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