Photoexcitation of Polarons and Molecular Excitons in Emeraldine Base

Abstract

We report the first observation of the photoinduced absorption spectrum of the emeraldine base form of polyaniline. The spectrum contains both subgap photoinduced bleaching at 1.8 eV and photoinduced absorptions at 0.9, 1.4, and 3.0 eV, as well as band-edge bleaching above 3.5 eV. The existence of the subgap bleaching peak is consistent with a model of optically excited localized molecular excitons. The energies of the three photoinduced absorption peaks and the dependence of the peak amplitudes on pump power give evidence for the photoexcitation of polaron pairs that recombine bimolecularly.