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

Azo-coupled macrocyclic chromoionophores incorporating benzene (L(1)) and pyridine (L(2)) subunits were synthesized, respectively. In a cation-induced color change experiment, both receptors showed Hg(2+) selectivity. However, L(1) gave a larger cation-induced hypsochromic shift than L(2), suggesting that the presence of the pyridine unit in L(2) may inhibit the Hg...N-azo interaction. The observed Hg(2+)-selective color changes for L(1) and L(2) were found to be controlled by anion-coordination ability. NMR titration of the proposed receptor ligand with Hg(II) salt was accomplished.