Thiaoxaaza-Macrocyclic Chromoionophores as Mercury(II) Sensors: Synthesis and Color Modulation

Azo-coupled macrocyclic chromoionophores incorporating benzene (L1) and pyridine (L2) subunits were synthesized, respectively. In a cation-induced color change experiment, both receptors showed Hg2+ selectivity. However, L1 gave a larger cation-induced hypsochromic shift than L2, suggesting that the presence of the pyridine unit in L2 may inhibit the Hg···N-azo interaction. The observed Hg2+-selective color changes for L1 and L2 were found to be controlled by anion-coordination ability. NMR titration of the proposed receptor ligand with Hg(II) salt was accomplished.