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The periodic layers and ordered nanochannels of covalent organic frameworks (COFs) make these materials viable open catalytic nanoreactors, but their low stability has precluded their practical implementation. Here we report the synthesis of a crystalline porous COF that is stable against water, strong acids and strong bases, and we demonstrate its utility as a material platform for structural design and functional development. We endowed a crystalline and porous imine-based COF with stability by incorporating methoxy groups into its pore walls to reinforce interlayer interactions. We subsequently converted the resulting achiral material into two distinct chiral organocatalysts, with the high crystallinity and porosity retained, by appending chiral centres and catalytically active sites on its channel walls. The COFs thus prepared combine catalytic activity, enantioselectivity and recyclability, which are attractive in heterogeneous organocatalysis, and were shown to promote asymmetric C–C bond formation in water under ambient conditions. Covalent organic frameworks (COFs) feature periodic layers and ordered pores that make them promising for applications in catalysis, but they typically suffer from poor stability. Now, adding methoxy groups to its pore walls has been shown to strengthen a COF's interlayer interactions, resulting in a stable, crystalline, porous material that can be further converted into chiral organocatalysts.

The design of large-pore proton conductors with well-defined high-order structures is challenging. Proton conduction in a crystalline covalent organic framework 2–4 orders of magnitude higher than microporous polymers is now demonstrated. Progress over the past decades in proton-conducting materials has generated a variety of polyelectrolytes 1 , 2 , 3 , 4 , 5 and microporous polymers 6 , 7 , 8 , 9 , 10 . However, most studies are still based on a preconception that large pores eventually cause simply flow of proton carriers rather than efficient conduction of proton ions, which precludes the exploration of large-pore polymers for proton transport. Here, we demonstrate proton conduction across mesoporous channels in a crystalline covalent organic framework. The frameworks are designed to constitute hexagonally aligned, dense, mesoporous channels that allow for loading of N -heterocyclic proton carriers. The frameworks achieve proton conductivities that are 2–4 orders of magnitude higher than those of microporous and non-porous polymers. Temperature-dependent and isotopic experiments revealed that the proton transport in these channels is controlled by a low-energy-barrier hopping mechanism. Our results reveal a platform based on porous covalent organic frameworks for proton conduction.

Progress over the past decades in water confinement has generated a variety of polymers and porous materials. However, most studies are based on a preconception that small hydrophobic pores eventually repulse water molecules, which precludes the exploration of hydrophobic microporous materials for water confinement. Here, we demonstrate water confinement across hydrophobic microporous channels in crystalline covalent organic frameworks. The frameworks are designed to constitute dense, aligned and one-dimensional polygonal channels that are open and accessible to water molecules. The hydrophobic microporous frameworks achieve full occupation of pores by water via synergistic nucleation and capillary condensation and deliver quick water exchange at low pressures. Water confinement experiments with large-pore frameworks pinpoint thresholds of pore size where confinement becomes dominated by high uptake pressure and large exchange hysteresis. Our results reveal a platform based on microporous hydrophobic covalent organic frameworks for water confinement. Research on water confinement in small hydrophobic pores remains scarce because of a preconception that small hydrophobic pores repulse water molecules. Here, the authors demonstrate water confinement across hydrophobic microporous channels in crystalline covalent organic frameworks.

Development of porous materials combining stability and high performance has remained a challenge. This is particularly true for proton-transporting materials essential for applications in sensing, catalysis and energy conversion and storage. Here we report the topology guided synthesis of an imine-bonded (C=N) dually stable covalent organic framework to construct dense yet aligned one-dimensional nanochannels, in which the linkers induce hyperconjugation and inductive effects to stabilize the pore structure and the nitrogen sites on pore walls confine and stabilize the H 3 PO 4 network in the channels via hydrogen-bonding interactions. The resulting materials enable proton super flow to enhance rates by 2–8 orders of magnitude compared to other analogues. Temperature profile and molecular dynamics reveal proton hopping at low activation and reorganization energies with greatly enhanced mobility. Development of porous proton-transporting materials combining stability and high performance has remained a challenge. Here, the authors report a stable covalent organic framework with excellent proton conductivity in which nitrogen sites on pore walls confine and stabilize a H3PO4 network in the channels via hydrogen-bonding interactions.

Covalent organic frameworks (COFs) are a class of crystalline porous polymer that allows the atomically precise integration of organic units into extended structures with periodic skeletons and ordered nanopores. One important feature of COFs is that they are designable; that is, the geometry and dimensions of the building blocks can be controlled to direct the topological evolution of structural periodicity. The diversity of building blocks and covalent linkage topology schemes make COFs an emerging materials platform for structural control and functional design. Indeed, COF architectures offer confined molecular spaces for the interplay of photons, excitons, electrons, holes, ions and guest molecules, thereby exhibiting unique properties and functions. In this Review, we summarize the major progress in the field of COFs and recent achievements in developing new design principles and synthetic strategies. We highlight cutting-edge functional designs and identify fundamental issues that need to be addressed in conjunction with future research directions from chemistry, physics and materials perspectives. Covalent organic frameworks are crystalline porous polymers with precisely ordered polygon architectures. In this Review we summarize recent advances in the design principles and synthetic reactions, highlight the current status in structural construction and functionality design, and predict challenging issues and future directions.

Charge transfer and mass transport to catalytic sites are critical factors in photocatalysis. However, achieving both simultaneously is challenging due to inherent trade-offs and interdependencies. Here we develop a microporous covalent organic framework featuring dense donor–acceptor lattices with engineered linkages. The donor–acceptor columnar π -arrays function as charge supply chains and as abundant water oxidation and oxygen reduction centres, while the one-dimensional microporous channels lined with rationally integrated oxygen atoms function as aligned conduits for instant water and oxygen delivery to the catalytic sites. This porous catalyst promotes photosynthesis with water and air to produce H 2 O 2 , combining a high production rate, efficiency and turnover frequency. This framework operates under visible light without the need of metal co-catalysts and sacrificial reagents, exhibits an apparent quantum efficiency of 17.5% at 420 nm in batch reactors and enables continuous, stable and clean H 2 O 2 production in flow reactors. Photocatalytic H 2 O 2 production from water and air is limited by the availability of these substrates and charge carriers at the catalytic sites. Here a donor–acceptor covalent organic framework acts as a supply chain for the delivery of charge, water and oxygen, resulting in 17.5% quantum efficiency under visible light irradiation.

Attempts to develop photocatalysts for hydrogen production from water usually result in low efficiency. Here we report the finding of photocatalysts by integrated interfacial design of stable covalent organic frameworks. We predesigned and constructed different molecular interfaces by fabricating ordered or amorphous π skeletons, installing ligating or non-ligating walls and engineering hydrophobic or hydrophilic pores. This systematic interfacial control over electron transfer, active site immobilisation and water transport enables to identify their distinct roles in the photocatalytic process. The frameworks, combined ordered π skeletons, ligating walls and hydrophilic channels, work under 300–1000 nm with non-noble metal co-catalyst and achieve a hydrogen evolution rate over 11 mmol g –1 h –1 , a quantum yield of 3.6% at 600 nm and a three-order-of-magnitude-increased turnover frequency of 18.8 h –1 compared to those obtained with hydrophobic networks. This integrated interfacial design approach is a step towards designing solar-to-chemical energy conversion systems. Attempts to develop hydrogen evolution photocatalysts usually result in low efficiency. Here the authors report a photocatalyst system by integrated interfacial design of stable covalent organic frameworks for high performance hydrogen evolution.

Covalent organic frameworks (COFs) are a class of important porous materials that allow atomically precise integration of building blocks to achieve pre-designable pore size and geometry; however, pore surface engineering in COFs remains challenging. Here we introduce pore surface engineering to COF chemistry, which allows the controlled functionalization of COF pore walls with organic groups. This functionalization is made possible by the use of azide-appended building blocks for the synthesis of COFs with walls to which a designable content of azide units is anchored. The azide units can then undergo a quantitative click reaction with alkynes to produce pore surfaces with desired groups and preferred densities. The diversity of click reactions performed shows that the protocol is compatible with the development of various specific surfaces in COFs. Therefore, this methodology constitutes a step in the pore surface engineering of COFs to realize pre-designed compositions, components and functions. Covalent organic frameworks form a porous skeleton with a precise pore size and geometry, but control of the pore surface is challenging. Here, a protocol is introduced for pore surface engineering of covalent organic frameworks, allowing the control of composition and density of organic groups in the pores.

Organic batteries free of toxic metal species could lead to a new generation of consumer energy storage devices that are safe and environmentally benign. However, the conventional organic electrodes remain problematic because of their structural instability, slow ion-diffusion dynamics and poor electrical conductivity. Here, we report on the development of a redox-active, crystalline, mesoporous covalent organic framework (COF) on carbon nanotubes for use as electrodes; the electrode stability is enhanced by the covalent network, the ion transport is facilitated by the open meso-channels and the electron conductivity is boosted by the carbon nanotube wires. These effects work synergistically for the storage of energy and provide lithium-ion batteries with high efficiency, robust cycle stability and high rate capability. Our results suggest that redox-active COFs on conducting carbons could serve as a unique platform for energy storage and may facilitate the design of new organic electrodes for high-performance and environmentally benign battery devices.

Covalent organic frameworks are a class of crystalline porous polymers that integrate molecular building blocks into periodic structures and are usually synthesized using two-component [1+1] condensation systems comprised of one knot and one linker. Here we report a general strategy based on multiple-component [1+2] and [1+3] condensation systems that enable the use of one knot and two or three linker units for the synthesis of hexagonal and tetragonal multiple-component covalent organic frameworks. Unlike two-component systems, multiple-component covalent organic frameworks feature asymmetric tiling of organic units into anisotropic skeletons and unusually shaped pores. This strategy not only expands the structural complexity of skeletons and pores but also greatly enhances their structural diversity. This synthetic platform is also widely applicable to multiple-component electron donor–acceptor systems, which lead to electronic properties that are not simply linear summations of those of the conventional [1+1] counterparts. Covalent organic frameworks are crystalline porous polymers integrating molecular building blocks into periodic structures. Here, the authors report a general multiple-component condensation strategy that enables the use of one knot and two or three linkers to synthesize complex, anisotropic frameworks.