Binding in Thiophene and Benzothiophene Dimers Investigated By Density Functional Theory with Dispersion-Correcting Potentials

We report the use of a newly developed dispersion-corrected density functional approach to study noncovalent binding in a series of thiophene and benzothiophene dimers. These are of interest in both petrochemistry and molecular electronics. We find increasing influence of dispersion forces over dipole interactions as the number of benzene moieties increases from 0 (thiophene) to 3 (tribenzothiophene). Binding in dimers of thiophene was benchmarked vs previously published CCSD(T) data (J. Am. Chem. Soc. 2002, 124, 12200). We have determined the fully optimized geometries and energies of 15 dimers of thiophene, 26 dimers of benzothiophene, 10 of dibenzothiophene, and 11 of tribenzothiophene using B971/6-31+G(d,p) with dispersion-correcting potentials (DCPs). These represent a mixture of T-shaped, tilted-T-shaped, a-stacked, and coplanar Structures. For thiophene we find the lowest energy T-shaped and a-stacked dimers to bind by 3.0 and 2.5 kcal/mol, respectively. However, for benzothiophene the lowest energy structure is a-stacked with binding energy, BE 5.8 kcal/mol, which compares to the most bound T-shaped dimer, BE = 4.1 kcal/mol. This difference between pi-stacked and T-shaped dimer binding increases further going to dibenzothiophene and tribenzothiophene (difference = ca. 6.0 and 6.7 kcal/mol, respectively). When calculations without dispersion corrections are performed on the dimer structures, many display significant changes in structural motif and reductions in binding energies of up to 80%. Therefore, the inclusion of dispersion corrections, for example, through the use of DCPs, is essential in describing the potential energy landscape of these complexes.