Fluorescence Visualization of Strain by Tetraphenylethylene/Ruthenium Complex Three-Dimensional Covalent Organic Framework Assemblies

Dynamic visualization of strain and its distribution in materials are still challenging. Herein, dual-fluorophore three-dimensional covalent organic frameworks (3D-COFs) and the PEGylated 3D-COFs (PEG-3D-COFs) were synthesized for the construction of physically interacted assemblies to realize fluorescence imaging on not only strain distribution but also strain-related surface friction and flow velocity distributions in various media including polymer elastomers, organic or aqueous dispersions. The responsiveness arises from the controllability of the aggregation structure of 3D-COFs and PEG-3D-COFs, showing concentration-dependent morphology and photoluminescence, and meanwhile having a concentration-deformation equivalence on the structural evolution dynamics which drives the color change of the COF emission in the solids and liquids with high sensitivity and reversibility, whenever the superstructure of the COF assemblies is affected by the applied strain on the matrices. The report will inspire further efforts to construct responsive COFs for optical measurement aims.

Unraveling the Surface Chemistry of Aluminum Oxo Archimedean Cages for Efficient Serial Adsorption

Multifunctional materials that meet diverse application needs hold profound significance in resource optimization, efficiency enhancement, and environmental sustainability. However, the development of these materials faces numerous challenges, including raw material acquisition, design feasibility, and long-term stability. This study demonstrates the innovative application of the surface chemistry of aluminum oxo Archimedean cages in efficient serial adsorption. The "Four-in-One" surface chemistry enables various single-crystal-to-single-crystal (SC-SC) structural transformations, involving ligand modification, cation exchange, post-synthetic metalation, and metal elimination, successfully achieving the first reversible SC-SC transformation from cluster structures to infinite frameworks. The fundamental reason behind these dynamic structural changes lies in the exceptional balance between rigidity and flexibility provided by the intercluster tri-pyrazole sites on the Archimedean cages. This diverse structural transformation characteristic offers extensive application potential for solid-liquid and solid-gas serial adsorption. For instance, this material effectively adsorbs heavy metal ions in water treatment and can subsequently be used for the permanent fixation of gaseous radionuclides. This work not only deepens our understanding of dynamic chemistry but also provides guiding significance for environmental remediation.

Discovery of an Interlocked and Interwoven Molecular Topology in Nanocarbons via Dynamic C-C Bond Formation

Topologically complex carbon nanostructures are an exciting but largely unexplored class of materials due to their challenging synthesis. Previous methods are low yielding because they rely on irreversible Csp2-Csp2 bond formation, which necessitates complex templating strategies to enforce entanglement. Here, reversible zirconocene coupling of alkynes is developed as a new method to access complex molecular topologies, where dynamic C-C bond formation facilitates entanglement under thermodynamic control, allowing the use of simple precursors without the need for preassembly. This strategy enables the scalable, high-yield synthesis of three topologically distinct nanocarbons, including the serendipitous discovery of a structure containing a new topological motif that was not previously identified or realized synthetically. This motif, consisting of an unusual combination of interlocking and interweaving, was recognized to be generalizable to a new topological class of molecules, introduced here as perplexanes.

Designing High-Mechanical-Property Organic Polymeric Crystals: Insights from Stress Dispersion and Energy Dissipation Strategies

Despite recent significant advancements in the applications of organic polymeric crystals (OPCs), a comprehensive understanding of the design principles for high-mechanical-property crystals remains somewhat elusive. Here, we investigate the mechanical properties of OPCs from the perspectives of stress dispersion and energy dissipation by examining crystals of a macrocycle and three analogous polymers with different solvent fillings, utilizing a novel research platform constructed via dative B-N bonds. Through a thorough mechanical study and investigation into the molecular mechanisms of these model topologies, it was demonstrated that structural expansion and solvent filling are effective pathways for enhancing the mechanical performance of the OPCs by employing stress dispersion and energy dissipation strategies. Overall, our research showcases precise control over the molecular topology of the OPC materials and elucidates specific pathways for stress dispersion and energy dissipation in modulating their mechanical performance, offering a broader design perspective for efficiently enhancing the mechanical properties of other crystalline polymers, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs).

Semiconducting Covalent Organic Frameworks

Semiconductors form the foundational bedrock of modern electronics and numerous cutting-edge technologies. Particularly, semiconductors crafted from organic building blocks hold immense promise as next-generation pioneers, thanks to their vast array of chemical structures, customizable frontier orbital energy levels and bandgap structures, and easily adjustable π electronic properties. Over the past 50 years, advancements in chemistry and materials science have facilitated extensive investigations into small organic π compounds, oligomers, and polymers, resulting in a rich library of organic semiconductors. However, a longstanding challenge persists: how to organize π building units or chains into well-defined π structures, which are crucial for the performance of organic semiconductors. Consequently, the pursuit of methodologies capable of synthesizing and/or fabricating organic semiconductors with ordered structures has emerged as a frontier in organic and polymeric semiconductor research. In this context, covalent organic frameworks (COFs) stand out as unique platforms allowing for the covalent integration of organic π units into periodically ordered π structures, thus facilitating the development of semiconductors with extended yet precisely defined π architectures. Since their initial report in 2008, significant strides have been made in exploring various chemistries to develop semiconducting COFs, resulting in a rich library of structures, properties, functions, and applications. This review provides a comprehensive yet focused exploration of the general structural features of semiconducting COFs, outlining the basic principles of structural design, illustrating the linkage chemistry and synthetic strategies based on typical one-pot polymerization reactions to demonstrate the growth of bulk materials, nanosheets, films, and membranes. By elucidating the interactions between COFs and various entities such as photons, phonons, electrons, holes, ions, molecules, and spins, this review categorizes semiconducting COFs into nine distinct sections: semiconductors, photoconductors, light emitters, sensors, photocatalysts, photothermal conversion materials, electrocatalysts, energy storage electrodes, and radical spin materials, focusing on disclosing structure-originated properties and functions. Furthermore, this review scrutinizes structure-function correlations and highlights the unique features, breakthroughs, and challenges associated with semiconducting COFs. Furnished with foundational knowledges and state-of-the-art insights, this review predicts the fundamental issues to be addressed and outlines future directions for semiconducting COFs, offering a comprehensive overview of this rapidly evolving and remarkable field.

Restructuring of mortise-and-tenon frameworks at the molecular level

Restructuring of mortise-and-tenon frameworks at the molecular level has never been achieved. We report the first example of restructuring in molecular mortise-and-tenon joints (MTF-4 and MTF-5). The obtained cross-locking mortise-and-tenon framework of MTF-5 exhibits higher stability, better mechanical stiffness, and superior optical limiting (OL) performance.

Interweaving Covalent Organic Polymer Chains Into Two-Dimensional Networks: Synthesis, Single Crystal Structure, and Application for Stabilizing Lithium Metal Anode

Macroscopic weaving has been proven to be the most enduring and effective method for manufacturing fabrics to meet the practical needs of humanity for thousands of years. However, the construction of molecular structures with exquisite topologies and specific properties based on molecular weaving is still in its infancy. Herein, we designed and fabricated a two-dimensional (2D) woven covalent organic polymer (COP) network (named as CityU-46) driven by the dative N→B bonds between the 1,4-bis(benzodioxa-borole)benzene (BACT) and 2,5-bis(4-pyridyl)-1,3,4-thiadiazole (BPT). The complex woven topology of CityU-46 was determined using a single-crystal X-ray diffraction technique, revealing that it features a well-defined two-over and two-under interweaving pattern at the molecular level. Due to its structural merits, CityU-46 can be used as an artificial organic solid-electrolyte interphase layer on the surface of Li metal anodes, significantly improving the stability and long-term performance of lithium metal cells.

Meta-Phenylenediamine-Derived Silver-Containing Nanoporous Hyper-Cross-Linked Polymer: An Innovative Fluorescence Probe for S2O32- ion Detection in Aqueous Media

The meta-phenylenediamine polymer, when hyper-cross-linked, exhibits a minimal fluorescence intensity. However, the introduction of silver ions induces a significant increase in intensity, attributed to the plasmonic effect. This heightened intensity is selectively increased more upon the addition of thiosulfate ions. Capitalizing on this property, a fluorescence probe was developed. The correlation between fluorescence intensity reduction and S2O32- concentration follows a linear and consistent pattern. The precursor's response to diverse anions such as SO42-, CO32-, HPO42-, Cr2O72-, F-, Cl-, Br-, I-, H2PO4-, CH3COO-, NO3-, ClO-, and HCO3- was also examined. Under optimal conditions, the probe exhibited a linear range of 0.5-3 µM with a detection limit of 0.01 µM. Its effectiveness was demonstrated in measuring thiosulfate concentrations in aqueous media.

Recent Progress of Covalent Organic Frameworks-Based Materials Used for CO2 Electrocatalytic Reduction: A Review

The excessive CO2 emissions from human activities severely impact the natural environment and ecosystems. Among the various technologies available, electrocatalytic CO2 reduction is regarded as one of the most promising routes due to its exceptional environmental friendliness and sustainability. Covalent organic frameworks (COFs) are crystalline, porous organic networks that are formed through thermodynamically controlled reversible covalent polymerization of organic linkers via covalent bonding. These materials exhibit high porosity, large surface area, excellent chemical and thermal stability, sustainability, high electron transfer efficiency, and surface functionalization capabilities, making them particularly effective in electrocatalytic CO2 reduction. First, this review briefly introduces the fundamental principles of electrocatalysis and the mechanism of electrocatalytic CO2 reduction. Next, it discusses the composition, structure, and synthesis methods of COF-based materials, as well as their applications in electrocatalytic CO2 reduction. Furthermore, it reviews the research progress in this field from the perspective of different types of COF-based catalysts. Finally, in light of the current research status, the development prospects of COF-based catalysts are explored, providing a reference for the development of more efficient and stable COF electrocatalysts for CO2 reduction.

Harnessing Mechanochemistry for Direct Synthesis of Imine-Based Metal-Organic Frameworks

The growth of metal-organic frameworks (MOFs) is most frequently accessed by the direct assembly of metal cations and multitopic ready-to-connect ligands under solvothermal conditions. However, such nonambient conditions are expected to impose a synthetic challenge to incorporate degradable ligands into MOFs. This explains why imine-based MOFs are scarce as the imine motif is usually prone to decompose through hydrolysis. This work not only showcases mechanochemistry as an ambient, sustainable, and high-yield strategy for synthesizing a variety of imine-based MOFs but also achieves the integration of ligand synthesis and MOF growth into a single tandem step. Thus, this work provides straightforward access to imine-based MOFs, a subfamily of historically challenging MOF materials.

Donor-Acceptor-π-Acceptor-Donor-Type Photosensitive Covalent Organic Framework for Effective Photocatalytic Aerobic Oxidation

Developing effective photocatalysts for the oxidation reaction is of great significance in chemical synthesis but is still challenging. Herein, linking photochromic triphenylamine with pyrene units by the in situ formed robust imidazole moieties, a covalent organic framework (COF), PyNTB-COF, containing a rare donor-acceptor-π-acceptor-donor (D-A-π-A-D) fragment, was successfully synthesized for photocatalytic aerobic oxidation. Structure characterizations confirm its crystalline framework, high porosity, and good stability. Property studies reveal its photoelectric semiconductor feature with high photoresponsive charge separation and migration activity derived from the D-A-π-A-D fragments, proven by the experimental results and theoretical calculations. Photocatalytic experiments not only display its highly effective photoresponsive activity in triggering the generation of ·O2- under visible light irradiation but also exhibit its high photocatalytic efficiency in the aerobic oxidations of toluene and the amidation of aldehydes. This work demonstrates that the integration of photochromic units into framework materials to construct π-conjugated D-A moieties could enhance photocatalytic charge separation and migration efficiency, achieving promising photocatalysts for photocatalytic aerobic oxidation.

Unravelling the Atomic Structure of a Metal-Covalent Organic Framework Assembled from Ruthenium Metalloligands

Covalent and metal-organic frameworks (COFs and MOFs) have shown great promise in light-driven processes mainly due to their ligand-to-metal charge-separation properties, as well as having access to a diverse range of photoactive metalloligands and organic linkers. However, both frameworks present individual drawbacks that can potentially be avoided by combining both systems (metal and covalent) to produce metal-covalent organic frameworks (MCOFs), exhibiting the advantages of both material types. Yet, due to their poor crystallinity, the understanding of the structure-properties relation of MCOFs remains unclear. Herein, we report photoactive linkers in the form of a [Ru(tpy)2]2+ (tpy: 2,2',6,2″-terpyridine) complex which covalently binds to a luminescent pyrene core to yield a new, photoactive Schiff-base MCOF. The structure, thermal, electronic, and optical properties of this novel material have been exhaustively characterized by a wide range of microscopy, spectroscopic, and computational methods. This combined experimental and computational work represents a significant step toward the fundamental understanding of the photoactive units within the framework, their hierarchical arrangement and interactions with substrates, which is essential for the future design of efficient photocatalytic materials.

Synthesis of three-dimensional covalent organic frameworks through a symmetry reduction strategy

Three-dimensional (3D) covalent organic frameworks (COFs) hold significant promise for a variety of applications. However, conventional design approaches using regular building blocks limit the structural diversity of 3D COFs. Here we design and synthesize two 3D COFs, designated as JUC-644 and JUC-645, through a methodology that relies on using eight-connected building blocks with reduced symmetry. Their structures are solved using continuous rotation electron diffraction and high-resolution transmission electron microscopy, which reveal a unique linkage with a double chain structure, a rare phenomenon in COFs. We deconstruct these structures into [4 + 3(+ 2)]-c nets, which leads to six different topologies. Furthermore, JUC-644 demonstrates high adsorption capacity for C3H8 and n-C4H10 (11.28 and 10.45 mmol g-1 at 298 K and 1 bar, respectively), surpassing most known porous materials, with notable selectivity for C3H8/C2H6 and n-C4H10/C2H6. This approach opens avenues for designing intricate architectures and shows the potential of COFs in C2H6 recovery from natural gas liquids.

Molecularly Woven Polymer Aerogels

Aerogels with abundant nanopores and large specific surface areas have extensive potential in various applications but are constrained by fragility and difficulty in degradation. Currently, the exploration of adaptive and reprocessing aerogels has become increasingly urgent, as the demand for intelligent and sustainable materials intensifies. Here, we present a molecular weaving strategy to construct molecularly woven polymer aerogels (WPAs) via catalyst-free aldimine condensation between prewoven aldehyde-functionalized Cu(I) bisphenanthroline (Cu(PBD)2) and flexible 4,4'-diaminodibenzyl (DB). The key feature of this system consists entirely of dense woven nodes that can be readily activated by external stimuli, where Cu(I) ions can also be reversibly removed as needed, while preserving porous structures. Consequently, we achieve adjustable mechanical properties of WPAs, with a 10-fold enhancement in elasticity after removing Cu(I) ions. Moreover, the destroyed WPAs demonstrate a straightforward reprocessing capacity rather than tedious monomer recovery due to the dissociation of Cu(I)-coordination bonds, the activation of sequential polymer thread motions, and the accelerated imine bond exchange enabled by adjacent Cu(I) ions. This work offers a new perspective on designing customizable and sustainable aerogels and verifies the feasibility of the emergent molecularly woven technique in a more complex functional material system.

Controllable Polymerization of Inorganic Ionic Oligomers for Precise Nanostructural Construction in Materials

The rational design of nanostructures is critical for achieving high-performance materials. The close-packing behavior of inorganic ions and their less controllable nucleation process impede the precise nanostructural construction of inorganic ionic compounds. The discovery of inorganic ionic oligomers (stable molecular-scale inorganic ionic compounds) and their polymerization reaction enables the controllable arrangement of inorganic ions for diverse nanostructures. This perspective aims to introduce inorganic ionic oligomers and their currently identified advantages in the precise design of inorganic and organic-inorganic hybrid nanostructures, directing the development of advanced materials with applications across the mechanical, energy, environmental, and biomedical fields. The challenges and opportunities for the controllable polymerization of inorganic ionic oligomers are presented at the end of this perspective. We suggest that inorganic ionic oligomers and their polymerization reaction offer a promising strategy for the preparation of inorganic and organic-inorganic hybrid materials.

From Fundamentals to Synthesis: Covalent Organic Frameworks as Promising Materials for CO2 Adsorption

Covalent organic frameworks (COFs) are highly crystalline polymers that possess exceptional porosity and surface area, making them a subject of significant research interest. COF materials are synthesized by chemically linking organic molecules in a repetitive arrangement, creating a highly effective porous crystalline structure that adsorbs and retains gases. They are highly effective in removing impurities, such as CO2, because of their desirable characteristics, such as durability, high reactivity, stable porosity, and increased surface area. This study offers a background overview, encompassing a concise discussion of the current issue of excessive carbon emissions, and a synopsis of the materials most frequently used for CO2 collection. This review provides a detailed overview of COF materials, particularly emphasizing their synthesis methods and applications in carbon capture. It presents the latest research findings on COFs synthesized using various covalent bond formation techniques. Moreover, it discusses emerging trends and future prospects in this particular field.

Urea/Thiourea Imine Linkages Provide Accessible Holes in Flexible Covalent Organic Frameworks and Dominates Self-Adaptivity and Exciton Dissociation

Unraveling the robust self-adaptivity and minimal energy-dissipation of soft reticular materials for environmental catalysis presents a compelling yet unexplored avenue. Herein, a top-down strategy, tailoring from the unique linkage basis, flexibility degree, skeleton electronics to trace-guest adaptability, is proposed to fill the understanding gap between micro-soft covalent organic frameworks (COFs) and photocatalytic performance. The thio(urea)-basis-dominated linkage within benzotrithiophene-based COFs induce the framework contraction/swelling (intralayer micro-flexibility) in response to tetrahydrofuran or water. Adaptability of micro-flexible thiourea-COF with pore hydrophilicity not only contributes to the favorable mass transfer, but also enhances the accessible redox active sites, culminating in nearly 100 % removal of micropollutant with low-energy dissipation in wastewater. The incorporating urea/thiourea into imine linkage facilitates polarization reduction and exciton dissociation within skeleton wall, inducing strong localization for holes. This transformation facilitates interchain charge transport and unbalanced distribution conducive to oxidative holes-mediated micropollutant decomposition.

Supramolecular Chemistry in Metal-Organic Framework Materials

Far from being simply rigid, benign architectures, metal-organic frameworks (MOFs) exhibit diverse interactions with their interior environment. From developing crystal sponges to studying reactions in framework materials, the role of both supramolecular chemistry and framework structure is evident. We explore the role of supramolecular chemistry in determining framework…guest interactions and attempts to understand the dynamic behavior in MOFs, including attempts to control pore behavior through the incorporation of mechanically-interlocked molecules. Appreciating and understanding the role of supramolecular interactions and dynamic behavior in metal-organic frameworks emerge as important directions for the field.

Molecular Weaving Towards Flexible Covalent Organic Framework Membranes for Efficient Gas Separations

Covalent organic frameworks (COFs) exhibit considerable potential in gas separations owing to their remarkable stability and tunable pore structures. Nevertheless, their application as gas separation membranes is hindered by limited size-sieving capabilities and poor processability. In this study, we propose a novel molecular weaving strategy that combines hydroxyl polymers and 2D TpPa-SO3H COF nanosheets, achieving high gas separation efficiency. Driven by the strong electrostatic interactions, the hydroxyl chains thread through the COF pores, effectively weaving and assembling the composites to achieve exceptional flexibility and high mechanical strength. The penetrated chains also reduce the effective pore size of COFs, and combined with the "secondary confinement effect" stemming from abundant CO2 sorption sites in the channels, the PVA@TpPa-SO3H membrane demonstrates a remarkable H2 permeance of 1267.3 GPU and an H2/CO2 selectivity of 43, surpassing the 2008 Robson upper bound limit. This facile strategy holds promise for the manufacture of large-area COF-based membranes for small-sized gas separations.

Computational measures of irregularity molecular descriptors of octahedral and icosahedral networks

Irregularity measures tend to describe the complexity of networks. Chemical graph theory is a branch of mathematical chemistry that has a significant impact on the development of the chemical sciences. The study of irregularity indices has recently become one of the most active research areas in chemical graph theory. Irregularity indices help us to examine many chemical and biological properties of chemical structures under study. In this article, we study the irregularity indices of the octahedral and icosahedral networks. These networks are used in crystallography, where the topology and structural aspects are carrying some important facts to determine the properties of large structures theoretically. Our results play an important role in pharmacy, drug design, and many other applied areas. We also compared our results graphically to conclude the irregularity with a change in the parameter of structures.

Determining Covalent Organic Framework Structures Using Electron Crystallography and Computational Intelligence

The structural characterization of new materials often poses immense challenges, especially when obtaining single-crystal structures is difficult, which is a common difficulty with covalent organic frameworks (COFs). Despite this, understanding the atomic structure is crucial as it provides insights into the arrangement and connectivity of organic building blocks, offering the opportunity to establish the correlation of structure-function relationships and unravel material properties. In this study, we present an approach for determining the structures of COFs, an integration of electron crystallography and computational intelligence (COF+). By applying established chemistry knowledge and employing particle swarm optimization (PSO) for trial structure generation, we overcome existing limitations, thus paving the way for advancements in COF structural determination. We have successfully implemented this technique on four representative COFs, each with unique characteristics. These examples underline the accuracy and efficacy of our approach in addressing the challenges tied to COF structural determination. Furthermore, our approach has revealed new structure candidates with different topologies or interpenetrations that are chemically feasible. This discovery demonstrates the capability of our algorithm in constructing trial COF structures without being influenced by topological factors. Our new approach to COF structure determination represents a significant advancement in the field and opens new avenues for exploring the properties and applications of COF materials.

Hydrogen-Bond-Regulated Mechanochemical Synthesis of Covalent Organic Frameworks: Cocrystal Precursor Strategy for Confined Assembly

Two-dimensional imine covalent organic frameworks (2D imine-COFs) are crystalline porous materials with broad application prospects. Despite the efforts into their design and synthesis, the mechanisms of their formation are still not fully understood. Herein, a one-pot two-step mechanochemical cocrystal precursor synthetic strategy is developed for efficient construction of 2D imine-COFs. The mechanistic investigation demonstrated that the cocrystal precursors of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (TAPT) and p-toluenesulphonic acid (PTSA) sufficiently regulate the crystalline structure of COF. Evidenced by characterizations and theoretical studies, a helical hydrogen-bond network was constructed by the N-H⋅⋅⋅O supramolecular synthons between amino and sulfonic groups in TAPT-PTSA, demonstrating the role of cocrystals in promoting the organized stacking of interlayer π-π interactions, layer arrangement, and interlayer spacing, thus facilitating the orderly assembly of COFs. Moreover, the protonation degree of TAPT amines, which tuned nucleophilic directionality, enabled the sequential progression of intra- and interlayer imine condensation reactions, inhibiting the formation of amorphous polymers. The transformation from cocrystal precursors to COFs was achieved through comprehensive control of hydrogen bond and covalent bond sites. This work significantly advances the concept of hydrogen-bond-regulated COF assembly and its mechanochemical method in the design and synthesis of 2D imine-COFs, further elucidating the mechanistic aspects of their mechanochemical synthesis.

Preserving High Porosity of Covalent Organic Frameworks via Functional Polymer Guest Introduction

Due to their high structural tunability, remarkable internal surface areas, readily accessible pore space, and host of possible applications, covalent organic frameworks (COFs) remain at the forefront of materials science research. Unfortunately, many COFs suffer from structural distortions or pore collapse during activation, which can lead to a substantial loss of crystallinity and functionality. Thus, herein, we demonstrate a facile method to address this issue by introducing polymer guests. The polymer adheres to the COF internal pore wall, acting as a supporting pillar during activation and effectively preserving the COF porosity and crystallinity. In fact, the surface area of one COF/polymer composite, known as TAPB-TA/PDA, was boosted by a factor of 16 when compared to the parent COF, TAPB-TA. More importantly, the now robust COF structure was able to resist layer shifting and order loss during both solvent immersion and removal. The introduction of functional polymer guests not only solidifies the COF structure and preserves its high porosity but is also shown to enhance the transport and separation of photogenerated charge carriers, thereby facilitating hydrogen evolution during photocatalytic water splitting. Molecular dynamics simulations further support experimental observations that the incorporation of PDA within the COF pores reinforces the walls, preventing its collapse. The proposed mechanism is based on the adsorption of PDA oligomers along the c direction of the unit cell, fastening the COF layers in place via van der Waals interactions. This kind of interaction locks -N═CH-Ph-CH═N- units in a trans-configuration in the COF pores.

3D Interlocking Metallo-COFs as a Visible Light Responsive Photocatalyst

Woven covalent organic frameworks (COFs) offer immense potential as photoactive materials because Cu(I) complexes are periodically integrated into the COF structure via a single synthetic step. A photoactive interlocking (woven) COF featuring Cu(I) photosensitizers that are spatially isolated and periodically arranged in three dimensions has been successfully synthesized and characterized. The optoelectronic properties of this COF, such as light absorption and photocatalytic performance toward the degradation of sulfamethoxazole (SMX) under visible light, are investigated. The reusability and stability of this COF are compared with the Cu(PDB)2BF4 complex which displayed rapid deactivation and is not reusable. Conversely, The metallo-COF is stable over several catalytic cycles, highlighting a distinct advantage of the stabilizing effects of the COF over discrete molecules.

Toward Molecular Textiles: Synthesis and Characterization of Molecular Patches

This works describes a new step into the assembly of molecular textiles by the use of covalent templating. To establish a well-founded base and to tackle pre-mature obstacles, expected during the fabrication of the desired 2D-material, we opted to investigate the in-solution synthesis of molecular patches e. g. cut-outs of a textile. A bi-functional cross-shaped monomer was designed, synthesized and was in-detail characterized by means of 1H-NMR and chiro-optical spectroscopy. In addition, x-ray structure crystallography was used to assess the absolute configuration. The monomer was used in an in-solution oligomerization to assemble the molecular patches via imine condensation, which revealed the formation of predominately dimeric patches. The imine-oligomer mixtures were further analyzed by reduction and cleaved to investigate the conditions required post mono-layer assembly. All reaction stages were followed by FT-IR and 1H-NMR analysis. Finally, we address the adsorption of the cross-shaped monomer onto a Au(111) surface, via high vacuum electrospray deposition. The subsequent annealing of the interface induced the on-surface imine condensation reaction, leading to unidimensional oligomers co-adsorbed with clusters of cyclic-dimers. Nc-AFM analysis revealed the tridimensional molecular structures, and together with electrospray deposition technique showed to be a promising pathway to investigate potential monomer candidates.

Photons, Excitons, and Electrons in Covalent Organic Frameworks

Covalent organic frameworks (COFs) are created by the condensation of molecular building blocks and nodes to form two-dimensional (2D) or three-dimensional (3D) crystalline frameworks. The diversity of molecular building blocks with different properties and functionalities and the large number of possible framework topologies open a vast space of possible well-defined porous architectures. Besides more classical applications of porous materials such as molecular absorption, separation, and catalytic conversions, interest in the optoelectronic properties of COFs has recently increased considerably. The electronic properties of both the molecular building blocks and their linkage chemistry can be controlled to tune photon absorption and emission, to create excitons and charge carriers, and to use these charge carriers in different applications such as photocatalysis, luminescence, chemical sensing, and photovoltaics. In this Perspective, we will discuss the relationship between the structural features of COFs and their optoelectronic properties, starting with the building blocks and their chemical connectivity, layer stacking in 2D COFs, control over defects and morphology including thin film synthesis, exploring the theoretical modeling of structural, electronic, and dynamic features of COFs, and discussing recent intriguing applications with a focus on photocatalysis and photoelectrochemistry. We conclude with some remarks about present challenges and future prospects of this powerful architectural paradigm.

Vertically Expanded Crystalline Porous Covalent Organic Frameworks

Covalent organic frameworks (COFs) can be developed for molecular confinement and separation. However, their proximate π stacks limit the interlayer distance to be only 3-6 Å, which is too small for guests to enter. As a result, COFs block access to the x-y space and limit guest entry/exit strictly to only the pores along the z direction. Therefore, the extended faces of each layer are hidden between layers, precluding any interactions with guest molecules. Here, we report a strategy for opening interlayer spaces of COFs to attain newly accessible nanospaces between layers. This becomes possible using coordination bonds to replace the conventional π-π stacks between layers. We demonstrate this concept by synthesizing two-dimensional covalent cobalt(II) porphyrin layers through topology-guided polymerization, which were piled up by bidentate axial pillars through coordination bonds with cobalt(II) porphyrin along the z direction, assembling vertically expanded COFs via a one-pot reaction. The resultant frameworks separate the layers with axial pillars and create discrete apertures between layers defined by the molecular length of the pillars. Consequently, the originally inaccessible interlayers are open for guest access, while the polygonal π planes are exposed to trigger various supramolecular interactions. Vapor sorption, breakthrough experiments, and computational studies mutually revealed that the vertically expanded frameworks with optimal interlayer slits induce additional interactions to discriminate benzene and cyclohexane and separate their mixtures efficiently under ambient conditions.

A comprehensive review of covalent organic frameworks (COFs) and their derivatives in environmental pollution control

Covalent organic frameworks (COFs) have gained considerable attention due to their design possibilities as the molecular organic building blocks that can stack in an atomically precise spatial arrangement. Since the inception of COFs in 2005, there has been a continuous expansion in the product range of COFs and their derivatives. This expansion has led to the evolution of three-dimensional structures and various synthetic routes, propelling the field towards large-scale preparation of COFs and their derivatives. This review will offer a holistic analysis and comparison of the spatial structure and synthesis techniques of COFs and their derivatives. The conventional methods of COF synthesis (i.e., ultrasonic chemical, microwave, and solvothermal) are discussed alongside the synthesis strategies of new COFs and their derivatives. Furthermore, the applications of COFs and their derived materials are demonstrated in air, water, and soil pollution management such as gas capture, catalytic conversion, adsorption, and pollutant removal. Finally, this review highlights the current challenges and prospects for large-scale preparation and application of new COFs and the derived materials. In line with the United Nations Sustainable Development Goals (SDGs) and the needs of digital-enabled technologies (AI and machine learning), this review will encompass the future technical trends for COFs in environmental pollution control.

Gas Adsorption in Flexible COF-506 and COF-506-Cu

Flexible covalent-organic frameworks (COFs) display a variety of guest-dependent dynamic behaviors, but because these are an emerging class of materials, very little experimental adsorption data exists. This work examines the adsorption properties of COF-506 and COF-506-Cu utilizing various adsorbates as probe molecules. These materials have small surface areas (<100 m2/g) but still have significant capacity for methanol and isopropanol compared to activated carbon, even though the COF contains approximately 1/10th the surface area of many activated carbons. Isotherms for ethane/ethylene collected up to 1 bar show moderate selectivity for ethylene, but interestingly, this selectivity is reversed when the isotherms are measured up to 5 bar. The change in selectivity occurs because the ethane isotherm has a distinct stepwise increase in capacity near 4 bar. The adsorption data indicate broad generalizations and analogies of COFs to activated carbon should be avoided; that the adsorption capacity COFs may not correlate to surface area; and that high-pressure adsorption isotherms may have steps in the adsorption isotherm where capacity increases significantly.

Interwoven Trimeric Cage-Catenanes with Topological Chirality

Catenanes have gained increasing attention for their unique features such as topological chirality. To date, the majority of works have focused on catenanes comprising monocyclic rings. Due to the lack of efficient synthetic strategy, catenanes of multiannulated monomers remain scarce. Here, we report the one-pot synthesis of an interwoven trimeric cage-catenane in high yield by dynamic imine condensation between diamine linkers of suitable length and trialdehyde panels in stoichiometry. The formation of cage-catenane is driven by the efficient 6-fold π-π stacking of panels. The monomeric cage and trimeric cage-catenane are interconvertible with reversible imine chemistry, with the latter thermodynamically being more favored. Using a topology-based statistical model, we first reveal that the formation probability of the interwoven catenane surpasses that of its chain-like isomer by 20%. When this pure mathematical model is refined by taking into account the strong template effect provided by the π-π stacking of aromatic panels, it shows that the interwoven structure emerges as the dominant species, almost ruling out the formation of the latter. Although composed of achiral cage monomers, the topological chirality of the interwoven trimeric catenane is unraveled by chiral-high-performance liquid chromatography (HPLC) and circular dichroism (CD) spectroscopy, and single-crystal X-ray diffraction (XRD) analysis of the interwoven cage-catenane also reveals a pair of two topological enantiomers. Our probability analysis-aided rationale would provide a design rationale for guiding the efficient synthesis of topologically sophisticated structures.

Molecularly Woven Cationic Covalent Organic Frameworks for Highly Selective Electrocatalytic Conversion of CO2 to CO

Coupling carbon capture with electrocatalytic carbon dioxide reduction (CO2R) to yield high-value chemicals presents an appealing avenue for combating climate change, yet achieving highly selective electrocatalysts remains a significant challenge. Herein, two molecularly woven covalent organic frameworks (COFs) are designed, namely CuCOF and CuCOF+, with copper(I)-bisphenanthroline complexes as building blocks. The metal-organic helical structure unit made the CuCOF and CuCOF+ present woven patterns, and their ordered pore structures and cationic properties enhanced their CO2 adsorption and good conductivity, which is confirmed by gas adsorption and electrochemical analysis. In the electrocatalytic CO2R measurements, CuCOF+ decorated with extra ethyl groups exhibit a main CO product with selectivity of 57.81%, outperforming the CuCOF with 42.92% CO at the same applied potential of 0.8 VRHE. After loading Pd nanoparticles, CuCOF-Pd and CuCOF+-Pd performed increased CO selectivity up to 84.97% and 95.45%, respectively. Combining the DFT theoretical calculations and experimental measurements, it is assumed that the molecularly woven cationic COF provides a catalytic microenvironment for CO2R and ensures efficient charge transfer from the electrode to the catalytic center, thereby achieving high electrocatalytic activity and selectivity. The present work significantly advances the practice of cationic COFs in real-time CO2 capture and highly selective conversion to value-added chemicals.

Single crystals of purely organic free-standing two-dimensional woven polymer networks

The aesthetic and practicality of macroscopic fabrics continue to encourage chemists to weave molecules into interlaced patterns with the aim of providing emergent physical and chemical properties when compared with their starting materials. Weaving purely organic molecular threads into flawless two-dimensional patterns remains a formidable challenge, even though its feasibility has been proposed on several occasions. Herein we describe the synthesis of a flawless, purely organic, free-standing two-dimensional woven polymer network driven by dative B-N bonds. Single crystals of this woven polymer network were obtained and its well-defined woven topology was revealed by X-ray diffraction analysis. Free-standing two-dimensional monolayer nanosheets of the woven polymer network were exfoliated from the layered crystals using Scotch Magic Tape. The surface features of the nanosheets were investigated by integrated low-dose and cryogenic electron microscopy imaging techniques. These findings demonstrate the precise construction of purely organic woven polymer networks and highlight the unique opportunities for the application of woven topologies in two-dimensional organic materials.

Dynamic Two-Dimensional Covalent Organic Frameworks with Large Solvent-Induced Lattice Expansion

Dynamic covalent organic frameworks (COFs) can switch reversibly between crystalline phases with different unit cell parameters and porosities upon physisorption of guest molecules. While impressive changes in unit cell volumes have been realized for three-dimensional frameworks, the solvent-induced volume changes of two-dimensional (2D) COFs have remained comparably small. We have now developed a series of 2D COFs where we systematically varied the length of the interconnecting bridge units. The optimized materials achieve solvent-induced expansions of up to 85% relative to the volume of the solvent-free contracted COFs. These structural changes are fully reversible and the frameworks fully retain their high degree of crystalline order. This study introduces a versatile design strategy for dynamic 2D COFs, which could enable future applications of these materials in gas separation and sensing.

Ionic Covalent Organic Frameworks Consisting of Tetraborate Nodes and Flexible Linkers

Covalent organic frameworks (COFs) have emerged as versatile materials with many applications, such as carbon capture, molecular separation, catalysis, and energy storage. Traditionally, flexible building blocks have been avoided due to their potential to disrupt ordered structures. Recent studies have demonstrated the intriguing properties and enhanced structural diversity achievable with flexible components by judicious selection of building blocks. This study presents a novel series of ionic COFs (ICOFs) consisting of tetraborate nodes and flexible linkers. These ICOFs use borohydrides to irreversibly deprotonate the alcohol monomers to achieve a high degree of polymerization. Structural analysis confirms the dia topologies. Reticulation is explored using various monomers and metal counterions. Also, these frameworks exhibit excellent stability in alcohols and coordinating solvents. The materials have been tested as single-ion conductive solid-state electrolytes. ICOF-203-Li displays one of the lowest activation energies reported for ion conduction. This tetraborate chemistry is anticipated to facilitate further structural diversity and functionality in crystalline polymers.

Super-Durable, Tough Shape-Memory Polymeric Materials Woven from Interlocking Rigid-Flexible Chains

Developing advanced engineering polymers that combine high strength and toughness represents not only a necessary path to excellence but also a major technical challenge. Here for the first time a rigid-flexible interlocking polymer (RFIP) is reported featuring remarkable mechanical properties, consisting of flexible polyurethane (PU) and rigid polyimide (PI) chains cleverly woven together around the copper(I) ions center. By rationally weaving PI, PU chains, and copper(I) ions, RFIP exhibits ultra-high strength (twice that of unwoven polymers, 91.4 ± 3.3 MPa), toughness (448.0 ± 14.2 MJ m-3), fatigue resistance (recoverable after 10 000 cyclic stretches), and shape memory properties. Simulation results and characterization analysis together support the correlation between microstructure and macroscopic features, confirming the greater cohesive energy of the interwoven network and providing insights into strengthening toughening mechanisms. The essence of weaving on the atomic and molecular levels is fused to obtain brilliant and valuable mechanical properties, opening new perspectives in designing robust and stable polymers.

3D Covalent Organic Framework Membranes for Molecular Separations

Membrane separation has become an indispensable separation technology in social production, playing an important role in drug production, mineral exploitation, water purification, etc. The key core of membranes lies in achieving efficient and precise sieving between substances. As a result, a typical trade-off arises: highly permeable membranes usually sacrifice selectivity and vice versa. To address this dilemma, long-term research has focused on comprehensive understanding and modelling of synthetic membranes at various scales. A significant advancement in this arena is the advent of three-dimensional covalent organic framework (3D COF) membranes, a novel category of long-range ordered porous organic polymer materials. Characterized by an abundance of interconnected channels, diverse pore wall properties, tunable structures, and robust thermal and chemical resilience, 3D COF membranes offer a promising approach for efficient substance separation. This review undertakes a meticulous investigation of the synthesis and physicochemical properties of 3D COF membranes, accentuating the underlying design principles, fabrication methods, and application attempts. A comprehensive assessment of their research trajectory and current standing in the field of membrane processes is provided. The review culminates in a forward-looking outlook, summarizing future research directions and highlighting the substantial potential of this innovative work to shape the future of efficient membrane separation processes.

Quasi-One-Dimensional Zigzag Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution from Water

Covalent organic frameworks (COFs) have potential applications in a wide range of fields. However, it remains a critical challenge to constrain their covalent expansions in the one-dimensional (1D) direction. Here, we developed a general approach to fabricate 15 different highly crystalline COFs with zigzag-packed 1D porous organic chains through the condensation of V-shaped ditopic linkers and X-shaped tetratopic knots. Appropriate geometrical combinations of a wide scope of linkers and knots with distinct aromatic cores, linkages, and functionalities offer a series of quasi-1D COFs with dominant pore sizes of 7-13 Å and surface areas of 116-784 m2 g-1. Among them, nitrogen (N)-doped 1D COFs with site-specific doping of heteroatoms favor a tunable control of band structures and conjugations and thus allow a remarkable hydrogen evolution rate up to 80 mmol g-1 h-1 in photocatalytic water splitting. This general strategy toward programming function in porous crystalline materials has the potential to tune the topologically well-defined electronic properties through precisely periodic doping.

Ultratough Supramolecular Polyurethane Featuring an Interwoven Network with Recyclability, Ideal Self-Healing and Editable Shape Memory Properties

Developing multifunctional polymers with excellent mechanical properties, outstanding shape memory characteristics, and good self-healing properties is a formidable challenge. Inspired by the woven cross-linking strategy, a series of supramolecular polyurethane (PU) with an interwoven network structure composed of covalent and supramolecular cross-linking nodes have been successfully synthesized by introducing the ureido-pyrimidinone (UPy) motifs into the PU skeleton. The best-performing sample exhibited ultrahigh strength (∼77.2 MPa) and toughness (∼312.7 MJ m-3), along with an ideal self-healing efficiency (up to 90.8% for 6 h) and satisfactory temperature-responsive shape memory effect (shape recovery rates up to 96.9%). Furthermore, it ensured recyclability. These favorable properties are mainly ascribed to the effective dissipation of strain energy due to the disassembly and reconfiguration of supramolecular nodes (i.e., quadruple hydrogen bonds (H-bonds) between UPy units), as well as the covalent cross-linking nodes that maintain the integrity of the polymer network structure. Thus, our work provides a universal strategy that breaks through the traditional contradictions and paves the way for the commercialization of high-performance multifunctional PU elastomers.

Unexpected Molecular Sieving of Xylene Isomer Using Tethered Ligand in Polymer-Metal-Organic Frameworks (polyMOFs)

Promising advances in adsorption technology can lead to energy-efficient solutions in industrial sectors. This work presents precise molecular sieving of xylene isomers in the polymer-metal-oragnic framework (polyMOF), a hybrid porous material derived from the parent isoreticular MOF-1 (IRMOF-1). PolyMOFs are synthesized by polymeric ligands bridged by evenly spaced alkyl chains, showing reduced pore sizes and enhanced stabilities compared to its parent material due to tethered polymer bridge within the pores while maintaining the original rigid crystal lattice. However, the exact configuration of the ligands within the crystals remain unclear, posing hurdles to predicting the adsorption performances of the polyMOFs. This work reveals that the unique pore structure of polyIRMOF-1-7a can discriminate xylene isomers with sub-angstrom size differences, leading to highly selective adsorption of p-xylene over other isomers and alkylbenzenes in complex liquid mixtures (αpX/OM = 15 and αpX/OME = 9). The structural details of the polyIRMOF-1-7a are elucidated through computational studies, suggesting a plausible configuration of alkyl chains within the polyMOF crystal, which enable a record-high p-xylene selectivity and stability in liquid hydrocarbon. With this unprecedented molecular selectivity in MOFs, "polymer-MOF" hybridization is expected to meet rigorous requirements for high-standard molecular sieving through precisely tunable and highly stable pores.

Nitrogen-contained Nanoporous Hyper-cross-linked Polymer: A New Turn-on Fluorescence Probe for Detection of Ag+ Ions in Aqueous Media

A fluorescence probe was designed using a nitrogen-contained mesoporous hyper-cross-linked polymer precursor (NH2-HCP) in order to selectively detect silver (Ag+) ions. NH2-HCP exhibits fluorescence intensity, but upon the addition of Ag+, a significant enhancement in fluorescence signal is observed. The relationship between fluorescence intensity enhancement and Ag+ concentration shows a linear and monotonic trend. The probe's response to various other cations such as Al3+, Fe3+, Cd2+, Ni2+, Cu2+, Fe2+, Hg2+, Mg2+, Zn2+, Pb2+, Mn2+, Co2+, Ca2+, Na+, and K+, as well as halogen anions like F-, Cl-, Br-, and I- was also investigated. Under optimal conditions, the probe demonstrated a linear range of 0.1-3 μM and a detection limit of 0.01 μM.

Design of Three-Dimensional Mesoporous Adamantane-Based Covalent Organic Framework with Exceptionally High Surface Areas

The development of three-dimensional (3D) covalent organic frameworks (COFs) with large pores and high specific surface areas is of critical for practical applications. However, it remains a tremendous challenge to reconcile the contradiction between high porosity and high specific surface areas, and increasing the length of building blocks leads to structural interpenetration in 3D COFs. Here, we report the preparation of mesoporous three-dimensional COF by a new steric hindrance engineering method. By incorporating adamantane into the monomers instead of carbon centers, we successfully achieve 2-fold interpenetrated diamondoid-structured 3D COFs, featuring permanent mesopores (up to 33 Å), exceptionally high surface areas (>3400 m2 g-1), and low crystal densities (0.123 g cm-3). These properties far surpass those of most conventional 3D COFs with similar topologies. This work not only aims to construct 3D COFs with low interpenetration but also to establish a foundation for the systematic design and structural control of 3D COFs.

Construction of Benzoxazine-linked One-Dimensional Covalent Organic Frameworks Using the Mannich Reaction

Covalent polymerization of organic molecules into crystalline one-dimensional (1D) polymers is effective for achieving desired thermal, optical, and electrical properties, yet it remains a persistent synthetic challenge for their inherent tendency to adopt amorphous or semicrystalline phases. Here we report a strategy to synthesize crystalline 1D covalent organic frameworks (COFs) composing quasi-conjugated chains with benzoxazine linkages via the one-pot Mannich reaction. Through [4+2] and [2+2] type Mannich condensation reactions, we fabricated stoichiometric and sub-stoichiometric 1D covalent polymeric chains, respectively, using doubly and singly linked benzoxazine rings. The validity of their crystal structures has been directly visualized through state-of-the-art cryogenic low-dose electron microscopy techniques. Post-synthetic functionalizations of them with a chiral MacMillan catalyst produce crystalline organic photocatalysts that demonstrated excellent catalytic and recyclable performance in light-driven asymmetric alkylation of aldehydes, affording up to 94 % enantiomeric excess.

Folding a Molecular Strand into a Trefoil Knot of Single Handedness with Co(II)/Co(III) Chaperones

We report the synthesis of a right-handed (Δ-stereochemistry of strand crossings) trefoil knot from a single molecular strand containing three pyrazine-2,5-dicarboxamide units adjacent to point-chiral centers and six pyridine moieties. The oligomeric ligand strand folds into an overhand (open-trefoil) knot through the assistance of coordinatively dynamic Co(II) "chaperones" that drive the formation of a three-metal-ion circular helicate. The entangled structure is kinetically locked by oxidation to Co(III) and covalently captured by ring-closing olefin metathesis to generate a trefoil knot of single topological handedness. The stereochemistry of the strand crossings in the metal-coordinated overhand knot is governed by the stereochemistry of the point-chiral carbon centers in the ligand strand. The overhand and trefoil knots were characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. Removal of the metal ions from the knot, followed by hydrogenation of the alkene, yielded the wholly organic trefoil knot. The metal-free knot and parent ligand were investigated by circular dichroism (CD) spectroscopy. The CD spectra indicate that the topological stereochemistry of the knot has a greater effect on the asymmetry of the chromophore environment than do the point-chiral centers of the strand.

Highly Efficient Self-Assembly of Heterometallic [2]Catenanes and Cyclic Bis[2]catenanes via Orthogonal Metal-Coordination Interactions

Although catenated cages have been widely constructed due to their unique and elegant topological structures, cyclic catenanes formed by the connection of multiple catenane units have been rarely reported. Herein, based on the orthogonal metal-coordination-driven self-assembly, we prepare a series of heterometallic [2]catenanes and cyclic bis[2]catenanes, whose structures are clearly evidenced by single-crystal X-ray analysis. Owing to the multiple positively charged nature, as well as the potential synergistic effect of the Cu(I) and Pt(II) metal ions, the cyclic bis[2]catenanes display broad-spectrum antibacterial activity. This work not only provides an efficient strategy for the construction of heterometallic [2]catenanes and cyclic bis[2]catenanes but also explores their applications as superior antibacterial agents, which will promote the construction of advanced supramolecular structures for biomedical applications.

Hierarchical single-crystal-to-single-crystal transformations of a monomer to a 1D-polymer and then to a 2D-polymer

Designing and synthesizing flawless two-dimensional polymers (2D-Ps) via meticulous molecular preorganization presents an intriguing yet challenging frontier in research. We report here the single-crystal-to-single-crystal (SCSC) synthesis of a 2D-P via thermally induced topochemical azide-alkyne cycloaddition (TAAC) reaction. A designed monomer incorporating two azide and two alkyne units is synthesized. The azide and alkyne groups are preorganized in the monomer crystal in reactive geometries for polymerizations in two orthogonal directions. On heating, the polymerizations proceed in a hierarchical manner; at first, the monomer reacts regiospecifically in a SCSC fashion to form a 1,5-triazolyl-linked 1D polymer (1D-P), which upon further heating undergoes another SCSC polymerization to a 2D-P through a second regiospecific TAAC reaction forming 1,4-triazolyl-linkages. Two different linkages in orthogonal directions make this an architecturally attractive 2D-P, as determined, at atomic resolution, by single-crystal X-ray diffraction. The 2D-P reported here is thermally stable in view of the robust triazole-linkages and can be exfoliated as 2D-sheets.

Dynamic two-dimensional covalent organic frameworks

Porous covalent organic frameworks (COFs) enable the realization of functional materials with molecular precision. Past research has typically focused on generating rigid frameworks where structural and optoelectronic properties are static. Here we report dynamic two-dimensional (2D) COFs that can open and close their pores upon uptake or removal of guests while retaining their crystalline long-range order. Constructing dynamic, yet crystalline and robust frameworks requires a well-controlled degree of flexibility. We have achieved this through a 'wine rack' design where rigid π-stacked columns of perylene diimides are interconnected by non-stacked, flexible bridges. The resulting COFs show stepwise phase transformations between their respective contracted-pore and open-pore conformations with up to 40% increase in unit-cell volume. This variable geometry provides a handle for introducing stimuli-responsive optoelectronic properties. We illustrate this by demonstrating switchable optical absorption and emission characteristics, which approximate 'null-aggregates' with monomer-like behaviour in the contracted COFs. This work provides a design strategy for dynamic 2D COFs that are potentially useful for realizing stimuli-responsive materials.

Designed 2D protein crystals as dynamic molecular gatekeepers for a solid-state device

The sensitivity and responsiveness of living cells to environmental changes are enabled by dynamic protein structures, inspiring efforts to construct artificial supramolecular protein assemblies. However, despite their sophisticated structures, designed protein assemblies have yet to be incorporated into macroscale devices for real-life applications. We report a 2D crystalline protein assembly of C98/E57/E66L-rhamnulose-1-phosphate aldolase (CEERhuA) that selectively blocks or passes molecular species when exposed to a chemical trigger. CEERhuA crystals are engineered via cobalt(II) coordination bonds to undergo a coherent conformational change from a closed state (pore dimensions <1 nm) to an ajar state (pore dimensions ~4 nm) when exposed to an HCN(g) trigger. When layered onto a mesoporous silicon (pSi) photonic crystal optical sensor configured to detect HCN(g), the 2D CEERhuA crystal layer effectively blocks interferents that would otherwise result in a false positive signal. The 2D CEERhuA crystal layer opens in selective response to low-ppm levels of HCN(g), allowing analyte penetration into the pSi sensor layer for detection. These findings illustrate that designed protein assemblies can function as dynamic components of solid-state devices in non-aqueous environments.

Epitaxially Grown Mechanically Robust 2D Thin Film of Secondary Interactions Led Molecularly Woven Material

Molecularly woven materials with striking mechanical resilience, and 2D controlled topologies like textiles, fishing nets, and baskets are highly anticipated. Molecular weaving exclusively apprehended by the secondary interactions expanding to laterally grown 2D self-assemblies with retained crystalline arrangement is stimulating. The interlacing entails planar molecules screwed together to form 2D woven thin films. Here, secondary interactions led 2D interlaced molecularly woven material (2°MW) built by 1D helical threads of organic chromophores twisted together via end-to-end CH···O connections, held strongly at inter-crossing by multiple OH···N interactions to prevent slippage is presented. Whereas, 1D helical threads with face-to-face O-H···O connections sans interlacing led the non-woven material (2°NW). The polarity-driven directionality in 2°MW led the water-actuated epitaxial growth of 2D-sheets to lateral thin films restricted to nano-scale thickness. The molecularly woven thin film is self-healing, flexible, and mechanically resilient in nature, while maintaining the crystalline regularity is attributed to the supple secondary interactions (2°).

Metalated covalent organic frameworks as efficient catalysts for multicomponent tandem reactions

Multicomponent tandem reactions have become indispensable synthetic methods due to their economic advantages and efficient usage in natural products and drug synthesis. The emergence of metalated covalent organic frameworks (MCOFs) has opened up new opportunities for the advancement of multicomponent tandem reactions. In contrast to commonly used homogeneous transition metal catalysts, MCOFs possess regular porosity, high crystallinity, and rich metal chelation sites that facilitate the uniform distribution and anchoring of metals within their cavities. Thus, they show extremely high activity and have recently been widely employed as catalysts for multicomponent tandem reactions. It is timely to conduct a review of MCOFs in multicomponent tandem reactions, in order to offer guidance and assistance for the synthesis of MCOF catalysts and their application in multicomponent tandem reactions. This review provides a comprehensive overview of the design and synthesis of MCOFs, their application and progress in multicomponent tandem reactions, and the primary challenges encountered during their current development with the aim of contributing to the promotion of the field.

Semi-crystalline polymers with supramolecular synergistic interactions: from mechanical toughening to dynamic smart materials

Semi-crystalline polymers (SCPs) with anisotropic amorphous and crystalline domains as the basic skeleton are ubiquitous from natural products to synthetic polymers. The combination of chemically incompatible hard and soft phases contributes to unique thermal and mechanical properties. The further introduction of supramolecular interactions as noncovalently interacting crystal phases and soft dynamic crosslinking sites can synergize with covalent polymer chains, thereby enabling effective energy dissipation and dynamic rearrangement in hierarchical superstructures. Therefore, this review will focus on the design principles of SCPs by discussing supramolecular construction strategies and state-of-the-art functional applications from mechanical toughening to sophisticated functions such as dynamic adaptivity, shape memory, ion transport, etc. Current challenges and further opportunities are discussed to provide an overview of possible future directions and potential material applications.