Electronic excitations of a conjugated polymer crystal

Abstract

A highly crystalline polymer is described in which all the polymer chains are parallel and the backbone of the chains is conjugated. It is postulated that the low-lying (<5 eV) electronic excitations are electrons and holes in one-dimensional bands confined to individual chains. The band structure is deduced. The crystal is a semiconductor, E G approximately=2 eV, for charge transfer along the chain direction and an insulator in perpendicular directions. Singular Van Hove optical transitions characteristic of one dimension are discussed and shown to lead to peaks in the reflectivity. The optical and Raman properties of the model are compared with experimental results.