Inter-chain versus intra-chain electron-hole photogeneration in trans-polyacetylene

Abstract

A theoretical study of the inter- and intra-chain photo-excitation of electron-hole pairs by light polarised both parallel (E/sub ///) and perpendicular (E_{perpendicular to} ) to the chain direction is presented and compared with experimental results for the anisotropic absorption coefficients, alpha /sub /// and alpha /sub ///. It is found that to account for the form of alpha _{perpendicular to} adjacent chains must be aligned out of phase, the resulting anisotropy being alpha /sub //// alpha _{perpendicular to} approximately=200, in reasonable agreement with experiment. It is also shown that alpha _{perpendicular to} is dominated by inter-chain transitions near the band gap and by intra-chain transitions further into the band, supporting the model for the anisotropic photo-excitation where electron-hole pairs initially created on separate chains are viewed as one of the most important sources of long-lived charge carriers.