Packing Structures of Thiophene Dimers and Their Effects on Excitation Energies of Thiophene Dimers1

The packing structures of thiophene dimers and their effects on excitation energies of thiophene dimers were studied by employing MP2/6-31 + G* and TDDFT calculations. Twelve optimized dimers with different orientations were obtained by means of MP2/6-31 +G* optimizations. Among them, five T-shaped and three π-stacked thiophene dimers are local minima in energy. The result shows that the preferable conformation of thiophene dimers is the T-shaped packing, which is in agreement with the results in references. All the excitation energies of both T-shaped dimers(5.34-5.48 eV) and π-stacked dimers(5.15-5.18 eV) are lower than that of the isolated thiophene(5.68 eV), indicating that inter-ring interactions decrease the excitation energies.