Salicylaldehyde hydrazones as fluorescent probes for zinc ion in aqueous solution of physiological pH

Salicylaldehyde hydrazones of 1 and 2 were synthesized and their potential as fluorescent probes for zinc ion was investigated in this paper. Both of the probes were found to show fluorescence change upon binding with Zn²⁺ in aqueous solutions, with good selectivity to Zn²⁺ over other metal ions such as alkali/alkali earth metal ions and heavy metal ions of Pb²⁺, Cd²⁺ and Hg²⁺. They showed 1:2 metal-to-ligand ratio when their Zn²⁺ complex was formed. By introducing pyrene as fluorophore, 2 showed interesting ratiometric response to Zn²⁺. Under optimal condition, 2 exhibited a linear range of 0-5.0 μM and detection limit of 0.08 μM Zn²⁺ in aqueous buffer, respectively. The detection of Zn²⁺ in drinking water samples using 2 as fluorescent probe was successful.