Polyaniline, a dynamic block copolymer: key to attaining its intrinsic conductivity?

Abstract

Photoluminescence studies of spun films of polyaniline base (emeraldine oxidation state) show that films prepared from NMP solution in air having a relative humidity between 43±2 and 57±2% (21°C) exhibit photoluminescence at 401 nm, which persists when the films are held in a dynamic vacuum. Films prepared from NMP solution containing water show similar behavior to those prepared in the above humidity range. When protonated (“doped”) with HCl the above photoluminescence disappears and is replaced by a photoluminescence peak at 467 nm. The reverse behavior occurs on deprotonation with NH 3 vapor, the 467 nm peak disappearing and the 401 nm peak reappearing. These results, together with photoluminescence studies on the phenyl/phenyl end-capped tetramer of aniline in both the emeraldine and leucoemeraldine oxidation states, lead to the conclusion that in solution the emeraldine base is a dynamic block copolymer in which reduced (benzenoid/amine) and oxidized (quinoid/imine) units are constantly interchanging positions via a tautomeric (hydrogen migration) process between nitrogen atoms. This process is promoted by water. The resulting production of long sequences of the reduced and oxidized units, which separate long sequences of the emeraldine base, persist when the NMP solvent is removed, resulting in microphase segregation of these sequences in the solid film. Since only the emeraldine base sequences can be doped by acids, the conductivity of the doped film is less than that of its predicted intrinsic conductivity.