Neutral photo-excitations in oriented polyacetylene

Abstract
Polarisation-dependent measurements of photo-induced absorption (PA) have been carried out on highly oriented films of polyacetylene prepared by the Durham precursor route. For temperatures below 100 K, the PA spectrum exhibits an absorption peak at 1.36 eV, as observed for Shirakawa polyacetylene. This feature is due to a neutral excited state. The PA peak is independent of probe-beam polarisation and some 200 times weaker than in Shirakawa samples. These results suggest that the neutral excitations are rendered metastable by interactions with existing structural defects in the polymer.