Light-activated 3D covalent organic framework membranes with adaptive pores for CO₂ recognition and separation

Creation of membrane channels capable of recognizing diverse molecules is desirable for advancing molecular transport and separation, but it remains difficult to precisely control their conformation and achieve dynamic adaption to specific molecules. Here, we demonstrate fine-tuning the pore environment within 3D covalent organic framework (COF) that can precisely control its pore size and polarity to recognize CO₂. The pores are integrated with azobenzene units with photo-adaptable trans-to-cis isomerization, enabling dynamic pore size regulation at angstrom scale. Moreover, the isomerization induces drastic changes in intrapore polarity, which exert profound effects on the intermolecular affinity through the dipole-quadrupole interaction. Featuring these dynamic natures, the 3D COF membrane cooperating the size exclusion effect with a molecular recognition ability toward CO₂. As a result, light-gating separation experiments show the superior CO₂ capture performance with a N₂/CO₂ selectivity of 27.6. Theoretical calculations reveal that cis-state azobenzene can reduce the electron transfer barrier from azobenzene to CO₂, thereby providing a molecular recognition pathway.