Yield of ions produced in the luminescence quenching of tris (2,2?-bipyridine)ruthenium(II) by dichlorophenolate ions

The electron-transfer quenching of Ru(bpy)(3)(2+) (tris(2,2'-bipyridine)ruthenium(II)) excited state by 2,4- dichlorophenol (2,4-DCP), 2,5-dichlorophenol (2,5-DCP) and 2,6-dichlorophenol (2,6-DCP), in their anionic forms, was studied in de-aerated solutions of neat methanol and 25, 50 and 75% v/v aqueous methanol at 30 degrees C. The quenching rate constants (k(q)) were determined and their values range from 1 x 10(7) to 8 x 10(9) M(-1) s(-1). In all the mixtures methanol:water the k(q) values for 2,5-DCP were lower than for 2,4-DCP and 2,6-DCP. This result was discussed in terms of the effect of chloro atom on the quencher oxidation reaction, The photoredox product Ru(bpy)(3)(+) was observed by laser flash photolysis and its quantum yield (phi(Ru( + ))) comparative method with the formation of zinctetraphenylporphyrin triplet state. The yields of cage escape (Y(c)e) for the different methanol/water mixtures were calculated from the obtained values of phi(Ru( + ))) increases from 0.1-0.2 in 25% v/v aqueous methanol to 0.5-0.6 in neat methanol. This change of Y-ce with the solvent composition was discussed in terms of combined effects of viscosity and solvent cage on the rate constant of cage escape (k(-d)) and the rate constant for back electron-transfer to the ground state from geminate pair (k(k)), respectively. The constants k(-d) were calculated with the Eigen equation. The constants k(bc) were estimated from Y-ce and k(-d) by applying a simplified reaction scheme. The k(bc) values range from 3.2 x 10(9) to 1.3 x 10(10) s(-1).