(E)-(4-Methoxyphenyl)-N-(4H-1,2,4-triazol-4-yl) methanimine: Solvent driven single molecule triple fluorescent “on” sensor for Cu2+, Cd2+ and Hg2+

Abstract

A single molecule, (E)-(4-methoxyphenyl)-N-(4H-1,2,4-triazol-4-yl) methanimine (Metho-tria-imine), can detect Cu2+, Cd2+ or Hg2+ depending on whether the solvent is H2O, CH3CN or C2H5OH respectively by fluorescence “on” mode. The enhancement in fluorescence intensity is found to be ca. 13 times for Cu2+, 70 times for Cd2+ and 57 times for Hg2+. The metal ions - Al3+, Co2+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Zn2+ (along with two metal ions out of Cu2+, Cd2+ and Hg2+ for which the sensor is not effective) do not interfere. The plot of absorbance versus metal ion concentration was sigmoidal for Cu2+ and Cd2+ and linear for Hg2+ which indicates formation of dimeric complexes in solution for Cu2+ and Cd2+. DFT studies showed metal-metal bonding in case of Metho-tria-imine forming complexes with Cu2+ and Cd2+ and hence dimeric complexes with highest binding energy for Cu2+ in H2O, Cd2+ in CH3CN, Hg2+ in C2H5OH. The detection limits are found to be 1.9×10-8 M, 7.0×10-7 M and 6.9×10-8 M respectively and Metho-tria-imine is reversible with respect to EDTA2- for all the three metal ions