VIBRATIONAL ANALYSIS OF POLYANILINE - A COMPARATIVE-STUDY OF LEUCOEMERALDINE, EMERALDINE, AND PERNIGRANILINE BASES

We present a comparative vibrational study of leucoemeraldine, emerald ine, and pernigraniline bases: fully reduced, half oxidized, and fully oxidized forms of polyaniline, respectively. By performing a general vibrational calculation based on the symmetrized dynamical matrix, we determine the force constants, the potential-energy distribution, and the Cartesian displacements for the three forms of polyaniline and ass ociated model compounds. We discuss the assignment of the fundamental Raman and ir vibrational modes of the polymers. The modifications of t he frequencies and consequently of the main force constants observed f rom one compound to the other are analyzed by considering the quinoid and aromatic characters along the chain. In this way, we determine a f orce field with physical significance which may be used to interpret t he electronic modification between neutral and protonated as well as p hotoexcited emeraldine forms. This comparative analysis demonstrates t he important changes of the electronic distribution around the nitroge n atom, which plays a major role in the conduction mechanism in this c lass of conducting polymers.