Complexes of C60 with cyclic oligothiophenes: a theoretical study.

Complexes of C60 and cyclic and linear oligothiophenes containing 8 and 12 repeating units have been modeled at the M05-2X/6-311G**//M05-2X/6-31G* level of theory. BSSE-corrected binding energies of neutral donor-acceptor complexes vary from 5 to 12 kcal/mol depending on the complex and donor type. Inclusion complexes formed by C60 and cyclooligothiophenes containing 8 repeating units were found to be the most stable ones. Only weak charge transfer from oligothiophene to C60 fragment (<0.1 electron) is observed in the ground state, whereas complete electron transfer from oligothiophene fragment to C60 has been found in the excited state. One electron oxidation or reduction increases binding energies of "tight" complexes and decreases donor-acceptor interaction for "loose" complexes. In the case of cation radicals, positive charge is totally concentrated at the oligothiophene fragment, whereas in anion radicals, negative charge is located at the C60 moiety. Calculations demonstrated that plane oligothiophene conformation and weak binding in a donor-acceptor complex favor the photoinduced charge-carrier formation.