Theoretical study of protonation effects in polyaniline oligomers

We study the electronic properties of eight-ring, phenyl-capped oligomers of polyaniline, in different oxidation states. The study was conducted through the Quantum Chemistry technique AM1 and comprised unrestricted ground state geometry optimization, for reduced and oxidized oligomers, including simulation of protonation. We find that oxidation induces linearization and planarization of the backbone, as expected. The protonation and biprotonation processes induce a pronounced charge concentration (over similar to2-3 rings), which is accompanied by localized chain distortion and characterizes polaron defects.