PULSED LASER-INDUCED PHOTOELECTROCHEMISTRY OF POLYPYRIDINIC RU(II) COMPLEXES IN WATER AND IN ACETONITRILE

The photoelectrochemistry (PEC) of a series of complexes Ru(bpy)i(tap)3-i2+ (bpy, 2,2'-bipyridine; tap, 1,4,5,8-tetraazaphenanthrene) is examined on a transparent SnO2 electrode under pulsed laser illumination. The kinetics of the photoinduced open-circuit photopotentials in long time domains extending to a few milliseconds, are analyzed as a function of various parameters such as the nature of the solvent, the complex, and the oxygen concentration. Different SnO2 photosensitization processes are shown to occur, and some of them are explained on the basis of the bulk photochemistry. Biphotonic (or bimolecular) photoelectron transfers that generate long-lived reducing and oxidizing electroactive intermediates in the bulk solution are mainly responsible for the SnO2 sensitization in long time domains; they give rise to electron injection into, or electron ejection from, the electrode, according to the experimental conditions and the complex. The measurement of the laser-induced open-circuit photopotentials as a function of time is shown to be a very useful method for studying these photosensitization mechanisms and may also be regarded as a technique complementary to the classical flash photolysis for the examination of photoinduced charge-transfer processes.