Structure, stability and spectroscopic properties of isomers of C48B6N6 heterofullerene with isolated and sequential BN substitutional patterns

Doping of fullerenes has received considerable attention, both experimentally and theoretically, as a tool to fine tuning their physical and chemical properties. In this contribution we report the results of quantum-chemical calculations on several isomers of the boron and nitrogen doped fullerene derivative C48B6N6. Optimized structures, relative stability and spectroscopic properties were computed at the B3LYP/6-31G* level of theory. The more stable structures were characterized by computing vibrational frequencies along with Raman and IR intensities and by modeling their absorption spectra with semiempirical and TD-DFT calculations of excitation energies and intensities. Owing to symmetry lowering with respect to C60, the first allowed transitions of the more stable C48B6N6 cages appear at lower energies. Despite this, the HOMO-LUMO energy gap, a measure of the semiconducting property, is only slightly reduced, compared to C60. The calculated atomic charge distributions indicate considerable localization of charge on the hetero-atoms. As a result, these isomers are expected to have more interesting condensed phase properties than C60 owing to their enhanced intermolecular interactions. Among the isomers considered, the reduced structural deformation and favorable electrostatic interactions lead to a preference for the S6 structure in which two B3N3 aggregates are located on opposite hexagons on the cage.