Construction of acid-base bifunctional covalent organic frameworks via Doebner reaction for catalysing cascade reaction

Pd NP-loaded covalent organic framework for pH-switched Pickering emulsion catalytic dechlorination

Quinoline carboxylic acid-linked and Pd nanoparticle (NP)-loaded COF nanospheres were constructed via a three-component one-pot Doebner reaction and post-synthetic metalation. The obtained Pd@DhaTAPB-COOH solid stabilizer can greatly promote the pH-switched recyclable Pickering interfacial dechlorination reaction, which sheds light on the bright future of smart Pickering emulsion catalysis.

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy

Nanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function-oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF-based anticancer nanomedicines and bringing COFs closer to clinical trials.

Robust links in photoactive covalent organic frameworks enable effective photocatalytic reactions under harsh conditions

Developing heterogeneous photocatalysts for the applications in harsh conditions is of high importance but challenging. Herein, by converting the imine linkages into quinoline groups of triphenylamine incorporated covalent organic frameworks (COFs), two photosensitive COFs, namely TFPA-TAPT-COF-Q and TFPA-TPB-COF-Q, are successfully constructed. The obtained quinoline-linked COFs display improved stability and photocatalytic activity, making them suitable photocatalysts for photocatalytic reactions under harsh conditions, as verified by the recyclable photocatalytic reactions of organic acid involving oxidative decarboxylation and organic base involving benzylamine coupling. Under strong oxidative condition, the quinoline-linked COFs show a high efficiency up to 11831.6 μmol·g-1·h-1 and a long-term recyclable usability for photocatalytic production of H2O2, while the pristine imine-linked COFs are less catalytically active and easily decomposed in these harsh conditions. The results demonstrate that enhancing the linkage robustness of photoactive COFs is a promising strategy to construct heterogeneous catalysts for photocatalytic reactions under harsh conditions.

Insight into the In-Situ Encapsulation-Reassembly Strategy To Fabricate PW12@NiCo-LDH Acid-Base Bifunctional Catalysts

Acid-base bifunctional catalysts have attracted increasing attention due to the improved overall efficiency of synthetic reactions. Herein, we reported the successful fabrication of a PW₁₂@NiCo-LDH acid-base bifunctional catalyst by using the in-situ encapsulation-reassembly strategy. The evolution process of morphology and structure was monitored carefully by various time-dependent characterizations. X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculations demonstrated that the terminal oxygen of PW₁₂ in PW₁₂@NiCo-LDH preferred to assemble with the oxygen vacancies on NiCo-LDH. When applied for deacetalization-Knoevenagel condensation, the PW₁₂@NiCo-LDH displayed >99% conversion of benzaldehyde dimethyl acetal (BDMA) and >99% yield of ethyl α-cyanocinnamate (ECC). Moreover, PW₁₂@NiCo-LDH can be recycled at least 10 cycles without obvious structural change, which can be attributed to the confinement of PW₁₂ into the NiCo-LDH nanocage. Such excellent catalytic activity of PW₁₂@NiCo-LDH was benefited from the short mass transfer pathway between acid sites and base sites, which was caused by the stable assembly between PW₁₂ and NiCo-LDH.

Facile Synthesis of Quinolinecarboxylic Acid-Linked Covalent Organic Framework via One-Pot Reaction for Highly Efficient Removal of Water-Soluble Pollutants

To efficiently eliminate highly polar organic pollutants from water has always been a difficult issue, especially in the case of ultralow concentrations. Herein, we present the facile synthesis of quinolinecarboxylic acid-linked COF (QCA-COF) via the Doebner multicomponent reaction, possessing multifunction, high specific surface area, robust physicochemical stability, and excellent crystallinity. The marked feature lies in the quinolinyl and carboxyl functions incorporated simultaneously to QCA-COF in one step. The major cis-orientation of carboxyl arms in QCA-COF was speculated by powder X-ray diffraction and total energy analysis. QCA-COF demonstrates excellent adsorption capacity for water-soluble organic pollutants such as rhodamine B (255.7 mg/g), methylene blue (306.1 mg/g), gentamycin (338.1 mg/g), and 2,4-dichlorophenoxyacetic acid (294.1 mg/g) in water. The kinetic adsorptions fit the pseudo-second order model and their adsorption isotherms are Langmuir model. Remarkably, QCA-COF can capture the above four water-soluble organic pollutants from real water samples at ppb level with higher than 95% removal efficiencies and excellent recycling performance.

Construction of Covalent Organic Frameworks via a Visible-Light-Activated Photocatalytic Multicomponent Reaction

Multicomponent reactions (MCRs), as a powerful one-pot combinatorial synthesis tool, have been recently applied to the synthesis of covalent organic frameworks (COFs). Compared with the thermally driven MCRs, the photocatalytic MCR-based COF synthesis has not yet been investigated. Herein, we first report the construction of COFs by a photocatalytic multicomponent reaction. Upon visible-light irradiation, a series of COFs with excellent crystallinity, stability, and permanent porosity are successfully synthesized via photoredox-catalyzed multicomponent Petasis reaction under ambient conditions. Additionally, the obtained Cy-N₃-COF exhibits excellent photoactivity and recyclability for the visible-light-driven oxidative hydroxylation of arylboronic acids. The concept of photocatalytic multicomponent polymerization not only enriches the methodology for COF synthesis but also opens a new avenue for the construction of COFs that might not be possible with the existing synthetic methods based on thermally driven MCRs.

Converting an amorphous covalent organic polymer to a crystalline covalent organic framework mediated by a repairing agent

We herein report a new approach to converting an amorphous covalent organic polymer to a crystalline heteropore covalent organic framework (COF), which is promoted by using an additive for structure repair. This provides a new method for the construction of COFs from cross-linked polymers.

Integrating Bifunctionality and Chemical Stability in Covalent Organic Frameworks via One-Pot Multicomponent Reactions for Solar-Driven H2O2 Production

Multicomponent reactions (MCRs) can be used to introduce different functionalities into highly stable covalent organic frameworks (COFs). In this work, the irreversible three-component Doebner reaction is utilized to synthesize four chemically stable quinoline-4-carboxylic acid DMCR-COFs (DMCR-1-3 and DMCR-1NH) equipped with an acid-base bifunctionality. These DMCR-COFs show superior photocatalytic H₂O₂ evolution (one of the most important industrial oxidants) compared to the imine COF analogue (Imine-1). This is achieved with sacrificial oxidants but also in pure water and under an oxygen or air atmosphere. Furthermore, the DMCR-COFs show high photostability, durability, and recyclability. MCR-COFs thus provide a viable materials' platform for solar to chemical energy conversion.

Construction of Covalent Organic Frameworks via Multicomponent Reactions

Multicomponent reactions (MCRs) combine at least three reactants to afford the desired product in a highly atom-economic way and are therefore viewed as efficient one-pot combinatorial synthesis tools allowing one to significantly boost molecular complexity and diversity. Nowadays, MCRs are no longer confined to organic synthesis and have found applications in materials chemistry. In particular, MCRs can be used to prepare covalent organic frameworks (COFs), which are crystalline porous materials assembled from organic monomers and exhibit a broad range of properties and applications. This synthetic approach retains the advantages of small-molecule MCRs, not only strengthening the skeletal robustness of COFs, but also providing additional driving forces for their crystallization, and has been used to prepare a series of robust COFs with diverse applications. The present perspective article provides the general background for MCRs, discusses the types of MCRs employed for COF synthesis to date, and addresses the related critical challenges and future perspectives to inspire the MCR-based design of new robust COFs and promote further progress in this emerging field.

Covalent organic frameworks and multicomponent reactions: an endearing give-and-take relationship

Covalent organic frameworks (COFs) are porous and crystalline materials which are assembled by dynamic covalent bonds with two- or three-dimensional (2D or 3D) features. Unlike other polymers, COFs have significant...