Fluorine-rich covalent organic framework material for realizing carbon-nitrogen coupling reaction through photocatalysis as well as preparation method and application of fluorine-rich covalent organic framework material

Abstract

The invention discloses a fluorine-rich covalent organic framework material for realizing a carbon-nitrogen coupling reaction through photocatalysis as well as a preparation method and application of the fluorine-rich covalent organic framework material. The phenyl pyrene group is connected by a long linking group formed by connecting three benzene rings; and an F element with strong electronegativity is introduced, so that the covalent organic framework material with a clearer D-A structure and stronger crystallinity and stability is constructed. Due to strong intermolecular pi-pi accumulation caused by a highly conjugated rigid planar skeleton, the absorption of sunlight is enhanced, and the band gap is shortened. Strong electronegativity F atoms and electron-rich donor pyrene groups form a D-A structure, so that the separation of photogenerated charges and the transfer of the charges in the axial direction are facilitated; the photocatalytic reaction is promoted. In the absence of transition metal, carboxyl and azo groups can be subjected to photocatalytic reaction, and C-N bonds are coupled; the photosensitive integrated, metal-free and recyclable carbon-nitrogen coupling reaction process is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of covalent organic framework functional materials, and particularly relates to a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, a preparation method thereof and an application thereof. Background Art

[0002] In the field of organic chemistry, the efficient construction of C-N bonds is very important because it is widespread in many natural products, drugs and functional materials. sp 2 There are several notable pathways for the formation of C-N bonds, including Buchwald-Hartwig reaction, Ullmann coupling reaction and Chan-Lam amination reaction. However, whether it is a nucleophilic substitution reaction between a nitrogen nucleophile and an alkyl halide, alkylation of an alcohol using a nitrogen nucleophile, carbonyl reductive amination or olefin hydroamination; most of the catalysts used in photocatalytic carbon-nitrogen coupling reactions are still noble metals and transition metals; or transition metal co-catalysis is required, and the catalysts are expensive and cannot be recycled and reused.

[0003] How to achieve metal-free photocatalytic reaction to construct C-N bonds is a more economical and environmentally friendly green preparation method. Among them, using abundant carboxylic acids as alkylating agents to form C-N bonds will be the first step to achieve this goal. Increasing functional group diversity, higher atom economy, and simply removing the only stoichiometric by-product (carbon dioxide) are potential additional advantages of replacing alkyl halides with carboxylic acids.

[0004] Therefore, metal-free visible light-responsive polymers with low-cost, long-lived photo-generated charges and abundant active sites are studied as potential catalysts for carbon-nitrogen coupling. Among these polymer materials, covalent organic frameworks (COFs) are crystalline porous organic polymers with ordered structures and extended π-π conjugation. The extended conjugation helps the transport of photo-generated charges, and the permanent porosity and structural diversity of COFs can promote mass transfer and adjust optoelectronic properties. The composition and structure of COF can be easily modified accordingly to obtain the desired optoelectronic properties, making COFs a photocatalyst for realizing carbon-nitrogen coupling.

[0005] In order to achieve high charge separation and transfer efficiency and find a broad-spectrum responsive photocatalyst with high solar energy utilization rate; new covalent organic framework materials should be prepared. Summary of the Invention

[0006] For the above reasons, the first object of the present invention is to provide a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction. Based on the phenylpyrene structure, a covalent organic framework material is constructed with multiple benzene rings as linking groups, and multiple strongly negatively charged F atoms are introduced onto the benzene rings. This not only constructs a strong D-A conjugated COF structure with the pyrene monomer, which is beneficial to the effective separation of photo-generated charges and holes, but also enhances the stability of the COF framework, enabling it to more effectively achieve the carbon-nitrogen coupling reaction.

[0007] The second object of the present invention is to provide a preparation method of a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction. By using the hydrothermal reaction conditions in the art, the amino ligand and the aldehyde ligand are coupled. The reaction operation is simple and the yield is high, which is suitable for large-scale preparation.

[0008] The third object of the present invention is to provide the application of a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction as a photocatalytic catalyst in the C-N bond coupling; it can effectively couple carboxylic acids and azo compounds to achieve a photocatalytic reaction without transition metal catalysis.

[0009] The first object of the present invention can be achieved by adopting the following technical solutions:

[0010] A fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, whose chemical structure is shown in Formula I:

[0011]

[0012] The second object of the present invention can be achieved by adopting the following technical solutions:

[0013] A preparation method of a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, in which the structural monomer shown in Formula II and 1,3,6,8-tetra-(p-aminophenyl)-pyrene are subjected to an amine-aldehyde condensation reaction under solvothermal reaction conditions, and the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction is obtained after the reaction ends;

[0014]

[0015] Furthermore, the molar ratio of the structural monomer shown in Formula II to the 1,3,6,8-tetra-(p-aminophenyl)-pyrene monomer is (2 - 2.5):1.

[0016] Furthermore, the solvent for the solvothermal reaction is a mixed solvent of ortho-dichlorobenzene and n-butanol, and the volume ratio of ortho-dichlorobenzene to n-butanol is 1:(0.5 - 2).

[0017] Further, the molar volume ratio of the structural monomer shown in Formula II to the solvent is (20 - 60) μmol : 1 mL.

[0018] Further, acetic acid is used as a crystal form regulator in the reaction. The concentration of acetic acid added is 5 - 7 mol / L, and the amount of acetic acid added is 5% - 15% of the volume of the solvent.

[0019] Further, the reaction conditions are: reacting at 100 - 140 °C for 12 - 96 h.

[0020] Further, after the reaction, solid-liquid separation is also included, and the purification process of the solid is as follows:

[0021] Purification includes washing and / or Soxhlet extraction; the solvents used for washing are DMF and / or tetrahydrofuran; the solvent used for Soxhlet extraction is tetrahydrofuran.

[0022] The third object of the present invention can be achieved by adopting the following technical solutions:

[0023] Application of the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction described in any one of the above as a photocatalytic catalyst in C-N bond coupling.

[0024] Further, N-carbobenzyloxy-D-proline and diethyl azodicarboxylate are subjected to C-N bond coupling with the above-mentioned For photocatalytic realization Fluorine-rich covalent organic framework materials for carbon-nitrogen coupling reaction as photocatalysts catalyst.

[0025] Further, the reaction conditions are: in the presence of CsF, using acetonitrile as the solvent, under an inert gas atmosphere, with a 456 nm 40 W lamp as the visible light source, carrying out a photocatalytic experiment for 24 - 96 h.

[0026] Further, the molar ratio of N-carbobenzyloxy-D-proline, diethyl azodicarboxylate, and CsF is 1 : (0.8 - 1.2) : (0.8 - 1.2).

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. A fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction of the present invention has a phenylpyrene group and a long linking group connected by three benzene rings, forming a highly crystalline main framework. The strongly electronegative F atoms on the linking group and the electron-rich donor pyrene group form a D-A structure, and the internal separation driving force formed by the connection of the donor and the acceptor is beneficial to promoting the separation of photogenerated charges. In addition, the large electronegative F atoms also form hydrogen bonds with the hydrogen atoms on the adjacent benzene rings, reducing the torsional angle caused by steric hindrance and maintaining the AA or AA+ stacking mode, promoting the charge transfer in the axial direction. The constructed planar strong D-A covalent organic framework material has strong intermolecular π-π stacking caused by a highly conjugated rigid planar skeleton, enhancing the absorption of sunlight and shortening the band gap.

[0029] 2. A preparation method of a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction of the present invention adopts a hydrothermal reaction, which is simple and convenient to synthesize, can be mass-produced without a cumbersome operation process.

[0030] 3. The application of a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction as a photocatalytic catalyst in the C-N bond coupling. In the absence of transition metals, it can photocatalytically react the carboxyl group with the azo group to form a C-N bond coupling; realizing a photosensitive integrated, metal-free, recyclable carbon-nitrogen coupling reaction process. Description of the Drawings

[0031] Figure 1 1H NMR spectrum (DMSO-d6) of 4F-CHO prepared in Example 1;

[0032] Figure 2 19F NMR spectrum of 4F-CHO prepared in Example 1;

[0033] Figure 3 Appearance picture of 4F-CHO prepared in Example 2;

[0034] Figure 4 X-ray powder diffraction patterns of 4F-CHO (a) prepared in Example 2 and 3Ph-COF (b) prepared in Comparative Example 1;

[0035] Figure 5 Schematic diagram of the simulated structure; wherein (a) is the simulated AA stacking structure of 4F-CHO prepared in Example 2; (b) is the simulated AA stacking structure of 3Ph-COF prepared in Comparative Example 1;

[0036] Figure 6 Mott-Schottky curves of 4F-CHO (a) prepared in Example 2 and 3Ph-COF (b) prepared in Comparative Example 1;

[0037] Figure 7Tauc plot of 4F-CHO (a) prepared in Example 2 and 3Ph-COF (b) prepared in Comparative Example 1;

[0038] Figure 8 Energy band structure diagrams of 4F-CHO (a) prepared in Example 2 and 3Ph-COF (b) prepared in Comparative Example 1;

[0039] Figure 9 1H NMR spectrum of the photocatalytic product;

[0040] Figure 10 Yield diagrams of the catalytic products of 4F-CHO prepared in Example 2 and 3Ph-COF prepared in Comparative Example 1 as photocatalysts;

[0041] Figure 11 X-ray powder diffraction diagrams of 4F-CHO prepared in Example 2 and 3Ph-COF prepared in Comparative Example 1 after recycling as photocatalysts;

[0042] Figure 12 Yield diagrams of the cyclic catalytic products of 4F-CHO prepared in Example 2 and 3Ph-COF prepared in Comparative Example 1 as photocatalysts. Detailed implementation manners

[0043] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0044] The design of the "donor-acceptor" (D-A) structure is one of the most traditional methods to promote the separation efficiency of photo-generated electrons to construct semiconductor photocatalytic materials. The band gap of a semiconductor with a donor-acceptor (D-A) structure usually corresponds to the difference between the highest occupied molecular orbital (HOMO) mainly distributed on the donor and the lowest unoccupied molecular orbital (LUMO) mainly distributed on the acceptor. Therefore, their band gaps are narrower than those of traditional organic semiconductors. Therefore, the design of COFs with a D-A structure can ensure better light absorption.

[0045] Therefore, the present application provides a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, its preparation method and application.

[0046] A fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, its chemical structure is shown in Formula I:

[0047]

[0048] The crystallinity and stability of the COF constructed with a long linking group connecting three benzene rings are insufficient; while the long linking group connecting three benzene rings contributes to the expansion of the pore size of the COF material. Therefore, the problem of how to construct a stable and efficient COF material with a long linking group connecting three benzene rings has not been solved. In this application, strongly electronegative F atoms are introduced onto the benzene ring; on the one hand, a highly conjugated rigid planar skeleton with a planar strong D-A structure is formed between the electron-rich donor pyrene graft and the COF material framework; the resulting strong intermolecular π-π stacking enhances the absorption of sunlight and shortens the band gap; on the other hand, the introduction of F atoms enhances the crystallinity and stability of the COF material framework, enabling the prepared COF material to be actually used.

[0049] The present invention also provides a preparation method of a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction. The structural monomer shown in Formula II and 1,3,6,8-tetra-(p-aminophenyl)-pyrene undergo an amine-aldehyde condensation reaction under solvothermal reaction conditions, and the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction is obtained after the reaction ends;

[0050]

[0051] As one of the embodiments, the molar ratio of the structural monomer shown in Formula II to the 1,3,6,8-tetra-(p-aminophenyl)-pyrene monomer is (2 - 2.5):1.

[0052] As one of the embodiments, the structural monomer shown in Formula II is prepared by the following method:

[0053] The structural monomer shown in Formula II is prepared by the Suzuki coupling reaction of 1,4-dibromotetrafluorobenzene and 4-formylphenylboronic acid; the reaction process is as follows:

[0054]

[0055] The reaction activity of fluorine atoms is poor, and the reaction activity of bromine is much higher than that of fluorine. Therefore, the Suzuki coupling reaction occurs at the bromine substitution position.

[0056] As one of the embodiments, the Suzuki coupling reaction conditions are: tetrakis(triphenylphosphine)palladium(0) as the catalyst, potassium carbonate as the base, and a mixed solution of 1,4-dioxane / water as the solvent; under an inert gas atmosphere, the reaction is carried out at 100 - 110 °C for 12 - 36 h. Under the catalyst system of tetrakis(triphenylphosphine)palladium(0) and potassium carbonate, the bromine atom and the boric acid group can react well coupling, while under the low activity of fluorine atoms, the coupling reaction with boric acid does not occur. 1,4-dioxane The mixed solution of dioxane and water is a commonly used solvent for the catalyst system of tetrakis(triphenylphosphine)palladium(0) and potassium carbonate, and an inert gas atmosphere is also one of the requirements of this system.

[0057] As one of the embodiments, after the reaction materials are added into the reactor, the reactor is evacuated and filled with inert gas repeatedly for multiple times; the organic solvent is bubbled with inert gas to remove oxygen and then added into the reactor to form an inert gas atmosphere. The inert gas is one or a combination of two of argon and nitrogen; preferably, the inert gas is nitrogen.

[0058] As one of the embodiments, the molar ratio of 1,4-dibromotetrafluorobenzene to 4-formylphenylboronic acid is 1:(2.5 - 3); the molar ratio of tetrakis(triphenylphosphine)palladium to potassium carbonate is 1:(40 - 80).

[0059] As one of the embodiments, the volume ratio of 1,4-dioxane to water is (2 - 6):1; the molar volume ratio of 1,4-dibromotetrafluorobenzene to the solvent is (50 - 100) μmol:1 ml.

[0060] As one of the embodiments, the molar ratio of 1,4-dibromotetrafluorobenzene to tetrakis(triphenylphosphine)palladium is (10 - 50):1.

[0061] As one of the embodiments, after the reaction is completed, solid-liquid separation is carried out, and the solid is washed successively with water, ethyl acetate and ethanol, and dried overnight at 60 - 80 °C to obtain the structural monomer shown in Formula II.

[0062] As one of the embodiments, the solvent for the solvothermal reaction is a mixed solvent of ortho-dichlorobenzene and n-butanol, and the volume ratio of ortho-dichlorobenzene to n-butanol is 1:(0.5 - 2).

[0063] As one of the embodiments, the molar volume ratio of the structural monomer shown in Formula II to the solvent is (20 - 60) μmol:1 mL.

[0064] As one of the embodiments, acetic acid is used as the crystal form regulator for the reaction, the concentration of the added acetic acid is 5 - 7 mol / L, and the amount of the added acetic acid is 5% - 15% of the volume of the solvent.

[0065] As one of the embodiments, the reaction conditions are: reacting at 100 - 140 °C for 12 - 96 h.

[0066] As one of the embodiments, after the reaction, solid-liquid separation is further included, and a purification process is carried out on the solid:

[0067] Purification includes washing and / or Soxhlet extraction; the solvents used for washing are DMF and / or tetrahydrofuran; the solvent used for Soxhlet extraction is tetrahydrofuran.

[0068] Use of the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction as defined in any of the above as a photocatalytic catalyst in C-N bond coupling.

[0069] As one embodiment, N-benzyloxycarbonyl-D-proline and diethyl azodicarboxylate are subjected to C-N bond coupling using the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction as defined in the above as a photocatalytic catalyst.

[0070] As one embodiment, the reaction conditions are as follows: in the presence of CsF, using acetonitrile as a solvent, under an inert gas atmosphere, with a 456 nm 40 W lamp as a visible light source, and carrying out a photocatalytic experiment for 24 - 96 h.

[0071] As one embodiment, the molar ratio of N-benzyloxycarbonyl-D-proline, diethyl azodicarboxylate and CsF is 1:(0.8 - 1.2):(0.8 - 1.2).

[0072] The following will be further described with specific examples.

[0073] Preparation of the structural monomer shown in Formula II in Example 1:

[0074] Weigh 1.6 mmol of raw material 1,4-dibromotetrafluorobenzene and 4.4 mmol of 4-formylphenylboronic acid, 0.097 mmol of catalyst tetrakis(triphenylphosphine)palladium(0), and 5.75 mmol of potassium carbonate, and add them to a 25 mL two-necked round-bottom flask. After evacuating the air in the flask, fill it with nitrogen; then add 4 mL of deionized water and 16 mL of ultra-dry 1,4-dioxane as solvents under a nitrogen atmosphere, and then stir at 100 °C for 24 h; after the reaction, wait for it to cool to room temperature, filter the obtained solid, wash it successively with a small amount of water, ethyl acetate and ethanol, and dry it overnight at 80 °C to obtain the structural monomer shown in Formula II, named 4F-CHO;

[0075] 1 1H NMR (400 MHz, DMSO-d6): δ 10.12 (s, 1H), 8.12 (d, J = 8.2 Hz, 2H), 7.85 (d, J = 8.0 Hz, 2H); the spectrum is as Figure 1 shown;

[0076] The fluorine nuclear magnetic resonance spectrum is as Figure 2 shown.

[0077] Preparation of 4F-COF in Example 2

[0078] Weigh 40 μmol of 4F-CHO prepared in Example 1 and 17.6 μmol of 1,3,6,8-tetra(p-aminophenyl)pyrene into a glass tube (8×150 mm), add 0.5 mL of o-dichlorobenzene, 0.5 mL of n-butanol, and 0.1 mL of 6 M acetic acid aqueous solution. Then, ultrasonically treat the mixture for 10 min; seal the glass tube with a hydrogen-oxygen flame and heat it in an oven at 120 °C for 72 h, and then naturally cool it to room temperature; collect the powder by filtration, wash the powder sample with DMF (5 mL×5) and THF (5 mL×5), then perform Soxhlet extraction in a THF solution for 3 days, and dry it in vacuo to obtain the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, named 4F-COF; the properties are as Figure 3 shown.

[0079] Preparation of Example 3 4F-COF

[0080] Weigh 40 μmol of 4F-CHO prepared in Example 1 and 20 μmol of 1,3,6,8-tetra(p-aminophenyl)pyrene into a glass tube (8×150 mm), add 0.67 mL of o-dichlorobenzene, 1.33 mL of n-butanol, and 0.3 mL of 6 M acetic acid aqueous solution. Then, ultrasonically treat the mixture for 10 min; seal the glass tube with a hydrogen-oxygen flame and heat it in an oven at 100 °C for 96 h, and then naturally cool it to room temperature; collect the powder by filtration, wash the powder sample with DMF (5 mL×5) and THF (5 mL×5), then perform Soxhlet extraction in a THF solution for 3 days, and dry it in vacuo to obtain the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, named 4F-COF.

[0081] Preparation of Example 4 4F-COF

[0082] Weigh 40 μmol of 4F-CHO prepared in Example 1 and 16 μmol of 1,3,6,8-tetra(p-aminophenyl)pyrene into a glass tube (8×150 mm), add 0.44 mL of o-dichlorobenzene, 0.23 mL of n-butanol, and 0.04 mL of 6 M acetic acid aqueous solution. Then, ultrasonically treat the mixture for 10 min; seal the glass tube with a hydrogen-oxygen flame and heat it in an oven at 140 °C for 12 h, and then naturally cool it to room temperature; collect the powder by filtration, wash the powder sample with DMF (5 mL×5) and THF (5 mL×5), then perform Soxhlet extraction in a THF solution for 3 days, and dry it in vacuo to obtain the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, named 4F-COF.

[0083] Comparative Example 1

[0084] Weigh 40 μmol of 1,4-bis(4-formylphenyl)benzene and 17.6 μmol of 1,3,6,8-tetra(p-aminophenyl)pyrene into a glass tube (8×150 mm), add 0.5 mL of o-dichlorobenzene, 0.5 mL of n-butanol, and 0.1 mL of 6M acetic acid aqueous solution. Then, ultrasonically treat the mixture for 10 min; seal the glass tube with a hydrogen-oxygen flame and heat it in an oven at 120 °C for 72 h, and then naturally cool it to room temperature; collect the powder by filtration, wash the powder sample with DMF (5 mL×5) and THF (5 mL×5), then perform Soxhlet extraction in a THF solution for 3 days, and dry it in vacuo to obtain the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, named 3Ph-COF.

[0085] Test examples:

[0086] (1) Perform X-ray powder diffraction tests on the 4F-COF prepared in Example 2 and the 3Ph-COF prepared in Comparative Example 1. The X-ray powder diffraction patterns are as shown in Figure 4 ; The schematic diagram of the simulated structure is as shown in Figure 5 .

[0087] It can be seen from the results of the X-ray powder diffraction test that the diffraction pattern of the 4F-COF prepared in Example 2 is highly consistent with the X-ray powder diffraction of the AA stacking structure simulated by Materials Studio software in terms of peak positions, indicating that the 4F-COF prepared in Example 2 is a two-dimensional layered structure with AA stacking. Moreover, it can also be seen from the diffraction pattern that compared with the 3Ph-COF prepared in Comparative Example 1 without fluorine, the diffraction peaks of the 4F-COF prepared in Example 2 are very strong and sharp, indicating that the covalent organic framework material 4F-COF prepared in Example 2 has high crystallinity.

[0088] (2) Perform Mott-Schottky tests on the 4F-COF prepared in Example 2 and the 3Ph-COF prepared in Comparative Example 1. The Mott-Schottky curves are as shown in Figure 6 ; The tauc plot is as shown in Figure 7 .

[0089] For the Mott-Schottky test curve, when the tangent slope is positive, it indicates that both the 4F-COF prepared in Example 2 and the 3Ph-COF prepared in Comparative Example 1 are n-type semiconductors. The band gap Eg of the 4F-COF prepared in Example 2 is calculated to be 2.36 eV through the Tauc plot; the band gap Eg of the 3Ph-COF prepared in Comparative Example 1 is 2.04 eV (as shown in Figure 8As shown). Since the 4F-COF prepared in Example 2 has a stronger D-A structure, the redox potential of the 4F-COF prepared in Example 2 is more suitable for photocatalytic carbon-nitrogen coupling through band structure calculation.

[0090] Example 5

[0091] Take 5 mg of the 4F-COF prepared in Example 2 and 5 mg of the 3Ph-COF sample prepared in Comparative Example 1 as photocatalysts, 0.08 mmol of N-benzyloxycarbonyl-D-proline, 0.08 mmol of diethyl azodicarboxylate, and 0.08 mmol of CsF in 4 mL of acetonitrile. After purging with argon for 30 min, seal the system; use a 456 nm 40 W lamp as the visible light source and carry out the photocatalytic reaction for 2 days. After the reaction, carry out treatment, through extraction and rotary evaporation to dryness.

[0092]

[0093] Perform nuclear magnetic resonance hydrogen spectrum detection on the product. The nuclear magnetic resonance hydrogen spectrum is as Figure 9 shown: 1 H NMR(400MHz,Chloroform-d)δ7.39-7.27(m,5H),

[0094] 6.78(s,1H),5.94(s,1H),5.11(dt,J=19.1,4.5Hz,2H),4.16(p,J=7.1Hz,4H),3.50(dt,J=27.8,8.6Hz,2H),2.21-1.73(m,4H),1.24(t,J=7.1Hz,6H).

[0095] Perform quantitative analysis on the product after the reaction by the nuclear magnetic internal standard method. The results are as Figure 10 shown. Using the 4F-COF prepared in Example 2 as the photocatalyst, the yield of the photocatalytic product reaches 85%; while the 3Ph-COF sample prepared in Comparative Example 1 does not contain fluorine, and the yield of the photocatalytic product is 50%.

[0096] After recycling, washing and drying the 4F-COF and 3Ph-COF after the photocatalytic reaction, perform X-ray powder diffraction testing. The X-ray powder diffraction pattern is as Figure 11 shown.

[0097] From Figure 11It can be seen that after one photocatalytic reaction, the positions and profiles of the XRD diffraction peaks of the 4F-COF prepared in Example 2 basically did not change, while the diffraction angles within 0-10° of the 3Ph-COF prepared in Example 1 almost disappeared after one photocatalytic reaction, indicating that the structure of 3Ph-COF changed. It also shows that 4F-COF has good stability, while 3Ph-COF has poor stability.

[0098] The recovered 4F-COF and 3Ph-COF were again subjected to photocatalytic reaction under the same photocatalytic reaction conditions, and the yields of the products were as Figure 12 shown.

[0099] As can be Figure 12 seen, after the 4F-COF was recycled, the yield of the product of the photocatalytic reaction was still close to 60%, while after the 3Ph-COF was recycled, there was almost no catalytic activity. Therefore, it also shows that introducing strongly electronegative F elements into the covalent organic framework to construct a more distinct D-A structure results in stronger crystallinity and stability of the COF, making it more suitable for the carbon-nitrogen coupling reaction.

[0100] In summary, the present invention discloses a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, which has a highly crystalline main framework, a highly conjugated rigid planar skeleton, and strong π-π stacking between molecules. Introducing strongly electronegative F atoms and electron-rich donor pyrene groups to form a D-A structure, while also forming hydrogen bonds with hydrogen atoms on adjacent benzene rings, reducing the torsional angle caused by steric hindrance, maintaining the AA or AA+ stacking mode, and promoting the transfer of charges in the axial direction. The internal separation driving force formed by the connection of the donor and acceptor is beneficial to promoting the separation of photogenerated charges; enhancing the absorption of sunlight and shortening the band gap. In the absence of transition metals, it can photocatalytically couple the C-N bond of the carboxyl group and the azo group; realizing a photosensitive integrated, metal-free, and recyclable carbon-nitrogen coupling reaction process.

[0101] The above embodiments are only the preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantive changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection required by the present invention.

Claims

1. A fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, characterized in that: Its chemical structure is shown in Formula I:

2. A method for preparing a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction, characterized in that: The structural monomer shown in formula II is subjected to an amine-aldehyde condensation reaction with 1,3,6,8-tetrakis-(p-aminophenyl)-pyrene under solvent thermal reaction conditions, and the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction is obtained after the reaction is completed; 3. The method for preparing a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction according to claim 2, characterized in that: The molar ratio of the structural monomer shown in formula II to the 1,3,6,8-tetrakis-(p-aminophenyl)-pyrene monomer is (2-2.5):

1.

4. The method for preparing a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction according to claim 2, characterized in that: The solvent for the solvothermal reaction is a mixed solvent of o-dichlorobenzene and n-butanol, and the volume ratio of o-dichlorobenzene to n-butanol is 1:(0.5-2); The molar volume ratio of the structural monomer shown in Formula II and the solvent is (20-60) μmol:1 mL.

5. The method for preparing a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction according to claim 2, characterized in that: Acetic acid is used as a crystal form regulator in the reaction, the concentration of the added acetic acid is 5-7 mol / L, and the amount of the added acetic acid is 5%-15% of the volume of the solvent.

6. The method for preparing a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction according to claim 2, characterized in that: The reaction conditions are: reaction at 100-140°C for 12-96h.

7. The method for preparing a fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction according to claim 2, characterized in that: After the reaction, solid-liquid separation is also included to purify the solid: The purification includes washing and / or Soxhlet extraction; the solvent used for washing is DMF and / or tetrahydrofuran; the solvent used for Soxhlet extraction is tetrahydrofuran.

8. Use of the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction as described in any one of claims 1 to 7 as a photocatalytic catalyst in CN bond coupling.

9. The use according to claim 8, characterized in that: N-benzyloxycarbonyl-D-proline and diethyl azodicarboxylate are subjected to CN bond coupling using the fluorine-rich covalent organic framework material for photocatalytic carbon-nitrogen coupling reaction described in any one of claims 1 to 7 as a photocatalytic catalyst.

10. The use according to claim 9, characterized in that: The reaction conditions are: in the presence of CsF, with acetonitrile as solvent, in an inert gas atmosphere, and a 456nm 40W lamp as a visible light source, the photocatalytic experiment is carried out for 24-96h; The molar ratio of N-benzyloxycarbonyl-D-proline, diethyl azodicarboxylate and CsF is 1:(0.8-1.2):(0.8-1.2).

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