The geometric parameters of the perylene substructure in fullerenes were analyzed and found to lie within the range characteristic of stable fullerenes, indicating that this substructure does not induce significant molecular strain. However, the small energy difference (10 kcal/mol) between the singlet and triplet states of perylene may contribute to fullerene instability, as the transition to the higher-symmetry triplet state (C2v) becomes favorable compared to the singlet state (C2). The closed-shell nature of perylene ensures that its geometric and electronic properties remain largely unchanged upon incorporation into fullerene frameworks. Three distinct configurations of perylene in fullerenes were identified: separated (no shared bonds), adjacent (shared bonds), and intercrossed (shared hexagons). Separated perylene exhibits a closed electron shell, while adjacent and intercrossed structures predominantly display open-shell characteristics. This finding was checked for the C78 fullerene, in which the structural distortions are most pronounced in hexagons with delocalized π-bonds. Given the prevalence of perylene in numerous fullerenes, these findings provide valuable insights into the structural and electronic factors influencing fullerene stability.
Furer et al. (Tue,) studied this question.