Optical spectroscopy of photoinduced and field-induced excitations in polyacetylene prepared by the Durham 'photoisomer' route

Abstract

The authors present a study of the optical, electronic and electro-optical properties of polyacetylene prepared by the Durham 'photoisomer' route. They show here that electronic and vibrational excitations of the polymer, although affected by the disorder, are not fundamentally changed in character and that, in particular, they still find evidence for electron states associated with soliton defects on the chain, which are of non-bonding character and lie in the centre of the gap. Photoinduced absorption measurements show the 'mid-gap' band to 'soliton' transition associated with charged photoexcitations at about 0.65 eV, significantly higher than that found for better ordered polyacetylene. The electronic and electro-optical properties of the field-induced charge accumulation layer formed in MIS device structures are also investigated. They have measured the 'mid-gap' optical absorption band associated with the charge present in the accumulation layer, and they find a broad absorption feature which peaks at 0.9 eV. They discuss the electronic properties of this form of polyacetylene and, in particular, the modelling of disorder on the electronic structure.