RADICAL IONS OF POLYSILANES WITH ALKYL AND ARYL SIDE GROUPS

Absorption spectra of radical ions of polysilanes with alkyl and aryl pendant groups were measured in rigid matrices at 77 K and in solution at room temperature by using gamma-irradiation and pulse radiolysis methods. The radical cations and anions of the polysilanes with alkyl pendant groups showed strong and sharp absorption bands in the ultraviolet region (approximately 360 nm). The absorption maxima shifted to longer wavelengths with increasing bulkiness of the pendant groups. The radical anions of polysilanes with phenyl pendant groups, poly(methylphenylsilane), and copolymers with alkyl-substituted polysilanes had the spectra slightly red-shifted relative to those with sterically unencumbered alkyl substituents. The structural dependence was less significant for the radical cations. The spectra of radical anions of polysilanes with naphthyl groups showed broad bands in the ultraviolet region and a sharp band at 800 nm, which are ascribable to the monomeric radical anion of the pendant naphthyl groups. The radical cations of naphthyl-substituted polysilanes had a band in the infrared region in addition to the visible bands, which indicate the existence of charge resonance interaction between two naphthyl side groups. Pulse radiolysis experiments in solution revealed that the lifetimes of the radical anions, 5-30-mu-s, are shorter than those of radical cations, 30-100-mu-s. The radical cations of polysilanes with aryl side groups have longer lifetimes than those of polysilanes with alkyl side groups.