Radical anions of polysilane derivatives studied by pulse radiolysis

Abstract

The electronic structure of polysilane charged radicals has been studied by transient absorption spectroscopy using nano-second pulse radiolysis technique. Radical anions of polysilanes with symmetric alkyl, asymmetric alkyl, and phenyl substituents displayed a near-UV absorption band with a 0–0.5 eV red shift from absorptions ascribed to exciton states. A near-IR transient absorption was also observed with the same kinetics as the UV band. Electron transfer from polysilane radical anions to pyrene was observed with rate constants from 4.5×10 9 to 7.3×10 9 M −1 s −1. Extinction coefficients ( ε( −)) of the radical anions were determined to be 8.5×10 4–1.6×10 5 M −1 cm −1. The value of ε( −) and band width of the transient absorption depended on the substitution of the Si main chains. The degree of electron delocalization was estimated based on the 1-D polaron model, and showed a clear relationship with the extinction coefficient ε of the band-gap transition and the viscosity index α of the polymers.