Covalent Organic Framework Films Research Articles

Dual Redox-active Covalent Organic Framework-based Memristors forHighly-efficient Neuromorphic Computing.

Organic memristors based on covalent organic frameworks (COFs) exhibit significant potential for future neuromorphic computing applications. The preparation of high-quality COF nanosheets through appropriate structural design and building block selection is critical for the enhancement of memristor performance. In this study, a novel room-temperature single-phase method was used to synthesize Ta-Cu3 COF, which contains two redox-active units: trinuclear copper and triphenylamine. The resultant COF nanosheets were dispersed through acid-assisted exfoliation and subsequently spin-coated to fabricate a high-quality COF film on an indium tin oxide (ITO) substrate. The synergistic effect of the dual redox-active centers in the COF film, combined with its distinct crystallinity, significantly reduces the redox energy barrier, enabling the efficient modulation of 128 non-volatile conductive states in the Al/Ta-Cu3 COF/ITO memristor. Utilizing a convolutional neural network (CNN) based on these 128 conductance states, image recognition for ten representative campus landmarks was successfully executed, achieving a high recognition accuracy of 95.13% after 25 training epochs. Compared to devices based on binary conductance states, the memristor with 128 conductance states exhibits a 45.56% improvement in recognition accuracy and significantly enhances the efficiency of neuromorphic computing.

Copper-surface-mediated synthesis of sp2 carbon-conjugated covalent organic framework photocathodes for photoelectrochemical hydrogen evolution.

Sp2-carbon (sp2-c) covalent organic frameworks (COFs), featuring distinctive π-conjugated network structures, facilitate the migration of photo-generated carriers, rendering them exceptionally appealing for applications in photoelectrochemical water splitting. However, owing to the powdery nature of COFs, leaving anchor the sp2-c COFs powder tightly onto a conductive substrate challenging. Here, we propose a method for preparing photoactive substance-conductive substrate integrated photocathodes through copper surface-mediated knoevenagel polycondensation (Cu-SMKP), this approach results in a uniform and stable sp2-c COF film, directly grown on commercial copper foam (COFTh-Cu). The COFTh-Cu demonstrates a high H2-evolution photocurrent density of 56 μA cm-2 at 0.3 V versus RHE, sustaining stability for 12 hours. The as-prepared COFTh-Cu represents a 4.5-fold increase in current density compared to traditional spin-coating methods and outperforms most COF photocathodes without cocatalysts. This innovative copper surface-mediated approach for preparing photocathodes opens up a crucial pathway towards the realization of highly active COF photocathodes.

Adaptive COF-PVDF composite artificial solid electrolyte interphase for stable aqueous zinc batteries

The cyclability of aqueous zinc (Zn) – based batteries is limited by the formation of dendrites and side reactions. Herein, this work presents a composite- artificial solid electrolyte interphase (ASEI) in two stages. Firstly, a covalent organic framework (COF) is synthesized via an interfacial reaction between aldehyde and amine linkers. Secondly, polyvinylidene fluoride (PVDF) is additionally coated on top of the COF film via spin coating. Results demonstrate that the COF-PVDF composite regulates Zn ion flux, preventing dendrite formation and reducing side reactions, while dynamically adapting to large volume changes. Zn plating/stripping tests with a symmetrical cell reveal that PVDF@COF@Zn exhibits enhanced stability and higher coulombic efficiency (CE) compared to bare Zn. Furthermore, the full cell incorporating PVDF@COFs@Zn//I2@C signifies significantly enhanced stability, making PVDF@COFs a promising ASEI material for stable aqueous Zn batteries. It is crucial to emphasize that the chemical and mechanical properties are the key parameters in designing the ASEI, as these factors directly influence its performance and longevity.

Interpenetrated Donor-Acceptor Heterojunctions in 2D Conjugated Dibenzo[g,p]chrysene-Based Kagome Covalent Organic Frameworks.

Dibenzo[g,p]chrysene can be viewed as a constrained propeller-shaped tetraphenylethylene with reduced curvature and has been utilized to construct dual-pore kagome covalent organic frameworks (COFs) with tightly packed two-dimensional (2D) layers owing to its rigid and more planar structural characteristics. Here, we introduce 2D COFs based on the node 4,4',4″,4‴-(dibenzo[g,p]chrysene-2,7,10,15-tetraphenyl)tetraamine (DBCTPTA) featuring extended conjugation compared to the dibenzo[g,p]chrysene-3,6,11,14-tetraamine (DBCTA) node. We establish two exceptionally crystalline imine-linked 2D COFs with a hexagonal dual-pore kagome structure based on the DBCTPTA core. The newly synthesized thienothiophene (TT) and benzodithiophene (BDT)-based DBCTPTA COFs show a tight stacking behavior between adjacent layers. Furthermore, we obtained an unprecedented, interpenetrated electron-donor/acceptor host-guest system with an electron-donating BDT DBCTPTA COF synthesized in situ with the soluble fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) serving as molecular acceptor. The BDT DBCTPTA COF@PCBM film shows a much shorter amplitude-averaged PL lifetime of 7 ± 2 ps compared to 30 ± 4 ps of the BDT DBCTPTA COF film, indicating the light-induced charge transfer process. The successful in situ formation of interpenetrated donor-acceptor heterojunctions within 2D COFs offers a promising strategy for establishing D-A heterojunctions in diverse framework materials with open channel systems.

Triphenylamine-Based Covalent Organic Framework Films for Dopamine-Responsive Electrofluorochromism.

Covalent organic framework (COF) film with electrofluorochromic (EFC) and electrochromic (EC) properties has been synthesized by using triphenylamine-based monomers. The film exhibited a high maximum fluorescence contrast of 151 when subjected to a drive voltage of 0.75 V vs the Ag/AgCl electrode, causing the fluorescence to be quenched, which resulted in the EFC process's "fluorescence off" state. The switching times for the fluorescence on and off states were 0.51 and 7.79 s, respectively. Over the same voltage range, the COF film also displayed EC properties, achieving a contrast of 50.23% and a coloration efficiency of 297.4 cm2 C-1 at 532 nm, with switching times of 18.6 s for coloration and 0.7 s for bleaching. Notably, the quenched fluorescence of the COF film could be restored by adding dopamine as a reductant. This phenomenon enabled the implementation of a NAND logic gate using the applied potential as a physical input and dopamine addition as a chemical input. This study demonstrates the successful development of COF films with bifunctional EFC and EC properties, showcasing their potential for use in constructing advanced optoelectronic devices.

Electron Transport over 2D Molecular Materials and Assemblies.

ConspectusTwo-dimensional (2D) molecular materials, in which the major interactions are confined in 2D planes with contrasted force fields acting in between the planes, have been key electronic functional materials since the past decade. Even without referring to the functionals of graphene-based systems, 2D electronic conjugated systems are expected to show extrawide dynamic ranges in electronic density of states (DOS) tuning, effective electron mass, electron mobility, and conductivity. A major advantage of 2D electronic systems is their compatibility with the ubiquitous electronic devices designed using planar structures, such as transistors and memories, which is associated with the utility of 2D active materials. The mobility of electrons in 2D systems is the key to their utility, and various conjugated molecular and 2D materials have been designed to optimize the mobility. This Account begins with an introduction for mobility assessment: using noncontact time-resolved microwave conductivity (TRMC) measurements as a technique to probe differential conductivity upon transient charge carrier injection into the materials. Electronic transport over 2D electronic materials such as graphenes, covalent organic frameworks (COFs), and metal-organic frameworks (MOFs) is discussed with a special emphasis on molecular building blocks, fine-tuning conducting species and linkages, topology of the framework, and controlling molecular doping. The superiority of β-ketoenamine-linked COF over imine-linked COF films in charge transport and dominant in-plane charge carrier mobility over out-of-plane mobility is also illustrated. Systematic molecular engineering of the building blocks of β-ketoenamine-linked COFs with varying degrees of donor-acceptor (D-A) conjugation, torsional angles, and reaction conditions resulted in the modulation of the efficiency of charge carrier generation/transport as well as exciton migration. The advantages of 2D systems are finally discussed in terms of the mobility interplaying with spatial arrangements of molecules as well as the substantial role of intermolecular interactions in stabilizing their condensed phases. The strong correlation between the dispersion of mobility and hierarchical intermolecular interactions sheds light on the way to overcome structural fluctuation on the optimization of charge transport in molecular electronic materials. The point of singularity in the dispersion at an intermolecular distance of d ∼ 0.3 nm is deduced from the overall mobility assessment in condensed phases of conjugated molecules, suggesting key roles of intermolecular electronic coupling: the new concept of electronic conjugation. Exceptional electronic coupling with relatively high charge carrier mobility was also observed, particularly in 2D spatial arrangements of chiral molecules in contrast to 3D analogues, where the reduction of gravitational density of the molecular condensates was impacting DOS: the Wallach's rule. 2D electronic systems are strong candidates for the violation of the long-lasting Wallach's rule in terms of DOS.

Enhanced Alkene Oxidative Cleavage in Water via Photoexcited FeIV Species within Covalent Organic Framework Thin Films.

The oxidative cleavage of alkenes is a crucial step in synthesizing key organic molecules featuring carbonyl functional groups prevalent in natural products and pharmaceuticals. We introduce a photochemical method for heterogeneous C=C bond cleavage, employing photo-catalytically generated [(bTAML)FeIV-O-FeIV(bTAML)]- species (where bTAML stands for biuret-modified tetraamido macrocyclic ligand) in aqueous environments under gentle conditions. Leveraging the photosensitizing properties of Covalent Organic Frameworks (COFs) and their advantageous morphological traits as films, we enhance the reaction by closely associating the substrate with the catalyst. This study marks the inaugural demonstration of Fe2IV-µ-oxo radical cation and FeIV=O species facilitating alkene cleavage in water against a backdrop of a hydrophobic COF. Through comprehensive mechanistic studies, including control experiments, we confirm that these two high-valent iron oxo species collaborate to cleave alkenes, forming an intermediate epoxide. Our approach yields moderate to high success across various alkenes, displaying diverse functional groups (achieving up to 75% yield) with notable efficiency and selectivity towards aldehyde/ketone products. Moreover, the heterogeneous COF film, immobilizing (Et4N)2[FeIII(Cl)bTAML], exhibits exceptional recyclability, enduring up to four cycles.

Enhanced Alkene Oxidative Cleavage in Water via Photoexcited FeIV Species within Covalent Organic Framework Thin Films

The oxidative cleavage of alkenes is a crucial step in synthesizing key organic molecules featuring carbonyl functional groups prevalent in natural products and pharmaceuticals. We introduce a photochemical method for heterogeneous C=C bond cleavage, employing photo‐catalytically generated [(bTAML)FeIV–O–FeIV(bTAML)]– species (where bTAML stands for biuret‐modified tetraamido macrocyclic ligand) in aqueous environments under gentle conditions. Leveraging the photosensitizing properties of Covalent Organic Frameworks (COFs) and their advantageous morphological traits as films, we enhance the reaction by closely associating the substrate with the catalyst. This study marks the inaugural demonstration of Fe2IV–µ–oxo radical cation and FeIV=O species facilitating alkene cleavage in water against a backdrop of a hydrophobic COF. Through comprehensive mechanistic studies, including control experiments, we confirm that these two high‐valent iron oxo species collaborate to cleave alkenes, forming an intermediate epoxide. Our approach yields moderate to high success across various alkenes, displaying diverse functional groups (achieving up to 75% yield) with notable efficiency and selectivity towards aldehyde/ketone products. Moreover, the heterogeneous COF film, immobilizing (Et4N)2[FeIII(Cl)bTAML], exhibits exceptional recyclability, enduring up to four cycles.

Dual Redox‐active Covalent Organic Framework‐based Memristors for Highly‐efficient Neuromorphic Computing

Organic memristors based on covalent organic frameworks (COFs) exhibit significant potential for future neuromorphic computing applications. The preparation of high‐quality COF nanosheets through appropriate structural design and building block selection is critical for the enhancement of memristor performance. In this study, a novel room‐temperature single‐phase method was used to synthesize Ta‐Cu3 COF, which contains two redox‐active units: trinuclear copper and triphenylamine. The resultant COF nanosheets were dispersed through acid‐assisted exfoliation and subsequently spin‐coated to fabricate a high‐quality COF film on an indium tin oxide (ITO) substrate. The synergistic effect of the dual redox‐active centers in the COF film, combined with its distinct crystallinity, significantly reduces the redox energy barrier, enabling the efficient modulation of 128 non‐volatile conductive states in the Al/Ta‐Cu3 COF/ITO memristor. Utilizing a convolutional neural network (CNN) based on these 128 conductance states, image recognition for ten representative campus landmarks was successfully executed, achieving a high recognition accuracy of 95.13% after 25 training epochs. Compared to devices based on binary conductance states, the memristor with 128 conductance states exhibits a 45.56% improvement in recognition accuracy and significantly enhances the efficiency of neuromorphic computing.

Dual-modal biosensor for mercuric ion detection based on Cu2O@Cu2S/D-TA COF heterojunction with excellent catalase-like, electrochemical and photoelectrochemical properties

In this study, a dual-mode biosensor based on the heterojunction of Cu2O@Cu2S/D-TA COF was constructed for ultra-sensitive detection of Hg2+ using both photoelectrochemical and electrochemical approaches. Briefly, a 2D ultra-thin covalent organic framework film (D-TA COF film) with excellent photoelectrochemical signals was prepared on ITO surfaces through an in situ growth method. Subsequently, the probe H1 was immobilized onto the biosensor via Au–S bonds. In the presence of Hg2+, the formation of T-Hg2+-T complexes triggered hybridization chain reactions (HCR), leading to the attachment of abundant Cu2O@Cu2S probes onto the biosensor. As a p-type semiconductor, Cu2O@Cu2S could form a heterojunction with the underlying D-TA COF films. Meanwhile, it exhibited catalase-like activity, and the O2 produced by its catalytic decomposition of H2O2 can interact with the D-TA COF films, thus achieving double amplification of the photocurrent signal. Benefiting from the excellent and inherent Cu2+/Cu+ redox pairs of Cu2O@Cu2S, satisfactory differential pulse voltammetry (DPV) signals were obtained. As expected, the dual-mode biosensor was realized with wider linear ranges and low detection limits. Additionally, the analytical performance for Hg2+ in real water samples was excellent. Briefly, this suggested approach offers a facile and highly efficient modality for monitoring heavy metal ions in aquatic environments.

In Situ Growth of COF/PVA-Carrageenan Hydrogel Using the Impregnation Method for the Purpose of Highly Sensitive Ammonia Detection.

Flexible ammonia (NH3) gas sensors have gained increasing attention for their potential in medical diagnostics and health monitoring, as they serve as a biomarker for kidney disease. Utilizing the pre-designable and porous properties of covalent organic frameworks (COFs) is an innovative way to address the demand for high-performance NH3 sensing. However, COF particles frequently encounter aggregation, low conductivity, and mechanical rigidity, reducing the effectiveness of portable NH3 detection. To overcome these challenges, we propose a practical approach using polyvinyl alcohol-carrageenan (κPVA) as a template for in the situ growth of two-dimensional COF film and particles to produce a flexible hydrogel gas sensor (COF/κPVA). The synergistic effect of COF and κPVA enhances the gas sensing, water retention, and mechanical properties. The COF/κPVA hydrogel shows a 54.4% response to 1 ppm NH3 with a root mean square error of less than 5% and full recovery compared to the low response and no recovery of bare κPVA. Owing to the dual effects of the COF film and the particles anchoring the water molecules, the COF/κPVA hydrogel remained stable after 70 h in atmospheric conditions, in contrast, the bare κPVA hydrogel was completely dehydrated. Our work might pave the way for highly sensitive hydrogel gas sensors, which have intriguing applications in flexible electronic devices for gas sensing.

Highly elastic 2D covalent organic framework films of interwoven single crystals.

Highly elastic 2D covalent organic framework films of interwoven single crystals.

Solar Carboxylation Using CO2: Interfacially Synthesized Flexible Covalent Organic Frameworks Film as a Photocatalyst for Highly Selective Solar Carboxylation of Arylamines with CO2.

Carbon dioxide (CO2) conversion into value-added chemicals/fuels by utilizing solar energy is a sustainable way to mitigate our dependence on fossil fuels and stimulate a carbon-neutral economy. However, the efficient and affordable conversion of CO2 is still an ongoing challenge. Here, we report an interfacially synthesized visible-light-active Ni(II)-integrated covalent organic frameworks (TaTpBpy-Ni COFs) film as a photocatalyst for efficient CO2 conversion into carboxylic acid under ambient conditions. Notably, the TaTpBpy-Ni COFs film showed excellent photocatalytic activity for the carboxylation of various arylamines with CO2 to the corresponding arylcarboxylic acid via C-N bond activation under solar-light irradiation. Moreover, this carboxylation protocol exhibits mild reaction conditions and good functional group tolerance without the necessity of using stoichiometric metallic reductants. This work shows a benchmark example of not only the interfacially synthesized COFs film used as a photocatalyst for solar-light energy utilization but also the selective solar chemical production system of arylcarboxylic acid directly from CO2.

Multistate Electrochromic Covalent Organic Framework Film for Electronic Safety Indicator

Multistate Electrochromic Covalent Organic Framework Film for Electronic Safety Indicator

Third-order nonlinear optical properties of phenothiazine-based imine covalent organic framework films

The manipulation of the chemical structure within covalent organic frameworks (COFs) is emerging as a potent approach to engineering materials with enhanced charge transfer efficiency and nonlinear optical (NLO) properties. This study introduces the synthesis of two donor-acceptor (D-A) COF films, PB-TZ and PT-TZ, via solvothermal processing, followed by a detailed examination of their third-order NLO characteristics. Notably, COF films demonstrated Saturation absorption and self-defocusing properties at a 532 nm laser irradiation, indicating their potential utility in optical applications. The third-order nonlinearly polarized magnetic induction (χ(3)) of the PT-TZ film is significantly higher compared with that of the PB-TZ film, reaching 16.05 ± 0.17 × 10−7 esu, which is 2.9 times higher than that of the PB-TZ film. This enhancement can be attributed to the superior acceptor ability of the triazine ring within PT-TZ, which promotes a more efficient electron transfer from the donor to the acceptor units. Consequently, this study provides a new idea for the development of COF films in the field of high-performance NLO.

A versatile photoelectrochemical biosensor based on in-situ grown 2D COFs film for sensitive detection of Hg2+ and aflatoxin B1

Herein, a highly stable and low-toxic photoelectrochemical (PEC) biosensor was constructed based on two-dimensional covalent organic frameworks (COFs) film composed of tris(4-aminophenyl)amine and 1,4-phthalaldehyde connected through imine bonds (TA-P COFs) was grown in situ on the electrode surface under mild conditions for detecting mercury ion (Hg2+) and aflatoxin B1 (AFB1). Impressively, the TA-P COF film adhered to the electrode surface through in-situ growth not only accelerated the charge transfer between the interfaces, but also improved the stability of the biosensor, further improving the accuracy of detection. Accordingly, when the cyclic amplification process was triggered in the presence Hg2+ to generate a large amount of output DNA, the signal probe with abundant quencher porous carbon hollow spheres s (PCHS) was modified on the electrode surface through the output DNA for the signal “OFF” detection of Hg2+. Meanwhile, due to the specific binding of the target to the aptamer, the released hairpin DNA 2 (H2) signal probe was modified on the electrode surface through base complementary pairing to achieve the signal “ON” detection of AFB1. The suggested multifunction biosensor achieved sensitive detection of Hg2+ in the range of 10 fM–100 nM and AFB1 in the range of 10 fg mL−1–10 ng mL−1, which showed great practical application potential in both environmental and food analysis.

Photochemical and Patternable Synthesis of 2D Covalent Organic Framework Thin Film Using Dynamic Liquid/Solid Interface.

2D covalent organic frameworks (COFs) are highly porous crystalline materials with promising applications in organic electronics. Current methods involve either on-surface synthesis (solid surface) or interfacial synthesis (liquid/liquid, liquid/gas interface) to create thin films for these applications, each with its drawbacks. On-surface synthesis can lead to contamination from COF powder or unreacted chemicals, while interfacial synthesis risks damaging the film during post-transfer processes. These challenges necessitate the development of alternative synthesis methods for high-quality 2D COF films. This study presents a novel approach for synthesizing homogeneous 2D COF thin films by combining photochemistry and a liquid-flowing system. Leveraging previous work on liquid flow systems to prevent contamination during solvothermal synthesis, this approach to the photochemical method, resulting in the synthesis of high-crystalline 2D COF films with tunable thickness is adopted. The photochemical approach offers spatially controllable energy sources, enabling patternable COF synthesis. Notably, it is successfully fabricated ultrasmooth patterned 2D COF films on hexagonal boron nitride, offering a streamlined process for optoelectronic device fabrication without additional pre, post-processing steps.

Chiral Covalent Organic Framework Films with Enhanced Photoelectrical Performances.

The desirable superimposed stacking of two-dimensional covalent organic frameworks (2D COFs) benefits out-of-plane charge transfer, whereas the actual stacking deviation cannot leverage the potential of 2D COFs for optoelectrical applications. Herein, we report a chirality-induced strategy to control the parallel AA-stacking sequence for the β-ketoenamine-linked COF film supported on a FTO substrate. The resulting chiral modules are periodically distributed at the framework node, ensuring identical mirrored configurations of layers for parallel stacking. Such unique architectonics exhibit the prolonged charge carrier lifetime, fast charge-transfer dynamics, and ultrahigh electron collection efficiency, thereby allowing for the excellent photocurrent response of 38 μA/cm2 at 0.25 V (vs RHE). The origin of superior performances lies in the intensified exciton gradient distribution and electron density for photoinduced electron-hole dissociation and charge transfer, in stark contrast to achiral analogues. This study highlights the stacking sequence regulated by chiral nanoarchitectonics and promises great potential of chiral COFs in photoelectrical catalysis.

One-Dimensional Covalent Organic Framework-Based Multilevel Memristors for Neuromorphic Computing.

Memristors are essential components of neuromorphic systems that mimic the synaptic plasticity observed in biological neurons. In this study, a novel approach employing one-dimensional covalent organic framework (1D COF) films was explored to enhance the performance of memristors. The unique structural and electronic properties of two 1D COF films (COF-4,4'-methylenedianiline (MDA) and COF-4,4'-oxydianiline (ODA)) offer advantages for multilevel resistive switching, which is a key feature in neuromorphic computing applications. By further introducing a TiO2 layer on the COF-ODA film, a built-in electric field between the COF-TiO2 interfaces could be generated, demonstrating the feasibility of utilizing COFs as a platform for constructing memristors with tunable resistive states. The 1D nanochannels of these COF structures contributed to the efficient modulation of electrical conductance, enabling precise control over synaptic weights in neuromorphic circuits. This study also investigated the potential of these COF-based memristors to achieve energy-efficient and high-density memory devices.

One‐Dimensional Covalent Organic Framework‐Based Multilevel Memristors for Neuromorphic Computing

AbstractMemristors are essential components of neuromorphic systems that mimic the synaptic plasticity observed in biological neurons. In this study, a novel approach employing one‐dimensional covalent organic framework (1D COF) films was explored to enhance the performance of memristors. The unique structural and electronic properties of two 1D COF films (COF‐4,4′‐methylenedianiline (MDA) and COF‐4,4′‐oxydianiline (ODA)) offer advantages for multilevel resistive switching, which is a key feature in neuromorphic computing applications. By further introducing a TiO2 layer on the COF‐ODA film, a built‐in electric field between the COF‐TiO2 interfaces could be generated, demonstrating the feasibility of utilizing COFs as a platform for constructing memristors with tunable resistive states. The 1D nanochannels of these COF structures contributed to the efficient modulation of electrical conductance, enabling precise control over synaptic weights in neuromorphic circuits. This study also investigated the potential of these COF‐based memristors to achieve energy‐efficient and high‐density memory devices.