By means of flash photolysis and low-temperature spectrophotometry, the formation of a complex between a Cu(I) ion and a peroxy radical of the solvent has been detected in ethanol, isopropanol, and dimethylformamide. The peroxy radical is generated in a reaction of a solvent radical with a molecule of dissolved oxygen. The solvent radical appears as a result of photoreduction of chloride complexes of Cu(II). The radical complex has a band in the optical absorption spectrum with a maximum at 415–420 nm in ethanol and isopropanol. The rate of formation of this complex is determined mainly by the reaction of the radical of the matrix (R.) with complexes of bivalent copper. The rate constant of this process in isopropanol at room temperature is (2–3)·108 liters/ mole·sec. Disappearance of the radical complex Cu(I)...RO2. takes place in a reaction with complexes Cu2+solv and CuCl+ with a rate constant of 2.3·107 liters/mole·sec at room temperature.