EFFECTS OF GEOMETRICAL DISORDER ON THE ELECTRONIC-STRUCTURE OF ALKYL-SUBSTITUTED POLYTHIOPHENES

In this work, the role of structure disorder on the alkyl-substituted polythiophene electronic spectrum is investigated. A series of AM1 calculations is carried out to estimate the total energy as a function of torsion angle of alkyl-thiophene dimers. The dependence of torsion energy on the radical length and substitution position are studied. The calculated torsion barriers are used to simulate the out-of-plane disordered twisting of thiophene rings within a simple statistical model. Electronic structure calculations on long disordered thiophene chains are performed by the combination of Valence Effective Hamiltonian method and the Negative Factor Counting technique. Thermally induced disorder on alkyl-substituted polythiophenes is shown to explain irreversible changes on infrared spectrum of the polymer upon heating and cooling cycles.