Electrode-Mediated Photochemical Disproportionation of a Polypyridylruthenium(II) Chromophore

On a metallic electrode embedded within a Nafion film, excitation at 470 nm of Ru(bpy)₂(dppn)²⁺ (bpy = 2,2'-bipyridine; dppn = benzo[i]dipyrido[3,2-a:2',3'-c]phenazine) produced photocurrents indicative of tunable charge transfer between the electrode and photosensitizer, with the direction and magnitude of current dependent on the applied bias potential. At a bias potential of 0.85 V vs dppn/dppn^•-, the oxidative and reductive photocurrents cancel, yielding no net current; transient spectroscopy under these conditions reveals the photoelectrochemical disproportionation of the sensitizer to Ru³⁺ and Ru⁺. The ∼2.8 eV photon energy could thus be coupled to the ground-state reduction potentials of the photosensitizer, simultaneously generating electrons and holes on a monolithic electrode at potentials milder than the formal potentials.