No abstract

The electron‐transfer quenching of Ru(bpy) 32+ (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°C. The quenching rate constants (kq) were determined and their values range from 1 × 107 to 8 × 109 M−1 s−1. In all the mixtures methanol : water the kq 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 (ΦRu(+)) calculated by using a comparative method with the formation of zinctetraphenylporphyrin triplet state. The yields of cage escape (Yce) for the different methanol/water mixtures were calculated from the obtained values of ΦRu(+)). Yce increases from 0·1–0·2 in 25% v/v aqueous methanol to 0·5–0·6 in neat methanol. This change of Yce 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 (kbc), respectively. The constants k−d were calculated with the Eigen equation. The constants kbc were estimated from Yce and k‐d by applying a simplified reaction scheme. The kbc kbc values range from 3·2 × 109 to 1·3 × 1010 s−1.

No abstract

No abstract

No abstract