ESR-Vis/NIR spectroelectrochemical study of C70(CF3)2-(*) and C70(C2F5)2-(*) radical anions.

A spectroelectrochemical study of the two isostructural asymmetric perfluoroalkyl derivatives C(1)-7,24-C(70)(CF(3))(2) and C(1)-7,24-C(70)(C(2)F(5))(2) is presented. Reversible formation of their stable monoanion radicals is monitored by cyclic voltammetry and by in situ ESR-Vis-NIR spectroelectrochemistry. The ESR spectrum of the C(70)(CF(3))(2) (-*) radical is a 1:3:3:1 quartet with a (19)F hyperfine coupling constant (a(F)) of 0.323(4) G, demonstrating that the unpaired spin is coupled to only one of the two CF(3) groups. The (13)C satellites are assigned to specific carbon atoms. The ESR spectrum of the C(70)(C(2)F(5))(2) (-*) radical is an apparent octet with an apparent a(F) value of 0.83(2) G. DFT calculations suggest that this pattern is due to the superposition of spectra for four nearly isoenergetic C(70)(C(2)F(5))(2) (-*) conformers. Time-dependent DFT calculations suggest that the NIR band at 1090 nm exhibited by both C(70)(R(f))(2) (-*) radical anions is assigned to the SOMO-->LUMO+3 transition. The analogous NIR band exhibited by the closed-shell C(70)(CF(3))(2) (2-) dianion was blue-shifted to 1000 nm.