Silver Ion Selective Fluoroionophores Based on Anthracene-Linked Polythiazaalkane or Polythiaalkane Derivatives

A dozen novel fluoroionophores have been synthesized which are polythiazaalkane and polythiaalkane derivatives coupled with an anthracene moiety by methyl, carbonyl, or methylphenylene bridging groups. The protonation and metal ion complexation behavior of analogues were examined in 1,4-dioxane-water solutions spectrophotometrically and spectrophotofluorometrically. The fluoroionophores, 1, 2, 5, and 6 contain basic nitrogen atoms and quench the fluorescence in the free forms because of photoinduced electron transfer (PET) from a nitrogen atom to a photoexcited anthracene unit. The fluorescence was recovered by the protonation on the nitrogen atom. The fluorescence intensities of the other fluoroionophores used here were not dependent on the pH of the solution. On the complexation of the protonated fluoroionophores 1, 2, 5, and 6 with metal ions under the acidic condition, the fluorescence intensities were decreased by the addition of silver ion selectively. Under the same conditions, the other fluoroionophores exhibited a decrease of the fluorescence intensity with the addition of silver ion selectively. These results imply that the fluoroionophores could form complexes and release a proton from the nitrogen atom of the protonated fluoroionophores. The quenching of the fluorescence of the complexed fluoroionophores 3, 4, 7, and 8-12 could be caused by the interaction of a silver ion with a pi-electron of the anthracene unit. The degree of spectral change on the complexation with silver ion is primarily dependent on the strength of the interaction of the bound silver ion with nitrogen atom, for 1, 2, 5, and 6, or with a pi-electron of the anthracene unit, for 3, 4, 7, and 8-12.