The bimolecular sensitization of nitric oxide release from weak interacting ruthenium units

This work reports on the bimolecular sensitization of nitric oxide release from cis-[Ru(bpy)2(iso)NO](PF6)3 (1) (iso = isoquinoline and bpy = 2,2′-bipyridine) by irradiating the MLCT transition of the chloro analog cis-[Ru(bpy)2(iso)Cl]PF6 (2). The compounds displayed peaks in the ESI-MS spectra at m/z 749.1 and m/z 578.1 ascribed, respectively, to ([1(NO0)−2PF6·CH3OH]2+) and ([2−PF6]+). In the cyclic voltammograms, the nitrosyl complex presented two redox waves related to the NO ligand at 0.48 and −0.37 V (versus Ag/AgCl, NO+/0/−1 processes), while the sensitizer showed two reversible waves at 0.79 and −1.46 V (versus Ag/AgCl, Ru2+/3+ and bpy 0/−1, respectively). The most important feature of this system is that the nitrosyl compound does not have significant absorption in the visible region, while the sensitizer has an intense band centered at 496 nm. The irradiation of an equimolar mixture of the two compounds in an ethanol:water solution (v:v) with light of λ > 500 nm leads to NO release, as probed by amperometric measurements. The variational method was applied, showing that the two compounds self-assembly in solution with a 1:1 stoichiometry. Fluorescence spectra acquired at 77 K provided the E0–0 for the system and, from the thermodynamic cycle it was estimated that the photoinduced electron transfer between the species has a ΔG value of −1.59 eV.