2D to 3D reversible covalent organic frameworks (COF) material is converted

Cross-linked polymer in the polymer as a change in the performance of the method has been around for more than a century of. However, most of the cross-connection is disordered, generally only orderly cross-linked by the MOF or supramolecular crystal engineering talent, and orderly links is an important method to obtain a controlled structure and properties. Meanwhile, layered 2D covalent organic framework materials (2D layered COF) received widespread attention as a novel material, because of its high surface area, can be varied molecular and crystal structures, and the class of electronic structure of graphene. However, the methods so far reported synthetic modifications COF was added to the introduction of new features are limited to single or double COF 2D, the change can not be effectively controlled in its 3D structure. Recently, McGill University in Canada professor Dmitrii Perepichka Study Group reported polyaromatic enables 2D to 3D conversion of ethylene ordered COF COF cyclobutane crystal – method of reversible conversion crystal , this is the first report COF-COF orderly transition from 2D to 3D. The work with the title \”between 2D and 3D Covalent Organic Frameworks via Transformation Reversible [2 + 2] Cycloaddition\” published in the top chemistry journal \”American Chemical Society\” ( \”JACS\”). First author is postdoctoral Thaksen Jadhav , postdoctoral a radius of and after 00 doctoral Liucheng Hao . It is noteworthy that this is the 00 doctoral Liucheng Hao Following the publication last year after another wonderful work \”of Germany should be\” the first author (after 00 doctoral hair \”of Germany should be\”: with hydrogen bonds conjugated electron control and supramolecular structure of the molecule).

可逆的2D到3D共价有机框架(COF)材料转化 Synthesis of
of FIG P2PV 1. 2D / P2NV of, 3D of P3PcB / P3NcB [2 + 2] photocycloaddition and thermal cracking. FIG.

The authors previously reported that they first discovered the COF (Angew. Chem. Int. Ed. 2019, 58,13753) having a photosensitivity, a long time after the light color from white to yellow, is a typical phenomenon of electron conjugated destroyed. After a series of experiments, the authors found that in a non-polar solvent, with the absorption edge of light is irradiated uniformly stirred and 2D layered polyarylene ethylene COF can be converted into 3D poly cyclobutane COF while preserving the crystalline state. This cross-linking can be reversed at 200 degrees Celsius cycloaddition, so cyclobutane while maintaining the crystal changes back to the olefin. The chemical nature of the cross-linked to IR, NMR and other methods prove, and brings a structural material, changing mechanical properties, electrical characteristics. Mechanical changes and structural transformation: X-ray diffraction and by calculating the first principle, the authors found that the original 2D lattice plane is substantially retained while greatly expanded in the direction of cross-linked polyethylene cyclobutane. BET specific surface area confirmed the results: COF increased surface area of ​​1037m 2 / g of 880m 2 / g, and calculates a display which retains the original 2D nanoporous structure, and added a new 3D nanoporous small plane. HRTEM able to clearly reveal the layered structure 2D COF, and in which only see the 3D COF hexagonal structure. Mechanical change: 2D monolayer of COF can easily be separated from the bulk of the layered structure at sulfuric acid, and the COF can not cross-linked.

FIG 2. P2PV (a), P3PcB (b), P2NV (c), P3NcB (d) a PXRD diffraction (red dots), Pawley refinement (black line), the difference (blue line) and its corresponding molecular modeling.
FIG 3. P2PV (a), P3PcB (b) a high resolution transmission electron microscopy. TEM after stratification P2PV (c) and P3PcB (d) was stirred in concentrated sulfuric acid. (E) P3PcB ultrasound in concentrated sulfuric acid lead to structural damage, and the ultrasound is still P2PV conjunction with (c) is the same.

Electronic structural changes: cyclobutane damage pi-electron conjugated form, the effect can be clearly reflected in the increased energy gap. In P2PV COF, the cross-linking results in the cycloaddition of fluorescent original COFQuenching light because it destroys the 2D electron conjugated. However, in another P2PN COF, but enhanced fluorescence cross-linking, because the molecular structure itself is fluorescent, but aggregate formation occurs 2D COF fluorescence quenching (ACQ), and deposited in the cycloaddition pi- it is destroyed, so some of this restored small molecule fluorescence. The first principle of density functional theory (DFT) calculations demonstrated COF 2D is itself Kagome lattice (Kagome lattice) semiconductor, and which results in it becoming 3D polymeric insulator. Changes are acid-doped conjugated charge transfer (acid-doping) after reflected. Here, the authors caution on the electronic structure, many recent studies have attempted to make the COF electrons become more conjugate, in particular to explore the use of olefins (-C = C-) link instead of the usual imide (-C = N- ) link, but this may result in these methods have a strong photosensitivity COF unsuitable photoconductor is used as a photocatalyst or reported. OF emphasized, although not evident in the cycloaddition reaction polyarylene ethylene 1D, 2D crystal structure but polyarylene ethylene-based polymer that can help this transition occurs (also reported before polyarylene 2D random ethylene cyclo into the reaction).

FIG. 4. P2PV, diffuse reflectance spectroscopy P3PcB, P2NV, P3NcB of (a, c), and fluorescence changes over time ultraviolet irradiation (b, d)

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可逆的2D到3D共价有机框架(COF)材料转化 Figure 5. monolayer P2PV (a) and P3PcB (b) band structures
Although the authors is confirmed that the polyarylene ethylene COF incompetent some applications, the authors demonstrated these possible uses of the COF –

ionic conductivity , such as in a battery. OF first with 7 Li solid state NMR confirmed the migration speed of lithium ions to be increased dramatically in the COF. Then, a series of manufacturing a device, it was confirmed polyarylene and poly ethylene COF COF of cyclobutane lithium ion conductivity can reach 1.3 ∙ 10 -3 S / cm and 7.5 ∙ 10 [ 123] -4 S / cm . Both the proton conductivity is more COF can reach 1.7 ∙ 10 -2 S/ Cm and 2.2 ∙ 10 -3 S / cm . The ionic conductivity is one of the best COF data field, the first time the use of olefins and paraffins hydrolytically stable ionic conductivity COF test.

FIG. 5. FIG P2PV Nyquist loading and P3PcB of LiClO4, and at a humidity of 40% (a) and vacuum pumped dry add a small amount of dimethyl carbonate (b) . The lithium ion conductivity and P3PcB P2PV Arrhenius FIG. (C). FIG P2PV Nyquist P3PcB loading and sulfuric acid, at a humidity of 40% (d). 可逆的2D到3D共价有机框架(COF)材料转化
This work COF art will revisit olefins COF possible applications, but also to post-polymerization modified COF provides a new research, especially in the conversion to the 2D 3D structure or need to CC key applications.

Thaksen Jadhav : Dr. Chemistry, Indian Institute of Technology (2012-2017). PBEEE postdoctoral, McGill University (2017-2020) Postdoctoral, King Abdullah University of Science and Technology (2020- present) a radius of : Bachelor of Biochemistry, Master of Chemistry, Concordia University (2006-2013) . Dr. Chemistry, University of Leuven (2013-2017). NSERC postdoctoral, McGill University (2017- present). Liucheng Hao : First Class BA Honors chemistry and computer, McGill University (2016-2019). Dr. Reading, McGill University, Montreal Institute for Learning Algorithm (2019- present). Dmitrii Perepichka : Dr. Organic Chemistry, National Academy of Sciences of Ukraine (1994-1999). Post-doctoral, University of Durham (1999-2001). University of California, Los Angeles (2001-2002). Assistant professor, INRS (2003-2005). Assistant professor, associate professor (2005-2014), professor (2014- present), the chemistry department at McGill University (2018- present). The full text link: https://pubs.ACS.org/do i / 10.1021 / 01990 i.e. from ACS.0