New highly selective turn-on fluorescence receptor for the detection of copper (II)

Three new receptors (1a-c) bearing a p-dimethylaminobenzamide fluorophore have been synthesized and evaluated in terms of their fluoroionophoric properties towards various metal ions. Notably, receptors 1a and 1c exhibited dramatic fluorescent enhancement towards Cu²⁺ in acetonitrile. Subsequent investigations revealed that the highly selective behavior of these receptors towards Cu²⁺ could be attributed to the Cu²⁺-mediated oxidative cyclization of these compounds to the corresponding 1,3,4-oxadiazoles. Solvent effects and quantum calculations indicated that 1a and 1c both possessed an intramolecular charge transfer channel, which could be obstructed by the oxidative cyclization of these receptors. Receptor 1a was successfully applied to the determination of the Cu²⁺ in drug sample with a low detection limit of 2.2×10^-8molL^-1.