Synthesis and anion recognition properties of two novel tetraamide calix[4](aza)crowns for optical anion sensor

Two new tetraamide calix[4](aza)crowns (5a, 5b) were synthesized and used for optical anion sensors. Addition of host 5a or 5b to the p-NO ₂C₆H₄O^- anion in CHCl₃ resulted in decreasing absorption of band at 423 nm and the yellow solution of p-NO₂C₆H₄O^- anion became colorless because of the formation of host-guest complexes between host 5a or 5b and p-NO₂C₆H₄O^-. The fluorescence response was observed in the presence of anions such as p-NO₂C ₆H₄O^-, F^-, H₂PO ₄^-, and the receptors 5a and 5b were highly selective toward p-NO₂C₆H₄O^-. The degree of change in the emission intensity was in the order of p-NO₂C ₆H₄O^->F^->H₂PO ₄^-≫Cl^-, Br^-, I^-. The fluorescence spectroscopy titration experiments indicated the formation of a 1:1 stoichiometry complex between receptor 5a (or 5b) and anion by nonlinear fitting curve.