Preparation method of donor-acceptor type covalent organic framework film material and third-order nonlinear optical application

Abstract

The invention discloses a preparation method of a donor-acceptor type covalent organic framework film material and a third-order nonlinear optical application thereof. The two-dimensional covalent organic framework material is formed by connecting a three-point ligand shown in formula (1) and a three-point ligand shown in formula (2) through covalent bonds; the two-dimensional covalent organic framework material is not only uniform and continuous, and has high light transmittance, but also has high crystallinity and an extended conjugated structure, so that the two-dimensional covalent organic framework material has wide visible light absorption and narrow optical band gap, and has good application prospects in third-order nonlinear optics.

Description

Technical Field

[0001] The invention belongs to the field of covalent organic framework (COFs) materials, and relates to a type of in-situ synthesis method for preparing a two-dimensional covalent organic framework film and its application in the field of third-order nonlinear optics. Background Art

[0002] Nonlinear optics (NLO) is the science that studies the nonlinear relationship between the response of matter and the intensity of the light field under the action of strong lasers. Molecules or materials with nonlinear optical properties have attracted widespread attention due to their potential applications in mode-locked laser systems, optical switches, optical limiting (OL), data storage, image transmission, sensors and biomedical devices. The main behaviors of third-order nonlinear optics include reverse saturated absorption (RSA), saturated absorption (SA), multiphoton absorption, second harmonics and third harmonics.

[0003] Compared with organic small molecule nonlinear optical materials, covalent organic frameworks (COFs) have the characteristics of high crystallinity, structural adjustability, diversity, and efficient π conjugation and charge transfer in the structure, which are conducive to the generation of third-order nonlinear behavior. However, covalent organic framework powders are insoluble, and it is usually necessary to disperse the sample in a solvent (such as N,N-dimethylformamide, 2-propanol or ethanol), or disperse the sample powder in potassium bromide by tableting. However, these methods have limitations such as low transmittance, large scattering rate, and easy deliquesce of potassium bromide, which seriously restrict their application in the field of third-order nonlinear optics. However, the uniform transparency of covalent organic framework films also makes it possible to reduce the optical scattering of materials, which makes covalent organic framework films have great application potential in the field of third-order nonlinear optics.

[0004] The present invention uses a glass sheet as a solid substrate, "triphenylamine" or "phenothiazine" as a donor unit, and prepares donor-acceptor covalent organic framework materials with different optical band gaps by changing different acceptor units. The donor-acceptor type long-range ordered conjugated structure in the covalent organic framework gives it a lower optical band gap and excellent third-order nonlinear optical properties. Summary of the invention

[0005] The present invention is used to provide a preparation method of a donor-acceptor type covalent organic framework film material and a third-order nonlinear optical application. The donor-acceptor type two-dimensional covalent organic framework material has high crystallinity, uniform and continuous film and narrow optical band gap characteristics, and has good application in third-order nonlinear optics.

[0006] The technical solution of the present invention is as follows:

[0007] A donor-acceptor type two-dimensional covalent organic framework (COFs) material and a preparation method thereof, wherein the preparation method comprises connecting a three-point ligand as shown in formula (1) and a three-point ligand as shown in formula (2) through covalent bonds,

[0008]

[0009] Wherein the R1 is the following structure:

[0010] The R2 is

[0011] The structure of the donor-acceptor type two-dimensional covalent organic framework (COFs) material is preferably as follows:

[0012]

[0013]

[0014]

[0015] The preparation method of the three-site ligand (2) phenothiazine-based ligand 2-2:

[0016]

[0017] Under nitrogen protection, 3,7-dibromo-10-(4-bromophenyl)-10H-phenothiazine is reacted with 4-aminophenylboronic acid pinacol ester in a mixed solvent under the action of base A and palladium catalyst A at 80-120° C. to obtain amino ligand 2-2.

[0018] The preparation method of the ligand 2-2 of the donor-acceptor type two-dimensional covalent organic framework (COFs) material, the mixed solvent is a mixture of a solvent (a) and a solvent (b), the solvent (a) is N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, toluene, 1,4-dioxane or tetrahydrofuran, the solvent (b) is water or methanol, preferably the mixed solvent is a toluene / methanol combination or a 1,4-dioxane / water combination; the volume ratio of the solvent (a) to the solvent (b) is 0.9:1 to 10:1, preferably 1:1-8:1; the volume dosage of the mixed solvent is based on the mass ratio of 3,7-dibromo-10-(4-bromophenyl)-10H-phenothiazine The amount of the catalyst is 30-50 mL / g, preferably 36-40 mL / g; the palladium catalyst A is [1,1'-bis(diphenylphosphino)ferrocene]dichloropalladium(II) and tetrakistriphenylphosphine palladium; the base A is sodium carbonate or potassium carbonate, preferably potassium carbonate; the molar ratio of the 3,7-dibromo-10-(4-bromophenyl)-10H-phenothiazine, 4-aminophenylboronic acid pinacol ester, base A and palladium catalyst A is 1:3:4:0.05-1:6:8:0.2, preferably 1:5:4:0.1-1:6:6:0.15; the coupling reaction time is 12-72 h, preferably 24-48 h; the reaction temperature is 80-120 ° C, preferably 85-110 ° C.

[0019] The preparation method of the donor-acceptor type two-dimensional covalent organic framework (COFs) material comprises the following steps:

[0020] S1, adding ligand (1), ligand (2), mixed solvent A, catalyst and solid substrate into a reaction container, performing a liquid nitrogen freezing-vacuuming-thawing cycle 2-3 times, vacuuming and sealing;

[0021] S2, placing the sealed container at a temperature of 100° C. to 150° C. for a heating reaction for 48 to 168 hours to generate the donor-acceptor type two-dimensional covalent organic framework (COFs) material on the solid matrix;

[0022] S3, washing the covalent organic framework material attached to the solid substrate obtained in step S2 with organic solvent B and then storing it in organic solvent C.

[0023] In the preparation method of a donor-acceptor type two-dimensional covalent organic framework (COFs) material, the mixed solvent A is composed of a non-polar solvent and a polar solvent, the non-polar solvent is a halogenated benzene, preferably a polychlorinated benzene, more preferably o-dichlorobenzene, p-dichlorobenzene or m-dichlorobenzene; the polar solvent is an alcohol solvent and an ether solvent, preferably a C2-C6 alcohol and a cyclic ether solvent, more preferably n-butanol and dioxane; the catalyst is an organic acid aqueous solution, preferably a C1-C5 straight-chain fatty acid aqueous solution, more preferably an acetic acid aqueous solution; the concentration of the organic acid aqueous solution is 3-12M, preferably a concentration of 6-9M; the solid substrate is ordinary glass, ITO glass, FTO glass, silicon wafer or copper sheet, preferably ordinary glass.

[0024] In the preparation method of the donor-acceptor type two-dimensional covalent organic framework (COFs) material, the molar ratio of the ligand (1) to the ligand (2) is 1:0.8-1.2, preferably 1:1.0-1.1; the added amount of the mixed solvent A is: the mass ratio of the total mass of the ligand (1) and the ligand (2) to the mixed solvent A is 1:40-60, preferably 1:45-55; the volume ratio of the non-polar solvent and the polar solvent in the mixed solvent A is: 1:0.2-5, preferably 1:0.3-3; the volume ratio of the mixed solvent to the catalyst is 10:0.5-1.5, preferably 10:0.9-1.1.

[0025] In the preparation method of the donor-acceptor type two-dimensional covalent organic framework (COFs) material, the organic solvent B is N,N-dimethylacetamide, acetone, and tetrahydrofuran; and the organic solvent C is acetone and ethyl acetate.

[0026] The application of the donor-acceptor type two-dimensional covalent organic framework (COFs) material in the field of third-order nonlinear optics.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a general method for preparing uniform and transparent covalent organic framework materials in situ. We use glass sheets as solid substrates, "triphenylamine" or "phenothiazine" as electron donors, introduce different acceptor units, and prepare two-dimensional covalent organic framework materials with different donor-absorber effects. The covalent organic framework film prepared by this method is uniform, continuous, and has good light transmittance, which solves the key problems of low transmittance and high scattering encountered in third-order nonlinear optical applications. The large π-electron conjugation and narrow optical band gap of the donor-acceptor in the covalent organic framework enhance the intramolecular charge transfer of the covalent organic framework structure, making it have good application prospects in the field of third-order nonlinear optics. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the synthesis of donor-acceptor type two-dimensional covalent organic framework materials in Examples 1 to 4 of the present invention.

[0030] Figure 2 Schematic diagram of the synthesis of donor-acceptor type two-dimensional covalent organic framework materials in Examples 5 to 9 of the present invention.

[0031] Figure 3 This is the infrared (FT-IR) spectrum of the donor-acceptor type two-dimensional covalent organic framework material in Examples 1 to 4 of the present invention.

[0032] Figure 4 This is the infrared (FT-IR) spectrum of the donor-acceptor type two-dimensional covalent organic framework material in Examples 6 to 9 of the present invention.

[0033] Figure 5 It is the powder X-ray diffraction (PXRD) spectrum of the donor-acceptor type two-dimensional covalent organic framework material in Examples 1-9 of the present invention.

[0034] Figures 6 to 13 These are scanning electron microscope (SEM) photographs of the donor-acceptor type two-dimensional covalent organic framework materials in Examples 1 to 4 and 6 to 9 of the present invention.

[0035] Fig.14 It is a solid ultraviolet-visible spectrum diagram of the donor-acceptor type two-dimensional covalent organic framework material in Examples 1 to 4 of the present invention.

[0036] Fig.15 It is a solid ultraviolet-visible spectrum diagram of the donor-acceptor type two-dimensional covalent organic framework material in Examples 6 to 9 of the present invention.

[0037] Fig.16 It is the Tauc spectra of the donor-acceptor type two-dimensional covalent organic framework materials in Examples 1 to 4 of the present invention.

[0038] Fig.17 This is the Tauc spectrum of the donor-acceptor type two-dimensional covalent organic framework material in Examples 6 to 9 of the present invention.

[0039] Figures 18 to 25 It is a third-order nonlinear performance diagram of the donor-acceptor type two-dimensional covalent organic framework material in Examples 1 to 4 and 6 to 9 of the present invention.

[0040] Fig.26 is the nuclear magnetic resonance hydrogen ( 1 HNMR) spectrum.

[0041] Fig. 27 is the carbon NMR spectrum of the three-site ligand (2) phenothiazine-based ligand 2-2 of the present invention (13 CNMR) diagram.

[0042] Fig.28 This is the infrared (IR) spectrum of the three-site ligand (2) phenothiazine-based ligand 2-2 in the present invention. DETAILED DESCRIPTION

[0043] The objectives, technical solutions and advantages of the present invention are further described in detail below in conjunction with the embodiments and drawings. The specific embodiments described are only used to explain the present invention but not to limit the present invention.

[0044] Three-site ligand (2) Phenothiazine-based ligand 2-2 Synthesis Example 1

[0045]

[0046] 3,7-Dibromo-10-(4-bromophenyl)-10H-phenothiazine (0.50 g, 0.97 mmol), 4-aminophenylboronic acid pinacol ester (1.28 g, 5.86 mmol), [1,1'-bis(diphenylphosphino)ferrocene] dichloropalladium (II) (0.11 g, 0.15 mmol) and potassium carbonate (0.81 g, 5.86 mmol) were added to a flask. 10 mL each of toluene / methanol (1:1 v / v) was added, the reaction system was vacuum-exchanged with nitrogen three times, and then refluxed at 85°C under nitrogen protection for 48 h. After the mixture was cooled to room temperature, it was extracted with saturated brine and the organic layer was dried over anhydrous sodium sulfate. After the solvent was removed under reduced pressure, the crude product was purified by column chromatography (eluent: petroleum ether: ethyl acetate = 1:1) to obtain 0.53 g of a light yellow solid with a yield of 74%.

[0047] Three-site ligand (2) Phenothiazine-based ligand 2-2 Synthesis Example 2

[0048] 3,7-Dibromo-10-(4-bromophenyl)-10H-phenothiazine (0.50g, 0.97mmol), 4-aminophenylboronic acid pinacol ester (1.07g, 4.88mmol), tetrakistriphenylphosphine palladium (0.11g, 0.098mmol) and potassium carbonate (0.54g, 3.90mmol) were added to a flask. 16mL of dioxane and 2mL of water (8:1v / v) were added respectively, and the reaction system was vacuum-exchanged with nitrogen three times, and then refluxed and stirred at 110°C for 24h under nitrogen protection. After the mixture was cooled to room temperature, it was extracted with saturated brine and the organic layer was dried over anhydrous sodium sulfate. After the solvent was removed under reduced pressure, the crude product was purified by column chromatography (eluent: petroleum ether: ethyl acetate = 1:1) to obtain 0.45g of light yellow solid with a yield of 63%.

[0049] Example 1

[0050] Preparation of donor-acceptor type two-dimensional covalent organic framework material COF-1

[0051] See also Figure 1 A, in a glass ampoule, 2-1 (80.0 mg, 0.154 mmol), 1-1 (23.0 mg, 0.142 mmol), o-dichlorobenzene (2.5 mL) and n-butanol (2.5 mL) were added. The mixture was sonicated for 5 minutes, and then a glass piece and 6M acetic acid (0.45 mL) were added to the mixture. Three freeze-vacuum-thaw cycles were performed under 77K liquid nitrogen conditions. The test tube was sealed and heated at 120°C for 120 h. After cooling to room temperature, the glass piece was washed with N,N-dimethylacetamide and acetone to obtain a COF-1 film, which was stored in acetone. The solid was filtered off and washed three times with N,N-dimethylacetamide (10 mL), acetone (10 mL) and ether (5 mL), respectively. After vacuum activation at 90°C for 24 h, COF-1 was a yellow powder (87 mg, yield 84%).

[0052] Example 2

[0053] Preparation of donor-acceptor type two-dimensional covalent organic framework material COF-2

[0054] See also Figure 1 B. In a glass ampoule, 2-1 (73.8 mg, 0.142 mmol), 1-2 (30.0 mg, 0.142 mmol), o-dichlorobenzene (3 mL) and n-butanol (2 mL) were added. The mixture was sonicated for 5 minutes, and then a glass piece and 6 M acetic acid (0.55 mL) were added to the mixture. Three freeze-vacuum-thaw cycles were performed under 77K liquid nitrogen conditions. The test tube was sealed and heated at 120°C for 72 h. After cooling to room temperature, the glass piece was washed with N,N-dimethylacetamide and acetone to obtain a COF-2 film, which was stored in acetone. The solid was filtered off and washed three times with N,N-dimethylacetamide (10 mL), acetone (10 mL) and ether (5 mL), respectively. After vacuum activation at 90°C for 24 h, COF-2 was an orange-red powder (92.8 mg, yield 89%).

[0055] Example 3

[0056] Preparation of donor-acceptor type two-dimensional covalent organic framework material COF-3

[0057] See also Figure 1C, in a glass ampoule, 2-1 (50.0 mg, 0.096 mmol), 1-3 (40.0 mg, 0.102 mmol), o-dichlorobenzene (1.3 mL) and n-butanol (3.7 mL) were added. The mixture was sonicated for 5 minutes, and then a glass piece and 9 M acetic acid (0.5 mL) were added to the mixture. Three freeze-vacuum-thaw cycles were performed under 77K liquid nitrogen conditions. The test tube was sealed and heated at 120°C for 72 h. After cooling to room temperature, the glass piece was washed with N,N-dimethylacetamide and acetone to obtain a COF-3 film, which was stored in acetone. The solid was filtered off and washed three times with N,N-dimethylacetamide (10 mL), acetone (10 mL) and ether (5 mL), respectively. After vacuum activation at 90°C for 24 h, COF-3 was a yellow powder (74 mg, yield 82%).

[0058] Example 4

[0059] Preparation of donor-acceptor type two-dimensional covalent organic framework material COF-4

[0060] See also Figure 1 D. In a glass ampoule, 2-1 (54 mg, 0.082 mmol), 1-4 (31.5 mg, 0.080 mmol), o-dichlorobenzene (1.00 mL) and n-butanol (3.00 mL) were added. The mixture was sonicated for 5 minutes, and then a glass piece and 9 M acetic acid (0.4 mL) were added to the mixture. Three freeze-vacuum-thaw cycles were performed under 77K liquid nitrogen conditions. The test tube was sealed and heated at 120°C for 168 h. After cooling to room temperature, the glass piece was washed with N,N-dimethylacetamide and acetone to obtain a COF-4 film, which was stored in acetone. The solid was filtered off and washed three times with N,N-dimethylacetamide (10 mL), acetone (10 mL) and ether (5 mL), respectively. After vacuum activation at 90°C for 24 h, COF-4 was a yellow powder (65 mg, yield 76%).

[0061] Example 5

[0062] Preparation of donor-acceptor type two-dimensional covalent organic framework material COF-5

[0063] See also Figure 2A. In a glass ampoule, 2-2 (14.0 mg, 0.025 mmol), 1-5 (10.4 mg, 0.024 mmol), o-dichlorobenzene (0.5 mL) and n-butanol (0.5 mL) were added. The mixture was ultrasonicated for 5 minutes, and then a glass piece and 6 M acetic acid (0.11 mL) were added to the mixture. Three freeze-vacuum-thaw cycles were performed under 77K liquid nitrogen conditions. The test tube was sealed and heated at 120°C for 72 h. After cooling to room temperature, the glass piece was washed with N,N-dimethylacetamide and acetone to obtain a COF-5 film, which was stored in acetone. The solid was filtered off and washed 3 times with N,N-dimethylacetamide (10 mL), acetone (10 mL) and ether (5 mL), respectively. COF-5 was a yellow powder (20 mg, yield 81%).

[0064] Example 6

[0065] Preparation of donor-acceptor type two-dimensional covalent organic framework material COF-6

[0066] See also Figure 2 B. In a glass ampoule, 2-2 (15 mg, 0.027 mmol), 1-2 (6 mg, 0.028 mmol), o-dichlorobenzene (0.5 mL) and n-butanol (0.5 mL) were added. The mixture was sonicated for 5 minutes, and then a glass piece and 3 M acetic acid (0.09 mL) were added to the mixture. Three freeze-vacuum-thaw cycles were performed under 77K liquid nitrogen conditions. The test tube was sealed and heated at 150°C for 96 h. After cooling to room temperature, the glass piece was washed with N,N-dimethylacetamide and acetone to obtain a COF-6 film, which was stored in ethyl acetate. The solid was filtered off and washed three times with N,N-dimethylacetamide (10 mL), acetone (10 mL) and ether (5 mL), respectively. After vacuum activation at 90°C for 24 h, COF-6 was an orange-red powder (18 mg, yield 86%).

[0067] Example 7

[0068] Preparation of donor-acceptor type two-dimensional covalent organic framework material COF-7

[0069] See also Figure 2C, in a glass ampoule, 2-2 (35 mg, 0.063 mmol), 1-1 (10.3 mg, 0.063 mmol), o-dichlorobenzene (1.25 mL) and n-butanol (1.25 mL) were added. The mixture was sonicated for 5 minutes, and then a glass piece and 6M acetic acid (0.25 mL) were added to the mixture. Three freeze-vacuum-thaw cycles were performed under 77K liquid nitrogen conditions. The test tube was sealed and heated at 110°C for 72 h. After cooling to room temperature, the glass piece was washed with N,N-dimethylacetamide and acetone to obtain a COF-7 film, which was stored in acetone. The solid was filtered off and washed three times with N,N-dimethylacetamide (10 mL), acetone (10 mL) and ether (5 mL), respectively. After vacuum activation at 90°C for 24 h, COF-7 was a yellow powder (42 mg, yield 93%).

[0070] Example 8

[0071] Preparation of donor-acceptor type two-dimensional covalent organic framework material COF-8

[0072] See also Figure 2 D. In a glass ampoule, 2-2 (14 mg, 0.0254 mmol), 1-3 (10 mg, 0.0254 mmol), o-dichlorobenzene (0.75 mL) and n-butanol (0.25 mL) were added. The mixture was sonicated for 5 minutes, and then a glass slide and 9 M acetic acid (0.1 mL) were added to the mixture. Three freeze-vacuum-thaw cycles were performed under 77K liquid nitrogen conditions. The test tube was sealed and heated at 120°C for 168 h. After cooling to room temperature, the glass slide was washed with N,N-dimethylacetamide and acetone to obtain a COF-8 film, which was stored in ethyl acetate. The solid was filtered off and washed three times with N,N-dimethylacetamide (10 mL), acetone (10 mL) and ether (5 mL), respectively. After vacuum activation at 90°C for 24 h, COF-8 was a yellow powder (20 mg, yield 83%).

[0073] Example 9

[0074] Preparation of donor-acceptor type two-dimensional covalent organic framework material COF-9

[0075] See also Figure 2E, in a glass ampoule, 2-2 (14 mg, 0.0254 mmol), 1-4 (10 mg, 0.0254 mmol), o-dichlorobenzene (0.5 mL) and n-butanol (0.5 mL) were added. The mixture was sonicated for 5 minutes, and then a glass piece and 6M acetic acid (0.1 mL) were added to the mixture. Three freeze-vacuum-thaw cycles were performed under 77K liquid nitrogen conditions. The test tube was sealed and heated at 120°C for 120 h. After cooling to room temperature, the glass piece was washed with N,N-dimethylacetamide and acetone to obtain a COF-9 film, which was stored in acetone. The solid was filtered off and washed three times with N,N-dimethylacetamide (10 mL), acetone (10 mL) and ether (5 mL), respectively. After vacuum activation at 90°C for 24 h, COF-9 was an orange powder (21 mg, yield 87%).

[0076] Product characterization and performance testing

[0077] See also Figure 3 Through Fourier transform infrared (FT-IR) spectroscopy, the infrared spectra of the relevant monomers required for synthesis were compared with those of the corresponding COF-1 to COF-4. The characteristic peaks of the aldehyde group (1697 to 1641 cm -1 ) and the characteristic peaks of amino groups (3451, 3365 cm -1 ) and the disappearance of -1 The characteristic stretching vibration of the -C=N bond was produced, proving the successful synthesis of COF-1 to COF-4.

[0078] See also Figure 4 Through Fourier transform infrared (FT-IR) spectroscopy, the infrared spectra of the relevant monomers required for synthesis were compared with those of the corresponding COF-6 to COF-9. The characteristic peaks of the aldehyde group (1697 to 1641 cm -1 ) and the characteristic peaks of amino groups (3460, 3367 cm -1 ) and the disappearance of -1 The characteristic stretching vibration of the -C=N bond was produced, proving the successful synthesis of COF-6~COF-9.

[0079] See also Figure 5 Through the measurement of powder X-ray diffraction (PXRD), COF-1 to COF-4 and COF-6 to COF-9 all have peaks at 3.7 to 4.7°, respectively, which proves the successful synthesis of COF-1 to COF-9.

[0080] See also Figures 6 to 13,Scanning electron microscope (SEM) images show that the surfaces of COF-1~COF-4 and COF-6~COF-9 films are uniform and continuous, with the morphology of nanosheets or nanoparticles, and the film thickness is between 50 and 350 nm.

[0081] See also Figures 14-15 The solid UV-visible absorption spectrum shows that COF-1~COF-4 and COF-6~COF-9 have a wide visible absorption range, and the absorption band edges are located between 580 and 660nm, respectively.

[0082] See also Figures 16-17 , the Tauc plot converted by the Kubelka-Munk function shows that COF-1~COF-4 and COF-6~COF-9 have narrow optical band gaps, E g The values ​​are between 1.54 and 1.80 eV respectively.

[0083] See also Figures 18 to 25 , the open hole Z-scan technique was used to test the third-order nonlinear performance of the covalent organic framework film. Test conditions: the laser is a mode-locked Nd:YAG 532nm laser, the laser pulse energy is 1~20μJ, the wavelength is 532nm, and the pulse width is 4~7ns. Figures 18 to 25 The third-order nonlinear experimental data and fitting curves of COF-1~COF-4 and COF-6~COF-9 at different pulse energies are shown, showing excellent third-order nonlinear absorption characteristics. The nonlinear absorption coefficient (β) is in the range of 0.87~78.5×10 -7 cm / GW.

[0084] The above-described embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. The technical features of the embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described, but as long as there are no contradictions in the combinations involved, they should be considered to be within the scope of the present specification. For those of ordinary skill in the art, several modifications and changes can be made without departing from the concept of the present invention, and these all belong to the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a donor-acceptor type covalent organic framework membrane material, characterized in that: It is prepared by connecting a three-point ligand as shown in formula (1) and a three-point ligand as shown in formula (2) through covalent bonds: Wherein, the R1 is the following structure: The R2 is The method for preparing the three-point ligand represented by formula (2) comprises the following steps: Under nitrogen protection, 3,7-dibromo-10-(4-bromophenyl)-10H-phenothiazine is reacted with 4-aminophenylboronic acid pinacol ester in a mixed solvent under the action of base A and palladium catalyst A at 80-120°C to undergo Suzuki coupling reaction to obtain a three-point ligand shown in formula (2), wherein R2 is a phenothiazine-based ligand with the structure of formula (2-2).

2. The method for preparing a donor-acceptor type covalent organic framework membrane material according to claim 1, characterized in that: The donor-acceptor type covalent organic framework membrane material has the following structure:

3. The method for preparing a donor-acceptor type covalent organic framework membrane material according to claim 1, characterized in that: The mixed solvent is formed by mixing a solvent (a) and a solvent (b), wherein the solvent (a) is N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, toluene, 1,4-dioxane or tetrahydrofuran, and the solvent (b) is water or methanol; The volume ratio of the solvent (a) to the solvent (b) is 0.9:1-10:

1.

4. The method for preparing a donor-acceptor type covalent organic framework membrane material according to claim 1, characterized in that: The palladium catalyst A is [1,1'-bis(diphenylphosphino)ferrocene]dichloropalladium(II) and tetrakistriphenylphosphine palladium; The base A is sodium carbonate or potassium carbonate; The molar ratio of the 3,7-dibromo-10-(4-bromophenyl)-10H-phenothiazine, 4-aminophenylboronic acid pinacol ester, base A and palladium catalyst A is 1:3-6:4-8:0.05-0.

2.

5. The method for preparing a donor-acceptor type covalent organic framework membrane material according to claim 1, characterized in that: The Suzuki coupling reaction time is 12 to 72 hours, and the reaction temperature is 80 to 120°C.

6. The method for preparing a donor-acceptor type covalent organic framework membrane material according to claim 1, characterized in that: The following steps are involved: S1, adding the three-point ligand represented by formula (1), the three-point ligand represented by formula (2), the mixed solvent A, the catalyst and the solid substrate into a reaction container, performing a liquid nitrogen freezing-vacuuming-thawing cycle for multiple times, vacuuming and sealing; S2, the sealed container is placed at a temperature of 100° C. to 150° C. for a heating reaction for 48 to 168 hours to generate the donor-acceptor type two-dimensional covalent organic framework material on the solid matrix.

7. The method for preparing a donor-acceptor type covalent organic framework membrane material according to claim 6, characterized in that: The mixed solvent A is composed of a non-polar solvent and a polar solvent, wherein the non-polar solvent is halogenated benzene; and the polar solvent is an alcohol solvent and an ether solvent; The catalyst is a C1-C5 straight-chain fatty acid aqueous solution.

8. The method for preparing a donor-acceptor type covalent organic framework membrane material according to claim 6, characterized in that: The molar ratio of the three-point ligand represented by formula (1) to the three-point ligand represented by formula (2) is 1:0.8-1.2; The volume ratio of the non-polar solvent to the polar solvent in the mixed solvent A is 1:0.2-5.

9. Application of the donor-acceptor type covalent organic framework film material prepared by the preparation method according to any one of claims 1 to 8 in the field of third-order nonlinear optics.

Images