Pore Segmentation Strategy of Calixarene-Based Covalent Organic Frameworks for Chiral Selective Transmembrane Transport of Amino Acids

Covalent organic frameworks (COFs) provide an exceptional platform for creating nanochannels with different pore environments and customized functionalities. However, precisely tuning the pore size and geometry of COF nanochannels and making them selectively recognizable are fraught with challenges. Herein, we present a macrocycle-driven pore segmentation strategy to construct COF nanochannels with precisely confined cavities, enabling highly efficient and enantioselective transmembrane transport. By employing calix[4]arene and calix[6]arene as building blocks, we fabricated calixarene-based COF nanochannels with tetragonal and hexagonal symmetries in the AA stacking mode. This design enabled the precise regulation of pore size and functionality, thereby creating tailor-made confined environments ideal for chiral separation. β-Cyclodextrin was subsequently anchored to the pore wall of the nanochannels via a "click" reaction to construct a chiral microenvironment. The mixed matrix membranes based on chiral COFs were further prepared, which exhibited remarkable selective transmembrane recognition and transport of D/L-tryptophan with enantiomer excess values approaching 100%, a notable advancement in membrane-based chiral separation. The intrinsic relationship between the crystal structure and pore structure of calixarene-based COFs and their selective recognition capabilities of amino acids was explored. This study facilitates the precise design and construction of macrocyclic-based COF artificial nanochannels, enabling the selective recognition and precise regulation of nanochannel pore structures and microenvironments.