Excitation Wavelength Dependent O₂ Release from Copper(II)–Superoxide Compounds: Laser Flash-Photolysis Experiments and Theoretical Studies

Irradiation of the copper(II)–superoxide synthetic complexes [(TMG3tren)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: λexc = 436 nm, ϕ = 0.29 (for 1), ϕ = 0.11 (for 2), and λexc = 683 nm, ϕ = 0.035 (for 1), ϕ = 0.078 (for 2), which was followed by fast O2-recombination with [(TMG3tren)CuI]+ (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.