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 the 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 heteroatoms. 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.