Yasuhiko Gondo

Electronic Structure and Spectra of Biphenyl and Its Related Compound

The Pariser—Parr method has been used to elucidate the electronic structure and the spectrum of biphenyl. The absorptions at 300, 250, 200, and 170 mμ seem to be explained reasonably. Simple forms of linear combinations of the symmetry orbitals constructed from 2pπAOs were used as molecular orbitals. Calculations were made for three conformations, the angle between the planes of two benzene rings being 0°, 45°, or 90°. In each of the conformations 16 singlet and 16 triplet excited configurations were taken into account. An application has been made to 2,2′‐bipyridyl, and its absorption spectrum has been explained.

The absorption spectrum of benzene in carbon tetrachloride at 77°K

Abstract The absorption spectrum of benzene has been studied in carbon tetrachloride solutions of various concentrations at 77°K and in 10 per cent solution at various temperatures from 30°C to 77°K. The so-called crystalline spectrum appeared strongly at low temperature and its occurrence was ascribed to the deformation of benzene due to crystal forces of the carbon tetrachloride matrix.

The ESR spectra of p-benzosemiquinone radical anion included in cyclodextrins

Abstract The ESR spectra of p -benzosemiquinone radical anion included in cyclodextrins (CyDxs) in aqueous solutions were observed and analyzed. Remarkable differences in the line shape were found between the spectrum in α-CyDx aqueous solution and that in 95% ethanol. They are explained in terms of the suppressed molecular rotation of the radical included in the α-CyDx cavity. The ESR spectra of the radicals included in β- and γ-CyDx in aqueous solutions are identical with that in 95% ethanol, hence in the β- and γ-CyDx cavities the radical rotates as freely as in 95% ethanol.

Energy‐donor phosphorescence and energy transfer by exchange interaction in a rigid matrix

The decay of the energy‐donor phosphorescence has been observed using a N2 laser on the benzophenone–naphthalene and p‐methoxybenzaldehyde–naphthalene systems, and the results have been examined in the light of the theory developed by Inokuti and Hirayama for energy transfer by exchange interaction. Substantial discrepancies have been found between the theory and the observed phosphorescence decay curves, in particular, for the short time region after excitation. We have introduced the concept of the nonvanishing closest donor–acceptor intermolecular distance into the framework of the theory. Over the whole range of time, the experimental data have been found to agree with the theory thus amended.

The structure and dynamics of 1,3,5-cycloheptatriene and 1,3-cycloheptadiene radical cations in low-temperature matrices. An ESR investigation

Abstract ESR spectra of the radical species derived from 60 Co γ-ray irradiation of 1,3,5-cycloheptatriene (1,3,5-CYT) and 1,3-cycloheptadiene (1,3-CYD) in halocarbon matrices have been studied in the temperature range 70–103 K. Ring inversion across the molecular plane occurs in the radical cation 1,3,5-CYT + in CCl 3 CF 3 , the activation energy being 1.7 kcal/mol. Above 90 K, 1,3,5-CYT + is deprotonated thermally in CCl 2 FCClF 2 . No dynamical effect has been observed for 1,3-CYD + .

Spectroscopic studies on the cyclodextrin inclusion complexes of aromatic compounds and radicals

Abstract We have studied three different subjects, i.e., the ESR line-shape changes, induced circular dichroism (ICD), and suppression of fluorescence quenching, all caused by inclusion complex formation with cyclodextrins.

Determination of the deuteron and alkyl-substituent hyperfine coupling constants in nitrobenzene radical anions by formation of cyclodextrin inclusion complexes

Abstract Stable β-cyclodextrin inclusion complexes with radical anions of thirteen different nitrobenzenes have been generated by chemical reduction in 50% aq especially in the central portions associated with the vanishing 14 N nuclear spin component. The high resolution obtained permits the estimation of the small hyperfine coupling constants in the guest radicals due to deuterons and alkyl substituents.

Concentration depolarization of phosphorescence

Abstract Two new findings are reported on the energy transfer between like molecules in rigid glass at 77 K: The depolarization of the phosphorescence is not mainly caused by the triplet-triplet energy transfer, but essentially by the singlet-singlet transfer. And the concentration where the depolarization starts to take place depends on the individual phosphor compounds.

Matrix dependence of the conformations of the 1,4-diethylbenzene radical cation at low temperatures

Abstract 1,4-Diethylbenzene radical cation generated in six different halocarbon matrices by 60 Co γ-ray irradiation has been studied by ESR at low temperatures. The spectra exhibit drastic variations in different matrices, showing that the conformation of the radical cation is largely dependent on the matrix.

Non-exponential phosphorescence decay of phenanthrene in biphenyl

Abstract Non-exponential phosphorescence decays of phenanthrene in biphenyl polycrystals have been observed. It is found that excitation with short duration quickens the decay while the decay is slower after excitation with weaker intensity. The origin of the non-exponentiality is ascribed to the distance-dependent interactions between guest molecules in the lowest excited triplet state.