Quenching mechanisms of 5BAMC by aniline in different solvents using Stern-Volmer plots

The fluorescence quenching of 5,6 benzo-4-azidomethyl coumarin (5BAMC) by aniline in five different solvents namely benzene, dioxane, tetrahydrofuran, acetonitrile and dimethylformamide has been carried out at room temperature with a view to understand the quenching mechanisms. The Stern-Volmer (S-V) plot has been found to be nonlinear with a positive deviation for all the solvents studied. In order to interpret these results, we have invoked the ground-state complex formation and sphere of action static quenching models. Using these models various quenching rate parameters have been determined. The magnitudes of these parameters suggest that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation is attributed to the static and dynamic quenching. Further, with the use of finite sink approximation model, it was possible to check these bimolecular reactions as diffusion limited and to estimate independently distance parameter R′ and mutual diffusion coefficient D. Finally, an effort has been made to correlate the values of R′ and D with the values of the encounter distance R and the mutual coefficient D determined using the Edward's empirical relation and Stokes-Einstein relation.