Shinagawa-ku, Japan
Shinagawa-ku, Japan

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Kowaka Y.,Kyoto University | Nakayama N.,Conflex Corporation | Ishimoto T.,Kyushu University | Nagashima U.,Japan National Institute of Advanced Industrial Science and Technology | And 4 more authors.
Chemical Physics | Year: 2012

Fluorescence excitation spectra and fluorescence lifetimes at single vibronic levels in the S1 state have been observed for jet-cooled pyrene. The fluorescence lifetimes at the zero-vibrational levels of the S11B3 u states of pyrene- h10 and pyrene- d10 are 1480 and 1470 ns, respectively, and the relaxation is considered to be dominated by the radiative process. For some vibrational levels, however, the lifetimes are remarkably shorter such as 765 ns at the 22 1 vibronic level of pyrene- h10 ( ν22 (b1 g); C-H bending and skeletal deforming mode), indicating that nonradiative transition occurs at a specific vibrational level. In this study, we demonstrate that the main process is internal conversion to the S01Ag state caused by nonadiabatic vibronic interaction via b3 u promoting modes. © 2012 Elsevier B.V. All rights reserved.


Suganuma Y.,Kyoto University | Kowaka Y.,Kyoto University | Ashizawa N.,Kyoto University | Nakayama N.,Conflex Corporation | And 8 more authors.
Molecular Physics | Year: 2011

We observed fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation of jet-cooled perylene-h 12 and perylene-d12, and carefully examined the vibrational structures of the SO 1Ag and S 1 1B2u states. We performed vibronic assignments on the basis of the results of ab initio calculation, and found that the vibrational energies in the S1 state are very similar to those in the SO state, indicating that the potential energy curves are not changed much upon electronic excitation. We conclude that the small structural change is the main cause of its slow radiationless transition and high fluorescence quantum yield at the zero-vibrational level in the S1 state. It has been already reported that the lifetime of perylene is remarkably short at specific vibrational levels in the S1 state. Here, we show that the mode-selective nonradiative process is internal conversion (IC) to the SO state, and the ν16(ag) in-plane ring deforming vibration is the promoting (doorway) mode in the S1 state which enhances vibronic coupling with the high-vibrational level (b2u) of the SO state. © 2011 Taylor & Francis.


Baba M.,Kyoto University | Kowaka Y.,Kyoto University | Nagashima U.,Japan National Institute of Advanced Industrial Science and Technology | Nagashima U.,Japan Science and Technology Agency | And 3 more authors.
Journal of Chemical Physics | Year: 2011

Geometrical structures of the isolated benzene and naphthalene molecules have been accurately determined by using ultrahigh-resolution laser spectroscopy and ab initio calculation in a complementary manner. The benzene molecule has been identified to be planar and hexagonal (D6h) and the structure has been determined with accuracies of 2 10-14 m (0.2 m; 1 = 1 10-10 m) for the C-C bond length and 1.0 10-13 m (1.0 m) for the C-H bond length. The naphthalene molecule has been identified to be symmetric with respect to three coordinate axes (D2h) and the structure has been determined with comparable accuracies. We discuss the effect of vibrational averaging that is a consequence of zero-point motions on the uncertainty in determining the bond lengths. © 2011 American Institute of Physics.


Kowaka Y.,Kyoto University | Suganuma Y.,Kyoto University | Ashizawa N.,Kyoto University | Nakayama N.,Conflex Corporation | And 5 more authors.
Journal of Molecular Spectroscopy | Year: 2010

A rotationally resolved ultrahigh-resolution fluorescence excitation spectrum of the S1 ← S0 transition of perylene has been observed using a collimated supersonic jet technique in conjunction with a single-mode UV laser. We assigned 1568 rotational lines of the 00 0 band, and accurately determined the rotational constants. The obtained value of inertial defect was positive, accordingly, the perylene molecule is considered to be planar with D2h symmetry. We determined the geometrical structure in the S0 state by ab initio theoretical calculation at the RHF/6-311+G(d,p) level, which yielded rotational constant values approximately identical to those obtained experimentally. Zeeman broadening of each rotational line with the external magnetic field was negligibly small, and the mixing with the triplet state was shown to be very small. This evidence indicates that intersystem crossing (ISC) in the S1 1B2u state is very slow. The rate of internal conversion (IC) is also inferred to be small because the fluorescence quantum yield is high. The rotational constants of the S1 1B2u state were very similar to those of the S0 1Ag state. The slow internal conversion (IC) at the S1 zero-vibrational level is attributed to a small structural change upon electronic transition. © 2009 Elsevier Inc. All rights reserved.


Nakayama N.,CONFLEX Corporation | Goto H.,Toyohashi University of Technology
Chirality | Year: 2015

The origin of P- or M-chirality of methyl substituted 1,3-cyclohexadienes are elucidated by time-dependent density functional theory (TD-DFT) calculation of 1,3-cyclohexadiene derivatives and acyclic 1,3-dienes. The sign-inversion of the rotatory strength of the lowest excited state between 1,3-cyclohexadiene and (5R)-axial-methyl-1,3-cyclohexadiene is caused by the conformation around the (C=)C-C(-Me) dihedral angle. The correlation between the sign of the rotatory strength and conformation has been found not only in methyl substituted derivatives but also fluoro substituted compounds. Chirality 27:476-478, 2015. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.


PubMed | Toyohashi University of Technology and CONFLEX Corporation
Type: Journal Article | Journal: Chirality | Year: 2015

The origin of P- or M-chirality of methyl substituted 1,3-cyclohexadienes are elucidated by time-dependent density functional theory (TD-DFT) calculation of 1,3-cyclohexadiene derivatives and acyclic 1,3-dienes. The sign-inversion of the rotatory strength of the lowest excited state between 1,3-cyclohexadiene and (5R)-axial-methyl-1,3-cyclohexadiene is caused by the conformation around the (C=)C-C(-Me) dihedral angle. The correlation between the sign of the rotatory strength and conformation has been found not only in methyl substituted derivatives but also fluoro substituted compounds.

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