Simultaneous Deep Protonation and Twist Modulation in Individual Covalent Organic Frameworks for Boosting...

Covalent organic frameworks (COFs) are promising photocatalysts, but improving their performance requires enhanced light harvesting and suppressed electron-hole recombination, often via postprotonation or conformational modulation. Here, using in situ liquid-phase dark-field optical microscopy (DFM), we directly image in real time that the chloroacetic acid (MCA) interacts with COF-300 as a prototype COF host to form a highly protonated and twisted host-guest complex (MCA@COF-300) at the single-particle level, whereas acetic acid or trichloroacetic acid induces only weak effects. Further real-time single-particle photocatalytic imaging experiments show the high activity of MCA@COF-300. Combining ensemble characterizations and theoretical calculations, the coexistence of deep protonation and twist modulation in MCA@COF-300 is uncovered to favor visible light absorption and single-triplet intersystem crossing, leading to the formation of long-lived charge-separated states for boosting photocatalysis. Moreover, we apply the MCA@COF-300 photocatalyst to capture ultratrace radioactive ¹³¹I^- from an aqueous solution. These findings provide key insights into the photocatalysis of the COFs.