Dynamics of photoexcitations in polyacetylene: picosecond transient Raman scattering

Abstract We present the theoretical results for the picosecond transient resonant Raman scattering in polyacetylene taking into account the dynamics of the photoexcitations in the excited states of the samples. The calculations are based on the model developed to interpret the power law decay t − α of the charge carrier recombination in the transient photoinduced bleaching in polyacetylene. The interchain and intrachain dynamics of the photoexcited charges are studied by numerical simulation, in the picosecond regime, as time behaviour of the random walk over chains (2000 sites long) formed by conjugated segments of different lengths, separated by random potential barriers. The transient changes in the Raman band shapes and in their intensities are calculated in two cases: (a) fully isomerized trans samples and (b) cis -rich samples. The calculated transient changes in the range Δt ∼20–100 ps, due to the energetically favourable diffusion of the survived photogenerated charges from segments at intermediate length to longer ones (case (a)) and from cis to trans segments (case (b)), are in good agreement with the experimental data.