Tris(2,2′-bipyridine)ruthenium(II) ion-sensitized photodechlorination of polychlorophenolate ions

Abstract

The luminescence quenching of excited tris(2,2′-bipyridine)ruthenium(II) complex (Ru(bpy) 3 2+) by polychlorophenols (PCPs) — 2,4-dichlorophenol, 2,6-dichlorophenol and 2,4,6-trichlorophenol — in their anionic forms was studied in deaerated solutions of methanol and methanol—water mixtures. The quenching rate constant k q increases on changing the solvent from water to methanol. The photoredox product Ru(bpy) 3 + has been detected by laser flash photolysis (337.1 nm) in deaerated alkaline methanolic solutions containing Ru(bpy) 3 2+ and PCP. Solutions of this type were used in continuous photolysis experiments by irradiating with visible light and they led to a decrease in PCP concentration and chloride ion formation. In order to rationalize these experimental results we propose a Ru(bpy) 3 2+-sensitized photochemical reaction for all the PCPs studied. The chloride ion formation after the electron transfer step may be interpreted in terms of a displacement of the chloride ion in the PCP − anion by the PCP radical.