The Electroactive Nature of Polyaniline. The Nature of the Chromaphores

Abstract

Thin films of polyaniline (PANi) prepared electrochemically can readily be investigated insitu. In this way, both the oxidation state and level of protonation can be precisely controlled. Insitu UV/VIS/NIR and Resonance Raman spectra are presented here. These results show that the usual polaron/bipolaron models applied to other conducting polymers are not consistent in the case of PANi. The structures of the chromaphores associated with the observed ‘dopant’ induced optical absorptions in PANi are quite different, which is inconsistent with polaron theory. Resonance Raman spectra show that the structure of the chromophore giving rise to absorption at ca. 3eV is that of a simple p-di-substituted phenylene moiety, whereas that of the absorption at ca. 1.6 eV is consistent with a mixed benizonoid/quinoid radical (eg. a semiquinone moiety). In both cases the chromophores are localised. Therefore a new model for PANi is proposed.