Theoretical study on the electronic structure and the absorption spectra of complexes of C60 and C59N with π-extended derivatives of tetrathiafulvalene

A theoretical study has been carried out on the ground and the excited electronic states of models of supramolecular complexes of π-extended derivatives of tetrathiafulvalene (exTTF) with fullerene and fulleropyrrolidine, as well as covalently bonded exTTF to fulleropyrrolidine and to azafullerene. Density Functional theory (DFT) and Time Dependent DFT (TDDFT) calculations employing B3LYP, MPWB1K and CAM-B3LYP functionals have been carried out on the above systems in the gas phase as well as in toluene solvent. The lowest 30-50 excited electronic states of these systems have been determined at the ground state optimum geometry. The results show that the exTTF absorption maximum calculated in the hybrid structures is only slightly shifted with respect to that calculated for free exTTF, with the largest red shift found for the hydrogen-bonded exTTF to fulleropyrrolidine complex. In all cases, charge-transfer excitations are found, involving electron excitation from exTTF to fullerene, contributing either to the character of the absorbing state or to that of a nearly-degenerate state.