Fluorescence quenching of newly synthesized biologically active coumarin derivative by aniline in binary solvent mixtures

The fluorescence quenching of newly synthesized coumarin (chromen-2-one) derivative, 4-(5-methyl-3-furan-2-yl-benzofuran-2-yl)-7-methyl-chromen-2-one (MFBMC) by aniline in different solvent mixtures of benzene and acetonitrile was determined at room temperature (296 K) by steady-state fluorescence measurements. The quenching is found to be appreciable and positive deviation from linearity was observed in the Stern–Volmer (S–V) plots in all the solvent mixtures. This could be explained by static and dynamic quenching models. The positive deviation in the S–V plot is interpreted in terms of ground-state complex formation model and sphere of action static quenching model. Various rate parameters for the fluorescence quenching process have been determined by using the modified Stern–Volmer equation. The sphere of action static quenching model agrees very well with experimental results. The dependence of Stern–Volmer constant KSV, on dielectric constant ε of the solvent mixture suggests that the fluorescence quenching is diffusion-limited. Further with the use of finite sink approximation model, it is concluded that these bimolecular quenching reactions are diffusion-limited. Using lifetime (τo) data, the distance parameter R′ and mutual diffusion coefficient D are estimated independently.