|Budget Amount *help
¥6,300,000 (Direct Cost: ¥6,300,000)
Fiscal Year 1989: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1988: ¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1987: ¥2,700,000 (Direct Cost: ¥2,700,000)
Combining a nanosecond ruby laser with a detection system (a polychromator and an image intensifier coupled with a linear position-sensitive detector) controlled by a personal computer, a convenient laser photolysis system was constructed. Using this system, we studied the photophysics of highly hindered molecules and the following results were obtained: (1) Multiple-components phosphorescences of 2,4,6-triisopropylbenzophenones at 77 K could be interpreted in terms of the existence of several conformers. (2) Triplet-triplet absorption spectra due to the lowest triplet (T_1) states of 2,4,6-triisopropylbenzophenones in solutions at room temperature shifted progressively to the blue with time on the subnanosecond time scale. This spectral shift was ascribed to the conformational change in the T_1 states. (3) Even for such a non-hindered molecule as methyl o-benzoylbenzoate, the existence of two T_1 states was observed at 77 K. (4) Phosphorescence spectra of 1,8-di-t-dutylanthraquinome,
1,2,3-tri-t-butylanthraquinone and 1,2-di-t-buty1-3-trimethylsilylanthraquinone were abnormally broad with short lifetimes of a few mus. These unusual T_1 states of pi pi^* or mixed npi^*-pi pi^* character were ascribed to the distortion of the geometrical structure of molecules. Although the transient absorption spectrum of 1,8-di-t-butylanthraquinone was assigned to a reaction intermediate, those of 1,2,3-tri-t-butylanthraquinone and 1,2-di-t-buty1-3-trimethylsilylanthraquinone were ascribed to the triplet-triplet absorptions.
We also obtained the following results: (5) In spite of a strong hydrogen-bonding ability of 2,2,2-trifltiorothanol (TFE), the phosphorescence spectra of anthraqtiinone, beta-halogenoanthraquinones, benzophenones, 1-indanone, flavone and flavanone in TFE at 77 K were identical with those in usual solvents. In contrast, the phosphorescence spectra in TFE/water could be interpreted in terms of the complex formation among triplet ketones, TFE and water(s), indicating that the change of the nature (or character) of pure solvents was not always the essential condition for interchanging the order of energy levels of triplet pi pi^* and pi pi^* states inherent to molecule itself. (6) From measurements of fluorescence and triplet-triplet absorption spectra of 9- and 9,10-dibromoanthracenes at various temperature, It was found that the direct intersystem crossing from the lowest excited singlet states to the T_1 states was the most important process to populate the T_1, state at low temperature (especially at 77 K). (7) For pliotochpmical reactions of 9-nitroanthracenes, it was confirmed that anthryloxy radicals as the reaction intermediates were produced via the higher excited triplet states of npi^* character. Less