A Photoconductive Covalent Organic Framework: Self-Condensed Arene Cubes Composed of Eclipsed 2D Polypyrene Sheets for Photocurrent Generation

An Azine-Linked Covalent Organic Framework: Synthesis, Characterization and Efficient Gas Storage

A azine-linked covalent organic framework, COF-JLU2, was designed and synthesized by condensation of hydrazine hydrate and 1,3,5-triformylphloroglucinol under solvothermal conditions for the first time. The new covalent organic framework material combines permanent micropores, high crystallinity, good thermal and chemical stability, and abundant heteroatom activated sites in the skeleton. COF-JLU2 possesses a moderate BET surface area of over 410 m(2)  g(-1) with a pore volume of 0.56 cm(3)  g(-1) . Specifically, COF-JLU2 displays remarkable carbon dioxide uptake (up to 217 mg g(-1) ) and methane uptake (38 mg g(-1) ) at 273 K and 1 bar, as well as high CO2 /N2 (77) selectivity. Furthermore, we further highlight that it exhibits a higher hydrogen storage capacity (16 mg g(-1) ) than those of reported COFs at 77 K and 1 bar.

Side-functionalized two-dimensional polymers synthesized via on-surface Schiff-base coupling

An imine-based 2D polymer side-functionalized with o-hydroxyl group was designed in regard to its potential ability to serve as a chelating agent and synthesized on a highly oriented pyrolytic graphite surface with a relatively low annealing temperature. When annealed to a higher temperature the o-hydroxyl group reacts further with the imine group, leading to the formation of oxazoline, which causes significant distortion to the network. The formation of oxazoline was further confirmed by ATR-FTIR.

3D Porous Crystalline Polyimide Covalent Organic Frameworks for Drug Delivery

Three-dimensional porous crystalline polyimide covalent organic frameworks (termed PI-COFs) have been synthesized. These PI-COFs feature non- or interpenetrated structures that can be obtained by choosing tetrahedral building units of different sizes. Both PI-COFs show high thermal stability (>450 °C) and surface area (up to 2403 m(2) g(-1)). They also show high loading and good release control for drug delivery applications.

Creation of Superheterojunction Polymers via Direct Polycondensation: Segregated and Bicontinuous Donor-Acceptor π-Columnar Arrays in Covalent Organic Frameworks for Long-Lived Charge Separation

By developing metallophthalocyanines and diimides as electron-donating and -accepting building blocks, herein, we report the construction of new electron donor-acceptor covalent organic frameworks (COFs) with periodically ordered electron donor and acceptor π-columnar arrays via direct polycondensation reactions. X-ray diffraction measurements in conjunction with structural simulations resolved that the resulting frameworks consist of metallophthalocyanine and diimide columns, which are ordered in a segregated yet bicontinuous manner to form built-in periodic π-arrays. In the frameworks, each metallophthalocyanine donor and diimide acceptor units are exactly linked and interfaced, leading to the generation of superheterojunctions-a new type of heterojunction machinery, for photoinduced electron transfer and charge separation. We show that this polycondensation method is widely applicable to various metallophthalocyanines and diimides as demonstrated by the combination of copper, nickel, and zinc phthalocyanine donors with pyrommellitic diimide, naphthalene diimide, and perylene diimide acceptors. By using time-resolved transient absorption spectroscopy and electron spin resonance, we demonstrated that the COFs enable long-lived charge separation, whereas the metal species, the class of acceptors, and the local geometry between donor and acceptor units play roles in determining the photochemical dynamics. The results provide insights into photoelectric COFs and demonstrate their enormous potential for charge separation and photoenergy conversions.

A 2D azine-linked covalent organic framework for gas storage applications

A new azine-linked covalent organic framework, ACOF-1, was synthesized by condensation of hydrazine hydrate and 1,3,5-triformylbenzene under solvothermal conditions. ACOF-1 has a high surface area and a small pore size, and it can store up to 177 mg g(-1) of CO2, 9.9 mg g(-1) of H2, and 11.5 mg g(-1) of CH4, at 273 K and 1 bar, with high selectivity towards CO2 over N2 and CH4.

Mesoporous 2D covalent organic frameworks based on shape-persistent arylene-ethynylene macrocycles

Covalent organic frameworks with high porosity and crystallinity have been synthesized, through macrocycle-to-framework strategy, using shape-persistent arylene-ethynylene macrocycles as the key components to control the topology and modulate the porosity.

Macrocycle-to-framework strategy was explored to prepare covalent organic frameworks (COFs) using shape-persistent macrocycles as multitopic building blocks. We demonstrate well-ordered mesoporous 2D COFs (AEM–COF-1 and AEM–COF-2) can be constructed from tritopic arylene-ethynylene macrocycles, which determine the topology and modulate the porosity of the materials. According to PXRD analysis and computer modelling study, these COFs adopt the fully eclipsed AA stacking mode with large accessible pore sizes of 34 or 39 Å, which are in good agreement with the values calculated by NLDFT modelling of gas adsorption isotherms. The pore size of COFs can be effectively expanded by using larger size of the macrocycles. Provided a plethora of polygonal shape-persistent macrocycles with various size, shape and internal cavity, macrocycle-to-framework strategy opens up a promising approach to expand the structural diversity of COFs and build hierarchical pore structures within the framework.

Electrochemically active, crystalline, mesoporous covalent organic frameworks on carbon nanotubes for synergistic lithium-ion battery energy storage

Organic batteries free of toxic metal species could lead to a new generation of consumer energy storage devices that are safe and environmentally benign. However, the conventional organic electrodes remain problematic because of their structural instability, slow ion-diffusion dynamics, and poor electrical conductivity. Here, we report on the development of a redox-active, crystalline, mesoporous covalent organic framework (COF) on carbon nanotubes for use as electrodes; the electrode stability is enhanced by the covalent network, the ion transport is facilitated by the open meso-channels, and the electron conductivity is boosted by the carbon nanotube wires. These effects work synergistically for the storage of energy and provide lithium-ion batteries with high efficiency, robust cycle stability, and high rate capability. Our results suggest that redox-active COFs on conducting carbons could serve as a unique platform for energy storage and may facilitate the design of new organic electrodes for high-performance and environmentally benign battery devices.

Room temperature synthesis of covalent-organic framework films through vapor-assisted conversion

We describe the facile synthesis of several two-dimensional covalent–organic frameworks (2D COFs) as films by vapor-assisted conversion at room temperature. High-quality films of benzodithiophene-containing BDT-COF and COF-5 with tunable thickness were synthesized under different conditions on various substrates. BDT-COF films of several micrometer thickness exhibit mesoporosity as well as textural porosity, whereas thinner BDT-COF films materialize as a cohesive dense layer. In addition, we studied the formation of COF-5 films with different solvent mixture compositions serving as vapor source. Room temperature vapor-assisted conversion is an excellent method to form COF films of fragile precursors and on sensitive substrates.

Well-defined two dimensional covalent organic polymers: rational design, controlled syntheses, and potential applications

Recent developments in the design, synthesis and application of 2D covalent organic polymers are reviewed, along with some perspectives and challenges.

A π-electronic covalent organic framework catalyst: π-walls as catalytic beds for Diels–Alder reactions under ambient conditions

Covalent organic frameworks were developed as heterogeneous catalysts to explore their π-walls as catalytic beds that enabled Diels–Alder reactions under ambient conditions.

Synthesis of conjugated covalent organic frameworks/graphene composite for supercapacitor electrodes

A novel imine-linked covalent organic framework on graphene composite with excellent electrochemical properties was conveniently synthesized in one step.

Solution and air stable host/guest architectures from a single layer covalent organic framework

Single-layer COF-1 hosts fullerene guests, which can be introduced by a brief immersion in fullerene solution.

A triazine-based covalent organic framework/palladium hybrid for one-pot silicon-based cross-coupling of silanes and aryl iodides

A palladium/COF hybrid material could efficiently catalyze the silicon-based one-pot cross-coupling reaction of silanes and aryl iodides with excellent selectivity.

A novel 3D covalent organic framework membrane grown on a porous α-Al2O3 substrate under solvothermal conditions

A compact and uniform 3D COF-320 membrane with a layer thickness of ∼4 μm was grown on a porous α-Al₂O₃ ceramic substrate.

Octavinylsilsesquioxane-based luminescent nanoporous inorganic–organic hybrid polymers constructed by the Heck coupling reaction

A class of luminescent nanoporous inorganic–organic hybrid polymers has been synthesized by the Heck coupling of octavinylsilsesquioxane with aromatic bromide monomers. The resulting materials exhibit porous and luminescent features, and show picric acid sensing behaviour.

Surface growth of highly oriented covalent organic framework thin film with enhanced photoresponse speed

An oriented photoconductive COF film was synthesized byin situgrowth method.

Graphene-like single-layered covalent organic frameworks: synthesis strategies and application prospects

Two-dimensional (2D) nanomaterials, such as graphene and transition metal chalcogenides, show many interesting dimension-related materials properties. Inspired by the development of 2D inorganic nanomaterials, single-layered covalent organic frameworks (sCOFs), featuring atom-thick sheets and crystalline extended organic structures with covalently bonded building blocks, have attracted great attention in recent years. With their unique graphene-like topological structure and the merit of structural diversity, sCOFs promise to possess novel and designable properties. However, the synthesis of sCOFs with well-defined structures remains a great challenge. Herein, the recent development of the bottom-up synthesis methods of 2D sCOFs, such as thermodynamic equilibrium control methods, growth-kinetics control methods, and surface-assisted covalent polymerization methods, are reviewed. Finally, some of the critical properties and application prospects of these materials are outlined.

Two-dimensional tetrathiafulvalene covalent organic frameworks: towards latticed conductive organic salts

The construction of a new class of covalent TTF lattice by integrating TTF units into two-dimensional covalent organic frameworks (2D COFs) is reported. We explored a general strategy based on the C2 +C2 topological diagram and applied to the synthesis of microporous and mesoporous TTF COFs. Structural resolutions revealed that both COFs consist of layered lattices with periodic TTF columns and tetragonal open nanochannels. The TTF columns offer predesigned pathways for high-rate hole transport, predominate the HOMO and LUMO levels of the COFs, and are redox active to form organic salts that exhibit enhanced electric conductivity by several orders of magnitude. On the other hand, the linkers between the TTF units play a vital role in determining the carrier mobility and conductivity through the perturbation of 2D sheet conformation and interlayer distance. These results open a way towards designing a new type of TTF materials with stable and predesignable lattice structures for functional exploration.

Oriented thin films of a benzodithiophene covalent organic framework

A mesoporous electron-donor covalent organic framework based on a benzodithiophene core, BDT-COF, was obtained through condensation of a benzodithiophene-containing diboronic acid and hexahydroxytriphenylene (HHTP). BDT-COF is a highly porous, crystalline, and thermally stable material, which can be handled in air. Highly porous, crystalline oriented thin BDT-COF films were synthesized from solution on different polycrystalline surfaces, indicating the generality of the synthetic strategy. The favorable orientation, crystallinity, porosity, and the growth mode of the thin BDT-COF films were studied by means of X-ray diffraction (XRD), 2D grazing incidence diffraction (GID), transmission and scanning electron microscopy (TEM, SEM), and krypton sorption. The highly porous thin BDT-COF films were infiltrated with soluble fullerene derivatives, such as [6,6]-phenyl C61 butyric acid methyl ester (PCBM), to obtain an interpenetrated electron-donor/acceptor host-guest system. Light-induced charge transfer from the BDT-framework to PCBM acceptor molecules was indicated by efficient photoluminescence quenching. Moreover, we monitored the dynamics of photogenerated hole-polarons via transient absorption spectroscopy. This work represents a combined study of the structural and optical properties of highly oriented mesoporous thin COF films serving as host for the generation of periodic interpenetrated electron-donor and electron-acceptor systems.

Thin film fabricated from solution-dispersible porous hyperbranched conjugated polymer nanoparticles without surfactants

Porous hyperbranched conjugated polymer nanoparticles with an average particle size of 20-60 nm and a specific surface area of 225 m(2) g(-1) have been prepared through Suzuki polymerization in a miniemulsion, which could be stably dispersed in common organic solvents after complete removal of surfactants. Furthermore, a simple spin-coating method for the preparation of homogeneous transparent thin films of the nanoparticle has been developed. Bright blue emission of the porous nanoparticle films could be reversibly quenched by nitroaromatics with enhanced sensitivity compared to dense films of the linear conjugated polymer analogue.

POSS-based luminescent porous polymers for carbon dioxide sorption and nitroaromatic explosives detection

Luminescent porous polymers based on octavinylsilsequioxane and triphenylamine units show tunable porosity and luminescence, a moderate uptake of CO₂ and high sensitivity for TNT.

Porosity control in mesoporous polymers using CO2-swollen block copolymer micelles as templates and their use as catalyst supports

Mesoporous polymers with tunable large mesopores (14–22 nm) were synthesized through a CO₂-swollen micelle templating route.

A novel azobenzene covalent organic framework

The first example of a novel Azo-linked 2D COF with a hexagonal skeleton, high crystallinity and permanent porosity. The trans-to-cis photoisomerization can lead to the decline of Azo-COF crystallinity but cannot impact the pore size of Azo-COF. The current results will provide a strategy for designing smart COF materials.

Tunable electrical conductivity in oriented thin films of tetrathiafulvalene-based covalent organic framework

Preorganization in a covalent organic framework leads to the generation of a more conductive mixed-valence state upon doping.