Photoexcited states in directly synthesized trans-polyacetylene films studied by photocurrent measurement

A trans-polyacetylene film was directly synthesized to reduce defects introduced during usual thermal isomerization treatment. A photocurrent excitation spectrum of this film showed very low efficiency around a reflection peak which was accompanied with phonon side bands. This strongly indicates that the lowest optically allowed state of trans-polyacetylene is a 11Bu exciton state like other conjugated polymers, such as polydiacetylenes. Misinterpretations of the experimental results under the SSH model, because of the use of a film of low quality, are pointed out and reinterpretations are made according to the present conclusion.