Photoexcitations in polyacetylene with controlled conjugation length

Abstract Photoexcitation of solitons has been studied by steady state and transient picosecond photomodulation spectroscopy in a form of soluble polyacetylene with controlled conjugation length. A systematic blue shift of the charged soliton band is observed by decreasing the average conjugation length from a few hundred to 20 CH units, showing that the chain segmentation has strong effects when the conjugation length becomes comparable or shorter than the soliton spatial extent. The linear dependence of the charged soliton band on the inverse of the average conjugation length is discussed, and an evaluation of the electron correlation energy is given. The effects of the decreased conjugation length have been also investigated by time-resolved photo-induced absorption. The transient electronic response in the time domain from 5 ps to 1 ns is interpreted in terms of soliton recombination associated with diffusion on chains distributed in length.