FULLERENE ANION FORMATION BY ELECTRON-TRANSFER FROM AMINO DONOR TO PHOTOEXCITED C-60 - ELECTRON-PARAMAGNETIC-RESONANCE STUDY

Upon UV irradiation of C-60 fullerene in 1:1 toluene/(methanol, acetonitrile, or toluene) solutions the photoexcited state of C-60 was quenched in the presence of Et(3)N, and single lines of anion radicals A and B were observed in in situ EPR measurements. The formation of A is accompanied by the appearance of a band at 1077 nm in vis/near-IR spectrum characteristic of C-60 monoanion. Radical B is a consecutive product of A (probably associate of C60(.-) or C-60 dianion). Monoanion A with g = 2.0000 and peak-to-peak width, pp = 0.09 mT converts to radical B with g = 2.0006 and pp = 0.035 mT increasingly after prolonged irradiation and at higher ratios of Et(3)N:C-60. The shortest lifetime of C-60 monoanion was found in the presence of methanol (t(1/2) = 28 s), and it increased considerably upon the addition of tetrabutylammonium perchlorate (TBAP) salt (t(1/2) = 210 s in 0.38 M TBAP) or if methanol was replaced by acetonitrile (tin = 260 s). Lowering the temperature from 300 to 200 K, the linewidth of A decreases from pp(300 K) = 0.09 mT to pp(200 K) = 0.038 mT. At 100 K a broadened line spread over 3 mT was found with a narrow line superimposed on it. The ratio of the broadened to the narrow line increases with the increased time intervals and is more pronounced following prior prolonged irradiation at 300 K or upon the addition of TBAP.