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

Liu, Yang; Tan, Yifei; Wu, Quan; Ma, Qijun; Long, Sitong; Wu, Zhongqi; Liu, Jilin; Yang, Liting et al. · Nano Lett · 2026

basic_science · Level V

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Abstract

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 <i>in situ</i> 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 <sup>131</sup>I<sup>-</sup> from an aqueous solution. These findings provide key insights into the photocatalysis of the COFs.