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The irreversible locking of reversible imine linkages in COFs into quinoline-4-carboxylic esters has been achieved for the first time through the Doebner–von Miller reaction. The high conversion efficiency and broad scope were demonstrated by synthesizing four quinoline-4-carboxylic ester-linked COFs (QCE-COFs). Subsequently, this approach was applied to create the chiral QCE-COF-Men containing L -menthol. Remarkably, QCE-COF-Men was found to release the flavorant L -menthol at elevated temperature by cleaving the weak ester bond without destroying the quinoline skeleton. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are emerging as promising heterogeneous photocatalysts for organic transformations, owing to their fascinating optical properties, excellent recyclability, and customizable chemical structures. To maximize the photocatalytic activity of COFs, various strategies have been explored, including metal complexation, construction of donor‐acceptor structures, modification of functional groups, hybridization with inorganic semiconductors, and linkage conversion. Among these, linkage conversion has proved to be particularly effective, driving the production of numerous value‐added organic chemicals. In this concept article, we present a comprehensive overview of the latest advancements in linkage conversion and highlight the most enlightening examples that have adopted such a strategy to boost the photocatalytic capabilities of COFs for organic transformations. It is anticipated that this concept will assist researchers in designing novel COFs with multifunctional linkages, paving the way towards their broader application in organic synthesis. [ABSTRACT FROM AUTHOR]

In the field of photocatalytic organic transformations, the spotlight is shining on covalent organic frameworks (COFs), the widespread utilization of which, however, is plagued by their high exciton dissociation energy (Eb). To address this issue, herein a facile strategy was developed to synthesize an ionic COF (NQ-COFD4-Me) with robust stability by grafting methyl groups onto the N ends of non-substituted quinoline (NQ) linkages. Ionization induced a strong polarization effect, giving rise to broad absorption in the visible light region and reduced Eb (78 meV versus 89 meV). With efficient generation, spatial separation, and transport of photogenerated charge carriers, the production of ˙O2− was accelerated over NQ-COFD4-Me. As a result, when applied in ˙O2− mediated photocatalytic benzimidazole synthesis, NQ-COFD4-Me achieved high yields of target products (91–98%), much better than those of the charge neutral counterpart NQ-COFD4. In addition, the wide substrate adaptability scope and excellent recyclability of NQ-COFD4-Me were also attested. [ABSTRACT FROM AUTHOR]

Inspired by the bidentate coordination chemistry of metal ions, we incorporated hydroxyl (OH) and methoxy (OMe) groups into the skeleton of imine-linked COFs to improve their protonation ability via intramolecular hydrogen bonds (O–H⋯N＝C). In comparison with the pristine COFs possessing monodentate nitrogen coordination sites, OH and OMe functionalized COFs with (N,O)-bidentate chelating sites exhibited up to 13.8 times faster photocatalytic hydrogen evolution rates (HERs). [ABSTRACT FROM AUTHOR]

Due to the advantages of high energy density and improved safety properties, Li metal batteries with gel polymer electrolyte (GPE) have drawn much attention in recent years. Herein, a novel gel thermoplastic polyurethane (TPU) electrolyte filled with ultrafine hydrophilic–lipophilic TiO2 nanoparticles was successfully prepared by using a phase separation technology. The gel electrolyte can protect the battery against the leakage of liquid electrolyte by means of its strong interaction with Li+ and solvents. This kind of GPE shows an ionic conductivity of 1.59 mS cm−1 and an electrochemical window of 4.3 V (vs. Li/Li+) at room temperature. Robust TiO2 nanoparticles embedded into TPU matrix can effectively block dendrite puncture and, besides, greatly improve the thermal stability of GPE. The cycling performance, rate capability and mechanical properties guarantee the reliability of the as-prepared GPE in Li-ion batteries. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have emerged as efficient heterogeneous photocatalysts for a wide range of relatively simple organic reactions, whereas their application in complex organic transformations, like site-selective functionalization of unactivated C-H bonds, is underexplored, which can be mainly attributed to the lack of highly active organophotocatalytic cores. Herein through bonding oxygen atoms at the N-terminus of quinolines in nonsubstituted quinoline-linked COFs (NQ-COFs), we successfully realized the embedding of active hydrogen atom transfer (HAT) moieties into the skeleton of COFs. This novel designed COF (NQ-COF E5 -O), serving as both an excellent photosensitizer and HAT catalyst, exhibited much higher efficiency in C-H functionalization than the corresponding NQ-COF E5 . Specially, we evaluated the photocatalytic performance of NQ-COF E5 -O on ten different substrates, including quinolines, benzothiazole, and benzoxazole, all of which were transferred to desired products in moderate to high yields (up to 93 %). Furthermore, the as-synthesized NQ-COF E5 -O displayed excellent photostability and could be reused with negligible loss of activity for five catalytic cycles., (© 2023 Wiley-VCH GmbH.)

Exploring new routes to lock the dynamic C=N bonds in imine-linked covalent organic frameworks (COFs) is highly desired for enhancing their stability and functionality. Herein, a novel C=N bridge locking strategy via rhodium-catalyzed [4+2] annulation is developed to construct nonsubstituted quinoline-linked COFs (NQ-COFs). The notable feature of this strategy includes high C=N conversion efficiency, oxidant-free, and generality for synthesis of a variety of NQ-COFs with high chemical stability. Particularly, after post-synthetic modification, the crystallinity, topology, and porosity of pristine imine-linked COFs are well retained. When used as photocatalysts, NQ-COFs display better visible light absorption and carriers' separation efficiency due to enhanced in-plane π conjugation ability, as well as more facile generation of superoxide anion radicals than their counterparts, thus leading to efficient synthesis of 2,4,6-tris(aryl)pyridines, benzimidazole, and sulfoxide derivatives., (© 2022 Wiley-VCH GmbH.)

By using the observational data obtained over the Bohai sea in Aug.-Sep., 2000, the variation characteristics of NOx, O3, SO2 and CO concentrations were firstly shown. The effects of solar radiation and weather conditions on the trace concentrations were analyzed. SO2 concentration was very stable, its' average value was about 0.006 mg.m-3. O3 concentration was mainly controlled by solar radiation. The concentration of CO and NOx was around 2.5-3.5 mg.m-3 and 0.1 mg.m-3, respectively, in weak weathers. Typhoon weather may made their concentrations increasing abruptly in a short time. The distinct differences of the pollutant concentrations between land and sea were also revealed, and the air quality over the Bohai sea in summer season was assessed based on the measurements.