Influence of substitutional impurities on soliton dynamics in t r a n s-polyacetylene

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Abstract
For different chains of trans-polyacetylene with various substituents the equations of motion of the coupled electron–phonon system are integrated within the Su–Schrieffer–Heeger model. NH+, N, and O+ as isoelectronic substitutions for a CH group as well as the effect of an NH and a CO group are investigated. The calculations for the time evolution of an end-generated kink show that neutral solitons can pass a nitrogen atom and an oxygen ion, but not an NH+, NH, or CO group. The negatively charged soliton is not able to pass any of the investigated substitutions. The CO unit, which is of special interest in the light of recent experimental results for acetylene–CO–copolymers with similar properties as trans-polyacetylene, represents a trap for both neutral and negatively charged kinks and a repulsive barrier for a positively charged kink. The limitations of the soliton model are discussed.