An iridium-bipyridine complex as a photosensitizer for the bromide oxidation to bromine by oxygen

An iridium(III)-bipyridine complex, [Ir(C³,N′-bpy)(bpy)₂]²⁺, was used as a photosensitizer in aqueous bromide solutions. Steady-state photolysis of oxygenated solutions by near-ultraviolet and visible light produces equal concentrations of Br₃^- and H₂O₂. The quantum yield of Br₃^- equivalents depends on pH, illumination dose, and bromide concentration. The initial yield (extrapolated) reaches a value of 0.08. A mechanism involving two exciplexes and the transients Br₂^-· and HO₂ is proposed, based on products analysis, steady-state emission, and pulsed laser experiments.