The fully oxidized form of polyaniline, pernigraniline, is studied in the framework of a Su-Schrieffer-Heeger-like Hamiltonian. The protonation process of a long oligomer is investigated. Protonation is modeled by a change in site energies around the protonated site. The results of the calculataions indicate that a phase separation occurs between protonated and nonprotonated regions. Inside a protonated region, a charge-density wave (CDW) develops which tends to keep the same periodicity as that of the original CDW of the unperturbed system. As a result, protonation is preferentially produced on every other nitrogen. The present findings are compared to those obtained previously in the case of emeraldine.

• Received 4 August 1989

DOI:https://doi.org/10.1103/PhysRevB.40.11997