Turn-on and reversible luminescent sensor for selective recognition of Al3+ using naphthol hydrazone

Two ligands 1 and 2 have been synthesized for the selective fluorescent recognition of Al3+ ions in aqueous medium (DMSO 5% v/v, pH 7). The ligand 2 displayed dramatic increment of emission intensity with considerable red shift in the presence of Al3+ and it exhibited better sensitivity compared to 1. The quantum yields for 2 and 2-Al3+ were determined as 0.006 and 0.196 respectively. Job plot indicated a 1:1 stoichiometric binding of 2 with Al3+ and the association constant for 2-Al3+ was determined as 1.3×104 M−1 by the Hill plot. The addition of Na2EDTA quenches the fluorescence of 2-Al3+ indicating that the ligand 2 is a reversible fluorescent chemosensor and it can detect submicromolar concentrations of Al3+. The crystal structure of 1 was obtained from single crystal X-ray diffractometry.