Synthesis and Fluorescence Sensing Properties of Calix[4]arenes Containing Fluorophores

New fluoroionophores 4 and 5 derived from calix[4]arene triester monoacid chloride with 2-amino-4-(1,3-benzothiazol-2-yl)phenol and 4-aminoquinaldine, respectively, have been synthesized. A preliminary test showed that the fluorescence intensity of 5 was very low, so only 4 was subjected to cation recognition investigation. In methanol, the fluorescence intensity of 4 was quenched by Na⁺. The fluorescence intensity decreased linearly with increasing Na⁺ concentration with a stability constant of log K = 2.91 ± 0.08. No significant response was observed for other alkali metal ions under the same experimental conditions.