10.1021/ja4115314 ; Irradiation of the copper(II)-superoxide synthetic complexes [(TMG 3tren)CuII(O2)]+ (1) and [(PV-TMPA)CuII(O2)]+ (2) with visible light resulted in direct photogeneration of O2 gas at low temperature (from -40 C to -70 C for 1 and from -125 to -135 C for 2) in 2-methyltetrahydrofuran (MeTHF) solvent. The yield of O2 release was wavelength dependent: ?exc = 436 nm, = 0.29 (for 1), = 0.11 (for 2), and ?exc = 683 nm, = 0.035 (for 1), = 0.078 (for 2), which was followed by fast O2-recombination with [(TMG3tren)Cu I]+ (3) and [(PV-TMPA)CuI]+ (4). Enthalpic barriers for O2 rebinding to the copper(I) center (~10 kJ mol-1) and for O2 dissociation from the superoxide compound 1 (45 kJ mol-1) were determined. TD-DFT studies, carried out for 1, support the experimental results confirming the dissociative character of the excited states formed upon blue- or red-light laser excitation.