A dihydrazone based fluorescent probe for selective determination of Al3+ ions

A highly selective fluorescent sensor N,N′-bis((2-hydroxynaphthalen-1-yl)methylene) oxalohydrazide (H2ohn) for the determination of Al3+ ions was synthesized and characterized by different physico-chemical and spectroscopic techniques. The single crystal structure of H2ohn receptor has also been reported. The H2ohn shows an enhanced fluorescence in the presence of Al3+ ions in ethanol-water (2:3 v/v) solution. Other cations viz. Na+, K+, Mg2+, Ca2+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+ and Hg2+ show no appreciable change in fluorescence intensity. The binding mode of H2ohn receptor with Al3+ was studied by UV-visible, fluorescence and 1H NMR titrations. The receptor acts as a dibasic hexadentate ligand and interacts with two Al3+ ions with a high binding constant KB=2.62×1011 M−2. The lowest detection limit for Al3+ complex of H2ohn was determined to be 8.56×10−10 M. The structures of H2ohn and its Al(III) complex were also optimized by DFT calculations.