Fluorophores as chemosensors based on calix[4]arenes and three different fluorescence reporters

The preparation and metal ion complexation reactions of three fluorescent ligands based on a calix[4]arene scaffold and crown ether or azacrown ether binding sites are reported. Three different fluorescent reporter groups were investigated: dansyl, anthracene, and coumarin. The N-dansyl azacrown-5 derivative in the cone conformation shows no change in fluorescence on complexation, but an open chain analog displayed highly selective quenching with mercury. The N-methylanthracene derivative with an azacrown-5 binding site in the 1,3-alt conformation is a photo-induced electron transfer (PET)-sensor showing chelation enhanced fluorescence (CHEF) effects with Hg(II), Cu(II), and Sr(II). The coumarin calix[4]arene crown-6 derivative in the 1,3-alt conformation is able to sense cesium selectively over sodium as well as potassium.