Guest-Induced Structural Torsion in Single Covalent Organic Frameworks for Enhanced Photocatalysis

Monitoring and understanding the photocatalytic reactions at individual covalent organic framework (COF) photocatalysts are crucial for gaining insights into their structure-activity relationships. Here, we report real-time imaging of the guest-induced structural torsion in single COF-300 microcrystals for enhanced photocatalysis utilizing <i>in situ</i> dark-field optical microscopy (DFM). Upon inclusion of ethyl acetate (EAC) into the COF-300 framework, deformed EAC-encapsulated COF-300 (EAC@COF-300) microcrystals with twisted diimine linkers are generated, resulting in an inert-to-active photocatalytic reactivity transformation. Impressively, this host-guest-enhanced photocatalysis strategy is also applicable to other guests. The combination of single-particle imaging, spectral characterizations, and theoretical calculations elucidates that structurally twisted EAC@COF-300 boosts the intersystem crossing process and spin-orbit coupling, facilitating the separation of photogenerated electron-hole pairs. Furthermore, the twisted EAC@COF-300 realizes the photocatalytic removal of radioactive ¹³¹I^- at the pg level. Our findings provide a general strategy for the rational design of efficient COF photocatalysts via twist engineering.