A simple but highly selective and sensitive fluorescence reporter for toxic CdII ion via excimer formation

High selectivity and fluorescence sensitivity of a well-recognized antiexcitotoxic and anticonvulsant drug, kynurenic acid (KA), toward CdII ion has been demonstrated by UV–vis, fluorescence, 1H NMR spectroscopy in combination with computational calculations. Upon complexation with CdII, KA exhibits a distinct excimer emission at 528 nm along with monomer emission at 402 nm. The sensing ability of drug KA toward CdII ion is distinctly different from sensing for HgII or CuII ion. KA can form dimer by intermolecular O–H⋯O hydrogen bonding between the –COOH groups. Presence of CdII metal ions promotes dimer formation in the excited state which exhibits excimer fluorescence.