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Electronic band structure and intermolecular interaction in substituted thiophene polymorphs

Total energy calculations based on a density-functional tight-binding scheme have been performed on polymorphic modifications of various thiophene crystals. The electronic band structures exhibit a quasi-one-dimensional interaction in the triclinic crystals, while the monoclinic modifications show no dispersion over the whole Brillouin zone. The main interaction mechanism can be described as a d-{pi} wave function overlap between sulfur and carbon. The strong intermolecular interaction may induce an interchain excitation, responsible for the different optical properties of the polymorphs.