Regioselectivity enhancement in synthesis of [70]fullerene derivatives by introduction of a branched structure.

Regio-purity in [70]fullerene derivatives is of great importance to improve the power conversion efficiencies of organic photovoltaics. We found that the introduction of a branched structure to [70]PCBM enhanced the yield of α-isomers. The effect of the steric group in the reaction mechanism was theoretically investigated and a difference in the activation energies within specific pathways was revealed.