Detection of TNP and sulfite ions in an aqueous medium using a pyrazinium-based chemosensor

Abstract

A fluorescent pyrazinium-based 1-benzyl-3,5-diphenylpyrazin-1-ium bromide (BPPyz) chemosensor was synthesized and well-characterized. A significant reduction in blue emission of BPPyz was observed in the presence of TNP as compared to other nitroaromatic compounds, indicating high selectivity towards TNP. In the presence of sulfite ions, BPPyz showed fluorescence quenching and rapid naked-eye detection with a significant color change. The sensing mechanism was investigated through UV–visible studies, time-resolved fluorescence results, and density functional theory (DFT) calculations. The quenching constants (K_SV) are 4.12 × 10⁵ M⁻¹ for TNP and 3.8 × 10⁵ M⁻¹ for sulfite with the detection limits of 9.5 nM and 46.17 nM for TNP and sulfite, respectively. The selectivity of BPPyz towards TNP was ascribed to the ground state charge transfer complex (GSC) formation and resonance energy transfer. Sulfite ion detection involved the formation of a GSC through hydrogen bonding with the pyrazinium proton.