Turn-off fluorescence studies of novel thiophene substituted 1,3,4-oxadiazoles for aniline sensing

Abstract

In the present work, fluorescence quenching of three novel thiophene substituted 1,3,4-oxadiazole derivatives namely; 2-(4-(thiophen-3-yl)phenyl)-5-(5-(thiophen-3-yl)thiophen-2-yl)1,3,4oxadiazole [TTO], 2-(4-(benzo[b]thiophen-2-yl)phenyl)-5-(5-(benzo[b]thiophen-2-yl)thiophen-2-yl)1,3,4oxadiazole [TBO] and 2-(4-(thiophen-2-yl)phenyl)-5-(5-(thiophen-2-yl)thiophen-2-yl)-1,3,4-oxadiazole [TMO] by aniline were carried out at room temperature in five different solvents like ethyl acetate, DMSO, methanol, ethanol and propan-2-ol through steady-state and time-resolved methods to understand the internal mechanisms and to characterize novel fluorophores as favorable aniline sensing media. Further, parameters like Stern-Volmer constants (ksv and ksv'), quenching rate parameters (kq & kq'), the probability of quenching per encounter (P & P') and activation energy of quenching (Ea & Ea') were determined from both the methods. Time-resolved measurements of fluorescence demonstrate that, quenching is dominated by collisional interactions between the 1,3,4-oxadiazole derivatives and the aniline with a minor static component. The magnitudes of the probability of encounter as well as activation energy of quenching also suggest that, quenching reaction is not solely controlled by material diffusion. Further, a linear variation in the fluorescence intensity of the dyes with quencher concentration and the large quenching constants reveals that TTO, TBO and TMO fluorophores may be used as aniline sensors for future detection of aniline via fluorescence quenching.