Azocalix[4]arene Strapped Calix[4]pyrrole: A Confirmable Fluoride Sensor

A new chromogenic fluoride sensor based on 1,3-di-p-nitrophenylazocalix[4]arene-calix[4]pyrrole (1) was designed and synthesized. The color of the solution of probe 1 changed upon the addition of any F–, CH3CO2–, PhCO2–, and H2PO4– ions. However, from these ions the highly specific sensing of F– is achieved by the addition of Ca2+ which leads to a color change from light sky blue (of 1·F–) back to the original light orange color of 1.