A new efficient and highly selective fluorescent chemosensor for determination of Pb (2+) has been obtained by covalent attachment of two pendent proton-ionizable dansylcarboxamide groups to the calix[4]arene preorganized in the partial cone conformation. This geometry of the calixarene moiety was chosen on the basis of the prior (1)H NMR study of conformations adopted by the flexible dansyl-containing prototype upon complexation with lead ion. In acidic MeCN-H2O (1:1 v/v) solutions, the partial cone fluoroionophore allowed for detection of Pb (2+) at the levels as low as 2.5 ppb, which is totally compatible with the regulations of the U.S. Environmental Protection Agency and the World Health Organization on the limiting content of this hazardous pollutant in drinking water.

A new fluorogenic, dansyl group-containing derivative of 1,3-alternate calix[4]arene-bis(crown-6-ether) provides optical recognition of Tl+ with selectivity over many other metal cations, including Na+, K+, Ca2+, Ag+, Hg2+ and Pb2+, and embodies the first example of a calixarene-based fluorescent Tl+-chemosensor.

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Optical sensing of metal ions using calixarenes with covalently attached chromophores (fluorophores) has attracted considerable attention of researchers. However, the alternative approach involving host-guest complexes of calixarenes with dyes in metal recognition has been scarcely explored. In this work, addition of different metal cations to the aqueous solutions for solvent extraction of a cationic dye trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide by calix[4]arenes containing lower-rim proton-ionizable groups was found to produce significant effect on the absorption and fluorescence spectra of the organic phases. The observed spectral changes are attributed to co-extraction of the two substrates via formation of supramolecular complexes dye-calixarene-metal cation.