POSSIBILITY OF POLARONIC STRUCTURE IN POLYANILINE LATTICE - A SEMIEMPIRICAL QUANTUM-CHEMICAL APPROACH

Polyaniline in dimeric, trimeric, tetrameric and pentameric forms have been theoretically investigated at various degrees of protonation. Us ing semiempirical AMI technique all the internal coordinates of N-meth yl capped aniline polymers have been fully optimized. A reduction of t orsion angle between adjacent rings has been observed upon protonation . This allows charge conjugation in the protonated forms of this molec ule. 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 p rotonation with those of its dimeric analogies indicates the possibili ty of stabilization of the polaronic defect state in the polymeric cha in of polyaniline. The spin dependence of the computed HOMO-LUMO gaps is analyzed. (C) 1997 Elsevier Science B.V.