Luminescence quenching of tris(4,4ʹ-dimethyl-2,2ʹ-bipyridyl)ruthenium(II) complex with quinones in aprotic polar medium

923-928The photoinduced electron transfer interaction between a luminescent metal-ligand probe, [Ru(dmbpy)3]2+ and quinones have been investigated by absorption and fluorescence spectroscopy. The reactions of quinones with the excited state ruthenium(II) complex in DMF have been studied by luminescence quenching technique and the bimolecular quenching rate constant kq values are found close to the diffusion controlled rate. The complex has an absorption maximum of 458 nm. It shows a photoluminescence at 608 nm. The lifetime of the complex in DMF is 164 ns. The ground state absorption measurements are used to confirm the nature of quenching. Transient absorption spectral measurements are performed and the oxidative nature of quenching is confirmed. The detection of semiquinone anion radical using time resolved transient absorption spectroscopy and the linear variation of log kq vs reduction potential of the quinones confirms the electron transfer nature of the reaction

Luminescence quenching studies of [Ru(dMeObpy)3]2+ complex using the quinone derivative-effect of micelles

Quinones are considered a class of organic compounds having a quinonoid group and are the ultimate electron acceptors. Due to this property, they have favourable redox potential and the ability to form stable hydrogen bonds. Luminescence quenching is one of the most important techniques used to get information regarding the structure and dynamics of a luminophore. A variety of transition metal complexes have been synthesized and studied to comprehend the quinones' electron-accepting characteristics. Among these, Ru(II) polypyridyl complexes have widespread applications in electron transfer reactions due to their well-defined photophysical and photochemical stability. The reaction of excited state Tris(4,4'-dimethoxy-2,2'-bipyridine)ruthenium(II)tetrafluoroborate [Ru(dMeObpy)3](BF4)2 complex with quinones was investigated through photoinduced electron transfer reaction in homogeneous and microheterogenous medium. The luminescence quenching technique has been used to study this reaction. The complex has an absorbance maximum of 448 nm in aqueous medium. The quenching rate constants were deduced using the Stern-Volmer equation. The interaction between the complex and the quinones in a cationic micellar medium, cetyltrimethylammonium bromide (CTAB), was analyzed based on electrostatic interaction and hydrophobicity. The plot between RTlnkq vs. reduction potential of the quinones, as well as the transient absorption spectra, confirmed the oxidative nature of quenching of the ruthenium complex in the presence of quinones. The quenching constant values are influenced by many factors, such as the nature of the ligand, medium, size, and structure of quenchers, and electron transfer distance between the donor and the acceptor. The formation of Ru3+ species is confirmed by its characteristic absorption at 600 nm