The stability of polaron and bipolaron in oligopyrrole

The results of Austin Model 1 (AM1) geometry optimization calculations are presented to determine the neutral and charged geometry properties of oligopyrrole. Comparing with the neutral states, the changes of the bond lengths of the charged states are very evident. The single oxidized state is corresponding to a polaron and the doubly oxidized state to a bipolaron. But in the case of the lengths n≥4m (m = 4) , the doubly oxidized state is corresponding to two separate polarons. It was found that a transition between bipolarons and polarons would be possible by adjusting the lengths of the chains. The investigation is helpful to understand spin-polarized transport in organic semiconductor materials.