Imine Covalent Organic Frameworks Research Articles

Asymmetric Potential Model of Two-Dimensional Imine Covalent Organic Frameworks with Enhanced Quantum Efficiency for Photocatalytic Water Splitting.

Two-dimensional (2D) covalent organic frameworks (COFs) assembled using building blocks have been widely employed in photocatalysis due to their customizable optoelectronic characteristics and porous structure, which facilitate charge carrier and mass movement. Nevertheless, the development of COF photocatalysts encounters a continuous obstacle in enhancing the efficiency of photocatalysis, impeded by a limited comprehension of the orbital interaction between molecular fragments and linkers. In this study, we present a model that examines the interaction between molecular fragments in an imine-based COF at the frontier molecular orbital level, enabling us to comprehend the impact of manipulating linkers on light adsorption, exciton efficiency, and catalytic activity. Our findings demonstrate that altering the connecting orientation of 14 R-C=N-R imine linkers in 2D COFs can enhance solar-to-hydrogen (STH) efficiency under visible light from 2.76% to 4.24%. This research has the potential to provide a valuable model for refining photocatalysts with enhanced photocatalytic performance.

Construction of Azo‐linked Covalent Organic Frameworks via Monomer Exchange for Enhanced Photocatalytic Performance

The structural uniqueness of covalent organic frameworks (COFs) has brought great potential for their applications in photocatalysis. However, existing linkages of COF always lead to poor electron delocalization and inadequate stability. Therefore, two novel azo‐linked COFs AZO‐B‐COF and AZO‐T‐COF were successfully constructed by the monomer exchange method. Significantly, two as‐synthesized azo COFs presented a much higher photodegradation rate of 96% and 51% for AZO‐T‐COF and AZO‐B‐COF, respectively, which was in sharp contrast to the almost 0 degradation rate of imine COFs. And as expected, AZO‐T‐COF could be cycled at least 5 runs without a significant decrease in catalytic efficiency. Systematical experiments and theoretical calculations showed that comparing with imine COFs, conjugated structure of azo COFs broadened the visible‐light absorption range and improved the transfer efficiency of the photocarriers. The N‐rich azo bonds acted as an electron acceptor and made the materials better planarity. This work not only enriches COFs family but also demonstrated the superiority of azo‐linked COFs.

Highly sensitive detection toward aniline vapor promoted by heterojunction between covalent organic frameworks and biocarbon

Development of sensors for detecting aniline for environment, food quality, and medical diagnostics is highly anticipated. However, the high operating temperatures of current aniline sensors hinder their practical use. In this work, the carbon material with micron tube structure (CMTs) derived from lavender straw was used as a template, and the imine covalent organic frameworks (iCOF) was synthesized on the CMTs template at room temperature, forming the iCOF-CMTs with a heterojunction structure. This pioneering study combines COFs materials with biocarbon materials for the first time, allowing us to compare the gas sensing properties of iCOF, CMTs and iCOF-CMTs composites. Due to the presence of heterojunction, the iCOF-CMTs composites exhibited the good gas-sensitive properties among the three materials, especially for aniline vapor. The iCOF-CMTs sensors were tested at room temperature to eight different gases, with the highest response of 2155.75 % for aniline. For the iCOF-CMTs sensor to aniline, the sum of response and recovery times does not exceed 26 s in a response-recovery cycle, and the limit of detection reached 10.26 ppb. This study demonstrated that the special heterojunction structure greatly improved the sensing performance of iCOF and CMTs, providing ideas for further development of COFs-based gas sensors.

Covalent organic frameworks based hierarchical porous hybrid monolithic capillary: Synthesis, characterization, and applications in trace metals analysis

The preparation of hierarchical porous monolithic column with high covalent organic frameworks (COF) loading and micropores accessibility is challenging due to the easy aggregability and sedimentation of COFs. Herein, a novel strategy based on high internal phase emulsion (HIPE) polymerization was proposed for preparing COF hybrid capillary monolithic column with hierarchical porosity. COFs with different frameworks including imine COFs (COF-OMe, COF-F and COF-SH), triazine COF (CTF-1) and boron-based COF (COF-5) were selected to investigate the universality of the preparation strategy. The presence of COF in the monolithic capillary was confirmed by scanning electron microscope, X-ray diffraction and fourier transform infrared spectroscopy. Nitrogen adsorption/desorption experiments and thermogravimetric analysis showed that the prepared COF hybrid monolithic capillary exhibited high COF loading (e.g., 28.7% for COF-SH) and accessibility (e.g., 98.5% for COF-SH), mainly due to the thin walls of void-window structures originated from polymerization of HIPE. The successful preparation of water-stable COF-F, COF-OMe, COF-SH and CTF-1 hybrid monolithic columns demonstrated the proposed synthesis strategy is universal to water-stable COF without tedious optimization of dispersion system, effectively avoiding the sedimentation of COF in pre-polymerization solution. Then, the sulfhydryl-modified COF hybrid polymer (poly(COF-SH-HIPE)) monolithic column was evaluated for the extraction of heavy metal ions, and a method based on poly(COF-SH-HIPE) monolithic capillary microextraction on-line coupled with inductively coupled plasma mass spectrometry detection was developed for analysis of trace Cd, Hg and Pb in human fluid samples.

Wavelength-Dependent Excitonic Properties of Covalent Organic Frameworks Explored by Theory and Experiments

Many aspects of the correlation between the physical structure, light harvesting, and excitonic properties of covalent organic frameworks (COFs) remain unclear despite being key properties determining their photocatalytic function. One area of COF research that could bring clarity is using both electronic structure theory and time-resolved spectroscopic analysis over a series of systematically varied COFs. Here, we show structure–property relationships between four imine COFs built from a combination of ditopic and tritopic monomers using transient absorption spectroscopy together with time-dependent density functional theory. We find that monomer selection only moderately affects the charge transfer (CT) behavior of the COFs. Instead, we infer that imine chemistry profoundly impacts CT by acting as a CT mediator. Moreover, we discover two distinct valence bands arising from varying degrees of locally excited/CT mixing, which is responsible for energy-dependent exciton dynamics. Finally, we use theory to hypothesize that interlayer interactions can modify excitonic properties that we correlate with tail states commonly observed but rarely investigated in COFs. These results reveal that imine chemistry should be recognized as a very important factor to consider in the development of COF photocatalysts and the correlation of their structural environment with light-harvesting and CT properties that should ultimately determine their photocatalytic function.

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.

Imine-linked covalent organic frameworks with stable and microporous structure for effective carbon dioxide and iodine uptake

In recent years, many environmental problems including global warming and climate change have emerged due to the excessive emission of carbon dioxide. Covalent organic frameworks (COFs) exhibit good porosity and excellent stability. They can be constructed into uniform channel and tunable skeleton which are ideal for gas uptake. Here, we designed two new imine-linked COFs (ESM-COF-1 and ESM-COF-2) by condensation of two C3 symmetrical monomers. Interestingly, ESM-COF-1 and ESM-COF-2 displayed microporous features because of short length building units employed, the pore size, which is much smaller than most two-dimensional (2D) imine COFs. This virtue is good for gas adsorption via pore surroundings. Furthermore, rich methoxy units as electron-donate units on the walls delocalized electronic clouds from building units to the imine bond through π-conjugation interaction, indicating outstanding stability in harsh conditions. High-density active units from walls (triphenylamine and methoxy groups) to the imine linkage also improved the gas adsorption via the weak interaction. Interestingly, ESM-COFs exhibited stability, microporous features, and active units from walls to linkage to give a high carbon dioxide uptake at 4.64 mmol g−1, which is the excellent one among the reported 2D COFs.

Amide Linkages in Pyrene-Based Covalent Organic Frameworks toward Efficient Photocatalytic Reduction of Uranyl

The bond linkages in covalent organic frameworks (COFs) partly determine its physical and chemical properties, thus affecting the photoreactive activity by influencing the generation of photoelectrons and the separation of excitons. Herein, pyrene-based amide COF 4,4',4″,4‴-(pyrene-1,3,6,8-tetrayl)tetrabenzaldehyde-3,8-diamino-6-phenylphenanthridine (TFPPy-DP) was synthesized by postsynthetic modification of imine COFs. Due to the introduction of oxygen atoms into the framework and the change in polarity, an increased number of photogenerated electrons and a wide band gap for amide COFs were found, hydrophilicity and dispersibility were prompted as well. Both imine and amide COF TFPPy-DP were applied in the photocatalytic reduction and removal of toxic U(VI) under visible light, the catalytic reduction equilibrium (91% removal percentage of 238 ppm U at pH 3) was achieved by imine COFs with 10 h of irradiation, while amide COFs only took 2 h of irradiation (82% removal percentage). The much faster photocatalytic reduction rate of U(VI) can be attributed to the fact that amide COF TFPPy-DP retained crystallinity and permanent porosity and exhibited lower electrochemical impedance and enhanced charge separation and accumulation. Further electronic excitation analysis based on time-dependent density functional theory calculations revealed that the intramolecular charge-transfer effect in amide TFPPy-DP enhanced its photocatalytic rate.

Covalent organic framework-immobilized wood membrane for efficient, durable, and high-flux nanofiltration

Covalent organic frameworks (COFs) are promising for the construction of nanofiltration membranes owing to their uniform, ordered channel structures and high chemical stability. However, developing a low-cost strategy for fabricating COF-based nanofiltration membranes and increasing the long-term stability of the membranes are challenging. Here, we developed a TpPa-wood membrane through the in-situ formation of massive imine COFs on the top surface of a wood block for the rapid and efficient nanofiltration-based separation of organic pollutants. The numerous hydroxyl groups of cellulose in wood provided nucleation sites for the growth of dense, defect-free COFs with a diameter of 1.8 nm. The nano porous COFs enabled efficient separation, while the long and low-tortuosity channels of wood with a diameter of 10–30 μm facilitated rapid water transport and augmented the mechanical robustness of the membrane. Therefore, the prepared TpPa-wood membrane showed an outstanding separation efficiency of ∼97.0% toward organic pollutants such as dyes and pharmaceutical molecules at a flux rate of 600 L m−2 h−1. In addition, the TpPa-wood membrane exhibited excellent stability at a wide pH range (3–11) and over continuous filtration for 48 h. The TpPa-wood membrane opens up a new avenue for rapid and efficient nanofiltration by combining the merits of nano porous COFs and biomass with numerous micro-channels and high hydrophilicity.

Enabling Solution Processable COFs through Suppression of Precipitation during Solvothermal Synthesis.

Covalent organic frameworks (COFs) are crystalline, nanoporous materials of interest for various applications, but current COF synthetic routes lead to insoluble aggregates which precludes processing for practical implementation. Here, we report a COF synthesis method that produces a stable, homogeneous suspension of crystalline COF nanoparticles that enables the preparation of COF monoliths, membranes, and films using conventional solution-processing techniques. Our approach involves the use of a polar solvent, diacid catalyst, and slow reagent mixing procedure at elevated temperatures which altogether enable access to crystalline COF nanoparticle suspension that does not aggregate or precipitate when kept at elevated temperatures. On cooling, the suspension undergoes a thermoreversible gelation transition to produce crystalline and highly porous COF materials. We further show that the modified synthesis approach is compatible with various COF chemistries, including both large- and small-pore imine COFs, hydrazone-linked COFs, and COFs with rhombic and hexagonal topologies, and in each case, we demonstrate that the final product has excellent crystallinity and porosity. The final materials contain both micro- and macropores, and the total porosity can be tuned through variation of sample annealing. Dynamic light scattering measurements reveal the presence of COF nanoparticles that grow with time at room temperature, transitioning from a homogeneous suspension to a gel. Finally, we prepare imine COF membranes and measure their rejection of polyethylene glycol (PEG) polymers and oligomers, and these measurements exhibit size-dependent rejection and adsorption of PEG solutes. This work demonstrates a versatile processing strategy to create crystalline and porous COF materials using solution-processing techniques and will greatly advance the development of COFs for various applications.

Linker Engineering of 2D Imine Covalent Organic Frameworks for the Heterogeneous Palladium-Catalyzed Suzuki Coupling Reaction.

Covalent organic frameworks (COFs) are an emerging class of porous organic polymers that have been utilized as scaffolds for anchoring metal active species to act as heterogeneous catalysts. Though several examples of such COFs exist, a thorough experimental and computational analysis on such catalysts is limited. In this work, a series of two-dimensional (2D) imine COFs (TTA-DFB COF (N), TTA-TBD COF (N∧O), and TTA-DFP COF(N∧N)) were synthesized by using suitable building units to obtain three different coordination sites (N, N∧O, and N∧N). These were post-modified with Pd(II) to catalyze the Suzuki-Miyaura coupling reaction. Pd@TTA-DFB COF, where Pd(II) was coordinated to N sites, showed the fastest reactivity and lower stability. Pd@TTA-DFP COF showed highest stability but slowest reactivity. Pd@TTA-TBD COF was the best among the three with both high stability and fast reactivity. By combining both experimental and computational results, we conclude that the Pd(II) to Pd(0) reduction is a key step in the difference between the catalytic reactivities of the three COFs. This study demonstrates the importance of the building block approach to design COFs for efficient heterogeneous catalysis and to understand the fate of the reaction profile.

Constitutional isomerism of the linkages in donor–acceptor covalent organic frameworks and its impact on photocatalysis

When new covalent organic frameworks (COFs) are designed, the main efforts are typically focused on selecting specific building blocks with certain geometries and properties to control the structure and function of the final COFs. The nature of the linkage (imine, boroxine, vinyl, etc.) between these building blocks naturally also defines their properties. However, besides the linkage type, the orientation, i.e., the constitutional isomerism of these linkages, has rarely been considered so far as an essential aspect. In this work, three pairs of constitutionally isomeric imine-linked donor-acceptor (D-A) COFs are synthesized, which are different in the orientation of the imine bonds (D-C=N-A (DCNA) and D-N=C-A (DNCA)). The constitutional isomers show substantial differences in their photophysical properties and consequently in their photocatalytic performance. Indeed, all DCNA COFs show enhanced photocatalytic H2 evolution performance than the corresponding DNCA COFs. Besides the imine COFs shown here, it can be concluded that the proposed concept of constitutional isomerism of linkages in COFs is quite universal and should be considered when designing and tuning the properties of COFs.

Constructing chemical stable 4-carboxyl-quinoline linked covalent organic frameworks via Doebner reaction for nanofiltration

Covalent linkages are the key component of covalent organic frameworks (COFs). The development of stable and functional linkages is essential to expand the COFs family and broaden their application prospects. In this work, we report the synthesis of crystalline and chemical stable 4-carboxyl-quinoline linked COFs (QL-COFs) via Doebner reactions in both one-pot (OP) and post-synthetic modification (PSM) methods. Both methods can be universally applied to most of the reported imine COFs family via bottom-up construction or linkage conversion. Owing to the contractive pore size, more hydrophilic structure and better chemical stability than the conventional imine COFs endowed by 4-carboxyl-quinoline linkage, QL-COFs are supposed to possess a wider application range. We further demonstrate the nanofiltration membrane (NFM) based on QL-COF exhibited a desirable separation capacity with high rejection for small dye molecules (> 90%), high water permeance (850 L m−2 h−1 MPa−1) and tolerance of extreme conditions (1 M HCl/NaOH), which were benefitted from the enhanced properties of QL-COFs. Additionally, efficient ion sieving properties were also achieved by QL-COF membrane. We anticipate that this work opens up a way for the construction of robust and functional COFs materials for practical applications.

A three-dimensional polycyclic aromatic hydrocarbon based covalent organic framework doped with iodine for electrical conduction

Covalent organic frameworks (COFs) are a class of crystalline porous organic materials with variable structures and fascinating properties. The intrinsic low conductivity impedes their widely application in optoelectronic. Iodine doping is an effective way to enhance the electrical conductivity of COFs. Here, a novel 3D imine COF with lvt topology is synthesized from two different pentacene derivatives with the same core in the form of structural complementarity. DDHP-COF is a highly crystalline material featuring high surface area of 1679 m2/g and excellent thermal stability up to 490 °C. Upon doping with iodine, the electrical conductivity can reach as high as 1.5 × 10−2 S/m which is significantly enhanced over 6 orders of magnitude compared with the pristine COF.

Reconstructed covalent organic frameworks

Covalent organic frameworks (COFs) are distinguished from other organic polymers by their crystallinity1–3, but it remains challenging to obtain robust, highly crystalline COFs because the framework-forming reactions are poorly reversible4,5. More reversible chemistry can improve crystallinity6–9, but this typically yields COFs with poor physicochemical stability and limited application scope5. Here we report a general and scalable protocol to prepare robust, highly crystalline imine COFs, based on an unexpected framework reconstruction. In contrast to standard approaches in which monomers are initially randomly aligned, our method involves the pre-organization of monomers using a reversible and removable covalent tether, followed by confined polymerization. This reconstruction route produces reconstructed COFs with greatly enhanced crystallinity and much higher porosity by means of a simple vacuum-free synthetic procedure. The increased crystallinity in the reconstructed COFs improves charge carrier transport, leading to sacrificial photocatalytic hydrogen evolution rates of up to 27.98 mmol h−1 g−1. This nanoconfinement-assisted reconstruction strategy is a step towards programming function in organic materials through atomistic structural control.

Constructing Stable Chromenoquinoline-Based Covalent Organic Frameworks via Intramolecular Povarov Reaction.

Chemically stable chromenoquinoline (CQ)-based covalent organic frameworks (COFs) were constructed by postsynthetic conversion of imine COFs. The key step of an intramolecular Povarov reaction can transform a preintegrated alkyne group to bridge the benzene rings on both sides of the imine linkage via chemical bonds, affording a ladder-type CQ linkage. This novel approach achieves a high cyclization degree of 80-90%, which endows the CQ-COFs with excellent chemical stability toward strong acid, base, and redox reagents. The synthetic approach can be applied to various monomers with different symmetries and functional core moieties. The absorption and fluorescence intensities of CQ-COFs are sensitive to acid, which allows for dual-mode sensing of strongly acidic environments.

Application of imine covalent organic frameworks in sample pretreatment

亚胺类共价有机骨架(I-COFs)是有机单体根据席夫碱(Schiff-base)反应原理缩合形成的一类新型多孔晶体有机材料。I-COFs具有骨架密度低、比表面积大、孔隙率高、单体种类丰富、孔径尺寸可控、结构可功能化、合成方法多样和物化稳定性好等优点。近年来,I-COFs已成为材料科学领域的研究前沿,并广泛用于气体吸附、存储、催化、传感、光电材料等方面。I-COFs材料优异的物理化学性能使其非常适于用作复杂样品中痕量目标物的分离富集介质,其高比表面积、高孔隙率性能赋予了它极高的吸附负载量,这些性能使得目标分析物可被高效富集;通过控制有机单体的链段长度、几何结构、掺杂元素、取代基团等方面精确调控I-COFs的孔洞结构和功能化基团,从而实现目标痕量物质的选择性富集。目前,I-COFs材料在样品前处理领域作为新型萃取介质已引起了极大关注。该文综述了近年来I-COFs材料的主要类型、合成方法及其在固相萃取、磁性固相萃取、分散固相萃取和固相微萃取方面的研究进展,同时展望了I-COFs在样品前处理领域的发展前景。

Correction to “Chemically Stable Carbazole-Based Imine Covalent Organic Frameworks with Acidochromic Response for Humidity Control Applications”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to “Chemically Stable Carbazole-Based Imine Covalent Organic Frameworks with Acidochromic Response for Humidity Control Applications”Leisan GilmanovaLeisan GilmanovaMore by Leisan Gilmanovahttps://orcid.org/0000-0002-0344-6919, Volodymyr Bon*Volodymyr BonMore by Volodymyr Bonhttps://orcid.org/0000-0002-9851-5031, Leonid ShupletsovLeonid ShupletsovMore by Leonid Shupletsov, Darius PohlDarius PohlMore by Darius Pohl, Marcus RaucheMarcus RaucheMore by Marcus Rauche, Eike BrunnerEike BrunnerMore by Eike Brunnerhttps://orcid.org/0000-0003-3511-9899, and Stefan Kaskel*Stefan KaskelMore by Stefan Kaskelhttps://orcid.org/0000-0003-4572-0303Cite this: J. Am. Chem. Soc. 2022, 144, 4, 2019Publication Date (Web):January 20, 2022Publication History Published online20 January 2022Published inissue 2 February 2022https://doi.org/10.1021/jacs.1c13191Copyright © 2022 The Authors. Published by American Chemical SocietyRIGHTS & PERMISSIONSACS AuthorChoiceCC: Creative CommonsBY: Credit must be given to the creatorNC: Only noncommercial uses of the work are permittedND: No derivatives or adaptations of the work are permittedArticle Views1653Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (817 KB) Get e-Alerts Get e-Alerts

Tuning the lattice parameters and porosity of 2D imine covalent organic frameworks by chemically integrating 4-aminobenzaldehyde as a bifunctional linker.

As the available building blocks are limited, improving the structural complexity of covalent organic frameworks (COFs) is still challenging. In this work, a new three-component COF synthesis strategy is established by using 4-aminobenzaldehyde as the bifunctional linker. The lattice parameters, crystallinity, and porosity of these COFs can be efficiently tuned by varying the amount of this linker. This work provides a new way to expand the structural diversity and complexity of imine-linked COFs.

Cationic covalent organic framework via cycloaddition reactions as sulfur-loaded matrix for lithium-sulfur batteries

The postsynthetic modification provided effective approaches for the functionalization of imine covalent organic frameworks (COFs). To address the rapid decline of sulfur cathodes caused by the shuttle effect of soluble lithium polysulfide, cationic COFs (COF-PA-AI) used as sulfur-loaded matrix materials for lithium-sulfur (Li-S) batteries was designed and prepared by cycloaddition. Benefiting from the ordered channels and the strong interaction between quaternary ammonium cations and polysulfide anions, COF-PA-AI/S displayed faster electrochemical kinetics, greater tolerance to high current shocks, and better rate performance as the cathode. Besides, the discharge capacity of COF-PA-AI/S also remained at 665.3 mA h/g after 200 cycles at 0.5 °C, which was higher than that of COF-Ph/S. This work not only demonstrated the possibility of a postfunctionalization method based on the intermediate COF-PA but also expanded the scope of application of the COFs and provided a new idea for the application of COF materials to the cathodes of Li-S batteries.