A mechanosynthesized, sequential, cyclic fluorescent probe for mercury and iodide ions in aqueous solutions

A fluorescent Hg 2+ -selective chemosensor, 2,5-dimethoxybenzaldehyde thiosemicarbazone ( 1 ), was quantitatively prepared by grinding 2,5-dimethoxybenzaldehyde and thiosemicarbazide together in a ball mill for 15   min. The excitation and emission maxima of compound 1 are 347 and 450   nm, respectively. The reaction of this ligand with Hg 2+ was investigated by FT-IR, 1 H NMR, and fluorescence titration. Results show that the composition of the resulting Hg complex 1 -Hg is 2:1 1 :Hg, and that the S and imino N atoms serve as the binding sites of the ligand to the Hg 2+ ions. Coordination-assisted fluorescence quenching results show that compound 1 exhibits a highly selective fluorescence response to trace amounts of Hg 2+ in water. More importantly, the resulting complex 1 -Hg can be used as a turn-on fluorescence probe for I − at a detection limit of 8.4   ×   10 −8   M. Thus, compound 1 is a relatively stable, sequential, cyclic fluorescent probe for Hg 2+ and I − .