Photochemical site-selective synthesis of [70]methanofullerenes.

Methanofullerenes such as the well-known [70]PCBM are commonly synthesized under harsh conditions to obtain the product as a mixture of site-isomers (namely α, β and minor γ) due to the D5h symmetry of the C70 cage. We report the first site-selective synthesis of [70]methanofullerenes under light irradiation and low temperatures, thus avoiding time-consuming and highly expensive HPLC separations. Pure major site-isomers α-[70]PCBM and α-[70]DPM have been thus efficiently prepared including the crystal structure of 5b. Photovoltaic preliminary results revealed a slightly beneficial performance for α-pure [70]PCBM site-isomer devices.