Observation of a defect dependent pinning mode in durham-polyactetylene

Summary form only given. Photoinduced infrared modes in polyacetylene (PA) are associated with a lattice distortion around photogenerated states (mostly referred to as solitons). It is generally accepted, that the frequency positions of these photoinduced infrared modes depend on the quality of the investigated sample. Especially the position of the pinning mode strongly depends on the effective conjugation length (1/sub c,eff/) and its observed shape is therefore explained by a distribution of I/sub c,eff/. We present photoinduced absorption (PIA) measurements with a high signal to noise ratio, which reveal a pronounced structure of the pinning mode in Durham-PA, which has not been observed before. In addition to the known absorption bands at 1374cm/sup -1/, 1286cm/sup -1/, and 500cm/sup -1/ we discuss new features in our PIA-spectra, which are caused by photogenerated states in Durham-PA. We studied the influence of oxidation in our PIA-spectra and observed a strong shift of the pinning mode to higher energies upon oxidation, which we explain with a decrease of 1/sub c,eff/.