Gap states of charged combined solitons in a pernigraniline-base polymer

Considering the electron–electron interactions, we have investigated the electronic structures of charged combined solitons in a pernigraniline-base polymer on the basis of Baranowski–Büttner–Voit model. The numerical results show that there exist two bound states in the Peierls gap for both positive and negative combined solitons, one is deep level and the other is shallow level. The energy of the deep level (for S+ is about 1.03 eV and S− 0.98 eV) agree with the photoinduced absorption data (∼1.0 eV) very well. The shallow one is newly discovered and it is about 0.22 eV under the bottom edge of the conduction band (positive soliton) or above the top edge of the valence band (negative soliton). Some other shallow states outside the energy bands are also predicted.