Luminescence quenching of tris(4,4′-dinonyl-2,2′-bipyridyl) ruthenium(II) cation with phenolate ions in DMSO

Abstract

The photoredox reactions of biologically important phenols (p-coumaric acid, ferulic acid, thymol, quercetin and gallic acid) with the excited state [Ru(nbpy)3]2+ (nbpy=4,4′-dinonyl-2,2′-bipyridine) complex proceed through photoinduced electron transfer reaction in DMSO and have been studied by luminescence quenching technique. The complex shows absorption and emission maximum at 457 and 628nm and it shows a lifetime of 804ns in DMSO. The excited state reduction potential of the complex ERu2+∗/+0 in DMSO is 0.72V vs Ag/Ag+. The dynamic nature of quenching is confirmed from the ground state absorption studies. The reductive quenching of [Ru(nbpy)3]2+ by phenolate ions has been confirmed from transient absorption spectra and from the linear variation of logkq vs oxidation potential of the phenols. The quenching rate constant, (kq) is highly sensitive to the availability of active phenolate ions, oxidation potential of the polyphenols, the free energy change (ΔG0) of the reaction and to the electron transfer distance between the complex and the quencher. Structural effects seem to play an important role in the photoinduced electron transfer reactions in DMSO.