Synthesis, Hole Doping, and Electrical Properties of a Semiconducting Azatriangulene-Based Covalent Organic Framework

Semiconducting Covalent Organic Frameworks

Semiconductors form the foundational bedrock of modern electronics and numerous cutting-edge technologies. Particularly, semiconductors crafted from organic building blocks hold immense promise as next-generation pioneers, thanks to their vast array of chemical structures, customizable frontier orbital energy levels and bandgap structures, and easily adjustable π electronic properties. Over the past 50 years, advancements in chemistry and materials science have facilitated extensive investigations into small organic π compounds, oligomers, and polymers, resulting in a rich library of organic semiconductors. However, a longstanding challenge persists: how to organize π building units or chains into well-defined π structures, which are crucial for the performance of organic semiconductors. Consequently, the pursuit of methodologies capable of synthesizing and/or fabricating organic semiconductors with ordered structures has emerged as a frontier in organic and polymeric semiconductor research. In this context, covalent organic frameworks (COFs) stand out as unique platforms allowing for the covalent integration of organic π units into periodically ordered π structures, thus facilitating the development of semiconductors with extended yet precisely defined π architectures. Since their initial report in 2008, significant strides have been made in exploring various chemistries to develop semiconducting COFs, resulting in a rich library of structures, properties, functions, and applications. This review provides a comprehensive yet focused exploration of the general structural features of semiconducting COFs, outlining the basic principles of structural design, illustrating the linkage chemistry and synthetic strategies based on typical one-pot polymerization reactions to demonstrate the growth of bulk materials, nanosheets, films, and membranes. By elucidating the interactions between COFs and various entities such as photons, phonons, electrons, holes, ions, molecules, and spins, this review categorizes semiconducting COFs into nine distinct sections: semiconductors, photoconductors, light emitters, sensors, photocatalysts, photothermal conversion materials, electrocatalysts, energy storage electrodes, and radical spin materials, focusing on disclosing structure-originated properties and functions. Furthermore, this review scrutinizes structure-function correlations and highlights the unique features, breakthroughs, and challenges associated with semiconducting COFs. Furnished with foundational knowledges and state-of-the-art insights, this review predicts the fundamental issues to be addressed and outlines future directions for semiconducting COFs, offering a comprehensive overview of this rapidly evolving and remarkable field.

Semiconducting Polyaromatic Covalent Organic Frameworks Constructed through Self-Aldol Condensation

The construction of semiconducting covalent organic frameworks (COFs) via single-component self-polymerization is of broad interest in reticular chemistry. Herein, two semiconducting polyaromatic COFs with all-fused-ring conjugation structures were synthesized through the self-aldol condensation of indanone-based building blocks. The resulting COFs exhibit n-type semiconducting properties and exceptional stability under harsh acidic and alkaline conditions. The electrical conductivity and charge carrier mobility of the polyaromatic COFs reached up to 5.5 × 10-3 S cm-1 and 0.62 cm2 V-1 s-1, which ranked as the highest values among n-type semiconducting COFs. The high crystallinity, intrinsic porosity, excellent conductivity, and abundant five-membered rings as active sites render these COFs as effective metal-free electrocatalysts toward oxygen reduction reaction (ORR). Notably, one of these COFs shows a half-wave potential of up to 0.77 V under alkaline conditions, which constitutes one of the highest values among the reported metal-free ORR electrocatalysts. In addition, owing to the strong robustness of the polyaromatic COFs, they also exhibit long-term catalytic durability. This study not only expands the diversity of semiconducting COFs but also establishes new paradigms for the development of high-performance metal-free electrocatalysts toward the ORR process.

Morphology Controlled Covalent Organic Framework Nano-Trap for Synergetic Uranium Adsorption and Photoreduction

Covalent organic frameworks (COFs) without donor-acceptor pairs or inefficient separation of photogenerated electrons are usually considered unfavorable for photocatalysis due to electron-hole recombination. However, the study demonstrates a nitrile (CN) functionalized covalent organic framework nano-traps (COF-nTs; COF-nTS1, COF-nTS2, and COF-nTS3), in which the CN groups act as electron-withdrawing centers, surrounding electron and facilitating charge separation, transport, and adsorption process. To further enhance the efficiency of charge carriers, a special approach is introduced to integrate morphology control through acid regulation and defect engineering. These key strategies optimize the key structure and improve photocatalytic performance, achieving a maximum uranium extraction capacity of 3548.1 mg g-1, which is significantly higher than previously reported COF-based photocatalysts under visible light. A flexible 3 × 6 cm film of COF-nTs3 is prepared by the blade coating method, successfully extracting uranium from spiked seawater with a 7-day capacity of 76 mg g-1, a saturation capacity of 193 mg g-1, and 0.2 day half saturation time. This demonstrates its potential for uranium extraction from aqueous solutions.

Hopping-Type Charge Transport in Controllably p-Doped Polaronic Two-Dimensional Polymers

In this work, we find that controllable p-type doping leads to Holstein-type polarons in four electron-rich two-dimensional polymers (2DPs). Substoichometrically injecting holes into these 2DPs leads to small optical bandgaps (<1.0 eV) and electrical conductivities (17 mS m-1) significantly higher than their undoped analogs. Fourier-transform infrared spectroscopy and continuous-wave electron paramagnetic resonance spectroscopy both reveal that this arises from the formation of paramagnetic polarons. We achieve maximal conductivities when 2DPs comprised of electron-rich nodes and electron-rich linkers are combined, which is a consequence of more delocalized polarons as unveiled by diffuse-reflectance UV-vis-NIR spectroscopy. Variable-temperature electrical conductivity measurements reveal two distinct Arrhenius regimes in all 2DPs investigated, which we attribute to the different thermally activated processes inherent to in-plane and cross-plane electronic transport in stacked 2DP multilayers. This resulted in a maximum electronic conductivity of 326 mS m-1 at an elevated temperature. Collectively, this report provides fundamental insight into polaron-based charge-transport in p-type 2D organic layers, which we expect will form the foundation for the eventual deployment of these materials in electronic devices.

A Donor-Acceptor-Type Two-Dimensional Poly(Arylene Vinylene) for Efficient Electron Transport and Sensitive Chemiresistors

Two-dimensional (2D) conjugated polymers and their layer-stacked 2D conjugated covalent organic frameworks, such as 2D poly(arylene vinylene)s (2D PAVs), are emerging as promising polymer semiconductors for electronics and photocatalysis. However, achieving narrow optical band gaps and efficient electron transport remains a significant challenge for this class of materials to enhance the device's performance. Here, we report a donor-acceptor-type 2D PAV (2DPAV-TBDT-IT, where TBDT = thienyl-benzodithiophene and IT = s-indacene-1,3,5,7(2H,6H)-tetraone) synthesized via an Aldol-type 2D polycondensation approach. Notably, 2DPAV-TBDT-IT benefits from an effective intralayer donor-acceptor effect, exhibiting an optical band gap of 1.15 eV, the smallest among the reported 2D conjugated polymers. Density functional theory calculations reveal a unique electron-dominating transport for 2DPAV-TBDT-IT, with a strongly dispersive conduction band minimum and, thus, a small effective mass for electrons half that for holes. Additionally, terahertz spectroscopy measurements indicate a high charge mobility of 26 cm2 V-1 s-1 at room temperature for the powder sample. Given the high electron-deficiency of 2DPAV-TBDT-IT for facile electron injection from hazardous gases and the high-mobility electron-dominating transport in the material, we further fabricate chemiresistors from 2DPAV-TBDT-IT, showing ultrasensitive SO2 analyte detection with limit of detection of 0.088 ppb, significantly surpassing the reported chemiresistive SO2 sensors.

A Fully Conjugated Benzo[1,2-b:4,5-b']Dithiophene-Based Covalent Organic Framework Enables Efficient Blue Light-Driven Photocatalytic Sulfoxidation

Covalent organic frameworks (COFs) are becoming increasingly attractive in photocatalytic transformations because of the designable structures grounded on the building blocks and linkages. Herein, benzo[1,2-b:4,5-b']dithiophene, essential for various organic optoelectronic materials, is adopted as the building block for COFs. Hence, a fully conjugated COF BDTT-sp2c-COF and an imine-linked COF BDTT-COF are constructed by the condensations of 5',5″″-(benzo[1,2-b:4,5-b']dithiophene-2,6-diyl)bis([1,1':3',1″-terphenyl]-4,4″-dicarbaldehyde) with p-phenyldiacetonitrile and p-phenylenediamine, respectively. Thorough characterizations and theoretical calculations disclose that BDTT-sp2c-COF is superior to BDTT-COF in terms of specific surface area, photocarrier separation, and electron transfer. As such, BDTT-sp2c-COF enables more efficient photocatalytic sulfoxidation with oxygen than BDTT-COF. The fully conjugated structure guarantees the recyclability of BDTT-sp2c-COF. The blue light-driven photocatalytic sulfoxidation is generally applicable and proceeds selectively via energy and electron transfers with oxygen over BDTT-sp2c-COF. The fully conjugated COFs are promising to enable efficient photocatalytic reactions.

A Dynamic Covalent Organic Framework with Entangled 2D Layers

Dynamic covalent organic frameworks (COFs) represent an emerging class of porous materials with an inherent structural flexibility. However, due to the challenges in their synthesis and structural characterization, research on dynamic COFs remains at an early stage and requires further exploration. Herein, we report the designed synthesis of a novel COF with entangled 2D layers that exhibits interesting dynamic behavior in response to organic vapor exposure. By employing the continuous rotation electron diffraction technique, we precisely resolved the crystal structures of the COF before and after vapor adsorption. Structural analysis revealed that the vapor-induced conformational changes, such as anthracene unit rotation, triggered layer adjustments and reduced entanglement angles, leading to significant pore structure alterations. This study not only introduces a new class of dynamic COFs but also provides a foundation for the rational design of entangled frameworks with structural flexibility for diverse applications.

Azatriangulene-Based Conductive C═C Linked Covalent Organic Frameworks with Near-Infrared Emission

Two near-infrared (NIR) emissive π-conjugated covalent organic frameworks (COFs) pTANG1 and pTANG2 are synthesized using Knoevenagel condensation of trioxaazatriangulenetricarbaldehyde (TATANG) with benzene- and biphenyldiacetonitriles, respectively. The morphology of the COFs is affected by the size of TATANG precursor crystals. Donor-acceptor interactions in these COFs result in small bandgaps (≈1.6 eV) and NIR emission (λmax = 789 nm for pTANG1). pTANG1 can absorb up to 9 molecules of water per unit cell, which is accompanied by a marked quenching of the NIR emission, suggesting applications as humidity sensors. p-Doping with magic blue significantly increases the electrical conductivities of the COFs by up to 8 orders of magnitude, with the room temperature conductivity of pTANG1 reaching 0.65 S cm-1, the highest among reported C═C linked COFs. 1H NMR relaxometry, temperature-dependent fluorescence spectroscopy, and DFT calculations reveal that the higher rigidity of the shorter phenylene linker is responsible for the more extended conjugation (red-shifted emission, higher electrical conductivity) of pTANG1 compared to pTANG2.

Integration of Perylene Diimide into a Covalent Organic Framework for Photocatalytic Oxidation

Perylene diimides (PDIs) have garnered considerable attention due to their immense potential in photocatalysis. However, manipulating the molecular packing within their aggregates and enhancing the efficiency of photogenerated carrier recombination remain significant challenges. In this study, we demonstrate the incorporation of a PDI unit into a covalent organic framework (COF), named PDI-PDA, by linking an ortho-substituted PDI with p-phenylenediamine (PDA) to control its intermolecular aggregation. The incorporation enables precise modulation of electron-transfer dynamics, leading to a ten-fold increase in the efficiency of photocatalytic oxidation of thioether to sulfoxide with PDI-PDA compared to the PDI molecular counterpart, with yields exceeding 90 %. Electron property studies and density functional theory calculations show that the PDI-PDA with its well-defined crystal structure, enhances π-π stacking and lowers the electron transition barrier. Moreover, the strong electron-withdrawing ability of the PDI unit promotes the spatial separation of the valency band maximum and conduction band minimum of PDI-PDA, suppressing the rapid recombination of photogenerated electron-hole pairs and improving the charge-separation efficiency to give high photocatalytic efficiency. This study provides a brief but effective way for improving the photocatalytic efficiency of commonly used PDI-based dyes by integrating them into a framework skeleton.

Tuning (Photo)Electronic Properties of an Electron Deficient Porous Polymer via n-Doping with Tetrathiafulvalene

Charge-transfer complex formation within the pores of porous polymers is an efficient way to tune their electronical properties. Introduction of electron accepting guests to the electron donating hosts to conduct their p-doping is intensively studied in this context. However, the vice versa scenario, n-doping by treating the electron deficient (i.e., n-type) porous polymers with electron donating dopants, is rare. In this work, synthesis of an n-type phenazine based conjugated microporous polymer and its exposure to strong electron donating tetrathiafulvalene (TTF) dopants are presented. The fundamental physical characterizations (e.g., elemental analysis, gas sorption) showed that the vacuum impregnation technique is a good approach to load the guest molecules inside the pores. Moreover, the formation of charge-transfer complexes between the phenazine building blocks of the polymeric network and TTF dopants are confirmed via spectral techniques such Fourier transform infra-red, UV-vis, steady-state/time-resolved photoluminescence, and transient absorbance spectroscopies. Effect of the doping to the electronical properties is monitored by employing photoelectrochemical measurements, which showed lower charge-transfer resistivity and nearly doubled photocurrents after the doping. The study is, therefore, an important advancement for the applicability of (n-type) porous polymeric materials in the field of photo(electro)catalysis and organic electronics.

Tailoring Catalysis of Encapsulated Platinum Nanoparticles by Pore Wall Engineering of Covalent Organic Frameworks

While supported metal nanoparticles (NPs) have shown significant promise in heterogeneous catalysis, precise control over their interaction with the support, which profoundly impacts their catalytic performance, remains a significant challenge. In this study, Pt NPs are incorporated into thioether-functionalized covalent organic frameworks (denoted COF-Sx), enabling precise control over the size and electronic state of Pt NPs by adjusting the thioether density dangling on the COF pore walls. Notably, the resulting Pt@COF-Sx demonstrate exceptional selectivity (> 99 %) in catalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline, in sharp contrast to the poor selectivity of Pt NPs embedded in thioether-free COFs. Furthermore, the conversion over Pt@COF-Sx exhibits a volcano-type curve as the thioether density increases, due to the corresponding change of accessible Pt sites. This work provides an effective approach to regulating the catalysis of metal NPs via their microenvironment modulation, with the aid of rational design and precise tailoring of support structure.

Structural Modulation of Covalent Organic Frameworks for Efficient Hydrogen Peroxide Electrocatalysis

The electrochemical production of hydrogen peroxide (H2O2) using metal-free catalysts has emerged as a viable and sustainable alternative to the conventional anthraquinone process. However, the precise architectural design of these electrocatalysts poses a significant challenge, requiring intricate structural engineering to optimize electron transfer during the oxygen reduction reaction (ORR). Herein, we introduce a novel design of covalent organic frameworks (COFs) that effectively shift the ORR from a four-electron to a more advantageous two-electron pathway. Notably, the JUC-660 COF, with strategically charge-modified benzyl moieties, achieved a continuous high H2O2 yield of over 1200 mmol g-1 h-1 for an impressive duration of over 85 hours in a flow cell setting, marking it as one of the most efficient metal-free and non-pyrolyzed H2O2 electrocatalysts reported to date. Theoretical computations alongside in situ infrared spectroscopy indicate that JUC-660 markedly diminishes the adsorption of the OOH* intermediate, thereby steering the ORR towards the desired pathway. Furthermore, the versatility of JUC-660 was demonstrated through its application in the electro-Fenton reaction, where it efficiently and rapidly removed aqueous contaminants. This work delineates a pioneering approach to altering the ORR pathway, ultimately paving the way for the development of highly effective metal-free H2O2 electrocatalysts.

2D Conjugated Polymer Thin Films for Organic Electronics: Opportunities and Challenges

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics.

Multi-Functional 2D Covalent Organic Frameworks with Diketopyrrolopyrrole as Electron Acceptor

2D covalent organic framework (COF) materials with extended conjugated structure and periodic columnar π-arrays exhibit promising applications in organic optoelectronics. However, there is a scarcity of reports on optoelectronic COFs, mainly due to the lack of suitable π-skeletons. Here, two multi-functional optoelectronic 2D COFs DPP-TPP-COF and DPP-TBB-COF are constructed with diketopyrrolopyrrole as electron acceptor (A), and 1,3,6,8-tetraphenylpyrene and 1,3,5-triphenylbenzene as electron donor (D) through imine bonds. Both 2D COFs showed good crystallinities and AA stacking with a rhombic framework for DPP-TPP-COF and hexagonal one for DPP-TBB-COF, respectively. The electron D-A and ordered intermolecular packing structures endow the COFs with broad UV-vis absorptions and narrow bandgaps along with suitable HOMO/LUMO energy levels, resulting in multi-functional optoelectronic properties, including photothermal conversion, supercapacitor property, and ambipolar semiconducting behavior. Among them, DPP-TPP-COF exhibits a high photothermal conversion efficiency of 47% under 660 nm laser irradiation, while DPP-TBB-COF exhibits superior specific capacitance of 384 F g-1. Moreover, P-type doping and N-type doping are achieved by iodine and tetrakis(dimethylamino)ethylene on a single host COF, resulting in ambipolar semiconducting behavior. These results provide a paradigm for the application of multi-functional optoelectronic COF materials.

Identification of two-dimensional covalent organic frameworks with topology and their application in photocatalytic hydrogen evolution

Covalent organic frameworks have attracted considerable attention in recent years as a distinct class of crystalline porous organic materials. Their functional properties are inherently linked to their structural characteristics. Although hundreds of COFs have been reported so far, the types of their topologic structure are still limited. In this article, we report the identification of mcm topology for three porphyrin-based two-dimensional COFs, which are constructed from [4 + 4] imine condensation reactions. The mcm net is generated by pentagonal tiling, which has not been identified for COFs before. The structure of the COFs is elucidated by a variety of experimental characterization and structural simulations, by which their reticular frameworks exclusively composed of pentagonal pores have been confirmed. Moreover, the COFs exhibit high performance in photocatalytic hydrogen evolution from water, with the best one up to 10.0 mmol g-1 h-1 after depositing 0.76 wt% Pt as a co-catalyst. This study identifies mcm topology for COFs for the first time and highlights the potential of these COFs as promising photocatalysts for sustainable hydrogen production from water.

Structural Regulation of Covalent Organic Frameworks for Catalysis

ConspectusChemical reactions can be promoted at lower temperatures and pressures, thereby reducing the energy input, by introducing suitable catalysts. Despite its significance, the quest for efficient and stable catalysts remains a significant challenge. In this context, addressing the efficiency of catalysts stands out as a paramount concern. However, the challenges posed by the vague structure and limited tailorability of traditional catalysts would make it highly desirable to fabricate optimized catalysts based on the understanding of structure-activity relationships. Covalent organic frameworks (COFs), a subclass of fully designed crystalline materials formed by the polymerization of organic building blocks through covalent bonds have garnered widespread attention in catalysis. The precise and customizable structures of COFs, coupled with attributes such as high surface area and facile functional modification, make COFs attractive molecular platforms for catalytic applications. These inherent advantages position COFs as ideal catalysts, facilitating the elucidation of structure-performance relationships and thereby further improving the catalysis. Nevertheless, there is a lack of systematic emphasis on and summary of structural regulation at the atomic/molecular level for COF catalysis. Consequently, there is a growing need to summarize this research field and provide deep insights into COF-based catalysis to promote its further development.In this Account, we will summarize recent advances in structural regulation achieved in COF-based catalysts, placing an emphasis on the molecular design of the structures for enhanced catalysis. Considering the unique components and structural advantages of COFs, we present the fundamental principles for the rational design of structural regulation in COF-based catalysis. This Account starts by presenting an overview of catalysis and explaining why COFs are promising catalysts. Then, we introduce the molecular design principle for COF catalysis. Next, we present the following three aspects of the specific strategies for structural regulation of COF-based catalysts: (1) By designing different functional groups and integrating metal species into the organic unit, the activity and/or selectivity can be finely modulated. (2) Regulating the linkage facilitates charge transfer and/or modulates the electronic structure of catalytic metal sites, and accordingly, the intrinsic activity/selectivity can be further improved. (3) By means of pore wall/space engineering, the microenvironment surrounding catalytic metal sites can be modulated to optimize performance. Finally, the current challenges and future developments in the structural regulation of COF-based catalysts are discussed in detail. This Account provides insight into the structural regulation of COF-based catalysts at the atomic/molecular level toward improving their performance, which would provide significant inspiration for the design and structural regulation of other heterogeneous catalysts.

Tailoring COFs: Transforming Nonconducting 2D Layered COF into a Conducting Quasi-3D Architecture via Interlayer Knitting with Polypyrrole

Improving the electronic conductivity and the structural robustness of covalent organic frameworks (COFs) is paramount. Here, we covalently cross-link a 2D COF with polypyrrole (Ppy) chains to form a quasi-3D COF. The 3D COF shows well-defined reflections in the SAED patterns distinctly indexed to its modeled crystal structure. This knitting of 2D COF layers with conjugated polypyrrole units improves electronic conductivity from 10-9 to 10-2 S m-1. This conductivity boost is affirmed by the presence of density of states near the Fermi level in the 3D COF, and this elevates the COF's valence band maximum by 0.52 eV with respect to the parent 2D pyrrole-functionalized COF, which agrees well with the opto-electro band gaps. The extent of HOMO elevation suggests the predominant existence of a polaron state (radical cation), giving rise to a strong EPR signal, most likely sourced from the cross-linking polypyrrole chains. A supercapacitor devised with COF20-Ppy records a high areal capacitance of 377.6 mF cm-2, higher than that of the COF loaded with noncovalently linked polypyrrole chains. Thus, the polypyrrole acts as a "conjugation bridge" across the layers, lowering the band gap and providing polarons and additional conduction pathways. This marks a far-reaching approach to converting many 2D COFs into highly ordered and conducting 3D ones.

Turning on Singlet Oxygen Generation by Outer-Sphere Microenvironment Modulation in Porphyrinic Covalent Organic Frameworks for Photocatalytic Oxidation

Singlet oxygen (1 O2 ) is ubiquitously involved in various photocatalytic oxidation reactions; however, efficient and selective production of 1 O2 is still challenging. Herein, we reported the synthesis of nickel porphyrin-based covalent organic frameworks (COFs) incorporating functional groups with different electron-donating/-withdrawing features on their pore walls. These functional groups established a dedicated outer-sphere microenvironment surrounding the Ni catalytic center that tunes the activity of the COFs for 1 O2 -mediated thioether oxidation. With the increase of the electron-donating ability of functional groups, the modulated outer-sphere microenvironment turns on the catalytic activity from a yield of nearly zero by the cyano group functionalized COF to an excellent yield of 98 % by the methoxy group functionalized one. Electronic property investigation and density-functional theory (DFT) calculations suggested that the distinct excitonic behaviors attributed to the diverse band energy levels and orbital compositions are responsible for the different activities. This study represents the first regulation of generating reactive oxygen species (ROS) based on the strategy of outer-sphere microenvironment modulation in COFs.

2D Covalent Organic Frameworks with Kagome Lattice: Synthesis and Applications

2D covalent organic frameworks with Kagome (kgm) topology are a promising class of crystalline frameworks that possess both triangular and hexagonal pores. These dual-pore structures enable kgm COFs to exhibit unique advantages in selective separation, mass transfer, and targeted drug release. However, the synthesis of 2D kgm COFs has been hindered by the reliance on empirical methods. This review systematically summarizes the conventional macrocycle-to-framework strategy, typical [4+2] co-polymerization synthetic strategy, and bifunctional molecules self-condensation approach for constructing 2D kgm COFs. Factors influencing the formation of kgm lattice are surveyed, such as monomer type, solvent polarity, substrate concentration, etc., and highlight the representative examples on targeted synthesis. Additionally, applications of 2D kgm COFs and relationships between structure and performances are summarized. Finally, key fundamental perspectives are proposed to accelerate the further development of this intriguing material.

Gold(I)-Organic Frameworks as Catalysts for Carboxylation of Alkynes with CO2

Construction of gold-based metal-organic frameworks (Au-MOFs) would bring the merits of gold chemistry into MOFs. However, it still remains challenging because gold cations are easily reduced to metallic gold under solvothermal conditions. Herein, we present the first example of Au-MOFs prepared from the networking of cyclic trinuclear gold(I) complexes by formal transimination reaction in a rapid (<15 min) and scalable (up to 1 g) fashion under ambient condition. The Au-MOFs feature uniform porosity, high crystallinity, and superior chemical stability toward base (i.e., 20 M NaOH). With open Au(I) sites in the skeleton, the Au-MOFs as heterogeneous catalysts delivered good performance and substrate tolerance for the carboxylation reactions of alkynes with CO2. This work demonstrates a facile approach to reticularly synthesize Au-MOFs by combining the coordination and dynamic covalent chemistry.

Hexaazatriphenylene-Based Two-Dimensional Conductive Covalent Organic Framework with Anisotropic Charge Transfer

The development of covalent organic frameworks (COFs) with efficient charge transport is of immense interest for applications in optoelectronic devices. To enhance COF charge transport properties, electroactive building blocks and dopants can be used to induce extended conduction channels. However, understanding their intricate interplay remains challenging. We designed and synthesized a tailor-made COF structure with electroactive hexaazatriphenylene (HAT) core units and planar dioxin (D) linkages, denoted as HD-COF. With the support of theoretical calculations, we found that the HAT units in the HD-COF induce strong, eclipsed π-π stacking. The unique stacking of HAT units and the weak in-plane conjugation of dioxin linkages leads to efficient anisotropic charge transport. We fabricated HD-COF films to minimize the grain boundary effect of bulk COFs, which resulted in enhanced conductivity. As a result, the HD-COF films showed an electrical conductivity as high as 1.25 S cm-1 after doping with tris(4-bromophenyl)ammoniumyl hexachloroantimonate.

Porous crystalline materials for memories and neuromorphic computing systems

Porous crystalline materials usually include metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs) and zeolites, which exhibit exceptional porosity and structural/composition designability, promoting the increasing attention in memory and neuromorphic computing systems in the last decade. From both the perspective of materials and devices, it is crucial to provide a comprehensive and timely summary of the applications of porous crystalline materials in memory and neuromorphic computing systems to guide future research endeavors. Moreover, the utilization of porous crystalline materials in electronics necessitates a shift from powder synthesis to high-quality film preparation to ensure high device performance. This review highlights the strategies for preparing porous crystalline materials films and discusses their advancements in memory and neuromorphic electronics. It also provides a detailed comparative analysis and presents the existing challenges and future research directions, which can attract the experts from various fields (e.g., materials scientists, chemists, and engineers) with the aim of promoting the applications of porous crystalline materials in memory and neuromorphic computing systems.