A highly selective chromogenic and fluorogenic chemodosimeter for dual detection of Cu based on a redox-active calix[4]arene with isoxazolylchloroanthracene.

Calix[4]arene 1, with two lower-rim isoxazolylchloroanthracene groups, is shown to be not only a chromogenic but also a fluorogenic chemodosimeter for the selective sensing of Cu. The binding properties of ligand 1 and control compounds 2 and 3 toward metal ions in CHCN/CHCl (v/v, 1 : 1) were investigated by UV-vis and fluorescence spectroscopy. The results showed that only ligand 1 was highly selective for Cu ions. When complexed with Cu, ligand 1 displayed a new absorption band around 435 nm and the color of the solution changed from colorless to yellow. Furthermore, the fluorescence of ligand 1 was severely quenched by Cu and the limit of detection (LOD) was determined to be 1.674 μM. Therefore, compound 1 is not only a chromogenic but also a fluorogenic sensor for the detection of Cu ions over other metal ions examined. When complexed with ligand 1, Cu was reduced to Cu by the free phenolic-OH of ligand 1 and concurrently the phenol was oxidized by Cu to quinones. The H NMR, EPR, and FTIR spectra provided evidence for the redox behavior of ligand 1 with Cu. The isolation of calix[4]diquinone 8 and Cu(CHCN)ClO from the reaction of ligand 1 with Cu(ClO) confirmed their redox reaction.