Study of Excited-State Dynamics of Organosilicon Compounds by means of Two-Step Two-Color Laser Photolysis

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Organosilicon compounds and polymers have attracted much attention because of their photo- and electro-luminescent properties and photo-conductivity. In this research, 1) in order to clarify the excited-state property of the organosilicon compounds we studied their photophysical and primary photochemical processes in solution by means of nanosecond laser flash photolysis and fluorescence measurements, and 2) to clarify the relation between the structure and function of polysilanes we studied the orientation of the polysilane molecules in their thin films, and also the control of the main chain conformation by means of photo-irradiation. The following results were obtained.【Results】1) Photophysical parameters were determined for more than ten organoslicon compounds such as 9,10-dihydro-9-silaphenanthrene and 9-silafluorene derivatives.2) Upon a silyl-group introduction to aromatic compounds as substituent(s), the fluorescence quantum yield markedly increased by the interaction between t … More he σ-electrons of a Si-C bond and π-electrons of aromatic ring. Whereas in the sila-substituted compounds such as 9,10-dihydro-9-silaphenanthrene and 9-silafluorene derivatives, the decrease in the fluorescence quantum yield was observed. This observation was explained by the enhancement of the intersystem crossing in the sila-substituted compound.3) By two-step two-color nanosecond photolysis of 9-silafluorene derivatives their radical cations were formed via the triplet state. The de-protonation of the radical cations takes place to form their fluorenyl radicals.4) The 9-silaphenanthrenes were prepared for the first time by the steady-state photolysis of 9,10-dihydro-9-silaphenanthrene derivatives and their electronic structure was clarified in comparison with that of phenanthrene.5) Thermal hysterisis was observed for the molecular orientation of poly(di-n-dihexylsilane) molecules in their film prepared on the stretched poly(vinyl alcohol) film. The orientation mechanism of poly(di-n-dihexylsilane) molecules were explained on the basis of molecular interaction.6) The conformational change from the helix to random coil of the main chain of the polymethylphenylsilanes with pendant groups of p-nitroazobenzene or p-cyanoazobenzene takes place upon photo-irradiation. This change was induced by the photoisomerization of the pendant azobenzene groups.【Conclusion】Excited-state dynamics of organosilicon compounds were clarified by means of laser flash photolysis and the control of the main chain Information was achieved by photo-irradiation. Less