Hydrogen-bonded organic frameworks (HOFs), self-assembled from strategically pre-designed molecular tectons with complementary hydrogen-bonding patterns, are rapidly evolving into a novel and important class of porous materials. In addition to their common features shared with other functionalized porous materials constructed from modular building blocks, the intrinsically flexible and reversible H-bonding connections endow HOFs with straightforward purification procedures, high crystallinity, solution processability, and recyclability. These unique advantages of HOFs have attracted considerable attention across a broad range of fields, including gas adsorption and separation, catalysis, chemical sensing, and electrical and optical materials. However, the relatively weak H-bonding interactions within HOFs can potentially limit their stability and potential use in further applications. To that end, this Perspective highlights recent advances in the development of chemically and thermally robust HOF materials and systematically discusses relevant design rules and synthesis strategies to access highly stable HOFs.

Three MOFs based on unsymmetrical diisophthalates exhibit selective C2H2/CH4 and CO2/CH4 adsorption and their adsorption selectivity can be improved by alkoxy group functionalization.

A ligand conformation preorganization strategy was employed to design a hexacarboxylate ligand, and its corresponding copper-based MOF was constructed, exhibiting a novel topological structure and the potential for the separation and purification of acetylene and natural gas.

A family of Ln-MOFs constructed from flexible hexacarboxylate derivatives exhibit substituent-driven structural diversity, and the methoxy-modified one displays the potential for natural gas purification.

Investigation of the impact of ligand-originated MOF (metal-organic framework) isomerism and ligand functionalization on gas adsorption is of vital importance because a study in this aspect provides valuable guidance for future fabrication of new MOFs exhibiting better performance. For the abovementioned purpose, two NbO-type ligand-originated MOF isomers based on methoxy-functionalized diisophthalate ligands were solvothermally constructed in this work. Their gas adsorption properties toward acetylene, carbon dioxide, and methane were systematically investigated, revealing their promising potential for the adsorptive separation of both acetylene/methane and carbon dioxide/methane gas mixtures, which are involved in the industrial processes of acetylene production and natural gas sweetening. In particular, compared to its isomer ZJNU-58, ZJNU-59 displays larger acetylene and carbon dioxide uptake capacities as well as higher acetylene/methane and carbon dioxide/methane adsorption selectivities despite its lower pore volume and surface area, demonstrating a very crucial role that the effect of pore size plays in acetylene and carbon dioxide adsorption. In addition, the impact of ligand modification with a methoxy group on gas adsorption was also evaluated. ZJNU-58 exhibits slightly lower acetylene and carbon dioxide uptake capacities but higher acetylene/methane and carbon dioxide/methane adsorption selectivities as compared to its parent compound NOTT-103. By contrast, enhanced adsorption selectivities and uptake capacities were observed for ZJNU-59 as compared to its parent compound ZJNU-73. The results demonstrated that the impact of ligand functionalization with a methoxy group on gas adsorption might vary from MOF to MOF, depending on the chosen parent compound. The results might shed some light on understanding the impact of both ligand-originated MOF isomerism and methoxy group functionalization on gas adsorption.

The rapid, discriminative, and portable detection of highly toxic chemical warfare agents is extremely important for response to public security emergencies but remains a challenge. One plausible solution involves the integration of porous molecular traps onto a photoelectrochemical (PEC) sensor. Here, a fast and facile protocol is developed to fabricate sub‐1 nm AgNPs encapsulated hydrogen‐bonded organic framework (HOF) nanocomposite materials through an in situ photoreduction and subsequent encapsulation process. Compared to traditional semiconductors and selected metal–organic frameworks (MOF) materials, these AgNPs@HOFs show significantly enhanced photocurrent. Most importantly, the portable PEC device based on AgNPs@HOF‐101 can selectively recognize 13 different mustard gas simulants, including 2‐chloroethyl ethyl sulfide (CEES), based on synergistic size‐exclusion and specific recognition. The extremely low detection limit for CEES (15.8 nmol L−1), reusability (at least 30 cycles), and long‐term working stability (at least 30 d) of the portable PEC device warrant its use as a chemical warfare agents (CWAs) sensor in practical field settings. More broadly, this work indicates that integrating porous molecular traps onto PEC sensors offers a promising strategy to further develop portable devices for CWAs detection with both ultrahigh sensitivity and selectivity.

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Owing to their switchable spin states and dynamic electronic character, organic-based radical species have been invoked in phenomena unique to a variety of fields. When incorporated in solid state materials, generation of organic radicals proves challenging due to aggregation. Metal−organic frameworks (MOFs) are promising candidates for immobilization and stabilization of organic radicals because of the tunable spatial arrangement of organic linkers and metal nodes, which sequesters the reactive species. Herein, a flexible, redox-active tetracarboxylic acid linker bearing two imidazole units was chosen to construct a new Zr 6 -MOF, NU-910, with scu topology. By exploiting the structural flexibility of NU-910, we successfully modulate the dynamics between an isolated organic radical species and an organic radical π-dimer species in the MOF system. Single-crystal X-ray diffraction analysis reveals that through solvent exchange from N,N-diethylformamide to acetone, NU-910 undergoes a structural contraction with interlinker distances decreasing from 8.32 Å to 3.20 Å at 100 K. Organic radical species on the bridging linkers are generated via UV light irradiation. Direct observation of temperature-induced spin switches from an isolated radical species to a magnetically silent radical π-dimer in NU-910 after irradiation in the solid state was achieved via variable-temperature single-crystal X-ray diffraction and variable-temperature electron paramagnetic resonance spectroscopy. Ultraviolet−visible−near infrared spectroscopy and density functional theory calculations further substantiated the formation of a radical cation π-dimer upon irradiation. This work demonstrates the potential of using flexible MOFs as a platform to modulate radical spin states in the solid phase.