Elementary excitations in poly-p-phenylene imine, the oxidized form of polyaniline

Among organic conjugated polymers, polyanilines are most interesting since variation in the relative amine/imine contents leads to variation in the population of the upper occupied π band. The fully oxidized polyaniline, poly(p-phenylene imine), has a doubly degenerate ground state and is topologically similar, although not identical, to polyacetylene. As a result, soliton distortions are expected to occur as elementary excitations. In this work, we present band structure calculations at the Hückel level for poly(p-phenylene imine). The Hückel parameters are optimized to reproduce the results of Valence Effective Hamiltonian (VEH) calculations. The electronic and geometric structures associated to soliton distortions are investigated by the use of a renormalization procedure. Two types of solitons are found, a situation reminiscent of what is predicted for an AB polymer.