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.

The present work deals with the first attempt to study the effect of l-tyrosine on the characteristics of the peroxyoxalate chemiluminescence. Berberine was applied as an efficient fluorophore. The investigated parameters include rise and fall rate constant for the chemiluminescence burst, theoretical and experimental maximum intensity, the time needed to reach maximum intensity and the total light yield emission, which is theoretically evaluated using the pooled intermediate model by a computerized non-linear least-squares curve fitting program (KINFIT). Furthermore, based on the observed quenching effect of tyrosine, the Stern–Volmer plot with KQ value of 7.7×104 M-1 in the quencher concentration range 4×10-6 –5×10-5 M. Moreover, this method is applied to determinate tyrosine in biological samples successfully.

The photo induced electron transfer reactions of three Ru(II) complexes with phenol ate ions of polyphenols (gallic acid, quercetin, p-coumaric acid, and ferulic acid) and thymol have been measured in 50 % aqueous acetonitrile at pH 11 and the observed quenching constant (kq) values are sensitive to the nature of the ligand and the structure of the phenol ate ion. The change of kq values with DG0 is in accordance with the Marcus semi classical theory of electron transfer. The static as well as dynamic nature of quenching is confirmed from the ground-state absorption studies. The reductive quenching of the Ru (II) complexes by the phenol ate ions has been confirmed from the transient absorption spectra. The formation of phenoxyl radical as a transient is confirmed by its characteristic absorption at 400 nm.

In the present work, the effect of fsDNA (fish sperm DNA) on kinetic parameters of chemiluminescence (CL) of the luminol–hydrogen peroxide system catalyzed by Mn(III)–Tetrakis (4-sulfonatophenyl)-porphyrin was investigated. These parameters including pseudo first-order rise and fall rate constant for the chemiluminescence burst, maximum level intensity, time to reach maximum intensity, total light yield, and values of the intensity at maximum CL were evaluated by computer fitting of the resulted intensity–time plots. Results reveal that CL parameters are dramatically affected due to interaction of metalloporphyrin with DNA. In order to observe quenching effect of DNA on CL intensity, Stern–Volmer plot with k Q value of 1.18×105 M-1 was calculated in the quencher concentration range of 4×10-6–8.5×10-5 M.

A new water-soluble Schiff base complex of [Ga (L)] NO3; where L denotes a N2O2 Schiff base ligand; was synthesized and characterized by IR, 1H-NMR, elemental analysis and UV-Vis spectroscopy. The mechanism of binding of this complex with bovine serum albumin (BSA) was studied by fluorescence spectroscopic technique. The results of this investigation showed that the intrinsic fluorescence of BSA was quenched by the complex which was rationalized in terms of the static quenching mechanism. Type of quenching, binding constants, Stern-Volmer constants, number of binding sites, and binding stoichiometries were determined by fluorescence quenching method. Additionally thermodynamic parameters were calculated by van’t Hoff equation, indicating that the binding was entropy driven and enthalpically disfavored. Also distance between complex and protein were calculated by forest equation.