Long-range exciton in a PNB polymer and its responses to electrostatic fields

Long-range excitons are obtained for an open chain of a PNB polymer with finite length, in the framework of the Baranowski-Buttner-Voit model. The results show: an applied field results in a blue shift (similar to0.25 eV) of the exciton absorption. As the field is stronger than 925 kV/cm, the exciton is dissociated into a soliton and an anti-soliton, while zero-field absorption of the exciton is split into two peaks at 1.1 and 1.3 eV, which is consistent with the observed two short-lived peaks of the photoinduced absorption in the polymer. We try to understand the observed electrochromism of the polymer by the blue shift.