Conformational analysis (ab initio HF/3-21G*) and optical properties of poly(thiophene-phenylene-thiophene) (PTPT)

The optical properties of two series of thiophene-based polymers are interpreted by torsion analysis. When approached by the calculated HOMO/LUMO energy gaps of model molecules, the wavelength shifts from solutions to films are reasonable in cyclohexyl-substituted series but not in hexyl-substituted series, indicating that solid packing force plays a more important role in the former than in the latter. The lengths of hexyl and cyclohexyl groups on bithiophene segment are the dominant factor that determines the distance of co-facial chain packing which affects the conformation of the polymer chain. In both series the photoluminescence (PL) efficiency increases as the equilibrium torsion angle decreases.