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

Photoluminescence studies of spun films of polyaniline base (emeraldine oxi dation state) show that films prepared from NMP solution in air having a re lative humidity between 43 +/- 2 and 57 +/- 2% (21 degreesC) exhibit photol uminescence at 401 nm, which persists when the films are held in a dynamic vacuum. Films prepared from NMP solution containing water show similar beha vior to those prepared in the above humidity range. When protonated ("doped ") with HCl the above photoluminescence disappears and is replaced by a pho toluminescence peak at 467 run. The reverse behavior occurs on deprotonatio n with NH3 vapor, the 467 nm peak disappearing and the 401 tun peak reappea ring, These results, together with photoluminescence studies on the phenyl/ phenyl end-capped tetramer of aniline in both the emeraldine and leucoemera ldine oxidation states, lead to the conclusion that in solution the emerald ine base is a dynamic block copolymer in which reduced (benzenoid/amine) an d oxidized (quinoid/imine) units are constantly interchanging positions via a tautomeric (hydrogen migration) process between nitrogen atoms. This pro cess is promoted by water. The resulting production of long sequences of th e reduced and oxidized units, which separate long sequences of the emeraldi ne base, persist when the NMP solvent is removed, resulting in microphase s egregation 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. (C) 2001 Published by Elsevier Science B.V.