Chromogenic ‘naked eye’ and fluorogenic ‘turn on’ sensor for mercury metal ion using thiophene-based Schiff base

Abstract

2-((3-Methylthiophen-2-yl)methyleneamino)benzenethiol (Probe 1) has been synthesized and successfully applied for the selective recognition of mercury metal ions and utilized as a fluorescence turn-on sensor for Hg²⁺ ion via chelation enhanced fluorescence (CHEF). The mechanism of the interaction of Probe 1 with metal ions has been deduced by the absorption, emission, ¹H-NMR, and MALDI-TOF Mass analysis that intimate the favourable coordination of Hg²⁺ metal ion by the mercapto unit. The 2 : 1 stoichiometry of the sensor complex 1 + Hg²⁺ was calculated from the Job’s plot based on UV-Vis absorption spectra. The binding constant (log β₂) of the 1 + Hg²⁺ complex was found to be 13.36 by Hill plot. The limit of detection (LOD) was also calculated from the fluorescence emission titration and found to be 20 μM. Moreover the density functional theory (DFT) studies were investigated for the 1 + Hg²⁺ binding mechanism. Cyclic voltammograms also confirmed the recognition of Hg²⁺ metal ion to the Probe 1.