Triazole- and azo-coupled calix[4]arene as a highly sensitive chromogenic sensor for Ca2+ and Pb2+ ions

A novel chromogenic calix[4]arene 3, which has within a molecule both the triazoles and the hydroxyl azophenols as the metal-binding sites and the azophenol moiety as a coloration sites was designed and synthesized. Calix[4]arene 3 is highly sensitive to Ca2+ and Pb2+ ions, which can be detected by the naked eye. Furthermore, the association constants for the 1:1 complexes of 3·Ca2+ and 3·Pb2+ were determined to be 7.06 × 104 M−1 and 8.57 × 103 M−1, respectively.