Dependence on pH of the luminescent properties of metal ion complexes of 5-chloro-8-hydroxyquinoline appended diaza-18-crown-6

Luminescent properties of 5-chloro-8-hydroxyquinoline (CHQ) free and appended to the amines in diaza-18-crown-6 (A(2)18C6) were determined. These properties were compared to those of bivalent alkaline earth and post-transition metal ion complexes of the appended macrocycle (CHQ-A218C6). The luminescent properties were found to be pH dependent. In the pH range 3 to 7, CHQ-A(2)18C6 forms luminescent complexes with only Zn2+ and Cd2+. At higher pH values, luminescent complexes were formed with Mg2+, Ca2+, Sr2+, and Ba2+. No luminescent complex was formed by Hg2+ over the pH range studied. This lariat macrocycle could find application as a chemosensor for several of the metal ions studied.