Theoretical Perspective on the Sensing Mechanism of a Pyrazinium-Based Fluorescent Probe Towards 2,4,6-Trinitrophenol

Rapid detection of chemical explosives plays a critical role in national security and public safety. An in-depth study of the sensing mechanism is particularly urgent for the development of highly efficient, sensitive, and selective chemical sensors for the precise detection of chemical explosives. Density functional theory (DFT) and time-dependent DFT approaches were used in this work to examine the sensing mechanism of a novel fluorescent probe 1-benzyl-3,5-di (thiophen-2-yl)pyrazin-1-ium bromide (BTPyz) for the detection of 2,4,6-trinitrophenol (TNP). A comprehensive theoretical exploration was carried out, and a different interaction mode between the probe and TNP from that in the original experiment was proposed. The π–π stacking was established to be the recognition interaction between BTPyz and TNP anion, and the active site was determined from the three potential sizes according to the Gibbs free energy analysis results. The rationality of the reaction mode and the π–π stacking product between the BTPyz and TNP (BTN) was further confirmed by the fluorescence properties (absorption and emission spectra). According to the findings of frontier molecular orbitals (FMOs), photoinduced electron transfer (PET) is the intrinsic mechanism through which TNP quenches the probe's fluorescence.