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.

"Turn-on" mode fluorescence detection of amines based on a cationic covalent organic framework linked with C-C single bond

Developing methods to detect amine pollutants at trace levels is urgently needed due to their high toxicity to both human health and environment. Covalent organic frameworks (COFs) have emerged as promising candidates for amine sensing due to their exceptional stability when exposed to corrosive amines. While several COF-based sensors have recently been developed for amine detection, to the best of our knowledge, fluorescent "turn-on" sensors have been limited to imine-linked COFs. However, the relatively low stability of imine linkages may compromise structural integrity in the presence of corrosive amines. Here, for the first time, we constructed a cationic C-C single bond linked COF (CSBL-COF-4) through the reaction between cationic porphyrin TMPyP and terephthaldicarboxaldehyde. The abundant cationic sites distributing throughout the networks not only improved the dispersity of CSBL-COF-4 in aqueous solution but also provided numerous acidic sites to enhance the affinity with alkaline amines via Lewis acid-base interaction. CSBL-COF-4 exhibited an efficient response to amine solutions or vapors and was further utilized to evaluate the freshness of meat samples, highlighting its potential for practical applications. Our result would thus open up a new avenue towards constructing a broader class of COF-based sensors for the fluorescence "turn-on" detection of amines.

Boosting Multicolor Emission Enhancement in Two-Dimensional Covalent-Organic Frameworks via the Pressure-Tuned π-π Stacking Mode

Covalent-organic frameworks (COFs) are dynamic covalent porous organic materials constructed from emissive molecular organic building blocks. However, most two-dimensional (2D) COFs are nonemissive or weakly emissive in the solid state owing to the intramolecular rotation and vibration together with strong π-π interactions. Herein, we report a pressure strategy to achieve the bright multicolor emission from yellow to red in the 2D triazine triphenyl imine COF (TTI-COF). Intriguingly, the TTI-COF experiences a 24-fold enhancement under a mild pressure of 2.7 GPa compared with the initial state. Joint experimental and theoretical results reveal that the restricted intramolecular chemical bond vibrations and the reduced π-π interactions originating from the offset stacking mode account for the significant pressure-induced emission enhancement. Furthermore, such piezochromic behavior may be ascribed to the decreased energy gap and enhanced intermolecular interaction. Our investigation offers constructive guidelines for designing 2D COF materials with high photoluminescence performance.

Hollow TiO2@TpPa S-Scheme Photocatalyst for Efficient H2O2 Production Through 1O2 in Deionized Water Using Phototautomerization

Hydrogen peroxide (H2O2) production through photocatalytic O2 reduction reaction (ORR) is a mild and cost-efficient alternative to the anthraquinone oxidation strategy. Of note, singlet state oxygen (1O2) plays a crucial role in ORR. Herein, a hollow TiO2@TpPa (TOTP) S-scheme heterojunction by the Schiff base reactions involving 1,3,5-triformylphloroglucinol (Tp) and paraphenylenediamine (Pa) for efficient photocatalytic H2O2 production in deionized water has been developed. Upon irradiation, rapid phototautomerization of TaPa from enol to keto form expands π-electron delocalization, facilitating effective conversion of the triplet excited state and consequent generation of 1O2. This mechanism is supported by time-resolved electron paramagnetic resonance (EPR) spectral analysis. Additionally, density functional theory calculations, in situ irradiated X-ray photoelectron spectroscopy, and femtosecond transient absorption spectroscopy reveal superior separation of photogenerated carriers in the TOTP S-scheme composites. In deionized water, the TOTP2.4 S-scheme heterojunction exhibits exceptional H2O2 production activity, yielding 891 µmol g-1 h-1, underscoring the critical role of 1O2 in the process. This research offers insights into the S-scheme heterojunctions and emphasizes the pivotal role of 1O2 in enhancing H2O2 production efficiency.

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.

Emissive Covalent Organic Frameworks: Improved Fluorescence via Flexible Building Blocks and Selective Sensing of Nitroaromatic Explosives

2D covalent organic frameworks (COFs) are attractive for fluorescence sensing due to their lightweight, robust, and highly ordered porous structures. However, the highly conjugated structures between adjacent layers of covalent organic frameworks can often result in aggregation-caused quenching (ACQ) properties. Here, the study designs two flexible hydrazone-linked COFs to suppress ACQ effects, thereby enhancing their luminescent activities. Furthermore, the high density of nitrogen and oxygen atoms on these flexible walls serves as binding sites for hydrogen bonding interactions, indicating sensitivity and selectivity towards 2,4,6-trinitrophenol detection.

A comparative study of topological entropy characterization and graph energy prediction for Marta variants of covalent organic frameworks

Covalent organic frameworks are a novel class of porous polymers, notable for their crystalline structure, intricate frameworks, defined pore sizes, and capacity for structural design, synthetic control, and functional customization. This paper provides a comprehensive analysis of graph entropies and hybrid topological descriptors, derived from geometric, harmonic, and Zagreb indices. These descriptors are applied to study two variations of Marta covalent organic frameworks based on contorted hexabenzocoronenes. We also conduct a comparative analysis using scaled entropies, offering refined tools for assessing the intrinsic topologies of these networks. Additionally, these hybrid descriptors are used to develop statistical models for predicting graph energy in higher-dimensional Marta-COFs.

Mild and Scalable Conditions for the Solvothermal Synthesis of Imine-Linked Covalent Organic Frameworks

A convenient method was developed that allows for the synthesis of highly crystalline and porous imine-linked covalent organic frameworks (COFs) in hours. The use of an apolar solvent in combination with a precise amount of water and acetic acid was crucial to obtain materials of optimal quality. Fifteen different COFs could be produced under the same reaction conditions, using a green solvent mixture of n-butanol, acetic acid and water at 70 °C for 16 hours with stirring. The crystallinity of the COFs produced in this manner is similar or better than that obtained by traditional solvothermal synthesis. The method could be easily scaled to synthesize over ten grams of COF in one batch. Optical microscopy, FTIR spectroscopy and in situ Raman spectroscopy gave insight in the role of the solvent on the aggregation of COF nanosheets and the resulting crystallinity, porosity and robustness of the material.

Assessing interactions between antibiotics and triazine porous organic polymeric sorbents by photophysics

This study purposes three triazine-based porous organic polymers (T-POPs 1-3) as advanced platforms for the early detection of antibiotic-polluted environments and effective water decontamination, in order to mitigate water pollution and antimicrobial resistance, which are two huge current problems damaging ecosystems and human health. T-POPs exhibited good performances as adsorbents for the removal of sulfamethazine (SMT) and tetracycline (TC) from water, with efficiencies up to 97% and 96%, and maximum adsorption capacities between (0.36-0.44) and (0.21-0.27) mmol g-1, respectively, which are similar or even higher (up to 40.3 times) than those reported for other materials. In addition, good reusability was achieved, particularly for T-POP2, despite being the polymer with the lowest surface area. A slightly higher selectivity of T-POPs for sulfonamides and the best performance of T-POP3 to remove six antibiotics from a micromolar solution were observed. T-POPs also acted as fluorescent chemosensors, since T-POP1 underwent linear Stern-Volmer fluorescence quenching in the presence of both SMT and TC, while the enhanced-fluorescent T-POP2 and T-POP3 experienced fluorescence extinction through a sphere of action mechanism in contact with TC, and bathochromic shift accompanied by a hyperchromic effect on the new fluorescent region with the increase in SMT concentration. Thus, T-POP2 and T-POP3 can both promote a selective on-site monitoring of each drug in contaminated water streams and an efficient water remediation, thanks to the synergy between hydrogen and van der Waals interactions. In summary, these triazine-based porous organic polymers are promising materials for the simultaneous monitoring and treatment of antibiotic-containing water and wastewaters.

Azatriangulene-Based Conductive C═C Linked Covalent Organic Frameworks with Near-Infrared Emission

Two near-infrared (NIR) emissive π-conjugated covalent organic frameworks (COFs) pTANG1 and pTANG2 are synthesized using Knoevenagel condensation of trioxaazatriangulenetricarbaldehyde (TATANG) with benzene- and biphenyldiacetonitriles, respectively. The morphology of the COFs is affected by the size of TATANG precursor crystals. Donor-acceptor interactions in these COFs result in small bandgaps (≈1.6 eV) and NIR emission (λmax = 789 nm for pTANG1). pTANG1 can absorb up to 9 molecules of water per unit cell, which is accompanied by a marked quenching of the NIR emission, suggesting applications as humidity sensors. p-Doping with magic blue significantly increases the electrical conductivities of the COFs by up to 8 orders of magnitude, with the room temperature conductivity of pTANG1 reaching 0.65 S cm-1, the highest among reported C═C linked COFs. 1H NMR relaxometry, temperature-dependent fluorescence spectroscopy, and DFT calculations reveal that the higher rigidity of the shorter phenylene linker is responsible for the more extended conjugation (red-shifted emission, higher electrical conductivity) of pTANG1 compared to pTANG2.

Photocarrier Dynamics of Two-Dimensional Aza-Fused Covalent Organic Frameworks as Bifunctional Photocatalysts toward Overall Water Splitting

Designing high-efficiency bifunctional photocatalysts toward photoinduced overall water splitting is one of the most promising and challenging research directions for clean energy generation. By employing static electronic structure calculation and nonadiabatic molecular dynamics (NAMD) simulation, we herein established a recently synthesized two-dimensional (2D) aza-fused covalent organic framework (aza-COF) as a potential bifunctional photocatalyst toward overall water splitting reactions. Our calculated results reveal that the overpotentials for hydrogen evolution reaction and oxygen evolution reaction are only 0.06 and 0.31 V, respectively, at pH = 4. The dynamics of photoexcited charge carriers studied through NAMD simulation predicts the electron-hole recombination time (25.15 ns), and this confirms that the photogenerated electron and hole carriers migrate to the active sites for the occurrence of reaction before they recombine. Therefore, our results suggest that the 2D aza-COFs exhibit great potential as metal-free and single-material photocatalysts toward overall water splitting under visible light.

Fluorescent Porous Materials Based on Aggregation-induced Emission for Biomedical Applications

Fluorescent porous materials based on aggregation-induced emission (AIE) are growing into a sparkling frontier in biomedical applications. Exploring those materials represents a win-win integration and has recently progressed at a rapid pace, mainly benefiting from intrinsic advantages including tunable pore size and structure, strong guest molecule encapsulation ability, superior biocompatibility, and photophysical outcomes. With the great significance and rapid progress in this area, this review provides an integrated picture on AIE luminogen-based porous materials. It encompasses inorganic, organic, and inorganic-organic porous materials, exploring fundamental concepts and the relationship between AIE performance and material design and highlighting significant breakthroughs and the latest trends in biomedical applications. In addition, some critical challenges and future perspectives in the development of AIE luminogen-based porous materials are also discussed.

Taming Two-Dimensional Polymerization by a Machine-Learning Discovered Crystallization Model

Rapidly synthesizing high-quality two-dimensional covalent organic frameworks (2D COFs) is crucial for their practical applications. While strategies such as slow monomer addition have been developed based on an empirical understanding of their formation process, quantitative guidance remains absent, which prohibits precise optimizations of the experimental conditions. Here, we use a machine-learning approach that overcomes the challenges associated with bottom-up model derivation for the non-classical 2D COF crystallization processes. The resulting model, referred to as NEgen1, establishes correlations among the induction time, nucleation rate, growth rate, bond-forming rate constants, and common solution synthesis conditions for 2D COFs that grow by a nucleation-elongation mechanism. The results elucidate the detailed competition between the nucleation and growth dynamics in solution, which has been inappropriately described previously by classical, empirical models with assumptions invalid for 2D COF polymerization. By understanding the dynamic processes at play, the NEgen1 model reveals a simple strategy of gradually increasing monomer addition speed for growing large 2D COF crystals. This insight enables us to rapidly synthesize large COF-5 colloids, which could only be achieved previously by prolonged reaction times or by introducing chemical modulators. These results highlight the potential for systematically improving the crystal quality of 2D COFs, which has wide-reaching relevance for many of the applications where 2D COFs are speculated to be valuable.

Aggregation Induced Emission-Based Covalent Organic Frameworks for High-Performance Optical Wireless Communication

Here, we report the first utilization of covalent organic frameworks (COFs) in optical wireless communication (OWC) applications. In the solid form, aggregation-induced emission (AIE) luminogen often shows promising emissive characteristics that augment radiative decays and improve fluorescence. We have synthesized an AIE-COF through the Knoevenagel condensation reaction by taking advantage of the ability to carefully design and alter the COF structure by integrating an AIE luminogen with linear building blocks. The synthesized AIE-COF exhibited a high solid-state photoluminescence quantum yield (∼39%) and a short photoluminescence lifetime (∼1 ns), crucial for achieving modulation bandwidth for high-speed OWC applications. For comparison, we constructed an aggregation-caused quenching based COF, showing a similar lifetime but almost insignificant quantum yield. The orthogonal frequency-division multiplexing modulation strategy employed by the AIE-COF demonstrates remarkable high-rate data transmission, with a wide -3 dB modulation bandwidth of nearly 200 MHz and achieving high net data rates of 825 Mb/s, outperforming traditional materials. These results open new avenues for the ability to design and finetune new COF materials for their utilization as color converters in developing cutting-edge OWC components, enabling faster and more efficient data transfer.

Piezofluorochromism in Covalent Organic Frameworks: Pressure-Induced Emission Enhancement and Blue-Shifted Emission

Achieving enhanced or blue-shifted emission from piezochromic materials remains a major challenge. Covalent organic frameworks (COFs) are promising candidates for the development of piezochromic materials owing to their dynamic structures and adjustable optical properties, where the emission behaviors are not solely determined by the functional groups, but are also greatly influenced by the specific geometric arrangement. Nevertheless, this area remains relatively understudied. In this study, a successful synthesis of a series of bicarbazole-based COFs with varying topologies, dimensions, and linkages was conducted, followed by an investigation of their structural and emission properties under hydrostatic pressure generated by a diamond anvil cell. Consequently, these COFs exhibited distinct piezochromic behaviors, particularly a remarkable pressure-induced emission enhancement (PIEE) phenomenon with a 16-fold increase in fluorescence intensity from three-dimensional COFs, surpassing the performance of CPMs and most organic small molecules with PIEE behavior. On the contrary, three two-dimensional COFs with flexible structures exhibited rare blue-shifted emission, whereas the variants with rigid and conjugated structures showed common red-shifted and reduced emission. Mechanism research further revealed that these different piezochromic behaviors were primarily determined by interlayer distance and interaction. This study represents the first systematic exploration of the structures and emission properties of COFs through pressure-treated engineering and provides a new perspective on the design of piezochromic materials.

2D Conjugated Polymer Thin Films for Organic Electronics: Opportunities and Challenges

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics.

Self-Standing Chiral Covalent Organic Framework Thin Films with Full-Color Tunable Guest-Induced Circularly Polarized Luminescence

Exploring self-standing chiral covalent organic framework (COF) thin films with controllable circularly polarized luminescence (CPL) is of paramount significance but remains a challenging task. Herein, we demonstrate the first example of self-standing chiral COF films employing a polymerization-dispersion-filtration strategy. Pristine, low-quality chiral COF films were produced by interfacial polymerization and then re-dispersed into COF colloidal solutions. Via vacuum assisted assembly, these COF colloids were densely stacked and assembled into self-standing, pure chiral COF films (L-/D-CCOF-F) that were transparent, smooth, crack-free and highly crystalline. These films were tunable in thicknesses, areas, and roughness, along with strong diffuse reflectance circular dichroism (DRCD) and cyan CPL signals, showing an intrinsic luminescence asymmetric factor (glum) of ~4.3×10-3. Furthermore, these COF films served as host adsorbents to load various achiral organic dye guests through adsorption. The effective chiral transfer and energy transfer between CCOF-F and achiral fluorescent dyes endowed the dyes with strong chirality and tunable DRCD, resulting in intense, full-color-tunable solid-state CPL. Notably, the ordered arrangement of dye guest molecules within the preferentially oriented chiral pores of CCOF-F contributed to an amplified |glum| factor of up to 7.2×10-2, which is state-of-the-art for COF-based CPL materials. This work provides new insights into the design and fabrication of self-standing chiral COF films, demonstrating their great potential for chiroptical applications.

Heavy-Atom-Free Covalent Organic Frameworks for Organic Room-Temperature Phosphorescence via Förster and Dexter Energy Transfer Mechanism

Covalent organic frameworks (COFs), with their accessible nanoscale porosity, selectable building blocks, and precisely engineered topology, offer unique benefits in the design of room-temperature phosphorescent (RTP) materials. However, their potential has been limited by phosphorescence quenching caused by interlayer π-π stacking interactions. This paper presents a novel strategy to enhance RTP in heavy-atom-free COFs by employing a donor-acceptor (D-A) system that leverages the Förster resonance energy transfer (FRET) and Dexter energy transfer (DET) mechanisms. Among the materials investigated, the best-performing COF exhibits a phosphorescence lifetime of 4.35 ms at room temperature. Spectral analysis, structural analysis, and theoretical calculations indicate the presence of intralayer FRET processes as well as interlayer DET processes within the D-A COF system. Potential anti-counterfeiting applications are explored by exploiting the unique phosphorescent properties of these materials. Additionally, the inherent permanent porosity of COFs presents new opportunities for future development and application. This strategy offers many promising prospects for advancing the RTP technology in COF materials and broadens their potential applications in various fields.

Covalent-Organic Frameworks for Selective and Sensitive Detection of Antibiotics from Water

As the consumption of antibiotics rises, they have generated some negative impacts on organisms and the environment because they are often unable to be effectively degraded, and seeking effective detection methods is currently a challenge. Covalent-organic frameworks (COFs) are new types of crystalline porous crystals created based on the strong covalent interactions between blocked monomers, and COFs demonstrate great potential in the detection of antibiotics from aqueous solutions because of their large surface area, adjustable porosity, recyclability, and predictable structure. This review aims to present state-of-the-art insights into COFs (properties, classification, synthesis methods, and functionalization). The key mechanisms for the detection of antibiotics and the application performance of COFs in the detection of antibiotics from water are also discussed, followed by the challenges and opportunities for COFs in future research.

Preparation of sp2 carbon-bonded π-conjugated COF aerogels by ultrasound-assisted mild solvothermal reaction for multi-functional applications

Molding COFs into aerogels from monomers can establish interpenetrating spatial network structures on the centimeter scale that increase the accessibility of dominant pore channels and the convenience of real application, which radically gets rid of the difficult reprocessing problems of insoluble and non-fusible powder COFs. However, the construction of bulk COF structures and achieving crystallinity are often incompatible, especially with sp2 carbon-based COFs, whose powder synthesis has been quite demanding. Herein, for the first time, we report an efficient method to prepare sp2 carbon-linked π-conjugated DFB-TMTA-COF (DT-COF) aerogels by an ultrasound-assisted mild solvothermal technique and freeze-drying. Particularly, unlike the typical synthesis methods of vacuum deoxygenation, high temperature and long reaction time, crystalline DT-COF aerogels can be obtained by reacting at 90 °C for 48 h without vacuum sealing. The fluffy, hierarchical porous flower-shaped microsphere clustering of DT-COF aerogels contributes to excellent mechanical properties and better host-guest interactions, which are favorable to utilize the benefits of the highly conjugated structure of channels. As a proof of concept, DT-COF aerogels have been used in absorption, batteries, and sensors, demonstrating enhanced functionality and effectiveness.

Linkage-Mixed Covalent Organic Frameworks Synthesized by a Liquid-Solid Two-Phase Strategy for Photoenhanced Uranium Extraction

Synthesizing COFs with hybrid linkage coupling with both reversible and irreversible natures remains a challenging issue. Herein, we report the synthesis of two rare COFs constructed by both reversible and irreversible linkages through a liquid-solid two-phase strategy. A systematic study reveals a one-pot, two-step reaction mechanism for the two COFs, the first step being a reversible Schiff base reaction and the second step being an irreversible Knoevenagel reaction. Interestingly, this hybrid linkage COF is found to show an outstanding photoenhanced uranium extraction performance. The results not only provide a general and green approach to develop the linkage chemistry of COFs but also enrich the synthesis toolboxes and application of 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.

Ionic Covalent Organic Framework as a Dual Functional Sensor for Temperature and Humidity

Visual sensing of humidity and temperature by solids plays an important role in the everyday life and in industrial processes. Due to their hydrophobic nature, most covalent organic framework (COF) sensors often exhibit poor optical response when exposed to moisture. To overcome this challenge, the optical response is set out to improve, to moisture by incorporating H-bonding ionic functionalities into the COF network. A highly sensitive COF, consisting of guanidinium and diformylpyridine linkers (TG-DFP), capable of detecting changes in temperature and moisture content is fabricated. The hydrophilic nature of the framework enables enhanced water uptake, allowing the trapped water molecules to form a large number of hydrogen bonds. Despite the presence of non-emissive building blocks, the H-bonds restrict internal bond rotation within the COF, leading to reversible fluorescence and solid-state optical hydrochromism in response to relative humidity and temperature.

Carbon and metal based magnetic porous materials - Role in drug removal: A Comprehensive review

Development of effective adsorbents for the removal of contaminants from wastewater is indispensable due to increasing water scarcity and a lack of pure drinking water, which are prevailing as a result of rapid industrialization and population growth. Recently, the development of new adsorbents and their effective use without generating secondary waste is receiving huge consideration. In order to protect the environment from primary and secondary pollution, the development of adsorbents from wastes and their recycling have become conventional practices aimed at waste management. As a result, significant progress has been made in the synthesis of new porous carbon and metal-organic frameworks as adsorbents, with the objective of using them for the removal of pollutants. While many different kinds of pollutants are produced in the environment, drug pollutants are the most vicious because of their tendency to undergo significant structural changes, producing metabolites and residues with entirely different properties compared to their parent compounds. Chemical reactions involving oxidation, hydrolysis, and photolysis transform drugs. The resulting compounds can have detrimental effects on living beings that are present in soil and water. This review stresses the development of adsorbents with adjustable porosities for the broad removal of primary drug pollutants and their metabolites, which are formed as a result of drug transformations in environmental matrices. This keeps adsorbents from building up in the environment and prevents them from becoming significant pollutants in the future. Additionally, it stops secondary pollution caused by the deterioration of the used adsorbents. Focus on the development of effective adsorbents with flexible porosities allows for the complete removal of coexisting contaminants and makes a substantial contribution to wastewater management. In order to concentrate more on the development of flexible pore adsorbents, it is crucial to comprehend the milestones reached in the research and applications of porous magnetic adsorbents based on metal and carbon, which are discussed here.

Precise Regulation in Chain-Edge Structural Microenvironments of 1D Covalent Organic Frameworks for Photocatalysis

Covalent organic frameworks (COFs) constitute a promising research topic for photocatalytic reactions, but the rules and conformational relationships of 1D COFs are poorly defined. Herein, the chain edge structure is designed by precise modulation at the atomic level, and the 1D COFs bonded by C, O, and S elements is directionally prepared for oxygen-tolerant photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) reactions. It is demonstrated that heteroatom-type chain edge structures (─O─, ─S─) lead to a decrease in intra-plane conjugation, which restricts the effective transport of photogenerated electrons along the direction of the 1D strip. In contrast, the all-carbon type chain edge structure (─C─) with higher intra-plane conjugation not only reduces the energy loss of photoexcited electrons but also enhances the carrier density, which exhibits the optimal photopolymerization performance. This work offers valuable guidance in the exploitation of 1D COFs for high photocatalytic performance. This work offers valuable guidance in the exploitation of 1D COFs for high photocatalytic performance.

The development of catalysts and auxiliaries for the synthesis of covalent organic frameworks

Covalent organic frameworks (COFs) have recently seen significant advancements. Large quantities of structurally & functionally oriented COFs with a wide range of applications, such as gas adsorption, catalysis, separation, and drug delivery, have been explored. Recent achievements in this field are primarily focused on advancing synthetic methodologies, with catalysts playing a crucial role in achieving highly crystalline COF materials, particularly those featuring novel linkages and chemistry. A series of reviews have already been published over the last decade, covering the fundamentals, synthesis, and applications of COFs. However, despite the pivotal role that catalysts and auxiliaries play in forming COF materials and adjusting their properties (e.g., crystallinity, porosity, stability, and morphology), limited attention has been devoted to these essential components. In this Critical Review, we mainly focus on the state-of-the-art progress of catalysts and auxiliaries applied to the synthesis of COFs. The catalysts include four categories: acid catalysts, base catalysts, transition-metal catalysts, and other catalysts. The auxiliaries, such as modulators, oxygen, and surfactants, are discussed as well. This is then followed by the description of several specific applications derived from the utilization of catalysts and auxiliaries. Lastly, a perspective on the major challenges and opportunities associated with catalysts and auxiliaries is provided.

Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence

Delayed luminescence (DF), including phosphorescence and thermally activated delayed fluorescence (TADF), and circularly polarized luminescence (CPL) exhibit common and broad application prospects in optoelectronic displays, biological imaging, and encryption. Thus, the combination of delayed luminescence and circularly polarized luminescence is attracting increasing attention. The encapsulation of guest emitters in various host matrices to form host-guest systems has been demonstrated to be an appealing strategy to further enhance and/or modulate their delayed luminescence and circularly polarized luminescence. Compared with conventional liquid crystals, polymers, and supramolecular matrices, porous crystalline frameworks (PCFs) including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), zeolites and hydrogen-bonded organic frameworks (HOFs) can not only overcome shortcomings such as flexibility and disorder but also achieve the ordered encapsulation of guests and long-term stability of chiral structures, providing new promising host platforms for the development of DF and CPL. In this review, we provide a comprehensive and critical summary of the recent progress in host-guest photochemistry via the encapsulation engineering of guest emitters in PCFs, particularly focusing on delayed luminescence and circularly polarized luminescence. Initially, the general principle of phosphorescence, TADF and CPL, the combination of DF and CPL, and energy transfer processes between host and guests are introduced. Subsequently, we comprehensively discuss the critical factors affecting the encapsulation engineering of guest emitters in PCFs, such as pore structures, the confinement effect, charge and energy transfer between the host and guest, conformational dynamics, and aggregation model of guest emitters. Thereafter, we summarize the effective methods for the preparation of host-guest systems, especially single-crystal-to-single-crystal (SC-SC) transformation and epitaxial growth, which are distinct from conventional methods based on amorphous materials. Then, the recent advancements in host-guest systems based on PCFs for delayed luminescence and circularly polarized luminescence are highlighted. Finally, we present our personal insights into the challenges and future opportunities in this promising field.

Stranski-Krastanov Growth of Two-Dimensional Covalent Organic Framework Films

Insights into the formation mechanisms of two-dimensional covalent organic frameworks (2D COFs) at both the in-plane and interlayer levels are essential for improving material quality and synthetic methodology. Here, we report the controllable preparation of 2D COF films via on-surface synthesis and investigate the growth mechanism using atomic force microscopy. Monolayer, bilayer, and layer-plus-island multilayer COF films were successfully constructed on hexagonal boron nitride in a controlled manner. The porphyrin-based COF films grow in the Stranski-Krastanov mode, i.e., a uniform bilayer COF film can be formed through layer-by-layer growth in the initial stage followed by island growth starting from the third layer. Furthermore, fluorescence quenching caused by π-π stacking interactions between 2D COF neighboring layers was revealed. These results provide new perspectives on the synthesis of high-quality 2D COF films with controllable thickness and morphology, paving the way for a diverse range of applications.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Powders to Thin Films: Advances in Conjugated Microporous Polymer Chemical Sensors

Chemical sensing of harmful species released either from natural or anthropogenic activities is critical to ensuring human safety and health. Over the last decade, conjugated microporous polymers (CMPs) have been proven to be potential sensor materials with the possibility of realizing sensing devices for practical applications. CMPs found to be unique among other porous materials such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) due to their high chemical/thermal stability, high surface area, microporosity, efficient host-guest interactions with the analyte, efficient exciton migration along the π-conjugated chains, and tailorable structure to target specific analytes. Several CMP-based optical, electrochemical, colorimetric, and ratiometric sensors with excellent selectivity and sensing performance were reported. This review comprehensively discusses the advances in CMP chemical sensors (powders and thin films) in the detection of nitroaromatic explosives, chemical warfare agents, anions, metal ions, biomolecules, iodine, and volatile organic compounds (VOCs), with simultaneous delineation of design strategy principles guiding the selectivity and sensitivity of CMP. Preceding this, various photophysical mechanisms responsible for chemical sensing are discussed in detail for convenience. Finally, future challenges to be addressed in the field of CMP chemical sensors are discussed.

Hot Carrier Controlled Nitrogen Fixation Reaction in Metal-Free Boron-Anchored Aza-COF: Insight from Nonadiabatic Molecular Dynamics Simulation

Designing highly efficient photocatalysts for the production of renewable energy is a challenging task that necessitates simultaneous control of chemical activity and photocarrier dynamics for a particular reaction. To this end, we have investigated the catalytic mechanism and real-time photocarrier dynamics of the nitrogen reduction reaction (NRR) at the metal-free boron-functionalized 2D aza-COF (B-aza-COF), an inexpensive and environmentally friendly semiconductor. By employing density functional theory (DFT) and time-dependent ab initio nonadiabatic molecular dynamics simulation, we have investigated the electronic structure, light harvesting ability, free energy change, and dynamics of photoexcited carriers. Our calculated results reveal that the gas phase N2 molecule can be effectively reduced into NH3 on B-aza-COF under UV-visible light. Therefore, our investigation on the design of efficient photocatalysts for the nitrogen reduction reaction (NRR) provides a cost-effective opportunity for the sustainable production of NH3.

Size-Dependent Deformation and Competition H-Bond Site-Induced Individual Fluorescence Response of a Single-Crystal Three-Dimensional Covalent Organic Framework

Understanding the individual fluorescence response mechanism of covalent organic frameworks (COFs) at a single-crystal level is of great significance for the rational design of COF-based microsensors but unreachable because all previous COF-based sensors are performed with average fluorescence response behavior of various sized polycrystalline COFs. Herein, we design to explore the fluorescence response of a monodisperse single-crystal COF and further reveal the individual heterogeneity of the response mechanism. Three-dimensional single-crystal COF-301 (SCOF-301) with an intramolecular H-bond-induced excited-state intramolecular proton-transfer effect is selected as a proof-of-concept SCOF. With ethanol, benzene, and ammonia as model analytes, three different deformation and competition H-bond site-induced fluorescence response mechanisms related to crystal size are revealed. Small single particles of SCOF-301 (SSCOF-301) exhibit a more flexible structure, leading to the dominant role of deformation in the fluorescence response of small-sized SSCOF-301. The decreasing flexibility of SSCOF-301 with the increase of crystal size results in involvement of competition of the H-bond site to the fluorescence response besides deformation. Further increase of the crystal size makes the large-sized SSCOF-301 difficult to deform; thus, the competition of the H-bond site dominates the fluorescence response. This work provides a deep understanding of the individual fluorescence response mechanism of COFs to guide the design of a functional COF sensor with suitable size and mechanism for different structural analytes.

Photostimulus-Responsive Peptide Dot-Centered Covalent Organic Polymers: Effective Pesticide Sensing via Enhancing Accessibility

Pesticide detection and monitoring are necessary for human health as the overapplication has serious consequences for environmental pollution. Herein, a proper modulation strategy was implemented to construct the photostimulus-responsive peptide-dot-centered covalent organic polymer (P-PCOP) nanoarchitecture for selective sensing of pesticides. The as-constructed P-PCOP was prepared at room temperature by using amino-containing peptide dots as a building block instead of common organic molecules, and the merits of P-PCOP enable it to reduce the steric hindrance of recognition, enhance the interfacial contact of the target, and facilitate the accessibility of sites, which promises to improve the sensitivity. The P-PCOF exhibited a low detection limit of 0.38 μg L-1 to cartap over the range of 1-80 μg L-1 (R2 = 0.9845), and the recoveries percentage in real samples was estimated to be 93.39-105.82%. More importantly, the DFT calculation confirmed the selective recognition ability of P-PCOP on chemical pesticides. In conjunction with a smartphone-integrated portable reading device, on-site chemical sensing is achieved. The proper modulation strategy of fixing a functional guest on the COP system contributes to the advanced structure-chemical properties that are conducive to their applications in chemical sensing.

Highlights in Interface of Wastewater Treatment by Utilizing Metal Organic Frameworks: Purification and Adsorption Kinetics

Polluted water has become a concern for the scientific community as it causes many severe threats to living beings. Detection or removal of contaminants present in wastewater and attaining purity of water that can be used for various purposes are a primary responsibility. Different treatment methods have already been used for the purification of sewage. There is a need for low-cost, highly selective, and reusable materials that can efficiently remove pollutants or purify contaminated water. In this regard, MOFs have shown significant potential for applications such as supercapacitors, drug delivery, gas storage, pollutant adsorption, etc. The outstanding structural diversity, substantial surface areas, and adjustable pore sizes of MOFs make them superior candidates for wastewater treatment. This Review provides an overview of the interaction science and engineering (kinetic and thermodynamic aspects with interactions) underpinning MOFs for water purification. First, fundamental strategies for the synthesis methods of MOFs, different categories, and their applicability in wastewater treatment are summarized, followed by a detailed explanation of various interaction mechanisms. Finally, current challenges and future outlooks for research on MOF materials toward the adsorption of hazardous components are discussed. A new avenue for modifying their structural characteristics for the adsorption and separation of hazardous materials, which will undoubtedly direct future work, is also summarized.

Facile synthesis of hydroxylated triazine-based magnetic microporous organic network for ultrahigh adsorption of phenylurea herbicides: An experimental and density-functional theory study

Microporous organic networks (MONs) are highly porous materials that are particularly useful in analytical chemistry. However, the use of these materials is often limited by the functional groups available on their surface. Here, we described the polymerization of a sea urchin-like structure material at ambient temperature, that was functionalized with hydroxyl, carboxyl, and triazine groups and denoted as OH-COOH-MON-TEPT. A substantial proportion of OH-COOH-MON-TEPT was intricately decorated EDA-Fe3O4, creating a well-designed configuration (EDA-Fe3O4 @OH-COOH-MON-TEPT-EDC) for superior adsorption of the target analytes phenylurea herbicides (PUHs) via magnetic solid-phase extraction (MSPE). The proposed method showed remarkably low limits of detection ranging from 0.03 to 0.22 ng·L-1. Experimental investigations and theoretical analyses unveiled the adsorption mode between EDA-Fe3O4 @OH-COOH-MON-TEPT-EDC and PUHs. These findings establish a robust foundation for potential applications of EDA-Fe3O4 @OH-COOH-MON-TEPT-EDC in the analysis of various polar contaminants.

Design and preparation of fluorescent covalent organic frameworks for biological sensing

Covalent organic frameworks (COFs) are a new class of functional solids featuring several fantastic structural characteristics, including a great diversity of building units and cross-linking patterns, precise integration of building blocks, and adjustable topology of porous architecture. In addition to the above features, some COF samples are constructed with high-density conjugated fragments, which have unique potential advantages in fluorescence imaging, and thus may have great potential applications in bioimaging. Herein, this article summarizes the recent progress in the design and preparation of fluorescent covalent organic frameworks. We investigate the systemic correlation between the structural qualities of COF networks and biological sensors. Finally, the significant advantages, major challenges, and future opportunities of fluorescent covalent organic frameworks are discussed for the development of next-generation porous materials for sensing applications.

Pore Space Partition Synthetic Strategy in Imine-linked Multivariate Covalent Organic Frameworks

Partitioning the pores of covalent organic frameworks (COFs) is an attractive strategy for introducing microporosity and achieving new functionality, but it is technically challenging to achieve. Herein, we report a simple strategy for partitioning the micropores/mesopores of multivariate COFs. Our approach relies on the predesign and synthesis of multicomponent COFs through imine condensation reactions with aldehyde groups anchored in the COF pores, followed by inserting additional symmetric building blocks (with C2 or C3 symmetries) as pore partition agents. This approach allowed tetragonal or hexagonal pores to be partitioned into two or three smaller micropores, respectively. The synthesized library of pore-partitioned COFs was then applied for the capture of iodine pollutants (i.e., I2 and CH3I). This rich inventory allowed deep exploration of the relationships between the COF adsorbent composition, pore architecture, and adsorption capacity for I2 and CH3I capture under wide-ranging conditions. Notably, one of our developed pore-partitioned COFs (COF 3-2P) exhibited greatly enhanced dynamic I2 and CH3I adsorption performances compared to its parent COF (COF 3) in breakthrough tests, setting a new benchmark for COF-based adsorbents. Results present an effective design strategy toward functional COFs with tunable pore environments, functions, and properties.

Membranes based on Covalent Organic Frameworks through Green and Scalable Interfacial Polymerization using Ionic Liquids for Antibiotic Desalination

Covalent organic framework (COF) membranes featuring uniform topological structures and devisable functions, show huge potential in water purification and molecular separation. Nevertheless, the inability of uniform COF membranes to be produced on an industrial scale and their nonenvironmentally friendly fabrication method are the bottleneck preventing their industrial applications. Herein, we report a new green and industrially adaptable scraping-assisted interfacial polymerization (SAIP) technique to fabricate scalable and uniform TpPa COF membranes. The process used non-toxic and low-volatility ionic liquids (ILs) as organic phase instead of conventional organic solvents for interfacial synthesis of TpPa COF layer on a support membrane, which can simultaneously achieve the purposes of (i) improving the greenness of membrane-forming process and (ii) fabricating a robust membrane that can function beyond the conventional membranes. This approach yields a large-area, continuous COF membrane (19×25 cm2 ) with a thickness of 78 nm within a brief period of 2 minutes. The resulting membrane exhibited an unprecedented combination of high permeance (48.09 L m-2 h-1 bar-1 ) and antibiotic desalination efficiency (e.g., NaCl/adriamycin separation factor of 41.8), which is superior to the commercial benchmarking membranes.

Hydrogen Isotope Effect Endows a Breakthrough in Photoluminescent Covalent Organic Frameworks

Luminescent covalent organic frameworks (LCOFs) have emerged as indispensable candidates in various applications due to their greater tunable emitting properties and structural robustness compared to small molecule emitters. An unsolved issue in this area is developing highly luminescent LCOFs of which the nonradiative quenching pathways were suppressed as much as possible. Here, a robust aminal-linked COF (DD-COF) possessing perdeuterated light-emitting monomers was designed and synthesized. The solid-state photoluminescence quantum yield of the DD-COF reaches 81%, significantly outcompeting all state-of-the-art LCOFs reported so far. The exceptional luminescent efficiency is attributed to the inhibition of different pathways of nonradiative decay, especially from bond vibrations where only substitution by a heavier isotope with a lower zero-point vibration frequency works. Furthermore, the prepared deuterated COF not only boosts higher photostability under UV irradiation but also enables superior fluorescence sensing performance for iodine detection compared to nondeuterated COF.

Crystalline, Porous Helicene Covalent Organic Frameworks

Helicenes are a class of fascinating chiral helical molecules with rich chemistry developed continuously over the past 100 years. Their helical, conjugated, and twisted structures make them attractive for constructing molecular systems. However, studies over the past century are mainly focused on synthesizing helicenes with increased numbers of aromatic rings and complex heterostructures, while research on inorganic, organic, and polymeric helicene materials is still embryonic. Herein, we report the first examples of helicene covalent organic frameworks, i.e., [7]Helicene sp2 c-COF-1, by condensing [7]Helicene dialdehyde with trimethyl triazine via the C=C bond formation reaction under solvothermal conditions. The resultant [7]Helicene sp2 c-COF-1 exhibits prominent X-ray diffraction peaks and assumes a highly ordered 2D lattice structure originated from the twisted configuration of [7]Helicene unit. The C=C linked [7]Helicene sp2 c-COF-1 materials exhibited extended π conjugation and broadly tuned their absorption, emission, redox activity, photoconductivity, and light-emitting activity, demonstrating rich multifunctionalities and great potentials in developing various applications. This work opens a way to a new family of COFs as well as helicene materials, enabling the exploration of unprecedented π architectures and properties.

Highly luminescent olefin-linked covalent organic frameworks

A new olefin-linked covalent organic framework (COF) was developed using 1,3,5-triformylbenzene (TFB) and tetraethyl p-xylylenediphosphonate (TEXDP) as building blocks through a Horner-Wadsworth-Emmons reaction. By combination of the aromatic columnar ordering and high conjugation, the resulting TFB-TEXDP-COF exhibits a fluorescence quantum yield of up to 41%, which constitutes the new record value among COFs.

In Situ Generated Dye@MOF/COF Heterostructure for Fluorescence Detection of Chloroquine Phosphate and Folic Acid via Different Luminescent Channels

Metal-organic framework (MOF) and covalent-organic framework (COF) hybrid materials can combine the unique properties of MOF and COF components, and their applications in fluorescence sensing have attracted more and more attention. Herein, ZIF-90 is grown on 3D-COF by a simple in situ growing method in which the 7-amino-4-methylcoumarin (AMC) is encapsulated in ZIF-90 to construct a fluorescent sensor. Chloroquine phosphate (CQP) can coordinate with Zn2+ to decompose the ZIF-90 and release AMC. At 365 nm excitation, the ratiometric fluorescence signal AMC/3D-COF (I430/I598) increases linearly with CQP in a linear range of 4 × 10-5 to 4 × 10-4 M in urine. Under 340 nm excitation, quantitative analysis of CQP in the serum (3 × 10-6 to 4 × 10-5 M) is based on the fluorescence intensity of Zn-CQP/3D-COF (I384/I598). In addition, AMC@ZIF-90/3D-COF (1) exhibits high anti-interference and selectivity in sensing of FA with a "turn off" mode, with a correlation range of 1 × 10-5 to 1 × 10-3 M. The fluorescence color changes triggered by CQP under different excitation conditions, and the different fluorescence responses caused by CQP make it a highly secure anticounterfeiting platform. The synthesized dye@MOF/COF hybrids not only provide a new way to integrate multiple emission to design fluorescent probes for differentiation detection but also offer ideas for the design of anticounterfeiting platforms.

Superstructure-Induced Hierarchical Assemblies for Nanoconfined Photocatalysis

Most attempts to synthesize supramolecular nanosystems are limited to a single mechanism, often resulting in the formation of nanomaterials that lack diversity in properties. Herein, hierarchical assemblies with appropriate variety are fabricated in bulk via a superstructure-induced organic-inorganic hybrid strategy. The dynamic balance between substructures and superstructures is managed using covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) as dual building blocks to regulate the performances of hierarchical assemblies. Significantly, the superstructures resulting from the controlled cascade between COFs and MOFs create highly active photocatalytic systems through multiple topologies. Our designed tandem photocatalysis can precisely and efficiently regulate the conversion rates of bioactive molecules (benzo[d]imidazoles) through competing redox pathways. Furthermore, benzo[d]imidazoles catalyzed by such supramolecular nanosystems can be isolated in yields ranging from 70 % to 93 % within tens of minutes. The multilayered structural states within the supramolecular systems demonstrate the importance of hierarchical assemblies in facilitating photocatalytic propagation and expanding the structural repertoire of supramolecular hybrids.

Covalent organic frameworks: linkage types, synthetic methods and bio-related applications

Covalent organic frameworks (COFs) are composed of small organic molecules linked via covalent bonds, which have tunable mesoporous structure, good biocompatibility and functional diversities. These excellent properties make COFs a promising candidate for constructing biomedical nanoplatforms and provide ample opportunities for nanomedicine development. A systematic review of the linkage types and synthesis methods of COFs is of indispensable value for their biomedical applications. In this review, we first summarize the types of various linkages of COFs and their corresponding properties. Then, we highlight the reaction temperature, solvent and reaction time required by different synthesis methods and show the most suitable synthesis method by comparing the merits and demerits of various methods. To appreciate the cutting-edge research on COFs in bioscience technology, we also summarize the bio-related applications of COFs, including drug delivery, tumor therapy, bioimaging, biosensing and antimicrobial applications. We hope to provide insight into the interdisciplinary research on COFs and promote the development of COF nanomaterials for biomedical applications and their future clinical translations.

Linkages Make a Difference in the Photoluminescence of Covalent Organic Frameworks

Covalent organic frameworks (COFs) with structural designability and tunability of photophysical properties enable them to be a promising class of organic luminescent materials by incorporating well-designed fluorescent units directly into the periodic skeletons. The photophysical properties of COFs are mainly affected by the structural features, which determine the conjugation degree, charge delocalization ability, and exciton dynamics of COFs. To understand the relationship between COF structures and their photophysical properties, two COFs with the same pyrene chromophore units but different linkages (imine or vinylene) were designed and synthesized. Interestingly, different linkages endow COFs with huge differences in solid-state photoluminescence quantum yield (PLQY) for imine- and vinylene-linked pyrene-based COFs, which possess PLQY values of 0.34 % and 15.43 %, respectively. The femtosecond-transient absorption spectra and time-dependent density functional theory reveal the different charge-transfer pathways in imine- and vinylene-linked COFs, which influence the exciton relaxation way and fluorescence intensity. In addition, an effective white-light device was obtained by coating the vinylene-linked COF on a light-emitting diode strip.

Molecular Insertion: A Master Key to Unlock Smart Photoelectric Responses of Covalent Organic Frameworks

Covalent organic frameworks (COFs) show potentials in prominent photoelectric responses by judicious structural design. However, from the selections of monomers and condensation reactions to the synthesis procedures, the acquisition of photoelectric COFs has to meet overmuch high conditions, limiting the breakthrough and modulation in photoelectric responses. Herein, the study reports a creative "lock-key model" based on molecular insertion strategy. A COF with suitable cavity size, TP-TBDA, is used as the host to load guests. Merely through the volatilization of mixed solution, TP-TBDA and guests can be spontaneously assembled via non-covalent interactions (NCIs) to produce molecular-inserted COFs (MI-COFs). The NCIs between TP-TBDA and guests acted as a bridge to facilitate charge transfer in MI-COFs, unlocking the photoelectric responses of TP-TBDA. By exploiting the controllability of NCIs, the MI-COFs can realize the smart modulation of photoelectric responses by simply changing the guest molecule, thus avoiding the arduous selection of monomers and condensation reactions required by conventional COFs. The construction of molecular-inserted COFs circumvents complicated procedures for achieving performance improvement and modulation, providing a promising direction to construct late-model photoelectric responsive materials.

Chiral Materials: Progress, Applications, and Prospects

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Lanthanide Functionalized Covalent Organic Frameworks Hybrid Materials for Luminescence Responsive Chemical Sensing

Covalent organic frameworks (COFs) possess several unique features of structural and functional chemistry, together with other modular photophysical performance, which make them candidates for luminescence responsive chemical sensing. Lanthanide (Ln3+ ) functionalized COFs hybrid materials still keep the parent COFs' virtues and also embody the abundant multiple luminescence response with both COFs and Ln3+ ions or other guest species. In this review, the summary is highlighted on the lanthanide functionalized COFs hybrid materials and their relevant systems for luminescence responsive chemical sensing. It is subdivided into five sections involving the three main topics. Firstly, the basic knowledges of COFs materials related to the luminescence responsive chemical sensing are introduced (including three sections), involving the chemistry, application and post-synthetic modification (PSM) of COFs, the luminescence and luminescence responsive chemical sensing, and the luminescence responsive chemical sensing of non-lanthanide functionalized COFs hybrids materials. Secondly, the systematic progresses are outlined on the lanthanide functionalized COFs hybrid materials in luminescence responsive chemical sensing, which is the emphasis for this review. Finally, the conclusion and prospect are given.

Covalent organic frameworks for direct photosynthesis of hydrogen peroxide from water, air and sunlight

Solar-driven photosynthesis is a sustainable process for the production of hydrogen peroxide, the efficiency of which is plagued by side reactions. Metal-free covalent organic frameworks (COFs) that can form suitable intermediates and inhibit side reactions show great promise to photo-synthesize H₂O₂. However, the insufficient formation and separation/transfer of photogenerated charges in such materials restricts the efficiency of H₂O₂ production. Herein, we provide a strategy for the design of donor-acceptor COFs to greatly boost H₂O₂ photosynthesis. We demonstrate that the optimal intramolecular polarity of COFs, achieved by using suitable amounts of phenyl groups as electron donors, can maximize the free charge generation, which leads to high H₂O₂ yield rates (605 μmol g^-1 h^-1) from water, oxygen and visible light without sacrificial agents. Combining in-situ characterization with computational calculations, we describe how the triazine N-sites with optimal N 2p states play a crucial role in H₂O activation and selective oxidation into H₂O₂. We further experimentally demonstrate that H₂O₂ can be efficiently produced in tap, river or sea water with natural sunlight and air for water decontamination.

Chiral Ionic Covalent Organic Framework as an Enantioselective Fluorescent Sensor for Phenylalaninol Determination

Phenylalaninol (PAL) is a significant chemical intermediate widely utilized in drug development and chiral synthesis, for instance, as a reactant for bicyclic lactams and oxazoloisoindolinones. Since the absolute stereochemical configuration significantly impacts biological action, it is crucial to evaluate the concentration and enantiomeric content of PAL in a quick and convenient manner. Herein, an effective PAL enantiomer recognition method was reported based on a chiral ionic covalent organic framework (COF) fluorescent sensor, which was fabricated via one-step postquaternization modification of an achiral COF by (1R, 2S, 5R)-2-isopropyl-5-methylcyclohexyl-carbonochloridate (L-MTE). The formed chiral L-TB-COF can be applied as a chiral fluorescent sensor to recognize the stereochemical configuration of PAL, which displayed a turn-on fluorescent response for R-PAL over that of S-PAL with an enantioselectivity factor of 16.96. Nonetheless, the single L-MTE molecule had no chiral recognition ability for PAL. Moreover, the ee value of PAL can be identified by L-TB-COF. Furthermore, density functional theory (DFT) calculations demonstrated that the chiral selectivity came from the stronger binding affinity between L-TB-COF and R-PAL in comparison to that with S-PAL. L-TB-COF is the first chiral ionic COF employed to identify chiral isomers by fluorescence. The current work expands the range of applications for ionic COFs and offers fresh suggestions for creating novel chiral fluorescent sensors.