Most two-dimensional (2D) covalent organic frameworks (COFs) are non-fluorescent in the solid state even when they are constructed from emissive building blocks. The fluorescence quenching is usually ...attributed to non-irradiative rotation-related or π-π stacking-caused thermal energy dissipation process. Currently there is a lack of guiding principle on how to design fluorescent, solid-state material made of COF. Herein, we demonstrate that the eclipsed stacking structure of 2D COFs can be used to turn on, and tune, the solid-state photoluminescence from non-emissive building blocks by the restriction of intramolecular bond rotation via intralayer and interlayer hydrogen bonds among highly organized layers in the eclipse-stacked COFs. Our COFs serve as a platform whereby the size of the conjugated linkers and side-chain functionalities can be varied, rendering the emission colour-tuneable from blue to yellow and even white. This work provides a guide to design new solid-state emitters using COFs.
The strong π-π interactions in the stacking layers of two-dimensional covalent organic frameworks (2D-COFs), together with rotationally labile imine linkages, make most of the solid state ...imine-linked COFs non-fluorescent due to fluorescence quenching processes. Here, we report the successful synthesis of highly photoluminescent imine-based 2D-COFs by integrating a non-planar building unit with a pyrene-based unit and transforming the COF into spherical, sub-micron particles. High photoluminescence quantum yields (PLQY) were achieved with COF sub-micron particles dispersed in organic solvents. The as-prepared COF sub-micron particles can be used as a chemical sensor for the detection of explosive chemicals, with high sensitivity and selectivity (up to ppm level).
Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials constructed from designer molecular building blocks that are linked and extended periodically via covalent ...bonds. Their high stability, open channels, and ease of functionalization suggest that they can function as a useful cathode material in reversible lithium batteries. Here, a COF constructed from hydrazone/hydrazide‐containing molecular units, which shows good CO2 sequestration properties, is reported. The COF is hybridized to Ru‐nanoparticle‐coated carbon nanotubes, and the composite is found to function as highly efficient cathode in a Li–CO2 battery. The robust 1D channels in the COF serve as CO2– and lithium‐ion‐diffusion channels and improve the kinetics of electrochemical reactions. The COF‐based Li–CO2 battery exhibits an ultrahigh capacity of 27 348 mAh g−1 at a current density of 200 mA g−1, and a low cut‐off overpotential of 1.24 V within a limiting capacity of 1000 mAh g−1. The rate performance of the battery is improved considerably with the use of the COF at the cathode, where the battery shows a slow decay of discharge voltage from a current density of 0.1 to 4 A g−1. The COF‐based battery runs for 200 cycles when discharged/charged at a high current density of 1 A g−1.
A covalent organic framework (COF) is deployed in a Li–CO2 battery to function as diffusion channels to improve gas/ion migration. Owing to its ability for CO2 capture/release, the COF greatly increases the battery's specific discharge capacity. Importantly, the COF also enhances the battery's rate performance and cycling life at high current density due to the presence of the 1D channels that enable fast gas/ion diffusion.
Covalent organic frameworks (COFs) represent a new type of crystalline porous materials that are covalently assembled from organic building blocks. Construction of functional COFs is, however, a ...difficult task because it has to meet simultaneously the requirements for crystallinity and functionality. We report herein a facile strategy for the direct construction of chiral-functionalized COFs from chiral building blocks. The key design is to use the rigid scaffold 4,4′-(1H-benzodimidazole-4,7-diyl)dianiline (2) for attaching a variety of chiral moieties. As a first example, the chiral pyrrolidine-embedded building block (S)-4,4′-(2-(pyrrolidin-2-yl)-1H-benzodimidazole-4,7-diyl)dianiline (3) was accordingly synthesized and applied for the successful construction of two chiral COFs, LZU-72 and LZU-76. Our experimental results further showed that these chiral COFs are structurally robust and highly active as heterogeneous organocatalysts.
Since December 2019, the 2019 coronavirus disease (COVID-19) has expanded to cause a worldwide outbreak that more than 600,000 people infected and tens of thousands died. To date, the clinical ...characteristics of COVID-19 patients in the non-Wuhan areas of Hubei Province in China have not been described.
We retrospectively analyzed the clinical characteristics and treatment progress of 91 patients diagnosed with COVID-19 in Jingzhou Central Hospital.
Of the 91 patients diagnosed with COVID-19, 30 cases (33.0%) were severe and two patients (2.2%) died. The severe disease group tended to be older (50.5 vs. 42.0 years; p = 0.049) and have more chronic disease (40% vs. 14.8%; p = 0.009) relative to mild disease group. Only 73.6% of the patients were quantitative polymerase chain reaction (qPCR)-positive on their first tests, while typical chest computed tomography images were obtained for each patient. The most common complaints were cough (n = 75; 82.4%), fever (n = 59; 64.8%), fatigue (n = 35; 38.5%), and diarrhea (n = 14; 15.4%). Non-respiratory injury was identified by elevated levels of aspartate aminotransferase (n = 18; 19.8%), creatinine (n = 5; 5.5%), and creatine kinase (n = 14; 15.4%) in laboratory tests. Twenty-eight cases (30.8%) suffered non-respiratory injury, including 50% of the critically ill patients and 21.3% of the mild patients.
Overall, the mortality rate of patients in Jingzhou was lower than that of Wuhan. Importantly, we found liver, kidney, digestive tract, and heart injuries in COVID-19 cases besides respiratory problems. Combining chest computed tomography images with the qPCR analysis of throat swab samples can improve the accuracy of COVID-19 diagnosis.
Although polymers have been studied for well over a century, there are few examples of covalently linked polymer crystals synthesised directly from solution. One-dimensional (1D) covalent polymers ...that are packed into a framework structure can be viewed as a 1D covalent organic framework (COF), but making a single crystal of this has been elusive. Herein, by combining labile metal coordination and dynamic covalent chemistry, we discover a strategy to synthesise single-crystal metallo-COFs under solvothermal conditions. The single-crystal structure is rigorously solved using single-crystal electron diffraction technique. The non-centrosymmetric metallo-COF allows second harmonic generation. Due to the presence of syntactic pendant amine groups along the polymer chains, the metallopolymer crystal can be further cross-linked into a crystalline woven network.
Mono- or few-layer sheets of covalent organic frameworks (COFs) represent an attractive platform of two-dimensional materials that hold promise for tailor-made functionality and pores, through ...judicious design of the COF building blocks. But although a wide variety of layered COFs have been synthesized, cleaving their interlayer stacking to obtain COF sheets of uniform thickness has remained challenging. Here, we have partitioned the interlayer space in COFs by incorporating pseudorotaxane units into their backbones. Macrocyclic hosts based on crown ethers were embedded into either a ditopic or a tetratopic acylhydrazide building block. Reaction with a tritopic aldehyde linker led to the formation of acylhydrazone-based layered COFs in which one basal plane is composed of either one layer, in the case of the ditopic macrocyclic component, or two adjacent layers covalently held together by its tetratopic counterpart. When a viologen threading unit is introduced, the formation of a host-guest complex facilitates the self-exfoliation of the COFs into crystalline monolayers or bilayers, respectively.
The marriage of dynamic covalent chemistry (DCC) and coordination chemistry is a powerful tool for assembling complex architectures from simple building units. Recently, the synthesis of woven ...covalent organic frameworks (COFs) with topologically fascinating structures has been achieved using this approach. However, the scope is highly limited and there is a need to discover new pathways that can assemble covalently linked organic threads into crystalline frameworks. Herein, we have identified branching pathways leading to the assembly of three‐dimensional (3D) woven COFs or one‐dimensional (1D) metallo‐COFs (mCOFs), where the mechanism is underpinned by the absence or presence of ligand exchange.
What far from tangled webs we weave: By combining dynamic covalent chemistry (DCC) and coordination chemistry, divergent paths for the construction of three‐dimensional (3D) woven covalent organic frameworks (COFs) or one‐dimensional (1D) metallo‐COFs (mCOFs) are identified. The paths are distinguished by the absence or presence of ligand exchange.
Two-dimensional (2D) covalent organic frameworks (COFs) are an emerging class of porous materials with potential for wide-ranging applications. Intense research efforts have been directed at tuning ...the structure and topology of COF, however the bandgap engineering of COF has received less attention, although it is a necessary step for developing the material for photovoltaic or photonic applications. Herein, we have developed an approach to narrow the bandgap of COFs by pairing triphenylamine and salicylideneaniline building units to construct an eclipsed stacked 2D COF. The ordered porous structure of 2D COF facilitates a unique moisture-triggered tautomerism. The combination of donor–acceptor charge transfer and tautomerization in the salicyclidineaniline unit imparts a large bandgap narrowing for the COF and turns it color to black. The synthesized COF with donor–acceptor dyad exhibits excellent nonlinear optical properties according to open aperture Z-scan measurements with 532 nm nanosecond laser pulses.
Two-dimensional covalent organic framework (COF) materials can serve as excellent candidates for gas storage due to their high density of periodically arranged pores and channels, which can be ...tethered with functional groups. However, post-functionalization tends to disturb the structure of the COF; thus, it is attractive to develop synthetic approaches that generate built-in functionalities. Herein, we develop a new strategy for the construction of 2D-COFs with built-in, unreacted periodic bonding networks by solvent-directed divergent synthesis. Tetraphenylethane (TPE), which combines both π-rigidity for stacking and rotational flexibility, is selected as the central core for COF construction. By solvent control, two distinct COF structures could be constructed, arising from a 4 + 4 condensation pathway (TPE-COF-I) or an unusual 2 + 4 pathway (TPE-COF-II). TPE-COF-II contains unreacted linker units arranged around its pores and shows greatly enhanced carbon dioxide adsorption performance (23.2 wt %, 118.8 cm3 g–1 at 1 atm, 273 K), which is among the best COF materials for CO2 adsorption reported to date.
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