A D-A type covalent organic framework based on an asymmetric benzothiadiazole ligand, its preparation method and application

Abstract

The present invention relates to the field of photocatalysis technology, and particularly relates to a D-A type covalent organic framework based on an asymmetric benzothiadiazole ligand, and a preparation method and application thereof. The D-A type covalent organic framework provided by the present invention uses an asymmetric benzothiadiazole ligand and 1,3,6,8-tetrakis(4-aminophenyl)pyrene as the main structure, and uses a double π-bridge as the connection to construct a D-π-π-A structure. The structural design with π-bridge extension effectively reduces the band gap of the framework material, improves the charge delocalization ability, enables the improvement of the charge transfer efficiency, and further improves the high photocatalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysis, and particularly relates to a donor-acceptor (D-A) type covalent organic framework based on an asymmetric benzothiadiazole ligand, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Covalent organic frameworks (COFs) are a class of organic porous polymers with periodicity formed by connecting organic building units through covalent bonds using light elements (such as C, H, O, B, N, etc.). Therefore, they have many unique properties, such as a rigid structure, high thermal stability, a large specific surface area, a tunable structure, a periodic π array, and a porous structure. They are currently widely used in fields such as guest molecule adsorption, energy storage materials, gas storage and separation, heterogeneous photocatalysis, sensing, and drug delivery, showing great development potential.

[0004] Introducing a donor-acceptor (D-A) structure into covalent organic frameworks is beneficial to reducing the exciton binding energy, promoting the separation and transfer of photo-generated carriers, and thus enhancing the photocatalytic performance of covalent organic frameworks. The benzothiadiazole unit has unique electron-deficient characteristics and a planar conjugated structure, which can be introduced into the covalent organic framework structure to prepare high-performance donor (D)-acceptor (A) type covalent organic framework photocatalysts. However, the charge transport efficiency of conventional benzothiadiazole-based covalent organic frameworks is still limited by the localized π-electron distribution and limited exciton dissociation channels, thereby affecting the photocatalytic performance. Therefore, it is urgent to solve the charge transport efficiency of benzothiadiazole-based covalent organic frameworks and enhance their photocatalytic performance. Summary of the Invention

[0005] To overcome the above problems, the present invention provides a donor-acceptor (D-A) type covalent organic framework based on an asymmetric benzothiadiazole ligand, a preparation method thereof, and an application thereof.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] In a first aspect of the present invention, there is provided a donor-acceptor (D-A) type covalent organic framework based on an asymmetric benzothiadiazole ligand, which uses the structure shown in formula (Ⅰ) as a structural repeating unit;

[0008]

[0009] Formula (Ⅰ).

[0010] In the second aspect of the present invention, there is provided an asymmetric benzothiadiazole ligand for constructing the D-A type covalent organic framework based on the asymmetric benzothiadiazole ligand described in the first aspect, and its structural formula is shown in Formula (Ⅱ);

[0011]

[0012] Formula (Ⅱ).

[0013] In the third aspect of the present invention, there is provided a preparation method of the D-A type covalent organic framework based on the asymmetric benzothiadiazole ligand described in the first aspect, including the following steps:

[0014] Dissolve the asymmetric benzothiadiazole ligand shown in Formula (Ⅱ) and 1,3,6,8-tetrakis(4-aminophenyl)pyrene in an organic solvent, add acetic acid as a catalyst, and perform a solvothermal reaction to synthesize the D-A type covalent organic framework based on the asymmetric benzothiadiazole ligand.

[0015] In one or more embodiments, the molar ratio of the asymmetric benzothiadiazole ligand shown in Formula (Ⅱ) to 1,3,6,8-tetrakis(4-aminophenyl)pyrene is (1.5~3):1, preferably 2:1.

[0016] In one or more embodiments, the organic solvent is a mixed solution of o-dichlorobenzene and absolute ethanol.

[0017] Preferably, the volume ratio of o-dichlorobenzene to absolute ethanol is (2.5~4):1, preferably 3:1.

[0018] In one or more embodiments, the concentration of the asymmetric benzothiadiazole ligand shown in Formula (Ⅱ) in the organic solvent is 0.04~0.08 mol / L, preferably 0.05 mol / L.

[0019] In one or more embodiments, the temperature of the solvothermal reaction is 100~150 °C, preferably 120 °C; the time of the solvothermal reaction is 60~80 h, preferably 72 h.

[0020] In the fourth aspect of the present invention, there is provided an application of the D-A type covalent organic framework based on the asymmetric benzothiadiazole ligand described in the first aspect or the D-A type covalent organic framework prepared by the preparation method described in the third aspect as a photocatalyst.

[0021] In one or more embodiments, the application includes: catalyzing the oxidation of sulfides to synthesize sulfoxides.

[0022] In one or more embodiments, the application includes: catalyzing the oxidation of tetrahydroisoquinoline compounds to synthesize isoquinolone compounds.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) The present invention relates to the field of photocatalysis technology, and particularly relates to a D-A type covalent organic framework based on an asymmetric benzothiadiazole ligand, its preparation method and application. The D-A type covalent organic framework provided by the present invention uses an asymmetric benzothiadiazole ligand and 1,3,6,8-tetrakis(4-aminophenyl)pyrene as the main structure, and uses a double π-bridge as the connection to construct a D-π-π-A structure. The structural design with π-bridge extension effectively reduces the band gap of the framework material, improves the charge delocalization ability, enables the charge transfer efficiency to be improved, and further improves the high photocatalytic activity.

[0025] (2) The D-A type covalent organic framework based on an asymmetric benzothiadiazole ligand provided by the present invention can efficiently photocatalytically oxidize benzyl methyl sulfide substrates to synthesize benzyl sulfoxide products with a yield of more than 90%; and can photocatalytically oxidize more difficult-to-oxidize tetrahydroisoquinoline compounds to synthesize isoquinolone compounds with a yield of more than 70%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0027] Figure 1 1H NMR spectrum of the asymmetric benzothiadiazole ligand;

[0028] Figure 2 Powder X-ray diffraction pattern of the D-A type covalent organic framework TPPy-PBT-COF-v of the asymmetric benzothiadiazole ligand;

[0029] Figure 3 Structural diagram of the D-A type covalent organic framework TPPy-PBT-COF-v of the asymmetric benzothiadiazole ligand simulated by Materials Studio software;

[0030] Figure 4 Fourier transform infrared (FT-IR) spectrum of the D-A type covalent organic framework TPPy-PBT-COF-v of the asymmetric benzothiadiazole ligand;

[0031] Figure 5 For the D-A type covalent organic framework TPPy-PBT-COF-v of the asymmetric benzothiadiazole ligand 13 13C CP / MAS NMR spectrum;

[0032] Figure 6N2 adsorption-desorption isotherm diagram of the D-A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand, where the inset is the pore size distribution diagram;

[0033] Figure 7 Solid-state ultraviolet-visible absorption spectrum of the D-A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand;

[0034] Figure 8 Tauc band gap of the D-A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand;

[0035] Figure 9 Cyclic voltammogram of the D-A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand;

[0036] Figure 10 Electrochemical impedance of the D-A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand;

[0037] Figure 11 Photocurrent response signal of the D-A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand;

[0038] Figure 12 1H NMR spectrum of the product after catalytic oxidation of substrate 1a;

[0039] Figure 13 1H NMR spectrum of the product after catalytic oxidation of substrate 1b;

[0040] Figure 14 1H NMR spectrum of the product after catalytic oxidation of substrate 1c;

[0041] Figure 15 1H NMR spectrum of the product after catalytic oxidation of substrate 1d;

[0042] Figure 16 1H NMR spectrum of the product after catalytic oxidation of substrate 1e;

[0043] Figure 17 Powder X-ray diffraction pattern of the D-A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand after being reused 5 times;

[0044] Figure 18 1H NMR spectrum of the product after catalytic oxidation of substrate 2a;

[0045] Figure 19 1H NMR spectrum of the product after catalytic oxidation of substrate 2b;

[0046] Figure 20 1H NMR spectrum of the product after catalytic oxidation of substrate 2c;

[0047] Figure 21 1H NMR spectrum of the product after catalytic oxidation of substrate 2d;

[0048] Figure 22 1H NMR spectrum of the product after catalytic oxidation of substrate 2e. Detailed implementation manners

[0049] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0050] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0051] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0052] Example 1

[0053] Preparation of asymmetric benzothiadiazole ligand:

[0054] 0.5 mmol of 7-(4-formylphenyl)-4-formylbenzo[c][1,2,5]thiadiazole (PBT), 1.1 mmol of ((1,3-dioxolan-2-yl)methyl)tributylphosphonium bromide (cas: 115754-62-6) and 2.5 mmol of sodium hydride (cas: 7646-69-7, 60% dispersed in kerosene) were dispersed in 10 mL of tetrahydrofuran and reacted at room temperature for 16 hours. After the reaction was completed, 3 - 4 mL of 10% hydrochloric acid aqueous solution was added to the above reaction solution, and the reaction solution was adjusted to be acidic and then stirred for another 4 hours. Saturated sodium bicarbonate aqueous solution was added, and the mixture was extracted with ethyl acetate, dried over anhydrous sodium sulfate, and the solvent was evaporated to obtain a crude product. The obtained crude product was purified by silica gel chromatography (eluent ratio dichloromethane:ethyl acetate (v / v) = 50:1), and finally an orange powder of asymmetric benzothiadiazole ligand (PBT-v), i.e., the compound shown in formula (Ⅱ) (C 18 H 12N2O2S, with a yield of approximately 77%), and its 1H NMR spectrum is as follows Figure 1 shown. 1 1H NMR (CDCl3, 400 MHz): δ (ppm) 9.81 - 9.79 (d, J J = 8.0 Hz, 1H) 9.71 - 9.69 (d, J J = 8.0 Hz, 1H) 8.02 - 8.00 (d, J J = 8.0 Hz, 2H) 7.88 - 7.85 (m, J J = 12.0 Hz, 2H) 7.78 - 7.77 (d, J J = 4.0 Hz, 1H) 7.71 - 7.68 (d, J J = 12.0 Hz, 2H) 7.61 - 7.52 (m, J J = 28.0 Hz, 1H) 7.52 - 7.48 (m, J J = 12.0 Hz, 1H) 6.78 - 6.72 (m, J J = 24.0 Hz, 1H).

[0055] Example 2

[0056] Preparation of D - A type covalent organic framework based on asymmetric benzothiadiazole ligand:

[0057] 0.04 mmol of asymmetric benzothiadiazole ligand (PBT - v), 0.02 mmol of 1,3,6,8 - tetra(4 - aminophenyl)pyrene (TPPy, cas: 1610471 - 69 - 6), 750 μL of o - dichlorobenzene and 250 μL of absolute ethanol were successively added into a heat - resistant glass tube (Pyrex tube). After ultrasonic treatment for 5 min, 100 μL of 6 mol∙L -1 acetic acid was added. The glass tube was frozen with liquid nitrogen, thawed, evacuated and degassed, and then sealed after repeating this process three times. It was heated in an oven at 120 °C for 72 hours. After cooling, a reddish - brown precipitate was obtained, which was thoroughly washed with absolute ethanol, N,N - dimethylformamide and dichloromethane, filtered, and dried in vacuum at 120 °C for 12 hours to obtain a reddish - brown powder, namely the D - A type covalent organic framework TPPy - PBT - COF - v of asymmetric benzothiadiazole ligand (C 80 H 48 N8S2, with a yield of approximately 93%).

[0058] Figure 2 is the powder X - ray diffraction pattern (PXRD) of the D - A type covalent organic framework TPPy - PBT - COF - v of asymmetric benzothiadiazole ligand, Figure 3This is the structural diagram of the D-A type covalent organic framework TPPy-PBT-COF-v of the asymmetric benzothiadiazole ligand simulated by Materials Studio software. According to the experimental powder X-ray diffraction pattern (PXRD) and combined with the structure simulated by Materials Studio software, it shows that the D-A type covalent organic framework TPPy-PBT-COF-v of the asymmetric benzothiadiazole ligand is an ordered framework structure. The PXRD of TPPy-PBTP-COF-v shows diffraction peaks at 2.71°, 3.82°, 5.45° and 8.13°, corresponding to the crystal planes (110), (200), (220) and (330) respectively. The simulated structure of TPPy-PBTP-COF-v is: monoclinic system, space group is P2 , and the unit cell parameters a = 46.507 Å, b = 45.653 Å, c = 3.549 Å, α = β = γ = 90º. The residual and profile differences between the PXRD and the AA stacking mode model of the simulated structure are small ( R wp = 6.15%, R p = 3.97%), indicating that TPPy-PBTP-COF-v is stacked layer by layer in the AA stacking mode.

[0059] Figure 4 This is the Fourier transform infrared (FT-IR) spectrum of the D-A type covalent organic framework TPPy-PBT-COF-v of the asymmetric benzothiadiazole ligand. Comparative analysis reveals that in the infrared spectrum of TPPy-PBT-COF-v, the N-H stretching vibration peaks (3325 cm -1 , 3347 cm -1 ) of the tetraamine of the ligand 1,3,6,8-tetrakis(4-aminophenyl)pyrene (TPPy) and the C=O stretching vibration peak at 1664 cm -1 disappear, while the appearance of the C=N and C=C-H peaks at 1614 cm -1 and 3029 cm -1 indicates the successful polymerization to form a crystalline covalent organic framework.

[0060] Figure 5 This is the 13C CP / MAS NMR spectrum. The chemical shift at 156 ppm of TPPy-PBT-COF-v is attributed to imine carbon, the peaks at 151 ppm and 145 ppm are carbons on the benzothiadiazole unit respectively, and the broad peak at 140 - 112 ppm is aromatic carbon. This also indicates the successful polymerization to form a covalent organic framework with high crystallinity.

[0061] Figure 6 N2 adsorption - desorption isotherm and pore size distribution (inset) of the D - A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand. N2 adsorption - desorption measurements were carried out at 77 K. TPPy-PBT-COF-v shows a typical type IV isotherm curve, with a surface area of 2321.94 m 2 g -1 , and the center of the pore size is 2.88 nm, indicating that it is a mesoporous material, which again proves that TPPy-PBT-COF-v has an AA type layer-by-layer stacking structure.

[0062] Figure 7 Solid-state UV - Vis absorption spectrum of the D - A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand. It can be seen from Figure 7 that TPPy-PBT-COF-v has a wide light absorption range, which can be redshifted to about 800 nm.

[0063] Figure 8 Tauc band gap of the D - A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand. It can be calculated from Figure 8 that TPPy-PBT-COF-v has a small band gap, and its value is 1.71 eV.

[0064] Figure 9 Cyclic voltammogram of the D - A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand. The reduction potential of TPPy-PBT-COF-v was measured by cyclic voltammetry (CV). The reduction potential is -0.69 eV, and the highest occupied molecular orbital (HOMO) is -4.11 eV. From the above Figure 8 it can be known that its Tauc band gap is 1.71 eV, so its lowest unoccupied molecular orbital (LUMO) is -5.82 eV.

[0065] Figure 10 Electrochemical impedance of the D - A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand, Figure 11 Photocurrent response signal of the D - A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand.

[0066] The structure of the covalent organic framework TPPy-PBT-COF for comparison is shown below:

[0067] ;

[0068] The structure of the covalent organic framework TPPy-PBT-COF-p for comparison is shown below:

[0069] .

[0070] From Figure 10 it can be seen that the Nyquist radius of TPPy-PBT-COF-v is significantly smaller than that of TPPy-PBT-COF-p and TPPy-PBT-COF, indicating that TPPy-PBT-COF-v has the smallest electrochemical resistance and the highest charge transfer ability. In addition, the photocurrent response signal shows ( Figure 11 ) that TPPy-PBT-COF-v exhibits a stronger photocurrent response signal compared to the other two COFs, further proving that TPPy-PBT-COF-v is an excellent highly efficient photocatalyst. This shows that the D-A type covalent organic framework provided by the present invention uses an asymmetric benzothiadiazole ligand and 1,3,6,8-tetrakis(4-aminophenyl)pyrene as the main structure, with a double π-bridge as the connection to construct a D-π-π-A structure. The structural design with extended π-bridges effectively reduces the band gap of the framework material, improves the charge delocalization ability, enables the improvement of the charge transfer efficiency, and thus enhances the high photocatalytic activity.

[0071] Example 3

[0072] The D-A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand catalyzes the synthesis of sulfoxides by oxidizing thioethers under visible light.

[0073] Weigh 10 mg of TPPy-PBT-COF-v as the catalyst for the photocatalytic reaction, 0.3 mmol of benzyl thioether substrates (Table 1, 1a - 1e), ethanol as the reaction solvent, a 10 W blue LED lamp, and an atmosphere of 1 bar of oxygen. Monitor the reaction progress by thin layer chromatography (TLC) to determine the reaction time. The product NMR uses diphenylacetonitrile as the internal standard, and the yield is determined by analyzing the 1 H NMR spectral data. The catalytic results are shown in Table 1.

[0074] Table 1 Synthesis of sulfoxides by the oxidation of thioethers catalyzed by TPPy-PBT-COF-v

[0075]

[0076] The 1H NMR spectra of the products after photocatalytic oxidation of 1a-1e benzyl sulfide substrates in Table 1 are as follows Figures 12 - 16 shown

[0077] As can be seen from Table 1, the reaction of catalytic oxidation of sulfide to synthesize sulfoxide under the catalysis of D-π-π-A type TPPy-PBT-COF-v can be completed within 6 hours, and the yield is as high as over 90%. It shows that the D-A type covalent organic framework containing benzothiadiazole unit shows great advantages in photocatalytic sulfide by increasing the π-bridge conjugated structure

[0078] Comparative Example 1

[0079] The difference from Example 3 is that TPPy-PBT-COF is used as the catalyst, and under visible light, sulfide is catalytically oxidized to synthesize sulfoxide. The catalytic results are shown in Table 2

[0080] Table 2 Catalytic oxidation of sulfide by TPPy-PBT-COF to synthesize sulfoxide

[0081]

[0082] Comparative Example 2

[0083] The difference from Example 3 is that TPPy-PBT-COF-p is used as the catalyst, and under visible light, sulfide is catalytically oxidized to synthesize sulfoxide. The catalytic results are shown in Table 3

[0084] Table 3 Catalytic oxidation of sulfide by TPPy-PBT-COF-p to synthesize sulfoxide

[0085]

[0086] Comparing Tables 1-3, it can be seen that: under the catalysis of D-π-π-A type TPPy-PBT-COF-v, the reaction can be completed within 6 h, and the yield is as high as over 90%; while the catalytic efficiencies of TPPy-PBT-COF-p and TPPy-PBT-COF without π-bridge structure are 11% - 45% under the same time (6 h), which are significantly lower than that of TPPy-PBT-COF-v. This shows that increasing the π-bridge structure can significantly improve the photocatalytic performance of D-A type COF based on benzothiadiazole unit

[0087] Example 4

[0088] To verify the stability and reusability of TPPy-PBT-COF-v, under visible light, benzyl sulfide 1a was catalytically oxidized to synthesize sulfoxide. The specific experimental process was the same as that of 1a in Example 3. The covalent organic framework was recovered and reused 5 times. The reaction time and yield of each reaction are shown in Table 4

[0089] Table 4 Yield of TPPy-PBT-COF-v after being reused 5 times

[0090]

[0091] Figure 17 is the PXRD image of TPPy-PBT-COF-v after being reused 5 times. It can be seen from Figure 17 that TPPy-PBT-COF-v remains stable after being reused 5 times, indicating its recyclable and reusable properties.

[0092] Example 5

[0093] The D-A type covalent organic framework TPPy-PBT-COF-v with an asymmetric benzothiadiazole ligand catalyzes the synthesis of isoquinolone compounds by the oxidation of tetrahydroisoquinoline compounds under visible light.

[0094] Weigh 10 mg of TPPy-PBT-COF-v as the catalyst for the photocatalytic reaction, 0.3 mmol of tetrahydroisoquinoline compounds (Table 5, 2a - 2e), ethanol as the reaction solvent, a 10 W blue LED lamp, and an atmosphere of 1 bar of oxygen. Monitor the reaction progress by thin layer chromatography (TLC) to determine the reaction time. The product NMR uses diphenylacetonitrile as the internal standard, and the yield is determined by 1 the analysis of the 1H NMR spectrum data.

[0095] Table 5 Synthesis of isoquinolone compounds by the catalytic oxidation of tetrahydroisoquinoline compounds

[0096]

[0097] The 1H NMR spectra of the products after the photocatalytic oxidation of the tetrahydroisoquinoline compounds 2a - 2e in Table 5 are as Figures 18 - 22 shown.

[0098] It can be seen from Table 5 that the D-π-π-A type TPPy-PBT-COF-v photocatalytically oxidizes more difficult-to-oxidize tetrahydroisoquinoline compounds to synthesize isoquinolone compounds, and the yield reaches over 70%.

[0099] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A DA-type covalent organic framework based on an asymmetric benzothiadiazole ligand, characterized in that: The structure represented by formula (I) is used as a structural repeating unit; Formula (I).

2. The asymmetric benzothiadiazole ligand of claim 1 is constructed based on the DA-type covalent organic framework of the asymmetric benzothiadiazole ligand, characterized in that: Its structural formula is shown in formula (II); Formula (II).

3. The method for preparing a DA-type covalent organic framework based on an asymmetric benzothiadiazole ligand according to claim 1, characterized in that: The steps include: The asymmetric benzothiadiazole ligand shown in formula (II) and 1,3,6,8-tetrakis(4-aminophenyl)pyrene are dissolved in an organic solvent, acetic acid is added as a catalyst, and a DA-type covalent organic framework based on the asymmetric benzothiadiazole ligand is synthesized by solvothermal reaction; Formula (II).

4. The preparation method according to claim 3, characterized in that: The molar ratio of the asymmetric benzothiadiazole ligand represented by formula (II) to 1,3,6,8-tetrakis(4-aminophenyl)pyrene is (1.5-3):

1.

5. The preparation method according to claim 3, characterized in that: The organic solvent is a mixed solution of o-dichlorobenzene and anhydrous ethanol; The volume ratio of o-dichlorobenzene and anhydrous ethanol is (2.5~4):

1.

6. The preparation method according to claim 3, characterized in that: The concentration of the asymmetric benzothiadiazole ligand represented by formula (II) in the organic solvent is 0.04-0.08 mol / L.

7. The preparation method according to claim 3, characterized in that: The temperature of the solvothermal reaction is 100~150 ℃; the time of the solvothermal reaction is 60~80 h.

8. Use of the DA type covalent organic framework based on asymmetric benzothiadiazole ligands as claimed in claim 1 or the DA type covalent organic framework based on asymmetric benzothiadiazole ligands prepared by the preparation method as claimed in claim 3 as a photocatalyst.

9. The use according to claim 8, characterized in that The application includes: catalytic oxidation of thioether to synthesize sulfoxide.

10. The use according to claim 8, characterized in that The application includes: catalytic oxidation of tetrahydroisoquinoline compounds to synthesize isoquinolone compounds.

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