Acid/Base-Tunable Unimolecular Chirality Switching of a Pillar[5]azacrown <i>Pseudo</i>[1]Catenane

Stimuli-responsive unimolecular chirality switching is a highly intriguing topic because the molecular structure as well as its function can be adjusted simultaneously by a switching process. Herein, a novel acid/base-tunable unimolecular chirality switching system based on a pillar[5]­azacrown pseudo[1]­catenane is reported. The bicyclic pillar[5]­azacrown pseudo[1]­catenane PN4 is synthesized through fusing an azacrown ring onto one repeating unit of a pillar[5]­arene. Protonation and deprotonation can reversibly regulate the conformational transformations of PN4 between self-inclusion and self-exclusion structures, which results in the chiroptical inversions of the pseudo[1]­catenane. NMR spectra, circular dichroism spectra, and single-crystal structures demonstrate these processes. This pseudo[1]­catenane is a novel pillararene-based unimolecular chirality switching system driven by acid/base responsiveness and reveals a new perspective on the supramolecular chirality chemistry of macrocycles.