A Unique Sensitive and Highly Selective Fluorescent Naphthodiaza-Crown Macrocyclic Ligand Chemosensor for Hg2+ in Water.

The noticeable enhancement in fluorescence emission of O2N2-donor naphthodiaza-crown macrocyclic ligand (L) in the presence of Hg2+ was observed in which the fluorescence quantum yield of free ligand L as well as L/Hg2+ complex were found to be as 0.29 and 0.49, respectively. The observed ultra-low limit of detection (LOD) for Hg2+ by L was determined as low as 1.0 × 10-11 M in water. A 1:1 stoichiometry was also established for L/Hg2+ together with a binding constant K BH = 66,543 by employing fluorescence spectrophotometry. The competition experiments on L/Hg2+ demonstrated highly selective detection of Hg2+ in the presence of the library cations. A two path mechanism for detection of metal ion in terms of coordination of metal ion to L and/or the formation of counter ion was proposed by using of 1H NMR and fluorescence spectroscopy. Graphical Abstract pH dependence mechanism of interaction between Hg2+ and macrocyclic ligand L.