Faculty Profiles - FURUKAWA Ko

Papers - FURUKAWA Ko

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Nitrogen-Bridged Metallodiazaporphyrin Dimers: Synergistic Effects of Nitrogen Bridges and meso-Nitrogen Atoms on Structure and Properties Reviewed International journal

Masahiro Kawamata, Takuma Sugai, Mao Minoura, Yasuhisa Maruyama, Ko Furukawa, Cole Holstrom, Victor N. Nemykin, Haruyuki Nakano, Yoshihiro Matano

Chemistry-An Asian Journal 12 ( 7 ) 816 - 821 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Wiley

NH-bridged and pyrazine-fused metallodiazaporphyrin dimers have been prepared from nickel(II) and copper(II) complexes of 3-amino-5,15-diazaporphyrin by Pd-catalyzed C-N cross-coupling and oxidative dimerization reactions, respectively. The synergistic effects of the nitrogen bridges and meso-nitrogen atoms play major roles in enhancing the light-harvesting properties and delocalization of an electron spin over the entire π-skeletons of the metallodiazaporphyrin dimers.

DOI： 10.1002/asia.201700204

Design, Synthesis, and Reaction of pi-Extended Coumarin-based New Caged Compounds with Two-photon Absorption Character in the Near-IR Region Reviewed

Youhei Chitose, Manabu Abe, Ko Furukawa, Claudine Katan

CHEMISTRY LETTERS 45 ( 10 ) 1186 - 1188 2016.10

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

Novel pi-extended coumarin-based chromophores were designed with two-photon absorption (TPA) character in the near-TR. region. Caged benzoates with a TP-responsive chromophore were synthesized, and their TP-uncaging reactions were conducted under near-IR light. The 6,7-dimethoxy-substituted derivative had a high TPA cross-section of 69 GM at 740 nm. The 7-methoxy-substituted derivative showed a high TPA uncaging efficiency with a TPA efficiency of 3.4 GM at 710 nm.

DOI： 10.1246/cl.160586

Design and Synthesis of a 4-Nitrobromobenzene Derivative Bearing an Ethylene Glycol Tetraacetic Acid Unit for a New Generation of Caged Calcium Compounds with Two-Photon Absorption Properties in the Near-IR Region and Their Application in Vivo Reviewed

Satish Jakkampudi, Manabu Abe, Naomitsu Komori, Ryukichi Takagi, Ko Furukawa, Claudine Katan, Wakako Sawada, Noriko Takahashi, Haruo Kasai

ACS Omega 1 ( 2 ) 193 - 201 2016.8

Language：English Publishing type：Research paper (scientific journal) Publisher：American Chemical Society

Among biologically active compounds, calcium ions (Ca2+) are one of the most important species in cell physiological functions. Development of new calcium chelators with two-photon absorption (TPA) properties is a state-of-the-art challenge for chemists. In this study, we report the first and efficient synthesis of 5-bromo-2-nitrobenzyl-substituted ethylene glycol tetraacetic acid (EGTA) as a platform for a new generation of calcium chelators with TPA properties in the near-infrared region. New calcium chelators with high TPA properties, that is, a two-photon (TP) fragmentation efficiency of δu = 20.7 GM at 740 nm for 2-(4-nitrophenyl)benzofuran (NPBF)-substituted EGTA (NPBF-EGTA, Kd = 272 nM) and δu = 7.8 GM at 800 nm for 4-amino-4′-nitro-1,1′-biphenyl (BP)-substituted EGTA (BP-EGTA, Kd = 440 nM) derivatives, were synthesized using Suzuki-Miyaura coupling reactions of the bromide with benzofuran-2-boronic acid and 4-(dimethylamino)phenyl boronic acid, respectively. The corresponding acetoxymethyl (AM) esters were prepared and successfully applied to the Ca2+-uncaging reaction triggered by TP photolysis in vivo.

DOI： 10.1021/acsomega.6b00119

Spontaneous Formation of an Air-Stable Radical upon the Direct Fusion of Diphenylmethane to a Triarylporphyrin Reviewed

Kenichi Kato, Wonhee Cha, Juwon Oh, Ko Furukawa, Hideki Yorimitsu, Dongho Kim, Atsuhiro Osuka

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 55 ( 30 ) 8711 - 8714 2016.7

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

The direct fusion of a diphenylmethane segment to a Ni-II 5,10,15-triarylporphyrin with three linkages furnished an air-and moisture-stable neutral radical through unexpected and spontaneous oxidation. This radical was demetalated by treatment with H2SO4 and CF3CO2H to provide the corresponding free-base radical. These porphyrin radicals are very stable owing to spin delocalization and have been fully characterized through UV/Vis/NIR absorption spectroscopy, X-ray crystallographic analysis, magnetic susceptibility measurements, electrochemical studies, laser-based ultrafast spectroscopic studies, and theoretical calculations. They were chemically oxidized and reduced to the corresponding cation and anion but did not react with hydrogen-atom donors.

DOI： 10.1002/anie.201602683

meso-to-meso Sulfide- and Disulfide-Bridged Subporphyrin Dimers Reviewed

Graeme Copley, Daiki Shimizu, Juwon Oh, Jooyoung Sung, Ko Furukawa, Dongho Kim, Atsuhiro Osuka

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY 0 ( 11 ) 1977 - 1981 2016.4

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

Treatment of meso-chlorosubporphyrin with controlled equivalents of Na(2)S9H(2)O in DMF led to the formation of either meso-to-meso sulfide (S)-bridged dimer 4 or disulfide (SS)-bridged subporphyrin dimer 6. S-bridged dimer 4 displayed a split Soret-like band and a large Stokes shift and became a fully delocalized one-quantum system in the S-1 state, as indicated by femtosecond transient absorption anisotropy measurements and theoretical calculations. Contrastingly, SS-bridged dimer 6 showed a broad but nonsplit Soret-like band, no fluorescence, and very fast S-1 decay with a lifetime of 4 ps, which indicated the presence of a rapid decay channel.

DOI： 10.1002/ejoc.201600285

Redox-Switchable 20-, 19-, and 18-Electron 5,10,15,20-Tetraaryl-5,15-diazaporphyrinoid Nickel(II) Complexes Reviewed

Takaharu Satoh, Mao Minoura, Haruyuki Nakano, Ko Furukawa, Yoshihiro Matano

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 55 ( 6 ) 2235 - 2238 2016.2

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

The first examples of air-stable 20-electron 5,10,15,20-tetraaryl-5,15-diaza-5,15-dihydroporphyrins, their 18-electron dications, and the 19-electron radical cation were prepared through metal-templated annulation of nickel(II) bis(5-arylamino-3-chloro-8-mesityldipyrrin) complexes followed by oxidation. The neutral 20-electron derivatives are antiaromatic and the cationic 18-electron derivatives are aromatic in terms of the magnetic criterion of aromaticity. The meso Natoms in these diazaporphyrinoids give rise to characteristic redox and optical properties for the compounds that are not typical of isoelectronic 5,10,15,20-tetraarylporphyrins.

DOI： 10.1002/anie.201510734

Isolation of Hypervalent Group-16 Radicals and Their Application in Organic-Radical Batteries Reviewed

Yasuyuki Imada, Hideyuki Nakano, Ko Furukawa, Ryohei Kishi, Masayoshi Nakano, Hitoshi Maruyama, Masaaki Nakamoto, Akira Sekiguchi, Masahiro Ogawa, Toshiaki Ohta, Yohsuke Yamamoto

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 138 ( 2 ) 479 - 482 2016.1

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

Using a newly prepared tridentate ligand, we isolated hypervalent sulfur and selenium radicals for the first time and characterized their structures. X-ray crystallography, electron spin resonance spectroscopy, and density functional theory calculations revealed a three-coordinate hypervalent structure. Utilizing the reversible redox reactions between hypervalent radicals and the corresponding anions bearing Li+, we developed organic radical batteries with these compounds as cathode-active materials. Furthermore, an all-radical battery, with these compounds as the cathode and a silyl radical as the anode, was developed that exhibited a practical discharge potential of similar to 1.8 V and stable cycle performance, demonstrating the potential of these materials for use in metal-free batteries that can replace conventional Li-ion batteries where Li is used in the metal form.

DOI： 10.1021/jacs.5b10774

Design and synthesis of a new chromophore, 2-(4-nitrophenyl)benzofuran, for two-photon uncaging using near-IR light Reviewed

Naomitsu Komori, Satish Jakkampudi, Ryusei Motoishi, Manabu Abe, Kenji Kamada, Ko Furukawa, Claudine Katan, Wakako Sawada, Noriko Takahashi, Haruo Kasai, Bing Xue, Takayoshi Kobayashi

CHEMICAL COMMUNICATIONS 52 ( 2 ) 331 - 334 2016

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

A new chromophore, 2-(4-nitrophenyl)benzofuran (NPBF), was designed for two-photon (TP) uncaging using near-IR light. The TP absorption (TPA) cross-sections of the newly designed NPBF chromophore were determined to be 18 GM at 720 nm and 54 GM at 740 nm in DMSO. The TP uncaging reaction of a caged benzoate with the NPBF chromophore quantitatively produced benzoic acid with an efficiency (delta(u)) of similar to 5.0 GM at 740 nm. The TP fragmentation of an EGTA unit was observed with delta(u) = 16 GM. This behavior makes the new chromophore a promising TP photoremovable protecting group for physiological studies.

DOI： 10.1039/c5cc07664a

Triarylporphyrin meso-Oxy Radicals: Remarkable Chemical Stabilities and Oxidation to Oxophlorin pi-Cations Reviewed

Daiki Shimizu, Juwon Oh, Ko Furukawa, Dongho Kim, Atsuhiro Osuka

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 137 ( 49 ) 15584 - 15594 2015.12

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

5-Hydroxy-10,15,20-triarylporphyrin (oxophlorin) and its Ni(II) and Zn(II) complexes were oxidized with PbO2 to give the corresponding porphyrin meso-oxy radicals as remarkably stable species. These radicals were fully characterized with X-ray diffraction analysis, UV/vis/NIR absorption and ESR spectroscopies, magnetic susceptibility measurement, electrochemical studies, and theoretical calculations. Free-base radical and its Ni(II) complex have been shown to exist as a monoradical in solution, while the Zn(II) complex exists in an equilibrium between monomer (doublet monoradical) and dimer (a non-Kekule singlet biradicaloid) with a dimerization constant of K-D = 3.0 x 10(5) M-1 in noncoordinating CH2Cl2 but becomes a pyridine-coordinated monoradical upon addition of pyridine. Variable temperature magnetic susceptibility measurements of these radicals revealed different magnetic interactions in the solid-states, which has been interpreted in terms of their different packing structures in a microscopic sense. These radicals undergo one-electron oxidation and reduction in a reversible manner within narrow potential windows of 0.57-0.82 V. Finally, one-electron oxidation of Ni(II) and Zn(II) porphyrin meso-oxy radicals with tris(4-bromophenyl)aminium hexachloroantimonate furnished oxophlorin pi-cations, which displayed nonaromatic closed-shell character, NIR absorption, and significant double bond character of the C-O bond.

DOI： 10.1021/jacs.5b11223

Microscopic evidence of a metallic state in the one-pot organic conductor ammonium tetrathiapentalene carboxylate Reviewed

Toshikazu Nakamura, Ko Furukawa, Takeshi Terauchi, Yuka Kobayashi

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 9 ( 8 ) 480 - 484 2015.8

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

H-1 NMR (nuclear magnetic resonance) and high-field ESR (electron spin resonance) measurements were carried out for self-doped organic conductors in the ammonium tetrathiapentalene carboxylate (TTPCOO)(2)[(NH41+)(1-x)(NH30)(x)] system. While the pristine TTPCOOH molecule is closed-shell, self-doped carriers are generated by substitution of the carboxyl proton by (NH30) and (NH41+), which can be regarded as a charge reservoir. The pi-extended system TTPCOO has a uniaxial g-tensor, indicating a 2D isotropic structure such as a herring-bone-like or parallel cross donor arrangement. The NMR-relaxation rate indicated the Korringa relation in the temperature dependence, and the ESR linewidth followed the Elliot mechanism. Both of these observations provide supporting evidence for a stable metallic state. In this paper, we introduce self-doped organic conductors as a branch of materials design, and emphasize that advanced magnetic resonance measurements are powerful tools for developing functional materials. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssr.201510206

Comparison of electronic effects of beta-aryl substituents on optical and electrochemical properties of 5,15-diazaporphyrin pi-systems Reviewed

Satoshi Omomo, Ko Furukawa, Haruyuki Nakano, Yoshihiro Matano

JOURNAL OF PORPHYRINS AND PHTHALOCYANINES 19 ( 6 ) 775 - 785 2015.6

Language：English Publishing type：Research paper (scientific journal) Publisher：WORLD SCI PUBL CO INC

The syntheses and optical/electrochemical properties of 3-aryl-10,20-dimesityl-5,15-diazaporphyrin-metal complexes (MDAPs; mesityl = 2,4,6-trimethylphenyl; M = Ni, Zn) are reported. Treatment of 3-bromo-MDAPs with arylboronic acids in the presence of a Pd catalyst and a bulky phosphine ligand in a dioxane-water mixed solvent afforded the corresponding 3-aryl-MDAPs in moderate to good yields. X-ray crystallographic analysis of p-EtO2CC6H4-NiDAP showed that the beta-aryl group was tilted toward the NiDAP ring, with a dihedral angle of 21.7 degrees. In the UV-visible absorption spectra, all the Ar-MDAPs showed intense Q-bands attributable to HOMO-to-LUMO transitions. The para substituents were found to influence the HOMO energies, which eventually resulted in fine tuning of the HOMO-LUMO gaps of the diazaporphyrin chromophores. It is worth noting that the p-Ph2NC6H4-ZnDAP showed broad absorption and emission bands in the visible-near-infrared regions. The large Stokes shifts and their linear solvation energy relationships vs. orientation polarizability show that this Ph2N-substituted derivative has intrinsically high charge transfer from the triphenylamine (donor) to the ZnDAP (acceptor) unit. These experimental observations were supported by theoretical calculations for model Ar-ZnDAP compounds. These results confirm that the introduction of a highly electron-donating aryl group at the peripheral beta-carbon is a promising strategy for enhancing the light-harvesting and light-emitting abilities of diazaporphyrin-based pi-systems in the visible-near-infrared regions.

DOI： 10.1142/S1088424615500509

Creation of Superheterojunction Polymers via Direct Polycondensation: Segregated and Bicontinuous Donor-Acceptor pi-Columnar Arrays in Covalent Organic Frameworks for Long-Lived Charge Separation Reviewed

Shangbin Jin, Mustafa Supur, Matthew Addicoat, Ko Furukawa, Long Chen, Toshikazu Nakamura, Shunichi Fukuzumi, Stephan Irle, Donglin Jiang

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 137 ( 24 ) 7817 - 7827 2015.6

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

By developing metallophthalocyanines and diimides as electron-donating and -accepting building blocks, herein, we report the construction of new electron donor-acceptor covalent organic frameworks (COFs) with periodically ordered electron donor and acceptor pi-columnar arrays via direct polycondensation reactions. X-ray diffraction measurements in conjunction with structural simulations resolved that the resulting frameworks consist of metallophthalocyanine and diimide columns, which are ordered in a segregated yet bicontinuous manner to form built-in periodic pi-arrays. In the frameworks, each metallophthalocyanine donor and diimide acceptor units are exactly linked and interfaced, leading to the generation of superheterojunctionsa new type of heterojunction machinery, for photoinduced electron transfer and charge separation. We show that this polycondensation method is widely applicable to various metallophthalocyanines and diimides as demonstrated by the combination of copper, nickel, and zinc phthalocyanine donors with pyrommellitic diimide, naphthalene diimide, and perylene diimide acceptors. By using time-resolved transient absorption spectroscopy and electron spin resonance, we demonstrated that the COFs enable long-lived charge separation, whereas the metal species, the class of acceptors, and the local geometry between donor and acceptor units play roles in determining the photochemical dynamics. The results provide insights into photoelectric COFs and demonstrate their enormous potential for charge separation and photoenergy conversions.

DOI： 10.1021/jacs.5b03553

meso-Hydroxysubporphyrins: A Cyclic Trimeric Assembly and a Stable meso-Oxy Radical Reviewed

Daiki Shimizu, Juwon Oh, Ko Furukawa, Dongho Kim, Atsuhiro Osuka

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 54 ( 22 ) 6613 - 6617 2015.5

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

Treatment of meso-chlorosubporphyrin with potassium hydroxide in DMSO followed by aqueous work up and recrystallization gave a cyclic trimer consisting of meso-hydroxysubporphyrin units linked between the central boron atoms and meso-hydroxy groups. Solutions of this trimer are nonfluorescent, but become fluorescent when exposed to acid or base, since hydrolytic cleavage of the axial BO bonds generates the meso-hydroxysubporphyrin monomer or its oxyanion. Ring cleavage of the trimer was also effected by reaction with phenylmagnesium bromide to produce meso-hydroxy-B-phenyl subporphyrin, which can be quantitatively oxidized with PbO2 to furnish a subporphyrin meso-oxy radical as a remarkably stable species as a result of spin delocalization over almost the entire molecule.

DOI： 10.1002/anie.201501592

Lowering the Reduction Potential of a Boron Compound by Means of the Substituent Effect of the Boryl Group: One-Electron Reduction of an Unsymmetrical Diborane(4) Reviewed

Hiroki Asakawa, Ka-Ho Lee, Ko Furukawa, Zhenyang Lin, Makoto Yamashita

CHEMISTRY-A EUROPEAN JOURNAL 21 ( 11 ) 4267 - 4271 2015.3

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

We have clarified and observed the high electron affinity of pinB-BMes(2) (1; Mes = mesityl, pin = pinacolato). By using electrochemistry, it was shown that 1 has a higher electron affinity than those of B(2)pin(2) and Mes(3)B. One-electron reduction of 1 gave the corresponding radical anion. The ESR spectroscopy and DFT calculation revealed the unsymmetrical distribution of electron density over the B-B bond. UV/Vis spectroscopy showed that the SOMO-related absorption supports the deep purple color of the radical anion. DFT studies on the torsion angle dependency of the LUMO levels and relative energies revealed the reason why 1 has high electron affinity as a result of the substituent effect of the Bpin group.

DOI： 10.1002/chem.201406609

Oxidation of an allene compound bearing 1,8-dichloroacridene moieties and photolysis of the halogenated allene compound for the generation of triplet carbenes Reviewed

Shin-ichi Fuku-en, Ko Furukawa, Takahiro Sasamori, Norihiro Tokitoh, Manabu Abe, Yohsuke Yamamoto

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY 28 ( 2 ) 79 - 87 2015.2

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

New allene compounds, 5c and 5d, bearing 1,8-dichloroacridene moieties were synthesized, and the oxidation of 5c and 5d was performed to generate thermally stable triplet carbenes. Since the oxidation resulted in the formation of decomposition products, the photolysis of brominated allene compound 18 was performed. UV-vis measurement at low temperatures indicated the generation of intermediates with decreasing starting material 18, although the efficiency of photolysis was quite low. ESR and electron spin transient nutation (ESTN) spectra suggested that the multiplicity of intermediates is triplet, probably the target triplet carbene 6d is generated. In terms of |D| values of the intermediates, ESR showed that unpaired electrons are more effectively delocalized in 6d by the introduction of nitrogen atoms in the skeleton (biradical character in Scheme1). The observed triplet species 6d was not stable enough to isolate. Copyright (c) 2014 John Wiley & Sons, Ltd.

DOI： 10.1002/poc.3398

Optical, Electrochemical, and Magnetic Properties of Pyrrole- and Thiophene-Bridged 5,15-Diazaporphyrin Dimers Reviewed

Satoshi Omomo, Yasuhisa Maruyama, Ko Furukawa, Taniyuki Furuyama, Haruyuki Nakano, Nagao Kobayashi, Yoshihiro Matano

CHEMISTRY-A EUROPEAN JOURNAL 21 ( 5 ) 2003 - 2010 2015.1

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

The first examples of pyrrole-and thiophene-bridged 5,15-diazaporphyrin (DAP) dimers are prepared through Stille coupling reactions of nickel(II) and copper(II) complexes of 3-bromo-10,20-dimesityl-5,15-diazaporphyrin (mesityl = 2,4,6-trimethylphenyl) with the respective 2,5-bis(tributylstannyl)heteroles. The effects of the heterole spacers and meso nitrogen atoms on the optical, electrochemical, and magnetic properties of the DAP dimers are investigated by UV/Vis absorption spectroscopy, density functional theory calculations, magnetic circular dichroism spectroscopy, cyclic voltammetry, and EPR spectroscopy. The heterole spacers are found to have a significant impact on the electronic transitions over the entire pi-system. In particular, the pyrrole-bridged DAP dimers exhibit high light-harvesting potential in the low-energy visible/near-infrared region owing to the intrinsic charge-transfer character of the lowest excitation.

DOI： 10.1002/chem.201405482

A Stable Organic π-Radical of a Zinc(II)-Copper(I)-Zinc(II) Complex of Decaphyrin Reviewed

Tanaka, Y., Yoneda, T., Furukawa, K., Koide, T., Mori, H., Tanaka, T., Shinokubo, H., Osuka, A.

Angewandte Chemie - International Edition 54 ( 37 ) 10908 - 10911 2015

Phenalenyl-fused porphyrins with different ground states Reviewed

Wangdong Zeng, Sangsu Lee, Minjung Son, Masatoshi Ishida, Ko Furukawa, Pan Hu, Zhe Sun, Dongho Kim, Jishan Wu

CHEMICAL SCIENCE 6 ( 4 ) 2427 - 2433 2015

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

Materials based on biradicals/biradicaloids have potential applications for organic electronics, photonics and spintronics. In this work, we demonstrated that hybridization of porphyrin and polycyclic aromatic hydrocarbon could lead to a new type of stable biradicals/biradicaloids with tunable ground state and physical property. Mono- and bis-phenalenyl fused porphyrins 1 and 2 were synthesized via an intramolecular Friedel-Crafts alkylation-followed-by oxidative dehydrogenation strategy. Our detailed experimental and theoretical studies revealed that 1 has a closed-shell structure with a small biradical character (y = 0.06 by DFT calculation) in the ground state, while 2 exists as a persistent triplet biradical at room temperature under inert atmosphere. Compound 1 underwent hydrogen abstraction from solvent during the crystal growing process while compound 2 was easily oxidized in air to give two dioxo-porphyrin isomers 11a/11b, which can be correlated to their unique biradical character and spin distribution. The physical properties of 1 and 2, their dihydro/tetrahydro-precursors 7/10, and the dioxo-compounds 11a/11b were investigated and compared.

DOI： 10.1039/c4sc03866e

Acid/base-regulated reversible electron transfer disproportionation of N-N linked bicarbazole and biacridine derivatives Reviewed

Palash Pandit, Koji Yamamoto, Toshikazu Nakamura, Katsuyuki Nishimura, Yuki Kurashige, Takeshi Yanai, Go Nakamura, Shigeyuki Masaoka, Ko Furukawa, Yumi Yakiyama, Masaki Kawano, Shuhei Higashibayashi

CHEMICAL SCIENCE 6 ( 7 ) 4160 - 4173 2015

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

Regulation of electron transfer on organic substances by external stimuli is a fundamental issue in science and technology, which affects organic materials, chemical synthesis, and biological metabolism. Nevertheless, acid/base-responsive organic materials that exhibit reversible electron transfer have not been well studied and developed, owing to the difficulty in inventing a mechanism to associate acid/base stimuli and electron transfer. We discovered a new phenomenon in which N-N linked bicarbazole (BC) and tetramethylbiacridine (TBA) derivatives undergo electron transfer disproportionation by acid stimulus, forming their stable radical cations and reduced species. The reaction occurs through a biradical intermediate generated by the acid-triggered N-N bond cleavage reaction of BC or TBA, which acts as a two electron acceptor to undergo electron transfer reactions with two equivalents of BC or TBA. In addition, in the case of TBA the disproportionation reaction is highly reversible through neutralization with NEt3, which recovers TBA through back electron transfer and N-N bond formation reactions. This highly reversible electron transfer reaction is possible due to the association between the acid stimulus and electron transfer via the acid-regulated N-N bond cleavage/formation reactions which provide an efficient switching mechanism, the ability of the organic molecules to act as multi-electron donors and acceptors, the extraordinary stability of the radical species, the highly selective reactivity, and the balance of the redox potentials. This discovery provides new design concepts for acid/base-regulated organic electron transfer systems, chemical reagents, or organic materials.

DOI： 10.1039/c5sc00946d

Persistent antimony- and bismuth-centered radicals in solution Reviewed

Shintaro Ishida, Fumiya Hirakawa, Ko Furukawa, Kenji Yoza, Takeaki Iwamoto

Angewandte Chemie International Edition 53 ( 42 ) 11172 - 11176 2014.7

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