Detection of Fe²⁺ in acetonitrile/water mixture by new 8-hydroxyquinolin based sensor through metal displacement mechanism

A 8-hydroxyquinoline-based (8-HQ) fluorescent ligand (2) was designed and synthesized by condensation of pyridine-2-carboxaldehide with 2-(quinolin-8-yloxy)acetohydrazide (1). Fluorometric titrations with various metal ions in 1:1 M ratio showed that Cu²⁺ and Ni²⁺ ions were fully quenched the fluorescence intensity of 2. But, a significant enhancement in the fluorescent intensity was observed when the bound Ni²⁺ and Cu²⁺ ions in the 2─Ni and 2─Cu complexes were displaced by Cr³⁺ and Fe⁺² ions, respectively. While 2─Ni exhibited low sensitivity toward Cr³⁺ ion, the fluorescent titration measurements showed that 2─Cu could be a good ‘‘on-off-on’’ selective and sensitive sensor (S) candidate for determination of Fe²⁺ in aqueous medium.