Showing papers by "Hiroshi Sekiya published in 1999"

Tunneling in jet-cooled 5-methyltropolone and 5-methyltropolone-od. coupling between internal rotation of methyl group and proton transfer

Abstract: The coupling of two large amplitude motions, the internal rotation of the methyl group and the intramolecular proton transfer, has been investigated for jet-cooled 5-methyltropolone, 5-methyltropolone–OD, and the 5-methyltropolone–(H2O)1 1:1 hydrogen-bonded complex by measuring the fluorescence excitation, dispersed fluorescence, and hole-burning spectra in the S1–S0 region. The vibronic bands in the excitation spectrum of 5-methyltropolone consist of four components originating from the transitions between the sublevels in the S1 and S0 states. The intensity of the bands, the frequencies, and the change in the stable conformation of the methyl group upon photoexcitation have been analyzed for 5-methyltropolone–(H2O)1 by calculating the one-dimensional periodic potential function, which provides the correlation between the internal rotational levels of 5-methyltropolone–(H2O)1 and the sublevels of 5-methyltropolone. It has been shown that the electronic transitions between the sublevels within the same sy...

Investigation of intramolecular hydrogen bonds in ortho-hydroxytropolone

Abstract: The S0–S1 electronic spectra of ortho-hydroxytropolone (o-OHTR) in supersonic jets were measured in order to study its isomerism. Only one isomer has been detected in a supersonic jet. A blue shift of electronic origin due to deuteration of two -OH groups was twice as large as that of one -OH group, suggesting that the configurations of the two -OH groups in o-OHTR are equivalent. This finding is consistent with the results of the ab initio calculations. The origin bands of the complexes with water and acetone were red-shifted from that of the bare molecule. The red-shift was explained in terms of two opposite effects of formation of an intermolecular hydrogen bond on each of two intramolecular hydrogen bonds.

The electronic spectra of jet-cooled 5-phenyltropolone: Phenyl torsion and its effect on proton tunneling

Abstract: The S1–S0 electronic spectra of jet-cooled 5-phenyltropolone were measured to elucidate the features of phenyl torsion and its effect on intramolecular proton transfer. Several bands in the fluorescence excitation spectra were assigned to phenyl torsion and other low-frequency modes with the aid of the ab initio calculation. The torsional potential energy function was investigated with the one-dimensional torsional potential function analysis for the S0 state. Presence of significant potential barriers due to the large H-atom steric repulsion between the phenyl ring and the tropolone ring were anticipated at the torsional angle φ=0° in both the S0 and S1 states. It was suggested that the large steric repulsion significantly influenced both phenyl torsion and proton transfer.

Intermolecular Excimer Formation in Dinuclear Metal Complexes

Abstract: In this paper the intramolecular/intermolecular excimer formations of [Fe2(bpmp)(1-pyace)2](BF4)2, [ZnFe(bpmp)(1-pyace)2](ClO4)2 and [Zn2(bpmp)(1-pyace)2]ClO4 which contain 1-pyreneacetic acid as a chromophore are reported. The fluorescent properties of the ZnZn complex offer the intramolecular dimers of the two chromophores in addition to intermolecular dimers due to the intermolecular stacking. The ZnFe and FeFe complexes are under the strong influence of quenching and show weak intramolecular/intermolecular excimer formation in the concentration more than 10−4 M. The emission intensities and intensity ratios (IE/IM) of the fluorescence are dependent on the metal ions.