Exciton narrow band model for 7,7,8,8-tetracyanoquino-dimethane salts

Abstract

A simple two-electron exciton model for narrow band exciton mode conduction is developed for simple and complex 7,7,8,8-tetracyanoquinodimethane (TCNQ) salts. The local exciton functions are defined in terms of Heitler–London configurations within discrete multicentre TCNQ sandwiches, which are then formed into exciton bands assuming tight-binding conditions. These exciton bands are then compared to first-order one-electron band structure. The two-centre exciton treatment for simple salts yields a very similar result to the one-electron band theory, but the three and four-centre exciton theory for the complex salts suggests that the effective charges of their valence and conduction excitons are small.