Mechanism for photogeneration of charge carriers in polyacetylene

In light of new experimental observations, a mechanism for the photogeneration of charge carriers in trans-polyacetylene is presented. By way of introduction, we discuss the qualitative changes in the picture of charged-soliton photogeneration that are expected due to the inclusion of electron correlation effects. In addition, we point out the unique implications the soliton model has for the generation of photocarriers by impurity-induced photoabsorption. Experimentally, we report two types of observations which are relevant to this discussion. First, measurements of the relative efficiency for photocarrier generation, as a function of photon energy, are presented for samples of varying thickness and impurity content. Second, we compare the optical absorption spectra of photocarriers created by intrinsic and extrinsic photoabsorption. Finally, we present a model for the relaxation of photoexcited polyacetylene which attempts to account for these, as well as earlier, observations.