(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 EDTA^2- for all the three metal ions.