Faculty Profiles - YAMAGUCHI, Shigehiro

Papers - YAMAGUCHI, Shigehiro

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Photodissociation of B-N Lewis Adducts: A Partially Fused Trinaphthylborane with Dual Fluorescence Reviewed

Kyohei Matsuo, Shohei Saito, Shigehiro Yamaguchi

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Vol. 136 ( 36 ) page： 12580 - 12583 2014.9

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

The synthesis of a planarized trinaphthylborane with partially fused structure is presented. This compound shows not only high chemical and thermal stability but also sufficient Lewis acidity to form Lewis adducts with pyridine derivatives in solution. The BN Lewis adducts exhibit unprecedented photodissociation behavior in the excited state, reminiscent of the photogeneration of carbenium ions from triarylmethane leuco dyes. Consequently, these BN Lewis adducts exhibit dual fluorescence emission arising from the initial tetracoordinate BN adducts and the photodissociated tricoordinate boranes.

DOI： 10.1021/ja506980p

Web of Science

PubMed

Dearomatization-Induced Transannular Cyclization: Synthesis of Electron-Accepting Thiophene-S,S-Dioxide-Fused Biphenylene Reviewed

Aiko Fukazawa, Hiroya Oshima, Soji Shimizu, Nagao Kobayashi, Shigehiro Yamaguchi

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Vol. 136 ( 24 ) page： 8738 - 8745 2014.6

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

The transannular cyclization of dehydroannulenes bearing several alkyne moieties in close proximity is a powerful synthetic method for producing polyc-yclic aromatic hydrocarbons. We report that the reactivity can be switched by the aromaticity of the ring skeletons fused with the dehydroannulene core. Thus, while thiophene-fused bisdehydro[12]annulene 1 was handled as a stable compound in the air at room temperature, the oxidation with m-chloroperbenzoic acid from the aromatic thiophene rings to the nonaromatic thiophene-S,S-dioxides induced the transannular cyclization, even at room temperature, which was completed within 1 day to produce the formal [2 + 2] cycloadduct 3. This is in stark contrast to the fact that the thermal cyclization of 1 itself required heating at 80 C for 9 days for completion. Experimental and theoretical studies indicate that the oxidation of even one thiophene ring in 1 sufficiently decreases the activation barrier for the transannular cyclization that proceeds through the 8 pi and 4 pi electrocyclic reaction sequence. The thiophene-S,S-dioxide-fused biphenylene 3 thus produced exhibits a set of intriguing properties, such as a higher electron affinity (E-1/2 = -1.17 V vs Fc and Fc(+)) and a stronger fluorescence (Phi(F) = 0.20) than the other relevant biphenylene derivatives, which have electron-donating and nonfluorescent characteristics.

DOI： 10.1021/ja503499n

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PubMed

A Strap Strategy for Construction of an Excited-State Intramolecular Proton Transfer (ESIPT) System with Dual Fluorescence Reviewed

N. Suzuki, A. Fukazawa, K. Nagura, S. Saito, H. Kitoh-Nishioka, D. Yokogawa, S. Irle, S. Yamaguchi

Angew. Chem. Int. Ed. Vol. 53 page： 8231-8235 2014.6

A Strap Strategy for Construction of an Excited-State Intramolecular Proton Transfer (ESIPT) System with Dual Fluorescence Reviewed

N. Suzuki, A. Fukazawa, K. Nagura, S. Saito, H. Kitoh-Nishioka, D. Yokogawa, S. Irle, S. Yamaguchi

Angew. Chem. Int. Ed. Vol. 53 page： 8231-8235 2014.6

Dearomatization-Induced Transannular Cyliczation: Synthesis of Electron-Accepting Thiophene-S,S-Dioxide-Fused Biphenylene Reviewed

A. Fukazawa, H. Oshima, S. Shimizu, N. Kobayashi, and S. Yamaguchi

J. Am. Chem. Soc. Vol. 136 page： 8738-8745 2014.6

Heterotriangulenes pi-Expanded at Bridging Positions Reviewed

Chih-Ming Chou, Shohei Saito, Shigehiro Yamaguchi

ORGANIC LETTERS Vol. 16 ( 11 ) page： 2868 - 2871 2014.6

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

A series of nitrogen-containing heterotriangulenes expanded at the bridging positions has been synthesized. Among them, a dibenzo[c,g]fluorenylidene-substituted derivative has a highly twisted conformation for the overcrowded alkene moieties, which impart a highly electron-accepting character to the electron-donating heterotriangulene skeleton and thereby an NIR absorption as well as multiredox properties with a low reduction potential.

DOI： 10.1021/ol501004g

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PubMed

The B(C6F5)(3) Boron Lewis Acid Route to Arene-Annulated Pentalenes Reviewed

Chao Chen, Marcel Harhausen, Aiko Fukazawa, Shigehiro Yamaguchi, Roland Froehlich, Constantin G. Daniliuc, Jeffrey L. Petersen, Gerald Kehr, Gerhard Erker

CHEMISTRY-AN ASIAN JOURNAL Vol. 9 ( 6 ) page： 1671 - 1681 2014.6

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

4,5-Dimethyl-1,2-bis(1-naphthylethynyl)benzene (12) undergoes a rapid multiple ring-closure reaction upon treatment with the strong boron Lewis acid B(C6F5)(3) to yield the multiply annulated, planar conjugated -system 13 (50% yield). In the course of this reaction, a C6F5 group was transferred from boron to carbon. Treatment of 12 with CH3B(C6F5)(2) proceeded similarly, giving a mixture of 13 (C6F5-transfer) and the product 15, which was formed by CH3-group transfer. 1,2-Bis(phenylethynyl)benzene (8a) reacts similarly with CH3B(C6F5)(2) to yield a mixture of the respective C6F5- and CH3-substituted dibenzopentalenes 10a and 16. The reaction is thought to proceed through zwitterionic intermediates that exhibit vinyl cation reactivities. Some B(C6F5)(3)-substituted species (26, 27) consequently formed by in situ deprotonation upon treatment of the respective 1,2-bis(alkynyl)benzene starting materials (24, 8) with the frustrated Lewis pair B(C6F5)(3)/P(o-tolyl)(3). The overall formation of the C6F5-substituted products formally require HB(C6F5)(2) cleavage in an intermediate dehydroboration step. This was confirmed in the reaction of a thienylethynyl-containing starting material 21 with B(C6F5)(3), which gave the respective annulated pentalene product 23 that had the HB(C6F5)(2) moiety 1,4-added to its thiophene ring. Compounds12-14, 23, and 26 were characterized by X-ray diffraction.

DOI： 10.1002/asia.201400096

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PubMed

Heterotriangulenes π-Expanded at Bridging Positions Reviewed

C. -M. Chou, S. Saito, S. Yamaguchi

Org. Lett. Vol. 16 page： 2868-2871 2014.5

Synthesis of Pyridine N-Oxide-BF2CF3 Complexes and Their Fluorescence Properties Reviewed

Tomoaki Nishida, Aiko Fukazawa, Eriko Yamaguchi, Hiroya Oshima, Shigehiro Yamaguchi, Motomu Kanai, Yoichiro Kuninobu

CHEMISTRY-AN ASIAN JOURNAL Vol. 9 ( 4 ) page： 1026 - 1030 2014.4

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

Pyridine N-oxide-BF2CF3 and -BF2C2F5 complexes and their derivatives were synthesized. Most of the complexes show fluorescence both in solution and in the solid state. By expanding the -conjugated skeleton, the color of the fluorescence could be changed dramatically. A fluorophore with a high solvent dependency could also be produced. Since such compounds can be synthesized on a gram scale in high yield, and are stable to oxygen, water, and heat, the complexes hold great potential as organic functional materials.

DOI： 10.1002/asia.201301688

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PubMed

Hybridization of a Flexible Cyclooctatetraene Core and Rigid Aceneimide Wings for Multiluminescent Flapping pi Systems Reviewed

Chunxue Yuan, Shohei Saito, Cristopher Camacho, Tim Kowalczyk, Stephan Irle, Shigehiro Yamaguchi

CHEMISTRY-A EUROPEAN JOURNAL Vol. 20 ( 8 ) page： 2193 - 2200 2014.2

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

The hybridization of flexible and rigid -conjugated frameworks is a potent concept for producing new functional materials. In this article, a series of multifluorescent flapping systems that combine a flexible cyclooctatetraene (COT) core and rigid aceneimide wings with various -conjugation lengths has been designed and synthesized, and their structure/properties relationships have been investigated. Whereas these molecules have a V-shaped bent conformation in the ground state, the bent structure changes to a planar conformation in the lowest excited singlet (S-1) state irrespective of the lengths of the aceneimide wings. However, the fluorescence behavior in solution is distinct between the naphthaleneimide system and the anthraceneimide system. The former has a nonemissive S-1 state owing to the significant contribution of the antiaromatic character of the planar COT frontier molecular orbitals, thereby resulting in complete fluorescence quenching in solution. In contrast, the latter anthraceneimide system shows an intense emission, which is ascribed to the planar but distorted S-1 state that shows the allowed transition between the -molecular orbitals delocalized over the COT core and the acene wings. The other characteristic of these systems is the significantly redshifted fluorescence in the crystalline state relative to their monomer fluorescence. The relationship between the packing structures and the fluorescence properties was investigated by preparing a series of hybrid systems with different sizes of substituents on the imide moieties, which revealed the effect of the twofold -stacked structure of the V-shaped molecules on the large bathochromic shift in emission.

DOI： 10.1002/chem.201303955

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PubMed

Hydroxyphenyl-Substituted Benzophosphole Oxides: Impact of the Intramolecular Hydrogen Bond on the Fluorescence Properties

Fukazawa Aiko, Osaki Hiroshi, Yamaguchi Shigehiro

ASIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 3 ( 2 ) page： 122 - 127 2014.2

Hydroxyphenyl-Substituted Benzophosphole Oxides: Impact of the Intramolecular Hydrogen Bond on the Fluorescence Properties Reviewed

Aiko Fukazawa, Hiroshi Osaki, Shigehiro Yamaguchi

ASIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 3 ( 2 ) page： 122 - 127 2014.2

COD ID: 4120128 Reviewed

Nagura Kazuhiko, Saito Shohei, Yusa Hitoshi, Yamawaki Hiroshi, Fujihisa Hiroshi, Sato Hiroyasu, Shimoikeda Yuichi, Yamaguchi Shigehiro

Crystallography Open Database 2014

Constraint-induced structural deformation of planarized triphenylboranes in the excited state Reviewed

Tomokatsu Kushida, Cristopher Camacho, Ayumi Shuto, Stephan Irle, Masayasu Muramatsu, Tetsuro Katayama, Syoji Ito, Yutaka Nagasawa, Hiroshi Miyasaka, Eri Sakuda, Noboru Kitamura, Zhiguo Zhou, Atsushi Wakamiya, Shigehiro Yamaguchi

CHEMICAL SCIENCE Vol. 5 ( 4 ) page： 1296 - 1304 2014

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

Triphenylboranes planarized with three methylene bridges exhibited dual fluorescence bands around 340 and 400 nm despite their structural constraint. To elucidate the origin, their excited state dynamics were experimentally and theoretically studied. The measurements of fluorescence lifetimes and transient absorption spectra indicated that the planarized triphenylboranes adopt two local minimum structures in the lowest-energy excited singlet (S-1) state. The TD-DFT potential energy surface of the S-1 state possesses at least two minimum energy structures associated with a planar and a bowl-shaped molecular structure. The theoretical S-1-S-0 transition energies at these geometries were in good agreement with the experimentally observed values. These results indicated that the plane-to-bowl structural relaxation in the S-1 state is the origin of the dual fluorescence. Based on the calculated partial atomic charge on the boron atom, the structural deformation to the bowl-shaped structure results in an increase in the electron density on the boron center. Thus, the enhanced intramolecular charge-transfer character plays a role in this structural deformation. Similar behavior was also observed for trigonally pi-expanded planarized borane derivatives. These results provide an important implication that structural constraint in a planar fashion is not only a strategy to construct a rigid skeleton, but also a viable mechanism to impart flexibility to the skeleton.

DOI： 10.1039/c3sc52751d

Web of Science

pi-Extended Planarized Triphenylboranes with Thiophene Spacers

Ayumi Shuto, Tomokatsu Kushida, Tatsuya Fukushima, Hironori Kaji, Shigehiro Yamaguchi

ORGANIC LETTERS Vol. 15 ( 24 ) page： 6234 - 6237 2013.12

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

Planarized triphenylboranes extended with thiophene or bithiophene spacers were synthesized, which showed intense fluorescences in solution and reversible redox waves for reduction in cyclic voltammetry. Organic light-emitting diodes (OLEDs) using these compounds as an electron-transporting material were fabricated.

DOI： 10.1021/ol403084x

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PubMed

Modification and Unexpected Reactivity of 2-Borylbenzaldimines: Acylated and Silylated Derivatives as Well as Dimeric Compounds

Benedikt Neue, Atsushi Wakarniya, Roland Froehlich, Birgit Wibbeling, Shigehiro Yamaguchi, Ernst-Ulrich Wuerthwein

JOURNAL OF ORGANIC CHEMISTRY Vol. 78 ( 23 ) page： 11747 - 11755 2013.12

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

Various novel N-alkyl and N-benzyl 2-borylbenzaldimines 3 were prepared by condensation of 2-(dimesitylboryl)benzaldehyde (1) with amines. Further functionalization of compound 3e was possible by deprotonation and subsequent regioselective reaction with electrophiles to give compounds 4. Applying similar conditions to 3a led to the unexpected formation of hitherto unknown dimeric compounds (5 and 6). All structural types were fully characterized, including by X-ray diffraction (XRD). Furthermore, quantum chemical calculations on the SCS-MP2 and DFT levels gave insights into the reaction mechanisms and the stereoselectivity. The BIN bonding situation in these molecules was analyzed using Wiberg bond indices. Preliminary UV-vis and fluorescence measurements indicate that the substitution reaction leading to compounds 4 can be utilized to tune the photophysical properties of these compounds.

DOI： 10.1021/jo401748d

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PubMed

A Radical Anion of Structurally Constrained Triphenylborane

Tomokatsu Kushida, Shigehiro Yamaguchi

ORGANOMETALLICS Vol. 32 ( 22 ) page： 6654 - 6657 2013.11

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

Chemical reduction of the structurally constrained triphenylborane 1 with K produced a radical anion. EPR analysis demonstrated the delocalization of the unpaired electron spin density over the entire pi skeleton to a greater extent than is the case for a nonconstrained Ph3B radical anion. DFT calculations indicated that the coplanarization of the benzene rings with the boron plane and the shortening of the B-C bond lengths by the structural constraint are responsible for the spin delocalization. The geometry optimization also suggested a bowl-shaped conformation as a viable local minimum structure in addition to the planar conformation. X-ray crystal structure analysis indeed revealed the nonplanar structure of the radical anion 1(center dot-).

DOI： 10.1021/om400560u

Web of Science

Diarylated Bi(thieno[2,3-c]thiophene)s: A Ring-Fusing Strategy for Controlling the Molecular Alignment of Oligoarenes Reviewed

Aiko Fukazawa, Daisuke Kishi, Yuki Tanaka, Shu Seki, Shigehiro Yamaguchi

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Vol. 52 ( 46 ) page： 12091 - 12095 2013.11

Constraint-induced Structural Deformation of Planarized Triphenylboranes in the Excited State Reviewed

T. Kushida, C. Camacho, A. Shuto, S. Irle, M. Muramatsu, T. Katayama, S. Ito, Y. Nagasawa, H. Miyasaka, E. Sakuda, N. Kitamura, Z. Zhou, A. Wakamiya, and S. Yamaguchi

Chem. Sci. Vol. ５ page： 1296-1304 2013.11

Photochemical Double 5-exo Cyclization of Alkenyl-Substituted Dithienylacetylenes: Efficient Synthesis of Diarylated Dithienofulvalenes Reviewed

Aiko Fukazawa, Takashi Karasawa, Hongyu Zhang, Kazumitsu Minemura, Cristopher Camacho, Jian Wang, Stephan Irle, Shigehiro Yamaguchi

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Vol. 52 ( 40 ) page： 10519 - 10523 2013.9

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

Smooth and selective: Upon photoirradiation, bis(3-alkenyl-2-thienyl) acetylenes smoothly and selectively undergo double 5-exo-dig cyclization to produce a series of thiophene-fused pentafulvalenes with various aryl substituents. In this fused π-conjugated skeleton, the fused thiophene rings and the aryl substituents significantly modulate the electronic structure of the pentafulvalene skeleton. Copyright © 2013 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

DOI： 10.1002/anie.201303738

Web of Science

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Papers - YAMAGUCHI, Shigehiro