Possibility of polaronic structure in polyaniline lattice: a semiempirical quantum chemical approach

Abstract

Polyaniline in dimeric, trimeric, tetrameric and pentameric forms have been theoretically investigated at various degrees of protonation. Using semiempirical AM1 technique all the internal coordinates of N-methyl capped aniline polymers have been fully optimized. A reduction of torsion angle between adjacent rings has been observed upon protonation. This allows charge conjugation in the protonated forms of this molecule. The results further indicate that this type of charge conjugation in protonated (polaronic or bipolaronic) forms of this molecule makes the two rings almost equivalent. A comparison of the energies of the fully optimized monomeric forms of polyaniline at various degrees of protonation with those of its dimeric analogies indicates the possibility of stabilization of the polaronic defect state in the polymeric chain of polyaniline. The spin dependence of the computed HOMO-LUMO gaps is analyzed.