A fluorescent carboxamide ligand, having combined ionophore/fluorophore moieties, exhibiting "On-Off" switching toward Zn2+ ion

A carboxamide ligand (N-(quinolin-8-yl)quinoline-2-carboxamide) (Hqcq) has been synthesized by a highly efficient procedure using the ionic liquid TBAB as an environmentally benign reaction medium. Selective "On-Off" switching behavior of the fluorescent ligand (Hqcq) in acetonitrile has been studied for Zn(II) ion. The Hqcq was weakly emissive in the absence of metal ions, but fluorescence intensity was increased significantly upon addition of two equivalent of Zn(II) ion. This enhancement was correlated to Zn(II) coordination of the qcq(-), producing an efficient chelation-enhanced fluorescence (CHEF) effect. Other interfering elements such as Cd(II) and Hg(II), show either no or slight change in the fluorescence intensity under similar experimental conditions. (C) 2016 Elsevier B.V. All rights reserved.