ELECTRONIC-STRUCTURE OF POLYDITHIENO[3,4-B,3',4'-D]THIOPHENE - A SMALL BANDGAP CONJUGATED POLYMER

We use a quantum chemical approach to investigate the chemical and ele ctronic structure of polydithieno[3,4-b;3',4'-d]thiophene (PDTT'), for which the monomer unit possesses four potential linking sites on alph a carbon positions. Semiempirical Austin Model 1 (AM1) calculations ar e performed on oligomer systems, considering different types of connec tion between the DTT' units, to determine the most favorable chain con formation and the relative stabilities of the oligomer segments. The e lectronic properties of the corresponding polymers are calculated with the Valence Effective Hamiltonian (VEH) method and compared to the re sults of optical spectroscopy.