Intermolecular interactions of oligothienoacenes: Do S•••S interactions positively contribute to crystal structures of sulfur-containing aromatic molecules?

Intermolecular interactions in the crystals of tetra-and penta-thienoacene were studied using ab initio molecular orbital calculations for evaluating the magnitude of characteristic S center dot center dot center dot S interactions with great attention paid to their origin. The interactions between the pi-stacked neighboring molecules are significantly greater than those between the neighboring molecules exhibiting the S center dot center dot center dot S contact, although it has sometimes been claimed that the S center dot center dot center dot S interactions play important roles in adjusting the molecular arrangement of sulfur-containing polycyclic aromatic molecules in the crystals owing to short S center dot center dot center dot S contacts. The coupled cluster calculations with single and double substitutions with noniterative triple excitation interaction energies at the basis set limit estimated for the pi-stacked and S center dot center dot center dot S contacted neighboring molecules in the tetrathienoacene crystal are -11.17 and -4.27 kcal/mol, respectively. Those for pi-stacked molecules in the pentathienoacene crystal is -14.38 kcal/mol, while those for S center dot center dot center dot S contacted molecules are -7.02 and -6.74 kcal/mol. The dispersion interaction is the major source of the attraction between the pi-stacked and S center dot center dot center dot S contacted molecules, while the orbital-orbital interactions are repulsive: The orbital-orbital interactions, which are significant for charge carrier transport properties, are not much more than the results of the short S center dot center dot center dot S contact caused by the strong dispersion interactions. Besides, the intermolecular interaction energy calculated for a trithienoacene dimer has strong orientation dependence. Published by AIP Publishing.