Faculty Profiles - YAMAGUCHI, Shigehiro

Papers - YAMAGUCHI, Shigehiro

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Antiaromatic Dithieno-1,2-dihydro-1,2-diborin Splits Diatomic Hydrogen Open Access

Takafumi Araki, Masato Hirai, Atsushi Wakamiya, Warren E. Piers, Shigehiro Yamaguchi

CHEMISTRY LETTERS Vol. 46 ( 12 ) page： 1714 - 1717 2017.12

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

B,B-Dimesityl-substituted dithieno-1,2-dihydro-1,2-diborin was synthesized and its properties and reactivity were studied. Owing to the noticeably electron-deficient and antiaromatic character of the 1,2-dihydro-1,2-diborin ring, this compound was found to homolytically cleave diatomic hydrogen (H-2) gas at ambient temperature under 1 atm to afford a hydrogen-bridged bis(borane). This reaction was accompanied by a dramatic color change from dark green to yellow in addition to a turn-on fluorescence response.

DOI： 10.1246/cl.170812

Phosphole P-Oxide-Containing pi-Electron Materials: Synthesis and Applications in Fluorescence Imaging Open Access

Yamaguchi Shigehiro, Fukazawa Aiko, Taki Masayasu

JOURNAL OF SYNTHETIC ORGANIC CHEMISTRY JAPAN Vol. 75 ( 11 ) page： 1179-1187 2017.11

Structural Monitoring of the Onset of Excited-State Aromaticity in a Liquid Crystal Phase

Masaki Hada, Shohei Saito, Sei'ichi Tanaka, Ryuma Sato, Masahiko Yoshimura, Kazuhiro Mouri, Kyohei Matsuo, Shigehiro Yamaguchi, Mitsuo Hara, Yasuhiko Hayashi, Fynn Roehricht, Rainer Herges, Yasuteru Shigeta, Ken Onda, R. J. Dwayne Miller

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Vol. 139 ( 44 ) page： 15792 - 15800 2017.11

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

Aromaticity of photoexcited molecules is an important concept in organic chemistry. Its theory, Baird's rule for triplet aromaticity since 1972 gives the rationale of photoinduced conformational changes and photochemical reactivities of cyclic pi-conjugated systems. However, it is still challenging to monitor the dynamic structural change induced by the excited-state aromaticity, particularly in condensed materials. Here we report direct structural observation of a molecular motion and a subsequent packing deformation accompanied by the excited-state aromaticity. Photoactive liquid crystal (LC) molecules featuring a pi-expanded cyclooctatetraene core unit are orientationally ordered but loosely packed in a columnar LC phase, and therefore a photoinduced conformational planarization by the excited-state aromaticity has been successfully observed by time-resolved electron diffractometry and vibrational spectroscopy. The structural change took place in the vicinity of excited molecules, producing a twisted stacking structure. A nanoscale torque driven by the excited-state aromaticity can be used as the working mechanism of new photoresponsive materials.

DOI： 10.1021/jacs.7b08021

An Expedient Procedure for the Synthesis of Benzo[4,5]silolo[2,3-b]thiophenes and Related Systems

Susanne Baehr, Hiroaki Ogasawara, Shigehiro Yamaguchi, Martin Oestreich

ORGANOMETALLICS Vol. 36 ( 20 ) page： 4013 - 4019 2017.10

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

The straightforward assembly of various thiophene-fused benzosiloles is accomplished by 2-fold metalation of benzo[b]thiophenes substituted at C3 with ortho-brominated aryl groups followed by electrophilic substitution with dichlorosilanes. The method relies on the innate acidity of the C(sp(2))-H bond at C2 of benzo[b]thiophenes and the halogen-metal exchange of the proximal C(sp(2))-Br bond. The related indole- and benzofuran-annulated systems are also accessible, but these siloles are chemically less stable. An example of a thiophene-fused benzogermole is included as well.

DOI： 10.1021/acs.organomet.7b00619

Boron-Stabilized Planar Neutral pi-Radicals with Well-Balanced Ambipolar Charge-Transport Properties

Tomokatsu Kushida, Shusuke Shirai, Naoki Ando, Toshihiro Okamoto, Hiroyuki Ishi, Hiroyuki Matsui, Masakazu Yamagishi, Takafumi Uemura, Junto Tsurumi, Shun Watanabe, Jun Takeya, Shigehiro Yamaguchi

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Vol. 139 ( 41 ) page： 14336 - 14339 2017.10

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

Organic neutral pi-monoradicals are promising semiconductors with balanced ambipolar carrier transport abilities, which arise from virtually identical spatial distribution of their singly occupied and unoccupied molecular orbitals, SOMO(alpha) and SOMO(beta), respectively. Herein, we disclose a boron-stabilized triphenylmethyl radical that shows outstanding thermal stability and resistance toward atmospheric conditions due to the substantial spin delocalization. The radical is used to fabricate organic Mott-insulator transistors that operate at room temperature, wherein the radical exhibits well-balanced ambipolar carrier transport properties.

DOI： 10.1021/jacs.7b05471

Structural Monitoring of the Onset of Excited-State Aromaticity in a Liquid Crystal Phase Reviewed

Hada, Masaki, Saito, Shohei, Tanaka, Sei'ichi, Sato, Ryuma, Yoshimura, Masahiko, Mouri, Kazuhiro, Matsuo, Kyohei, Yamaguchi, Shigehiro, Hara, Mitsuo, Hayashi, Yasuhiko, Röhricht, Fynn, Herges, Rainer, Shigeta, Yasuteru, Onda, Ken, Miller, R J Dwayne

Journal of the American Chemical Society Vol. 139 page： 15792 - 15800 2017.10

Photochemical Intramolecular C-H Addition of Dimesityl(hetero)arylboranes through a [1,6]-Sigmatropic Rearrangement

Naoki Ando, Aiko Fukazawa, Tomokatsu Kushida, Yoshihito Shiota, Shuhei Itoyama, Kazunari Yoshizawa, Yasunori Matsui, Yutaro Kuramoto, Hiroshi Ikeda, Shigehiro Yamaguchi

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Vol. 56 ( 40 ) page： 12210 - 12214 2017.9

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

A new reaction mode for triarylboranes under photochemical conditions was discovered. Photoirradiation of dimesitylboryl-substituted (hetero)arenes produced spirocyclic boraindanes, where one of the C-H bonds in the ortho-methyl groups of the mesityl substituents was formally added in a syn fashion to a C-C double bond of the (hetero)aryl group. Quantum chemical calculations and laser flash photolysis measurements indicated that the reaction proceeds through a [1,6]-sigmatropic rearrangement. This behavior is reminiscent of the photochemical reaction mode of arylalkenylketones, thus demonstrating the isosteric relation between tricoordinate organoboron compounds and the corresponding pseudo-carbocationic species in terms of pericyclic reactions. Despite the disrupted -conjugation, the resulting spirocyclic boraindanes exhibited a characteristic absorption band at relatively long wavelengths (=370400 nm).

DOI： 10.1002/anie.201706929

Selective Conversion of P=O-Bridged Rhodamines into P=O-Rhodols: Solvatochromic Near-Infrared Fluorophores

Marek Grzybowski, Masayasu Taki, Shigehiro Yamaguchi

CHEMISTRY-A EUROPEAN JOURNAL Vol. 23 ( 53 ) page： 13028 - 13032 2017.9

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

The substitution of an oxygen atom in rhodols with a phosphine oxide (P=O) moiety affords P=O-bridged rhodols as a new type of near-infrared (NIR) fluorophore. This compound class can be readily accessed upon exposure of the corresponding rhodamines to aqueous basic conditions. The electron-withdrawing effect of the P=O group facilitates the hydrolytic deamination, and, moreover, prolonged exposure to aqueous basic conditions generates P=O-bridged fluoresceins, that is, a series of three P=O-bridged xanthene dyes is available in one simple operation. The P=O-bridged rhodols show significant bathochromic shifts of the longest-wavelength absorption maximum (Delta lambda = 125 nm; > 3600 cm(-1)) upon changing the solvent from toluene to water, whereas the emission is shifted less drastically (Delta lambda = 70 nm; 1600 cm @ 1). The hydrogen bonding between the P=O and C=O groups with protic solvents results in substantial stabilization of the LUMO level, which is responsible for the solvatochromism.

DOI： 10.1002/chem.201703456

Photochemical Intramolecular C−H Addition of Dimesityl(hetero)arylboranes through a [1,6]-Sigmatropic Rearrangement Reviewed

Naoki Ando, Aiko Fukazawa, Tomokatsu Kushida, Yoshihito Shiota, Shuhei Itoyama, Kazunari Yoshizawa, Yasunori Matsui, Yutaro Kuramoto, Hiroshi Ikeda, Shigehiro Yamaguchi

Angewandte Chemie Vol. 129 ( 40 ) page： 12378 2017.9

Synthesis of seminaphtho-phospha-fluorescein dyes based on the consecutive arylation of aryldichlorophosphines

Aiko Fukazawa, Junichi Usuba, Raul A. Adler, Shigehiro Yamaguchi

CHEMICAL COMMUNICATIONS Vol. 53 ( 61 ) page： 8565 - 8568 2017.8

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

Seminaphtho-phospha-fluorescein (SNAPF), a phosphine-oxide-containing unsymmetric fluorescein dye, was synthesized based on the consecutive arylation of PhPCl2, followed by Friedel-Crafts cyclization. The resulting SNAPF exhibited several attractive photo-physical properties including an intense fluorescence in the NIR region and a large Stokes shift.

DOI： 10.1039/c7cc04323f

Super-Photostable Phosphole-Based Dye for Multiple-Acquisition Stimulated Emission Depletion Imaging

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

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Vol. 139 ( 30 ) page： 10374 - 10381 2017.8

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

As stimulated emission depletion (STED) microscopy can provide structural details of cells with an optical resolution beyond the diffraction limit, it has become an indispensable tool in cell biology. However, the intense STED laser beam usually causes rapid photobleaching of the employed fluorescent dyes, which significantly limits the utility of STED microscopy from a practical perspective. Herein we report a new design of super-photostable dye, PhoxBright 430 (PB430), comprising a fully ring-fused pi-conjugated skeleton with an electron-accepting phosphole pi-oxide unit. We previously developed a super-photostable dye C-Naphox by combining the phosphole unit with an electron-donating triphenylamine moiety. In PB430, removal of the amino group alters the transition type from intramolecular charge transfer character to pi-pi* transition character, which gives rise to intense fluorescence insensitive to molecular environment in terms of fluorescence colors and intensity, and bright fluorescence even in aqueous media. PB430 also furnishes high solubility in water, and is capable of labeling proteins with maintaining high fluorescence quantum yields. This dye exhibits outstanding resistance to photoirradiation even under the STED conditions and allows continuous acquisition of STED images. Indeed, using a PB430-conjugated antibody, we succeed in attaining a 3-D reconstruction of super-resolution STED images as well as photostability-based multicolor STED imaging of fluorescently labeled cytoskeletal structures.

DOI： 10.1021/jacs.7b04418

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 Open Access

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

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