Optical properties of highly oriented fibrous polyacetylene

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Abstract
The optical reflectivity of thick-film (20–30 μm) polyacetylene, highly oriented by mechanical stretching, has been measured using polarized light. A Kramers-Kronig analysis of the data has been used to determine the optical absorption coefficient for polarization parallel and perpendicular to the chain axis. These novel optical data for fibrous polyacetylene are compared with those already reported on Durham polyacetylene. We have worked out a tight-binding model, extended to include the electronic coupling between neighboring chains within a three-dimensional periodic lattice. From a rough evaluation of the transverse hopping integral derived from the width of the vibronic absorption peaks an estimate of the number of the interchain photocarriers generated by radiation polarized perpendicular to the chain direction is provided. A comparison between calculated and experimental optical anisotropies indicates that the measured optical response perpendicular to the chain direction originates entirely from the chain misalignment.