Photoinitiator with space charge transfer property as well as preparation method and application thereof

Abstract

The invention relates to a photoinitiator with a space charge transfer property and a preparation method and application thereof, and belongs to the technical field of photoinitiators. The photoinitiator is formed by connecting spirofluorene as a bridging group with different electron donor and acceptor units. Under the condition of low-power visible light or sunlight illumination, the molecule can form an excited state through a space charge transfer mechanism, and then charge transfer is carried out between the molecule and an electron acceptor to generate active free radicals, so that free radical polymerization is efficiently initiated. Experiments show that the polymerization efficiency and the monomer conversion rate of the photoinitiator are superior to those of a commercial photoinitiator ITX under the irradiation of 365 nm, 405 nm, 450 nm and sunlight. The invention not only expands the application range of MR-TADF molecules, but also provides a new design thought for developing an efficient visible light initiator.

Description

Technical Field

[0001] This application relates to the field of organic photoinitiator materials technology, and more specifically, to a photoinitiator with space charge transfer properties, its preparation method and application. Background Technology

[0002] Photopolymerization technology has been widely used in coatings, inks, adhesives, and 3D printing due to its advantages such as high efficiency, energy saving, and environmental friendliness. The core of this technology lies in photoinitiators, which generate active species (such as free radicals or cations) under light irradiation, thereby initiating monomer polymerization and crosslinking.

[0003] Currently, while commercially available photoinitiator systems (such as ITX) perform well under conventional ultraviolet light or high-power visible light, their applications still face significant limitations. First, many highly efficient photoinitiators concentrate their absorption primarily in the ultraviolet region, exhibiting low utilization efficiency for visible light, especially long-wavelength visible light (e.g., 450 nm), which restricts their application in deep curing and ultraviolet-sensitive systems (such as biological tissues). Second, achieving efficient curing typically requires high light power, which not only increases energy consumption and equipment costs but may also lead to substrate damage due to localized overheating. Furthermore, oxygen in the air has a significant inhibitory effect on free radical polymerization, resulting in poor surface curing, which is particularly pronounced under low-power light conditions. Therefore, developing a novel photoinitiator capable of overcoming oxygen inhibition and achieving efficient polymerization under low-power, wide-wavelength visible light, and even sunlight, has become an urgent need in this field. Summary of the Invention

[0004] To overcome at least one of the problems existing in the prior art, the primary objective of this application is to provide a low-power, high-efficiency photoinitiator under visible light. This type of photoinitiator improves the excited-state lifetime through space charge transfer, while employing an MR-TADF framework molecule to provide its ability to absorb visible light and transfer excited-state electrons.

[0005] Another objective of this application is to provide a method for preparing the aforementioned photoinitiator with space charge transfer properties.

[0006] Another object of this application is to provide the application of the above-mentioned photoinitiator with space charge transfer properties in photopolymerization.

[0007] To solve the above-mentioned technical problems, the technical solution adopted in this application is: A photoinitiator with space charge transfer properties, wherein the photoinitiator is a spirofluorene-based bridge and has one of the following molecular structures: ; Where R represents the multiple resonance-thermally activated delayed fluorescence functional group.

[0008] Preferably, the photoinitiator with space charge transfer properties has any one of the following molecular structures: .

[0009] More preferably, the photoinitiator with space charge transfer properties has one of the following molecular structures: .

[0010] This application also provides a method for preparing the above-mentioned photoinitiator with space charge transfer properties, the method comprising the following steps: S1. Preparation of intermediate PXZ-Br PXZ, 2-bromoiodobenzene, cuprous iodide, 18-crown-6 ether, and potassium carbonate were dissolved in a two-necked flask containing o-dichlorobenzene. The mixture was then refluxed at 180°C under a nitrogen atmosphere for 48 hours. The reaction solution was cooled to room temperature, and the solvent was rotary evaporated. The mixture was repeatedly extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography to obtain the intermediate PXZ-Br. The structural formula of PXZ-Br is as follows: ; S2. Preparation of intermediate LW-Br Under argon atmosphere, PXZ-Br was dissolved in tetrahydrofuran in a 200 mL double-necked flask. After cooling the solution to -78°C, 1.6 M n-butyllithium was added dropwise using a syringe. The resulting mixture was stirred at -78°C for 1 hour, followed by the addition of compound 1-bromo-9H-fluorene-9-one over 15 minutes. After reacting at -78°C for 2 hours, the mixture was stirred at room temperature. Water was added to quench the reaction, and the tetrahydrofuran was evaporated under reduced pressure. The resulting solid was dissolved in dichloromethane and washed with water. The organic layer was then separated, dried with sodium sulfate, filtered, and evaporated. This solid was used directly in the next reaction without further purification. The crude product was dissolved in acetic acid and hydrochloric acid and reacted at 110°C. After cooling to room temperature, it was repeatedly extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography with pure petroleum ether to obtain the intermediate LW-Br. The structural formula of LW-Br is as follows: ; S3. Preparation of intermediate PZ-Br 2,6-Difluorobromobenzene, 3,6-di-tert-butylcarbazole, and potassium carbonate were dissolved in a two-necked flask containing N,N-dimethylformamide. The mixture was then refluxed at 150°C under a nitrogen atmosphere for 24 hours. After cooling to room temperature, water was added to precipitate the product. No further purification was required to obtain the intermediate PZ-Br. The structural formula of PZ-Br is as follows: ; S4. Preparation of intermediate MR The PZ-Br obtained in step S3 was dissolved in a two-necked flask containing ultra-dry o-xylene solution. Then, under a nitrogen atmosphere, the mixture was cooled to -20°C, and a hexane solution containing n-butyllithium was slowly added dropwise. After reacting for 15 min, the mixture was reacted at room temperature for 2 h. Next, in a cryogenic reactor, boron tribromide was added dropwise, and the mixture was reacted at low temperature for 15 min. Then, the mixture was stirred at room temperature for 1 h. Finally, N,N-diisopropylethylamine was added dropwise at low temperature, and the mixture was reacted at low temperature for 15 min. Then, the temperature was increased to 120°C and reacted for 12 h. After the reaction was complete, the mixture was extracted with water and ethyl acetate, evaporated to dryness, and recrystallized with ethanol solution to finally obtain the yellow solid product MR. The structural formula of MR is as follows: ; S5. Preparation of intermediate MR-Bpin The MR obtained in step S4, 1,5-cyclooctadiene iridium chloride dimer, pinacol diborate, and 4,4'-di-tert-butyl-2,2'-dipyridine were dissolved in a two-necked flask containing an ultra-dry tetrahydrofuran solution. The mixture was then reacted at 120°C for 12 h under a nitrogen atmosphere. After the reaction was complete, the product was extracted with water and ethyl acetate. The crude product was purified by silica gel column chromatography to obtain a yellow solid product, MR-Bpin. The structural formula of MR-Bpin is as follows: ; S6. Preparation of the final product MR-1 LW-Br, MR-Bpin, and potassium carbonate were dissolved in a mixture of tetrahydrofuran and water. Pd3(PPd3)4 was then added under N2 atmosphere. The reaction mixture was heated to 66°C and refluxed with stirring for 12 hours. After cooling to room temperature, the product was extracted with dichloromethane and water and dried with anhydrous sodium sulfate. The crude product was purified by silica gel column chromatography to obtain product MR-1.

[0011] More preferably, the method for preparing the photoinitiator with space charge transfer properties further includes: Preparation of S7 intermediate BP-Br Under nitrogen atmosphere, PXZ-Br was dissolved in tetrahydrofuran in a double-necked flask. After cooling the solution to -78°C, 1.6 M n-butyllithium was added dropwise using a syringe. The resulting mixture was stirred at -78°C for 1 hour, followed by the addition of compound 2-bromobenzophenone over 15 minutes. After reacting at -78°C for 2 hours, the mixture was stirred at room temperature for 3 hours. Water was added to quench the reaction, and the tetrahydrofuran was evaporated under reduced pressure. The resulting solid was dissolved in dichloromethane and washed with water. The organic layer was then separated, dried with sodium sulfate, filtered, and evaporated. This solid was used directly in the next reaction without further purification. The crude product was dissolved in acetic acid and hydrochloric acid and reacted at 110°C for 4 hours. After cooling to room temperature, it was repeatedly extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography with pure petroleum ether to obtain product BP-Br. The structural formula of BP-Br is as follows: ; Preparation of S8 final product MR-2 BP-Br, MR-Bpin, and potassium carbonate were dissolved in a mixture of tetrahydrofuran / water. Pd3(PPd3)4 was then added under N2 atmosphere. The reaction mixture was heated to 66°C and refluxed with stirring for 12 hours. After cooling to room temperature, the product was extracted with dichloromethane and water and dried with anhydrous sodium sulfate. The crude product was purified by silica gel column chromatography to obtain product MR-2.

[0012] Preferably, the crude product in step S1 is purified by silica gel column chromatography with dichloromethane:petroleum ether = 3:7.

[0013] Preferably, the crude product, pure petroleum ether, described in step S2 is purified by silica gel column chromatography.

[0014] Preferably, the crude product in step S5 is purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 1:1, and the crude product in step S6 is purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 1:4.

[0015] This application also provides a photopolymerization system, which is composed of the photoinitiator, co-initiator and acrylic resin monomer described in claim 1, wherein the molar ratio of photoinitiator:co-initiator:acrylic resin in the photopolymerization system is 0.01:10:100 ~ 0.001:1:1000.

[0016] Finally, this application also provides the application of the above-mentioned photoinitiator in photoresist.

[0017] Compared with the prior art, the beneficial effects of this application are: This application provides a photoinitiator with space charge transfer properties, using spirofluorene as a bridging group to connect different electron donor and acceptor units. Under low-power visible light or sunlight irradiation, this molecule can form an excited state through a space charge transfer mechanism, subsequently undergoing charge transfer with the electron acceptor to generate active free radicals, thereby efficiently initiating free radical polymerization. Experiments show that this photoinitiator exhibits superior polymerization efficiency and monomer conversion rate compared to the commercial photoinitiator ITX under 365 nm, 405 nm, 450 nm, and sunlight irradiation. This invention not only expands the application range of MR-TADF molecules but also provides new design ideas for developing highly efficient visible light photoinitiators. Attached Figure Description

[0018] Figure 1 The molecular hydrogen spectrum of MR-1, the photoinitiator prepared in Example 1 of this application.

[0019] Figure 2 The nuclear magnetic resonance carbon spectrum of MR-1, the photoinitiator prepared in Example 1 of this application.

[0020] Figure 3 The image shows the HRMS plot of the photoinitiator MR-1 prepared in Example 1 of this application.

[0021] Figure 4 The photoinitiator MR-2 prepared in Example 2 of this application has a hydrogen nuclear magnetic resonance spectrum.

[0022] Figure 5 The nuclear magnetic resonance carbon spectrum of MR-2, the photoinitiator prepared in Example 2 of this application.

[0023] Figure 6 The image shows the HRMS plot of the photoinitiator MR-2 prepared in Example 2 of this application.

[0024] Figure 7 The MR-1 prepared in Example 1 was at 1×10 -5 UV-Vis absorption spectrum of acetonitrile in mol / L.

[0025] Figure 8 The MR-1 prepared in Example 1 was at 1×10 -5 Fluorescence emission spectrum in mol / L acetonitrile.

[0026] Figure 9 The MR-2 prepared in Example 2 was at 1×10 -5 UV-Vis absorption spectrum of acetonitrile in mol / L.

[0027] Figure 10 The MR-2 prepared in Example 2 was at 1×10 -5 Fluorescence emission spectrum in mol / L acetonitrile.

[0028] Figure 11 The images show real-time infrared polymerization of DMA monomers prepared in Examples 1-2 of this application under different wavelengths of LED light.

[0029] Figure 12 This is a polymerization diagram of MR-1, MR-2 and ITX prepared in Examples 1-2 of this application in DMA monomers under sunlight. Detailed Implementation

[0030] 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 shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0031] It should be noted that: Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0032] In this application, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0033] 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.

[0034] In seeking solutions, the applicant has come to focus on multiple resonance-thermally activated delayed fluorescence (MR-TADF) materials due to their unique photophysical properties. These materials achieve spatial separation of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) through multiple resonance effects, thus exhibiting both narrow-spectrum emission and high exciton utilization, demonstrating great potential in fields such as organic light-emitting diodes (OLEDs). MR-TADF molecules typically possess efficient intersystem crossing and long-lived triplet excitons, theoretically providing an ideal platform for efficient photophysical processes such as energy transfer or electron transfer. However, current research on MR-TADF materials is almost entirely focused on the optoelectronic display field; their enormous potential as sensitizers or initiators for photochemical reactions, particularly in low-power visible light-initiated polymerization, has not yet been effectively developed and systematically studied.

[0035] Although existing research has focused on developing visible light initiators, there are still few reports of initiators capable of achieving ultra-high efficiency polymerization in air at multiple wavelengths, including 365 nm, 405 nm, and 450 nm, especially at extremely low light power densities as low as 1 mW / cm². For example, the commercially available visible light initiator ITX fails to meet the requirements for efficient production under these demanding conditions in terms of polymerization efficiency and monomer conversion. This precisely highlights the limitations of current molecular design approaches.

[0036] Therefore, this application aims to break through the traditional design paradigm of photoinitiators and, for the first time, combine the core advantages of MR-TADF molecules with the needs of photopolymerization to provide a novel photoinitiator design scheme based on the space charge transfer mechanism, so as to solve the shortcomings of existing technologies in the field of high-performance visible light photoinitiators.

[0037] This application addresses the problem of insufficient initiation efficiency of existing photoinitiators under low-power visible light and sunlight by providing a highly efficient photoinitiator based on a space charge transfer mechanism, its preparation method, and its application in photopolymerization reactions.

[0038] This application provides a photoinitiator with space charge transfer properties, wherein the photoinitiator is a spirofluorene-based bridged photoinitiator and has one of the following molecular structures: ; Where R represents the multiple resonance-thermally activated delayed fluorescence functional group.

[0039] In some preferred embodiments, the photoinitiator having space charge transfer properties has any of the following molecular structures: .

[0040] In some preferred embodiments, the photoinitiator having space charge transfer properties has one of the following molecular structures: .

[0041] The method for preparing the photoinitiator with space charge transfer properties described above in this application includes the following steps: S1. Preparation of intermediate PXZ-Br PXZ, 2-bromoiodobenzene, cuprous iodide, 18-crown-6 ether, and potassium carbonate were dissolved in a two-necked flask containing o-dichlorobenzene. The mixture was then refluxed at 180°C under a nitrogen atmosphere for 48 hours. The reaction solution was cooled to room temperature, and the solvent was rotary evaporated. The mixture was repeatedly extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography to obtain the intermediate PXZ-Br. The structural formula of PXZ-Br is as follows: ; S2. Preparation of intermediate LW-Br Under argon atmosphere, PXZ-Br was dissolved in tetrahydrofuran in a 200 mL double-necked flask. After cooling the solution to -78°C, 1.6 M n-butyllithium was added dropwise using a syringe. The resulting mixture was stirred at -78°C for 1 hour, followed by the addition of compound 1-bromo-9H-fluorene-9-one over 15 minutes. After reacting at -78°C for 2 hours, the mixture was stirred at room temperature. Water was added to quench the reaction, and the tetrahydrofuran was evaporated under reduced pressure. The resulting solid was dissolved in dichloromethane and washed with water. The organic layer was then separated, dried with sodium sulfate, filtered, and evaporated. This solid was used directly in the next reaction without further purification. The crude product was dissolved in acetic acid and hydrochloric acid and reacted at 110°C. After cooling to room temperature, it was repeatedly extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography with pure petroleum ether to obtain the intermediate LW-Br. The structural formula of LW-Br is as follows: ; S3. Preparation of intermediate PZ-Br 2,6-Difluorobromobenzene, 3,6-di-tert-butylcarbazole, and potassium carbonate were dissolved in a two-necked flask containing N,N-dimethylformamide. The mixture was then refluxed at 150°C under a nitrogen atmosphere for 24 hours. After cooling to room temperature, water was added to precipitate the product. No further purification was required to obtain the intermediate PZ-Br. The structural formula of PZ-Br is as follows: ; S4. Preparation of intermediate MR The PZ-Br obtained in step S3 was dissolved in a two-necked flask containing ultra-dry o-xylene solution. Then, under a nitrogen atmosphere, the mixture was cooled to -20°C, and a hexane solution containing n-butyllithium was slowly added dropwise. After reacting for 15 min, the mixture was reacted at room temperature for 2 h. Next, in a cryogenic reactor, boron tribromide was added dropwise, and the mixture was reacted at low temperature for 15 min. Then, the mixture was stirred at room temperature for 1 h. Finally, N,N-diisopropylethylamine was added dropwise at low temperature, and the mixture was reacted at low temperature for 15 min. Then, the temperature was increased to 120°C and reacted for 12 h. After the reaction was complete, the mixture was extracted with water and ethyl acetate, evaporated to dryness, and recrystallized with ethanol solution to finally obtain the yellow solid product MR. The structural formula of MR is as follows: ; S5. Preparation of intermediate MR-Bpin The MR obtained in step S4, 1,5-cyclooctadiene iridium chloride dimer, pinacol diborate, and 4,4'-di-tert-butyl-2,2'-dipyridine were dissolved in a two-necked flask containing an ultra-dry tetrahydrofuran solution. The mixture was then reacted at 120°C for 12 h under a nitrogen atmosphere. After the reaction was complete, the product was extracted with water and ethyl acetate. The crude product was purified by silica gel column chromatography to obtain a yellow solid product, MR-Bpin. The structural formula of MR-Bpin is as follows: ; S6. Preparation of the final product MR-1 LW-Br, MR-Bpin, and potassium carbonate were dissolved in a mixture of tetrahydrofuran and water. Pd3(PPd3)4 was then added under N2 atmosphere. The reaction mixture was heated to 66°C and refluxed with stirring for 12 hours. After cooling to room temperature, the product was extracted with dichloromethane and water and dried with anhydrous sodium sulfate. The crude product was purified by silica gel column chromatography to obtain product MR-1.

[0042] In some more preferred embodiments, the method for preparing the photoinitiator with space charge transfer properties further includes: Preparation of S7 intermediate BP-Br Under nitrogen atmosphere, PXZ-Br was dissolved in tetrahydrofuran in a double-necked flask. After cooling the solution to -78°C, 1.6 M n-butyllithium was added dropwise using a syringe. The resulting mixture was stirred at -78°C for 1 hour, followed by the addition of compound 2-bromobenzophenone over 15 minutes. After reacting at -78°C for 2 hours, the mixture was stirred at room temperature for 3 hours. Water was added to quench the reaction, and the tetrahydrofuran was evaporated under reduced pressure. The resulting solid was dissolved in dichloromethane and washed with water. The organic layer was then separated, dried with sodium sulfate, filtered, and evaporated. This solid was used directly in the next reaction without further purification. The crude product was dissolved in acetic acid and hydrochloric acid and reacted at 110°C for 4 hours. After cooling to room temperature, it was repeatedly extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography with pure petroleum ether to obtain product BP-Br. The structural formula of BP-Br is as follows: ; Preparation of S8 final product MR-2 BP-Br, MR-Bpin, and potassium carbonate were dissolved in a mixture of N,N-dimethylformamide / water. Pd3(PPd3)4 was then added under a N2 atmosphere. The reaction mixture was heated to 90°C and refluxed with stirring for 12 hours. After cooling to room temperature, the product was extracted with dichloromethane and water and dried with anhydrous sodium sulfate. The crude product was purified by silica gel column chromatography to obtain product MR-2.

[0043] In some preferred embodiments, the crude product in step S1 is purified by silica gel column chromatography with dichloromethane:petroleum ether = 3:7.

[0044] In some preferred embodiments, the crude product, pure petroleum ether, described in step S2 is purified by silica gel column chromatography.

[0045] In some preferred embodiments, the crude product in step S5 is purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 1:1, and the crude product in step S6 is purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 1:4.

[0046] This application also provides a photopolymerization system, which is composed of the photoinitiator, co-initiator and acrylic resin monomer described in claim 1, wherein the molar ratio of photoinitiator:co-initiator:acrylic resin in the photopolymerization system is 0.01:10:100 ~ 0.001:1:1000.

[0047] Finally, this application also provides the application of the above-mentioned photoinitiator in photoresist.

[0048] Next, the preparation method of the photoinitiator with space charge transfer properties of this application will be described in detail with specific embodiments.

[0049] Example 1 Preparation of MR-1, a low-power, high-efficiency photoinitiator under visible light The chemical reaction equations involved in this embodiment are as follows: ; The specific implementation process of step a, i.e. step S1, is as follows: PXZ (1.83 g, 10.0 mmol), 2-bromoiodobenzene (4.23 g, 15.0 mmol), cuprous iodide (0.7 g, 3.7 mmol), 18-crown-6 ether (0.1 g, 0.38 mmol), and potassium carbonate (5.0 g, 36.2 mmol) were dissolved in a two-necked flask containing 80 mL of o-dichlorobenzene. The mixture was then refluxed at 180 °C under a nitrogen atmosphere for 48 h. After cooling to room temperature, the solvent was rotary evaporated. The solution was extracted three times with dichloromethane and water, dried over anhydrous sodium sulfate, and the crude product was purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 3:7 to give 2.36 g of product PXZ-Br. The yield was 70%.

[0050] The specific implementation process of step b, i.e. step S2, is as follows: PXZ-Br (1011 mg, 3.0 mmol) was dissolved in 60 mL of tetrahydrofuran under argon atmosphere in a 200 mL double-necked flask. After cooling the solution to -78 °C, 1.6 M n-butyllithium (2.0 mL, 3.20 mmol) was added dropwise using a syringe. The resulting mixture was stirred at -78 °C for 1 hour, followed by the addition of compound 1-bromo-9H-fluorene-9-one (771 mg, 3.0 mmol) over 15 minutes. After reacting at -78 °C for 2 hours, the mixture was stirred at room temperature for 3 hours. 10 mL of water was added to quench the reaction, and the tetrahydrofuran was evaporated under reduced pressure. The resulting solid was dissolved in 100 mL of dichloromethane and washed with water (3 × 50 mL). The organic layer was then separated, dried over sodium sulfate, filtered, and evaporated, and used directly for the next reaction without further purification. The crude product was dissolved in 30 mL of acetic acid and 8 mL of hydrochloric acid. After reacting at 110 °C for 4 hours, the mixture was cooled to room temperature and extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography with pure petroleum ether to give 479 mg of product LW-Br. The yield was 32%.

[0051] The specific implementation process of step c, i.e. step S3, above is as follows: 1 (5.76 g, 30.0 mmol), 3,6-di-tert-butylcarbazole (16.74 g, 60.0 mmol), and potassium carbonate (4.14 g, 30.0 mmol) were dissolved in a two-necked flask containing 100 mL of N,N-dimethylformamide. The mixture was then refluxed at 150 °C under a nitrogen atmosphere for 24 h. After cooling the reaction solution to room temperature, water was added to precipitate the product. No further purification was required, yielding 18.46 g of product PZ-Br. The yield was 86.7%.

[0052] The specific implementation process of step d, i.e. step S4, above is as follows: PZ-Br (8.8 g, 12.4 mmol) was dissolved in a two-necked flask containing 100 mL of ultra-dry o-xylene solution. The solution was then cooled to -20°C under a nitrogen atmosphere, and a hexane solution containing n-butyllithium (10.3 mL, 2.4 M, 24.8 mmol) was slowly added dropwise. After reacting for 15 min, the mixture was reacted at room temperature for 2 h. The mixture was then placed in a cryogenic reactor, and boron tribromide (2.5 mL, 26.3 mmol) was added dropwise. After reacting at low temperature for 15 min, the mixture was stirred at room temperature for 1 h. Then, N,N-diisopropylethylamine (3.5 mL, 25.2 mmol) was added dropwise at low temperature. After reacting at low temperature for 15 min, the temperature was increased to 120°C and reacted for 12 h. After the reaction was complete, the mixture was extracted with water and ethyl acetate, evaporated to dryness, and recrystallized with ethanol solution to finally obtain 4.5 g of the yellow solid product MR, with a yield of 56.7%.

[0053] The specific implementation process of step e, i.e. step S5, is as follows: MR (4.2 g, 6.6 mmol), 1,5-cyclooctadiene iridium chloride dimer (43.1 mg, 0.064 mmol), pinacol diborate (1.68 g, 6.6 mmol), and 4,4'-di-tert-butyl-2,2'-dipyridine (34.9 mg, 0.13 mmol) were dissolved in a two-necked flask containing 100 mL of ultra-dry tetrahydrofuran solution. The mixture was then reacted at 120 °C for 12 h under a nitrogen atmosphere. After the reaction was complete, the product was extracted with water and ethyl acetate. The crude product was purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 1:1 to give 3.5 g of the yellow solid product MR-Bpin, with a yield of 69.2%.

[0054] The specific implementation process of step f above, i.e. step S6, is as follows: LW-Br (73 mg, 0.14 mmol), MR-Bpin (130 mg, 0.17 mmol), and potassium carbonate (96 mg, 0.7 mmol) were dissolved in a tetrahydrofuran / water mixture (6 ml / 1 ml). Pd3(PPd3)4 (6 mg, 0.005 mmol) was then 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 product was extracted with dichloromethane and water and dried over anhydrous sodium sulfate. The crude product was purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 1:4 to give product MR-1 65 mg. The yield was 43.8%.

[0055] Example 2 Preparation of a photoinitiator MR-2 with space charge transfer properties induced by multiple resonance effects The chemical reaction equations involved in this embodiment are as follows: ; The specific implementation process of step a, i.e. step S7, above is as follows: Under nitrogen atmosphere, PXZ-Br (1011 mg, 3.0 mmol) was dissolved in 60 mL of tetrahydrofuran in a 200 mL double-necked flask. After cooling the solution to -78 °C, 1.6 M n-butyllithium (2.0 mL, 3.20 mmol) was added dropwise using a syringe. The resulting mixture was stirred at -78 °C for 1 hour, followed by the addition of compound 2-bromobenzophenone (783 mg, 3.0 mmol) over 15 minutes. After reacting at -78 °C for 2 hours, the mixture was stirred at room temperature for 3 hours. 10 mL of water was added to the mixture to quench the reaction, and the tetrahydrofuran was then evaporated under reduced pressure. The resulting solid was dissolved in 100 mL of dichloromethane and washed with water (3 × 50 mL). The organic layer was then separated, dried over sodium sulfate, filtered, and evaporated, and used directly for the next reaction without further purification. The crude product was dissolved in 30 mL of acetic acid and 8 mL of hydrochloric acid. After reacting at 110 °C for 4 hours, the mixture was cooled to room temperature and extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography with pure petroleum ether to give 463 mg of BP-Br. The yield was 30.1%.

[0056] The specific implementation process of step b above, i.e. step S8, is as follows: BP-Br (75 mg, 0.14 mmol), MR-Bpin (130 mg, 0.17 mmol), and potassium carbonate (96 mg, 0.7 mmol) were dissolved in a tetrahydrofuran / water mixture (6 ml / 1 ml). Then, Pd3(PPd3)4 (6 mg, 0.005 mmol) 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 product was extracted with dichloromethane and water and dried over anhydrous sodium sulfate. The crude product was purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 1:4 to give product MR-2 60 mg. The yield was 40.4%.

[0057] Compound structure determination: Bruker 400MHz superconducting nuclear magnetic resonance spectrometer, deuterated dichloromethane as solvent; Mass spectrometry detection: MR-1 and MR-2 obtained in Examples 1-2 were dissolved in dichloromethane to prepare a solution with a concentration of 1 mg / mL, and mass spectrometry was performed using a liquid chromatography-mass spectrometry (LCMS-2020) instrument.

[0058] Ultraviolet absorption spectroscopy detection: Shimadzu UV-2700 UV-Vis spectrophotometer was used, with a scanning range of 300–500 nm; Emission spectroscopy detection: A steady-state / transient fluorescence spectrometer (FLS980) was used, with an excitation wavelength of 365 nm and a test temperature of 298 K.

[0059] The test results are as follows: The molecular proton spectrum of the photoinitiator MR-1 prepared in Example 1 is as follows: Figure 1 As shown, it can be seen that: 1 H NMR (400 MHz, Methylene Chloride- d 2) δ 9.07–8.95 (m, 2H), 8.48 (d, J =1.9 Hz, 2H), 8.25 (d, J = 1.9 Hz, 2H), 8.04–7.91 (m, 2H), 7.59 (t, J = 7.6 Hz,1H), 7.49–7.30 (m, 7H), 7.25 –7.16 (m, 2H), 6.89 (d, J = 7.6 Hz, 1H), 6.78 (d, J = 44.1 Hz, 2H), 6.55 (d, J = 7.9 Hz, 3H), 6.31 (s, 1H), 6.18 (dd, J = 7.9, 1.4Hz, 1H), 6.06–5.78 (m, 3H), 5.53 (s, 1H), 1.68 (s, 18H), 1.51 (s, 18H). The above 1H NMR peak energies correspond one-to-one with the target product, and the number is reasonable; indicating that the photoinitiator MR-1 was prepared in Example 1, and that the compound has a simple structure and high purity.

[0060] The carbon NMR spectrum of the photoinitiator MR-1 prepared in Example 1 is as follows: Figure 2 As shown, it can be seen that: 13 C NMR (100 MHz, Methylene Chloride- d 2) δThe molecular carbon spectrum peaks 146.5, 146.0, 144.1, 142.8, 139.2, 131.3, 130.9, 130.05, 129.5, 128.9, 128.0, 127.8, 127.0, 125.4, 124.8, 121.7, 121.2, 121.1, 116.0, 115.6, 110.3, 36.4, 35.9, 33.3, and 32.9 correspond one-to-one with the target product, and the number is reasonable; this indicates that the photoinitiator MR-1 was prepared in Example 1, and the compound has a simple structure and high purity.

[0061] Figure 3 The image shows the HRMS (mass spectrum) of the photoinitiator MR-1 prepared in Example 1. Calculations show that the theoretical value of C for the photoinitiator MR-1, which possesses space charge transfer properties, is... 77 H 66 BN3O [(M+H) + The actual m / z value, determined by mass spectrometry, is 1060.5372, consistent with the relative molecular mass of the synthesized photoinitiator MR-1. This further confirms that the compound prepared in Example 1 is indeed the photoinitiator MR-1 with space charge transfer properties, and that the compound has a simple structure and high purity. Combining the above NMR and mass spectrometry results, it is clear that the product obtained in Example 1 is the photoinitiator MR-1.

[0062] like Figure 4 The image shows the 1H NMR spectrum of the photoinitiator MR-2 with space charge transfer properties prepared in Example 2. It can be seen that: 1 H NMR (400 MHz, Methylene Chloride- d 2) δ9.12 (s, 2H), 8.50 (d, J = 1.8Hz, 2H), 8.27 (d, J = 2.1 Hz, 2H), 7.73 (d, J = 8.8 Hz, 1H), 7.65 (s, 2H),7.55 (dd, J = 8.8, 2.1 Hz, 3H), 7.44 (s, 3H), 7.23 (d, J = 48.2 Hz, 6H), 7.02 (d, J = 35.6 Hz, 4H), 6.80 (s, 2H), 6.53 (s, 2H), 6.13 (s, 1H), 5.93 (t, J =26.9 Hz, 2H), 1.55 (d, J = 4.6 Hz, 18H). The above-mentioned proton NMR spectrum peak energies correspond one-to-one with the target products, and the quantities are reasonable; indicating that the photoinitiator MR-2 was prepared in Example 2, and that the compound has a simple structure and high purity.

[0063] The carbon NMR spectrum of the photoinitiator MR-2 prepared in Example 2 is as follows: Figure 5 As shown, it can be seen that: 13 C NMR (100 MHz, Methylene Chloride- d 2) δ 13 C NMR (100 MHz, MethyleneChloride- d 2) 146.49, 146.33, 142.88, 142.82, 139.34, 130.94, 128.03, 125.64, 124.82, 121.95, 118.38, 118.28, 115.84, 115.52, 36.40, 35.99, 33.25, 32.90. The molecular carbon spectrum peaks correspond one-to-one with the target product, and the number is reasonable; this indicates that the photoinitiator MR-2 was successfully prepared in Example 2, and that the compound has a simple structure and high purity.

[0064] Figure 6 The image shows the HRMS (mass spectrum) of the photoinitiator MR-2 prepared in Example 2. Calculations show that the theoretical value of the photoinitiator MR-2 with space charge transfer properties is: C 77 H 69 BN3O + [(M+H) +The relative molecular mass (m / z) of the synthesized photoinitiator MR-2 was 1062.5528, while the actual m / z value obtained by mass spectrometry was 1062.5520, consistent with the relative molecular mass of the synthesized photoinitiator MR-2. This further confirms that the compound prepared in Example 2 is indeed the photoinitiator MR-2 with space charge transfer properties, and that the compound has a simple structure and high purity. Combining the above NMR and mass spectrometry results, it is clear that the product obtained in Example 2 is the photoinitiator MR-2.

[0065] Using a Shimadzu UV-2700 UV-Vis spectrophotometer, MR-1 and MR-2 prepared in Examples 1 and 2, respectively, were dissolved in dichloromethane solution to prepare a 1×10⁻⁶ solution. -3 The stock solution was diluted to 1×10 mol / L. -5 The test was conducted at mol / L.

[0066] Fluorescence emission spectroscopy was used: an FLS980 fluorescence spectrometer was used to prepare a 1×10⁻⁶ solution of MR-1 and MR-2 obtained in the examples by dissolving them in dichloromethane. -3 The stock solution, initially at mol / L, was diluted to 1×10⁻⁶ for testing. -5 mol / L.

[0067] Figure 7 Including MR-1 prepared in Example 1 at 1×10 -5 The UV-Vis absorption spectrum of acetonitrile in mol / L solution. Figure 7 It is known that MR-1 has a high molar extinction coefficient and its absorption is located in the ultraviolet-visible band.

[0068] Figure 8 Including MR-1 prepared in Example 1 at 1×10 -5 Fluorescence emission spectrum in acetonitrile at mol / L. From Figure 8 It can be seen that MR-1 has a broad emission spectrum and weak fluorescence emission, exhibiting space charge transfer properties.

[0069] Figure 9 Including the MR-2 prepared in Example 2 at 1×10 -5 The UV-Vis absorption spectrum of acetonitrile in mol / L solution. Figure 9 It is known that MR-2 has a high molar extinction coefficient and its absorption is located in the ultraviolet band.

[0070] Figure 10 Including the MR-2 prepared in Example 2 at 1×10 -5 Fluorescence emission spectrum in acetonitrile at mol / L. From Figure 10 It can be seen that MR-2 has a broad emission spectrum and weak fluorescence emission, exhibiting space charge transfer properties, but its charge transfer is weaker than that of MR-1.

[0071] Examples of optical aggregation applications The above-mentioned photoinitiator, coinitiator, and acrylic resin monomer are combined to form a polymerization system. In the above photopolymerization system, the molar ratio of photoinitiator:co-initiator:acrylic resin is 0.01:10:100 ~ 0.001:1:1000. Figure 11 The MR-1 and MR-2 photoinitiators prepared in Examples 1-2 of this application were formulated into a photopolymerization system with a co-initiator and monomers, using 365 nm, 405 nm, 450 nm, and 1 mW / cm². 2 The photopolymerization system irradiated by the light source shows that a high degree of polymerization can be achieved in a short time under different photoinitiators, indicating that such photoinitiators have the advantages of low excitation power and high polymerization efficiency.

[0072] Figure 12 The MR-1 and MR-2 photoinitiators prepared in Examples 1-2 of this application were formulated into a photopolymerization system with co-initiators and monomers. Photopolymerization under sunlight showed that a high degree of polymerization was achieved in a short time under different photoinitiator polymerization systems. Sunlight polymerization combines the most natural energy with the most cutting-edge chemical materials technology, representing an important direction for green manufacturing and sustainable development.

[0073] In summary, this application successfully developed a novel photoinitiator with spirofluorene as a bridging framework and space charge transfer properties. Its innovation lies in its ability to simultaneously generate active free radicals using low-power visible light and even sunlight through efficient intramolecular and intermolecular charge transfer processes, thereby initiating free radical polymerization. Experimental data fully demonstrate that this initiator significantly outperforms the commercial photoinitiator ITX in key performance indicators across a wide wavelength range of 365-450 nm and under sunlight. This invention not only opens up entirely new application directions for MR-TADF materials but also provides a disruptive design approach for designing next-generation, highly efficient, and energy-saving visible light initiators.

[0074] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0075] Although several embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A photoinitiator with space charge transfer properties, characterized in that: The photoinitiator, spirofluorene, is a bridged structure and has one of the following molecular structures: ； Where R represents the multiple resonance-thermally activated delayed fluorescence functional group.

2. The photoinitiator with space charge transfer properties according to claim 1, characterized in that: It has any of the following molecular structures: 。 3. The photoinitiator with space charge transfer properties according to claim 2, characterized in that: It has one of the following molecular structures: 。 4. The method for preparing the photoinitiator with space charge transfer properties according to claim 3, characterized in that: Includes the following steps: S1. Preparation of intermediate PXZ-Br PXZ, 2-bromoiodobenzene, cuprous iodide, 18-crown-6 ether, and potassium carbonate were dissolved in a two-necked flask containing o-dichlorobenzene. The mixture was then refluxed at 180°C under a nitrogen atmosphere for 48 hours. The reaction solution was cooled to room temperature, and the solvent was rotary evaporated. The mixture was repeatedly extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography to obtain the intermediate PXZ-Br. The structural formula of PXZ-Br is as follows: ； S2. Preparation of intermediate LW-Br Under argon atmosphere, PXZ-Br was dissolved in tetrahydrofuran in a 200 mL double-necked flask. After cooling the solution to -78°C, 1.6 M n-butyllithium was added dropwise using a syringe. The resulting mixture was stirred at -78°C for 1 hour, followed by the addition of compound 1-bromo-9H-fluorene-9-one over 15 minutes. After reacting at -78°C for 2 hours, the mixture was stirred at room temperature. Water was added to quench the reaction, and the tetrahydrofuran was evaporated under reduced pressure. The resulting solid was dissolved in dichloromethane and washed with water. The organic layer was then separated, dried with sodium sulfate, filtered, and evaporated. This solid was used directly in the next reaction without further purification. The crude product was dissolved in acetic acid and hydrochloric acid and reacted at 110°C. After cooling to room temperature, it was repeatedly extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography with pure petroleum ether to obtain the intermediate LW-Br. The structural formula of LW-Br is as follows: ； S3. Preparation of intermediate PZ-Br 2,6-Difluorobromobenzene, 3,6-di-tert-butylcarbazole, and potassium carbonate were dissolved in a two-necked flask containing N,N-dimethylformamide. The mixture was then refluxed at 150°C under a nitrogen atmosphere for 24 hours. After cooling to room temperature, water was added to precipitate the product. No further purification was required to obtain the intermediate PZ-Br. The structural formula of PZ-Br is as follows: ； S4. Preparation of intermediate MR The PZ-Br obtained in step S3 was dissolved in a two-necked flask containing ultra-dry o-xylene solution. Then, under a nitrogen atmosphere, the mixture was cooled to -20°C, and a hexane solution containing n-butyllithium was slowly added dropwise. After reacting for 15 min, the mixture was reacted at room temperature for 2 h. Next, in a cryogenic reactor, boron tribromide was added dropwise, and the mixture was reacted at low temperature for 15 min. Then, the mixture was stirred at room temperature for 1 h. Finally, N,N-diisopropylethylamine was added dropwise at low temperature, and the mixture was reacted at low temperature for 15 min. Then, the temperature was increased to 120°C and reacted for 12 h. After the reaction was complete, the mixture was extracted with water and ethyl acetate, evaporated to dryness, and recrystallized with ethanol solution to finally obtain the yellow solid product MR. The structural formula of MR is as follows: ； S5. Preparation of intermediate MR-Bpin The MR obtained in step S4, 1,5-cyclooctadiene iridium chloride dimer, pinacol diborate, and 4,4'-di-tert-butyl-2,2'-dipyridine were dissolved in a two-necked flask containing an ultra-dry tetrahydrofuran solution. The mixture was then reacted at 120°C for 12 h under a nitrogen atmosphere. After the reaction was complete, the product was extracted with water and ethyl acetate. The crude product was purified by silica gel column chromatography to obtain a yellow solid product, MR-Bpin. The structural formula of MR-Bpin is as follows: ； S6. Preparation of the final product MR-1 LW-Br, MR-Bpin, and potassium carbonate were dissolved in a mixture of tetrahydrofuran and water. Pd3(PPd3)4 was then added under a N2 atmosphere. The reaction mixture was heated to 66°C and refluxed with stirring for 12 hours. After cooling to room temperature, the product was extracted with dichloromethane and water and dried with anhydrous sodium sulfate. The crude product was purified by silica gel column chromatography to obtain product MR-1.

5. The method for preparing the photoinitiator with space charge transfer properties according to claim 4, characterized in that: Also includes: Preparation of S7 intermediate BP-Br Under nitrogen atmosphere, PXZ-Br was dissolved in tetrahydrofuran in a double-necked flask. After cooling the solution to -78°C, 1.6 M n-butyllithium was added dropwise using a syringe. The resulting mixture was stirred at -78°C for 1 hour, followed by the addition of compound 2-bromobenzophenone over 15 minutes. After reacting at -78°C for 2 hours, the mixture was stirred at room temperature for 3 hours. Water was added to quench the reaction, and the tetrahydrofuran was evaporated under reduced pressure. The resulting solid was dissolved in dichloromethane and washed with water. The organic layer was then separated, dried with sodium sulfate, filtered, and evaporated. This solid was used directly in the next reaction without further purification. The crude product was dissolved in acetic acid and hydrochloric acid and reacted at 110°C for 4 hours. After cooling to room temperature, it was repeatedly extracted three times with dichloromethane and water. After drying with anhydrous sodium sulfate, the crude product was purified by silica gel column chromatography with pure petroleum ether to obtain product BP-Br. The structural formula of BP-Br is as follows: ； Preparation of S8 final product MR-2 BP-Br, MR-Bpin, and potassium carbonate were dissolved in a mixture of N,N-dimethylformamide / water. Pd3(PPd3)4 was then added under a N2 atmosphere. The reaction mixture was heated to 90°C and refluxed with stirring for 12 hours. After cooling to room temperature, the product was extracted with dichloromethane and water and dried with anhydrous sodium sulfate. The crude product was purified by silica gel column chromatography to obtain product MR-2.

6. The method for preparing a photoinitiator with space charge transfer properties according to claim 4, characterized in that: The crude product described in step S1 was purified by silica gel column chromatography with dichloromethane:petroleum ether = 3:

7.

7. The method for preparing a photoinitiator with space charge transfer properties according to claim 4, characterized in that: The crude product, pure petroleum ether, described in step S2 is purified by silica gel column chromatography.

8. The method for preparing a photoinitiator with space charge transfer properties according to claim 4, characterized in that, The crude product in step S5 is purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 1:1, and the crude product in step S6 is purified by silica gel column chromatography with a polarity of dichloromethane:petroleum ether = 1:

4.

9. A photopolymerization system, characterized in that: It is composed of the photoinitiator, co-initiator and acrylic resin monomer as described in claim 1, wherein the molar ratio of photoinitiator:co-initiator:acrylic resin in the photopolymerization system is 0.01:10:100 ~ 0.001:1:1000.

10. The use of the photoinitiator of claim 1 in photoresist.

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