Spectroscopy of Photo-Induced Solitons in cis-rich and trans-Polyacetylene
We present detailed measurements of the vibrational and electronic transitions of photogenerated solitons in cis-rich and all-trans polyacetylene prepared by the Shirakawa method. We find that the saturation concentration of excitations on the trans sequences in cis-rich material (30% trans) can be substantially higher than in all-trans and consider that these long-lived states are pairs of like-charged solitons. For both this cis-rich material and also for all-trans we find that photoinduced bleaching occurs only above the band edge, as expected if the photogenerated soliton states are formed from band states. In addition to the ‘translational’ IR modes previously reported, we find weaker absorptions from the shape modes of the soliton. These are present in both cis-rich and all-trans polyacetylene, and we consider that we have observed the IR-active ‘third bound mode’ calculated by WADA and colleagues.
KeywordsRecombination Soliton Acetylene Thiophene Maki
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