Conjugated organic framework with three-dimensionally ordered stable structure and delocalized π clouds

The research progress on COF solid-state electrolytes for lithium batteries

Lithium metal batteries have garnered significant attention due to their high energy density and broad application prospects. However, the practical use of traditional liquid electrolytes is constrained by safety and stability challenges. In the exploration of novel electrolytes, solid-state electrolyte materials have emerged as a focal point. Covalent organic frameworks (COFs), with their large conjugated structures and unique electronic properties, are gradually gaining attention as an emerging class of solid-state electrolyte materials. In recent years, outstanding electrochemical performance has been achieved through the design and synthesis of various types of COF-based solid-state electrolytes, along with successful integration with other functional materials. This review will provide an overview of the research progress on COFs as solid-state electrolyte materials for lithium metal batteries and offer insights into their future potential in battery technology.

Self-Exfoliating Benzotristriazine Macrocyclic Network: A New 2D Material for High-Performance Electrochemical Energy Storage

Aza-fused aromatic π-conjugated networks are an important class of 2D graphitic analogs, which are generally constructed using aromatic precursors. Herein, the study describes a new synthetic approach and electrochemical properties of a self-exfoliating benzotristriazine 2D network (BTTN) constructed using aliphatic precursors, under relatively mild conditions. The obtained BTTN exhibits a nanodisc-like morphology, the self-exfoliation tendency of which is ascribed to the presence of structurally different macrocycles with high electronic repulsion between the layers. The benzotristriazine repeat units of BTTN is electroactive and holds higher carbon/nitrogen ratio when compared with the conventional graphitic aza-fused π-conjugated networks. The self-exfoliated BTTN nanodiscs show excellent electrochemical energy storage of 485 and 333 F g-1 at 1 A g-1 in three-electrode and two-electrode measurements, respectively. BTTN in a symmetric coin-cell architecture exhibits a high specific energy value of 46 Wh kg-1 at a power density of 1 kW kg-1 and shows excellent cyclic stability of 96% for 10 000 and 90% for 30 000 charge-discharge cycles at a higher current density of 5 A g-1, surpassing the device performance of most of the reported all-organic pseudocapacitive 2D networks.

Hydrazone-Linked Covalent Organic Frameworks

Hydrazone-linked covalent organic frameworks (COFs) with structural flexibility, heteroatomic sites, post-modification ability and high hydrolytic stability have attracted great attention from scientific community. Hydrazone-linked COFs, as a subclass of Schiff-base COFs, was firstly reported in 2011 by Yaghi's group and later witnessed prosperous development in various aspects. Their adjustable structures, precise pore channels and plentiful heteroatomic sites of hydrazone-linked structures possess much potential in diverse applications, for example, adsorption/separation, chemical sensing, catalysis and energy storage, etc. Up to date, the systematic reviews about the reported hydrazone-linked COFs are still rare. Therefore, in this review, we will summarize their preparation methods, characteristics and related applications, and discuss the opportunity or challenge of hydrazone-linked COFs. We hope this review could provide new insights about hydrazone-linked COFs for exploring more appealing functions or applications.

The development of catalysts and auxiliaries for the synthesis of covalent organic frameworks

Covalent organic frameworks (COFs) have recently seen significant advancements. Large quantities of structurally & functionally oriented COFs with a wide range of applications, such as gas adsorption, catalysis, separation, and drug delivery, have been explored. Recent achievements in this field are primarily focused on advancing synthetic methodologies, with catalysts playing a crucial role in achieving highly crystalline COF materials, particularly those featuring novel linkages and chemistry. A series of reviews have already been published over the last decade, covering the fundamentals, synthesis, and applications of COFs. However, despite the pivotal role that catalysts and auxiliaries play in forming COF materials and adjusting their properties (e.g., crystallinity, porosity, stability, and morphology), limited attention has been devoted to these essential components. In this Critical Review, we mainly focus on the state-of-the-art progress of catalysts and auxiliaries applied to the synthesis of COFs. The catalysts include four categories: acid catalysts, base catalysts, transition-metal catalysts, and other catalysts. The auxiliaries, such as modulators, oxygen, and surfactants, are discussed as well. This is then followed by the description of several specific applications derived from the utilization of catalysts and auxiliaries. Lastly, a perspective on the major challenges and opportunities associated with catalysts and auxiliaries is provided.

Photochromic radical states in 3D covalent organic frameworks with zyg topology for enhanced photocatalysis

Covalent-organic frameworks (COFs) with photoinduced donor-acceptor (D-A) radical pairs show enhanced photocatalytic activity in principle. However, achieving long-lived charge separation in COFs proves challenging due to the rapid charge recombination. Here, we develop a novel strategy by combining [6 + 4] nodes to construct zyg-type 3D COFs, first reported in COF chemistry. This structure type exhibits a fused Olympic-rings-like shape, which provides a platform for stabilizing the photoinduced D-A radical pairs. The zyg-type COFs containing catalytically active moieties such as triphenylamine and phenothiazine (PTZ) show superior photocatalytic production rates of hydrogen peroxide (H2O2). Significantly, the photochromic radical states of these COFs show up to 400% enhancement in photocatalytic activity compared to the parent states, achieving a remarkable H2O2 synthesis rate of 3324 μmol g-1 h-1, which makes the PTZ-COF one of the best crystalline porous photocatalysts in H2O2 production. This work will shed light on the synthesis of efficient 3D COF photocatalysts built on topologies that can facilitate photogenerating D-A radical pairs for enhanced photocatalysis.

An Appraisal for Providing Charge Transfer (CT) Through Synthetic Porous Frameworks for their Semiconductor Applications

In recent years, there has been considerable focus on the development of charge transfer (CT) complex formation as a means to modify the band gaps of organic materials. In particular, CT complexes alternate layers of aromatic molecules with donor (D) and acceptor (A) properties to provide inherent electrical conductivity. In particular, the synthetic porous frameworks as attractive D-A components have been extensively studied in recent years in comparison to existing D-A materials. Therefore, in this work, the synthetic porous frameworks are classified into conjugated microporous polymers (CMPs), covalent organic frameworks (COFs), and metal-organic frameworks (MOFs) and compare high-quality materials for CT in semiconductors. This work updates the overview of the above porous frameworks for CT, starting with their early history regarding their semiconductor applications, and lists CT concepts and selected key developments in their CT complexes and CT composites. In addition, the network formation methods and their functionalization are discussed to provide access to a variety of potential applications. Furthermore, several theoretical investigations, efficiency improvement techniques, and a discussion of the electrical conductivity of the porous frameworks are also highlighted. Finally, a perspective of synthetic porous framework studies on CT performance is provided along with some comparisons.

New Advances in Covalent Network Polymers via Dynamic Covalent Chemistry

Covalent network polymers, as materials composed of atoms interconnected by covalent bonds in a continuous network, are known for their thermal and chemical stability. Over the past two decades, these materials have undergone significant transformations, gaining properties such as malleability, environmental responsiveness, recyclability, crystallinity, and customizable porosity, enabled by the development and integration of dynamic covalent chemistry (DCvC). In this review, we explore the innovative realm of covalent network polymers by focusing on the recent advances achieved through the application of DCvC. We start by examining the history and fundamental principles of DCvC, detailing its inception and core concepts and noting its key role in reversible covalent bond formation. Then the reprocessability of covalent network polymers enabled by DCvC is thoroughly discussed, starting from the significant milestones that marked the evolution of these polymers and progressing to their current trends and applications. The influence of DCvC on the crystallinity of covalent network polymers is then reviewed, covering their bond diversity, synthesis techniques, and functionalities. In the concluding section, we address the current challenges faced in the field of covalent network polymers and speculates on potential future directions.

Regioisomerism in Thienothiophene-Based Covalent Organic Frameworks─A Tool for Band-Gap Engineering

The craft of tuning optical properties is well-established for crystalline inorganic and hybrid solids. However, a far greater challenge is to tune the optical properties of organic materials systematically by design. We now introduce a synthesis concept that enables us to alter the optical properties of crystalline covalent organic frameworks (COFs) systematically using isomeric structures of thienothiophene-based building blocks (T23/32T) combined with a variety of tetratopic aromatic amines, e.g., the Wurster moiety (W-NH2). This concept is demonstrated for the synthesis of COFs in bulk and film forms and provides highly crystalline and porous isomeric COFs featuring predesigned photophysical properties. The band gap of the framework can be tuned continuously and precisely by chemically doping the pristine W23TT COF with its related constitutional isomer building block. Density-functional theory investigations of COF model compounds indicate that the extent of π-conjugation is among the key characteristics enabling the band-gap engineering.

Covalent Organic Framework/Graphene Hybrids: Synthesis, Properties, and Applications

To address current energy crises and environmental concerns, it is imperative to develop and design versatile porous materials ideal for water purification and energy storage. The advent of covalent organic frameworks (COFs), a revolutionary terrain of porous materials, is underscored by their superlative features such as divinable structure, adjustable aperture, and high specific surface area. However, issues like inferior electric conductivity, inaccessible active sites impede mass transfer and poor processability of bulky COFs restrict their wider application. As a herculean stride forward, COF/graphene hybrids amalgamate the strengths of their constituent components and have in consequence, enticed significant scientific intrigue. Herein, the current progress on the structure and properties of graphene-based materials and COFs are systematically outlined. Then, synthetic strategies for preparing COF/graphene hybrids, including one-pot synthesis, ex situ synthesis, and in situ growth, are comprehensively reviewed. Afterward, the pivotal attributes of COF/graphene hybrids are dissected in conjunction with their multifaceted applications spanning adsorption, separation, catalysis, sensing, and energy storage. Finally, this review is concluded by elucidating prevailing challenges and gesturing toward prospective strides within the realm of COF/graphene hybrids research.

Enhanced Removal of Ultratrace Levels of Gold from Wastewater Using Sulfur-Rich Covalent Organic Frameworks

In view of the increasing global demand and consumption of gold, there is a growing need and effort to extract gold from alternative sources besides conventional mining, e.g., from water. This drive is mainly due to the potential benefits for the economy and the environment as these sources contain large quantities of the precious metal that can be utilized. Wastewater is one of these valuable sources in which the gold concentration can be in the ppb range. However, the effective selective recovery and recycling of ultratrace amounts of this metal remain a challenge. In this article, we describe the development of a covalent imine-based organic framework with pores containing thioanisole functional groups (TTASDFPs) formed by the condensation of a triazine-based triamine and an aromatic dialdehyde. The sulfur-functionalized pores served as effective chelating agents to bind Au3+ ions, as evidenced by the uptake of more than 99% of the 9 ppm Au3+ solution within 2 min. This is relatively fast kinetics compared with other adsorbents reported for gold adsorption. TTASDFP also showed a high removal capacity of 245 mg·g-1 and a clear selectivity toward gold ions. More importantly, the material can capture gold at concentrations as low as 1 ppb.

A two-dimensional covalent organic framework with single-atom manganese for electrochemical NO reduction: a computational study

Covalent organic frameworks (COFs) exhibit great potential for electrocatalysis. Here, using DFT calculations and constant-potential modelling, we report the feasibility of a series of COFs toward NO reduction via regulating their central metal atoms and linking ligands. A COF with single-atom Mn is identified to possess superior activity while maintaining high NH3 selectivity.

Synthetic Strategies to Extended Aromatic Covalent Organic Frameworks

π-Conjugated materials are highly attractive owing to their unique optical and electronic properties. Covalent organic frameworks (COFs) offer a great opportunity for precise arrangement of building units in a π-conjugated crystalline matrix and tuning of the properties through choice of functionalities or post-synthetic modification. With this review, we aim at summarizing both the most representative as well as emerging strategies for the synthesis of π-conjugated COFs. We give examples of direct synthesis using large, π-extended building blocks. COFs featuring fully conjugated linkages such as vinylene, pyrazine, and azole are discussed. Then, post-synthetic modification methods that result in the extension of the COF π-system are reviewed. Throughout, mechanistic insights are presented when available. In the context of their utilization as film devices, we conduct a concise survey of the prominent COF layer deposition techniques reported and their aptness for the deposition of fused aromatic systems.

3D Covalent Organic Frameworks from Design, Synthesis to Applications in Optoelectronics

Covalent organic frameworks (COFs), a new class of crystalline materials connected by covalent bonds, have been developed rapidly in the past decades. However, the research on COFs is mainly focused on two-dimensional (2D) COFs, and the research on three-dimensional (3D) COFs is still in the initial stage. In 2D COFs, the covalent bonds exist only in the 2D flakes and can form 1D channels, which hinder the charge transport to some extent. In contrast, 3D COFs have a more complex pore structure and thus exhibit higher specific surface area and richer active sites, which greatly enhance the 3D charge carrier transport. Therefore, compared to 2D COFs, 3D COFs have stronger applicability in energy storage and conversion, sensing, and optoelectronics. In this review, it is first introduced the design principles for 3D COFs, and in particular summarize the development of conjugated building blocks in 3D COFs, with a special focus on their application in optoelectronics. Subsequently, the preparation of 3D COF powders and thin films and methods to improve the stability and functionalization of 3D COFs are summarized. Moreover, the applications of 3D COFs in electronics are outlined. Finally, conclusions and future research directions for 3D COFs are presented.

Strategies for Enhancing the Photocatalytic and Electrocatalytic Efficiency of Covalent Triazine Frameworks for CO2 Reduction

Converting carbon dioxide (CO2) into fuel and high-value-added chemicals is considered a green and effective way to solve global energy and environmental problems. Covalent triazine frameworks (CTFs) are extensively utilized as an emerging catalyst for photo/electrocatalytic CO2 reduction reaction (CO2RR) recently recognized for their distinctive qualities, including excellent thermal and chemical stability, π-conjugated structure, rich nitrogen content, and a strong affinity for CO2, etc. Nevertheless, single-component CTFs have the problems of accelerated recombination of photoexcited electron-hole pairs and restricted conductivity, which limit their application for photo/electrocatalytic CO2RR. Therefore, emphasis will then summarize the strategies for enhancing the photocatalytic and electrocatalytic efficiency of CTFs for CO2RR in this paper, including atom doping, constructing a heterojunction structure, etc. This review first illustrates the synthesis strategies of CTFs and the advantages of CTFs in the field of photo/electrocatalytic CO2RR. Subsequently, the mechanism of CTF-based materials in photo/electrocatalytic CO2RR is described. Lastly, the challenges and future prospects of CTFs in photo/electrocatalytic CO2RR are addressed, which offers a fresh perspective for the future development of CTFs in photo/electrocatalytic CO2RR.

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.

Effect of interlayer slipping on the geometric, thermal and adsorption properties of 2D covalent organic frameworks: a comprehensive review based on computational modelling studies

Two-dimensional covalent organic frameworks (2D-COFs) are a class of crystalline porous organic polymers, consisting of 2D-planar sheets stacked together perpendicularly via noncovalent forces. Since their discovery, 2D-COFs have attracted extensive attention for optoelectronic and adsorption applications. Owing to the layer stacking nature of 2D COFs, various new slipped structures that are energetically favourable can be designed. These interlayer slipped structures are actively responsible for tuning (mostly enhancing) the optoelectronic properties, thermal properties, and mechanical strength of 2D COFs. This review summarizes the effect of interlayer slipping on the energetic stability, electronic behaviour and gas adsorption properties of 2D layered COFs, which is explained through computational modelling simulations. Since computational modelling offers a deep insight into electronic behaviour at the atomic scale, which is potentially impossible through experimental techniques, the introduction and role of computational techniques in such studies have also been described.

Covalent organic frameworks: spotlight on applications in the pharmaceutical arena

Covalent organic frameworks (COFs) have much potential in the field of analytical separation research due to their distinctive characteristics, including easy modification, low densities, large specific surface areas and permanent porosity. This article provides a historical overview of the synthesis and broad perspectives on the applications of COFs. The use of COF-based membranes in gas separation, water treatment (desalination, heavy metals and dye removal), membrane filtration, photoconduction, sensing and fuel cells is also covered. However, these COFs also demonstrate great promise as solid-phase extraction sorbents and solid-phase microextraction coatings. In addition to various separation applications, this work aims to highlight important advancements in the synthesis of COFs for chiral and isomeric compounds.

Recent advances in two-dimensional polymers: synthesis, assembly and energy-related applications

Two-dimensional polymers (2DPs) are a class of 2D crystalline polymer materials with definite structures, which have outstanding physical-chemical and electronic properties. They cleverly link organic building units through strong covalent bonds and can construct functional 2DPs through reasonable design and selection of different monomer units to meet various application requirements. As promising energy materials, 2DPs have developed rapidly in recent years. This review first introduces the basic overview of 2DPs, such as their historical development, inherent 2D characteristics and diversified topological advantages, followed by the summary of the typical 2DP synthesis methods recently (including "top-down" and "bottom-up" methods). The latest research progress in assembly and processing of 2DPs and the energy-related applications in energy storage and conversion are also discussed. Finally, we summarize and prospect the current research status, existing challenges, and future research directions of 2DPs.

Nonsymmetric Pyrene-Fused Pyrazaacenes via Green Oxidation of 2,7-Di-tert-butylpyrene

We disclose a four-step oxidize-condense-oxidize-condense synthesis pathway to prepare nonsymmetric pyrene-fused pyrazaacenes (PPAs) using our recently discovered oxidation conditions for 2,7-di-tert-butylpyrene. The new pathway results in marked improvements in yields and simplifies purification as compared with the sequential condensation strategy previously employed to make these compounds.

Covalent Organic Frameworks: Cutting-Edge Materials for Carbon Dioxide Capture and Water Harvesting from Air

The implacable rise of carbon dioxide (CO2 ) concentration in the atmosphere and acute water stress are one of the central challenges of our time. Present-day chemistry is strongly inclined towards more sustainable solutions. Covalent organic frameworks (COFs), attributable to their structural designability with atomic precision, functionalizable chemical environment and robust extended architectures, have demonstrated promising performances in CO2 trapping and water harvesting from air. In this Review, we discuss the major developments in this field as well as sketch out the opportunities and shortcomings that remain over large-scale COF synthesis, device engineering, and long-term performance in real environments.

Chemical Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks (COFs) are a type of crystalline porous polymer composed of light elements through strong covalent bonds. COFs have attracted considerable attention due to their unique designable structures and excellent material properties. Currently, COFs have shown outstanding potential in various fields, including gas storage, pollutant removal, catalysis, adsorption, optoelectronics, and their research in the sensing field is also increasingly flourishing. In this review, we focus on COF-based sensors. Firstly, we elucidate the fundamental principles of COF-based sensors. Then, we present the primary application areas of COF-based sensors and their recent advancements, encompassing gas, ions, organic compounds, and biomolecules sensing. Finally, we discuss the future trends and challenges faced by COF-based sensors, outlining their promising prospects in the field of sensing.

Recent advances in supramolecular fullerene chemistry

Fullerene chemistry has come a long way since 1990, when the first bulk production of C60 was reported. In the past decade, progress in supramolecular chemistry has opened some remarkable and previously unexpected opportunities regarding the selective (multiple) functionalization of fullerenes and their (self)assembly into larger structures and frameworks. The purpose of this review article is to provide a comprehensive overview of these recent developments. We describe how macrocycles and cages that bind strongly to C60 can be used to block undesired addition patterns and thus allow the selective preparation of single-isomer addition products. We also discuss how the emergence of highly shape-persistent macrocycles has opened opportunities for the study of photoactive fullerene dyads and triads as well as the preparation of mechanically interlocked compounds. The preparation of two- or three-dimensional fullerene materials is another research area that has seen remarkable progress over the past few years. Due to the rapidly decreasing price of C60 and C70, we believe that these achievements will translate into all fields where fullerenes have traditionally (third-generation solar cells) and more recently been applied (catalysis, spintronics).

Carbon Nanotube Template-Assisted Synthesis of Conjugated Microporous Polytriphenylamine with High Porosity for Efficient Supercapacitive Energy Storage

Engineering of conjugated microporous polymers (CMPs) with high porosity, redox activity, and electronic conductivity is of significant importance for their practical applications in electrochemical energy storage. Aminated-multiwall carbon nanotubes (NH2 -MWNT) are utilized to modulate the porosity and electronic conductivity of polytriphenylamine (PTPA), which is synthesized via Buchwald-Hartwig coupling reaction of tri(4-bromophenyl)amine and phenylenediamine as constitutional units in a one-step in situ polymerization process. Compared to PTPA, the specific surface area of core-shell PTPA@MWNTs has been greatly improved from 32 to 484 m2  g-1 . The PTPA@MWNTs exhibites an improved specific capacitance, with the highest value 410 F g-1 in 0.5 M H2 SO4 at a current of 10 A g-1 achieve for PTPA@MWNT-4 due to the hierarchical meso-micro pores, high redox-activity and electronic conductivity. Symmetric supercapacitor assemble by PTPA@MWNT-4 has a capacitance of 216 F g-1 of total electrode materials and retains 71% of initial capacitance after 6000 cycles. This study gives new insights into the role of CNT templates in the adjustment of molecular structure, porosity, and electronic property of CMPs for the high-performance electrochemical energy storage.

Pure Covalent-Organic Framework Membrane as a Label-Free Biomimetic Nanochannel for Sensitive and Selective Sensing of Chiral Flavor Substances

Chiral flavor substances play an important role in the human perception of different tastes. Here, we report a pure covalent-organic framework (COF) membrane nanochannel in combination with a chiral gold nanoparticles (AuNPs) selector for sensing chiral flavor substances. The pure COF membrane with a proper pore size is selected as the nanochannel, while l-cysteine-modified AuNPs (l-Cys-AuNPs) are used as the chiral selector. l-Cys-AuNPs show stronger binding to the S-enantiomer than the R-enantiomer, causing current reduction to different degrees for the R- and S-enantiomer to achieve chiral sensing due to the synergistic effect of the size exclusion of the COF nanochannel and the chiral selectivity of l-Cys-AuNPs. The developed COF membrane nanochannel sensing platform not only allows an easy balance of the permeability and selectivity, which is difficult to achieve in traditional polymer membrane nanochannel sensors, but also exhibits better chiral performance than commercial artificial anodic aluminum oxide (AAO) nanochannel sensors. The developed nanochannel sensor is successfully applied for sensing flavor enantiomers such as limonene, propanediol, methylbutyric acid, and butanol with the enantiomer excess values of 55.2% (propanediol) and 72.4% (limonene) and the low detection limits of 36 (limonene) and 71 (propanediol) ng L-1. This study provides a new idea for the construction of nanochannel platforms based on the COF for sensitive and selective chiral sensing.

Influence of Building Block Symmetry on the Band Structure of Stacked 2D Polyimide Covalent Organic Frameworks

Covalent organic frameworks (COFs) are a class of crystalline porous materials distinctively built solely from organic elements, carbon, oxygen, hydrogen, and often nitrogen or boron. They form light, mechanically rigid, and chemically stable networks that have many advantages, but their low solubility and poor processability create issues with developing large-scale films or membranes. Two-dimensional (2D) COFs possess periodic porous crystallinity, functionality, modularity, and layered one-dimensional (1D) transport channels. All of these traits, along with the semiconducting properties of selected COFs, make them interesting candidates for integration in optoelectronic devices. Therefore, it is still a challenge to explore computationally and structurally the semiconductivity of COFs and to determine their final potential. Herein, we report on the possible semiconducting properties and results of polyimide-COF materials using density functional theory calculations. Our analysis includes monolayers and multilayers (AA- and AB-stacked modes) of mellitic triimide frameworks designed from mellitic trianhydride (MTA) as the main building knot, including MTI-TAPB-COF, which was previously synthesized from the condensation reaction of MTA and 1,3,5-tris(4-aminophenyl)benzene (TAPB), and other previously unreported structures based on MTA. Respective frameworks have been selected due to the difference in building block symmetry (C3 + C2 and C3 + C3) and different chemical linkages, either by benzene or by pyridine rings. We find the polyimide multilayers to be stable and with varying electronic properties. The finite band gap exhibited by every structure (monolayer and stacked) was sensitive to atomic arrangement. Stacking introduces dispersion to an otherwise flat band structure of the materials, which appeared to be highly sensitive to stacking direction. The effect of stacking was similar for each COF, but the magnitude of band structure change was different and dependent on the symmetry of the building blocks.

Photo-Driven Quasi-Topological Transformation Exposing Highly Active Nitrogen Cation Sites for Enhanced Photocatalytic H2 O2 Production

Herein, the exposure of highly-active nitrogen cation sites has been accomplished by photo-driven quasi-topological transformation of a 1,10-phenanthroline-5,6-dione-based covalent organic framework (COF), which contributes to hydrogen peroxide (H2 O2 ) synthesis during the 2-electron O2 photoreduction. The exposed nitrogen cation sites with photo-enhanced Lewis acidity not only act as the electron-transfer motor to adjust the inherent charge distribution, powering continuous and stable charge separation, and broadening visible-light adsorption, but also providing a large number of active sites for O2 adsorption. The optimal catalyst shows a high H2 O2 production rate of 11965 μmol g-1  h-1 under visible light irradiation and a remarkable apparent quantum yield of 12.9 % at 400 nm, better than most of the previously reported COF photocatalysts. This work provides new insights for designing photo-switchable nitrogen cation sites as catalytic centers toward efficient solar to chemical energy conversion.

Recent Advances in and Applications of Electrochemical Sensors Based on Covalent Organic Frameworks for Food Safety Analysis

The international community has been paying close attention to the issue of food safety as a matter of public health. The presence of a wide range of contaminants in food poses a significant threat to human health, making it vital to develop detection methods for monitoring these chemical contaminants. Electrochemical sensors using emerging materials have been widely employed to detect food-derived contaminants. Covalent organic frameworks (COFs) have the potential for extensive applications due to their unique structure, high surface area, and tunable pore sizes. The review summarizes and explores recent advances in electrochemical sensors modified with COFs for detecting pesticides, antibiotics, heavy metal ions, and other food contaminants. Furthermore, future challenges and possible solutions will be discussed regarding food safety analysis using COFs.

Conductive Covalent Organic Frameworks of Polymetallophthalocyanines as a Tunable Platform for Electrocatalysis

Developing an electrocatalyst platform that can control the interplay among activity, selectivity, and stability at atomic precision remains a grand challenge. Here, we have synthesized highly crystalline polymetallophthalocyanines (pMPcs, M = Fe, Co, Ni, and Cu) through the annulation of tetracyanobenzene in the presence of transition metals. The conjugated, conductive, and stable backbones with precisely installed metal sites render pMPcs a unique platform in electrochemical catalysis, where tunability emerges from long-range interactions. The construction of pCoNiPc with a Co and Ni dual-site integrates the advantageous features of pCoPc and pNiPc in electrocatalytic CO2 reduction through electronic communication of the dual-site with an unprecedented long atomic separation of ≥14 chemical bonds. This integration provides excellent activity (current density, j = -16.0 and -100 mA cm-2 in H-type and flow cell, respectively), selectivity (CO Faraday efficiency, FECO = 94%), and stability (>10 h), making it one of the best-performing reticular materials.

Carborane-Based Three-Dimensional Covalent Organic Frameworks

The predesignable porous structure and high structural flexibility of covalent organic frameworks (COFs) render this material desirable as a platform for addressing various cutting-edge issues. Precise control over their composition, topological structure, porosity, and stability to realize tailor-made functionality still remains a great challenge. In this work, we developed a new kind of three-dimensional (3D) carborane-based COF with a 7-fold interpenetrating dia topological diagram. The resulting COFs exhibited high crystallinity, exceptional porosity, and strong robustness. The slightly lower electronegativity of boron (2.04) than that of hydrogen (2.20) can lead to the polarization of the B-H bond into a Bδ+-Hδ- mode, which renders these COFs as high-performance materials for the adsorption and separation of hexane isomers through the B-Hδ-···Hδ+-C interaction. Significantly, the carborane content of obtained COFs reached up to 54.2 wt %, which gets the highest rank among all the reported porous materials. Combining high surface area, strong robustness, and high content of carborane, the obtained COFs can work as efficient adsorbents for the separation of the five hexane isomers with high separation factors. This work not only enhances the diversity of 3D functional COFs but also constitutes a further step toward the efficient separation of alkane isomers.

Research Progress in Donor-Acceptor Type Covalent Organic Frameworks

Covalent organic frameworks (COFs) are new organic porous materials constructed by covalent bonds, with the advantages of pre-designable topology, adjustable pore size, and abundant active sites. Many research studies have shown that COFs exhibit great potential in gas adsorption, molecular separation, catalysis, drug delivery, energy storage, etc. However, the electrons and holes of intrinsic COF are prone to compounding in transport, and the carrier lifetime is short. The donor-acceptor (D-A) type COFs, which are synthesized by introducing D and A units into the COFs backbone, combine separated electron and hole migration pathway, tunable band gap and optoelectronic properties of D-A type polymers with the unique advantages of COFs and have made great progress in related research in recent years. Here, the synthetic strategies of D-A type COFs are first outlined, including the rational design of linkages and D-A units as well as functionalization approaches. Then the applications of D-A type COFs in catalytic reactions, photothermal therapy, and electronic materials are systematically summarized. In the final section, the current challenges, and new directions for the development of D-A type COFs are presented.

Covalent organic frameworks: linkage types, synthetic methods and bio-related applications

Covalent organic frameworks (COFs) are composed of small organic molecules linked via covalent bonds, which have tunable mesoporous structure, good biocompatibility and functional diversities. These excellent properties make COFs a promising candidate for constructing biomedical nanoplatforms and provide ample opportunities for nanomedicine development. A systematic review of the linkage types and synthesis methods of COFs is of indispensable value for their biomedical applications. In this review, we first summarize the types of various linkages of COFs and their corresponding properties. Then, we highlight the reaction temperature, solvent and reaction time required by different synthesis methods and show the most suitable synthesis method by comparing the merits and demerits of various methods. To appreciate the cutting-edge research on COFs in bioscience technology, we also summarize the bio-related applications of COFs, including drug delivery, tumor therapy, bioimaging, biosensing and antimicrobial applications. We hope to provide insight into the interdisciplinary research on COFs and promote the development of COF nanomaterials for biomedical applications and their future clinical translations.

Narrow-Pore Engineering of Vinylene-Linked Covalent Organic Frameworks with Weak Interaction-Triggered Multiple Responses

Vinylene-linked covalent organic frameworks (COFs) are emerging as promising crystalline materials, but their narrow pore engineering is severely impeded by the weak reversibility of the carbon-carbon double bond formation reaction, which has led to less exploration of their ultramicroporous structures and properties. Herein, we developed a single aromatic ring-based tetratopic monomer, tetramethylpyrazine, which undergoes a smooth Knoevenegal condensation at its four arylmethly carbon atoms with linear aromatic dialdehyde monomers upon the self-catalyzed activation of pyridine nitrogen-containing monomers in the presence of an organic anhydride. This has resulted in the formation of two vinylene-linked COFs, which both crystallized in orthorhombic lattices, and layered in AA stacking fashions along the vertical directions. They exhibit high surface areas and well-tailored ultramicropore sizes up to 0.5 nm. The unique cross-linking mode at two pairs of para-positions of each pyrazine unit through carbon-carbon double bonds afford them with π-extended conjugation over the in-plane backbones and substantial semiconducting characters. The resultant COFs can be well-dispersed in water to form stable sub-microparticles with negative charges (zeta potentials: ca. -30 mV), and exhibiting tunable aggregation behaviors through protonation/deprotonation. As a consequence, they exhibit pore-size-dependent colorimetric responses to various anions with different pKa values in high selectivity.

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.

Naphthodithiophene-Fused Porphyrins: Synthesis, Characterization, and Impact of Extended Conjugation on Aromaticity

The fusion of tetrapyrroles with aromatic heterocycles constitutes a useful tool for manipulating their opto-electronic properties. In this work, the synthesis of naphthodithiophene-fused porphyrins was achieved through a Heck reaction-based cascade of steps followed by the Scholl reaction. The naphthodithiophene-fused porphyrins display a unique set of optical and electronic properties. Fusion of the naphtho[2,1-b:3,4-b']dithiophene to porphyrin (F2VTP) leads to a ~20% increase in the fluorescence lifetime, which is accompanied, unexpectedly, by a more than two-fold drop in the emission quantum yield (ϕ=0.018). In contrast, fusion of the isomeric naphtho[1,2-b:4,3-b']dithiophene to porphyrin (F3VPT) results in a ~1.5-fold increase in the fluorescence quantum yield (ϕ=0.13) with a concomitant ~30 % increase in the fluorescence lifetime. This behavior suggests that fusion of the porphyrin with the naphthodithiopheno-system mainly affects the radiative rate constant in the Q-state deactivation pathway, where the effects of the isomeric naphtho[2,1-b:3,4-b']dithiophene- versus naphtho[1,2-b:4,3-b']dithiophene-fusion are essentially the opposite. Interestingly, nucleus-independent chemical shifts analysis revealed a considerable difference between the aromaticities of these two isomeric systems. Our results demonstrate that subtle structural differences in the fused components of the porphyrin can be reflected in rather significant differences between the photophysical properties of the resulting systems.

Gradient Channel Segmentation in Covalent Organic Framework Membranes with Highly Oriented Nanochannels

Covalent organic frameworks (COFs) offer an exceptional platform for constructing membrane nanochannels with tunable pore sizes and tailored functionalities, making them promising candidates for separation, catalysis, and sensing applications. However, the synthesis of COF membranes with highly oriented nanochannels remains challenging, and there is a lack of systematic studies on the influence of postsynthetic modification reactions on functionality distribution along the nanochannels. Herein, we introduced a "prenucleation and slow growth" approach to synthesize a COF membrane featuring highly oriented mesoporous channels and a high Brunauer-Emmett-Teller surface area of 2230 m2 g-1. Functional moieties were anchored to the pore walls via "click" reactions and coordinated with Cu ions to serve as segmentation functions. This led to a remarkable H2/CO2 separation performance that surpassed the Robeson upper bound. Moreover, we found that the functionalities distributed along the nanochannels could be influenced by functionality flexibility and postsynthetic reaction rate. This strategy paved the way for the accurate design and construction of COF-based artificial solid-state nanochannels with high orientation and precisely controlled channel environments.

Design and Synthesis of a Polyketone Building Block with Vinyl Groups-9,10-Diethyl-9,10-ethenoanthracene-2,3,6,7(9H,10H)-tetraone-and a Preliminary Photoelectrical Property Study of Its Azaacene Derivatives

Polyketone compounds are powerful building blocks to synthesize various organic functional materials. Despite that a great many number of planar and non-planar polyketone building blocks have been developed, one issue is that generally there are only ketone functional groups on the molecular skeleton, which will constrain their transformation and further limit the development of functional materials. In this work, we report the design and synthesis of a building block 9,10-diethyl-9,10-ethenoanthracene-2,3,6,7(9H,10H)-tetraone with additional vinyl functional groups. In addition, its azaacene derivatives were also synthesized, and their preliminary physicochemical properties were studied.

Single Site Coordination Enabled Construction of Metal-Diketimine-Linked Covalent Organic Frameworks for Boosted Electrooxidation of Biomass Derivative

Aromatic aldehydes are widely used for the construction of covalent organic frameworks (COFs). However, due to the high flexibility, high steric hindrance, and low reactivity, it remains challenging to synthesize COFs using ketones as building units, especially the highly flexible aliphatic ones. Here, the single nickel site coordination strategy is reported to lock the configurations of the highly flexible diketimine to transform discrete oligomers or amorphous polymers into highly crystalline nickel-diketimine-linked COFs (named as Ni-DKI-COFs). The strategy has been successfully extended to the synthesis of a series of Ni-DKI-COFs by the condensation of three flexible diketones with two tridentate amines. Thanks to the ABC stacking model with high amount and easily accessible single nickel (II) sites on their 1D channels, Ni-DKI-COFs are exploited as well-defined electrocatalyst platforms for efficiently electro-upgrading biomass-derived 5-Hydroxymethylfurfural (HMF) into value-added 2,5-furandicarboxylic acid (FDCA) with a 99.9% yield and a 99.5% faradaic efficiency as well as a high turnover frequency of 0.31 s-1 .

Engineering of Phenylpyridine- and Bipyridine-Based Covalent Organic Frameworks for Photocatalytic Tandem Aerobic Oxidation/Povarov Cyclization

Covalent organic frameworks (COFs) are emerging as a new class of photoactive organic semiconductors, which possess crystalline ordered structures and high surface areas. COFs can be tailor-made toward specific (photocatalytic) applications, and the size and position of their band gaps can be tuned by the choice of building blocks and linkages. However, many types of building blocks are still unexplored as photocatalytic moieties and the scope of reactions photocatalyzed by COFs remains quite limited. In this work, we report the synthesis and application of two bipyridine- or phenylpyridine-based COFs: TpBpyCOF and TpPpyCOF. Due to their good photocatalytic properties, both materials were applied as metal-free photocatalysts for the tandem aerobic oxidation/Povarov cyclization and α-oxidation of N-aryl glycine derivatives, with the bipyridine-based TpBpyCOF exhibiting the highest activity. By expanding the range of reactions that can be photocatalyzed by COFs, this work paves the way toward the more widespread application of COFs as metal-free heterogeneous photocatalysts as a convenient alternative for commonly used homogeneous (metal-based) photocatalysts.

Regulating the proximity effect of heterocycle-containing AIEgens

Proximity effect, which refers to the low-lying (n,π*) and (π,π*) states with close energy levels, usually plays a negative role in the luminescent behaviors of heterocyclic luminogens. However, no systematic study attempts to reveal and manipulate proximity effect on luminescent properties. Here, we report a series of methylquinoxaline derivatives with different electron-donating groups, which show different photophysical properties and aggregation-induced emission behaviors. Experimental results and theoretical calculation reveal the gradually changed energy levels and different coupling effects of the closely related (n,π*) and (π,π*) states, which intrinsically regulate proximity effect and aggregation-induced emission behaviors of these luminogens. With the intrinsic nature of heterocycle-containing compounds, they are utilized for sensors and information encryption with dynamic responses to acid/base stimuli. This work reveals both positive and negative impacts of proximity effect in heterocyclic aggregation-induced emission systems and provides a perspective to develop functional and responsive luminogens with aggregation-induced emission properties.

Recent Advances in the Use of Covalent Organic Frameworks as Heterogenous Photocatalysts in Organic Synthesis

Organic photochemistry is intensely developed in the 1980s, in which the nature of excited electronic states and the energy and electron transfer processes are thoroughly studied and finally well-understood. This knowledge from molecular organic photochemistry can be transferred to the design of covalent organic frameworks (COFs) as active visible-light photocatalysts. COFs constitute a new class of crystalline porous materials with substantial application potentials. Featured with outstanding structural tunability, large porosity, high surface area, excellent stability, and unique photoelectronic properties, COFs are studied as potential candidates in various research areas (e.g., photocatalysis). This review aims to provide the state-of-the-art insights into the design of COF photocatalysts (pristine, functionalized, and hybrid COFs) for organic transformations. The catalytic reaction mechanism of COF-based photocatalysts and the influence of dimensionality and crystallinity on heterogenous photocatalysis performance are also discussed, followed by perspectives and prospects on the main challenges and opportunities in future research of COFs and COF-based photocatalysts.

Construction of highly-stable covalent organic framework with combined enol-imine and keto-enamine linkages

A novel covalent organic framework (COF) (Tp-BI-COF) with combined ketimine-type enol-imine and keto-enamine linkages was prepared through a cascade of ketimine condensation followed by aldimine condensation and characterized by XRD, solid state ¹³C NMR, IR, TGA and BET. Tp-BI-COF showed high stability toward acid, organic solvent, and boiling water. The 2D COF exhibited photochromic properties after being irradiated with a xenon lamp. The stable COF, with aligned one-dimensional nanochannels, provided nitrogen sites on pore walls, which confine and stabilize the H₃PO₄ in the channel via hydrogen-bonding interactions. After loading with H₃PO₄, the material showed excellent anhydrous proton conductivity.

Electrostatic Design of the Nanoscale Internal Surfaces of Porous Covalent Organic Frameworks

It is well established that the collective action of assemblies of dipoles determines the electronic structure of surfaces and interfaces. This raises the question, to what extent the controlled arrangement of polar units can be used to also tune the electronic properties of the inner surfaces of materials with nanoscale pores. In the present contribution, state-of-the-art density-functional theory calculations are used to show for the prototypical case of covalent organic frameworks (COFs) that this is indeed possible. Decorating pore walls with assemblies of polar entities bonded to the building blocks of the COF layers triggers a massive change of the electrostatic energy within the pores. This, inevitably, also changes the relative alignment between electronic states in the framework and in guest molecules and is expected to have significant impacts on charge separation in COF heterojunctions, on redox reactions in COFs-based electrodes, and on (photo)catalysis.

2D Covalent Organic Frameworks Based on Heteroacene Units

Covalent organic frameworks (COFs) are a unique new class of porous materials that arrange building units into periodic ordered frameworks through strong covalent bonds. Accompanied with structural rigidity and well-defined geometry, heteroacene-based COFs have natural advantages in constructing COFs with high stability and crystallinity. Heteroacene-based COFs usually have high physical and chemical properties, and their extended π-conjugation also leads to relatively low energy gap, effectively promoting π-electron delocalization between network units. Owing to excellent electron-withdrawing or -donating ability, heteroacene units have incomparable advantages in the preparation of donor-acceptor type COFs. Therefore, the physicochemical robust and fully conjugated heteroacene-based COFs solve the problem of traditional COFs lacking π-π interaction and chemical stability. In recent years, significant breakthroughs are made in this field, the choice of various linking modes and building blocks has fundamentally ensured the final applications of COFs. It is of great significance to summarize the heteroacene-based COFs for improving its complexity and controllability. This review first introduces the linkages in heteroacene-based COFs, including reversible and irreversible linkages. Subsequently, some representative building blocks are summarized, and their related applications are especially emphasized. Finally, conclusion and perspectives for future research on heteroacene-based COFs are presented.

One-Dimensional π-d Conjugated Coordination Polymer Intercalated MXene Compound for High-Performance Supercapacitor Electrode

MXenes possess the characteristics required for high-performance supercapacitors, such as high metallic conductivity and electrochemical activity, but their full potential remains unrealized owing to their tendency to self-restack when fabricated into an electrode. Designing an MXene interlayer with an effective intercalant has, therefore, become an important criterion to alleviate the restacking issue while also synergistically interact with MXene to further improve its electrochemical activity. This study reports the intercalation of 1D π-d conjugated coordination polymer (Ni-BTA) within the Ti₃ C₂ T_x nanosheet for the fabrication of a highly efficient supercapacitor electrode. Ni-BTA, which consists of a nickel center and 1,2,4,5-benzenetetramine (BTA) organic chain, is uniformly intercalated by direct synthesis on the abundant oxygen terminals on the Ti₃ C₂ T_x nanosheet surface. The intercalated Ni-BTA acts as an effective charge carrier transportation pathway through its 1D stretched delocalized π-d electrons while participating in pseudocapacitive activity with the Ni centers. As a result, the Ni-BTA/MXene film exhibits excellent rate performance and a gravimetric specific capacitance of 264.4 F g^-1 at 5 mV s^-1 . This magnitude is retained up to 94.6% after 10 000 cycles. The present study provides insights into the design of MXene interlayers for the fabrication of highly robust and stable supercapacitors.

Cu2O/2D COFs Core/Shell Nanocubes with Antiphotocorrosion Ability for Efficient Photocatalytic Hydrogen Evolution

Photocorrosion of highly active photocatalysts is an urgent problem to be solved in the field of photocatalysis; however, searching for effective strategies for inhibiting photocorrosion of photocatalysts is still a grand challenge. Herein, we design and construct a class of Cu₂O/2D PyTTA-TPA COFs (PyTTA: 1,3,6,8-Tetrakis(4-aminophenyl)pyrene, TPA: p-benzaldehyde) core/shell nanocubes to greatly boost the performance of photocatalytic hydrogen evolution and significantly inhibit the photocorrosion. The optimal Cu₂O/PyTTA-TPA COFs core/shell nanocubes exhibit an excellent photocatalytic H₂ evolution rate of 12.5 mmol h^-1 g^-1, which is ∼8.0-fold and ∼20.0-fold higher than those of PyTTA-TPA COFs and Cu₂O nanocube, respectively, and also is the best in all the reported metal oxides catalytic materials. The mechanism studies demonstrate that the appropriate matching band gaps and tight integration of PyTTA-TPA COFs and Cu₂O nanocubes can significantly facilitate the separation of photogenerated electron-hole pairs in the Cu₂O/PyTTA-TPA COFs core/shell nanocube during the photocatalytic process, which ameliorates the photocatalytic H₂ evolution activity. Most importantly, the 2D PyTTA-TPA COFs shell with outstanding intrinsic stability protects Cu₂O nanocubes core from photocorrosion by showing no morphology and crystal structure change after 1000 times of photoexcitation.

Photo-responsive oxidase-like nanozyme based on a vanadium-docked porphyrinic covalent organic framework for colorimetric L-Arginine sensing

This study reports the development of a vanadium-docked porphyrinic covalent organic framework as a novel class of highly polar photoactive materials. Thanks to its extended π-electron conjugation and high chemical stabilities, this framework can serve as an oxidase-Like photo-nanozyme for photocatalytic oxidation of o-phenylenediamine (o-PDA) and a colorimetric substrate for the production of the yellow-colored oxidized o-PDA (o-PDAox). The physicochemical properties of the as-prepared photo-nanozyme were characterized by several analytical techniques. Its enhanced light harvesting and charge separation and transfer were also verified by electrochemical and spectroscopic analysis. This photo-nonenzymatic colorimetric assay was applied for the sensitive L-Arginine (L-Arg) detection as a typical amino acid in the linear range of 8.1 nM-330 μM with a limit of detection (LOD) of 3.5 nM. The findings of this research confirmed the safety and feasibility of the proposed photo-nonenzymatic colorimetric sensing strategy for the detection of L-Arg and other similar biomolecules in food samples. Kinetic investigation revealed that the photo-responsive oxidase mimic exhibits satisfactory K_m (0.47 mM) and V_max (42.0 μM/s) values. This work broadened our insight into the development of modified porphyrinic-COF-based visible light-responsive oxidase-like photo-nanozyme for environmentally friendly colorimetric biosensing.

Targeted Synthesis of Isomeric Naphthalene-Based 2D Kagome Covalent Organic Frameworks

Targeted synthesis of kagome (kgm) topologic 2D covalent organic frameworks remains challenging, presumably due to the severe dependence on building units and synthetic conditions. Herein, two isomeric "two-in-one" monomers with different lengths of substituted arms based on naphthalene core (p-Naph and m-Naph) are elaborately designed and utilized for the defined synthesis of isomeric kgm Naph-COFs. The two isomeric frameworks exhibit splendid crystallinity and showcase the same chemical composition and topologic structure with, however, different pore channels. Interestingly, C₆₀ is able to uniformly be encapsulated into the triangle channels of m-Naph-COF via in situ incorporation method, while not the isomeric p-Naph-COF, likely due to the different pore structures of the two isomeric COFs. The resulting stable C₆₀ @m-Naph-COF composite exhibits much higher photoconductivity than the m-Naph-COF owing to charge transfer between the conjugated skeletons and C₆₀ guests.

Understanding the electronic pi-system of 2D covalent organic frameworks with Wannier functions

We investigate a family of hexagonal 2D covalent organic frameworks (COFs) with phenyl and biphenyl spacer units and different chemical linker species. Chemical trends are elucidated and attributed to microscopic properties of the [Formula: see text]-electron-system spanned by atomic [Formula: see text]-orbitals. We systematically investigate the electronic structure, delocalization of electronic states, effects of disorder, bond torsion, and doping, and correlate these with variable [Formula: see text]-conjugation and nucleus-independent chemical shift (NICS) aromaticity. Molecular orbitals are obtained from maximally localized Wannier functions that have [Formula: see text]- and [Formula: see text]-character, forming distinct [Formula: see text]- and [Formula: see text]-bands for all valence states. The Wannier-orbital description goes beyond simple tight-binding models and enables a detailed understanding of the electronic topology, effective electronic coupling and delocalization. It is shown that a meaningful comparison between COFs with different chemical elements can only be made by examining the entire [Formula: see text]-electron system, while a comparison of individual bands (e.g., bands near the Fermi energy) can be a insufficient to derive general design rules for linker and spacer monomer selection. We further identify delocalized states that are spread across tens or hundreds of pores of the 2D COFs and analyze their robustness against structural and energetic disorders like out-of-plane rotations of molecular fragments, different strength of energetic disorder and energetic shifts due to chemical doping.