Imaging the Iodine Sorption-Induced Synchronous Skeleton–Pore Interactions of Single Covalent Organic Framework Particles

Covalent organic frameworks (COFs) are promising iodine adsorbents. For improved performances, it is critical and essential to fundamentally understand the underlying mechanism. Here, using the operando dark-field optical microscopy (DFM) imaging technique, the observation of an extraordinary structure shrinkage of 2D triphenylbenzene (TPB)-dimethoxyterephthaldehyde (DMTP)-COF upon the adsorption of I 2 vapor at the single-particle resolution is reported. Combining single-particle DFM imaging with other experimental and theoretical methods, it is revealed that the shrinkage mechanism of the TPB-DMTP-COF is attributed to the I 2 sorption-induced synchronous skeleton-pore interactions. The redox reaction of I 2 and TPB-DMTP-COF yields some cationic skeletons and I 3 − species, which triggers the multi-directional halogen-bonding interactions of I 2 and I 3 − as well as strong cation-π interactions between neutral and cationic skeletons, accompanying the synchronous in-plane skeleton shrinking in the xy plane and compact out-of-plane layer packing in the z- direction. This understanding of the synchronous action between the skeleton and pore breaks the perspective on the structure robustness of 2D COFs with excellent stability during the I 2 uptake, which offers pivotal guidance for the rational design and creation of advanced microporous adsorbents.