A stable, broad ESR signal (g = 1.998, ΔH pp = 37.0 G) of the C60 •- anion radical was generated by irradiation of a C60−toluene solution in the presence of organic salt, [(ph)3P]2N+(ph)4B-, and 14.3% methanol. Upon exposure to molecular oxygen, the broad band gradually diminishes and a narrow band of g = 2.0008 and ΔH pp = 3.32 G (hereafter, band b) grows, which further transforms to another narrow band of g = 2.0026 and ΔH pp = 1.67 G (hereafter, band c). The transformation rate of bands b to c was found to be negative temperature dependent, i.e., the higher the temperature, the slower the transformation rate. At high temperatures (e.g., 365 K) and in polar solvents (e.g., 30% methanol in toluene), band c can reversibly transform back to band b. Microwave power saturation experiments show that band c has much longer relaxation times than band b. Both bands b and c resemble the “spike” commonly observed in the C60 •- anion radical ESR spectra and were designated to two isomers of the C60O2 •- anion radical. A kinetic model was derived to account for the negative temperature-dependent transformation rate of bands b to c.

Irradiation of C60-toluene solution at room temperature affords two ESR bands with g and ΔH pp values of (2.0013, 0.5 G) and (2.0024, 0.75 G), respectively. In the presence of 6% methanol or 12% benzonitrile, the latter band disappears completely. Below 200 K, only the former band was observed. They were assigned to be 3C60 and C60 •+, respectively. In the presence of tetraphenylphosphonium tetraphenylborate, the g value of the C60 •+ cation radical shifts to 2.0006, and an additional broad band of g = 1.9992 and ΔH pp= 30 G was observed. Upon cooling, the line width of this new band drops from 30 G at 300 K to 4 G at 77 K. This new band was assigned to be the C60 •- anion radical according to its characteristic behavior. At room temperature, photolysis causes the C60−toluene solution's color to turn from purple to brown, and then brown precipitates formed. Desorption chemical ionization (DCI) mass analysis of the brown precipitates indicates the formation of C60·H n (tolyl) n (n = 1−4) adducts. The formation of C60 •+ and C60 •- was rationalized in terms of disproportionation of two 3C60. The brown precipitates were due to the chemical reaction between the C60 •+ cation radical and the solvent molecules, which rationalizes the “photodegradation” of fullerene as reported in literature. The important role of the C60 •+ and C60 •- to the peculiar photochemical behavior of fullerene solutions or films, such as nonlinear optical property, photoinduced polymerization in solid film, nonlinear photoconductivity, etc, will be discussed.