By means of Delta-SCF and time-dependent density functional theory (DFT) calculations on [Ru(LL)3]2+ (LL = bpy = 2,2'-bipyridyl or bpz = 2,2' -bipyrazyl) complexes, we have found that emission of these two complexes could originate from two metal-to-ligand charge-transfer triplet states (3MLCT) that are quasi-degenerate and whose symmetries are D3 and C2. These two states are true minima. Calculated absorption and emission energies are in good agreement with experiment; the largest error is 0.14 eV, which is about the expected accuracy of the DFT calculations. For the first time, an optimized geometry for the metal-centered (MC) state is proposed for both of these complexes, and their energies are found to be almost degenerate with their corresponding 3MLCT states. These [RuII(LL)(eta1-LL)2]2+ MC states have two vacant coordination sites on the metal, so they may react readily with their environment. If these MC states are able to de-excite by luminescence, the associated transition (ca. 1 eV) is found to be quite different from those of the 3MLCT states (ca. 2 eV).

The processes that are photoinduced by [Ru(bpz)(3)](2+) (bpz = 2,2'-bipyrazyl) in the presence of Cu/Zn superoxide dismutase (Cu/Zn SOD) are investigated by laser flash photolysis and electron paramagnetic resonance (EPR) spectroscopy; they are compared to those of the system [Ru(bpy)(3)(2+)-Cu/Zn SOD]. Although the mechanism is complicated, primary and secondary reactions can be evidenced. First, the excited [Ru(bpz)(3)](2+) complex is quenched reductively by Cu/Zn SOD with the production of a reduced complex and an oxidized enzyme. The oxidation site of Cu/Zn SOD is proposed to correspond to amino acids located on the surface of the protein. Afterward and only when this reductive electron transfer to the excited complex has produced enough oxidized protein, another electron-transfer process can be evidenced. In this case, however, the charge-transfer process takes place in the other direction, i.e., from the excited complex to the Cu(II) center of the SOD with the formation of Ru(III) and Cu(I) species. This proposed mechanism is supported by the fact that [Ru(bpy)(3)](2+), which is less photo-oxidizing than [Ru(bpz)(3)](2+), exhibits no photoreaction with Cu/Zn SOD. Because Ru(III) species are generated as intermediates with [Ru(bpz)(3)](2+), they are proposed to be responsible for the enhancement of [poly(dG-dC)](2) and [poly(dA-dT)](2) oxidation observed when Cu/Zn SOD is added to the [Ru(bpz)(3)](2+)-DNA system.