Endohedral alkali cations promote charge transfer transitions in complexes of C₆₀ with [10]cycloparaphenylenes

[10]cycloparaphenylene ([10]CPP) effectively encapsulates ionic endofullerenes M⁺C₆₀ (M = Li⁺, Na⁺, K⁺) as revealed by dispersion-corrected density functional theory methods. The interaction between [10]CPP and these fullerenes is dominated by dispersion, though it is stronger than with pristine C₆₀ due to a reinforcement of electrostatic and induction contributions to the stability. The C₆₀ carbon cage effectively shields the cations and distributes the charge among all carbon atoms, so the nature of the endohedral cation has no noticeable effect upon the final stability of the complexes. However, the presence of the cation induces important changes in the absorption spectra of the complexes, and new absorption bands near the infrared region appear. These bands are associated with charge transfer transitions from [10]CPP to the fullerene, suggesting the suitability of these complexes for use in organic photovoltaic devices.