Calix[4]pyrroles with Shortest Possible Strap: Exclusively Selective toward Fluoride Ion

Four
new calix[4]­pyrroles with the shortest possible strap so far
through ortho-linking of the aromatic unit have been synthesized,
including a naphthalene-derived fluorescent receptor. They show exclusive
selectivity toward the fluoride ion as confirmed by 1H
NMR, isothermal titration calorimetry, and fluorescence spectroscopic
study. Anion affinity could also be modulated further via functionalization
at the strap. Computational analysis displays calix[4]­pyrroles binding
to fluoride ion in a very unusual 1,3-alternate conformation where
the anion resides on the opposite side of the strap.