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 [(TMG(3)tren)Cu-II(O-2)](+) (1) and [(PV-TMPA)Cu-II(O-2)](+) (2) with visible light resulted in direct photogeneration of O-2 gas at low temperature (from -40 degrees C to -70 degrees C for 1 and from -125 to -135 degrees C for 2) in 2-methyltetrahydrofuran (MeTHF) solvent. The yield of O-2 release was wavelength dependent: lambda(exc) = 436 nm, phi = 0.29 (for 1), phi = 0.11 (for 2), and lambda(exc) = 683 nm, phi = 0.035 (for 1), phi = 0.078 (for 2), which was followed by fast O-2-recombination with [(TMG(3)tren)Cu-I](+) (3) and [(PV-TMPA)Cu-I](+) (4). Enthalpic barriers for O-2 rebinding to the copper(I) center (similar to 10 kJ mol(-1)) and for O-2 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.