[60]fullerene adducts with improved electron acceptor properties

The synthesis of C-60-based dyads in which the C-60 core is covalently attached to a strong electron acceptor moiety such as quinones, TCNQ or DCNQI derivatives, has been carried out by 1,3-dipolar cycloaddition of "in situ" generated azomethyne ylides or nitrile oxides to C-60. As expected, the obtained pyrrolidino[3',4':1,2][60]fullerenes exhibit reduction potentials of the C-60 framework which are cathodically shifted in comparison with the parent C-60. In contrast, isoxazolo[4',5':1,2][60]fullerenes show reduction waves for the fullerene core that are anodically shifted in comparison with the parent C-60, which indicates that they are remarkably stronger accepters than C-60. The electron acceptor organic addend also undergoes an anodic shift due to the electronic interaction with the C-60 moiety. The molecular geometry of pyrrolidinofullerenes has been calculated at the semiempirical PM3 level and reveals a highly distorted geometry for the acceptor moiety in compound 13, and a most stable conformation in which both dicyanomethylene units are far away from the C-60 surface.