Role of sp³ carbon and 7-membered rings in fullerene annealing and fragmentation

Abstract

WHEN fullerenes^1,2 are fragmented by laser irradiation, they lose C₂ fragments and retain a closed carbon cage³. The detailed mechanism of this process remains unknown, although survival of the cage implies that annealing (rearrangement of the bonding) must play an important role^3,4. Here we use ab initio quantum-chemical calculations to show that fullerene annealing happens more readily than fragmentation, and that both are intimately related. Our findings imply that the assumptions commonly made about fullerenes⁵—that they are composed of five- and six-membered rings of sp² carbons— are not valid under high-energy conditions. In particular, the appearance of sp³ carbon and seven-membered rings is central in both the annealing and fragmentation processes. Our theoretical predictions imply that the high-energy processes of fullerene growth^6–11 and coalescence¹² are much richer than previously thought, and that their mechanisms may also involve structures containing sp³ carbon and seven-membered rings. Our results may aid in the design of experimental methods for controlling the nature of fullerene cages (for example, doping, opening and re-closing them).