Colorimetric Sensing of Fluoride Ion by New Expanded Calix[4]pyrrole through Anion−π Interaction

Three new expanded calix[4]pyrroles were synthesized, where the two dialkylldipyrromethane units are linked via C–C double bonds. One of them, calix[2]bispyrrolylethene, colorimetrically senses fluoride ion only, owing to anion−<b>π</b> interaction in polar aprotic solvents