Facile synthesis of an optical sensor for CO<sub>3</sub><sup>2−</sup> and HCO<sub>3</sub><sup>−</sup> detection

<div><p>A novel fluorogenic signalling probe (<i>E</i>)-3-(4-methoxyphenyl)-4-[(4-nitrobenzylidene)amino]-1<i>H</i>-1,2,4-triazole-5(4<i>H</i>)-thione (6) for the carbonate and bicarbonate ions has been developed through microwave assisted Schiff base formation reaction. The anion recognition occurs through hydrogen bonding assessed by <sup>1</sup>H NMR titration experiments. The photophysical results of probe 6 corroborates its applicability as an optical sensing platform for carbonate as well as bicarbonate ions in mixed aqueous organic media depending on pH of reaction solution. The fluorescence emission signal enhancement at 424 nm and considerable shift in the signal position as well as molar absorptivity to the probe absorption bands upon CO<sub>3</sub><sup>2−</sup> and HCO<sub>3</sub><sup>−</sup> addition suggest the affinity of probe 6 towards these ions in comparison to a variety of competitive ions in aqueous/ethanol (7:3, v/v) at neutral pH and ambient temperature. From the fluorescence titration experiment, the limit of detection was calculated to be 1.91 μM.</p></div>