CN114656439B - Single-component flavonol sulfonate visible light initiator and preparation method and application thereof - Google Patents

Abstract

The invention discloses a single-component flavonol sulfonate visible light initiator, which has a natural product flavonol skeleton structure and has the following structural general formula:wherein R is ₁ One selected from triphenylamine, carbazole, phenothiazine, naphthalene, anthracene, pyrene and quinoline; the alkyl group attached to N on carbazole or phenothiazine is selected from C ₁ ‑C ₂₀ Straight chain alkyl or C ₁ ‑C ₂₀ Branched alkyl; r is R ₂ One selected from methyl, trifluoromethyl, phenyl, 4-methylphenyl and 4-trifluoromethylphenyl. The photoinitiator has low bond energy due to ester bonds, generates active species to initiate free radical polymerization under mild visible light irradiation, has high molar extinction coefficient in a visible light region, and is sufficient to initiate TPGDA polymerization under low concentration; meanwhile, compared with a common visible light initiation system, the light-sensitive wave band is longer, the light absorption capacity is stronger, the molecular structure is simple, the preparation is easy, the cost is low, and the method has industrial application potential.

Description

A one-component flavonol sulfonate visible light initiator and its preparation method and application

Technical field

The invention belongs to the technical field of new materials and organic chemicals, and specifically relates to a single-component flavonol sulfonate visible light initiator and its preparation method and application.

Background technique

Light curing technology is an environmentally friendly green technology due to its characteristics of fast curing speed, less pollution, and excellent cured product performance. It has been widely used in many industrial fields such as: printing, inks, coatings, adhesives, optics, etc. devices, electronic circuits, etc. Although the amount of photoinitiator used in light-curing formulas is very small, its role is the most critical and important.

The Chinese patent application with publication number CN102120783A discloses a method for preparing a thioxanthone photoinitiator containing an aliphatic tertiary amine group. This method first passes thiosalicylic acid and an aliphatic primary amine salt containing a benzene ring through Condensation into a ring, the primary amine group is introduced into the thioxanthone structure, and then the primary amine group is hydroxyalkylated through an epoxy alkane to convert the primary amine group into a tertiary amine group, and two active hydroxyl groups are introduced at the same time. A thioxanthone photoinitiator containing amine as coinitiator was obtained. This photoinitiator can only be cured by UV light and cannot be used in the visible light region.

However, UV curing has the following disadvantages: ① UV radiation easily generates ozone, which pollutes the environment, is harmful to the human body, and has poor environmental safety; ② UV light penetration is weak, and some components or pigment substances in the photo-curing formula have conjugated structures. It has strong absorption of ultraviolet light, resulting in severe light intensity attenuation, incomplete curing, and poor performance of the light-cured film. Visible light curing abandons the above-mentioned shortcomings of ultraviolet light curing technology. Therefore, visible light curing has received more and more research and attention. The development of light-emitting diodes (LEDs) provides a cheap and easily available light source for the widespread application of visible light photoinitiated polymerization technology.

In photopolymerization under visible light sources, the development of novel dye molecules with various effective photoinitiators plays a crucial role. The only commercial visible light initiator is CQ (camphorquinone). CQ synthesis costs are high and is generally only used in the blue light band.

At present, there are several ways to obtain visible light initiators: ① Modify existing UV photoinitiators and increase the conjugated structure of the molecule to red-shift the light absorption to the visible light region; ② Use photosensitive dyes that absorb in the visible light region as photosensitizers. Combine co-initiators and synergists to form a visible light initiating system; ③ develop and discover new structural visible light photoinitiators; ④ functional modification of existing visible light photosensitizers to improve application performance.

The foreign Jacques Lalev′ee research group, the Yagci research group, the Previtali research group, the Fouassier research group, and the domestic Nie Jun research group, and the Xiao Pu research group have developed many structurally novel visible light-initiated systems based on these four approaches, and many others. Researchers are also working on this work. However, existing photosensitizers have shortcomings such as poor solubility, strong fluorescence, short triplet lifetime, poor sensitivity improvement effect, long photocuring time, and low photocuring efficiency. At present, progress has been made in using natural product skeleton structures as low-toxicity photosensitizers, but the use of natural product skeleton structures as single-component high-efficiency initiators is still blank in photopolymerization technology.

Contents of the invention

One of the technologies to be solved by the present invention is to provide a single-component flavonol sulfonate visible light initiator with high photocuring efficiency.

In order to solve the above technical problems, the present invention provides the following technical solutions:

A one-component flavonol sulfonate visible light initiator, its general structural formula is as follows:

Among them, R ₁ is selected from one of triphenylamine, carbazole, phenothiazine, naphthalene, anthracene, pyrene and quinoline; the alkyl group connected to N on carbazole or phenothiazine is selected from C ₁ -C ₂₀ straight Alkyl or C ₁ -C ₂₀ branched alkyl; R ₂ is selected from methyl, trifluoromethyl, phenyl, 4-methylphenyl, 4-trifluoromethylphenyl.

This new type of photoinitiator has a high molar extinction coefficient at 405nm, which can reduce the amount of this type of initiator and reduce the cost of photocuring. At the same time, the migration amount of this type of initiator from the cured surface is reduced, and the toxicity of the cured material is reduced, thereby contributing to the promotion of photopolymerization technology in the biological field.

The second technology to be solved by the present invention is to provide a method for preparing a single-component flavonol sulfonate visible light initiator with high photocuring efficiency.

In order to solve the above technical problems, the present invention provides the following technical solutions:

The preparation method of the above one-component flavonol sulfonate visible light initiator, the specific steps are as follows

(1) 2-Hydroxyacetophenone and an aldehyde containing R ₁ are synthesized as intermediate I by the Algar-Flynn-Oyamada method;

(2) After intermediate I is dissolved in the solvent, the flavonol sulfonate is synthesized through a substitution reaction with the sulfonyl chloride containing R ₂ in the presence of triethylamine; the specific synthesis route is as follows:

Among them, the molar ratio of 2-hydroxyacetophenone to the aldehyde containing R ₁ is 1:1, and the molar ratio of intermediate I, triethylamine, and sulfonyl chloride containing R ₂ is 1:2:2.

Preferably, the solvent in step (2) is methylene chloride.

The third technical problem to be solved by the present invention is to provide the application of a single-component flavonol sulfonate visible light initiator with high photocuring efficiency.

In order to solve the above technical problems, the present invention provides the following technical solutions:

Application of the above one-component flavonol sulfonate visible light initiator in a free radical visible LED light curing system.

Further, the specific steps are as follows:

(1) Formulate a single-component flavonol sulfonate visible light initiator into a visible light initiating system;

(2) Add the visible light initiating system to the free radical polymerization monomer and mix thoroughly to obtain a transparent and clear photo-curing system;

(3) Use LED light source to irradiate the light curing system;

(4) Use online infrared method to estimate the polymerization conversion rate through changes in its characteristic peaks;

Preferably, the light source is an LED visible light source with a wavelength greater than 405 nm.

Preferably, the weight ratio of the single-component flavonol sulfonate visible light initiator and free radical polymerization monomer is (0.05-2):100.

The beneficial effects of the present invention are:

1. The flavonol sulfonate photoinitiator of the present invention has a high molar extinction coefficient at 405nm. Due to the light shielding effect, the amount of initiator can be reduced, the photocuring cost can be reduced, and at the same time, the cytotoxicity of the cured material can be reduced. .

2. The photoinitiator of the flavonol sulfonate esters of the present invention has low ester bond energy. Under the irradiation of a mild 405nm LED light source, the ester bond can be broken and active free radicals are generated to initiate free radical monomer/prepolymerization. Effective light curing of the body.

3. Compared with commonly reported visible light initiating systems, the ketol sulfonate photoinitiator of the present invention has a longer photosensitive wavelength band, stronger light absorption capacity, simple molecular structure, easy preparation, low cost, and potential for industrial application. .

Description of the drawings

Figure 1: Structures of flavonol sulfonates 3HF-1, 3HF-2 and 3HF-3.

Figure 2: UV absorption spectra of flavonol sulfonate esters 3HF-1, 3HF-2 and 3HF-3.

Figure 3: ¹ H NMR of substance 3HF-1.

Figure 4: ¹ H NMR of substance 3HF-2.

Figure 5: ¹ H NMR of substance 3HF-3.

Figure 6: The change curve of the double bond conversion rate of TPGDA initiated by 3HF-1, 3HF-3 and CQ single-component initiating system as a function of illumination time.

Detailed ways

The technical solution of the present invention will be further described in detail below through specific examples. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any formal modifications or changes made to the present invention will fall within the protection scope of the present invention.

In the present invention, unless otherwise specified, all parts and percentages are units of weight, and the equipment and raw materials used can be purchased from the market or are commonly used in the field.

The test methods in the examples are described below:

This article uses near-infrared spectroscopy to monitor the change of TPGDA double bond characteristic peaks with illumination time to calculate the photocuring conversion rate.

Monitor the change of TPGDA double bond characteristic peak at 6165cm ^-1 with illumination time through NIR spectrum, and calculate the double bond conversion rate at different illumination times according to formula 1-1.

In the formula, St represents the peak area of the double bond characteristic absorption peak at 6165 cm ^-1 when the illumination time is t, and S ₀ is the peak area of the characteristic peak before illumination.

Example 1

Synthesis of initiator 2-(4-(diphenylamino)phenyl)-4-oxo-4H-benzofuran-3-ylbenzenesulfonate

The synthesis process is shown in the following formula:

Add 38.6 mL DMF, 37.3 mL phosphorus oxychloride, and 24.8 g triphenylamine dissolved in 1,2-dichloroethane into a 500 ml single-neck bottle, and heat to 80°C. TLC detects that the raw material point disappears. Pour the reaction solution into 100 mL of ice water, adjust the pH value to neutral with sodium hydroxide, extract multiple times with dichloromethane, and concentrate to obtain 4-(diphenylamino)benzaldehyde.

Add 12g sodium hydroxide to a 500ml round-bottomed flask, dissolve 30ml water, lower the temperature to room temperature, then add 20ml ethanol, weigh 4.86g 2-hydroxyacetophenone and 9.78g 4-(diphenylamino)benzaldehyde and mix, Dissolve and dilute with 70 ml of ethanol, drop half of the mixed solution into the round-bottomed flask, and add the remaining half after 30 minutes. Insulate at 50°C until the reactants are dissolved, react for 12 hours, then add 12 ml H ₂ O ₂ and continue the reaction for 12 hours. After TLC detection, the raw material point disappears. Adjust pH to 7 with dilute hydrochloric acid. The crude product was obtained by suction filtration. Recrystallization from ethanol/water (1:1) gave 2-(4-(diphenylamino)phenyl)-3-hydroxy-4H-benzofuran-4-one.

Add 2g of 2-(4-(diphenylamino)phenyl)-3-hydroxy-4H-benzofuran-4-one into a 100ml round-bottomed flask, dissolve it in 30ml of dichloromethane, and add 1.0g of triethylamine. Slowly add 1.74g benzene sulfonyl chloride dropwise into the round bottom flask, and detect by TLC. After the raw material point disappears. Add water to remove water-soluble impurities, then rotary evaporate to remove the solvent, and use column chromatography to separate and obtain 2.1g of 2-(4-(diphenylamino)phenyl)-4-oxo-4H-benzofuran-3-ylbenzenesulfonic acid. salt (named 3HF-1, its structure is shown in Figure 1), the yield was 78%.

The structure of product 3HF-1 was confirmed by hydrogen nuclear magnetic resonance spectrum (as shown in Figure 3). The specific characterization results are as follows:

¹ H NMR (400MHz, CDCl ₃ ) δ8.20 (dd, J＝8.0, 1.5Hz, 1H), 8.01 (dd, J＝8.4, 1.2Hz, 2H), 7.87–7.80 (m, 2H), 7.72– 7.61(m,2H),7.56–7.48(m,3H),7.45–7.30(m,5H),7.16(dd,J＝12.6,7.4Hz,6H),7.04–6.97(m,2H).MS( ESI) calculated for C ₃₃ H ₂₃ NO ₅ S 545.13, found546.1683(M+H ⁺ ).

The ultraviolet absorption spectrum of flavonol sulfonate 3HF-1 obtained in Example 1 is shown in Figure 2. From Figure 2, it can be seen that 3HF-1 has good absorption in the visible light region and matches the visible light LED light source.

Example 2

Synthesis of initiator 2-(10-ethyl-10H-phenothiazin-3-yl)-4-oxo-4H-chromium-3-yl benzene sulfonate

The synthesis process is shown in the following formula:

Add 38.6 mL DMF, 37.3 mL phosphorus oxychloride, and 23.0 g 10-ethyl-10H-phenothiazine dissolved in 1,2-dichloroethane into a 500 ml single-neck bottle, and heat to 80°C. TLC detects that the raw material point disappears. Pour the reaction solution into 100 mL ice water, adjust the pH value to neutral with sodium hydroxide, extract multiple times with dichloromethane, and concentrate to obtain 10-ethyl-10H-phenothiazine-3- formaldehyde.

Add 12g sodium hydroxide to a 500ml round-bottomed flask, dissolve 30ml water, bring the temperature to room temperature, then add 20ml ethanol, weigh 4.86g 2-hydroxyacetophenone and 9.13g 10-ethyl-10H-phenothiazine- 3- Mix formaldehyde, dissolve and dilute with 70 ml of ethanol, drop half of the mixed solution into the round-bottomed flask, and add the remaining half after 30 minutes. Insulate at 50°C until the reactants are dissolved, react for 12 hours, then add 12 ml H ₂ O ₂ and continue the reaction for 12 hours. After TLC detection, the raw material point disappears. Adjust pH to 7 with dilute hydrochloric acid. The crude product was obtained by suction filtration. Recrystallization from ethanol/water (1:1) gave 2-(10-ethyl-10H-phenothiazin-3-yl)-3-hydroxy-4H-benzofuran-4-one.

Add 1.91g of 2-(10-ethyl-10H-phenothiazin-3-yl)-3-hydroxy-4H-benzofuran-4-one into a 100ml round bottom flask, dissolve it in 30ml of dichloromethane, and add 1.0g triethylamine, 1.74g benzenesulfonyl chloride was slowly added dropwise into the round-bottomed flask, and TLC detected that the raw material point disappeared. Water was added to remove water-soluble impurities, then the solvent was removed by rotary evaporation, and 1.6g of 2-(10-ethyl-10H-phenothiazin-3-yl)-4-oxo-4H-chromium-3-yl was obtained by column chromatography. Benzenesulfonate (named 3HF-2, its structure is shown in Figure 1), the yield is 68%.

The structure of product 3HF-2 was confirmed by hydrogen nuclear magnetic resonance spectrum (as shown in Figure 4). The specific characterization results are as follows:

¹ H NMR (400MHz, CDCl ₃ ) δ8.24(d,J＝7.9Hz,1H),7.85(d,J＝7.2Hz,2H),7.70(t,J＝7.0Hz,2H),7.52(d ,J＝8.4Hz,1H),7.48(s,1H),7.42(t,J＝7.6Hz,1H),7.34(dt,J＝14.7,7.1Hz,3H),7.19(s,1H),7.12 (d,J＝7.3Hz,1H),7.06–6.86(m,2H),6.79(s,1H),3.95(s,2H),1.45(t,J＝6.9Hz,3H).MS(ESI) calculated for C ₂₉ H ₂₁ NO ₅ S ₂ 527.61,found528.0939(M+H ⁺ ).

The ultraviolet absorption spectrum of flavonol sulfonate 3HF-2 obtained in Example 2 is shown in Figure 2. It can be seen from Figure 2 that 3HF-2 has good absorption in the visible light region and matches the visible light LED light source.

Example 3

Synthesis of initiator 2-(9-hexyl-9H-carbazol-3-yl)-4-oxo-4H-benzofuran-3-yl 4-(trifluoromethyl)benzenesulfonate

The synthesis process is shown in the following formula:

Add 38.6 mL DMF, 37.3 mL phosphorus oxychloride, and 25.4 g 9-hexyl-9H-carbazole dissolved in 1,2-dichloroethane into a 500 ml single-neck bottle, and heat to 80°C. TLC detects that the raw material point disappears. Pour the reaction solution into 100 mL of ice water, adjust the pH value to neutral with sodium hydroxide, extract multiple times with dichloromethane, and concentrate to obtain 9-hexyl-9H-carbazole-3-carbaldehyde.

Add 12g sodium hydroxide to a 500ml round-bottomed flask, dissolve 30ml water, lower the temperature to room temperature, then add 20ml ethanol, weigh 4.86g 2-hydroxyacetophenone and 9.99g 9-hexyl-9H-carbazole-3- Mix formaldehyde, dissolve and dilute with 70 ml of ethanol, drop half of the mixed solution into the round-bottomed flask, and add the remaining half after 30 minutes. Insulate at 50°C until the reactants are dissolved, react for 12 hours, then add 12 ml H ₂ O ₂ and continue the reaction for 12 hours. After TLC detection, the raw material point disappears. Adjust pH to 7 with dilute hydrochloric acid. The crude product was obtained by suction filtration. Recrystallization from ethanol/water (1:1) gave 2-(9-hexyl-9H-carbazol-3-yl)-3-hydroxy-4H-benzofuran-4-one.

Add 2.03g of 2-(9-hexyl-9H-carbazol-3-yl)-3-hydroxy-4H-benzofuran-4-one into a 100ml round-bottomed flask, dissolve it in 30ml of dichloromethane, and add 1.0g For triethylamine, slowly add 2.41g of 4-(trifluoromethyl)benzenesulfonyl chloride dropwise into the round-bottomed flask, and detect by TLC. After the raw material point disappears. Add water to remove water-soluble impurities, then rotary evaporate to remove the solvent, and use column chromatography to separate and obtain 1.8g of 2-(9-hexyl-9H-carbazol-3-yl)-4-oxo-4H-benzofuran-3-yl. 4-(Trifluoromethyl)benzenesulfonate (named 3HF-3, its structure is shown in Figure 1), with a yield of 71%.

The structure of product 3HF-3 was confirmed by hydrogen nuclear magnetic resonance spectrum (as shown in Figure 5). The specific characterization results are as follows:

¹ H NMR (400MHz, CDCl ₃ ) δ8.61(d,J＝1.5Hz,1H),8.28(dd,J＝8.0,1.4Hz,1H),8.08(d,J＝7.7Hz,1H),8.00 –7.89(m,3H),7.78–7.69(m,1H),7.61(d,J＝8.1Hz,1H),7.54(t,J＝7.6Hz,1H),7.50–7.35(m,5H), 7.32(t,J＝7.4Hz,1H),4.30(t,J＝7.4Hz,2H),1.89(p,J＝7.5Hz,2H),1.49–1.23(m,6H),0.89(t,J =7.0Hz,3H).MS(ESI)calculated forC ₃₄ H ₂₈ F ₃ NO ₅ S 619.66, found 620.1889(M+H ⁺ ).

The ultraviolet absorption spectrum of the flavonol sulfonate 3HF-3 obtained in Example 3 is shown in Figure 2. It can be seen from Figure 2 that 3HF-3 has good absorption in the visible light region and matches the visible light LED light source.

Example 4

Application of photoinitiator 3HF-1 prepared in Example 1 in free radical visible LED light curing system:

Prepare the visible light initiating system according to 0.125wt% photoinitiator 3HF-1. Taking the weight of the free radical polymerization monomer as 100%, add the visible light initiating system to the free radical polymerization monomer TPGDA and mix thoroughly to obtain a transparent and clear photocuring reaction. liquid.

Add the prepared light curing system to a rubber ring mold with a thickness of 1.0mm and a diameter of 7.0mm, fix it with two clean glass pieces, and illuminate it with a 405nm laser diode to ensure that the distance between the sample and the excitation light source is 3cm. , the light source is a 30W LED lamp: purple LED (JH-100B14G30-Z1C, 405nm). (LEDGUHON/Juhong Optoelectronics). In order to ensure the credibility of the experimental results, three NIR tests were performed on each light-curing system sample, and the average result was used as the final result.

Example 5

Application of the photoinitiator 3HF-3 prepared in Example 3 in the free radical visible LED light curing system:

Prepare the visible light initiating system according to 0.125wt% photoinitiator 3HF-3. Taking the weight of the free radical polymerization monomer as 100%, add the visible light initiating system to the free radical polymerization monomer TPGDA and mix thoroughly to obtain a transparent and clear photocuring reaction. liquid.

Add the prepared light curing system to a rubber ring mold with a thickness of 1.0mm and a diameter of 7.0mm, fix it with two clean glass pieces, and illuminate it with a 405nm laser diode to ensure that the distance between the sample and the excitation light source is 3cm. , the light source is a 30W LED lamp: purple LED (JH-100B14G30-Z1C, 405nm). (LEDGUHON/Juhong Optoelectronics). In order to ensure the credibility of the experimental results, three NIR tests were performed on each light-curing system sample, and the average result was used as the final result.

Comparative example 1

Application of camphorquinone (CQ) in free radical visible LED light curing system:

Prepare the visible light initiating system according to 0.125wt% camphorquinone. Taking the weight of the free radical polymerization monomer as 100%, add the visible light initiating system to the free radical polymerization monomer TPGDA and mix thoroughly to obtain a transparent and clear photocuring reaction solution.

Add the prepared light curing system to a rubber ring mold with a thickness of 1.0mm and a diameter of 7.0mm, fix it with two clean glass pieces, and illuminate it with a 405nm laser diode to ensure that the distance between the sample and the excitation light source is 3cm. , the light source is a 30W LED lamp: purple LED (JH-100B14G30-Z1C, 405nm). (LEDGUHON/Juhong Optoelectronics). In order to ensure the credibility of the experimental results, three NIR tests were performed on each light-curing system sample, and the average result was used as the final result.

Result analysis

As can be seen from Figure 1: the structure involved in the embodiments of this article.

It can be seen from Figure 2 that flavonol sulfonate 3HF-1, 3HF-2 and 3HF-3 have good absorption at visible light (>405nm), which is consistent with the emission of visible light sources.

Figures 3, 4 and 5 are ¹ H NMR of 3HF-1, 3HF-2 and 3HF-3 respectively. It can be seen that the structure in the embodiment is correct.

In the above-mentioned Examples 4 and 5 and Comparative Example 1, the conversion rate of radical photocuring initiated by the photoinitiating system is shown in Figure 6.

It can be seen from Figure 6 that the single-component 3HF-1 and 3HF-3 initiating systems can initiate the curing of TPGDA under the 405nm LED light source. Among them, when irradiated for 150 seconds, under the 405nm light source, the conversion rates of 3HF-1 and 3HF-3 can reach more than 80%, while the conversion rate of CQ is only 30%.

In summary: 3HF-1 and 3HF-3 have high molar extinction coefficients at 405nm, which are sufficient to initiate TPGDA polymerization at concentrations as low as 0.125%, and the initiation efficiency is higher than that of CQ.

Therefore, the photoinitiator disclosed in the present invention can be used in conventional light curing systems and can be well matched with visible-LED light sources, thus solving the shortcomings of traditional light curing systems that cannot be cured or have a low curing rate under LED light sources, and expand The application space of light curing system has been expanded. At the same time, compared with the commercial initiator CQ, it has higher initiating efficiency, indicating that the photoinitiator of the present invention has efficient performance.

Claims (7)

1. A preparation method of a single-component flavonol sulfonate visible light initiator is characterized by comprising the following steps: the structural general formula of the single-component flavonol sulfonate visible light initiator is as follows:

wherein R is ₁ Selected from carbazole having alkyl substitution on the N atom thereof, said alkyl being selected from C ₁ -C ₂₀ Straight chain alkyl or C ₁ -C ₂₀ Branched alkyl; r is R ₂ Selected from 4-methylphenyl or 4-trifluoromethylphenyl;

the method comprises the following specific steps:

(1) 2-hydroxyacetophenone and R-containing ₁ An aldehyde of (a) is synthesized into an intermediate I by an Algar-Flynn-Oyamada method;

(2) Intermediate I is soluble in solventAfter decomposition, in the presence of triethylamine and in the presence of R ₂ Synthesizing flavonol sulfonate through substitution reaction; the specific synthetic route is as follows:

wherein, 2-hydroxyacetophenone contains R ₁ The molar ratio of aldehydes is 1:1, intermediate I, triethylamine, containing R ₂ The molar ratio of the sulfonyl chloride is 1:2:2.

2. the method for preparing the single-component flavonol sulfonate visible light initiator according to claim 1, which is characterized in that: the solvent in the step (2) is methylene dichloride.

3. The method for preparing the single-component flavonol sulfonate visible light initiator according to claim 1, which is characterized in that: the synthesis process of the initiator 3HF-3 is shown in the following formula:

38.6mL of DMF, 37.3mL of phosphorus oxychloride and 25.4g of 9-hexyl-9H-carbazole are added into a 500mL single-port bottle and dissolved in 1, 2-dichloroethane, the temperature is heated to 80 ℃, the TLC detects the disappearance of the raw material point, the reaction liquid is poured into 100mL of ice water, the pH value is regulated to be neutral by sodium hydroxide, the dichloromethane is used for multiple extraction, and the 9-hexyl-9H-carbazole-3-formaldehyde is obtained by concentration;

adding 12g of sodium hydroxide and 30ml of water into a 500ml round bottom flask for dissolution, cooling to room temperature, then adding 20ml of ethanol, weighing 4.86g of 2-hydroxyacetophenone and 9.99g of 9-hexyl-9H-carbazole-3-formaldehyde for mixing, dissolving and diluting with 70ml of ethanol, adding half of the mixed solution into the round bottom flask dropwise, adding the rest half after 30min, preserving heat at 50 ℃ until reactants are dissolved, reacting for 12H, and then adding 12ml of H ₂ O ₂ Continuing the reaction for 12h, detecting by TLC, adjusting pH to 7 with dilute hydrochloric acid after the raw material point disappears, and suction filtering to obtain crude productRecrystallizing the product by ethanol/water to obtain 2- (9-hexyl-9H-carbazole-3-yl) -3-hydroxy-4H-benzofuran-4-one, wherein the volume ratio of ethanol to water in the ethanol/water is 1:1, a step of;

2.03g of 2- (9-hexyl-9H-carbazol-3-yl) -3-hydroxy-4H-benzofuran-4-one was dissolved in 30ml of dichloromethane, 1.0g of triethylamine was added to the flask, 2.41g of 4- (trifluoromethyl) benzenesulfonyl chloride was slowly added dropwise to the flask, TLC was checked, after the starting point had disappeared, water-soluble impurities were removed by adding water, and then the solvent was removed by rotary evaporation, and 1.8g of 3HF-3 was obtained by column chromatography.

4. The application of a single-component flavonol sulfonate visible light initiator in a free radical type visible LED light curing system is characterized in that: the structural general formula of the single-component flavonol sulfonate visible light initiator is as follows:

wherein R is ₁ Selected from carbazole having alkyl substitution on the N atom thereof, said alkyl being selected from C ₁ -C ₂₀ Straight chain alkyl or C ₁ -C ₂₀ Branched alkyl; r is R ₂ Selected from 4-methylphenyl or 4-trifluoromethylphenyl.

5. The use of the one-component flavonol sulfonate visible light initiator according to claim 4, wherein the one-component flavonol sulfonate visible light initiator is characterized in that: the method comprises the following specific steps:

(1) Preparing a single-component flavonol sulfonate visible light initiator into a visible light initiation system;

(2) Adding a free radical polymerization monomer into a visible light initiation system, and mixing to obtain a transparent and clear photocuring system;

(3) Irradiating the photocurable system with a light source;

(4) The polymerization conversion was estimated by the change of its characteristic peak by the method of on-line infrared.

6. The use of a one-component flavonol sulfonate visible light initiator according to claim 5, wherein: the light source is an LED visible light source with the wavelength larger than 405 nm.

7. The use of a one-component flavonol sulfonate visible light initiator according to claim 5, wherein: the weight ratio of the single-component flavonol sulfonate visible light initiator to the free radical polymerization monomer is (0.05-2) 100.