Molecular structure of ‘‘trans’’-polyacetylene: The presence of remnantcisunits and their influence on soliton formation and diffusion

We report the infrared spectra of ‘‘trans’’-polyacetylene that has been prepared by thermal isomerization of Shirakawa cis-(CH${)}_x$. The minimum of ∼5% residual 740-${\mathrm{cm}}^{\mathrm{-}1}$ absorption observed for all cases studied is suggested to be due to isolated remnant cis linkages. It is shown that these remnant cis linkages may confine the neutral soliton and hence affect the neutral-soliton diffusion coefficient. Implications for the soliton-generation mechanism and for conjugation lengths derived from Raman spectra are pointed out.