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

摘要

Irradiation of the copper(II)-superoxide synthetic complexes [(TMG3tren)Cu^II(O2)]⁺ (>1) and [(PV-TMPA)Cu^II(O2)]⁺ (>2) with visible light resulted in direct photo-generation of O2 gas at low temperature (from −40 °C to −70°C for >1 and from −125 °C 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)Cu^I]⁺ (>3) and [(PV-TMPA)Cu^I]⁺ (>4). Enthalpic barriers for O2 re-binding 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.