Static and dynamic quenching of biologically active coumarin derivative by aniline in benzene-acetonitrile mixtures

The fluorescence quenching of coumarin derivative, 4-(5-chloro-3-furan-2-yl-benzofuran-2-yl)-6-methyl-2H-chromen-2-one (ClFBMC), in the presence of aniline in different proportion of benzene-acetonitrile mixture was studied by means of steady-state measurement (296 K). The quenching process was characterized by Stern-Volmer (S-V) plots, which display positive (upward) deviation. The positive deviation from linearity suggests that the quenching is due to the simultaneous presence of dynamic and static quenching, which is interpreted in terms of the ground-state complex formation and the sphere of action static quenching model. The sphere of action static quenching model agrees very well with experimental results. Further with the use of finite sink approximation model, it is concluded that the bimolecular quenching reactions are diffusion-limited. Various rate parameters for the fluorescence quenching process have been determined. The value of quenching constant k_q increases with increase in dielectric constant of the mixed solvent, suggesting the charge transfer character of the excited complex.