Spectroscopic studies of protonation, oxidation and light irradiation of polyaniline solutions

Abstract

The absorption spectra of emeralidine base and the fully reduced leucoemeraldine in N-methylpyrrolidinone (NMP) indicate that the former is stable in this solvent but the latter undergoes oxidation of the amine units to imine units in the presence of dissolved oxygen. The presence of imine units is confirmed by X-ray photoelectron spectroscopy and infra-red absorption spectroscopy. Under light irradiation, this oxidation process is accelerated. Both this polymer and emeraldine base undergo further degradation of the polymer chain. Comparison of the spectra of leucoemeraldine and emeraldine base solutions with aqueous HClO4 added indicates that protonation can occur at the amine units of the former, although this process is not as effective as protonation of the imine units of emeraldine base. The polymers gradually undergo deprotonation resulting in quinoid-imine structures in both cases when oxygen is present, and the deprotonation process is also accelerated by light. On the other hand, the addition of Cu(ClO4)2. 6H2O to the leucoemeraldine and emeraldine base solutions results in the polymers approaching the fully oxidized state which is much more stable under light irradiation than the pristine polymer solutions. The similarities and differences between the results obtained in solution and in solid-state are also discussed. © 1992.