The Polyanilines: Model Systems for Diverse Electronic Phenomena

Abstract

Polyaniline has three stable insulating forms, leucoemeraldine base (LEB), emeraldine base (EB), and pernigraniline base (PNB). These three forms exhibit differing phenomena ranging from intramonomer luminescing excitons and ring rotation polarons in LEB, to nonluminescing charge transfer excitons and also ring rotation polarons in EB, to a degenerate ground state with bond order parameter solitons and ring order parameter polarons in PNB. The electronic structure and excitations of these three forms are contrasted. The LEB form can be p-doped (oxidatively doped), the EB form can be protonic acid doped and the PNB form can be n-doped (reductively doped) to form conducting systems. The essential role of crystallinity and coherence in the metallic state of the emeraldine salt form is reviewed. The role of derivatization in controlling the electronic phenomena in the insulating and conducting forms is outlined.