Organic conjugated polymer containing benzothiadiazole unit, synthetic method and application

Abstract

The invention relates to the technical field of organic synthesis and hydrogen production, in particular to an organic conjugated polymer containing a benzothiadiazole unit and application of the organic conjugated polymer in photocatalytic hydrogen evolution. The structure of the organic conjugated polymer is as follows: # imgabs0 #, wherein the polymerization degree n is 10-200. Test experiments prove that the polymer has a wide light wave absorption range, small polymer forbidden bandwidth and energy level difference and higher light conversion efficiency and hydrogen production rate, so that an efficient photocatalytic hydrogen evolution catalyst is obtained, and the development of a photocatalytic hydrogen evolution technology and a hydrogen energy industry is promoted.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis and hydrogen production, and in particular to an organic conjugated polymer containing benzothiadiazole units and application thereof in photocatalytic hydrogen evolution. Background Art

[0002] Energy issues have always been a focus of attention. Hydrogen, a renewable energy source, has attracted more and more attention due to its high energy, abundant sources, and no pollutants produced after combustion. In order to fully develop hydrogen energy, researchers began to study photocatalytic hydrogen evolution. Photocatalytic hydrogen evolution technology has simple reaction conditions and is harmless, so it has become the main method for converting solar energy into hydrogen energy. Among them, high-efficiency photocatalysts are the focus and hotspot of research.

[0003] Benzothiadiazole and certain monomers have been widely studied for photocatalytic hydrogen evolution. For example, 2,1,3-benzothiadiazole (BTD) is an important heterocyclic precursor and one of the most important atomic nuclei in the chemistry of photoluminescent compounds. Based on BTD, researchers have obtained different polymers by synthesizing monomers of different geometric shapes and structures or connecting different heteroatoms or metals, or by connecting different substituents and functional groups. It has been found that a variety of reactive coupling groups can be used to modify organic conjugated polymers containing benzothiadiazole units, such as halogen groups, boric acid, amines, aldehydes, etc. In 2023, He et al. published a study in the Journal of Hydrochloric Acid Research on the effect of different connection positions of benzothiadiazole on the photocatalytic performance and photoelectrochemical properties of the material. Among several different polymers, especially 1,6-connected pyrene-benzothiadiazole, the photocatalytic hydrogen evolution rate was 6.81 mmol / (h·g), far exceeding several other polymers. In 2022, Sun modified the monomer containing benzothiadiazole units with metallic copper and reacted with 1,3,5-tri-(4-aminophenyl)-benzene and 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin to obtain products, and the catalytic efficiency of the products was significantly improved. In 2023, Wang et al. studied the synthesis of four small molecule receptors with dithiobenzothiadiazole units and cyanoindanones (IC, IC-2F, IC-2Cl, IC-Br) as end groups, and studied the effect of end-group small molecules on material properties. However, except for the high open-circuit voltage, other properties were not ideal. He then optimized the end-group small molecules and introduced halogen atoms (Br and F) to synthesize two non-condensed ring small molecules. Tests showed that the introduction of fluorine atoms and chlorine atoms optimized the small molecules, the absorption spectrum was red-shifted, and the molar absorption coefficient of the end-fluorinated small molecules reached 198148 L·mol -1 cm -1. In 2022, Du et al. synthesized two polymers FS1 and FS2 using monomers containing benzothiadiazole units through the SonogashiraG Hagihara cross-coupling reaction. The 5-position of the BT unit in FS1 does not contain a substituent, while FS2 has a methyl substituent. Various performance studies have shown that the two polymers have good photocatalytic hydrogen evolution ability, with photocatalytic hydrogen evolution rates of 11574μmol / (g·h) and 10061μmol / (g·h), respectively. The ultraviolet absorption of FS2 is blue-shifted compared to FS1, indicating that the presence of methyl substituents can change the polymer conjugation level and have little effect on the hydrogen evolution performance of the polymer.

[0004] In order to further promote the development of photocatalytic hydrogen evolution technology and the hydrogen energy industry, the present invention hopes to expand more photocatalytic hydrogen evolution catalysts with high hydrogen evolution rates. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides an organic conjugated polymer containing benzothiadiazole units, a synthesis method and an application thereof in photocatalytic hydrogen evolution. The polymer has a wider light wave absorption range and a smaller polymer bandgap width and energy level difference, higher light conversion efficiency and hydrogen production rate, thereby obtaining a highly efficient photocatalytic hydrogen evolution catalyst, which is helpful to promote the development of photocatalytic hydrogen evolution technology and hydrogen energy industry.

[0007] (II) Technical solution

[0008] In a first aspect, the present invention provides an organic conjugated polymer containing benzothiadiazole units, the structure of which is shown in Formula I:

[0009]

[0010] Wherein, the degree of polymerization n is 10-2000.

[0011] In a second aspect, the present invention relates to the use of an organic conjugated polymer as shown in formula I in photocatalytic hydrogen evolution.

[0012] In a third aspect, the present invention provides a method for synthesizing an organic conjugated polymer containing a benzothiadiazole unit, comprising:

[0013] S1. Using 4,7-dibromo-2,1,3-benzothiadiazole and 4-ethynylbenzaldehyde as raw materials, using anhydrous DMF and triethylamine v / v 1:1 as the reaction solvent, and carrying out Sonogashira reaction under the protection of nitrogen atmosphere and the presence of monovalent copper salt and palladium catalyst to obtain a monomer having the structure shown in formula II; the reaction process is expressed as follows:

[0014]

[0015] S2, the monomer shown in formula II and 2,5-diamino-1,4-benzenedithiol dihydrochloride are used as monomers, and a lower alcohol is used as a reaction solvent for heating and reflux reaction. After the reaction is completed, a hydrogen peroxide solution is added to continue heating and reflux reaction until an orange-red solid is precipitated, and the solid is separated, washed, and dried to obtain an organic conjugated polymer shown in formula I; the reaction process is expressed as follows:

[0016]

[0017] According to a preferred embodiment of the present invention, in S1, the palladium catalyst is Pd(PPh3)2Cl2 or Pd(PPh3)4.

[0018] According to a preferred embodiment of the present invention, in S1, the monovalent copper salt is CuI or CuBr.

[0019] According to a preferred embodiment of the present invention, in S1, the reaction is carried out at 25-95°C. After the reaction is completed, the solid product is collected by filtration and washed with ethyl acetate to obtain a monomer with a structure shown in Formula II.

[0020] According to a preferred embodiment of the present invention, in S1, the amount of palladium catalyst used is 10-15% of the mass of 4,7-dibromo-2,1,3-benzothiadiazole, the volume of the reaction solvent is 12-15 times the mass of the reaction materials, and the total reaction materials are the sum of the mass of the reaction raw materials, monovalent copper salt and palladium catalyst.

[0021] The Sonogashira reaction, also known as the Sonogashira coupling reaction or the Sonogashira-Hagihara coupling reaction, is a cross-coupling reaction used to form carbon-carbon bonds in organic synthesis. This reaction uses a palladium catalyst and a monovalent copper salt as a co-catalyst to form a new carbon-carbon bond between a terminal alkyne and an aryl or vinyl halide to prepare a substituted alkyne. The reaction is relatively mild and must be strictly oxygen-free to prevent oxidation of the alkyne. Copper salts (such as CuI or CuBr) are used to avoid handling explosive acetylene copper. The Sonogashira reaction can effectively construct alkyne compounds with large conjugated systems and has good compatibility with functional groups in the substrate.

[0022] According to a preferred embodiment of the present invention, in S2, the reaction is carried out in a pressure-resistant container. First, the monomer represented by Formula II and 2,5-diamino-1,4-benzenedithiol dihydrochloride are added to the pressure-resistant container at a molar ratio of 1:1, and anhydrous ethanol is added as a solvent to fully and evenly disperse the two reaction monomers. The reaction is refluxed at 60-88°C for 20-30h; after the reaction, the reaction solution is cooled to room temperature, an aqueous solution of hydrogen peroxide is added, and the reaction is continued at 60-88°C for 4-10h until an orange-red solid is precipitated, and the reaction is terminated; the reaction system is cooled to room temperature, the orange-red solid is separated by centrifugation, and the solid is washed with anhydrous ethanol for more than 3 times and dried to obtain an organic conjugated polymer represented by Formula I.

[0023] According to a preferred embodiment of the present invention, the drying condition is drying at 50-70° C. for 5-10 hours.

[0024] According to a preferred embodiment of the present invention, the aqueous hydrogen peroxide solution is a 28-33 wt % hydrogen peroxide solution, and the added amount is 2% of the total volume of the reaction system.

[0025] (III) Beneficial effects

[0026] The light absorption range of the organic conjugated polymer with the structure shown in Formula I synthesized in the embodiment of the present invention extends to 510nm, and the band gap is small; the E-MBT of the polymer with the structure shown in Formula I is measured by UV-visible diffuse reflection and cyclic voltammetry curves, and the LUMO is about -0.25eV, which has a small energy level difference; the photoelectric value of the polymer is about 1.566μA.cm -2 , with high light conversion efficiency. The photocatalytic hydrogen evolution test shows that the average hydrogen production rate of the polymer shown in Formula I synthesized in the embodiment of the present invention reaches 11.42mmol / (g·h), and the high hydrogen production rate is conducive to promoting the development and industrial application of photocatalytic hydrogen production technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 (a) is the solid-state NMR of the conjugated polymer of formula I synthesized in Example 1, and (b) is the solid-state NMR of the polymer MBT synthesized in Comparative Example 1.

[0028] Figure 2 The infrared spectra of the conjugated polymer of formula I synthesized in Example 1 and the polymer MBT synthesized in Comparative Example 1 are shown.

[0029] Figure 3 XRD spectra of the conjugated polymer of formula I synthesized in Example 1 and the polymer MBT synthesized in Comparative Example 1.

[0030] Figure 4(b) is a scanning electron microscope photograph of the conjugated polymer of formula I synthesized in Example 1, and (a) is a scanning electron microscope photograph of the polymer MBT synthesized in Comparative Example 1.

[0031] Figure 5 The UV-visible absorption spectra of the conjugated polymer of formula I synthesized in Example 1 and the polymer MBT synthesized in Comparative Example 1.

[0032] Figure 6 (a) is the cyclic voltammetry curve of the conjugated polymer of formula I synthesized in Example 1, and (b) is the cyclic voltammetry curve of the polymer MBT synthesized in Comparative Example 1.

[0033] Figure 7 Schematic diagram of the energy band positions of HOM0 and LUM0 of the conjugated polymer of formula I synthesized in Example 1 and the polymer MBT synthesized in Comparative Example 1.

[0034] Figure 8 Electrochemical impedance spectroscopy (EIS) of the conjugated polymer of formula I synthesized in Example 1 and the polymer MBT synthesized in Comparative Example 1.

[0035] Fig. 9 The photocurrent variation curves of the conjugated polymer of formula I synthesized in Example 1 and the polymer MBT synthesized in Comparative Example 1 are plotted over time.

[0036] Fig.10 This is a graph showing the relationship between the photocatalytic hydrogen evolution of the conjugated polymer of formula I synthesized in Example 1 and the polymer MBT synthesized in Comparative Example 1 and time. DETAILED DESCRIPTION

[0037] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0038] Example 1

[0039] The process of synthesizing the organic conjugated polymer of structure 1 in this embodiment is as follows:

[0040] (1) 0.3 g of 4,7-dibromo-2,1,3-benzothiadiazole, 0.4 g of 4-ethynylbenzaldehyde, 0.078 g of cuprous iodide, and 0.03 g of tetrakistriphenylphosphine palladium (the catalyst accounts for 10% of the mass of 4,7-dibromo-2,1,3-benzothiadiazole) were weighed and added to a three-necked flask, and 5 mL of DMF and 5 mL of triethylamine were added as solvents. Nitrogen was introduced as a protective gas (the air was replaced in advance), and Sonogashira reaction was carried out at 90° C. for 6 h. The solid product was filtered to obtain a solid product, which was washed with ethyl acetate three times to obtain an orange solid (0.28 g).

[0041]

[0042] (2) The monomer compound represented by formula II and 2,5-diamino-1,4-benzenedithiophenol dihydrochloride are used as monomers to synthesize an organic polymer. The specific process is as follows: prepare a clean and dry 100 mL pressure-resistant bottle, add 123 mg of the monomer compound represented by formula II (molecular weight 392) and 77 mg of 2,5-diamino-1,4-benzenedithiophenol dihydrochloride (molecular weight 245.20) into the pressure-resistant bottle, the molar weight of the two is 0.314 mmol, and the molar ratio is 1:1. Then measure 25 mL of anhydrous ethanol as the reaction solvent.

[0043] The reaction is divided into two stages. Stage 1: Tighten the pressure-resistant bottle and put it into ultrasound for dispersion for 30 minutes to evenly disperse the two monomers. Put it into a drying oven at 80°C for reflux reaction for 24 hours. Observe the precipitation of solids in the bottle during the reaction process. The reaction ends after 24 hours, and the reaction liquid is cooled to room temperature. Reaction stage 2: Add 0.5mL of 30wt% hydrogen peroxide solution, put it into a drying oven at 80°C for continued reflux reaction for 6 hours, and slowly precipitate an orange-red solid. Cool the reaction system to room temperature and take it out. Centrifuge to obtain a solid, wash it 5 times with anhydrous ethanol, put it in a drying oven at 60°C for 6 hours, and obtain an orange-red solid polymer (structure shown in Formula I).

[0044]

[0045] The polymer prepared in this example was subjected to solid nuclear magnetic resonance and red light detection. Figure 1 (a) shows the solid NMR spectrum of the product. Figure 2 The infrared spectrum of the product confirms that the product is a conjugated polymer with the structure shown in Formula I.

[0046] Comparative Example 1

[0047] In this comparative example, "4-ethynylbenzaldehyde" in Example 1 is replaced with "4-formylphenylboronic acid" to obtain a monomer, and then the monomer is reacted with 2,5-diamino-1,4-benzenedithiophenol dihydrochloride to generate a conjugated polymer without an alkynyl group. The synthesis process and product structure of this comparative example are as follows:

[0048] (1) 1 g of 4,7-dibromo-2,1,3-benzothiadiazole, 4.8 g of phenylboric acid, 4.8 g of potassium carbonate, 0.03 g of 10% tetraphenylphosphine palladium catalyst, 20 mL of dioxane and 5 mL of water were weighed into a three-necked flask, and nitrogen was used as a protective gas to carry out a Suzuki coupling reaction at 90° C. After reacting for 6 hours, the product was detected by thin layer chromatography, and the solid product was filtered to obtain a solid product, which was washed with ethyl acetate 2-3 times to obtain an orange-yellow solid (0.86 g), which was recorded as FBT monomer. The reaction process is shown as follows:

[0049]

[0050] (2) FBT monomer and 2,5-diamino-1,4-benzenedithiophenol dihydrochloride monomer are synthesized into a polymer, the steps of which are as follows: prepare a clean and dry 100 mL pressure bottle, add 117 mg of FBT monomer and 83 mg of 2,5-diamino-1,4-benzenedithiophenol dihydrochloride into the pressure bottle, and take 25 mL of anhydrous ethanol as a reaction solvent. The molar ratio of FBT monomer to 2,5-diamino-1,4-benzenedithiophenol dihydrochloride is 1:1.

[0051] The pressure-resistant bottle was tightened and placed in an ultrasonic dispersion for 30 minutes to disperse the two monomers evenly, and then placed in a drying oven at 80°C for reflux reaction for 24 hours. During the reaction, the solid precipitation in the bottle was observed, and the reaction was terminated after 24 hours. After the reaction solution was cooled to room temperature, 0.5 mL of 30% hydrogen peroxide solution was added, and the reaction was continued at 80°C in a drying oven for 6 hours to slowly precipitate an orange solid. After the reaction was completed, the reaction solution was cooled to room temperature, and the solid was obtained by centrifugation. It was washed with anhydrous ethanol 5 times, and placed in a drying oven at 60°C for 6 hours to obtain an orange solid polymer, which was recorded as MBT (125 mg).

[0052] The reaction process is shown as follows:

[0053]

[0054] The polymer MBT prepared in this example was subjected to solid-state nuclear magnetic resonance and red light detection, such as Figure 1 (b) shows the solid NMR spectrum of the product. Figure 2 The infrared spectrum of the product confirms that the product is a polymer with the structure shown in Formula III.

[0055] Polymer characterization and pore performance testing

[0056] (1) Characterization of the chemical structure, crystal form and micromorphology of polymers

[0057] 1. Solubility: The polymers prepared in Example 1 and Comparative Example 1 are both insoluble powders. In solvent tests, they are insoluble in common solvents such as water, chloroform, methanol, acetone, etc., and do not change in common acid or alkali aqueous solutions, indicating that the polymer represented by Formula I and polymer MBT have good solvent stability and chemical stability.

[0058] ② By Figure 1 From the solid NMR spectrum, it can be seen that the spectra of polymer MBT and the polymer of formula 1 are similar. The signal peak at 168 ppm is attributed to the carbon atom in the thiazole ring. Compared with polymer MBT, the signal peaks at 98 ppm and 87 ppm of the polymer of formula 1 are attributed to the signal peaks of the asymmetric alkynyl group, which proves the existence of alkynyl group in the polymer of formula 1.

[0059] ③ By Figure 2 The infrared spectra of polymer MBT and polymer of formula I show that -1 There is an obvious peak at 1480cm -1 and 1600cm -1 A series of absorption peaks appear in the range, which is the stretching vibration of the aromatic ring carbon-carbon double bond. As can be seen from the figure, at 1671cm -1 A characteristic peak appears at , which is the absorption peak caused by the stretching vibration of the C=N bond, thus confirming that the polymer MBT and the polymer of formula I contain a thiazole ring structure; Figure 2 It can also be seen that the polymer of formula I has a peak at 2202 cm -1 A characteristic peak appears at , which is attributed to the stretching vibration peak of the carbon-carbon triple bond of the alkynyl group.

[0060] ④ The morphology of the polymer MBT prepared in Comparative Example 1 and the conjugated polymer of the structure shown in Formula I prepared in Example 1 were observed by scanning electron microscopy; Figure 4 As shown in FIG. 1 , the polymer MBT has a stacked irregular rod-like and flake-like morphology, while the polymer of Formula 1 has a nanocluster morphology with smaller particles and uniform morphology. This indicates that the introduction of the alkyne group significantly changes the morphology of the polymer and significantly reduces the particle size.

[0061] ⑤ The crystal forms of the polymer MBT prepared in Comparative Example 1 and the conjugated polymer of the structure shown in Formula I prepared in Example 1 were analyzed by XRD scanning. Figure 3 As shown, both polymer MBT and polymer of formula I present a broad peak in the 2θ value range of 10-35°, which indicates that the polymer is an amorphous material; the difference is that polymer MBT presents some high and low peaks in the 2θ value range of 23-40°, which indicates that polymer MBT without alkynyl modification has higher crystallinity, and the disordered structure with low crystallinity may introduce more surface dangling bonds or defect sites, accelerating charge capture.

[0062] (2) UV-Vis absorption and fluorescence spectroscopy analysis

[0063] like Figure 5 As shown, it is the UV-visible absorption spectrum of the polymers synthesized in Example 1 and Comparative Example 1. As shown in the figure, the light absorption edge of the polymer of Formula I in Example 1 extends to 510nm, and the light absorption edge of the polymer MBT in Comparative Example 1 is 460nm. It can be seen that the polymer of Formula I synthesized in Example 1 has a wider light absorption region. According to the absorption edge, the optical bandwidths of the polymer of Formula I and the polymer MBT are calculated to be 1.94eV and 2.02eV respectively, and the bandgap width of the polymer of Formula I is smaller.

[0064] (3) Electrochemical performance

[0065] ① Such as Figure 6 The figure shows the cyclic voltammetry (CV) curves of two polymers, namely, the polymer MBT of comparative example 1 and the polymer of formula I of example 1. As can be seen from the figure, the peak potential of the polymer of formula I of example 1 is 1.69V, and the peak potential of the polymer MBT is 1.74V, which means that the polymer MBT requires higher energy to undergo redox reaction.

[0066] See also Figure 7 As shown, the LUMO of the polymer MBT of comparative example 1 is -0.28 eV as measured by UV-visible diffuse reflectance and cyclic voltammetry curves; while the LUMO of the polymer of formula I synthesized in example 1 is -0.25 eV. It can be seen that the introduction of the alkyne group in the polymer of example 1 reduces the energy level difference. The LUMO values ​​of the polymers of example 1 and comparative example 1 are both much greater than the reduction potential of H2O / H2 (-4.5 eV), indicating that both polymers can provide sufficient thermodynamic driving force to decompose water to produce hydrogen.

[0067] ②The interfacial electron transfer behavior of the polymer was tested by electrochemical impedance spectroscopy (EIS). Figure 8 As shown, the AC impedance of the polymer with structure I prepared in Example 1 is smaller than that of the polymer MBT synthesized in Comparative Example 1. The photocurrent value of the polymer with structure I is 1.566 μA / cm 2 , is the polymer MBT photocurrent value of 0.672μA / cm 2 It can be seen that the polymer with structure I prepared in Example 1 has better light conversion efficiency. This shows that the introduction of carbon-carbon triple bonds improves the charge separation efficiency of the polymer.

[0068] ③If Fig. 9 As shown, it is a graph of the photocurrent change over time of the polymer BMT of Comparative Example 1 and the polymer of Formula I of Example 1; it can be seen from the figure that the photocurrent response of both polymers shows good repeatability and stability, and each time the light is turned on and off, the photocurrent can quickly reach a peak and fall back to the baseline, indicating that the photoresponse characteristics of the two polymers are stable and reversible. The peak photocurrent of the polymer of Formula I is significantly higher than that of the polymer MBT. This shows that the polymer of Formula I can generate a larger photocurrent under the same lighting conditions, indicating that it has better photocatalytic activity.

[0069] (4) Visible light-driven photocatalytic water splitting to produce hydrogen

[0070] Into a 80mL special quartz test tube with a stirrer, add 20mL of a mixed solvent of water and triethanolamine (v:v=4:1), disperse 20mg of the photocatalyst (two polymers synthesized in Example 1 and Comparative Example 1) into the mixed solvent, and triethanolamine is used as a sacrificial agent. The sealing plug is sealed, and high-purity argon gas is bubbled into the test tube for 0.5h to exhaust the air in the system, and the catalyst is evenly dispersed in the mixed solvent by ultrasound for 0.5h. The dispersed test tube is placed in a closed reactor, a 300W xenon lamp is used as a light source, and stirred under light to carry out a photocatalytic water decomposition reaction. Circulating cooling water is introduced to keep the reaction temperature at 25°C, and 0.4mL of gas is extracted with a syringe every hour to monitor the hydrogen evolution rate online through an Agilent 7890A gas chromatograph equipped with TCD. The hydrogen evolution rate (unit: μmol / (g·h) is calculated using the following formula.

[0071]

[0072] Where: GC is the peak area of ​​the detected peak, 9.39494×10 -11 is the conversion factor. 68×10 6 is the volume of air in the reaction vessel, 0.4 is the injection volume, in mL, and 0.02 is the mass of the catalyst sample, in g.

[0073] The experimental results show that both polymers synthesized in Example 1 and Comparative Example 1 exhibit stable hydrogen evolution effects. Among them, the photocatalytic hydrogen production rate of the polymer of formula I is 11.42 mmol / (g·h), the average hydrogen production rate of the polymer MBT in Comparative Example 1 is 7.02 mmol / (g·h), and the catalytic hydrogen production rate of the polymer in Example 1 is 1.627 times that of the polymer in Comparative Example.

[0074] See also Fig.10 The graph shows the relationship between the photocatalytic water decomposition hydrogen production and time (h) of the polymer BMT of Comparative Example 1 and the polymer of Formula I of Example 1. As can be seen from the figure, the photocatalytic water decomposition hydrogen production rate of the polymer of Formula I prepared in Example 1 is faster, and the hydrogen production is higher in the same time.

[0075] In summary, the photocatalytic hydrogen evolution rate of the polymer with structure of formula I provided by the present invention is higher than that of most similar polymer catalysts currently known, and has good application potential for photocatalytic hydrogen production.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. These modifications or replacements, or the technical features in the above embodiments may be combined in the manner described in the embodiments if they do not conflict with each other, and these modifications, replacements or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An organic conjugated polymer containing benzothiadiazole units, characterized in that: The structure of the organic conjugated polymer is shown in Formula I: Wherein, the degree of polymerization n is 10-200.

2. Application of the organic conjugated polymer represented by formula I in photocatalytic hydrogen evolution.

3. A method for synthesizing an organic conjugated polymer containing benzothiadiazole units, characterized in that: It includes the following steps: S1. Using 4,7-dibromo-2,1,3-benzothiadiazole and 4-ethynylbenzaldehyde as raw materials, using anhydrous DMF and triethylamine v / v 1:1 as the reaction solvent, and carrying out Sonogashira reaction under the protection of nitrogen atmosphere and the presence of monovalent copper salt and palladium catalyst to obtain a monomer with the structure shown in formula II; the reaction process is expressed as follows: S2, the monomer shown in formula II and 2,5-diamino-1,4-benzenedithiol dihydrochloride are used as monomers, and a lower alcohol is used as a reaction solvent for heating and reflux reaction. After the reaction is completed, a hydrogen peroxide solution is added to continue heating and reflux reaction until an orange-red solid is precipitated, and the solid is separated, washed, and dried to obtain an organic conjugated polymer shown in formula I; the reaction process is expressed as follows:

4. The synthesis method according to claim 3, characterized in that In S1, the palladium catalyst is Pd(PPh3)2Cl2 or Pd(PPh3)4; the monovalent copper salt is CuI or CuBr.

5. The synthesis method according to claim 3, characterized in that In S1, the reaction is carried out at 25-95°C. After the reaction is completed, the solid product is collected by filtration and washed with ethyl acetate to obtain a monomer with a structure shown in Formula II.

6. The synthesis method according to claim 3, characterized in that In S1, the amount of palladium catalyst used is 10-15% of the mass of 4,7-dibromo-2,1,3-benzothiadiazole, the volume of the reaction solvent is 12-15 times the mass of the reaction materials, and the total reaction materials are the sum of the mass of the reaction raw materials, the monovalent copper salt and the palladium catalyst.

7. The synthesis method according to claim 3, characterized in that In S2, the reaction is carried out in a pressure-resistant container. First, the monomer represented by formula II and 2,5-diamino-1,4-benzenedithiol dihydrochloride are added to the pressure-resistant container at a molar ratio of 1:1, and anhydrous ethanol is added as a solvent to fully and evenly disperse the two reaction monomers. The reaction is refluxed at 60-88°C for 20-30h. After the reaction is completed, the reaction solution is cooled to room temperature, and an aqueous hydrogen peroxide solution is added. The reaction is continued at 60-88°C for 4-10h until an orange-red solid is precipitated, and the reaction is completed. The reaction system is cooled to room temperature, the orange-red solid is separated by centrifugation, and the solid is washed with anhydrous ethanol for more than 3 times and dried to obtain an organic conjugated polymer represented by formula I.

8. The synthesis method according to claim 7, characterized in that The drying conditions are 50-70°C for 5-10 hours.

9. The synthesis method according to claim 7, characterized in that: The aqueous hydrogen peroxide solution is a 28-33 wt % hydrogen peroxide solution, and the added amount is 2% of the total volume of the reaction system.

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