Photoinduced electron transfer between C70 fullerene and 3,3′,5,5′-tetramethylbenzidine studied by electron paramagnetic resonance

Electron paramagnetic resonance (EPR) in situ spectroscopy was applied in the study of photoinduced electron transfer between 3,3',5,5'-tetramethylbenzidine (TMB) and C-70 in different solvent systems. The changes found in UV-vis spectra pointed at ground state charge transfer complex formation {C-70-TMB} in benzonitrile. Upon selective excitation of C-70 using steady-state monochromatic irradiation with a wavelength of 546 nm, two EPR singlets were observed, which were assigned to C-70 mono- and di-anion. In the photochemical and cathodic in situ reductions, identical EPR spectra of anion radicals were obtained. C-70 mono-anion was investigated also in frozen 1,2-dichlorobenzene solutions within the temperature range from 110 to 210 K, and at 110 K the anisotropic EPR spectrum of C-70 mono-anion was simulated assuming an axially symmetric g-matrix with g(parallel to) - g(perpendicular to) = 0.00165. (C) 2000 Elsevier Science B.V. All rights reserved.