Synthesis and characterization of new acetalized [60]fullerenes

Acetalized [60]fullerenes were synthesized from cyclohexanone-fused [60]fullerene, which was facilely prepared by Diels–Alder reaction of C60 with silylether diene, on treatment of various aliphatic alcohols under TiCl4 catalyst. The spiro-cyclic acetalized [60]fullerenes having five, six, and seven-membered rings were also synthesized by using the corresponding diols under the same condition. The slightly raised reduction potentials Ered (∼0.04 V) relative to those of PCBM were observed by cyclic voltammetry measurement, depending on the identity of alkyl group/chain. The noncyclic acetalized [60]fullerenes showed lower thermal stability up to 200 °C, while the cyclic ones exhibited the drastically improved thermal stability up to 350 °C under nitrogen atmosphere. The acid-catalyzed hydrolysis easily removed the acetal moiety quantitatively, resulting in a considerable change of solvent solubility of the fullerene.