Faculty Profiles - OKUNO Tsunehisa

Published Papers - OKUNO Tsunehisa

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Preparation and properties of two-legged ladder polymers based on polydiacetylenes

Hideyuki Tabata, Hiroaki Tokoyama, Hideo Yamakado, Tsunehisa Okuno

JOURNAL OF MATERIALS CHEMISTRY ( ROYAL SOC CHEMISTRY ) 22 ( 1 ) 115 - 122 2012 [Refereed]

A novel diacetylene derivative, N,N'-bis[5-(3-tolylaminocarbonyloxy)-1,3-pentadiynyl]-N,N'-diphenyl-1,4- phenylenediamine (1), was prepared, where two diacetylene groups were connected by a 1,4-phenylenediamine moiety. The molecules stacked one-dimensionally and showed solid-state-polymerization reactivity above 80 degrees C. The decay of the monomers at 100 degrees C proceeded gradually without a marked induction period and was fully completed after 400 h. The obtained polymer was a crystalline solid judged by powder X-ray diffraction (PXRD) patterns and SEM imaging. The conjugated pi-system of the obtained polymer was classified as a two-legged conjugated ladder. The polymer showed a broad absorption from the visible to the near IR region, indicating a decrease in the optical band gap of ca. 1.0 eV, because of the expansion of the pi-conjugated system from a one-dimensional system to a ladder. The ladder polymer showed high conductivity after I(2) doping from sigma(293K) = 5 x 10(-12) S cm(-1) to 1.2 x 10(-5) S cm(-1). The conductivity depended heavily on the pressure of iodine and reached s373K 2.3 x 10(-1) S cm(-1). The activation energy of the ladder polymer was also estimated as 360 meV.

N1,N4-Diethynyl-N1,N4-diphenylbenzene-1,4-diamine

H. Tabata, T. Okuno

Acta Cryst. E 67 o3169 - o3169 2011.10 [Refereed]

Two polymorphs of N1,N4-bis(5-hydroxypenta-1,3-diynyl)-N1,N4-diphenylbenzene-1,4-diamine

H. Tabata, N. Kubo, T. Okuno （Part： Last author,　Corresponding author )

Acta Cryst. C 67 492 - 495 2011.09 [Refereed]

Solid State Polymerization of Diacetylenes with Amide Groups

T. Okuno, K. Yamane, D. J. Sandman

Mol. Cryst. Liq. Cryst. 456 33 - 44 2006.07 [Refereed]

Solid state polymerization of diacetylenes incorporating ynamine moiety

Tsunehisa Okuno, Satoshi Ikeda, Natsuki Kubo, D. J. Sandman （Part： Lead author,　Corresponding author )

MOLECULAR CRYSTALS AND LIQUID CRYSTALS ( TAYLOR & FRANCIS LTD ) 456 35 - 44 2006 [Refereed]

Novel ynamine. compounds, 5-hydroxy-1-(phenothiazine-10-yl)-1,3-pentadiyne (1), its S-oxide (2) and S-dioxide (3), were prepared. Compound 2 was found to show thermal reactivity to give polydiacetylene, however 1 and 3 did not show any reactivity. Compound 2 stacks along the c axis, forming a columnar structure. The condition of molecular arrangement satisfied Baughman's criterion. Significant intermolecular contact between the oxygen atoms of sulfoxide groups and the adjacent sulfur atoms was recognized.

Spin density distributions of p-N-alkylpyridinium nitronyl nitroxides studied by solid-state high-resolution NMR

G Maruta, S Takeda, A Yamaguchi, T Okuno, K Awaga

POLYHEDRON ( PERGAMON-ELSEVIER SCIENCE LTD ) 22 ( 14-17 ) 1989 - 1994 2003.07 [Refereed]

The electron spin density distributions of p-N-alkylpyridinium alpha-nitronyl nitroxides with alkyl = methyl (p-MPYNN) and n-butyl (p-BPYNN) were determined in their iodide salts from the temperature dependence of the solid-state high-resolution H-1 MAS NMR spectra. The results were compared with that of p-pyridyl alpha-nitronyl nitroxide (p-PYNN) to see how positive charge on the aromatic ring affects the spin density distribution. This effect was not significant contrary to the effect of incorporation of a nitrogen atom into the aromatic group. The change in the magnitude of the spin density can be ascribed to the dihedral angle between nitroxide and aromatic moieties. Relatively large hyperfine coupling constant of N-methyl proton, which is almost half as large as those of beta-methyl proton, implies the utility of the N-methyl group as an intermolecular magnetic coupler. (C) 2003 Published by Elsevier Science Ltd.

Crystal structures and magnetic properties of (m- or p-MPYNN)(2) Ni-II(tdaS)(2)

T Okuno, K Kuwamoto, W Fujita, K Awaga, W Nakanishi

POLYHEDRON ( PERGAMON-ELSEVIER SCIENCE LTD ) 22 ( 14-17 ) 2311 - 2315 2003.07 [Refereed]

Novel Ni-II(tdaS)(2) complexes, (m - or p-MPYNN)(2)Ni(tdas)(2) (MPYNN = N-methylpyridinium alpha-nitronyl nitroxide and tdas = 1,2,5-thiadiazole-3,4-dithiolate), were prepared. The Ni(tdaS)2 anions are located on the lattice points and at the lattice center in the crystal of (m -MPYNN)(2)Ni(tdas)(2). The m -MPYNN cations form a centrosymmetric dimer, and the anion is sandwiched by a pair of the dimers, forming alternate stacks along the a axis. In the crystal of the (p-MPYNN)2Ni(tdas)(2) complex, the Ni(tdas)(2) anions are located on the lattice points and at the center of the bc plane. The anion is surrounded by four p-MPYNN cations. The p-MPYNN cations also form a centrosymmetric dimer. Each cation has a short contact with a different Ni(tdas)(2) anion. The magnetic susceptibilities of both complexes decrease with decreasing temperature, indicating antiferromagnetic interaction within the radicals. The behavior of (m- and p-MPYNN)(2)Ni(tdas)(2) was understood with the singlet-triplet model and the Curie-Weiss law. (C) 2003 Elsevier Science Ltd. All rights reserved.

Nuclear magnetic relaxation of H-1 in the organic radical salts m-MPYNN+center dot ClO4- and m-MPYNN+center dot BF4-

Y Fujii, T Goto, A Oyamada, T Okuno, K Awaga

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN ( PHYSICAL SOC JAPAN ) 69 ( 5 ) 1294 - 1297 2000.05 [Refereed]

We have measured nuclear spin-lattice relaxation limes T-1 of H-1 in the organic salts mMPYNN(+). ClO4- and m-MPYNN+. BF4- in the temperature range between 2 K and 100 Ii under external fields up to 70 kOe. In these salts, two cationic (spin-1/2) radicals constitute a dimer due to the ferromagnetic interaction J(1). We interpreted the experimental results of T-1(-1) below about 10 K (similar to J(1)/k(B)) in terms of two relaxation processes based on the energy levels of the ferromagnetic dimer. The flip-flop and the direct processes which are due to longitudinal and transverse spin fluctuations become dominant at higher and lower fields, respectively, the crossover field being around 10 kOe. For the field dependence of T-1(-1) at higlrer temperatures, the spin diffusive model of spin-1/2 in a two-dimensional system is satisfactorily applied.

Magic angle spinning H-1-NMR study of the spin density distribution of pyridyl nitronyl nitroxides in the crystalline phase

G Maruta, S Takeda, A Yamaguchi, T Okuno, K Awaga, K Yamaguchi

MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS ( GORDON BREACH PUBLISHING, TAYLOR & FRANCIS GROUP ) 334 295 - 304 1999 [Refereed]

The electron spin density distribution was investigated for p- and m-pyridyl nitronyl nitroxides (p-PYNN and m-PYNN) in the crystalline phase by the temperature dependence of the solid state high resolution H-1-MAS NMR spectrum. The results were compared with that of phenyl nitronyl nitroxide (PNN) for elucidating the effect of incorporation of a nitrogen atom into the aromatic group. For p-PYNN, the magnitude of the negative spin density at 3 and 5 positions of the pyridyl group was suppressed by 30% in comparison with that of PNN and the positive spin density at 2 and 6 positions was slightly enhanced by 10%. On the other hand, the positive spin density at 2, 4 and 6 positions of pyridyl group of m-PYNN was suppressed by 30% in average and the negative one at 5 was also suppressed by 20%. The DFT calculation at UBLYP/6-31G(d, p) level suggested that the molecular geometry largely contributed to the change of the spin density in addition to the effect of incorporation of the nitrogen atom. In fact, the spin density distribution of the aromatic ring of p-PYNN was remarkably reduced in solution compared with that in the crystalline phase.

Muon-spin-relaxation study of the ground state of the two dimensional S=1 kagome antiferromagnet [2-(3-N-methyl-pyridium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-l-oxyl-3-N-oxide]BF4

Watanabe, I, N Wada, H Yano, T Okuno, K Awaga, S Ohira, K Nishiyama, K Nagamine

PHYSICAL REVIEW B ( AMER PHYSICAL SOC ) 58 ( 5 ) 2438 - 2441 1998.08 [Refereed]

Zero- and longitudinal-field positive muon spin relaxation (mu(+) SR) measurements were carried out from 300 K to 30 mK to study a ground state of m-MPYNN . BF4 which is known to be a two-dimensional kagome antiferromagnet with S=1 by ac-susceptibility measurements. An implanted muon is expected to make a hydrogen bonding state with F- ions in the crystal. Muon-spin depolarization by a dynamically fluctuating component of an internal field was still observed at 30 mK. This fluctuating component is suggested to be caused by an intradimer ferromagnetic interaction of 2J(0)/k(B) = 23.3 K between radicals. No clear long-range magnetic ordering of the dimer spins was observed down to 30 mK, suggesting that the ground state of m-MPYNN . BF4 was nonmagnetic.

Observation of spontaneous magnetization in the layered perovskite ferromagnet, (p-chloroanilinium)(2)CuBr4

T Sekine, T Okuno, K Awaga

INORGANIC CHEMISTRY ( AMER CHEMICAL SOC ) 37 ( 9 ) 2129 - 2133 1998.05 [Refereed]

The crystal structure and magnetic properties of the layered perovskite, (p-chloroanilinium)(2)CuBr4 (1) have been investigated. The crystal of 1 belongs to the orthorhombic Pbca space group [a = 7.551(2) Angstrom, b = 32.082(10) Angstrom, c = 7.879(2) Angstrom, and Z = 4], which is typical of the material family. The temperature dependence of the ac susceptibility (chi(lac) = (partial derivative M/partial derivative H)) of a polycrystalline sample shows magnetic ordering at 15 K with an abrupt increase of the value. In the ordered state, the field dependence of chi(ac), namely the differential susceptibility, and the de magnetization indicate a hysteresis loop of the magnetization, which can be ascribed to the presence of spontaneous magnetization. Furthermore, single-crystal magnetic measurements indicate that the magnetic properties of 1 are quite anisotropic. When the field is along the b axis (perpendicular to the inorganic layer), the field dependence of chi(ac) shows the hysteresis behavior, as observed for the polycrystals, but when it is parallel to the a axis (parallel to the layer), chi(ac) shows metamagnetic transitions. The observed anisotropy can be understood in terms of a magnetic easy axis parallel to the a axis, an antiferromagnetic interlayer interaction, and a spin canting which produces spontaneous magnetization along the b axis.

Proton spin-lattice relaxation in m-MPYNN+center dot X- (X = ClO4, BF4) at ultra low temperatures

Y Fujii, T Goto, K Awaga, T Okuno, Y Sasaki, T Mizusaki

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS ( ELSEVIER SCIENCE BV ) 177 991 - 992 1998.01 [Refereed]

The nuclear spin-lattice relaxation times T-1 of H-1 in organic radical salts m-MPYNN+.X-.1/3(acetone)(X = ClO4, BF4) were measured at ultra low temperatures down to 0.1 K. The T-1 in BF4 salt was almost temperature-independent below 1 K. The experimental results suggest that temperature-independent magnetic fluctuation is caused by frustration effect associated with quantum spin tunnelling in kagome antiferromagnet of S = 1 dimer. (C) 1998 Elsevier Science B.V. All rights reserved.

Low Temperature Physical Properties of Distorted Organic Kagome Antiferromagnets,m-AlkylPYNN^+・X^-

YOSHIMARU Masahiro, YAMAGUCHI Akira, AWAGA Kunio, YANO Hideo, WADA Nobuo, OKUNO Tsunehisa

Meeting Abstracts of the Physical Society of Japan ( The Physical Society of Japan ) 53 375 - 375 1998

Observation of spin-gap state in two-dimensional spin-1 Kagome antiferromagnet m-MPYNN center dot BF4

N Wada, T Kobayashi, H Yano, T Okuno, A Yamaguchi, K Awaga

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN ( PHYSICAL SOC JAPAN ) 66 ( 4 ) 961 - 964 1997.04 [Refereed]

Low temperature properties of the organic spin-1 Kagome' antiferromagnet, m-MPYNN . BF4, have been studied by measuring heat capacity and magnetic susceptibility down to 35 mK. The heat capacity maximum due to a magnetic short-range order was observed at 1.4 K, which is about half of the antiferromagnetic interaction 2\J\/k(B)=3.1 K in the Kagome' lattice. As temperature decreases, the susceptibility begins to decrease below 0.24 K. The susceptibilities both parallel and perpendicular to the Kagome' lattice collapse to almost zero at the lowest temperature, which indicates a nonmagnetic ground state. The temperature dependence suggests that the gap energy of the magnetic state is about 0.25 K.

Unusual crystal structures and magnetic properties of nitronylnitroxide radical ions

K Awaga, K Takeda, A Yamaguchi, T Okuno, H Yano, N Wada

SYNTHETIC METALS ( ELSEVIER SCIENCE SA ) 85 ( 1-3 ) 1643 - 1646 1997.02 [Refereed]

We report unusual crystal structures and magnetic properties of nitronylnitroxide radical ions. (i) A nitronylnitroxide anion, p-(nitronyl nitroxide)ben to ate (p-NNBA), is found to crystallize with Mn2+ and water molecules in the form of Mn(p-NNBA)(2)(H2O)(2). In this crystal, the manganese(II) ion is in an octahedral environment, surrounded by two NO groups, two CO2 groups and two H2O. The magnetic properties are well interpreted in terms of the trimer model of [p-NNBA (S=1/2)][Mn2+ (S=5/2)]-[p-NNBA (S=1/2)]. (ii) A nitronylnitroxide cation, m-N-methylpyridinium nitronylnitroxide (m-MPYNN), crystallizes with I-, BF4-, or ClO4- into a trigonal space group, where the spin system is regarded as a spin-1 Kagome antiferromagnet with spin frustration. Low-temperature magnetic measurements reveal a spin-gap state below 0.24 K.

Ferromagnetic interaction between nitronyl nitroxide radical cations in a semiconducting salt

H Imai, T Inabe, T Otsuka, T Okuno, K Awaga

SYNTHETIC METALS ( ELSEVIER SCIENCE SA LAUSANNE ) 85 ( 1-3 ) 1705 - 1706 1997.02 [Refereed]

Ferromagnetic intermolecular interaction of N-protonated pyridylphenylcarbene

T Okuno, K Awaga

MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS ( GORDON BREACH SCI PUBL LTD ) 305 579 - 586 1997 [Refereed]

The HCl and DCl salts of phenyl-4-pyridyldiazomethane were prepared and irradiated at 6 K to generate the carbenes. Their ESR spectra indicated presence of plural triplet carbenes with slightly-different zero-field splitting constants. Besides the triplet species, we found a quintet species whose signal intensity decreases with increasing temperature. The quintet spin state was concluded to be a ground state which was produced by an intermolecular ferromagnetic interaction of the triplet carbenes. The ferromagnetic interaction would be explained by the McConnell mechanism, judging from the crystal structure of the HCl salt of phenyl-4-pyridylketone.

31P-L-5 Doping effects and magnetic field dependence of 2D spin-gap anitiferromagnets m-MPYNN salts

Wada N., Kobayashi T., Yano H., Yamaguchi A., Okuno T., Awaga K.

Meeting Abstracts of the Physical Society of Japan ( The Physical Society of Japan ) 52 511 - 511 1997

5p-PSA-5 Crystal Structures, Magnetic Properties and Heat Capacities of Organic Kagome Antiferromagnets, m-AlkylPYNN・I

Yamaguchi Akira, Hasegawa Morikuni, Awaga Kunio, Kobayashi Tatsuya, Yano Hideo, Wada Nobuo, Okuno Tsunehisa

Meeting Abstracts of the Physical Society of Japan ( The Physical Society of Japan ) 52 435 - 435 1997

Hydrogen-bonded acid-base molecular complexes of nitronylnitroxides

T Otsuka, T Okuno, M Ohkawa, T Inabe, K Awaga

MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS ( GORDON BREACH SCI PUBL LTD ) 306 285 - 292 1997 [Refereed]

Intermolecular hydrogen-bonded complexes of p-nitronylnitroxide benzoic acid (p-NNBA-H) with m- and p-pyridylnitronylnitroxides (m-and p-PYNN, respectively) were prepared. The m-PYNN . p-NNBA-H complex crystallizes into the monoclinic P2(1)/c space group [a = 6.685(3) Angstrom, b = 17.657(2) Angstrom, c = 22.169(1) Angstrom, beta = 92.90(1)degrees, V = 261.3(1) Angstrom(3), Z = 4], while the crystal of p-PYNN. p-NNBA H belongs to the monoclinic P2(1)/n space group [a=12.199(3) Angstrom, b = 23.265(4) Angstrom, c = 9.522(2) Angstrom, beta = 101.84(2)degrees, V = 2644.9(9) Angstrom(3), Z = 4]. In their crystals, there is an intermolecular hydrogen bond between the nitrogen atom on the pyridyl ring of PYNN and one of the oxygen atoms of the carboxyl group of p-NNBA-H. The intermolecular N ... O distances are 2.642(5) Angstrom in m-PYNN . p-NNBA-H and 2.613(6) Angstrom in p-PYNN . p-NNBA-H, indicating rather intense hydrogen bonds. The magnetic properties of m-PYNN . p-NNBA-H and p-PYNN . p-NNBA-H are well interpreted in terms of the singlet-triplet model with 2J(AF)/k(B) = -16.0 K and the Curie-Weiss law with theta = -0.68 K, respectively.

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