The excited state of ruthenium(II) tris(bipyrazine) (Ru(bipyz)32+*) is quenched by the sacrificial electron acceptors, S2O82- and Co(NH3)5Cl2+. Under acidic solutions (pH 0), Ru(bipyz)32+* is quenched by protons and therefore quite short-lived (τ = 50 ns). At pH 0, steady-state irradiation of the Ru(bipyz)32+ in the presence or absence of either S2O82- or Co(NH3)5Cl2+ did not produce any permanent products. In addition, no O2 evolution was observed when an O2 catalyst was added. At pH 6, Ru(bipyz)32+* is much longer-lived (τ = 1.04 μs) and steady-state irradiation of a Ru(bipyz)32+ solution containing S2O82-, rather than Co(NH3)5Cl2+, did produce changes in absorbance, emission and pH, due to the oxidative degradation of the sensitiser. Microsecond flash photolysis work indicated that Ru(bipyz)32+* is oxidatively quenched by the S2O8- ions leading to the generation of Ru(bipyz)33+, a very strong and unstable oxidant. Steady-state irradiations carried out on the Ru(bipyz)32+/S2O8- photochemical system at pH 6, in the presence of an O2 catalyst, resulted in O2 generation (φ(O2) = 0.0025), however photodegradation of the Ru(bipyz)32+ sensitiser still took place, albeit at a reduced rate.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry