Photoinitiators with low power visible light and solar light induced polymerization properties and methods of preparation

Abstract

The present application relates to the technical field of light-cured materials, and particularly relates to a photoinitiator with low-power visible light and sunlight-induced polymerization characteristics and a preparation method thereof.The photoinitiator takes a spirofluorene structure as a bridging unit, and is composed by connecting an electron donor unit and an electron acceptor unit; the electron acceptor unit comprises a sulfur element.The photoinitiator can form an excited state through a space charge transfer mechanism under the condition of low-power visible light or sunlight irradiation, and then charge transfer occurs between the electron donor and the acceptor, thereby generating active free radicals, efficiently initiating free radical polymerization, effectively solving the pain points of the prior art, and providing a new design idea for developing efficient visible light photoinitiators.

Description

Technical Field

[0001] This invention relates to the field of photocurable materials technology, and in particular to a photoinitiator with low-power visible light and sunlight-induced polymerization properties and its preparation method. Background Technology

[0002] Photopolymerization technology, due to its advantages such as high efficiency, energy saving, and environmental friendliness, is widely used in coatings, inks, adhesives, 3D printing, microelectronics, and dental materials. The core of this technology lies in photoinitiators, which generate active species (such as free radicals or cations) under light irradiation, thereby initiating cross-linking polymerization of monomers and achieving material curing. Although photopolymerization technology is widely used, traditional photoinitiator systems still have a series of inherent drawbacks, which significantly restrict the further development and application expansion of photopolymerization technology.

[0003] Traditional photoinitiator systems primarily rely on ultraviolet (UV) light sources. However, the short wavelength of UV light results in insufficient penetration into materials, easily leading to incomplete curing of the coating substrate and affecting product quality. Furthermore, high-power UV light sources are not only expensive but also consume significant amounts of energy and have stringent heat dissipation requirements, significantly increasing equipment investment and subsequent maintenance burdens during production.

[0004] Chinese invention patent application CN1545643A discloses red-shift mono- and bis-acylphosphine oxides and phosphine sulfide, and their applications as photoinitiators. Through the reaction of dimetallic phosphine with acyl halides, combined with appropriate solvents and temperatures, compounds of general formula I are prepared, solving the difficulties in preparing red-shift mono- and bis-acylphosphine oxides and phosphine sulfide photoinitiators in the prior art. This achieves an efficient and readily available preparation method, improving product purity. Chinese invention patent CN106478843B discloses a thiophene ring-containing bisoxime ester photoinitiator, its preparation method, and its application. By developing a thiophene ring-containing bisoxime ester photoinitiator, the problems of insufficient heat resistance and difficulty in curing high-end color filters in existing photoinitiators are solved, achieving high photosensitivity and thermal stability, suitable for LED light sources, and improving the efficiency of photocuring and image quality. However, these existing technologies do not solve the aforementioned technical problems and still require ultraviolet light conditions for initiation, making them difficult to fully adapt to low-energy-consumption, high-penetration visible light or LED curing scenarios, limiting the high-end applications of photoinitiators.

[0005] Therefore, existing technologies still have significant shortcomings in the field of high-performance visible light / sunlight initiators, and there is an urgent need to break through the traditional design paradigm of photoinitiators and develop new photoinitiators to solve the above problems. Summary of the Invention

[0006] To overcome the aforementioned problems in the prior art, this application aims to provide a photoinitiator that can induce polymerization under low-power visible light / sunlight and its preparation method. This type of photoinitiator has visible light absorption capability and excited-state electron transfer capability, and extends the excited-state lifetime through space charge transfer. It can effectively solve the technical problems of traditional photoinitiators that rely on ultraviolet light sources, have poor curing effect and high energy consumption, and promote the application expansion of photocuring technology.

[0007] The first aspect of the present invention provides a photoinitiator with low-power visible light and sunlight-induced polymerization properties. The photoinitiator is composed of a spirofluorene-like structure as a bridging unit, which connects an electron donor unit and an electron acceptor unit. The electron acceptor unit includes sulfur.

[0008] During its research and development, the applicant discovered that ultraviolet light, due to its high photon energy, easily causes yellowing or aging of photosensitive substrates, and its high-energy characteristics also limit its application in sensitive fields such as biomedicine. In contrast, visible light has stronger penetrating power in materials, and visible light LED technology is becoming increasingly mature, possessing significant advantages such as low cost, low energy consumption, and long lifespan. Furthermore, sunlight, as an readily available and free visible light source, aligns with the industrial trends of green manufacturing and sustainable development, and has broad application prospects.

[0009] Based on the free radical generation mechanism, photopolymerization reactions can be divided into two types: Type I and Type II. Type I photoinitiators can directly undergo homolytic bond cleavage after photoexcitation, thereby generating active free radicals. Type II photoinitiators, on the other hand, require a bimolecular reaction with a co-initiator to synergistically generate active free radicals. While Type I photoinitiators are easy to use, their absorption spectra are mainly concentrated in the ultraviolet region, and the generated free radicals are easily quenched by oxygen. Therefore, high-power light irradiation or inert gas protection is usually required to overcome the problem of poor surface curing, which undoubtedly increases the complexity of the process and production costs.

[0010] In contrast, the absorption spectrum of the Type II photoinitiation system can be red-shifted and extended into the visible light region through molecular structure modification. Furthermore, through synergistic pairing with co-initiators, it can significantly optimize free radical yield and polymerization rate. The photocatalytic Type II initiation system consists of a photosensitizer, an electron donor, and an electron acceptor co-initiator. Its mechanism of action is as follows: after photoexcitation, the photosensitizer steals an electron from the electron donor, converting the electron donor into an active free radical, which then initiates the polymerization reaction. The photosensitizer, having gained an electron, transfers the electron to the electron acceptor in the system, returning to its ground state and participating in the next catalytic cycle. Simultaneously, the electron acceptor generates an active free radical upon gaining an electron, further initiating the polymerization reaction. This catalytic system, with its highly efficient electron transfer, can significantly improve the polymerization rate, overcoming the shortcomings of traditional photoinitiators, such as low initiation efficiency and slow polymerization rate. Against this backdrop, this invention uses spirofluorene-like structures as bridging units to design a novel photoinitiator by connecting electron donor units and sulfur-containing electron acceptor units. This type of photoinitiator can undergo efficient polymerization under visible light and sunlight, and its polymerization characteristics are significantly better than those of existing photoinitiators. This provides a novel molecular design idea and strategy for developing a new generation of efficient and energy-saving broadband visible light initiators.

[0011] Spirofluorene structures refer to a class of rigid aromatic structures with a fluorene ring or its fused-ring derivative as the core skeleton. They may include spirodifluorene, fluorene and other fused-ring aromatic bridging units. Their molecules have the characteristics of strong rigidity, moderate conjugation and suitable steric hindrance. In this application, they are used as bridging units to connect and separate electron donor units and electron acceptor units, which is conducive to the formation of stable space charge transfer states.

[0012] Electron donor units refer to aromatic conjugated structural units with electron-rich properties that can provide electrons. These units can transfer electrons to electron acceptor units under photoexcitation, providing an electron source for the visible light response and excited state regulation of photoinitiators.

[0013] The electron acceptor unit refers to an aromatic conjugated structural unit with electron-deficient properties that can accept electrons. The electron acceptor unit includes sulfur and can form an effective electron transfer system with the electron donor unit, thereby extending the excited state lifetime and increasing the light absorption range, so that the photoinitiator can efficiently generate active species under low-power visible light and sunlight.

[0014] The electron acceptor unit includes BTXI (benzothionimide).

[0015] BTXI and its derivatives possess excellent broad-spectrum visible light harvesting capabilities and exhibit strong light absorption in the visible light band, making them promising light-absorbing groups for initiation using long-wavelength light and even sunlight. Currently, these compounds are primarily used in OLEDs and biological probes, but their application in electron transfer-based photocatalytic polymerization systems is relatively rare. The core reason for this is their low electron transfer efficiency with electron donors / acceptors in photocatalytic systems, which limits their application in photoinitiation systems. In previous research, the applicant discovered that space charge transfer molecules can effectively improve electron transfer efficiency, but the absorption spectra of these molecules are limited to the ultraviolet band, failing to meet the application requirements of visible light and sunlight initiation. This invention, through a specific synthetic route, introduces BTXI into a spirofluorene-based bridging framework, resulting in a novel space charge transfer photoinitiator that combines broad-spectrum visible light absorption with high electron transfer efficiency.

[0016] The photoinitiator has one of the following molecular structures: .

[0017] The photoinitiator has one of the following molecular structures: .

[0018] Optionally, the raw materials for preparing the photoinitiator include intermediate A and intermediate B; Optionally, the intermediate A includes LW-CZ or LW-PXZ; Optionally, the intermediate B includes BTXI-Bpin; When intermediate A is LW-CZ, the photoinitiator is BTXI-1; when intermediate A is LW-PXZ, the photoinitiator is BTXI-2.

[0019] The structural formula of LW-CZ is: The structural formula of LW-PXZ is .

[0020] Optionally, the preparation steps of LW-CZ include: dissolving CZ-Br and LW-Br in tetrahydrofuran, cooling to -70~-80℃ under argon protection, adding n-butyllithium solution, maintaining low temperature and stirring for 0.5-3 hours, then maintaining low temperature and adding LW-Br within 30 minutes, continuing to react at -70~-80℃ for 0.5-2 hours after addition, raising to room temperature and stirring for 1-5 hours, adding water to quench after the reaction, removing the solvent by vacuum evaporation, dissolving the obtained solid in dichloromethane and washing with water, wherein the organic phase is dried with anhydrous sodium sulfate, filtered and concentrated to obtain a crude intermediate, dissolving the crude intermediate in a mixed solution of acetic acid and concentrated hydrochloric acid, heating to 100-120℃ and refluxing for 2-6 hours, cooling to room temperature and filtering the precipitate, washing with petroleum ether, purifying the crude product by silica gel column chromatography to obtain product LW-CZ.

[0021] The structural formula of CZ-Br is as follows: The structural formula of LW-Br is .

[0022] Optionally, when preparing LW-CZ, silica gel is used as the stationary phase, and a mixture of dichloromethane and petroleum ether is used as eluent A for purification.

[0023] Optionally, the volume ratio of dichloromethane to petroleum ether in eluent A is (1-5):(4-10); further optionally, it is 3:7.

[0024] Optionally, the molar ratio of CZ-Br to LW-Br is 1:(0.8-1.2); further optionally, it is 1:1.

[0025] In some embodiments, the preparation steps of LW-CZ include: dissolving CZ-Br and LW-Br in tetrahydrofuran, cooling to -78°C under argon protection, then slowly adding 1-2M n-butyllithium solution, stirring at low temperature for 1 hour, then adding LW-Br within 15 minutes while maintaining the low temperature, continuing the reaction at -78°C for 2 hours, then slowly raising to room temperature and stirring for 3 hours, quenching with water after the reaction is completed, removing the solvent by vacuum evaporation, dissolving the obtained solid in dichloromethane, and washing with deionized water 2-3 times, wherein the organic phase is dried over anhydrous sodium sulfate, filtered and concentrated to obtain a crude intermediate, dissolving the crude intermediate in a mixed solution of acetic acid and concentrated hydrochloric acid, heating to 110°C and refluxing for 4 hours, cooling to room temperature, filtering the precipitate and washing with petroleum ether, and purifying the crude product by silica gel column chromatography to obtain the white solid product LW-CZ.

[0026] Optionally, the preparation steps of the LW-PXZ include: (1) PXZ, 2-bromoiodobenzene, cuprous iodide, 18-crown ether-6 and potassium carbonate were dissolved in o-dichlorobenzene. The mixture was heated to 160-190℃ and refluxed under a nitrogen atmosphere. After reacting for 24-72 hours, the reaction solution was cooled to room temperature. After removing o-dichlorobenzene by rotary evaporation, it was extracted with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography to obtain the intermediate product PXZ-Br. (2) Under an argon atmosphere, PXZ-Br was dissolved in tetrahydrofuran, cooled to -70~-80℃, and then n-butyllithium solution was added. The mixture was stirred at -70~-80℃ for 0.5-2 hours, and then 1-bromo-9-fluorenone was added. The mixture was reacted at -70~-80℃ for 1-3 hours. Water was added to the reaction system to quench the reaction, and then the solvent was removed by vacuum evaporation. The obtained solid was dissolved in dichloromethane and washed with water. The organic layer was then separated, dried with anhydrous sodium sulfate, filtered and evaporated to obtain the crude product, which was directly used for the next step. The crude product was dissolved in a mixture of acetic acid and hydrochloric acid and reacted at 100-130℃ for 2-6 hours. The reaction solution was cooled to room temperature and extracted with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography to obtain product LW-PXZ.

[0027] The structural formula of PXZ (phenoxazine) is as follows: The structural formula of PXZ-Br is .

[0028] Optionally, when preparing PXZ-Br, silica gel is used as the stationary phase, and a mixture of dichloromethane and petroleum ether is used as eluent B for purification.

[0029] Optionally, the volume ratio of dichloromethane to petroleum ether in the eluent B is (1-5):(4-10); further optionally, it is 3:7.

[0030] Optionally, LW-PXZ can be prepared using silica gel as the stationary phase and petroleum ether as the eluent C for purification.

[0031] Optionally, the molar ratio of PXZ to 2-bromoiodobenzene is 1:(1-3); further optionally, it is 1:1.5.

[0032] Optionally, the molar ratio of PXZ-Br to 1-bromo-9-fluorenone is 1:(0.8-1.2); more preferably, it is 1:1.

[0033] Optionally, the volume ratio of acetic acid to hydrochloric acid is (20-40):(2-10); further optionally, it is 30:8.

[0034] Optionally, the preparation steps of the BTXI-Bpin include: (1) Dissolve BNA, 2-aminothiophenol and potassium carbonate in N,N-dimethylformamide, heat to 120-180℃ under nitrogen atmosphere, stir and reflux for 0.5-3 hours. After the reaction is completed, cool the reaction solution to room temperature, extract the reaction solution with dichloromethane and water, dry with anhydrous sodium sulfate, filter and evaporate under reduced pressure to remove the solvent to obtain crude product; purify the crude product by silica gel column chromatography to obtain intermediate product BNA-ABT; (2) Dissolve BNA-ABT and isoamyl nitrite in N,N-dimethylformamide, heat to 130-180℃ under nitrogen atmosphere and reflux. After reacting for 0.2-1 hours, cool the reaction solution to room temperature, add water to precipitate the product, and obtain the intermediate product BTXA without further purification. (3) Under a nitrogen atmosphere, BTXA, imidazole and 2-ethylhexylamine were mixed and stirred at 120-160℃ for 3-10 hours. After the reaction solution was cooled to room temperature, it was extracted with dichloromethane and water. The organic phase was dried with anhydrous sodium sulfate and the solvent was removed by vacuum evaporation. The crude product was purified by column chromatography to obtain the intermediate product BTXI. (4) Dissolve BTXI in dichloromethane, add a dichloromethane solution containing 0.1-2M Br2, stir at room temperature for 8-16 hours, wash with saturated sodium thiosulfate solution, water and saturated brine in sequence, dry the organic phase with anhydrous sodium sulfate, evaporate the solvent under reduced pressure to obtain the crude product, purify the crude product by silica gel column chromatography to obtain the intermediate product BTXI-Br; (5) Under a nitrogen atmosphere, potassium acetate was added to anhydrous 1,4-dioxane containing BTXI-Br and pinacol diborate. After the reaction solution was bubbled with nitrogen to remove oxygen, [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride was added. The mixture was heated to 80-95°C and stirred for 10-15 hours under nitrogen protection. After the reaction solution was cooled to room temperature, it was mixed with water and extracted with dichloromethane. The organic phase was dried with anhydrous sodium sulfate and the solvent was removed by vacuum evaporation. The crude product was purified by silica gel column chromatography to obtain the product BTXI-Bpin.

[0035] The structural formula of BNA is: The structural formula of BNA-ABT is The structural formula of BTXA is The structural formula of BTXI is The structural formula of BTXI-Br is .

[0036] Optionally, BNA-ABT can be prepared using silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether as eluent D for purification.

[0037] Optionally, the volume ratio of dichloromethane to petroleum ether in the eluent D is 1:(0.4-2); more preferably, it is 1:1.

[0038] Optionally, the molar ratio of BNT to 2-aminothiophenol is 1:(0.5-3); more preferably, it is 1:1.

[0039] Optionally, the molar ratio of BNA-ABT to amyl nitrite is 1:(0.5-3); further optionally, it is 1:1.

[0040] Optionally, BTXI can be prepared using silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether as eluent E for purification.

[0041] Optionally, the volume ratio of dichloromethane to petroleum ether in the eluent E is 1:(0.4-2); more preferably, it is 1:1.

[0042] Optionally, the molar ratio of BTXA, imidazole and 2-ethylhexylamine is 1:(15-30):(2-30).

[0043] Optionally, silica gel can be used as the stationary phase and dichloromethane can be used as the eluent F for purification during the preparation of BTXI-Br.

[0044] Optionally, the molar ratio of BTXI to Br2 is 1:(0.5-1.5); more preferably, it is 1:1.

[0045] Optionally, when preparing BTXI-Bpin, silica gel is used as the stationary phase and a mixture of dichloromethane and petroleum ether is used as the eluent G for purification.

[0046] Optionally, the volume ratio of dichloromethane to petroleum ether in the eluent G is 1:(0.4-2); more preferably, it is 1:1.

[0047] Optionally, the molar ratio of BTXI-Br, pinacol diboronate, and 1,4-dioxane is (0.5-2):(3-6):(3-6).

[0048] A second aspect of the present invention provides a method for preparing a photoinitiator with low-power visible light and sunlight-induced polymerization properties, wherein the preparation steps of the photoinitiator include: S1. Provide intermediate A; S2. Provide intermediate B; S3. Intermediate A and intermediate B are mixed and subjected to palladium-catalyzed coupling reaction to prepare a photoinitiator.

[0049] Optionally, step S3 includes: Intermediate A, intermediate B, and potassium carbonate were dissolved in a mixed solvent of tetrahydrofuran and water. Palladium catalyst was added under a nitrogen atmosphere, and the reaction solution was heated to 60-70°C and stirred under reflux for 8-14 hours. After the reaction solution was cooled to room temperature, it was extracted with dichloromethane and water. The organic phase was dried over anhydrous sodium sulfate and the solvent was removed by vacuum evaporation. The crude product was purified by silica gel column chromatography to obtain the photoinitiator product.

[0050] The palladium catalysts include, but are not limited to: Pd(PPh3)4, Pd(dppf)Cl2, Pd(dba)2, Pd2(dba)3, Pd(OAc)2, PdCl2, PdCl2(PPh3)2, Pd(CH3CN)2Cl2, Pd-PEPPSI-IPr, Pd-PEPPSI-iPr, (NHC)Pd(allyl)Cl, Pd / C, Pd / Al2O3, etc.; optionally, the palladium catalysts include Pd(PPh3)4.

[0051] In some embodiments, when the photoinitiator is BTXI-1, step S3 includes: LW-CZ, BTXI-Bpin, and potassium carbonate were dissolved in a mixed solvent of tetrahydrofuran and water. Pd(PPh3)4 was added under a nitrogen atmosphere. The reaction solution was heated to 60-70°C and stirred under reflux for 8-14 hours. After the reaction solution was cooled to room temperature, it was extracted with dichloromethane and water. The organic phase was dried over anhydrous sodium sulfate and the solvent was removed by vacuum evaporation. The crude product was purified by silica gel column chromatography to obtain product BTXI-1 (orange).

[0052] Optionally, the molar ratio of LW-CZ, BTXI-Bpin and Pd(PPh3)4 is (0.1-0.3):(0.1-0.5):(0.001-0.01); further optionally, it is 0.14:0.17:0.005.

[0053] Optionally, the volume ratio of tetrahydrofuran to water in the mixed solvent is (3-10):1.

[0054] Optionally, BTXI-1 can be prepared using silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether as the eluent H for purification.

[0055] Optionally, the volume ratio of dichloromethane to petroleum ether in the eluent H is 1:(5-15); more preferably, it is 1:10.

[0056] In some embodiments, when the photoinitiator is BTXI-2, step S3 includes: LW-PXZ, BTXI-Bpin, and potassium carbonate were dissolved in a mixed solvent of tetrahydrofuran and water. Pd(PPh3)4 was added under a nitrogen atmosphere. The reaction solution was heated to 60-70°C and stirred under reflux for 8-14 hours. After the reaction solution was cooled to room temperature, it was extracted with dichloromethane and water. The organic phase was dried over anhydrous sodium sulfate and the solvent was removed by vacuum evaporation. The crude product was purified by silica gel column chromatography to obtain product BTXI-2 (red).

[0057] Optionally, the molar ratio of LW-PXZ, BTXI-Bpin and Pd(PPh3)4 is (0.1-0.3):(0.1-0.5):(0.001-0.01); further optionally, it is 0.14:0.17:0.005.

[0058] Optionally, the volume ratio of tetrahydrofuran to water in the mixed solvent is (3-10):1.

[0059] Optionally, when preparing BTXI-2, silica gel is used as the stationary phase and a mixture of dichloromethane and petroleum ether is used as eluent I for purification.

[0060] Optionally, the volume ratio of dichloromethane to petroleum ether in eluent I is 1:(5-15); more preferably, it is 1:10.

[0061] A third aspect of the present invention provides an application of a photoinitiator with low-power visible light and sunlight-induced polymerization properties, wherein the photoinitiator is applied to photopolymer materials.

[0062] The photoinitiator is applied to photopolymer materials; the raw materials for preparing the photopolymer materials include a photoinitiator, a co-initiator, and an acrylic resin monomer; the molar ratio of the photoinitiator, co-initiator, and acrylic resin monomer is 0.01~0.1:0.5~1:95~100.

[0063] Optionally, the photoinitiator includes BTXI-1 or BTXI-2.

[0064] Optionally, the amount of photoinitiator added is 0.01-1 mol.

[0065] The co-initiators may include diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroarsenate, diphenyliodonium tetrafluoroborate, substituted diphenyliodonium salts, aryl iodonium salts, ethyl 4-dimethylaminobenzoate (EDB), methyl 4-dimethylaminobenzoate, isooctyl 4-dimethylaminobenzoate, triethanolamine, triethylamine, N,N-dimethylaniline, N,N-dimethyl-p-toluidine, etc.

[0066] Optionally, the co-initiator includes DPI (diphenyliodonium hexafluorophosphate) and / or EDB (ethyl 4-dimethylaminobenzoate).

[0067] The acrylic resin monomers may include, but are not limited to, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), methyl methacrylate (MMA), ethyl methacrylate, butyl methacrylate, ethylene glycol diacrylate (EGDA), propylene glycol diacrylate (PGDA), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), ethoxylated trimethylolpropane triacrylate, ethoxylated pentaerythritol tetraacrylate, ethylene glycol phenyl ether acrylate (EGPEA), etc., with EGPEA being an option.

[0068] The fourth aspect of the present invention provides an application of a photoinitiator with low-power visible light and sunlight-induced polymerization properties, wherein the photoinitiator is applied to a photoresist.

[0069] Beneficial effects: This invention provides a photoinitiator with low-power visible light and sunlight-induced polymerization properties and its preparation method, which has the following advantages: (1) This invention provides a photoinitiator composed of spirofluorene as a bridging group and connecting different electron donor and acceptor units. This novel photoinitiator solves the technical pain point that existing photoinitiators cannot simultaneously achieve both broad-spectrum visible light absorption and high-efficiency electron transfer efficiency. It realizes high-efficiency free radical polymerization induced by low-power visible light and sunlight, and provides a new molecular design idea and technical solution for the development of a new generation of high-efficiency visible light initiators. (2) This invention introduces BTXI (thiobenzothiaxanthraimide) into the molecular structure through a specific synthetic route, giving full play to BTXI’s excellent broad-spectrum visible light capture ability. At the same time, it combines the spatial structural advantages of the spirofluorene bridging skeleton with the synergistic effect of electron donor and acceptor units, which significantly improves the electron transfer efficiency between the photoinitiator and the electron donor / acceptor in the photocatalytic system, effectively making up for the shortcomings of traditional BTXI compounds in the field of photopolymerization. (3) The photoinitiator synthesized in this invention can form an excited state through space charge transfer mechanism under low power visible light (such as 450nm band) and solar irradiation conditions, efficiently transfer charge with electron donors and acceptors and generate active free radicals, thereby efficiently initiating free radical polymerization; experimental results confirm that its polymerization efficiency and monomer conversion rate are significantly better than commercial photoinitiators (such as ITX), and it has mild, energy-saving and efficient polymerization characteristics, which are suitable for the needs of green manufacturing and sustainable development. Attached Figure Description

[0070] Figure 1 Example 1: Synthetic route diagram of photoinitiator BTXI-1; Figure 2 Example 2: Synthesis route of photoinitiator BTXI-2; Figure 3 1H NMR spectrum of photoinitiator BTXI-1 prepared in Example 1; Figure 4 . Carbon NMR spectrum of photoinitiator BTXI-1 prepared in Example 1; Figure 5 HRMS image of photoinitiator BTXI-1 prepared in Example 1; Figure 6 1H NMR spectrum of the photoinitiator BTXI-2 prepared in Example 2; Figure 7 . Carbon NMR spectrum of photoinitiator BTXI-2 prepared in Example 2; Figure 8 HRMS image of photoinitiator BTXI-2 prepared in Example 2; Figure 9 The UV-Vis absorption spectrum of BTXI-1 prepared in Example 1; Figure 10 Fluorescence emission spectrum of BTXI-1 prepared in Example 1; Figure 11 The UV-Vis absorption spectrum of BTXI-2 prepared in Example 2; Figure 12 Fluorescence emission spectrum of BTXI-2 prepared in Example 2; Figure 13 The polymerization conversion results of photopolymer materials in Application Examples 1-3 under 450nm illumination; Figure 14 Application Example 1-3: Polymerization conversion rate of photopolymer materials under sunlight. Detailed Implementation

[0071] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0072] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to a person skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this application.

[0073] In the specific implementation, the solvent for the n-butyllithium solution is n-hexane, and the concentration of n-butyllithium in the solution is 1.6 mol / L.

[0074] Unless otherwise specified, the solvent of the solution involved in this invention is water; the concentrations involved are mass concentrations, and the room temperature is 25°C.

[0075] Example 1 This embodiment provides a photoinitiator with low-power visible light and sunlight-induced polymerization properties, specifically BTXI-1, and its synthesis route is described below. Figure 1 The preparation steps include: S1. Synthetic intermediate A (LW-CZ) Dissolve 3.0 mmol CZ-Br in 60 mL of tetrahydrofuran and cool to -78 °C under argon protection. Then, slowly add 2.0 mL of 1.6 M n-butyllithium solution and stir the reaction at low temperature for 1 hour. Then, while maintaining the low temperature, add 3.0 mmol CZ-Br over 15 minutes. LW-Br was added and the reaction was continued at -78℃ for 2 hours, then slowly raised to room temperature and stirred for 3 hours. After the reaction was completed, water was added to quench the reaction, and the solvent was removed by evaporation under reduced pressure. The obtained solid was dissolved in dichloromethane and washed three times with deionized water. The organic phase was dried over anhydrous sodium sulfate, filtered, and concentrated to obtain a crude intermediate. The crude intermediate was dissolved in a mixed solution of acetic acid and concentrated hydrochloric acid (the volume ratio of acetic acid to concentrated hydrochloric acid was 10:1, and the concentration of concentrated hydrochloric acid was 36wt%), heated to 110℃ and refluxed for 4 hours. After cooling to room temperature, the precipitate was filtered and washed with petroleum ether. The crude product was purified by silica gel column chromatography (using silica gel as the stationary phase, and a mixture of dichloromethane and petroleum ether as eluent A, with a volume ratio of dichloromethane to petroleum ether of 3:7) to obtain a white solid product LW-CZ 464 mg, with a yield of 32%.

[0076] S2. Synthetic intermediate B (BTXI-Bpin) S2.1 Preparation of BNA-ABT 10.0 mmol BNA, 10.0 mmol 2-aminobenzylthiophenol, and 21.7 mmol potassium carbonate were dissolved in 50 mL of anhydrous N,N-dimethylformamide. The mixture was heated to 150 °C under a nitrogen atmosphere and stirred under reflux for 1 hour. After the reaction was completed, the reaction solution was cooled to room temperature. The reaction solution was extracted three times with a mixture of dichloromethane and water (mass ratio 1:1). After drying with anhydrous sodium sulfate, the solution was filtered and the solvent was removed by vacuum evaporation to obtain the crude product. The crude product was purified by silica gel column chromatography (using silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether as eluent D, with a volume ratio of dichloromethane to petroleum ether of 1:1) to obtain 1.21 g of intermediate product BNA-ABT, with a yield of 38%. S2.2 Preparation of BTXA 20.0 mmol BNA-ABT and 20.0 mmol amyl nitrite were dissolved in 100 mL N,N-dimethylformamide. The mixture was heated to 150 °C and refluxed for 0.5 h under a nitrogen atmosphere. The reaction solution was then cooled to room temperature, and water was added to precipitate the product, yielding 4.20 g of intermediate product BTXA, with a yield of 69%. S2.3 Preparation of BTXI Under a nitrogen atmosphere, 8.2 mmol BTXA, 236.7 mmol imidazole, and 27.9 mmol 2-ethylhexylamine were mixed and stirred at 140 °C for 6 hours. After the reaction solution was cooled to room temperature, it was extracted three times with a mixture of dichloromethane and water (mass ratio 1:1). The organic phase was dried over anhydrous sodium sulfate, and the solvent was removed by vacuum evaporation. The crude product was purified by column chromatography (using silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether as eluent E, with a volume ratio of dichloromethane to petroleum ether of 1:1) to obtain 2.2 g of intermediate BTXI, with a yield of 64%. S2.4 Preparation of BTXI-Br 1.34 mmol BTXI was dissolved in 100 mL of dichloromethane, and a dichloromethane solution containing 1 M Br2 (1.34 mmol Br2) was added. The mixture was stirred at room temperature for 12 hours. The solution was washed successively with saturated sodium thiosulfate solution, water, and saturated brine. The organic phase was dried over anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography (using silica gel as the stationary phase and dichloromethane as the eluent F) to obtain the intermediate product BTXI-Br 568 mg, with a yield of 93%. Preparation of BTXI-Bpin using S2.5 Under a nitrogen atmosphere, 4.52 mmol of potassium acetate was added to 40 mL of anhydrous 1,4-dioxane containing 1.52 mmol of BTXI-Br and 4.33 mmol of pinacol diborate. The reaction solution was bubbled with nitrogen to remove oxygen for 30 min. 0.07 mmol of [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride was added, and the mixture was heated to 85 °C and stirred for 12 h under nitrogen protection. After cooling to room temperature, the reaction solution was added to 200 mL of water and extracted with dichloromethane (3 times, 50 mL each time). The organic phase was dried over anhydrous sodium sulfate, and the solvent was removed by vacuum evaporation. The crude product was purified by silica gel column chromatography (using silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether as eluent G, with a volume ratio of dichloromethane to petroleum ether of 1:1) to obtain 675 mg of BTXI-Bpin, with a yield of 82%.

[0077] S3. Preparation of photoinitiator (BTXI-1) 0.14 mmol LW-CZ, 0.17 mmol BTXI-Bpin, and 0.7 mmol potassium carbonate were dissolved in a mixed solvent of 6 mL tetrahydrofuran and 1 mL water. 0.005 mmol Pd(PPh3)4 was added under a nitrogen atmosphere. The reaction mixture was heated to 66 °C and refluxed with stirring for 12 hours. After cooling to room temperature, the mixture was extracted three times with a 1:1 mixture of dichloromethane and water. The organic phase was dried over anhydrous sodium sulfate, and the solvent was removed by vacuum evaporation. The crude product was purified by silica gel column chromatography (using silica gel as the stationary phase and a 1:10 volume ratio of dichloromethane to petroleum ether as eluent G) to obtain 60 mg of the orange product BTXI-1, with a yield of 52%.

[0078] Example 2 This embodiment provides a photoinitiator with low-power visible light and sunlight-induced polymerization properties, specifically BTXI-2, and its synthesis route is described below. Figure 2 Its preparation steps include: S1. Synthetic intermediate A (LW-PXZ) S1.1 Preparation of PXZ-Br 10.0 mmol PXZ, 15.0 mmol 2-bromoiodobenzene, 3.7 mmol cuprous iodide, 0.38 mmol 18-crown ether-6, and 36.2 mmol potassium carbonate were dissolved in 80 mL o-dichlorobenzene. The mixture was heated to 180 °C and refluxed under a nitrogen atmosphere for 48 hours. After cooling to room temperature, the o-dichlorobenzene was removed by rotary evaporation. The mixture was then extracted three times with a mixture of dichloromethane and water (1:1 by mass). After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography (using silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether as eluent B, with a volume ratio of dichloromethane to petroleum ether of 3:7) to obtain 2.36 g of intermediate product PXZ-Br, with a yield of 70%. S1.2 Preparation of LW-PXZ Under an argon atmosphere, 3.0 mmol of PXZ-Br was dissolved in 60 mL of tetrahydrofuran. After cooling to -78 °C, 2.0 mL of 1.6 M n-butyllithium solution was added dropwise using a syringe. The mixture was stirred at -78 °C for 1 hour, and then 3.0 mmol of PXZ-Br was added. 1-Bromo-9-fluorenone was reacted at -78°C for 2 hours. 10 mL of water was added to the reaction system to quench the reaction, and then the solvent was removed by vacuum evaporation. The resulting solid was dissolved in 100 mL of dichloromethane and washed with water (3 times, 50 mL each time). The organic layer was then separated, dried with anhydrous sodium sulfate, filtered, and evaporated. The crude product was dissolved in a mixture of 30 mL of acetic acid and 8 mL of hydrochloric acid and reacted at 110°C for 4 hours. The reaction solution was cooled to room temperature and extracted three times with a mixture of dichloromethane and water (mass ratio 1:1). After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography (using silica gel as the stationary phase and petroleum ether as eluent C) to obtain product LW-PXZ 479 mg, with a yield of 32%.

[0079] S2. Synthesize intermediate B (BTXI-Bpin, preparation steps are the same as step S2 in Example 1); S3. Preparation of photoinitiator (BTXI-2) 0.14 mmol LW-CZ, 0.17 mmol BTXI-Bpin, and 0.7 mmol potassium carbonate were dissolved in a mixed solvent of 6 mL tetrahydrofuran and 1 mL water. 0.005 mmol Pd(PPh3)4 was added under a nitrogen atmosphere. The reaction mixture was heated to 66 °C and refluxed with stirring for 12 hours. After cooling to room temperature, the mixture was extracted three times with a 1:1 mixture of dichloromethane and water. The organic phase was dried over anhydrous sodium sulfate, and the solvent was removed by vacuum evaporation. The crude product was purified by silica gel column chromatography (using silica gel as the stationary phase and a 1:10 volume ratio of dichloromethane to petroleum ether as eluent I) to obtain 74 mg of the red product BTXI-2, with a yield of 63%.

[0080] Application Example 1 A photopolymer material; the raw materials for preparing the photopolymer material include a photoinitiator (BTXI-1 obtained in Example 1), a co-initiator (DPI and EDB) and an acrylic resin monomer (EGPEA); the molar ratio of BTXI-1, DPI, EDB and EGPEA is 0.05:0.5:0.5:100.

[0081] The preparation method of the photopolymer material is as follows: the raw materials for preparing the photopolymer material are mixed, stirred and dissolved evenly at room temperature, and then a polymerization reaction is carried out; the polymerization conditions are 450nm visible light polymerization or sunlight polymerization (see the test section for details).

[0082] Application Example 2 A photopolymer material, the specific implementation is the same as in application example 1; the difference is that the photoinitiator is replaced with BTXI-2 obtained in example 2.

[0083] Application Example 3 A photopolymer material, the specific implementation is the same as in application example 1; the difference is that the photoinitiator is replaced with the commercial photoinitiator ITX.

[0084] Performance testing 1. Compound Characterization (1) Nuclear magnetic resonance hydrogen spectrum ( 1 (1H NMR): BTXI-1 prepared in Example 1 and BTXI-2 prepared in Example 2 were characterized by proton NMR using a Bruker 400 MHz superconducting nuclear magnetic resonance spectrometer with deuterated dichloromethane as solvent; the test results are shown in […]. Figure 3 , Figure 6 .

[0085] (2) Carbon nuclear magnetic resonance spectrum ( 13C10 NMR): BTXI-1 prepared in Example 1 and BTXI-2 prepared in Example 2 were characterized using a Bruker 400 MHz superconducting nuclear magnetic resonance spectrometer with deuterated dichloromethane as the solvent; the test results are shown in […]. Figure 4 , Figure 7 .

[0086] (3) High-resolution mass spectrometry (HRMS): BTXI-1 and BTXI-2 were dissolved in dichloromethane to prepare test solutions of 1 mg / mL. High-resolution mass spectrometry was performed using an LCMS-2020 liquid chromatography-mass spectrometry system. The test results are shown in […]. Figure 5 , Figure 8 .

[0087] (4) Ultraviolet-visible absorption spectrum: Using a Shimadzu UV-2700 ultraviolet-visible spectrophotometer, the absorption spectra of BTXI-1 and BTXI-2 in the range of 300–600 nm were measured at 1 × 10⁻⁶ nm. -5 The UV-Vis absorption spectrum of dichloromethane in an aqueous solution of mol / L was used for detection; the test results are shown in [Figure number missing]. Figure 9 , Figure 11 .

[0088] (5) Fluorescence emission spectrum: Using a steady-state / transient fluorescence spectrometer FLS980 with an excitation wavelength of 440 nm, BTXI-1 and BTXI-2 were analyzed at a wavelength of 1×10⁻⁶ nm. -5 The fluorescence emission spectrum of the mol / L tetrahydrofuran aqueous solution was used for detection; the test results are shown in […]. Figure 10 , Figure 12 .

[0089] Figure 3 The 1H NMR spectrum of BTXI-1 prepared in Example 1 is as follows: 1 H NMR (400 MHz, Chloroform- d ) δ 8.14 (d, J = 8.0 Hz, 1H), 8.04 (d, J = 8.0 Hz, 1H), 7.96 (d, J =8.0 Hz, 1H), 7.93 – 7.85 (m, 1H), 7.61 – 7.50 (m, 2H), 7.51 – 7.43 (m, 2H),7.37 – 7.33 (m, 2H), 7.28 (q, 2H), 7.25–7.07 (m, 4H), 7.06 – 6.97 (m, 2H), 6.97 – 6.87 (m, 2H), 6.84 (d, J= 8.0 Hz, 1H), 6.74 (d, J = 8.0 Hz, 1H), 6.67 –6.67 (m, 2H), 4.24 – 4.03 (m, 2H), 2.02 (d, J = 16.0 Hz, 1H), 1.55 – 1.34 (m, 8H), 1.11 – 0.86 (m, 6H). By proton NMR spectrum ( 1 ¹H NMR analysis showed that the signal peaks at each chemical shift corresponded one-to-one with the molecular structure of the target product BTXI-1, with clear peak shapes and reasonable results, and no obvious impurity peaks. These results indicate that the photoinitiator BTXI-1 was successfully prepared in Example 1, and the product has a simple structure and high purity.

[0090] Figure 4 The carbon NMR spectrum of BTXI-1 prepared in Example 1 is as follows: 13 C NMR (100 MHz, Chloroform- d ) δ 157.2, 140.0, 137.1, 132.5, 132.0, 131.6, 130.3, 129.9, 129.1, 128.9, 128.5, 127.9, 127.4, 127.2, 126.8, 126.5, 126.4, 125.3, 125.3, 124.7, 123.3, 121.8, 121.5, 121.1, 120.9, 120.0, 120.0, 119.6, 118.3, 117.4, 113.7, 111.5, 56.4, 44.0, 38.3, 38.1, 31.0, 30.8, 28.9, 24.1, 23.2, 14.3, 10.9, 10.8. These values ​​were obtained from carbon NMR spectroscopy. 13 C10 NMR analysis showed that the signal peaks at each chemical shift corresponded one-to-one with the molecular structure of the target product BTXI-1, with clear peak shapes and reasonable results, and no obvious impurity signals. These results indicate that the photoinitiator BTXI-1 was successfully prepared in Example 1, and the product has a simple structure and high purity.

[0091] Figure 5 The image shows the HRMS plot of BTXI-1 obtained in Example 1. The theoretical value C of the photoinitiator BTXI-1, which possesses space charge transfer properties, was calculated. 57 H 43 N2O2S + [(M+H) +The m / z value was 819.3040, while the actual m / z value obtained by mass spectrometry was 819.3044, which is consistent with the relative molecular mass of the synthesized photoinitiator BTXI-1. This further proves that the compound prepared in Example 1 is the target product BTXI-1, and that the compound has a simple structure and high purity. Combining the above NMR and mass spectrometry results, it can be concluded that the product obtained in Example 1 is the photoinitiator BTXI-1.

[0092] Figure 6 The 1H NMR spectrum of BTXI-2 prepared in Example 2 is as follows: 1 H NMR (400 MHz,Methylene Chloride- d 2) δ 8.37 – 8.34 (m, 1H), 8.18 – 8.13 (m, 1H), 8.06 – 8.03(m, 1H), 8.01 – 7.84 (m, 2H), 7.59 – 7.53 (m, 1H), 7.45 – 7.33 (m, 2H), 7.28– 7.12 (m, 5H), 7.02 (d, J = 8 Hz, 1H), 6.97 – 6.91 (m, 2H), 6.85 (d, J = 8.0Hz, 1H), 6.73 – 6.39 (m, 5H), 6.36 – 6.23 (m, 1H), 6.11 (d, J = 8.0 Hz, 1H), 6.06 – 6.00 (m, 1H), 4.07 – 3.82 (m, 2H), 1.95 – 1.81 (m, 1H), 1.43 – 1.27 (m, 8H), 1.00 – 0.88 (m, 6H). By proton NMR spectrum ( 1 ¹H NMR analysis showed that the signal peaks at each chemical shift corresponded one-to-one with the molecular structure of the target product BTXI-2, with clear peak shapes and reasonable results, and no obvious impurity peaks. These results indicate that Example 2 successfully prepared the photoinitiator BTXI-2, and the product has a simple structure and high purity.

[0093] Figure 7 The carbon NMR spectrum of BTXI-2 prepared in Example 2 is as follows: 13 C NMR (100 MHz,Methylene Chloride- d 2) δ160.5, 164.7, 137.6, 133.6, 133.4, 132.9, 131.7, 130.7, 130.4, 130.34, 130.3, 129.5, 129.1, 128.8, 128.6, 128.0, 127.8, 127.3, 127.0, 122.4, 121.0, 120.8, 120.4, 39.2, 39.1, 32.0, 32.0, 30.1, 30.0, 25.2, 25.1, 24.5, 24.5, 15.3, 15.3, 11.7, 11.7. Carbon NMR spectroscopy 13 C10 NMR analysis showed that the signal peaks at each chemical shift corresponded one-to-one with the molecular structure of the target product BTXI-2, with clear peak shapes and reasonable results, and no obvious impurity signals. These results indicate that the photoinitiator BTXI-2 was successfully prepared in Example 2 with high product purity.

[0094] Figure 8 The image shows the HRMS plot of BTXI-2 prepared in Example 2. The theoretical value C of the photoinitiator BTXI-2, which possesses space charge transfer properties, was calculated. 57 H 43 N2O3S + [(M+H) + The relative molecular mass of the synthesized photoinitiator BTXI-2 was 835.2989, while the actual m / z value obtained by mass spectrometry was 835.2990. This is consistent with the relative molecular mass of the synthesized photoinitiator BTXI-2. This further proves that the compound prepared in Example 2 is the target product BTXI-2, and that the compound has a simple structure and high purity. Combining the above NMR and mass spectrometry results, it can be concluded that the product obtained in Example 2 is the photoinitiator BTXI-2.

[0095] Figure 9 , Figure 11 BTXI-1 prepared in Example 1 and BTXI-2 prepared in Example 2 were respectively tested at 1×10⁻⁶. -5m UV-Vis absorption spectrum of dichloromethane in ol / L. From Figure 9 It can be seen that BTXI-1 has a high molar extinction coefficient in the visible light region, and its absorption is located in the ultraviolet-visible band; from Figure 10 It can be seen that BTXI-2 has a high molar extinction coefficient in the visible light region, and its absorption is located in the ultraviolet-visible band.

[0096] Figure 10 , Figure 12 BTXI-1 prepared in Example 1 and BTXI-2 prepared in Example 2 were respectively tested at 1×10⁻⁶. -5m Fluorescence emission spectrum in tetrahydrofuran at ol / L. From Figure 10 It can be seen that BTXI-1 has a broad emission spectrum and weak fluorescence emission, exhibiting space charge transfer emission properties; from Figure 12 It can be seen that BTXI-2 has a broad emission spectrum and weak fluorescence emission, exhibiting emission properties of space charge transfer.

[0097] 2. Polymerization characteristics This application employs real-time infrared spectroscopy to monitor the photopolymerization behavior of different photoinitiation systems (Application Examples 1-3). By tracking the change in the intensity of the infrared absorption peak of characteristic double bonds in the monomer over time, the monomer conversion rate (%) was calculated, and a polymerization conversion graph was plotted accordingly. Figure 13 and Figure 14 ;in Figure 13 The polymerization conversion results of the photopolymer materials in Application Examples 1-3 under 450nm illumination are shown. Figure 14 The results show the polymerization conversion rate of the photopolymer materials in Examples 1-3 under sunlight.

[0098] The polymerization efficiency of the photopolymerization systems in Application Examples 1-3 varies significantly depending on the type of photoinitiator. Under identical conditions of 50 seconds of 450nm visible light irradiation, exposure power, and system composition, BTXI-2 achieved a conversion rate of 98% in EGPEA monomers, BTXI-1 achieved 90%, while the commercial photoinitiator ITX achieved only 0.06%. Under sunlight irradiation, BTXI-2 also exhibited a faster polymerization rate and higher conversion rate in EGPEA monomers. These results demonstrate that the photoinitiators described in this application exhibit excellent polymerization initiation capabilities under low-power, long-wavelength visible light and even sunlight irradiation, possessing the potential for efficient photopolymerization under mild and environmentally friendly conditions.

[0099] In summary, this application successfully designed and synthesized a class of photoinitiators using spirofluorene-like structures as bridging units, connecting electron donor and electron acceptor units, exhibiting significant space charge transfer characteristics. The core advantage of this class of photoinitiators lies in their ability to generate active free radicals in situ under low-power visible light and even sunlight irradiation through efficient intramolecular and intermolecular charge transfer mechanisms, thereby efficiently initiating free radical polymerization reactions. Experimental results show that the polymerization characteristics of this class of photoinitiators under 450nm visible light and sunlight are significantly superior to existing photoinitiators (such as ITX), providing novel molecular design ideas and strategies for developing a new generation of efficient and energy-saving broadband visible light photoinitiators, with broad application prospects.

Claims

1. A photoinitiator with low-power visible light and sunlight-induced polymerization properties, characterized in that, The photoinitiator is composed of spirofluorene-like structures as bridging units, which connect electron donor units and electron acceptor units; The electron acceptor unit includes sulfur.

2. The photoinitiator according to claim 1, characterized in that, The electron acceptor unit includes BTXI.

3. The photoinitiator according to claim 2, characterized in that, The photoinitiator has one of the following molecular structures: 。 4. The photoinitiator according to claim 3, characterized in that, The photoinitiator has one of the following molecular structures: 。 5. The photoinitiator according to claim 4, characterized in that, The raw materials for preparing the photoinitiator include intermediate A and intermediate B; The intermediate A includes LW-CZ or LW-PXZ; The intermediate B includes BTXI-Bpin; When intermediate A is LW-CZ, the photoinitiator is BTXI-1; when intermediate A is LW-PXZ, the photoinitiator is BTXI-2.

6. A method for preparing the photoinitiator according to claim 5, characterized in that, The preparation steps of the photoinitiator include: S1. Provide intermediate A; S2. Provide intermediate B; S3. Intermediate A and intermediate B are mixed and subjected to palladium-catalyzed coupling reaction to prepare a photoinitiator. Step S3 includes: Intermediate A, intermediate B, and potassium carbonate were dissolved in a mixed solvent of tetrahydrofuran and water. Palladium catalyst was added under a nitrogen atmosphere, and the reaction solution was heated to 60-70°C and stirred under reflux for 8-14 hours. After the reaction solution was cooled to room temperature, it was extracted with dichloromethane and water. The organic phase was dried over anhydrous sodium sulfate and the solvent was removed by vacuum evaporation. The crude product was purified by silica gel column chromatography to obtain the photoinitiator product.

7. The method for preparing the photoinitiator according to claim 6, characterized in that, The preparation steps of LW-CZ include: dissolving CZ-Br and LW-Br in tetrahydrofuran, cooling to -70~-80℃ under argon protection, adding n-butyllithium solution, maintaining low temperature and stirring for 0.5-3 hours, then maintaining low temperature and adding LW-Br within 30 minutes, continuing to react at -70~-80℃ for 0.5-2 hours after addition, raising to room temperature and stirring for 1-5 hours, adding water to quench after the reaction, removing the solvent by vacuum evaporation, dissolving the obtained solid in dichloromethane and washing with water, wherein the organic phase is dried with anhydrous sodium sulfate, filtered and concentrated to obtain a crude intermediate, dissolving the crude intermediate in a mixed solution of acetic acid and concentrated hydrochloric acid, heating to 100-120℃ and refluxing for 2-6 hours, cooling to room temperature and filtering the precipitate, washing with petroleum ether, purifying the crude product by silica gel column chromatography to obtain product LW-CZ; The preparation steps of the LW-PXZ include: PXZ, 2-bromoiodobenzene, cuprous iodide, 18-crown ether-6, and potassium carbonate were dissolved in o-dichlorobenzene. The mixture was heated to 160-190℃ and refluxed under a nitrogen atmosphere for 24-72 hours. The reaction solution was then cooled to room temperature, and o-dichlorobenzene was removed by rotary evaporation. The mixture was then extracted with dichloromethane and water, dried over anhydrous sodium sulfate, and the crude product was purified by silica gel column chromatography to obtain the intermediate product PXZ-Br. Under an argon atmosphere, PXZ-Br was dissolved in tetrahydrofuran, cooled to -70 to -80°C, and then n-butyllithium solution was added. The mixture was stirred at -70 to -80°C for 0.5 to 2 hours, followed by the addition of 1-bromo-9-fluorenone. The reaction was carried out at -70 to -80°C for 1 to 3 hours. Water was added to the reaction system to quench the reaction, and the solvent was removed by vacuum evaporation. The resulting solid was dissolved in dichloromethane and washed with water. The organic layer was then separated, dried with anhydrous sodium sulfate, filtered, and evaporated to obtain the crude product, which was directly used for the next step. The crude product was dissolved in a mixture of acetic acid and hydrochloric acid and reacted at 100 to 130°C for 2 to 6 hours. The reaction solution was cooled to room temperature and extracted with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography to obtain product LW-PXZ. The intermediate A satisfies at least one of the following conditions: (1) When preparing LW-CZ, silica gel was used as the stationary phase and a mixture of dichloromethane and petroleum ether was used as eluent A for purification. (2) The volume ratio of dichloromethane to petroleum ether in the eluent A is (1-5):(4-10); (3) The molar ratio of CZ-Br and LW-Br is 1:(0.8-1.2); (4) When preparing PXZ-Br, silica gel is used as the stationary phase and a mixture of dichloromethane and petroleum ether is used as eluent B for purification; (5) The volume ratio of dichloromethane to petroleum ether in the eluent B is (1-5):(4-10); (6) When preparing LW-PXZ, silica gel was used as the stationary phase and petroleum ether was used as the eluent C for purification; (7) The molar ratio of PXZ to 2-bromoiodobenzene is 1:(1-3); (8) The molar ratio of PXZ-Br and 1-bromo-9-fluorenone is 1:(0.8-1.2).

8. The method for preparing the photoinitiator according to claim 6, characterized in that, The preparation steps of the BTXI-Bpin include: BNA, 2-aminobenzylthiophenol, and potassium carbonate were dissolved in N,N-dimethylformamide and heated to 120-180°C under a nitrogen atmosphere. The mixture was stirred and refluxed for 0.5-3 hours. After the reaction was completed, the reaction solution was cooled to room temperature and extracted with dichloromethane and water. The solution was dried over anhydrous sodium sulfate, filtered, and the solvent was removed by vacuum evaporation to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain the intermediate product BNA-ABT. BNA-ABT and isoamyl nitrite were dissolved in N,N-dimethylformamide, heated to 130-180℃ and refluxed under a nitrogen atmosphere. After reacting for 0.2-1 hours, the reaction solution was cooled to room temperature, and water was added to precipitate the product, yielding the intermediate product BTXA. Under a nitrogen atmosphere, BTXA, imidazole and 2-ethylhexylamine were mixed and stirred at 120-160℃ for 3-10 hours. After the reaction solution was cooled to room temperature, it was extracted with dichloromethane and water. The organic phase was dried with anhydrous sodium sulfate and the solvent was removed by vacuum evaporation. The crude product was purified by column chromatography to obtain the intermediate product BTXI. BTXI was dissolved in dichloromethane, and a dichloromethane solution containing 0.1-2M Br2 was added. The mixture was stirred at room temperature for 8-16 hours. The mixture was washed successively with saturated sodium thiosulfate solution, water, and saturated brine. The organic phase was dried over anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain the intermediate product BTXI-Br. Under a nitrogen atmosphere, potassium acetate was added to anhydrous 1,4-dioxane containing dissolved BTXI-Br and pinacol diborate. After bubbling the reaction solution to remove oxygen, [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride was added. The mixture was heated to 80-95°C and stirred for 10-15 hours under nitrogen protection. After cooling the reaction solution to room temperature, it was mixed with water and extracted with dichloromethane. The organic phase was dried over anhydrous sodium sulfate, and the solvent was removed by vacuum evaporation. The crude product was purified by silica gel column chromatography to obtain the product BTXI-Bpin. The intermediate B satisfies at least one of the following conditions: (1) When preparing BNA-ABT, silica gel was used as the stationary phase and a mixture of dichloromethane and petroleum ether was used as eluent D for purification; (2) The volume ratio of dichloromethane to petroleum ether in the eluent D is 1:(0.4-2); (3) The molar ratio of BNT and 2-aminothiophenol is 1:(0.5-3); (4) The molar ratio of BNA-ABT and isoamyl nitrite is 1:(0.5-3); (5) When preparing BTXI, silica gel was used as the stationary phase and a mixture of dichloromethane and petroleum ether was used as eluent E for purification; (6) The volume ratio of dichloromethane to petroleum ether in the eluent E is 1:(0.4-2); (7) The molar ratio of BTXA, imidazole and 2-ethylhexylamine is 1:(15-30):(2-30); (8) When preparing BTXI-Br, silica gel was used as the stationary phase and dichloromethane was used as the eluent F for purification; (9) The molar ratio of BTXI to Br2 is 1:(0.5-1.5); (10) When preparing BTXI-Bpin, silica gel was used as the stationary phase and a mixture of dichloromethane and petroleum ether was used as the eluent G for purification. (11) The volume ratio of dichloromethane to petroleum ether in the eluent G is 1:(0.4-2); (12) The molar ratio of BTXI-Br, pinacol diboronic acid ester and 1,4-dioxane is (0.5-2):(3-6):(3-6).

9. An application of the photoinitiator according to any one of claims 1-5, characterized in that, The photoinitiator is applied to photopolymer materials; the raw materials for preparing the photopolymer materials include a photoinitiator, a co-initiator, and an acrylic resin monomer; the molar ratio of the photoinitiator, co-initiator, and acrylic resin monomer is 0.01~0.1:0.5~1:95~100.

10. An application of the photoinitiator according to any one of claims 1-5, characterized in that, The photoinitiator is applied to the photoresist.

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