Optical properties of pyrrolyl-substituted polysilanes

Pyrrolyl-substituted polysilanes were synthesized in the present study. The pyrrolyl rings directly attached to the Si conjugated main chains with SiN bonds. Poly(alkylpyrrolylsilane) and poly(phenylpyrrolylsilane) showed a chromophore which is attributed to σ–σ* transition in the conjugated system associated with near-UV fluorescence. However, a strong photoluminescence band was observed at 450–500 mn other than the near-UV photoluminescence for the polysilanes. The luminescence is due to the energy relaxation from σ* to an inter-band level produced by σ–π mixing between main chain σ-conjugated system and pyrrolyl groups as suggested by theoretical calculations. Transient spectroscopy of the polysilanes was also carried out showing a new chromophore at the vis-IR region (800 nm) other than near-UV (300–400 nm) and IR (∼2000 nm) absorption bands typically observed for alkyl- and phenyl-substituted polysilanes. It also supports the presence of the mid-gap level in the pyrrolyl-substituted polysilanes.