Electron-localization effects on the conducting and magnetic states in polyaniline copolymers

The methyl-ring-substituted derivative of polyaniline shows increased electron localization compared to polyaniline, and the mechanism for this increased localization has been proposed as due to a decrease in the interchain diffusion rate caused mainly by enhanced disorder due to random positioning of the methyl groups. We have investigated this issue by studying the magnetic and transport behavior of the copolymer poly(aniline)ₓ(p-fluoroaniline)_1-x at five values of x. We find that the electron-localization length in the copolymer is nearly equal to the conjugation length, and it decreases on decreasing x. The comparison of this behavior with that for poly(o-toluidine) and other alkyl-ring-substituted derivatives of polyaniline shows that the primary cause of electron localization in the polyaniline derivatives is enhanced interchain disorder. Our results also seem to provide some support for a model of polyaniline comprised of metallic islands consisting of single, isolated strands of the polymer.