Deciphering the Entropy-Driven Host–Guest Interactions within Single Covalent Organic Frameworks for Trapping of ¹³¹I^–

By combining dark-field optical microscopy with an <i>in situ</i> thermochemical aqueous solution system, we report a single-particle imaging strategy to investigate the host-guest interactions between covalent organic framework-300 (COF-300) as a representative COF host and a series of linear-chain fatty amines. The thermodynamic parameters, such as dissociation constant, Gibbs free energy changes, enthalpy changes, and entropy changes for the binding events within COF-300 are quantified. Correlation between the hydrophobicity of various amines and other data suggests that the mechanism of the host-guest bindings arises from the entropy-driven noncovalent interactions such as hydrogen bonds and van der Waals forces. These mechanistic insights allow for the rational design and preparation of COF-300-encapsulated <i>n</i>-octylamine with enhanced trapping performance of radioactive ¹³¹I^-. This study not only provides thermodynamic insights into the host-guest interactions within the COF framework but also establishes a structure-property relationship between fatty amines and energetic magnitude information.