Fullerene "superhalogen" radicals: the substituent effect on electronic properties of 1,7,11,24,27-C60X5.

Hexasubstituted fullerenes with the skew pentagonal pyramid (SPP) addition pattern are predominantly formed in many types of reactions and represent important and versatile building blocks for supramolecular chemistry, biomedical and optoelectronic applications. Regioselective synthesis and characterization of the new SPP derivative, C60(CF3)4(CN)H, in this work led to the experimental identification of the new family of "superhalogen fullerene radicals", species with the gas-phase electron affinity higher than that of the most electronegative halogens, F and Cl. Low-temperature photoelectron spectroscopy and DFT studies of different C60X5 radicals reveal a profound effect of X groups on their electron affinities (EA), which vary from 2.76 eV (X=CH3) to 4.47 eV (X=CN). The measured gas-phase EA of the newly synthesized C60(CF3)4CN equals 4.28(1) eV, which is about 1 eV higher than the EA of Cl atom. An observed remarkable stability of C60(CF3)4CN(-) in solution under ambient conditions opens new venues for design of air-stable molecular complexes and salts for supramolecular structures of electroactive functional materials.