A Corrole-Based Covalent Organic Framework Featuring Desymmetrized Topology

Herein, for the first time, we present the successful synthesis of a novel two-dimensional corrole-based covalent organic framework (COF) by reacting the unusual approximately T-shaped 5,10,15-tris(p-aminophenyl)corrole H₃TPAPC with terephthalaldehyde, which adopts desymmetrized hcb topology and consists of a staggered AB stacking structure with elliptical pores. The resultant corrole-based COF, TPAPC-COF , exhibits high crystallinity and excellent chemical stability. The combination of extended π-conjugated backbone and interlayer noncovalent π–π interactions endows TPAPC-COF with excellent absorption capability in the entire visible-light and even near-infrared regions. Moreover, this work suggests the promise of TPAPC-COF as a new class of photoactive material for efficient singlet-oxygen generation with potential photodynamic therapy application as demonstrated by in vitro anticancer studies.     

Nanoparticle Size-Fractionation through Self-Standing Porous Covalent Organic Framework Films

Covalent organic frameworks (COFs) have attracted attention due to their ordered pores leading to important industrial applications like storage and separation. Combined with their modular synthesis and pore engineering, COFs could become ideal candidates for nanoseparations. However, the fabrication of these microcrystalline powders as continuous, crack-free, robust films remains a challenge. Herein, we report a simple, slow annealing strategy to construct centimeter-scale COF films ( Tp-Azo and Tp-TTA ) with micrometer thickness. The as-synthesized films are porous (SA_BET=2033 m² g⁻¹ for Tp-Azo ) and chemically stable. These COFs have distinct size cut-offs (ca. 2.7 and ca. 1.6 nm for Tp-Azo and Tp-TTA , respectively), which allow the size-selective separation of gold nanoparticles. Unlike, other conventional membranes, the durable structure of the COF films allow for excellent recyclability (up to 4 consecutive cycles) and easy recovery of the gold nanoparticles from the solution.     

Amidation,Esterification, and Thioesterification of a Carboxyl-Functionalized Covalent Organic Framework

Three new post-synthetic modification reactions, namely amidation, esterification, and thioesterification, were demonstrated on a novel highly crystalline two-dimensional covalent organic framework (COF), COF-616, bearing pre-installed carboxyl groups. The strategy can be used to introduce a large variety of functional groups into COFs and the modifications can be carried out under mild reaction conditions, with high yields, and an easy work-up protocol. As a proof of concept, various chelating functionalities were successfully incorporated into COF-616 to yield a family of adsorbents for efficient removal of several contaminants in the water.     

Redox-Active Two-Dimensional Covalent Organic Frameworks (COFs) for Selective Reductive Separation of Valence-Variable,Redox-Sensitive and Long-Lived Radionuclides

We report the first example of 2D covalent organic framework nanosheets (Redox-COF1) for the selective reduction and in situ loading of valence-variable, redox-sensitive and long-lived radionuclides (abbreviated as VRL nuclides). Compared with sorbents based on chemical adsorption and physical adsorption, the redox adsorption mechanism of Redox-COF1 can effectively reduce the impact of functional group protonation under the usual high-acidity conditions in chemisorption, and raise the adsorption efficiency from the monotonous capture by pores in physisorption. The adsorption selectivity for UO₂²⁺ reaches up to unprecedented ca. 97 % at pH 3, more than for any analogous adsorbing material.     

Two-Dimensional Boronate Ester Covalent Organic Framework Thin Films with Large Single Crystalline Domains for a Neuromorphic Memory Device

Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin-film through solvothermal method and on-solid-surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin-film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to ≈1.5 μm), the reported thin-film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate a general and efficient synthesis of crystalline two-dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF-PP or 2D BECOF-PN ) by employing a surfactant-monolayer-assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF-PP is featured as free-standing thin film with large single-crystalline domains up to ≈60 μm² and tunable thickness from 6 to 16 nm. A hybrid memory device composed of 2D BECOF-PP film on silicon nanowire-based field-effect transistor is demonstrated as a bio-inspired system to mimic neuronal synapses, displaying a learning–erasing–forgetting memory process.     

Acid Exfoliation of Imine-linked Covalent Organic Frameworks Enables Solution Processing into Crystalline Thin Films

Covalent organic frameworks (COFs) are highly modular porous crystalline polymers that are of interest for applications such as charge-storage devices, nanofiltration membranes, and optoelectronic devices. COFs are typically synthesized as microcrystalline powders, which limits their performance in these applications, and their limited solubility precludes large-scale processing into more useful morphologies and devices. We report a general, scalable method to exfoliate two-dimensional imine-linked COF powders by temporarily protonating their linkages. The resulting suspensions were cast into continuous crystalline COF films up to 10 cm in diameter, with thicknesses ranging from 50 nm to 20 μm depending on the suspension composition, concentration, and casting protocol. Furthermore, we demonstrate that the film fabrication process proceeds through a partial depolymerization/repolymerization mechanism, providing mechanically robust films that can be easily separated from their substrates.     

Designing Covalent Organic Frameworks with a Tailored Ionic Interface for Ion Transport across One-Dimensional Channels

A strategy based on covalent organic frameworks for ultrafast ion transport involves designing an ionic interface to mediate ion motion. Electrolyte chains were integrated onto the walls of one-dimensional channels to construct ionic frameworks via pore surface engineering, so that the ionic interface can be systematically tuned at the desired composition and density. This strategy enables a quantitative correlation between interface and ion transport and unveils a full picture of managing ionic interface to achieve high-rate ion transport. Moreover, the effect of interfaces was scaled on ion transport; ion mobility is increased in an exponential mode with the ionic interface. This strategy not only sets a benchmark system but also offers a general guidance for designing ionic interface that is key to systems for energy conversion and storage.     

A Novel Strategy for the Construction of Covalent Organic Frameworks from Nonporous Covalent Organic Polymers

The field of covalent organic frameworks (COFs) has been developed significantly in the past decade on account of their important characteristics and vast application potential. On the other hand, the discovery of novel synthetic methodology is still a challenging task to further promote the preparation of COFs. Herein, an interesting protocol for the conversion of amorphous nonporous covalent organic polymers (COPs) to COFs was established, affording four COFs with high crystallinity and porosity. Specifically, imine‐linked amorphous COP‐1 was successfully converted to COF‐1–4 by replacing one type of linker with other organic building blocks. The realization of this conversion provides a facile method for constructing COFs from COPs.     

Covalent Organic Framework for Improving Near‐Infrared Light Induced Fluorescence Imaging through Two‐Photon Induction

Fluorescent materials exhibiting two‐photon induction (TPI) are used for nonlinear optics, bioimaging, and phototherapy. Polymerizations of molecular chromophores to form π‐conjugated structures were hindered by the lack of long‐range ordering in the structure and strong π–π stacking between the chromophores. Reported here is the rational design of a benzothiadiazole‐based covalent organic framework (COF) for promoting TPI and obtaining efficient two‐photon induced fluorescence emissions. Characterization and spectroscopic data revealed that the enhancement in TPI performance is attributed to the donor‐π‐acceptor‐π‐donor configuration and regular intervals of the chromophores, the large π‐conjugation domain, and the long‐range order of COF crystals. The crystalline structure of TPI‐COF attenuates the π–π stacking interactions between the layers, and overcomes aggregation‐caused emission quenching of the chromophores for improving near‐infrared two‐photon induced fluorescence imaging.     

Fabrication of a Hydrogen-Bonded Organic Framework Membrane through Solution Processing for Pressure-Regulated Gas Separation

Ordered and flexible porous frameworks with solution processability are highly desirable to fabricate continuous and large-scale membranes for the efficient gas separation. Herein, the first microporous hydrogen-bonded organic framework (HOF) membrane has been fabricated by an optimized solution-processing technique. The framework exhibits the superior stability because of the abundant hydrogen bonds and strong π–π interactions. Thanks to the flexible HOF structure, the membrane possesses the unprecedented pressure-responsive H₂/N₂ separation performance. Furthermore, the scratched membrane can be healed by the treatment of solvent vapor, achieving the recovery of separation performance.     

Heat-Treated Aerogel as a Catalyst for the Oxygen Reduction Reaction

Aerogels are fascinating materials that can be used for a wide range of applications, one of which is electrocatalysis of the important oxygen reduction reaction. In their inorganic form, aerogels can have ultrahigh catalytic site density, high surface area, and tunable physical properties and chemical structures—important features in heterogeneous catalysis. Herein, we report on the synthesis and electrocatalytic properties of an iron–porphyrin aerogel. 5,10,15,20-(Tetra-4-aminophenyl)porphyrin (H₂TAPP) and Fe^II were used as building blocks of the aerogel, which was later heat-treated at 600 °C to enhance electronic conductivity and catalytic activity, while preserving its macrostructure. The resulting material has a very high concentration of atomically dispersed catalytic sites (9.7×10²⁰ sites g⁻¹) capable of catalyzing the oxygen reduction reaction in alkaline solution (E_onset=0.92 V vs. RHE, TOF=0.25 e⁻ site⁻¹ s⁻¹ at 0.80 V vs. RHE).     

Superprotonic Conductivity in Flexible Porous Covalent Organic Framework Membranes

Poor mechanical stability of the polymer electrolyte membranes remains one of the bottlenecks towards improving the performance of the proton exchange membrane (PEM) fuel cells. The present work proposes a unique way to utilize crystalline covalent organic frameworks (COFs) as a self‐standing, highly flexible membrane to further boost the mechanical stability of the material without compromising its innate structural characteristics. The as‐synthesized p‐toluene sulfonic acid loaded COF membranes (COFMs) show the highest proton conductivity (as high as 7.8×10⁻² S cm⁻¹) amongst all crystalline porous organic polymeric materials reported to date, and were tested under real PEM operating conditions to ascertain their practical utilization as proton exchange membranes. Attainment of 24 mW cm⁻² power density, which is the highest among COFs and MOFs, highlights the possibility of using a COF membrane over the other state‐of‐the‐art crystalline porous polymeric materials reported to date.     

Covalent Organic Frameworks as Favorable Constructs for Photodynamic Therapy

Covalent organic frameworks (COFs) with 2D π‐conjugation were designed and synthesized as molecular photosensitizers for efficient photodynamic therapy. Two molecules, 5′,5′′′′‐(1,4‐phenylene)bis(([1,1′:3′,1′′‐terphenyl]‐4,4′′‐dicarbaldehyde)) (L‐3C) and 4,4′,4′′‐(1,4‐phenylene)bis(([2,2′:6′,2′′‐terpyridine]‐5,5′′‐dicarbaldehyde)) (L‐3N), inactive to generating reactive oxygen species (ROS), were linked to form two COFs, COF‐808 and COF‐909, respectively, exhibiting excellent ROS production efficiency. The high permanent porosity of these COFs (surface areas 2270 and 2610 m² g^?1) promoted diffusion of both oxygen and release of ROS in cells. This, combined with the excellent photostability and biocompatibility, led to excellent PDT performance. In vitro, over 80 % of tumor cells were killed after PDT treatment using COF‐909 at the concentration of 50 μg mL^?1 for 150 s. In vivo, drastic reduction of tumor size was observed (from 9 mm to less than 1 mm) after 10 day treatment.     

An Olefin‐Linked Covalent Organic Framework as a Flexible Thin‐Film Electrode for a High‐Performance Micro‐Supercapacitor

Developing effective synthetic strategies as well as enriching functionalities for sp²‐carbon‐linked covalent organic frameworks (COFs) still remains a challenge. Now, taking advantage of a variant of Knoevenagel condensation, a new fully conjugated COF ( g‐C₃₄N₆‐COF ) linked by unsubstituted C=C bonds was synthesized. Integrating 3,5‐dicyano‐2,4,6‐trimethylpyridine and 1,3,5‐triazine units into the molecular framework leads to the enhanced π‐electron communication and electrochemical activity. This COF shows uniform nanofibrous morphology. By assembling it with carbon nanotubes, a flexible thin‐film electrode for a micro‐supercapacitor (MSC) can be easily obtained. The resultant COF‐based MSC shows an areal capacitance of up to 15.2 mF cm^?2, a high energy density of up to 7.3 mWh cm^?3, and remarkable rate capability. These values are among the highest for state‐of‐the‐art MSCs. Moreover, this device exhibits excellent flexibility and integration capability.     

Semiconductor/Covalent-Organic-Framework Z-Scheme Heterojunctions for Artificial Photosynthesis

A strategy to covalently connect crystalline covalent organic frameworks (COFs) with semiconductors to create stable organic–inorganic Z-scheme heterojunctions for artificial photosynthesis is presented. A series of COF–semiconductor Z-scheme photocatalysts combining water-oxidation semiconductors (TiO₂, Bi₂WO₆, and α-Fe₂O₃) with CO₂ reduction COFs (COF-316/318) was synthesized and exhibited high photocatalytic CO₂-to-CO conversion efficiencies (up to 69.67 μmol g⁻¹ h⁻¹), with H₂O as the electron donor in the gas–solid CO₂ reduction, without additional photosensitizers and sacrificial agents. This is the first report of covalently bonded COF/inorganic-semiconductor systems utilizing the Z-scheme applied for artificial photosynthesis. Experiments and calculations confirmed efficient semiconductor-to-COF electron transfer by covalent coupling, resulting in electron accumulation in the cyano/pyridine moieties of the COF for CO₂ reduction and holes in the semiconductor for H₂O oxidation, thus mimicking natural photosynthesis.     

Stable 2D Heteroporous Covalent Organic Frameworks for Efficient Ionic Conduction

Two‐dimensional (2D) covalent organic frameworks (COFs) feature open and ordered one‐dimensional column nanochannels which offer immense possibilities for incorporation of various guests for specific functions. However, the relatively low chemical stability of most COFs originating from the dynamic covalent linkages hinders their practical application. In this work, a highly crystalline and heteroporous dibenzo[g,p]chrysene‐based COF (DBC‐2P) was synthesized and served as a host material for ionic conduction. DBC‐2P exhibits excellent stability both in strong acid and base due to the large conjugated DBC‐based knot that reinforces the interlayer interactions. Subsequent encapsulation of linear polyethylene glycol (PEG) and PEG‐LiBF₄ salt into the nanochannels of DBC‐2P affords a hybrid material with a high ionic conductivity of 2.31×10^?3 S cm^?1. This work demonstrates an efficient post‐synthetic strategy for the development of new COF–polymer composites with intriguing properties.     

Stable Heterometallic Cluster-Based Organic Framework Catalysts for Artificial Photosynthesis

A series of stable heterometallic Fe₂M cluster-based MOFs ( NNU-31-M , M=Co, Ni, Zn) photocatalysts are presented. They can achieve the overall conversion of CO₂ and H₂O into HCOOH and O₂ without the assistance of additional sacrificial agent and photosensitizer. The heterometallic cluster units and photosensitive ligands excited by visible light generate separated electrons and holes. Then, low-valent metal M accepts electrons to reduce CO₂, and high-valent Fe uses holes to oxidize H₂O. This is the first MOF photocatalyst system to finish artificial photosynthetic full reaction. It is noted that NNU-31-Zn exhibits the highest HCOOH yield of 26.3 μmol g⁻¹ h⁻¹ (selectivity of ca. 100 %). Furthermore, the DFT calculations based on crystal structures demonstrate the photocatalytic reaction mechanism. This work proposes a new strategy for how to design crystalline photocatalyst to realize artificial photosynthetic overall reaction.     

Strong-Base-Assisted Synthesis of a Crystalline Covalent Triazine Framework with High Hydrophilicity via Benzylamine Monomer for Photocatalytic Water Splitting

Methods to synthesize crystalline covalent triazine frameworks (CTFs) are limited and little attention has been paid to development of hydrophilic CTFs and photocatalytic overall water splitting. A route to synthesize crystalline and hydrophilic CTF-HUST-A1 with a benzylamine-functionalized monomer is presented. The base reagent used plays an important role in the enhancement of crystallinity and hydrophilicity. CTF-HUST-A1 exhibits good crystallinity, excellent hydrophilicity, and excellent photocatalytic activity in sacrificial photocatalytic hydrogen evolution (hydrogen evolution rate up to 9200 μmol g⁻¹ h⁻¹). Photocatalytic overall water splitting is achieved by depositing dual co-catalysts in CTF-HUST-A1, with H₂ evolution and O₂ evolution rates of 25.4 μmol g⁻¹ h⁻¹ and 12.9 μmol g⁻¹ h⁻¹ in pure water without using sacrificial agent.     

Rational Design of Crystalline Covalent Organic Frameworks for Efficient CO2 Photoreduction with H2O

Solar energy‐driven conversion of CO₂ into fuels with H₂O as a sacrificial agent is a challenging research field in photosynthesis. Herein, a series of crystalline porphyrin‐tetrathiafulvalene covalent organic frameworks (COFs) are synthesized and used as photocatalysts for reducing CO₂ with H₂O, in the absence of additional photosensitizer, sacrificial agents, and noble metal co‐catalysts. The effective photogenerated electrons transfer from tetrathiafulvalene to porphyrin by covalent bonding, resulting in the separated electrons and holes, respectively, for CO₂ reduction and H₂O oxidation. By adjusting the band structures of TTCOFs, TTCOF‐Zn achieved the highest photocatalytic CO production of 12.33 μmol with circa 100 % selectivity, along with H₂O oxidation to O₂. Furthermore, DFT calculations combined with a crystal structure model confirmed the structure–function relationship. Our work provides a new sight for designing more efficient artificial crystalline photocatalysts.