Photoinduced electron transfer between C 70 fullerene and 3,3′,5,5′-tetramethylbenzidine studied by electron paramagnetic resonance

Abstract

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 ‖− g ⊥=0.00165.