SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF FLUORESCENT INDICATORS FOR NA+ AND K+

The synthesis and the spectral and cation binding properties of new fl uorescent indicators for Na+, dicaesium taoxacyclopentadecin-15-yl)-2- thienyl]isophthalate (Benzos), and for K+, dicaesium exaoxacyclooctade cin-18-yl)-2-thienyl]isophthalate (Benzop), are reported. Both indicat ors consist of a benzocrown ether with an appropriate cavity for the s odium and the potassium cation, respectively, linked to an aryl thioph ene fluorophore. In aqueous solution, the indicators have an absorptio n maximum at 340 nm and an emission maximum at 430 nn. The chelating a bilities of Benzos and Benzop with Na+, K+, Li+, Cs+, Mg2+ and Ca2+ we re studied by means of their fluorescence properties. Upon cation bind ing, a change in the fluorescence intensity is observed, whereas the s pectral distribution remains unaltered. While Benzos cannot discrimina te between Na+ and other monovalent cations, Benzop shows a three-fold selectivity for K+ over Na+.