Synthesis and logic gate application of quinoline schiff base probe for fluorescence detection of mercury ions

Herein, we report the synthesis of a small molecule quinoline Schiff-base "turn-on" fluorescence probe L, denoted as (2-NC9H6)C(H)=N(C6H4OCH3-p), utilizing 4-aminoanisole and quinoline-2-carboxaldehyde as precursors. The synthesized probe was comprehensively characterized through EA,1H/13C NMR, FT-IR, and ESI-MS spectral analysis. In a CH3CN/H2O solution (1/1, v/v, 0.01 M PBS buffer, pH = 7.30), probe L responded to Hg(II) with high sensitivity (LOD = 2.98 × 10−7 M) and selectivity. Upon binding to Hg(II), the fluorescence of the probe shifted from being initially off to a distinct blue emission. The probe L to Hg(II) binding ratio was 1:1 and the binding constant was 1.955 × 104 M−1. The detection mechanism of Hg(II) by probe L is due to the complex formation between the metal ion and imine nitrogen (–CH = N), thus causing chelation-enhanced fluorescence. TD-DFT studies at the B3LYP/6-31G(d) level of theory further confirmed that the complexation of L and Hg(II) occurred. Finally, probe L could reversibly identify Hg(II) upon adding EDTA, thus developing a molecular logic gate. In addition, this probe was successfully used to detect Hg(II) in actual water samples.