Molecular Design of Chromogenic Calix[4]crowns Which Show Very High Na+ Selectivity

Abstract
Chromogenic calix[4]crowns bearing a short crown strap for the metal recognition and an azophenol unit for the optical reading-out were designed and synthesized. Two-phase solvent-extraction established that they show remarkably high Na+/K+(>103.1) selectivity. This discrimination ability is high enough to apply them as a Na+-selective ionophore for optical sensing systems.