Charge Carrier Mobilities in Substituted Polysilylenes:  Influence of Backbone Conformation

Abstract

The results of a systematic study of charge migration in the crystalline, liquid-crystalline, and amorphous states of organo-substituted polysilylenes, using the pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) method are summarized. A homologous series of symmetrically substituted poly(di- n -alkylsilylene)s with alkyl side chain lengths ranging from n -butyl to n -decyl has been studied, as well as a copolymer with branched substituents and two nonsymmetrically substituted amorphous polymers: poly(hexylmethylsilylene) and poly(methylphenylsilylene). The charge carrier mobilities of the dialkyl-substituted polysilylenes varied from 4 × 10 -5 m 2 /(V s) for charge transport along the all-trans silicon backbone of poly(di- n -decylsilylene) to 2 × 10 -7 m 2 /V s for the amorphous poly(hexylmethylsilylene). An increase of conformational disorder in the columnar mesophase as compared to the solid crystalline phase leads to an abrupt, reversible decrease in the charge carrier mobilities. A direct relationship between charge carrier mobilities and polysilylene backbone conformation has been established. The introduction of a phenyl group lowers the charge carrier mobility to 4 × 10 -8 m 2 /(V s).