Triggering White-Light Emission in a 2D Imine Covalent Organic Framework Through Lanthanide Augmentation.

Emissive covalent organic frameworks (COFs) are a promising class of crystalline materials that have demonstrated applications for sensing and light-emitting diodes. However, white light emission from a single COF has not been achieved yet as it requires multicomponent organic chromophores that simultaneously emit blue, green, and red light. In this work, we report the successful synthesis of a single COF with efficient white light emission by utilizing tunable emission properties of 2,1,3-benzothiadazole after incorporating different functional groups on its core structure, which results in the formation of three ligands, i.e., 4',4-(benzothiadiazole-4,7-diyl)-dibenzaldehyde (BTD), 4,4'-(benzoselenadiazole-4,7-diyl)-dibenzaldehyde (BSD), and 4,4'-(naphtho[2,3-c][1,2,3] selenadiazole-4,9-diyl)-dibenzaldehyde (NSD), that emit in the blue, green, and red regions of the visible light spectrum. We show that white light emission can only occur when BTD, BSD, and NSD are assembled in a single COF structure due to the facilitated energy transfer process from BTD to BSD/NSD. This work demonstrates a unique approach to developing new white light-emitting materials based on the COF structure.

Covalent organic frameworks (COFs) are crystalline, nanoporous materials of interest for various applications, but current COF synthetic routes lead to insoluble aggregates which precludes processing for practical implementation. Here, we report a COF synthesis method that produces a stable, homogeneous suspension of crystalline COF nanoparticles that enables the preparation of COF monoliths, membranes, and films using conventional solution-processing techniques. Our approach involves the use of a polar solvent, diacid catalyst, and slow reagent mixing procedure at elevated temperatures which altogether enable access to crystalline COF nanoparticle suspension that does not aggregate or precipitate when kept at elevated temperatures. On cooling, the suspension undergoes a thermoreversible gelation transition to produce crystalline and highly porous COF materials. We further show that the modified synthesis approach is compatible with various COF chemistries, including both large- and small-pore imine COFs, hydrazone-linked COFs, and COFs with rhombic and hexagonal topologies, and in each case, we demonstrate that the final product has excellent crystallinity and porosity. The final materials contain both micro- and macropores, and the total porosity can be tuned through variation of sample annealing. Dynamic light scattering measurements reveal the presence of COF nanoparticles that grow with time at room temperature, transitioning from a homogeneous suspension to a gel. Finally, we prepare imine COF membranes and measure their rejection of polyethylene glycol (PEG) polymers and oligomers, and these measurements exhibit size-dependent rejection and adsorption of PEG solutes. This work demonstrates a versatile processing strategy to create crystalline and porous COF materials using solution-processing techniques and will greatly advance the development of COFs for various applications.

Sol-gel processing of a covalent organic framework for the generation of hierarchically porous monolithic adsorbents

Isoreticular chemically stable two-dimensional imine covalent organic frameworks (COFs), further denoted as DUT-175 and DUT-176, are obtained in a reaction of 4,4′-bis(9H-carbazol-9-yl)biphenyl tetraaldehyde with phenyldiamine and benzidine. The crystal structures, solved and refined from the powder X-ray diffraction data and confirmed by high-resolution transmission electron microscopy, indicate AA-stacked layer structures. Both structures feature distorted hexagonal channel pores, assuring remarkable porosity (SBET = 1071 m2 g–1 for DUT-175 and SBET = 1062 m2 g–1 for DUT-176), as confirmed by adsorption of gases and vapors. The complex conjugated π system of the COFs involves electron-rich carbazole building units, which in combination with the imine groups allow reversible pH-dependent protonation of the frameworks, accompanied by charge transfer and shift of the absorption bands in the UV–vis spectrum. The sigmoidal shape of the water vapor adsorption and desorption isotherms with a steep adsorption step at p/p0 = 0.4–0.6 in combination with excellent stability over dozens of adsorption and desorption cycles ranks these COFs among the best materials for indoor humidity control applications.

Effects of Light Quality on Root Elongation and Nodulation of Zamia floridana DC. Seedlings in Sterile Culture

Machine Learning-Guided Equations for Super-Fast Prediction of Methane Storage Capacities of COFs

Covalent organic frameworks (COFs) with structural designability and tunability of photophysical properties enable them to be a promising class of organic luminescent materials by incorporating well-designed fluorescent units directly into the periodic skeletons. The photophysical properties of COFs are mainly affected by the structural features, which determine the conjugation degree, charge delocalization ability, and exciton dynamics of COFs. To understand the relationship between COF structures and their photophysical properties, two COFs with the same pyrene chromophore units but different linkages (imine or vinylene) were designed and synthesized. Interestingly, different linkages endow COFs with huge differences in solid-state photoluminescence quantum yield (PLQY) for imine- and vinylene-linked pyrene-based COFs, which possess PLQY values of 0.34 % and 15.43 %, respectively. The femtosecond-transient absorption spectra and time-dependent density functional theory reveal the different charge-transfer pathways in imine- and vinylene-linked COFs, which influence the exciton relaxation way and fluorescence intensity. In addition, an effective white-light device was obtained by coating the vinylene-linked COF on a light-emitting diode strip.

Mn-1,4-BDC MOF based a COF for ultrafast and simultaneous removal of cationic dyes

Are there advantages in implanting a yellow IOL to reduce the risk of AMD?

Binding of fluorescent molecules to the porous matrix through noncovalent interactions will synergistically expand their application spectrum. In this regard, we report an integrative self-assembly of molecule 1 with benzothiadizole and 9,9-dihexyl fluorene units, and covalent organic frameworks (COFs) via an emulsion-modulated polymerization process, within which molecules of 1 are able to interact with the scaffolds of COFs through CH-π interactions. Thus the π-π interactions between the fluorescent molecules are largely suppressed, giving rise to their remarkable monomer-like optical properties. Of particular interest is that, given by the specific interaction between COFs and a nerve agent simulant diethyl chlorophosphite (DCP), these assembled composites show the ability of ultrasensitive detection of DCP with a detection limit of ~40 ppb. Moreover, the present integrative assembly strategy can be extended to encapsulate multiple fluorescent molecules, enabling the assemblies with white light emission. Our results highlight opportunities for the development of highly emissive porous materials by molecular self-assembly of fluorophores and molecular units of COFs.

The effect of monochromatic light and the interaction of blue and red lights on leaf blade inclination in wheat plants) Triticum aestivum L., cv. Shirasagi-Komugi) were studied.1) Blue light caused inclination of the blades of the first leaves. When 7-day-old seedlings grown in darkness were exposed to blue, green, yellow, red, far-red and white lights, and to darkness for 72 hours, the angles of the leaf blade were 113°, 13°, 13°, 14°, 30°, 30° and 12°.2) The spectral regions effective for inclination were the wavelengths between 380 and 510 nm, with a marked response at 430-480 nm.3) Blue light of 2000 erg/cm2/sec was fully effective, the maximum inclination response was obtained 72 hours after the start of irradiation. Photosensitivity to blue light showed a maximum response 2-3 days after the laminar joint appeared from the top of the coleoptile.4) Red or yellow lights applied simultaneously with blue light counteracted inclination. The counteracting spectral regions appeared at wavelengths between 560 and 690 nm with a marked response at 630-640 nm.5) The counteracting effect of red light on blue light differed with the mixed ratio of red light to blue light (R/B ratio) . The blade angle of leaves in wheat plants exposed to blue light (2000 erg/cm2/sec) for 72 hours was about 100°, whereas the angle for the R/B ratio of 1/10 was about 40°, 30° for the 1/4 ratio, 25° for the 1/2 ratio, and 20° for the 1/1 ratio.

Effects of monochromatic light on quality properties and antioxidation of meat in broilers

Highly sensitive detection toward aniline vapor promoted by heterojunction between covalent organic frameworks and biocarbon

Porous materials with high surface areas have drawn more and more attention in recent years because of their wide applications in physical adsorption and energy-efficient adsorptive separation processes. Most of the reported porous materials are macromolecular porous materials, such as zeolites, metal-organic frameworks (MOFs), or porous coordination polymers (PCPs), and porous organic polymers (POPs) or covalent organic frameworks (COFs), in which the building blocks are linked together by covalent or coordinative bonds. These materials are barely soluble and thus are not solution-processable. Furthermore, the relatively low chemical, moisture, and thermal stability of most MOFs and COFs cannot be neglected. On the other hand, molecular porous materials such as porous organic cages (POCs), which have been developed very recently, also show promising applications in adsorption and separation processes. They can be soluble in organic solvents, making them solution-processable materials. However, they are usually sensitive to acid/base and humid environments since most of them are based on dynamic covalent bonding. These macromolecular and molecular porous materials usually have two similar features: high Brunauer-Emmett-Teller (BET) surface areas and rigid pore structures, which are stable during adsorption and separation processes. In this Account, we describe a novel class of solid materials for adsorption and separation, nonporous adaptive crystals (NACs), which function at the supramolecular level. They are nonporous in the initial crystalline state, but the intrinsic or extrinsic porosity of the crystals along with a crystal structure transformation is induced by preferable guest molecules. Unlike solvent-induced crystal polymorphism phenomena of common organic crystals that occur at the solid-liquid phase, NACs capture vaporized guests at the solid-gas phase. Upon removal of guest molecules, the crystal structure transforms back to the original nonporous structure. Here we focus on the discussion of pillararene-based NACs for adsorption and separation and the crystal structure transformations from the initial nonporous crystalline state to new guest-loaded structures during the adsorption and separation processes. Single-crystal X-ray diffraction, powder X-ray diffraction, gas chromatography, and solution NMR spectroscopy are the main techniques to verify the adsorption and separation processes and the structural transformations. Compared with traditional porous materials, NACs of pillararenes have several advantages. First, their preparation is simple and cheap, and they can be synthesized on a large scale to meet practical demands. Second, pillararenes have better chemical, moisture, and thermal stability than crystalline MOFs, COFs, and POCs, which are usually constructed on the basis of reversible chemical bonds. Third, pillararenes are soluble in many common organic solvents, which means that they can be easily processed in solution. Fourth, their regeneration is simple and they can be reused many times with no decrease in performance. It is expected that this class of materials will not only exert a significant influence on scientific research but also show practical applications in chemical industry.

Covalent organic frameworks (COFs), which are constructed from organic linkers, are a new class of crystalline porous materials comprising periodically extended and covalently bound network structures. The intrinsic structures and the tailorable organic linkers endow COFs with a low density, large surface area, tunable pore size and structure, and facilely-tailored functionality, attracting increasing interests in different fields including membrane separations. Exciting research activities ranging from fabrication strategies to separation applications of COF-based membranes have appeared. This review analyzes the synthesis and applications of diverse continuous/discontinuous COF membranes, such as COF-based mixed matrix membranes (MMMs), COF-based thin film nanocomposite (TFN) membranes, and free-standing COF films. Special attention was given to pore size, stability, hydrophilicity/hydrophobicity and surface charge of COFs in view of determining proper COFs for membrane fabrication, along with the approaches to fabricate COF-based membranes, such as blending, in situ growth, layer-by-layer stacking and interfacial polymerization (IP). Moreover, applications of COF-based membranes in gas separation, water treatment (deaslination and dye removal), organic solvent nanofiltration (OSN), pervaporation and fuel cell are disscussed. Finally, we illustrate the advantages and disadvantages of COF-based membranes through a comparison with MOF-based membranes, and the remaining challenges and future opportunities in this field.