Knoevenagel Condensation Reaction Research Articles

A novel multi-stimuli responsive fluorescence liquid crystal material with aggregation-induced emission effect

ABSTRACT Scientists are faced with a formidable problem in improving the smart properties of multi-stimuli responsive fluorescent materials. Here, we integrated two kinds of stimuli-responsive materials: aggregation-induced emission (AIE) and liquid crystals (LCs) into one system. An AIE-active fluorescence liquid crystal compound of α-cyanodistyrene derivate Py-CN-LBM8 was synthesised using knoevenagel condensation reaction. Its AIE effect, LC behaviour, multi-stimuli responsive properties and mechanisms were investigated by polarised optical microscopes (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), UV-visible (UV-vis) absorption spectra and photoluminescence (PL) spectra. The results showed that Py-CN-LBM8 exhibited significant physical response to external stimuli including temperature, mechanical force, solvent, pH and trace water. This work provided a strategy for designing new multi-stimuli responsive materials and made it possible to apply in the multifunction anti-counterfeit, sensor and information storage fields.

Study of N‐methyl‐5‐nitroindazolylacrylonitriles as a Function of Quantum Parameters Employing Density Function Theory Methods: Comparative Theoretical Study and Nonlinear Optical Properties

AbstractThe synthesis of N‐methyl‐5‐nitroindazolylacrylonitriles 2 a–l by a Knoevenagel condensation reaction with a series of aldehydes in the presence of piperidine allowed the preparation of the desired products the yields are good to excellent. N‐Methyl‐5‐nitroindazolylacrylonitriles (2 a–l) were verified by 1H, 13C NMR and mass spectrometry. In this current work, the reactivity indices defined within the Conceptual DFT of the targeted molecules through DFT/B3LYP/6‐311G(d,p) calculations were studied. The 1H NMR, UV‐vis and IR spectroscopy chemical shifts of all synthesized 5‐nitroindazoles 2 a–l were calculated and the results were compared to the results of the experimental data. In this series of compounds, the 2 e has the lowest hyperpolarizability, which results being the most stable and having the least response to nonlinear optics (NLO). In contrast, the compound 2 l has the highest hyperpolarizability, which fallouts being the least stable and having a high response to NLO. Every chemical has a significant three‐dimensional p‐electronic delocalization, which is crucial for understanding NLO responses.

Diazo-coupled porous organic polymers as efficient catalysts for metal-free Henry and Knoevenagel reactions

Owing to linkage and building block diversity, Porous Organic Polymers (POPs) are versatile materials with high potential in organic catalysis. Herein, nitrogen-rich POPs bearing –OH phenolic groups were synthesized via the diazo-coupling reactions between phloroglucinol and benzidine (PgBd-POP), and between 1,3,5-tris(4-aminophenyl)triazine and 4,4'-[1,1′-biphenyl]-4,4′-diylbis(diazene-2,1-diyl))diphenol (TAPT-Bd(PhOH)2-POP), under mild reaction conditions. The mesoporous polymers exhibited a BET surface area of 276 ± 4 m2 g−1 and 1.94 ± 0.06 m2 g−1, and chemical stability up to 315 °C and 330 °C, respectively. Both POPs were used as catalysts in metal-free Henry and Knoevenagel condensation reactions between aromatic aldehydes and nitromethane and ethyl cyanoacetate, respectively, under mild conditions. PgBd-POP showed a remarkable efficiency of up to 99% conversion and >99% selectivity, for the Henry nitroaldol reaction between 4-nitrobenzaldehyde and nitromethane, after only 1 h at room temperature, whereas TAPT-Bd(PhOH)2-POP generally exhibited the highest catalytic activity towards the Knoevenagel reaction, with up to 99% conversion for the condensation of 4-nitrobenzaldehyde with ethyl cyanoacetate, after 1 h at room temperature. These results confirm the potential of this class of porous materials as green catalysts for organic reactions.

An Updated Review on Recent Advancements in the Diverse Biological Applications of Medicinally Privileged Scaffold: Chalcone and its derivatives

Fused heterocyclic compounds rank among the most significant systems in medicinal chemistry because of their wide-ranging biological effects. Among the various class of compounds, chalcones and their derivatives are found to be one of the important classes in the field of synthetic and pharmaceutical chemistry. These derivatives are mainly synthesized by means of Claisen-Schmidt condensation, Crossed Aldol condensation and Knoevenagel condensation reactions, which provides wider applications in the field of medicine. Due to the broader biological applications like antimicrobial, anticancer, antimalarial, antioxidant, anti-inflammatory, antitubercular, antidiabetic, antileishmanial, anti-vitiligo and neuroprotective properties, these derivatives extended their role in coordination chemistry and also act as intermediates for the synthesis of various organic derivatives containing isoxazole, pyrazole, pyrimidine, naphthalene, indole, polyamine and other moieties as hybrid molecules. The present review discusses the biological applications of various chalcone derivatives. Due to their easiest way of synthesis, nowadays, these types of derivatives were tried for various ailments and by means of implementing various greener chemistry approaches, novel and potent derivatives can be synthesized and applied for various applications. Thus, this review will be helpful for the design of potent chalcone derivatives for numerous applications in the future. Keywords: Chalcones, 1,3-diphenyl-2-propene-1-one, microbial properties, anticancer, antioxidant, neuroprotective and biological applications

An expedient synthesis of C3-arylidene-oxindole derivatives using calcite nanoflowers as an efficient heterogeneous catalyst

α-β unsaturated heterocyclic compounds such as C3-arylidene-oxindoles, with five-member rings containing nitrogen, have an important role in the realm of medicine. This study aims to synthesize the C3-arylindene-oxindoles derivative compounds using calcite nanoflowers (CaCO3 NFs) as a heterogeneous catalyst for the first time. These CaCO3 NFs prepared by the thermal decomposition method, which is an active and reusable catalyst for stereospecific Knoevenagel condensation reaction between 2-oxindole and aromatic aldehyde under different solvent conditions like water, ethyl alcohol, and 50% aqueous ethyl alcohol. This catalytic method is employed with a wide range of aromatic aldehydes to produce high yields of C3-arylidene-oxindoles (93-99%), with stereo-specifically E-isomers (100%) for 50% alcohol and alcohol as a solvent.

Heterometallic YbCo–Organic Framework for Efficiently Catalyzing Cycloaddition of CO2 with Epoxides and Knoevenagel Condensation

Due to the excellent catalytic performance of Co-MOFs and Ln-MOFs on the chemical fixation of CO2, the self-assembly of microporous heterometallic compounds with the aid of designed functional ligands is carried out in our group. Herein, the solvothermal self-assembly of Co2+, Yb3+, and 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H5BDCP) generated a rarely reported {CoYb}n-chain-based framework of {[CoYb(BDCP)(H2O)]·3DMF·3H2O}n (NUC-70) with quasi-nanoporous channels (aperture ca. 11.4 Å) shaped by six rows of {CoYb(CO2)5(H2O)}n nodes. To the best of our knowledge, this is a rare 3d-4f heterometallic chain of {CoYb(CO2)5(H2O)}n with a staggered arrangement of Co2+ and Yb3+. After removing the associated water molecules, NUC-70a possesses the excellent characteristics of a large specific surface area, unsaturated open metal sites of Co2+ and Yb3+ as Lewis acid sites, and high heat/water-resistant physicochemical properties. Catalytic experiments showed that NUC-70a possessed a high catalytic activity on the cycloaddition reactions of epoxides with CO2 under mild conditions. Furthermore, the experiments performed confirmed that the Knoevenagel condensation reactions of aldehydes and malononitrile could be efficiently catalyzed by NUC-70a. This work illustrates that characteristic ligand design plays a key role in the self-assembly of MOFs with specific functions.

Ln-substituted polytungstates as efficient hetergeneous catalysts for Knoevenagel condensation reaction

Three isomorphic polytungstates, Cs9K18H10{[Sm2(H2O)4W4O10(AsW9O33)3]2(N(CH2PO3)2)}·46.5H2O (1), Cs10K9H18{[Eu2(H2O)4W4O10(AsW9O33)3]2(N(CH2PO3)2)}·41.5H2O (2), Cs10K9H18{[Gd2(H2O)4W4O10 (AsW9O33)3]2(N(CH2PO3)2)}·46H2O (3), have been successfully synthesized and characterized by routine methods, and demonstrated excellent catalytic activities in Knoevenagel condensation reaction as heterogeneous catalysts. Notably, catalyst 1 achieved higher reaction activity than catalysts 2 and 3, where a satisfactory reaction yield (95%) and high TON value (6380) could be obtained at moderate reaction condition. In addition, in the scale-up experiment, with the help of catalyst 1, 7.8 g benzaldehyde and 5.7 g ethyl cyanoacetate could transform into corresponding condensation product with a satisfactory yield (83%) and impressive TON value (13,883).

CO2-Switchable Hierarchically Porous Zirconium-Based MOF-Stabilized Pickering Emulsions for Recyclable Efficient Interfacial Catalysis.

Stimuli-responsive Pickering emulsions are recently being progressively utilized as advanced catalyzed systems for green and sustainable chemical conversion. Hierarchically porous metal-organic frameworks (H-MOFs) are regarded as promising candidates for the fabrication of Pickering emulsions because of the features of tunable porosity, high specific surface area and structure diversity. However, CO2-switchable Pickering emulsions formed by hierarchically porous zirconium-based MOFs have never been seen. In this work, a novel kind of the amine-functionalized hierarchically porous UiO-66-(OH)2 (H-UiO-66-(OH)2) has been developed using a post-synthetic modification of H-UiO-66-(OH)2 by (3-aminopropyl)trimethoxysilane (APTMS), 3-(2-aminoethylamino)propyltrimethoxysilane (AEAPTMS) and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEAEAPTMS), and employed as emulsifiers for the construction of Pickering emulsions. It was found that the functionalized H-UiO-66-(OH)2 could stabilize a mixture of toluene and water to give an emulsion even at 0.25 wt % content. Interestingly, the formed Pickering emulsions could be reversibly transformed between demulsification and re-emulsification with alternate addition or removal of CO2. Spectral investigation indicated that the mechanism of the switching is attributed to the reaction of CO2 with amino silane on the MOF and the generation of hydrophilic salts, leading to a reduction in MOF wettability. Based on this strategy, a highly efficient and controlled Knoevenagel condensation reaction has been gained by using the emulsion as a mini-reactor and the emulsifier as a catalyst, and the coupling of catalysis reaction, product isolation and MOF recyclability has become accessible for a sustainable chemical process.

Chitosan bead containing metal–organic framework encapsulated heteropolyacid as an efficient catalyst for cascade condensation reaction

Using cyclodextrin and chitosan that are bio-based compounds, a novel bi-functional catalytic composite is designed, in which metal–organic framework encapsulated phosphomolybdic acid was incorporated in a dual chitosan-cyclodextrin nanosponge bead. The composite was characterized via XRD, TGA, ICP, BET, NH3-TPD, FTIR, FE-SEM/EDS, elemental mapping analysis and its catalytic activity was examined in alcohol oxidation and cascade alcohol oxidation–Knoevenagel condensation reaction. It was found that the designed catalyst that possess both acidic feature and redox potential could promote both reactions in aqueous media at 55 °C and various substrates with different electronic features could tolerate the aforementioned reactions to furnish the products in 75–95% yield. Furthermore, the catalyst could be readily recovered and recycled for five runs with slight loss of the catalytic activity. Notably, in this composite the synergism between the components led to high catalytic activity, which was superior to each component. In fact, the amino groups on the chitosan served as catalysts, while cyclodextrin nanosponge mainly acted as a phase transfer agent. Moreover, measurement of phosphomolybdic acid leaching showed that its incorporation in metal–organic framework and bead structure could suppress its leaching, which is considered a drawback for this compound. Other merits of this bi-functional catalyst were its simplicity, use of bio-based compounds and true catalysis, which was proved via hot filtration.

Amide Functionalized Mesoporous MOF LOCOM-1 as a Stable Highly Active Basic Catalyst for Knoevenagel Condensation Reaction.

Acyl-amide is extensively used as functional group and is a superior contender for the design of MOFs with the guest accessible functional organic sites. A novel acyl-amide-containing tetracarboxylate ligand, bis(3,5-dicarboxy-pheny1)terephthalamide, has been successfully synthesized. The H4L linker has some fascinating attributes as follows: (i) four carboxylate moieties as the coordination sites confirm affluent coordination approaches to figure a diversity of structure; (ii) two acyl-amide groups as the guest interaction sites can engender guest molecules integrated into the MOF networks through H-bonding interfaces and have a possibility to act as functional organic sites for the condensation reaction. A mesoporous MOF ([Cu2(L)(H2O)3]·4DMF·6H2O) has been prepared in order to produce the amide FOS within the MOF, which will work as guest accessible sites. The prepared MOF was characterized by CHN analysis, PXRD, FTIR spectroscopy, and SEM analysis. The MOF showed superior catalytic activity for Knoevenagel condensation. The catalytic system endures a broad variety of the functional groups and presents high to modest yields of aldehydes containing electron withdrawing groups (4-chloro, 4-fluoro, 4-nitro), offering a yield > 98 in less reaction time as compared to aldehydes with electron donationg groups (4-methyl). The amide decorated MOF (LOCOM-1-) as a heterogeneous catalyst can be simply recovered by centrifugation and recycled again without a flagrant loss of its catalytic efficiency.

Open-Source Chromatographic Data Analysis for Reaction Optimization and Screening.

Automation and digitalization solutions in the field of small molecule synthesis face new challenges for chemical reaction analysis, especially in the field of high-performance liquid chromatography (HPLC). Chromatographic data remains locked in vendors' hardware and software components, limiting their potential in automated workflows and data science applications. In this work, we present an open-source Python project called MOCCA for the analysis of HPLC-DAD (photodiode array detector) raw data. MOCCA provides a comprehensive set of data analysis features, including an automated peak deconvolution routine of known signals, even if overlapped with signals of unexpected impurities or side products. We highlight the broad applicability of MOCCA in four studies: (i) a simulation study to validate MOCCA's data analysis features; (ii) a reaction kinetics study on a Knoevenagel condensation reaction demonstrating MOCCA's peak deconvolution feature; (iii) a closed-loop optimization study for the alkylation of 2-pyridone without human control during data analysis; (iv) a well plate screening of categorical reaction parameters for a novel palladium-catalyzed cyanation of aryl halides employing O-protected cyanohydrins. By publishing MOCCA as a Python package with this work, we envision an open-source community project for chromatographic data analysis with the potential of further advancing its scope and capabilities.

High-precision luminescent covalent organic frameworks with sp2-carbon connection for visual detecting of nereistoxin-related insecticide

A new strategy for nereistoxin-related insecticide, cartap, detection in foodstuff and the environment is of great importance due to its poisoning of human beings through direct exposure or via biomagnification. Herein, a highly planar conjugated sp2 carbon-connected COF (F-Csp2-TT) was synthesized via Knoevenagel condensation reaction followed by the post-modification to develop a new platform for cartap visual detection in agricultural and food samples. The synergistic effect of highly planar conjugation and dense functional groups in the opened framework endowed F-Csp2-TT with a high-precision luminescence sensing performance. Meanwhile, the exquisitely designed F-Csp2-TT presented robust chemical stability, radiation stability, and good reproducibility. Benefiting from these advantages, high-precision luminescent F-Csp2-TT achieves a low detection limit of 0.51 μg/L to cartap over the range of 1–300 μg/L (R2=0.9938), and the recoveries percentage in food products was calculated as 95.90%− 119.3%. More significantly, the smartphone-based high-precision platform by F-Csp2-TT was established and successfully applied to portable monitoring of cartap and water content. Therefore, our work revealed the enormous potential of Csp2-connected COF, which opened a new situation for insecticide detection.

Synthesis of pyrene-centered D-π-a structured dyes for efficient dye-sensitized solar cells

An asymmetric pyrene derivative was designed as a dye with D-π-A structure. This dye was synthesized by the following steps (acylation reaction, Friedele Crafts acylation reaction, bromination reaction, Hagiharae Sonogashira cross-coupling reaction, and knoevenagel condensation reactions). The structure of the dye was analyzed and identified by FT-IR and 1H-NMR. The dye-sensitized solar cells were prepared with the dye and TiO2 electrode. Futhermore, the I-V curves and IPCE curves of the dye-sensitized solar cells were investigated detailedly. The result showed that the photoelectric conversion efficiency of the dye-sensitized solar cells reached 33.5% of N719 dye cells.

Covalent Immobilization of Natural Biomolecules on Chitin Nanocrystals.

As a highly crystalline and renewable natural polymer nanomaterial, chitin nanocrystals (ChNCs) have attracted intense interest in the biomedical field. The structure of a ChNC is composed of an acetylglucosamine unit containing two hydroxyl groups and an acetyl group. The acetyl group can be converted to the active amino group through deacetylation, which is under the condition of maintaining the rod-like morphology and high crystalline property and is beneficial for the following modification and potential application. We investigated the relationship between different treatments and varied crystallinities of the modified ChNC, which obtained surface amino groups and aldehyde groups and retained high crystallinity. The natural biomolecules were covalently immobilized on the surface of the ChNC. The etherification was performed based on the hydroxyl groups. Based on the amino groups and the aldehyde groups, the carboxyamine and Knoevenagel condensation reactions were realized on ChNCs. Finally, natural biomolecule-modified ChNCs showed no or low cytotoxicity, antibacterial properties, and high antioxidant properties, which extended their potential biomedical applications.

The selective turn-on recognition of fluoride ions using 5-aryl-rhodanines: Colorimetric & fluorescent detection

The main goal of this study is to obtain 5-Ar-Rhs by Knoevenagel condensation without using any catalyst as an ion-sensing organic ligand and investigate their sensing abilities. The 5-Ar-Rhs were obtained as the main product from the no-catalyst reactions carried out at high temperatures. Following synthesis, the anion-sensing properties of 5-Ar-Rhs were studied using colorimetric detection, and spectroscopic methods. The results showed that the 5-Ar-Rhs is only selective for F¯¯ion in the presence of different ions. The binding ratios of 5-Ar-Rhs to F¯ were found to be 1:1 according to Job's plot experiments. The binding constant of 3A and 3B were calculated and found to be 7.05 × 105 M−1 and 1.45 × 104 M−1 for F¯, respectively. The LOD values of 3A and 3B were calculated and found to be 22.4 µM and 27.3 µM, respectively. In addition, theoretical studies by DFT methods were also carried out to optimize the structure and explained the fluoride anion binding mechanism of 5-Ar-Rhs 3A and 3B. As a result, temperature and solvent-controlled Knoevenagel condensation reactions of the 3-NH2-Rh (1), which has a reactive amino group, were examined. Additionally, we can understand that 3A and 3B are good selective candidate sensors that can be used for fluoride detection from sensing studies.

Oxygen activity excited thiophene-diketopyrrolopyrrole-based organic molecules as anode for lithium-ion batteries with enhanced interfacial storage capacity and long cycling capability

In this work, we synthesized various thiophene-diketopyrrolopyrrole-based (DPP-2T-based) molecules by Knoevenagel condensation and halogenation reaction, which applied DPP-2T-based small molecules as anode for lithium-ion batteries (LIBs) for the first time. We studied the different substituents on battery performance and explored the charge–discharge mechanism for DPP-2T-based molecules. DPP-2T-based molecules exhibit different electrochemical properties by substituting various groups at nitrogen positions, where DPP-2T-TA (tert-butyl acetate) electrode possesses better capacity and long-term cycle performance than that of DPP-2T-H (no substitution) and DPP-2T-C6 (hexane) electrode. DPP-2T-TA electrode present an unusual upward tendency for its discharge specific capacity during cycling, which displays that of 530 mAh/g (1000 mA g−1) after 2000 cycles and the capacity retention reaches up to 142.5 %. It is better than those of DPP-2T-H (439 mAh/g, 108.1 %) and DPP-2T-C6 (423 mAh/g, 113.1 %) electrode, which is ascribed to oxygen activity excitation in tert-butyl acetate. This moment, the energy density and power density of DPP-2T-TA electrode are 346 Wh kg−1 and 699 W kg−1, respectively. To further explain this phenomenon, we used many ex-situ measurgin methods such as differential specific capacity (dQ/dV) curves, scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectrometer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and natural bond orbital (NBO) analysis to characterize the detailed lithiation/delithiation process of DPP-2T-TA electrode. The results suggest that the unusual capacity amplification for DPP-2T-TA electrode attributed to lithium-ions inserted into unsaturated carbons and increases its interfacial storage capacity. We believe that the synthesis of DPP-2T-based organic molecules can provide a novel strategy for the development of organic electrode materials for LIBs.

Zn3Sb4O6F6 and KI-Doped Zn3Sb4O6F6: A Metal Oxyfluoride System for Photocatalytic Activity, Knoevenagel Condensation, and Bacterial Disinfection

Zn3Sb4O6F6 crystallites were synthesized by a pH-regulated hydrothermal synthetic approach, while doping on Zn3Sb4O6F6 by KI was performed by the "incipient wetness impregnation technique." The effect of KI in Zn3Sb4O6F6 is found with the changes in morphology in the doped compound, i.e., needle-shaped particles with respect to the irregular cuboid and granular shaped in the pure compound. Closer inspection of the powder diffraction pattern of doped compounds also reveals the shifting of Braggs' peaks toward a lower angle and the difference in cell parameters compared to the pure compound. Both metal oxyfluoride comprising lone pair elements and their doped compounds have been successfully applied as photocatalysts for methylene blue dye degradation. Knoevenagel condensation reactions were performed using Zn3Sb4O6F6 as the catalyst and confirmed 99% yield even at 60 °C temperature under solvent-free conditions. Both pure and KI-doped compounds were tested against several standard bacterial strains, i.e., Enterobacter sp., Escherichia coli, Staphylococcus sp., Salmonella sp., Bacillus sp., Proteous sp., Pseudomonas sp., and Klebsiella sp. by the "disk diffusion method" and their antimicrobial activities were confirmed.

Thermally activated bipyridyl-based Mn-MOFs with Lewis acid-base bifunctional sites for highly efficient catalytic cycloaddition of CO2 with epoxides and Knoevenagel condensation reactions.

Metal-organic frameworks (MOFs) have become preferred heterogeneous catalytic materials for many reactions due to their advantages such as porosity and abundant active sites. Here, a 3D Mn-MOF-1 [Mn2(DPP)(H2O)3]·6H2O (DPP = 2,6-di(2,4-dicarboxyphenyl)-4-(pyridine-4-yl)pyridine) was successfully synthesized under solvothermal conditions. This Mn-MOF-1 possesses a 3D structure constructed by the combination of a 1D chain and the DPP4- ligand and features a micropore with a 1D drum-like shaped channel. Interestingly, Mn-MOF-1 can maintain the structure unchanged by the removal of coordinated and lattice water molecules, whose activated state (denoted as Mn-MOF-1a) contains rich Lewis acid sites (tetra- and pentacoordinated Mn2+ ions) and Lewis base sites (Npyridine atoms). Furthermore, Mn-MOF-1a shows excellent stability, which can be used to catalyze CO2 cycloaddition reactions efficiently under eco-friendly, solvent-free conditions. In addition, the synergistic effect of Mn-MOF-1a resulted in its promising potential in Knoevenagel condensation under ambient conditions. More importantly, the heterogeneous catalyst Mn-MOF-1a can be recycled and reused without an obvious decrease of activity for at least 5 reaction cycles. This work not only paves the way for the construction of Lewis acid-base bifunctional MOFs based on pyridyl-based polycarboxylate ligands but also demonstrates that Mn-based MOFs hold great promise as a heterogeneous catalyst toward both CO2 epoxidation and Knoevenagel condensation reactions.

Structural Analysis of Calcium Oxide Derived from Waste Egg’s Shells and their Application for Knoevenagel Condensation Reactions

The present study demonstrates the simple and easy synthesis of calcium oxide (CaO) from waste egg’s shells. Fine egg’s shells powder were calcinated at 500, 700 and 800 ºC. The structural and morphological evaluation of calcium oxide derived from waste egg’s shell were examined by using XRD, FT-IR, SEM, EDS and TEM techniques. The sintered calcium oxide was used as heterogeneous catalyst for the synthesis of 5-arylidene malononitrile and 5-arylidene barbituric acid derivatives by the condensation of various aromatic aldehyde and active methylene compounds via Knoevenagel condensations reaction under ultrasound irradiation method. The reaction completed within a very short reaction time with high yields of product. The present method describes easy synthesis of calcium oxide catalyst from the waste egg’s shells, short reaction times, simple product isolation, excellent yield and reusability of the catalyst.

Molecular engineering of donor–acceptor sp2-carbon-linked covalent organic frameworks for enhancing photocatalytic hydrogen production

Three sp2-carbon-linked D–A COFs have been successfully synthesized via a Knoevenagel condensation reaction. The TTh-COF with strong electron-donating unit of benzotrithiophene exhibits an impressive hydrogen evolution rate 22.22 mmol h−1 g−1.