A two-dimensional covalent organic framework and a preparation method and application thereof

Abstract

The application provides a two-dimensional covalent organic framework and a preparation method and application thereof, the two-dimensional covalent organic framework is prepared by reacting two cyan monomers with a pyrene group chromophore and aldehyde group monomers, in at least a part of the new two-dimensional covalent organic framework, each cyan monomer is connected with four adjacent aldehyde group monomers respectively, each aldehyde group monomer is connected with four adjacent cyan monomers respectively, forming a two-dimensional topological structure with carbon-carbon double bond as a connecting unit; the covalent organic framework has excellent crystallinity and rich pore structure, meanwhile, carbon-carbon double bond is used as a connecting unit and the covalent organic framework has a high conjugated structure, so that the new covalent organic framework has the advantages of good stability and good luminescent performance, and has a good application prospect in the field of photoluminescence.

Description

Technical Field

[0001] The present invention belongs to the technical field of covalent organic frameworks (COFs) materials, and specifically relates to a two-dimensional covalent organic framework, a preparation method thereof, and an application thereof. Background Art

[0002] Although research on phosphors for light-emitting diodes has been ongoing for over two decades, nearly all commercially successful phosphors contain rare earth elements, which are expensive, scarce, and unsustainable. From a sustainable development perspective, the development of phosphors free of rare earth and metal elements is extremely important. Due to their powerful electroluminescent properties and flexible, tunable band gap, conjugated polymers have excellent optical properties that have led to their widespread application in light-emitting diodes, field-effect transistors, solar cells, and biomedicine. By changing the main chain groups or side chain substituents of conjugated polymers, the length and distribution of their conjugated structure can be easily altered, thereby improving the luminescence performance of the material. However, the disordered microstructure limits the effective solid-state conjugation length of conjugated polymers. Covalent organic frameworks with highly conjugated structures offer a solution to this problem.

[0003] To fully exploit the strong light absorption capacity of the conjugated structure of covalent organic frameworks (COFs), various mechanisms, such as aggregation-induced emission, intramolecular charge transfer, and excited-state intramolecular proton transfer, have been employed to enhance the photoluminescence properties of COFs. While these luminescence mechanisms can reveal the source of COF fluorescence, COFs currently remain unable to replace commercial inorganic phosphors. This is due to the difficulty in balancing the stability and luminescence properties of COFs. To address this dilemma, COFs with carbon-carbon double bonds have emerged. Due to their exceptional stability and charge delocalization, they have rapidly developed in applications such as photocatalysis, metal ion detection and adsorption, electrochemiluminescence, and the fabrication of light-emitting devices. Finding a COF with carbon-carbon double bonds that balances the stability and luminescence properties of COFs, thereby creating a series of highly stable luminescent materials to replace commercial rare earth luminescent materials, is a significant challenge.

[0004] CN102933588A discloses a crystalline covalent organic framework, which comprises a phthalocyanine group and a boron-containing multifunctional linking group connected by a boron ester bond. This covalent organic framework has good luminescence performance, but it will spontaneously degrade in an acidic environment or even when exposed to air, and has poor stability.

[0005] Most existing two-dimensional covalent organic framework materials suffer from non-radiative relaxation caused by intramolecular bond rotation / vibration and aggregation-induced quenching (ACQ) produced by π-π layered stacking, which significantly reduces the fluorescence emission intensity of the two-dimensional covalent organic framework. In addition, the stability and luminescence performance of two-dimensional covalent organic framework materials are difficult to coordinate, and they cannot replace commercial inorganic phosphors. Therefore, finding a luminescent material with both good stability and luminescence performance that can replace commercial inorganic phosphors is a key issue. Summary of the Invention

[0006] In response to the deficiencies in the prior art, the present invention aims to provide a two-dimensional covalent organic framework, a preparation method, and an application thereof. The design of the raw materials and process steps enables the obtained two-dimensional covalent organic framework to have the advantages of both good stability and good luminescence performance, and has good application prospects in the field of photoluminescence.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a two-dimensional covalent organic framework, which is formed by interconnecting a cyano monomer having a structure shown in Formula I and an aldehyde monomer having a structure shown in Formula II in a two-dimensional plane.

[0009]

[0010] In at least a portion of the two-dimensional covalent organic framework, each cyano monomer is connected to four adjacent aldehyde monomers, and each aldehyde monomer is connected to four adjacent cyano monomers to form a two-dimensional topological structure.

[0011] The molar ratio of the cyano monomer to the aldehyde monomer is (0.8-1):1, for example, it can be 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, and specific ratios between the above ratios. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific ratios included in the range.

[0012] The connecting groups in the two-dimensional covalent organic framework include a dynamic covalent bond -C=C(CN)-.

[0013] Preferably, the two-dimensional covalent organic framework comprises a skeleton unit represented by formula III.

[0014]

[0015] In formula III, the dotted line represents the connection.

[0016] The two-dimensional covalent organic framework provided by the present invention contains a relatively large conjugated structure, namely a pyrene group, which can serve as a chromophore. The high planarity and rigidity of the pyrene group endow the covalent organic framework with excellent crystallinity. The dynamic covalent bond -C=C(CN)- generated by the Knoevenagel condensation reaction of a cyano monomer and an aldehyde monomer serves as a connecting group, which can significantly improve the chemical stability of the covalent organic framework and further improve the effectiveness of π conjugation between building blocks in the system. This highly conjugated structure helps to improve the light absorption capacity of the covalent organic framework and enhance the luminescence performance of the covalent organic framework. In addition, -C=C(CN)- serves as a connecting group, so that the charge transfer mode of the two-dimensional covalent organic framework is intralayer charge transfer, thereby avoiding the ACQ effect, so that the covalent organic framework has a higher fluorescence quantum yield, and further improves the luminescence performance of the covalent organic framework.

[0017] In a second aspect, the present invention provides a method for preparing a two-dimensional covalent organic framework, the preparation method comprising: reacting a cyano monomer having a structure shown in formula I with an aldehyde monomer having a structure shown in formula II to obtain the two-dimensional covalent organic framework.

[0018] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0019] As a preferred technical solution, the reaction is carried out in the presence of a catalyst.

[0020] Preferably, the catalyst is an alkaline substance, more preferably an aqueous solution of a metal hydroxide.

[0021] Preferably, the concentration of the metal hydroxide in the metal hydroxide aqueous solution is 3 to 5 mol / L, for example, it can be 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0022] Preferably, based on 1 mmol of the cyano monomer, the volume of the metal hydroxide aqueous solution is 2 to 6 mL, for example, 2 mL, 3 mL, 4 mL, 5 mL, 6 mL, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0023] Preferably, the metal hydroxide aqueous solution includes a KOH aqueous solution and / or a NaOH aqueous solution.

[0024] As a preferred technical solution, the reaction is carried out in the presence of a solvent.

[0025] Preferably, the solvent comprises a combination of ethanol and 1,2-dichlorobenzene.

[0026] Preferably, the volume ratio of ethanol and 1,2-dichlorobenzene is (1 to 1.5): 1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, and specific ratios between the above ratios. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific ratios included in the range.

[0027] Preferably, based on 1 μmol of the cyano monomer, the volume of the solvent is 0.02 to 0.06 mL, for example, 0.02 mL, 0.03 mL, 0.04 mL, 0.05 mL, 0.06 mL, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0028] As a preferred technical solution, the preparation method specifically includes: mixing the cyano monomer, aldehyde monomer, solvent and catalyst, freezing, vacuumizing and sealing, and then reacting to obtain the two-dimensional covalent organic framework.

[0029] Preferably, the freezing temperature is 65-80K, for example, 65K, 70K, 75K, 80K, and specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range.

[0030] Preferably, the reaction temperature is 150-180°C, for example, it can be 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0031] Preferably, the reaction time is 65 to 80 hours, for example, 65 hours, 70 hours, 75 hours, 80 hours, and specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range.

[0032] As a preferred technical solution, the reaction further includes a post-treatment step after completion.

[0033] Preferably, the post-treatment steps include filtration, washing, Soxhlet extraction and drying.

[0034] Preferably, the washing solvent of the washing is an organic solvent.

[0035] Preferably, the organic solvent includes a first organic solvent and a second organic solvent.

[0036] Preferably, the first organic solvent comprises tetrahydrofuran, and the second organic solvent comprises acetone.

[0037] Preferably, the washing method is: washing the solid product obtained after filtering with the first organic solvent and the second organic solvent in sequence.

[0038] Preferably, the Soxhlet extraction method is: extracting the solid product with the first organic solvent and the second organic solvent for 24 to 48 hours, for example, 24 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, 48 ​​hours, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0039] Preferably, the drying temperature is 60-80°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, and specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range.

[0040] Preferably, the drying time is 24 to 36 hours, for example, it can be 24 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0041] As a preferred technical solution, the preparation method specifically comprises the following steps:

[0042] (1) A cyano monomer having a structure shown in Formula I, an aldehyde monomer having a structure shown in Formula II, a solvent consisting of ethanol and 1,2-dichlorobenzene, and a KOH aqueous solution are mixed, and the mixture is frozen, vacuumized, and sealed to react to obtain a solid-liquid mixture.

[0043] The molar ratio of the cyano monomer to the aldehyde monomer is (0.8-1):1.

[0044] The volume ratio of the ethanol to 1,2-dichlorobenzene is (1-1.5):1.

[0045] The concentration of KOH in the KOH aqueous solution is 3 to 5 mol / L; based on 1 mmol of the cyano monomer, the volume of the KOH aqueous solution is 2 to 6 mL.

[0046] Based on 1 μmol of the cyano monomer, the volume of the solvent is 0.02 to 0.06 mL.

[0047] The freezing temperature is 65-80K.

[0048] The reaction temperature is 150-180°C.

[0049] The reaction time is 65 to 80 hours.

[0050] (2) Cooling the solid-liquid mixture of step (1) to room temperature and filtering to obtain a solid product, and then washing, Soxhlet extraction and drying the solid product to obtain a two-dimensional covalent organic framework.

[0051] The washing method comprises: washing the solid product with tetrahydrofuran and acetone in sequence.

[0052] The Soxhlet extraction method is: extracting the solid product with tetrahydrofuran and acetone for 24 to 48 hours respectively.

[0053] The drying temperature is 60-80°C.

[0054] The drying time is 24 to 36 hours.

[0055] In a third aspect, the present invention provides an application of a two-dimensional covalent organic framework in a photoluminescent material.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] The two-dimensional covalent organic framework provided by the present invention uses a pyrene group, which itself has a relatively large conjugated structure, as a chromophore to impart excellent crystallinity to the covalent organic framework. The dynamic covalent bond -C=C(CN)- is used as a connecting group to further enhance the conjugation degree of the covalent organic framework while ensuring the chemical stability of the covalent organic framework. The covalent organic framework is also endowed with a special charge transfer mode, namely, charge transfer within the covalent organic framework layer. As a result, the novel covalent organic framework has a high fluorescence quantum yield of up to 15.43%, and has good application prospects in the field of photoluminescence. In addition, the two-dimensional covalent organic framework has excellent crystallinity and a rich pore structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 is the H NMR spectrum of Py-CN;

[0059] Figure 2 is the carbon NMR spectrum of Py-CN;

[0060] Figure 3 is the mass spectrum of Py-CN;

[0061] Figure 4Schematic diagram of the synthesis of the two-dimensional covalent organic framework viCOF provided in Example 1;

[0062] Figure 5 Schematic diagram of the synthesis of the two-dimensional covalent organic framework imCOF provided in Comparative Example 1;

[0063] Figure 6 This is an infrared spectrum of the two-dimensional covalent organic framework viCOF provided in Example 1;

[0064] Figure 7 Another infrared spectrum of the two-dimensional covalent organic framework viCOF provided in Example 1;

[0065] Figure 8 This is the powder X-ray diffraction pattern of the viCOF provided in Example 1;

[0066] Figure 9 Another powder X-ray diffraction pattern of viCOF provided in Example 1;

[0067] Figure 10 Schematic diagram of the stacking model of viCOF provided in Example 1;

[0068] Figure 11 This is a graph showing nitrogen adsorption and desorption of the viCOF provided in Example 1;

[0069] Figure 12 This is the pore size distribution diagram of the viCOF provided in Example 1;

[0070] Figure 13 A comparison chart of 3D printing applications of the two-dimensional covalent organic framework provided in Example 1 and Comparative Example 1 under different lighting conditions;

[0071] Figure 14 This is a diagram of the white light diode application of the viCOF provided in Example 1;

[0072] Figure 15 This is the CIE coordinate diagram of the viCOF provided in Example 1. DETAILED DESCRIPTION

[0073] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0074] The materials used in the following examples and comparative examples are as follows:

[0075] (1) Cyanomonomer Py-CN: 2,2',2",2"'-(pyrene-1,3,6,8-tetrayltetra(benzene-4,1-diyl))tetraacetonitrile was synthesized in the laboratory. The specific information of the synthetic raw materials is as follows:

[0076] 1,3,6,8-Tetrabromopyrene (Py-Br): purchased from Shanghai Bidex Pharmaceutical Technology Co., Ltd.

[0077] 4-(Cyanomethyl)phenylboronic acid: purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd.

[0078] Bistriphenylphosphine palladium dichloride (PdCl2(PPh3)2): purchased from Beijing Bailingwei Technology Co., Ltd.;

[0079] Potassium carbonate (K2CO3): purchased from Sinopharm Chemical Reagent Co., Ltd.

[0080] The synthesis of Py-CN was as follows: Py-Br (517.8 mg, 1.0 mmol), 4-(cyanomethyl)phenylboronic acid (965.8 mg, 6.0 mmol), PdCl2(PPh3)2 (59.7 mg, 0.085 mmol), and K2CO3 (1.1 g, 8.0 mmol) were placed in a two-necked flask. The reaction system was then evacuated for 5 minutes and protected with a nitrogen stream. After repeating this process three times, 1,4-dioxane (15 mL) was added to the two-necked flask. The mixture was then heated to 85°C and stirred for 72 hours. After the reaction, the system was cooled to room temperature, and the reaction product was washed with dilute hydrochloric acid solution (HCl:H2O volume ratio of 1:6) and extracted with DCM. The organic layer obtained by extraction was distilled to remove the solvent under reduced pressure. The reaction product obtained after distillation was purified by silica gel chromatography using DCM as the eluent to obtain Py-CN (245.1 mg, 37% yield) as a pale yellow solid.

[0081] The reaction formula for synthesizing Py-CN is:

[0082]

[0083] (2) Aldehyde monomer Py-CHO: 1,3,6,8-tetrakis(4-formaldehydephenyl)pyrene, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0084] (3) Ethanol: purchased from Sinopharm Chemical Reagent Co., Ltd.

[0085] (4) 1,2-Dichlorobenzene: purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0086] (5) KOH: purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0087] (6) High-purity nitrogen (99.99%): purchased from Beijing Haike Yuanchang Practical Gas Co., Ltd.;

[0088] (7) Tetrahydrofuran (THF): purchased from Sinopharm Chemical Reagent Co., Ltd.

[0089] (8) Acetone: purchased from Sinopharm Chemical Reagent Co., Ltd.

[0090] (9) Amino monomer Py-NH2: 1,3,6,8-tetrakis-(p-aminophenyl)-pyrene, purchased from Jilin Zhongkexun Technology Co., Ltd.;

[0091] (10) Mesitylene: purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0092] (11) Benzyl alcohol: purchased from Sinopharm Chemical Reagent Co., Ltd.

[0093] Example 1

[0094] A two-dimensional covalent organic framework (viCOF) is formed by interconnecting a cyano monomer 2,2',2",2"'-(pyrene-1,3,6,8-tetrakis(benzene-4,1-diyl))tetraacetonitrile (Py-CN) with an aldehyde monomer 1,3,6,8-tetrakis(4-formaldehydephenyl)pyrene (Py-CHO) in a two-dimensional plane. The viCOF preparation method includes the following steps:

[0095] (1) See synthesis diagram Figure 4 Py-CN (15.9 mg, 24.0 μmol), Py-CHO (15.0 mg, 24.2 μmol), ethanol (0.5 mL), 1,2-dichlorobenzene (0.5 mL), and aqueous KOH (4 M, 0.1 mL) were added to a 10 mL glass ampoule. The mixture was quickly frozen in a liquid nitrogen bath at 77 K and subjected to three cycles of rapid freezing, vacuuming, and thawing. After degassing, the ampoule was sealed under vacuum with an alcohol burner and placed in an oven at 180°C for 72 h.

[0096] (2) After the reaction is completed, the obtained product is slowly cooled to room temperature; the reaction mixture in the ampoule is transferred to a 50 mL centrifuge tube, and the mixture is washed with THF solution several times until the supernatant is almost colorless. It is then washed three times with acetone solution and collected by high-speed centrifugation to obtain a crude product. Finally, the crude product is repeatedly extracted with tetrahydrofuran and acetone in a Soxhlet extractor for 24 hours, and the purified product is dried in a vacuum drying oven at 80°C for 24 hours. The final viCOF is a yellow solid powder.

[0097] Comparative Example 1

[0098] A two-dimensional covalent organic framework (imCOF) is formed by connecting amino monomers Py-NH2 and aldehyde monomers Py-CHO in a two-dimensional plane. The imCOF is prepared as follows:

[0099] See synthesis instructions Figure 5 , amino monomer Py-NH2 (3.5 mg, 5.1 μmol), aldehyde monomer Py-CHO (3.1 mg, 5 μmol), mesitylene (333 μL), benzyl alcohol (167 μL), and acetic acid aqueous solution (6 mol / L, 50 μL) were added to a 10 mL glass ampoule. Quickly freeze at 77K in a liquid nitrogen bath, repeat the rapid freezing-vacuuming-thawing process three times, and then degas. The ampoule was sealed with an alcohol burner under vacuum conditions and placed in a 120°C oven for 72 hours. After the reaction, the resulting product was slowly cooled to room temperature. The reaction mixture in the ampoule was transferred to a 50 mL centrifuge tube and the mixture was washed with THF solution several times until the supernatant was almost colorless. It was then washed three times with acetone solution and collected by high-speed centrifugation to obtain a solid crude product. Finally, the solid crude product was repeatedly purified by tetrahydrofuran and acetone in a Soxhlet extractor, and the purified product was dried in a vacuum drying oven at 80°C for 24 hours. The final imCOF was obtained as a yellow solid powder.

[0100] Material characterization and performance testing:

[0101] (1) Liquid Nuclear Magnetic Resonance (NMR) Spectroscopy Test: The Py-CN in Example 1 was tested using an AVANCE III HD400 NMR spectrometer produced by Bruker, Germany. The deuterated reagent contained tetramethylsilane (TMS) as an internal standard. The test results are shown in Figure 2. Figure 1 and Figure 2 shown.

[0102] Depend on Figure 1 Py-CN 1 The H-NMR spectrum (solvent: deuterated DMSO, units in ppm) shows a doublet at 7.76 ppm and 7.60 ppm, with a 1:1 ratio of hydrogen atoms. These correspond to the hydrogen atoms on the carbon atoms on the benzene ring close to and farthest from the pyrene group, respectively. The absorption peaks at 3.33 ppm and 2.51 ppm are due to water and deuterated DMSO, respectively. The ratios of the remaining peak areas correspond one-to-one to the ratio of hydrogen atoms in the Py-CN structure.

[0103] Depend on Figure 2 Py-CN 13 The C-NMR spectrum (solvent deuterated DMSO, unit is ppm) shows that there are absorption peaks at 22.69ppm, 119.76ppm, 127.91ppm, 128.92ppm, 131.28ppm, 131.51ppm, 136.88ppm, and 139.75ppm, which correspond one to one with the carbon atoms in the Py-CN skeleton. The absorption peak at 40.00ppm is that of deuterated DMSO. Figure 1and Figure 2 The synthesis of Py-CN could be confirmed.

[0104] (2) Mass spectrometry: The Py-CN in Example 1 was tested using a Solarix 9.7T mass spectrometer produced by Bruker, Germany. The test results are shown in the figure. Figure 3 shown.

[0105] Depend on Figure 3 It can be seen that the molecular weight of the measured compound is 662.24643, which is consistent with the calculated relative molecular mass of Py-CN, 662.24705, and the synthesis of Py-CN is verified again.

[0106] (3) Infrared spectroscopy characterization: The viCOF provided in Example 1 was subjected to Fourier transform infrared (FT-IR) spectroscopy testing using a Perkin-Elmer Spectrum One infrared spectrometer manufactured by Perkin-Elmer Instruments, Inc., USA (samples were prepared by pressing potassium bromide tablets). The test results are shown in the figure below: Figure 6 and Figure 7 shown.

[0107] pass Figure 6 It can be seen that the Py-CHO monomer is at 1696 cm -1 The C=O stretching vibration peak belonging to the aldehyde group disappears in the FT-IR spectrum of the reaction product viCOF, indicating that the C=O in the Py-CHO monomer participates in the condensation reaction. Figure 7 It can be seen that due to the different chemical environments of the cyano groups in viCOF and Py-CN, the original Py-CN is located at 2251 cm -1 The -C≡N vibration band at viCOF is shifted to 2215 cm -1 The formation of -C=C(C≡N)- group in viCOF was confirmed.

[0108] (4) Powder X-ray diffraction (PXED) test: The test was performed using a Xeuss SAXS / WAXS X-ray diffractometer produced by Xenocs, France, with the Kα ray generated by a copper target.

[0109] pass Figure 8 、 Figure 9 and Figure 10It can be seen that the diffraction angles (2θ) of the main diffraction peaks of viCOF are 5.0°, 7.0°, 10.1°, 17.5° and 23.2°, and these diffraction peaks are attributed to the (100), (110), (200), (210) and (001) crystal planes, respectively. The structural simulation and Pawley refinement of viCOF were performed using the software Materials Studio. From the deviation between the refined data and the experimental data, it can be observed that the PXRD curve output by the AB stacking model obtained by viCOF simulation is quite different from the experimentally measured data, while the difference between the PXRD curve output by the AA stacking model and the experimentally observed curve is negligible (Rwp = 0.68%, RP = 0.53%). It can be inferred that viCOF is arranged in layers according to AA stacking. The calculated unit cell parameters of viCOF are: α=γ=90°, β=7.83°.

[0110] (5) Nitrogen adsorption-desorption isotherm and specific surface area test: The test was carried out using a 3-flex three-station full-function multi-purpose gas adsorption instrument produced by Micromeritics Instruments, Inc., USA. The nitrogen adsorption-desorption isotherm was measured at 77K and used to calculate the specific surface area (SBET) value of the sample. The specific calculation results were based on the Brunauer–Emmett–Teller theory, and were calculated by selecting points in the relative pressure range of 0.05–0.20 through the adsorption branch of the isotherm. The pore size distribution curve was obtained by simulation calculation using nonlocal density functional theory (NLDFT). The pore volume was calculated at a relative pressure of 0.99. All porous materials were measured after vacuum degassing at 120°C for 12 hours.

[0111] pass Figure 11 and Figure 12 It can be seen that according to the International Union of Pure and Applied Chemistry (IUPAC) classification, viCOF exhibits the characteristics of a combination of type I and type IV adsorption isotherms, indicating the presence of both micropores and mesopores in viCOF. Based on the Brunauer–Emmett–Teller theory, the specific surface area of ​​viCOF was calculated to be 845 m 2 g -1 Non-local density functional theory (NLDFT) calculations revealed a pore size of approximately 1.7 nm for viCOF. This pore size, calculated using NLDFT, is consistent with the 1.7 nm pore size simulation of AA stacking, confirming the presence of AA stacking between viCOF layers.

[0112] (6) Fluorescence quantum yield test: Fluorescence quantum yield was tested using a FluoroMax Plus fluorescence spectrometer produced by HORIBA, Japan. The photoluminescence quantum yield of the viCOF powder was measured to be 15.43%.

[0113] (7) Luminescence intensity test: 10 mg of viCOF or 10 mg of imCOF was dissolved in 10 mL of toluene and transferred to a beaker. The mixture was ultrasonicated at room temperature for 10 minutes. After uniform dispersion, 10 g of PMMA (polymethyl methacrylate, molecular weight 500,000 g / moL, purchased from Aladdin Reagent (Shanghai) Co., Ltd.) powder was slowly added and magnetically stirred at room temperature until PMMA was fully dissolved. When the system became transparent, stirring was stopped. The system was transferred to an ultrasonic cleaning machine and ultrasonicated at room temperature for 15 minutes. During this period, the bubbles generated during stirring were discharged to the liquid surface. After the beaker was taken out and allowed to stand for 1 hour, a dense PMMA film was formed on the liquid surface. After the PMMA film was taken out with tweezers, the remaining PMMA mixture in the beaker was the printing slurry, which was transferred to the 3D printing syringe for later use.

[0114] Using an Adventuretech 3D-LB-Printer-0030 3D printer manufactured by Shenzhen Qiyu Technology Co., Ltd., and using Repetier-Host software to simulate the printing path, the prepared printing syringe containing the printing slurry was mounted on the 3D printer. The printing platform temperature was set to 50°C, and the device was printed according to the pre-set path. After printing, the device was placed in a drying oven at 50°C for 10 hours before being removed to obtain the COF / PMMA device.

[0115] The luminescence performance of the COF / PMMA device was tested under natural light and 365nm ultraviolet light, and the comparison of the 3D printing application of the two-dimensional covalent organic framework provided in Example 1 and Comparative Example 1 under different lighting conditions was obtained. Figure 13 As shown, under natural light and 365nm ultraviolet light illumination conditions, the luminescence intensity of viCOF is significantly higher than that of imCOF, indicating that the luminescence performance of the two-dimensional covalent organic framework with -C=C(CN)- as the connecting unit is better than that of the two-dimensional covalent organic framework with -C=N- as the connecting unit.

[0116] (8) Performance test of white light emitting diode (WLED) devices: organic encapsulation silica gel A glue (Shenzhen Zhanwanglong Technology Co., Ltd.) and glue B glue (Shenzhen Zhanwanglong Technology Co., Ltd.) of light emitting diodes were added into a small beaker at a mass ratio of 1:4 and mixed evenly. 5 mg of viCOF was weighed and added into 5 mL of the mixed glue and stirred evenly with a glass rod. The protective cover of a blue light emitting diode with an emission wavelength of 470 nm was opened with tweezers, and the mixed powder-glue mixture was dropped onto the blue light emitting diode. The CIE value of the device was tested with an LED spectrometer (Hongpu HP9000). After the CIE value of the device was adjusted to be close to the white light point (0.33, 0.33), it was placed in an oven and baked at 100°C for about 1 hour to obtain a WLED device.

[0117] Depend on Figure 14 and Figure 15 It can be concluded that, based on the principle of complementary colors, LEDs with a wavelength of 470nm are suitable for the preparation of WLEDs. The CIE coordinates of the resulting device (0.35, 0.33) are close to those of a standard WLED (0.33, 0.33), and the correlated color temperature (CCT) is 4463K, resulting in natural white light. WLED devices prepared using viCOF as a phosphor exhibit excellent optical properties, demonstrating the promising application of viCOF in WLEDs.

[0118] The applicant declares that the present invention uses the above-described embodiments to illustrate the detailed process flow of the present invention, but the present invention is not limited to the above-described detailed process flow, that is, it does not mean that the present invention must rely on the above-described detailed process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A two-dimensional covalent organic framework, characterized in that The two-dimensional covalent organic framework is formed by connecting a cyano monomer having a structure shown in Formula I and an aldehyde monomer having a structure shown in Formula II in a two-dimensional plane. Formula I Formula II; The connecting group in the two-dimensional covalent organic framework is a dynamic covalent bond -C=C(CN)-; The skeleton unit of the two-dimensional covalent organic framework is shown in Formula III: Formula III In formula III, the dotted line represents the connection.

2. The two-dimensional covalent organic framework according to claim 1, characterized in that In at least a portion of the two-dimensional covalent organic framework, each cyano monomer is connected to four adjacent aldehyde monomers, and each aldehyde monomer is connected to four adjacent cyano monomers to form a two-dimensional topological structure.

3. The two-dimensional covalent organic framework according to claim 1, characterized in that The molar ratio of the cyano monomer to the aldehyde monomer is (0.8-1):

1.

4. A method for preparing a two-dimensional covalent organic framework according to any one of claims 1 to 3, characterized in that: The preparation method comprises: reacting a cyano monomer having a structure shown in formula I with an aldehyde monomer having a structure shown in formula II to obtain the two-dimensional covalent organic framework.

5. The preparation method according to claim 4, characterized in that The molar ratio of the cyano monomer to the aldehyde monomer is (0.8-1):

1.

6. The preparation method according to claim 4, characterized in that The reaction is carried out in the presence of a catalyst.

7. The preparation method according to claim 6, characterized in that The catalyst is an alkaline substance.

8. The preparation method according to claim 7, characterized in that The catalyst is a metal hydroxide aqueous solution.

9. The preparation method according to claim 8, characterized in that The concentration of the metal hydroxide in the metal hydroxide aqueous solution is 3 to 5 mol / L.

10. The preparation method according to claim 8, characterized in that Based on 1 mmol of the cyano monomer, the volume of the metal hydroxide aqueous solution is 2 to 6 mL.

11. The preparation method according to claim 8, characterized in that The metal hydroxide aqueous solution includes a KOH aqueous solution and / or a NaOH aqueous solution.

12. The preparation method according to claim 4, characterized in that The reaction is carried out in the presence of a solvent.

13. The preparation method according to claim 12, characterized in that The solvent includes a combination of ethanol and 1,2-dichlorobenzene.

14. The preparation method according to claim 13, characterized in that The volume ratio of the ethanol to 1,2-dichlorobenzene is (1-1.5):

1.

15. The preparation method according to claim 12, characterized in that Based on 1 μmol of the cyano monomer, the volume of the solvent is 0.02-0.06 mL.

16. The preparation method according to claim 4, characterized in that The preparation method specifically comprises: mixing the cyano monomer, the aldehyde monomer, the solvent and the catalyst, freezing, vacuumizing and sealing, and then reacting to obtain the two-dimensional covalent organic framework.

17. The preparation method according to claim 16, characterized in that The freezing temperature is 65-80 K.

18. The preparation method according to claim 16, characterized in that The reaction temperature is 150-180°C.

19. The preparation method according to claim 16, characterized in that The reaction time is 65-80 h.

20. The preparation method according to claim 4, characterized in that After the reaction is completed, a post-processing step is also included.

21. The preparation method according to claim 20, characterized in that The post-treatment steps include filtration, washing, Soxhlet extraction and drying.

22. The preparation method according to claim 21, characterized in that The washing solvent for the washing is an organic solvent.

23. The preparation method according to claim 22, characterized in that The organic solvent includes a first organic solvent and a second organic solvent.

24. The preparation method according to claim 23, characterized in that The first organic solvent includes tetrahydrofuran, and the second organic solvent includes acetone.

25. The preparation method according to claim 23, characterized in that The washing method comprises: washing the crude product obtained after filtering with the first organic solvent and the second organic solvent in sequence.

26. The preparation method according to claim 25, characterized in that The Soxhlet extraction method comprises extracting the crude product with the first organic solvent and the second organic solvent for 24 to 48 hours respectively.

27. The preparation method according to claim 21, characterized in that The drying temperature is 60-80°C.

28. The preparation method according to claim 21, characterized in that The drying time is 24 to 36 hours.

29. The preparation method according to claim 4, characterized in that The preparation method specifically comprises the following steps: (1) mixing a cyano monomer having a structure shown in formula I, an aldehyde monomer having a structure shown in formula II, a solvent consisting of ethanol and 1,2-dichlorobenzene, and a KOH aqueous solution, freezing, evacuating, and sealing the mixture to react and obtain a solid-liquid mixture; The molar ratio of the cyano monomer to the aldehyde monomer is (0.8-1):1; The volume ratio of the ethanol to 1,2-dichlorobenzene is (1-1.5):1; The concentration of KOH in the KOH aqueous solution is 3 to 5 mol / L; based on 1 mmol of the cyano monomer, the volume of the KOH aqueous solution is 2 to 6 mL; Based on 1 μmol of the cyano monomer, the volume of the solvent is 0.02-0.06 mL; The freezing temperature is 65-80 K; The reaction temperature is 150-180°C; The reaction time is 65 to 80 hours; (2) cooling the solid-liquid mixture of step (1) to room temperature and filtering to obtain a crude product, and then washing, Soxhlet extraction and drying the crude product to obtain the two-dimensional covalent organic framework; The washing method comprises: washing the crude product with tetrahydrofuran and acetone in sequence; The Soxhlet extraction method comprises: extracting the crude product with tetrahydrofuran and acetone for 24 to 48 hours respectively; The drying temperature is 60-80°C; The drying time is 24 to 36 hours.

30. Use of the two-dimensional covalent organic framework according to any one of claims 1 to 3 in a photoluminescent material.

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