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 selfinclusion 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.

Metrics & MoreArticle Recommendations CONSPECTUS: Supramolecular polymers, generated by connecting monomers through noncovalent interactions, have received considerable attention over the past years, as they provide versatile platforms for developing diverse aesthetically pleasing polymeric structures with promising applications in a variety of fields, such as medicine, catalysis, and sensing. In the development of supramolecular polymers, macrocyclic hosts play a very important role. Benefiting from their abundant host− guest chemistry and self-assembly characteristics, macrocycles themselves or their host−guest complexes can self-assemble to form well-ordered supramolecular polymeric architectures including pseudopolyrotaxanes and polyrotaxanes. The integration of these topological structures into supramolecular polymeric materials also imbues them with some unforeseen functions. Current interest in macrocyclebased supramolecular polymers is mostly focused on the development of supramolecular soft materials in solution or gel-state, in which the dynamic nature of noncovalent interactions endows supramolecular polymers with a wealth of "smart" properties, such as multiresponsiveness and self-repair capabilities. While preparation of macrocycle-derived supramolecular polymers in the solid state is a relatively challenging but intriguing prospect, they are an important part of the field of supramolecular polymers. On one hand, the construction of macrocycle-based solid-state supramolecular polymers enables us to obtain new materials with novel properties and functions such as mechano-responsiveness. On the other hand, the molecular structures and arrangements in these materials are well-identified by Xray crystallography techniques, offering a direct visual representation of the supramolecular polymerization process. The analysis of the role of noncovalent interactions in these architectures allows us to design more sophisticated and elegant supramolecular polymers in a highly rationalized and controllable manner. This Account serves to summarize the research progress on macrocyclebased solid-state supramolecular polymers (MSSPs), including the contributions toward this field made by our group. For constructing MSSPs, the key point is to control noncovalent interactions. Thus, in this Account, we primarily classify these MSSPs by different noncovalent interactions involved to connect the monomers, including metal−ligand interactions, host−guest interactions, π•••π stacking, and halogen bonding. These noncovalent interactions are highly associated with the structures and functions of the resultant MSSPs. For instance, using metal−ligand interactions as driving forces, metal clusters can be introduced in MSSPs which afford systems with solid-state luminescence or proton conduction properties; supramolecular polymerization using macrocycle-based host−guest interactions can modulate the molecular arrangement of some specific molecules in the solid state, which further influences their solid-state properties; π•••π sta...

Supramolecular tessellation is a newly emerging and promising area in supramolecular chemistry because of its unique structural aesthetics and potential applications. Herein, we investigate the "exo−wall" interactions of pillar[n]arenes and prepare fantastic hexagonal supramolecular tessellations based on perethylated pillar[6]arenes (EtP6) with electron-deficient molecules 1,5-difluoro-2,4-dinitrobenzene (DFN) and tetrafluoro-1,4benzoquinone (TFB). The crystal structures clearly confirm that EtP6 can form highly ordered hexagonal 2D tiling patterns with DFN/TFB as linkers through cocrystallization. Moreover, the selfassembled packing arrangements in the ultimate cocrystal superstructures can be adjusted under different crystallization conditions. This work not only explores the rare exo−wall interactions based on pillar[n]arenes but also reports the fabrication of supramolecular tessellations based on pillararenes for the first time, showing a new perspective in supramolecular chemistry.