Interactions of Environmental Pollutant Aromatic Amines with photoexcited states of Thiophene Substituted 1,3,4-Oxadiazole Derivative: Fluorescence quenching studies

Abstract

In the present work, the ଂuorescence quenching of novel thiophene substituted 1,3,4-oxadiazole derivative 2-(4-(4-vinylphenyl) phenyl)-5-(5-(4-vinylphenyl)thiophen-2-yl)-1,3,4-oxadiazole (TSO) by five different environmental pollutant aromatic amine derivatives like 2,4-dimethylaniline, 3-chloroaniline, 4-chloroaniline, o-anisidine, and m-toluidine has been studied at room temperature through steady-state, and time-resolved methods. The fluorescence intensity of fluorophore TSO decreased as the concentration of aromatic amines increased. The fluorescence quenching mechanism between TSO and aromatic amines is analysed through Stern-Volmer plots. The steady state Stern-Volmer plots were found to be nonlinear with a positive deviation, whereas time resolved Stern-Volmer plots show linearity with an increase in quencher concentration. Further, the Stern-Volmer constants (k sv ), quenching rate parameters (k q ), static quenching constant (V) and radius of the sphere of action (r) are calculated. The magnitude of these parameters suggests that the sphere of action static quenching model is responsible for the overall quenching mechanism. Further, with the use of ଁnite sink approximation model to check these bimolecular reactions as diffusion-limited and to estimate independently S-V constant, the distance parameter (R'), mutual diffusion coefficient (D), and diffusion controlled parameter (k d ) were calculated. These values indicate that the bimolecular quenching reactions are due to the collective effect of dynamic and static quenching mechanisms and these results are confirmed by the time-resolved measurements. The higher values of Gibb’s free energy determined from the Rehm-Weller relation through cyclic voltammetry studies suggests that, the ଂuorescence quenching is due to electron transfer and the same is confirmed by the DFT theoretical studies. Further, the binding equilibria analysis confirm, 1:1 stoichiometry ratio between fluorophore and quencher and also strong binding between the fluorophore and aromatic amines.