaru Sotome, Hajime Okajima, Soichi Yokoyama, Yumi Nakaike, Akihiro Kashiwagi, Chigusa Mori, Yuki Nakada, Shigehiro Yamaguchi, Atsuhiro Osuka, Akira Sakamoto, Hiroshi Miyasaka, Shohei Saito

JOURNAL OF MATERIALS CHEMISTRY C Vol. 5 ( 21 ) page： 5248 - 5256 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

A variety of fluorescent molecular viscosity probes have been widely used for mapping the local viscosity in cells and for monitoring the microenvironments in materials. However, their viscosity-sensing structural design still relies strongly on molecular rotors featuring intramolecular rotational dynamics. Here we report flapping molecules (FLAP) as a ratiometric viscosity-sensing fluorophore that shows polarity-independent dual fluorescence. Viscosity-sensing mechanism is based on a unique V-shaped-to-planar conformational change in the singlet excited state (S-1), in which the flexible motion of an eight-membered ring plays an important role. Fast conformational dynamics have been studied by time-resolved spectroscopies, and the viscochromic properties have been quantitatively analyzed. Application of FLAP to monitoring the curing process of epoxy resins has also been demonstrated, in which other typical environment-sensitive dyes did not work as a local viscosity probe.

DOI： 10.1039/c7tc01533j

Synthesis and Physical Properties of Strained Doubly Phosphorus-Bridged Biaryls and Viologens

Tobias W. Greulich, Eriko Yamaguchi, Carsten Doerenkamp, Maximilian Luebbesmeyer, Constantin G. Daniliuc, Aiko Fukazawa, Hellmut Eckert, Shigehiro Yamaguchi, Armido Studer

CHEMISTRY-A EUROPEAN JOURNAL Vol. 23 ( 25 ) page： 6029 - 6033 2017.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

New P/N-containing -electron systems comprising fully planar biaryl arrays are synthesized by multiple radical phosphanylation. The biaryl moiety in these highly strained planar -systems is rigidified by double P-bridging. The electronic properties of the core biaryl entity are varied by introducing N-donor substituents or by installing N-atoms within the -system, thereby moving to the viologen core structure. The electrochemical and photophysical properties of these compounds are discussed and compared with those of related systems.

DOI： 10.1002/chem.201605272

Facile Synthesis of Polycyclic Pentalenes with Enhanced Huckel Antiaromaticity

Hiroya Oshima, Aiko Fukazawa, Shigehiro Yamaguchi

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Vol. 56 ( 12 ) page： 3270 - 3274 2017.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

Pentalenes represent highly reactive Huckel antiaromatics with 8 pi electrons. Usually, pentalenes are stabilized by incorporation of two benzene rings in a fused fashion. In dibenzo[a,e]pentalenes, however, the high aromaticity of the fused benzene rings compromises the inherent antiaromaticity of the pentalene core. Herein, we disclose that this forfeited antiaromaticity can be restored by fusing four additional aromatic rings onto the peripheral positions of dibenzo[ a, e]pentalenes. Such polycyclic pentalenes were prepared by successive transannular cyclizations via in situ-generated tetrakisdehydro[16]annulenes. The thus obtained compounds showed intriguing properties, for example, characteristic absorptions in the visible-to-near-infrared (NIR) region and low reduction potentials. These results hence afford a design principle to produce highly antiaromatic yet stable pentalenes. The antiaromaticity of the pentalene core can be widely tuned via the degree of aromaticity of the peripherally fused rings.

DOI： 10.1002/anie.201611344

Color-tunable fluorescent nanoparticles encapsulating trialkylsilyl-substituted pyrene liquids

Masayasu Taki, Saki Azeyanagi, Kenzo Hayashi, Shigehiro Yamaguchi

JOURNAL OF MATERIALS CHEMISTRY C Vol. 5 ( 8 ) page： 2142 - 2148 2017.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

The development of emissive liquid dyes containing trialkylsilyl groups, and their use in the preparation of fluorescent organic nanoparticles (FONs) are described. A series of trialkylsilyl-substituted pyrenes is synthesized as oils, whose viscosity depends on the nature of the alkyl groups. The neat compounds show intense excimer emission with maxima of around 460-480 nm and quantum yields of 0.5-0.7. The low viscosity (eta = 162 cP) of 2-tri((Z)-3-hexen-1-yl)silylpyrene (1) allows the preparation of spherical nanoparticles (NP1) in the presence of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and cholesterol. NP1 shows a hydrodynamic diameter of 161 +/- 48 nm and maintains an excimer emission similar to that of neat 1. NP1 in water spontaneously absorbs dopant dyes into its liquid core, and simultaneous doping with two dyes is also possible. When using green-emissive C545T and red-emissive DCJTB dyes as dopants, efficient Forster resonance energy transfer (FRET) occurs from the pyrene excimer to the dyes. Extensive emission color tuning is thus achieved as evident from a plot of the emission colors of doped and undoped NP1 on the CIE 1931 xy chromaticity diagram. These results demonstrate the efficacy of the present design strategy for color-tunable FONs that do not require premixing of dopant dyes.

DOI： 10.1039/c6tc05208h

Color-tunable fluorescent nanoparticles encapsulating trialkylsilyl-substituted pyrene liquids

Masayasu Taki, Saki Azeyanagi, Kenzo Hayashi, Shigehiro Yamaguchi, Shigehiro Yamaguchi

Journal of Materials Chemistry C Vol. 5 page： 2142 - 2148 2017.1

© The Royal Society of Chemistry. The development of emissive liquid dyes containing trialkylsilyl groups, and their use in the preparation of fluorescent organic nanoparticles (FONs) are described. A series of trialkylsilyl-substituted pyrenes is synthesized as oils, whose viscosity depends on the nature of the alkyl groups. The neat compounds show intense excimer emission with maxima of around 460-480 nm and quantum yields of 0.5-0.7. The low viscosity (η = 162 cP) of 2-tri((Z)-3-hexen-1-yl)silylpyrene (1) allows the preparation of spherical nanoparticles (NP1) in the presence of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and cholesterol. NP1 shows a hydrodynamic diameter of 161 ± 48 nm and maintains an excimer emission similar to that of neat 1. NP1 in water spontaneously absorbs dopant dyes into its liquid core, and simultaneous doping with two dyes is also possible. When using green-emissive C545T and red-emissive DCJTB dyes as dopants, efficient Förster resonance energy transfer (FRET) occurs from the pyrene excimer to the dyes. Extensive emission color tuning is thus achieved as evident from a plot of the emission colors of doped and undoped NP1 on the CIE 1931 xy chromaticity diagram. These results demonstrate the efficacy of the present design strategy for color-tunable FONs that do not require premixing of dopant dyes.

DOI： 10.1039/c6tc05208h

Quantum Dots Embedded in Graphene Nanoribbons by Chemical Substitution Reviewed

Eduard Carbonell-Sanroma, Pedro Brandimarte, Richard Balog, Martina Corso, Shigeki Kawai, Aran Garcia-Lekue, Shohei Saito, Shigehiro Yamaguchi, Ernst Meyer, Daniel Sanchez-Portal, Jose Ignacio Pascual

NANO LETTERS Vol. 17 ( 1 ) page： 50 - 56 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Bottom-up chemical reactions of selected molecular precursors on a gold surface can produce high quality graphene nanoribbons (GNRs). Here, we report on the formation of quantum dots embedded in an armchair GNR by substitutional inclusion of pairs of boron atoms into the GNR backbone. The boron inclusion is achieved through the addition of a small amount of boron substituted precursors during the formation of pristine GNRs. In the pristine region between two boron pairs, the nanoribbons show a discretization of their valence band into confined modes compatible with a Fabry-Perot resonator. Transport simulations of the scattering properties of the boron pairs reveal that they selectively confine the first valence band of the pristine ribbon while allowing an efficient electron transmission of the second one. Such band-dependent electron scattering stems from the symmetry matching between the electronic wave functions of the states from the pristine nanoribbons and those localized at the boron pairs.

DOI： 10.1021/acs.nanolett.6b03148

Steric Shielding vs Structural Constraint in a Boron-Containing Polycyclic Aromatic Hydrocarbon Reviewed

V. M. Hertz, N. Ando, M. Hirai, M. Bolte, H.-W. Lerner, S. Yamaguchi, M. Wagner

Organometallics 2016.12

Stable Red-Emissive Cationic Dithienotropylium Dyes Reviewed

Kengo Asai, Aiko Fukazawa, Shigehiro Yamaguchi

CHEMISTRY-A EUROPEAN JOURNAL Vol. 22 ( 49 ) page： 17571 - 17575 2016.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

A series of thiophene-fused tropylium ions, containing various electron-donating amino groups at the terminal positions, was synthesized. The fusion of the thiophene rings, as well as the presence of the terminal amino groups endows the cationic tropylium ion with excellent stability and high pK(R)(+) values. X-ray crystallographic analysis of these compounds revealed a pronounced quinoidal character for the amino-substituted dithienotropylium skeletons. These compounds exhibit attractive photophysical properties such as strong absorption in the visible region combined with red fluorescence. Theoretical calculations suggested that the 3,3'-bithiophene substructure should be crucial for attaining these photophysical properties.

DOI： 10.1002/chem.201604509

A Soluble Dynamic Complex Strategy for the Solution-Processed Fabrication of Organic Thin-Film Transistors of a Boron-Containing Polycyclic Aromatic Hydrocarbon Reviewed

K. Matsuo, S. Saito, S. Yamaguchi

Angew. Chem. Int. Ed. Vol. 55 ( 39 ) page： 11984 - 11988 2016.9

Light-melt adhesive based on dynamic carbon frameworks in a columnar liquid-crystal phase Reviewed

Shohei Saito, Shunpei Nobusue, Eri Tsuzaka, Chunxue Yuan, Chigusa Mori, Mitsuo Hara, Takahiro Seki, Cristopher Camacho, Stephan Irle, Shigehiro Yamaguchi

NATURE COMMUNICATIONS Vol. 7 page： 12094 2016.7

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Liquid crystal (LC) provides a suitable platform to exploit structural motions of molecules in a condensed phase. Amplification of the structural changes enables a variety of technologies not only in LC displays but also in other applications. Until very recently, however, a practical use of LCs for removable adhesives has not been explored, although a spontaneous disorganization of LC materials can be easily triggered by light-induced isomerization of photoactive components. The difficulty of such application derives from the requirements for simultaneous implementation of sufficient bonding strength and its rapid disappearance by photoirradiation. Here we report a dynamic molecular LC material that meets these requirements. Columnar-stacked V-shaped carbon frameworks display sufficient bonding strength even during heating conditions, while its bonding ability is immediately lost by a light-induced self-melting function. The light-melt adhesive is reusable and its fluorescence colour reversibly changes during the cycle, visualizing the bonding/nonbonding phases of the adhesive.

DOI： 10.1038/ncomms12094

A Macrocyclic Fluorophore Dimer with Flexible Linkers: Bright Excimer Emission with a Long Fluorescence Lifetime Reviewed

Hiroshi Osaki, Chih-Ming Chou, Masayasu Taki, Kai Welke, Daisuke Yokogawa, Stephan Irle, Yoshikatsu Sato, Tetsuya Higashiyama, Shohei Saito, Aiko Fukazawa, Shigehiro Yamaguchi

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Vol. 55 ( 25 ) page： 7131 - 7135 2016.6

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

Bright fluorescent molecules with long fluorescence lifetimes are important for the development of lifetime-based fluorescence imaging techniques. Herein, a molecular design is described for simultaneously attaining long fluorescence lifetime (tau) and high brightness (Phi(F) x epsilon) in a system that features macrocyclic dimerization of fluorescent p-conjugated skeletons with flexible linkers. An alkylene-linked macrocyclic dimer of bis(thienylethynyl)anthracene was found to show excimer emission with a long fluorescence lifetime (tau approximate to 19 ns) in solution, while maintaining high brightness. A comparison with various relevant derivatives revealed that the macrocyclic structure and the length of the alkylene chains play crucial roles in attaining these properties. In vitro time-gated imaging experiments were conducted as a proof-of-principle for the superiority of this macrocyclic fluorophore relative to the commercial fluorescent dye Alexa Fluor 488.

DOI： 10.1002/anie.201602239

Pyridyl Directed Catalyst-Free trans-Hydroboration of Internal Alkynes Reviewed

Kang Yuan, Naoya Suzuki, Soren K. Mellerup, Xiang Wang, Shigehiro Yamaguchi, Suning Wang

ORGANIC LETTERS Vol. 18 ( 4 ) page： 720 - 723 2016.2

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

We report the first examples of straightforward trans-hydroboration of internal alkynes at room temperature with 9-BBN, producing five-membered BN-heterocycles. Contrary to conventional cis-hydroboration, we demonstrate that the introduction of a pyridyl group switches the stereoselectivity of the reaction. A hydride migration mechanism has been proposed and supported by DFT calculations for the trans-hydroboration. This new hydroboration approach allows facile construction of new blue fluorescent BN-heterocyclic compounds.

DOI： 10.1021/acs.orglett.5b03698

Phospha-fluorescein: a red-emissive fluorescein analogue with high photobleaching resistance Reviewed

Aiko Fukazawa, Shinji Suda, Masayasu Taki, Eriko Yamaguchi, Marek Grzybowski, Yoshikatsu Sato, Tetsuya Higashiyama, Shigehiro Yamaguchi

CHEMICAL COMMUNICATIONS Vol. 52 ( 6 ) page： 1120 - 1123 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Phospha-fluorescein (POF), a phosphine oxide-containing analogue of fluorescein, was synthesized and its photophysical properties were examined. Compared with fluorescein and sila-fluorescein, POF displayed significantly red-shifted absorption and fluorescence as well as superior photobleaching resistance, while retaining the pH-responsive characteristics of fluorescein dyes.

DOI： 10.1039/c5cc09345g

A biphenyl containing two electron-donating and two electron-accepting moieties: a rigid and small donor-acceptor-donor ladder system Reviewed

Tobias W. Greulich, Naoya Suzuki, Constantin G. Daniliuc, Aiko Fukazawa, Eriko Yamaguchi, Armido Studer, Shigehiro Yamaguchi

CHEMICAL COMMUNICATIONS Vol. 52 ( 11 ) page： 2374 - 2377 2016

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Ladder pi-conjugated materials and also push-pull systems belong to important classes of compounds for the development of organic electronic devices. In this communication, a novel pi-conjugated material that unifies the properties of both of these classes is presented. The material comprises a rigid biphenyl framework, which bears two bridging electron-accepting phosphine oxide moieties as well as two electron-donating amino groups. The structure and photophysical properties of this compound are discussed and compared with those of a related system lacking the second P-moiety.

DOI： 10.1039/c5cc03063c

A planarized 9-phenylanthracene: a simple electron-donating building block for fluorescent materials Reviewed

Hideaki Iwahara, Tomokatsu Kushida, Shigehiro Yamaguchi

CHEMICAL COMMUNICATIONS Vol. 52 ( 6 ) page： 1124 - 1127 2016

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

A 9-phenylanthracene, constrained in a coplanar fashion by two methylene tethers, was synthesized and its optoelectronic properties were investigated. The rigid planarization increased its electron-donating character and induced a bathochromic shift of its absorption, as well as an increased molar absorption coefficient and intense fluorescence. These properties render this compound a promising building block for fluorescent materials.

DOI： 10.1039/c5cc08259e

Boron-doped nanographene: Lewis acidity, redox properties, and battery electrode performance Reviewed

Shinichiro Osumi, Shohei Saito, Chuandong Dou, Kyohei Matsuo, Keita Kume, Hirofumi Yoshikawa, Kunio Awagaa, Shigehiro Yamaguchi

CHEMICAL SCIENCE Vol. 7 ( 1 ) page： 219 - 227 2016

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

The preparation of boron-doped nanocarbon scaffolds with well-defined structures is important for the understanding of the impact of boron doping on their properties and behavior at the molecular level. We recently succeeded in the synthesis of a structurally well-defined nanographene molecule, bearing two boron atoms at the central positions. In this study, the characteristic properties and functions of this boron-doped nanographene were investigated in terms of (1) Lewis acidity, (2) redox properties, and (3) electrode performance in a battery. This boron-doped nanographene was susceptible to chemical adsorption with various Lewis bases, resulting in significant changes in the absorption and fluorescence properties, as well as in the conformation of the honeycomb framework. The two-electron reduction of this boron-doped nanographene produced a dianionic species that showed a substantial biradical character with a triplet ground state. A Li battery electrode, composed of a boron-doped nanographene with small peripheral substituents, displayed a stable performance in the 1.5-4.0 V range with a first discharge capacity of 160 mA h g(-1). These results provide important insights into the effect of boron doping on nanocarbon compounds.

DOI： 10.1039/c5sc02246k

A Phosphole Oxide Based Fluorescent Dye with Exceptional Resistance to Photobleaching: A Practical Tool for Continuous Imaging in STED Microscopy Reviewed

Chenguang Wang, Aiko Fukazawa, Masayasu Taki, Yoshikatsu Sato, Tetsuya Higashiyama, Shigehiro Yamaguchi

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Vol. 54 ( 50 ) page： 15213 - 15217 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

The development of stimulated emission depletion (STED) microscopy represented a major breakthrough in cellular and molecular biology. However, the intense laser beams required for both excitation and STED usually provoke rapid photobleaching of fluorescent molecular probes, which significantly limits the performance and practical utility of STED microscopy. We herein developed a photoresistant fluorescent dye C-Naphox as a practical tool for STED imaging. With excitation using either a lambda = 405 or 488 nm laser in protic solvents, C-Naphox exhibited an intense red/orange fluorescence (quantum yield phi(F) > 0.7) with a large Stokes shift (circa 5900 cm(-1)). Even after irradiation with a Xe lamp (300 W, lambda(ex) = 460 nm, full width at half maximum (FWHM) = 11 nm) for 12 hours, 99.5 % of C-Naphox remained intact. The high photoresistance of C-Naphox allowed repeated STED imaging of HeLa cells. Even after recording 50 STED images, 83 % of the initial fluorescence intensity persisted.

DOI： 10.1002/anie.201507939

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