Fluorescence Quenching and Electron Transfer Dynamics of a Thiophene-Substituted 1,3,4-Oxadiazole Derivative with Nitroaromatic Compounds

This study investigates the fluorescence quenching behavior of a newly synthesized thiophene-substituted 1,3,4-oxadiazole derivative, 2-(4-(4-vinylphenyl)phenyl)-5-(5-(4-vinylphenyl)thiophene-2-yl)-1,3,4-oxadiazole (TSO), in the presence of various nitroaromatic compounds (NACs), including 2-nitrotoluene, 4-nitrotoluene, nitrobenzene, and picric acid (2,4,6-trinitrophenol). The interactions were examined in an ethanol medium at room temperature using steady-state and time-resolved fluorescence spectroscopy. Steady-state fluorescence analysis revealed a non-linear Stern-Volmer (SV) plot exhibiting positive deviation, while time-resolved measurements displayed a linear relationship. To interpret these findings, ground-state complex formation and the sphere-of-action static quenching models were applied. The study determined key quenching parameters, including the Stern-Volmer constant, quenching rate constant, static quenching constant, and sphere-of-action radius. Notably, fluorescence quenching efficiency increased with the number of NO₂ groups in the NACs.Electrochemical analysis, complemented by Density Functional Theory (DFT) calculations, confirmed that electron transfer was the primary quenching mechanism. Furthermore, binding site analysis demonstrated a 1:1 binding stoichiometry between TSO and NACs, with picric acid exhibiting the highest binding affinity. Given the growing interest in fluorescence-based sensing approaches, these findings contribute valuable insights into the development of advanced sensors for detecting nitroaromatic pollutants and explosive residues.