Photogenerated Gap States in Polyacetylene

This paper reports the first observation of photogenerated gap states in polyacetylene, ${\left(\mathrm{CH}\right)}_x$. A transient optical absorption, at photon energies less than the band gap, is produced by photogeneration of electron-hole pairs. The spectrum of this absorption is measured in both cis and trans isomers of ${\left(\mathrm{CH}\right)}_x$. From a comparison of these spectra with similar spectra seen in molecular analogs of ${\left(\mathrm{CH}\right)}_x$, it is concluded that these gap states are intrinsic, self-localized excitations of the semiconductor chain.