Anion Responsive Molecular Switch Based on a Doubly Strapped Calix[4]pyrrole

A calix[4]pyrrole receptor bearing two proximally meso-meso linking isophthaloyl straps displays open and closed states depending on the conformation. In crystal structures in non-polar solvent, adopts 1,3-alternate conformation with sides. Anion binding triggers a state of providing types interactions an aromatic benzoate guest: hydrogen bonds from pyrrolic NH groups ????? phenyl straps. Slow exchange dynamics was observed NMR timescale indicating that benzoate, acetate chloride anions, which bind relatively low affinity get kinetically trapped as insects Venus flytrap.