Supramolecular Protection-Deprotection for Switching Pore-Surface Functionality in a Crystalline Porous Organic Salt

The precise installation of highly interactive functional groups on pore surfaces remains a central challenge in crystalline porous materials since such groups often interfere with framework formation. In this study, supramolecular protection-deprotection was performed in a porous organic salt that temporally separated framework construction from the emergence of pore-surface functionality. During crystallization, the phenolic OH groups were protected by hydrogen bonding with dimethyl sulfoxide (DMSO), enabling the formation of a crystalline framework based on charge-assisted hydrogen bonds. Stepwise removal of DMSO induced a two-step single-crystal-to-single-crystal phase transition, affording first a dormant state (Form II), in which the OH groups remained protected, and subsequently an active state (Form III), in which the OH groups were exposed on the pore surface together with the emergence of porosity. The dormant state was re-formed by exposure to DMSO or N,N-dimethylacetamide vapor, whereas other solvents failed to induce the same structural response. In contrast, the active state showed markedly enhanced NH₃ uptake relative to the dormant state and preferential adsorption of NH₃ over CO₂, N₂, H₂, and O₂ under the investigated conditions. These results demonstrate that supramolecular protection-deprotection provides a useful strategy for temporally controlling pore-surface functionality in dynamic crystalline porous materials.