A chelation enhanced selective fluorescence sensing of Hg2+ by a simple quinoline substituted tripodal amide receptor

Two tris(2-aminoethyl) amine (tren) based tripodal amide fluoroionophores, 1 and 2, functionalized with quinoline (chelating fluorophore) and naphthalene (non-chelating fluorophore) respectively, are synthesized in good yields. Fluoroionophore 1 shows a selective UV-Vis spectral shift in the case of Hg2+ in acetonitrile among different metal ions like Li+, Na+, Ca2+, Mg2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Pb2+, and Ag+. On the other hand, fluoroionophore 2 shows no selectivity towards any of the above metal ions in the UV-Vis study. Furthermore, 1 shows a selective chelation induced fluorescence enhancement in the presence of Hg2+ whereas 2 shows the enhancement of fluorescence with most of the metal ions via a photoinduced charge transfer mechanism. The naked eye detection of Hg2+ in an acetonitrile solution of 1 shows a greenish fluorescence upon UV light irradiation. The isolated Hg2+ complex of 1, 3, shows a similar UV-Vis and fluorescence spectral output as observed from in situ spectroscopic studies of 1 in the presence of Hg2+. Infra-red (IR) and H-1- NMR studies also reveal the interaction of Hg2+ with the quinoline nitrogen atoms as well as with the amide functionality.