Picosecond photoinduced exciton bleaching in emeraldine base: Crossover in decay mechanisms

We report picosecond photoinduced bleaching (PB) of the exciton absorption of the emeraldine base form of polyaniline. The temperature- (T-) independent dispersive decay, {~}t^-0.11, observed in this study differs markedly from the dynamics of earlier studied semiconductors. It also contrasts with long-time PB, which varies as t^-β with {β}{~}0.5, and is weakly T dependent. These results point to the likely role of rotations in ring-containing polymers.