Photochemical Orifice Expansion of a Cage-Opened C60 Derivative.

Upon light irradiation, a tetraketosulfoxide derivative of C60 was transformed into a diketosulfide carboxylic anhydride via intermolecular nucleophilic addition of the sulfoxide moiety. The thus-formed 18-membered ring enables a spontaneous insertion of an Ar atom. In this encapsulation/release process, the phenyl ring on the orifice works as a dynamic stopper, which potentially adopts three conformations: an open form reduces distortion energy at the transition state while semiopen and closed forms reduce the orifice size.