Photochemical Properties of Network and Branched Polysilanes

Linear, branched, and network polysilanes were synthesized by the copolymerization of dichloromethylphenylsilane and trichlorophenylsilane. The influence of the Si-skeleton on absorption and emission spectra was investigated. The sharp σ-σ* absorption band (λ_max 334 nm) of linear poly-(methylphenylsilylene) changed into a broad one with branching. The shift of the absorption edge to a longer wavelength (410 nm) suggests that the increase of σ-conjugation is due to the silicon network structure. The sharp emission (λ_max 355 nm) of linear poly(methylphenylsilylene) also shifted to the broad emission (λ_max 471 nm) for network poly(phenylsilyne). The intermediates formed during the photodegradation of polysilanes with various Si-skeletons were investigated by flash photolysis. The time-resolved absorption spectra exhibited the absorption bands of a silyl radical and silylenes. The significant influence of the excitation wavelength was observed. Silylene was produced effectively by the excitation at shorter wavelength (π-π* excitation). The transient absorption spectrum for network poly(phenylsilyne) suggested the formation of a silylsilylene in the silicon network structure. The absorption of the silylsilylene appeared at longer wavelength (λ_max 550 nm) compared to that of low molecular weight silylene (λ_max 480 nm).