The electronic structure of oligothiophenes

In the present work we report on quantum chemical calculations of oligothiophenes. The conformation and the electronic structure associated to single molecules and molecular pairs in the ground and first excited states, as well as intermolecular polaron pairs were obtained and their binding energies were calculated as a function of oligomer size. Calculations at the Hartree-Fock level using 3-21G* basis set were carried out to obtain molecular conformations. Correlation effects at the second order Moller Plesset perturbation theory were accounted for in the calculation of ground state energies, whereas a full singles configuration interaction using 6-31G* basis was performed to calculate excited states energies. Polaron pairs were shown to be stable species even in small oligomers, supporting the polaron model of elementary excitations. The results will be analyzed in the light of new experimental findings on polaron pairs. (C) 2004 Elsevier B.V. All rights reserved.