Reversibly switchable methanofullerene by photoexcitation and reduction.

A cyclopropanated derivative of the trifluoromethylated fullerene C s -C 70 (CF 3 ) 8 demonstrates reversible switching behavior triggered by excited state electron transfer or by negative charging. The switching between the state with connected 62-electron π-system and the state with disjoint 28- and 32-electron conjugated caps is effected by opening/closure of the cyclopropanated bond. A pronounced alteration of the electronic properties upon seemingly minor changes in a large fullerene molecule is an attractive feature for the organic electronic devices where similar fullerene compounds are commonly utilized as electron acceptor materials.