Enabling Solution Processable COFs through Suppression of Precipitation during Solvothermal Synthesis.

PTSA-mediated interfacial catalytic polymerization of crystalline dense covalent organic framework membranes for enhanced desalination

Sol-gel processing of a covalent organic framework for the generation of hierarchically porous monolithic adsorbents

Heteroaromatic molecular building blocks can be assembled in the highly ordered spatial environment of covalent organic frameworks (COFs), forming two-dimensional (2D) and 3D crystalline architectures. For example, photoactive molecular moieties such as porphyrins and other chromophores can be spatially integrated into their crystalline lattice, allowing us to create models for organic bulk heterojunctions, chemical sensors and porous electrodes for photoelectrochemical systems.Here, we will discuss different strategies aimed at creating electroactive networks capable of light-induced and electrochemical charge transfer. In earlier work, we have developed COF-based heterojunctions containing stacked thienothiophene-based building blocks acting as electron donors with a 3 nm open pore system, which show light-induced charge transfer to an intercalated fullerene acceptor phase.[1] We now create interpenetrated donor-acceptor COF phases with novel dibenzochrysene-based building blocks that can be viewed as constrained propeller-shaped tetraphenylethylene with reduced curvature engaging in very tight π-stacking.[2] Thienothiophene- (TT) and benzodithiophene-2,6-dicarboxaldehyde based 2D kagome COFs were synthesized in situ with a fullerene derivative to create interpenetrated electron-donor/acceptor host-guest systems showing efficient charge transfer within ps from the COF to the fullerene guest.Contrasting the above approach, one can design COF integrated heterojunctions consisting of alternating columns of stacked donor and acceptor molecules, promoting the photo-induced generation of mobile charge carriers inside the COF network.[3] Synthetic efforts have led to several COFs integrating extended chromophores capable of efficient harvesting of visible and near infrared light, for example.[4] Notably, heterocyclic regioisomers that can be embedded in the same COF crystal structure allow for fine-tuning of optical absorption and luminescence.[5]Extending thin film growth methodology to create a solvent-stable oriented 2D COF photoabsorber structure, COF films can serve in photoelectrochemical water splitting systems.[6] The detailed mechanism of excited state dynamics in light-harvesting conjugated COFs has been revealed by means of transient absorption spectroscopy,[7] while ongoing work establishes efficient excited state diffusion – even across grain boundaries – in 2D COF thin films. Many optoelectronic applications of COFs depend on significant electrical conductivity. Here, Wurster-type structural motifs are attractive building blocks for imparting high conductivity in the corresponding COFs,[8] which feature tunable optical properties upon integrating donor-acceptor moieties. COF films can also act as ultrafast solvatochromic chemical sensors,[9] as photodetectors,[10] and show very efficient electrochromic response.[11]While guest-responsive (breathing) MOFs have been studied for some time, to date few guest-responsive COF structures have been described. We have now developed dynamic two-dimensional COFs that can open and close their pores upon uptake or removal of guests while fully retaining their crystalline long-range order.[12] Here, a wine rack design based on rigid, π-stacked columns of perylene diimides (PDIs) interconnected by non-stacked, flexible bridges shows stepwise phase transformations between contracted pore and open pore forms with up to 40% increase in unit cell volume. By reversibly tuning π-interactions via guest sorption, we modulate excitonic coupling within the COFs, where the PDI moieties can be switched from excimer-forming H-aggregates to null-aggregates with monomer-like absorption and emission characteristics. These findings open new pathways towards designing stimuli-responsive optical, electronic, or spintronic materials.Ongoing work focuses on the design of ultra-large pore donor-acceptor COFs with extended light-harvesting abilities and optimized charge separation, illustrating their intriguing structural diversity leading to enhanced optoelectronic functionality.[13]References Dogru et al., Chem. Int. Ed. 2013, 52, 2920.Xue et al., to be submitted Calik et al., J. Am. Chem. Soc. 2014, 136, 17802.Keller et al., J. Am. Chem. Soc. 2017, 139, 8194.Guntermann et al., 2024, in revision. Sick et al., J. Am. Chem. Soc. 2018, 140, 2085.Jakowetz et al., J. Am. Chem. Soc. 2019, 141, 11565.Rotter et al., Chem. Sci. 2020, 11, 12843.Ascherl et al., Nature Commun. 2018, 9, 3802.Bag et al., J. Am. Chem. Soc. 2023, 145, 1649.Muggli et al., ACS Nanosci. Au 2023, 3, 153.Auras et al., Nature Chem. 2024, 16, 1373. Blätte, Ortmann, Bein, J. Am. Chem. Soc., 2024, 146, 32161.

The optoelectronic properties of covalent organic frameworks (COFs) can be controlled by the design of their molecular building blocks and assembly. Here, a facile and efficient synthetic route is reported for the novel thiophene-enriched tetrathienonaphthalene (TTN)-based node 4,4',4″,4'″-(naphtho[1,2-b:4,3-b':5,6-b″:8,7-b″']tetrathiophene-2,5,8,11-tetrayl)tetraaniline (TTNTA) for constructing imine-linked COFs. Utilizing TTNTA, highly crystalline, thiophene-enriched donor-donor (D-D) and donor-acceptor (D-A) COFs, denoted as TT COF and BDT(BT)2 COF,are synthesized using two distinct aldehyde-functionalized linear linkers: [2,2'-bithiophene]-5,5'-dicarbaldehyde (TT) and 7,7'-(4,8-diethoxybenzo[1,2-b:4,5-b']dithiophene-2,6-diyl)bis(benzo[c][1,2,5]thiadiazole-4-carbaldehyde) (BDT(BT)2), respectively. Highly crystalline and oriented TTNTA COF films on various substrates via a solvothermal method enabled further comprehensive optical and electronic characterizations. Optical-pump terahertz-probe spectroscopy revealed effective charge-carrier mobility values φμ = 0.34 ± 0.04 and 0.18 ± 0.02 cm2V-1s-1 for TT and BDT(BT)2 COF films, respectively. These results reveal distinct charge-transport characteristics and provide mechanistic insights into their ultrafast charge-carrier dynamics. The COFs are demonstrated to be photoactive, showing promising potential as photocathodes without co-catalysts in photoelectrochemical water splitting, with notable photocurrent densities of 10 and 15.3µA cm-2 after 1h illumination, respectively. This work highlights the potential of TTNTA-based COFs in optoelectronic applications and provides insights into the design of thiophene-enriched COFs with high crystallinity and photoactive behavior.

This work addresses the long-standing challenge of insufficient permselectivity in two-dimensional (2D) covalent organic framework (COF) membranes by developing a generalizable and potentially scalable self-templating interfacial assembly method to synthesize vertically aligned 2D COF polycrystalline nanofilms. Experiments and molecular simulations reveal that molecular amphiphilicity-driven spontaneous confinement and directional alignment of framework-building units at the organic/aqueous interface instigate the vertical growth of COF monolayers. The superior sieving ability of sub–4 angstrom interlayer nanochannels enables vertically aligned COF membranes to efficiently intercept salt ions, electrically neutral small molecules, and hazardous chemicals, outperforming conventional COF membranes. The implemented strategy can be extended to other building blocks and framework topologies, opening up avenues for fine-tuning the pore structure of 2D COF membranes.

In this Review we survey the molecular sieving behaviour of metal-organic framework (MOF) and covalent organic framework (COF) membranes, which is different from that of classical zeolite membranes. The nature of MOFs as inorganic-organic hybrid materials and COFs as purely organic materials is powerful and disruptive for the field of gas separation membranes. The possibility of growing neat MOFs and COFs on membrane supports, while also allowing successful blending into polymer-filler composites, has a huge advantage over classical zeolite molecular sieves. MOFs and COFs allow synthetic access to more than 100,000 different structures and tailor-made molecular gates. Additionally, soft evacuation below 100 °C is often enough to achieve pore activation. Therefore, a huge number of synthetic methods for supported MOF and COF membrane thin films, such as solvothermal synthesis, seed-mediated growth and counterdiffusion, exist. Among them, methods with high scale-up potential, for example, layer-by-layer dip- and spray-coating, chemical and physical vapour deposition, and electrochemical methods. Additionally, physical methods have been developed that involve external stimuli, such as electric fields and light. A particularly important point is their ability to react to stimuli, which has allowed the 'drawbacks' of the non-ideality of the molecular sieving properties to be exploited in a completely novel research direction. Controllable gas transport through membrane films is a next-level property of MOFs and COFs, leading towards adaptive process deviation. MOF and COF particles are highly compatible with polymers, which allows for mixed-matrix membranes. However, these membranes are not simple MOF-polymer blends, as they require improved polymer-filler interactions, such as cross-linking or surface functionalization.

Covalent organic framework (COF) membrane holds great promise in water treat-ment. Improving the antifouling property of COF membrane is critical for practical application while rare investigations have been reported. Grafting fluorinated chains on the COF membrane surface is expected an effective strategy but quite challenging due to the lack of grafting sites. In this work, the defect engineering strategy is adopted to generate free amino groups as grafting sites through the Schiff-base reaction between amine monomer and mixed aldehyde monomers, then perfluoroalkyl chains are grafted on the COF membrane surface through the reaction between the free amino groups and the perfluorooctanoyl chloride. The content of perfluoroalkyl chains can be regulated and optimized by controlling the amount of free amino groups. The fluorinated COF membrane shows superior antifouling performance with a significantly increased flux recovery ratio and reduced flux decline ratio against oil/water emulsions and humic acid (FRR ≈ 98%, DRt = 10%). Furthermore, the fluorinated COF membrane exhibits high water permeance up to ≈115 L m-2 h-1 bar-1 while acquiring a high salt/dye selective factor. This work affords an effective approach to the development of antifouling, high-separation-performance COF membranes, and other kinds of organic molecular sieve membranes.

Covalent organic frameworks (COFs), which are constructed from organic linkers, are a new class of crystalline porous materials comprising periodically extended and covalently bound network structures. The intrinsic structures and the tailorable organic linkers endow COFs with a low density, large surface area, tunable pore size and structure, and facilely-tailored functionality, attracting increasing interests in different fields including membrane separations. Exciting research activities ranging from fabrication strategies to separation applications of COF-based membranes have appeared. This review analyzes the synthesis and applications of diverse continuous/discontinuous COF membranes, such as COF-based mixed matrix membranes (MMMs), COF-based thin film nanocomposite (TFN) membranes, and free-standing COF films. Special attention was given to pore size, stability, hydrophilicity/hydrophobicity and surface charge of COFs in view of determining proper COFs for membrane fabrication, along with the approaches to fabricate COF-based membranes, such as blending, in situ growth, layer-by-layer stacking and interfacial polymerization (IP). Moreover, applications of COF-based membranes in gas separation, water treatment (deaslination and dye removal), organic solvent nanofiltration (OSN), pervaporation and fuel cell are disscussed. Finally, we illustrate the advantages and disadvantages of COF-based membranes through a comparison with MOF-based membranes, and the remaining challenges and future opportunities in this field.

High-throughput computational screening of Covalent−Organic framework membranes for helium purification

Hydrated-ion transport and desolvation dominate energy transfer and ionic selectivity in membrane separation, electrochemical energy storage, and catalytic systems, whereas achieving fast ion conduction with low hydration remains highly challenging. In this work, we discover that pyridinyl-based covalent organic framework (COF) membranes enable the fast transport of hydrated ions with efficient desolvation. This originates from a soft Lewis acid-mediated competitive coordination mechanism, where pyridinyl groups partially displace hydration shells. The ordered channels with optimized coordination not only stabilize desolvated ions but also provide continuous hopping pathways for ion migration, resulting in rapid ion transport with reduced desolvation barriers. As a proof-of-concept application, the pyridinyl COF membranes were studied in aqueous zinc batteries. Electrochemical tests reveal that partial zinc ion desolvation lowers the thermodynamic barrier for zinc nucleation, while rapid ion transport balances interfacial reaction kinetics, effectively suppressing dendrite growth and parasitic reactions. Consequently, a zinc anode paired with pyridyl COF membranes exhibits reversible stripping/plating over 2000 cycles in a conventional ZnSO4 electrolyte without additives, outperforming most of the current aqueous battery separators. This work demonstrates the unique desolvation transport behavior of hydrated ions in pyridinyl COF membranes and provides new insights for the rational design of COFs for electrochemical energy storage.

Recently, covalent organic frameworks (COFs) have emerged as an interesting class of porous materials, featuring tunable porosity and fluorescence properties based on reticular construction principles. Some COFs display highly emissive monocolored luminescence, but attaining white-light emission from COFs is difficult as it must account for a wide wavelength range. White-light emission is highly desired for solid-state lighting applications, and obtaining it usually demands the combination of red-, green-, and blue-light components. Hence, to achieve the targeted white-light emission, we report for the first time grafting of lanthanides (Eu3+/Tb3+) on a two-dimensional imine COF (TTA-DFP-COF). We studied the luminescence properties of the hybrid materials prepared by anchoring Eu3+ (red light) and Tb3+ (green light) β-diketonate complexes onto the TTA-DFP-COF. Reticular construction is exploited to design strong coordination of Eu3+ and Tb3+ ions into nitrogen-rich pockets of the imine COF. Mixed Eu3+/Tb3+ materials are then prepared to incorporate red and green components along with the inherent blue light from the organic moieties of the COF to produce white-light emission. We show that COFs have the potential for hosting Eu3+ and Tb3+ complexes, which can be tuned to obtain desired excitations for applications in the field of optoelectronics, microscopy, optical sensing, and bioassay.

Covalent organic frameworks (COFs) are structurally tuneable, porous and crystalline polymers constructed through the covalent attachment of small organic building blocks as elementary units. Using the myriad of such building blocks, a broad spectrum of functionalities has been applied for COF syntheses for broad applications, including heterogeneous catalysis. Herein, we report the synthesis of a new family of porous and crystalline COFs using a novel acridine linker and benzene‐1,3,5‐tricarbaldehyde derivatives bearing a variable number of hydroxy groups. With the broad absorption in the visible light region, the COFs were applied as photocatalysts in metallaphotocatalytic C−N cross‐coupling. The fully β‐ketoenamine linked COF showed the highest activity, due to the increased charge separation upon irradiation. The COF showed good to excellent yields for several aryl bromides, good recyclability and even catalyzed the organic transformation in presence of green light as energy source.

Covalent organic frameworks (COFs) are promising materials for a variety of applications, including membrane-based separations, thin-film electronics, and as separators for electrochemical devices. Robust mechanical properties are critical to these applications, but there are no reliable methods for patterning COFs or producing free-standing thin films for direct mechanical testing. Mechanical testing of COFs has only been performed on films supported by a rigid substrate. Here, we present a method for patterning, transferring, and measuring the tensile properties of free-floating nanoscale COF films. We synthesized COF powders by condensation of 1,3,5-tris(4-aminophenyl)benzene (TAPB) and terephthalaldehyde (PDA) and prepared uniform thin films by spin casting from a mixture of trifluoroacetic acid and water. The COF films were then reactivated to recover crystallinity and patterned by plasma etching through a poly(dimethylsiloxane) (PDMS) mask. The films were transferred to the surface of water, and we performed direct tensile tests. We measured a modulus of approximately 1.4 GPa for TAPB-PDA COF and a fracture strain of 2.5%, which is promising for many applications. This work advances the development of COFs for thin-film applications by demonstrating a simple and generally applicable approach to cast, pattern, and transfer COF thin films and to perform direct mechanical analysis.

Photoelectrochemical biosensing platform based on in situ generated ultrathin covalent organic framework film and AgInS2 QDs for dual target detection of HIV and CEA

Covalent organic frameworks (COFs) build a versatile platform for constructing separation membranes, affording them disruptive candidates for nanoscale molecule/ion sieving. However, the reported aperture of COFs mainly concentrates on 0.8–10.0 nm, leaving a daunting challenge in fabrication of ultramicroporous (<0.7 nm) COF membranes. Herein, the channel partition of COF membranes is elaborately implemented by taking advantage of the copper‐catalyzed azide–alkyne cycloaddition (CuAAC) based on click chemistry. Two kinds of novel alkynyl COF membranes bearing symmetric alkynyl monomers are predesigned and synthesized. The alkynyl groups can react with dual‐azide molecules to form triazole ring bridge, which allows the partition of hexagonal or tetragonal channels. Moreover, the π‐electron‐rich structures of triazole ring offer cation‐philic or anion‐repulsive region, showing great potentials in precise ion separations. Consequently, the superior performance is obtained in separating ternary/binary ion mixtures: Li + /Mg 2+ /(K + ) and F − /SO 4 2− /(Cl − ). Example of dealing with a K + /Li + /Mg 2+ ternary mixture, the optimum p ‐TpPa‐C≡CH membrane exhibits an actual selectivity of 101.2 for K + /Mg 2+ and 30.9 for Li + /Mg 2+ . The strong adaptability and wide range of application scenarios of our COF membranes exceed the ever‐reported membranes. This work provides a fundamental to comprehending the channel manipulation mechanisms and advances the development of high‐performance ion separation membranes.