Coumarin oxime ester compound as well as preparation method and application thereof

Abstract

The invention belongs to the field of photoinitiators, and particularly relates to a high-activity coumarin oxime ester compound with a push-pull electron structure, a preparation method of the coumarin oxime ester compound and application of the coumarin oxime ester compound as a photoinitiator. Specific electron-withdrawing and electron-donating groups are selected to be substituted at proper positions of the coumarin oxime ester compound, so that the compound has good performance and can be used as a photoinitiator.

Description

Technical Field

[0001] The present invention belongs to the field of photoinitiators, and in particular relates to a class of highly active coumarin oxime ester compounds with a push-pull electron structure, a preparation method thereof, and use of the compounds as photoinitiators. Background Art

[0002] Photoinitiators are key components in photocurable materials. Their mechanism of action typically involves absorbing light energy to generate reactive species such as free radicals or acids, which then initiate polymerization. Norrish I (cleavage-type) photoinitiators directly generate free radicals through molecular bond cleavage. Compared to Norrish II (hydrogen abstraction-type) photoinitiators, these agents offer higher initiation efficiency and are therefore more widely used in industrial production. Among these, coumarin oxime ester derivatives are a type I photoinitiator that combine a coumarin chromophore with a photosensitizing oxime ester bond. They exhibit excellent photophysical properties (strong absorption, fluorescence, and a large Stokes shift) and an absorption spectrum that can be tunable through structural modification. Furthermore, the coumarin nucleus possesses excellent biocompatibility, making coumarin-based photoinitiators widely used not only in industrial photopolymerization but also in biomedical applications.

[0003] The specific advantages of the current photoinitiators with coumarin oxime ester structures are: (1) easy structural modification, high stability, and low cost. Compared with other complex photoinitiators, the introduction reaction of the oxime ester bond is simple and can be formed under mild conditions. The resulting compound has good chemical stability during storage and use. (2) Efficient photolysis to generate free radicals. The unique structure of the coumarin oxime ester molecule contains a C=N double bond and an N−O single bond. The C=N double bond can undergo cis-trans isomerization under light, effectively absorbing and converting light energy; the N−O single bond has a low dissociation energy and is the key cleavage site of the photoreaction. Under the photoexcitation state, coumarin oxime ester preferentially undergoes N−O bond homolysis to generate imine radicals and acyloxy radicals, generally following the Norrish I type cleavage mechanism. (3) High initiation efficiency and few side reactions. After the oxime ester bond is cleaved, an irreversible decarboxylation reaction occurs, releasing carbon dioxide. Decarboxylation alters the free radical structure, preventing radical recombination and improving initiation efficiency. Furthermore, the released CO₂ creates an inert atmosphere within the resin, preventing oxygen diffusion and thus mitigating oxygen inhibition. These characteristics enable oxime ester photoinitiators to generate sufficient free radicals at relatively low light intensities, initiating polymerization rapidly and efficiently. Furthermore, the introduction of a coumarin chromophore allows the absorption wavelength of this type of photoinitiator to be tuned to the visible light range, reducing the energy required for photoinitiation.

[0004] Previous studies have shown that by introducing different electron donor and acceptor substituents into coumarin molecules, their absorption spectra can be significantly red-shifted and their photoinitiation activity enhanced. For example, Li et al. first reported four coumarin oxime ester photoinitiators (named O-4, O-3, O-3F, and O-3O) based on a 7-diethylaminocoumarin backbone, capable of initiating polymerization under visible light at a wavelength of approximately 450 nm. These studies demonstrate that coumarin oxime esters can be molecularly designed to respond to visible light, exhibiting rapid initiation and photobleaching during the photocuring of thicker materials, facilitating light penetration and enabling the curing of samples up to 10 mm thick. This suggests that coumarin oxime ester photoinitiators have the potential to become a new generation of highly efficient visible light photoinitiators.

[0005] However, due to the wide variety of commonly used electron-withdrawing and electron-donating substituent structures, the photoinitiating performance of coumarin oxime esters is influenced by numerous factors, including chromophore structure, the electron-donating / withdrawing effects of the substituents, N−O bond energy, and molecular orbital energy distribution. New functional group substitution schemes for coumarin oxime esters typically require extensive theoretical design combined with experimental analysis of performance indicators such as absorption peak position and photolysis efficiency to ultimately obtain coumarin oxime ester photoinitiators with strong photoinitiating properties. This is why coumarin oxime ester photoinitiators currently have limited application areas, are expensive, and are difficult to commercialize on a large scale. Summary of the Invention

[0006] To address the difficulties and bottlenecks in the structural design and preparation of these coumarin oxime ester photoinitiators, as well as the limitations of their photoinitiating performance, the present invention provides a coumarin oxime ester photoinitiator with high activity and strong initiating characteristics. This invention aims to efficiently develop a coumarin oxime ester photoinitiator with a strong push-pull charge effect and excellent photoinitiating performance, surpassing existing similar structures.

[0007] The technical solution of the present invention:

[0008] The technical problem to be solved by the present invention is to provide a highly active coumarin oxime ester photoinitiator molecule and a preparation method thereof, comprising: (1) constructing a coumarin skeleton through aldol condensation, (2) introducing an oxime hydroxyl functional group through oximation reaction, and (3) introducing an electron-withdrawing acyl group through acyl chloride esterification.

[0009] The first technical problem to be solved by the present invention is to provide a coumarin oxime ester compound represented by formula (I),

[0010]

[0011] Formula (I)

[0012] Wherein, R1 is selected from H, phenyl; R2 is selected from -NR a Rb , R a 、R b Each independently selected from H, C 1-4 Alkyl; R3 is selected from H, C 1-4 Alkyl; R4 is selected from unsubstituted or halogen-substituted phenyl, 5-membered heteroaryl, the 5-membered heteroaryl containing 1, 2 or 3 heteroatoms selected from N, O and S, the 5-membered heteroaryl is unsubstituted or substituted by nitro.

[0013] Preferably, in the above coumarin oxime ester compounds, R1 is selected from H.

[0014] Preferably, in the above-mentioned coumarin oxime ester compounds, R2 is selected from −N(Me)2 and −N(Et)2.

[0015] Preferably, in the above coumarin oxime ester compounds, R3 is selected from H, methyl, and ethyl.

[0016] Furthermore, in the above coumarin oxime ester compounds, R3 is selected from methyl.

[0017] Preferably, in the above coumarin oxime ester compounds, R4 is selected from unsubstituted or halogen-substituted phenyl, 5-membered heteroaryl, the 5-membered heteroaryl contains 1, 2 or 3 N heteroatoms, and the 5-membered heteroaryl is unsubstituted or substituted by nitro.

[0018] Furthermore, in the above coumarin oxime ester compounds, R4 is selected from fluorine-substituted phenyl and triazole, and the triazole is unsubstituted or substituted by nitro.

[0019] Furthermore, in the above coumarin oxime ester compounds, R4 is selected from fluorine-substituted phenyl.

[0020] Furthermore, in the above-mentioned coumarin oxime ester compounds, R4 is selected from 、 .

[0021] Furthermore, in the above coumarin oxime ester compounds, R4 is selected from .

[0022] As a preferred technical solution of the present invention, the above-mentioned coumarin oxime ester compound has the following structure:

[0023] .

[0024] The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned coumarin oxime ester compounds. The preparation method comprises the following steps: (1) With β-ketoester compounds The intermediate A is reacted under the catalysis of an organic base to obtain an intermediate A; (2) the intermediate A is reacted with a hydroxylamine compound under the catalysis of an organic base to obtain an intermediate B; (3) the intermediate B is reacted with an acyl halide reagent to obtain the coumarin oxime ester compound. c Removed during the reaction. c It can be selected from H, methyl, ethyl, etc.

[0025] Specifically, in the preparation method of the above-mentioned coumarin oxime ester compound, in step (1), the aromatic aldehyde compound is selected from one or more of 4-diethylaminosalicylaldehyde and 4-dimethylaminosalicylaldehyde.

[0026] Specifically, in the preparation method of the above-mentioned coumarin oxime ester compound, in step (1), the β-ketoester compound is selected from one or more of ethyl acetoacetate and methyl acetoacetate.

[0027] Specifically, in the preparation method of the above-mentioned coumarin oxime ester compound, in step (1), the organic base is selected from one or more of L-proline, D-proline, triethanolamine, and piperidine.

[0028] Specifically, in the preparation method of the above-mentioned coumarin oxime ester compound, in step (2), the hydroxylamine compound is selected from one or more of hydroxylamine hydrochloride, hydroxylamine sulfate or free hydroxylamine aqueous solution.

[0029] Specifically, in the preparation method of the above-mentioned coumarin oxime ester compound, in step (2), the organic base is selected from one or more of piperidine, pyrrolidine, morpholine, and triethylamine.

[0030] Specifically, in the above-mentioned method for preparing coumarin oxime ester compounds, in step (3), the acyl halide reagent is an acyl chloride reagent.

[0031] Furthermore, in the preparation method of the above-mentioned coumarin oxime ester compound, in step (3), the acyl chloride reagent is selected from one of benzoyl chloride, p-fluorobenzoyl chloride, and perfluorobenzoyl chloride.

[0032] The third technical problem to be solved by the present invention is to provide the use of the above-mentioned coumarin oxime ester compounds as photoinitiators.

[0033] Beneficial effects of the present invention:

[0034] The coumarin oxime ester photoinitiator of the present invention can simultaneously meet the maximum absorption wavelength (λ max ) ≥ 400 nm, the conversion rate is ≥ 80% when irradiated at 405 nm wavelength for 300 s, the hyperfine coupling constants aN(G) ≥ 14.8, and aH(G) ≥ 2.9.

[0035] The coumarin oxime ester photoinitiator of the present invention exhibits excellent photoinitiating properties, simultaneously achieving multiple indicators of a highly active photoinitiator. For example, its maximum absorption wavelength is greater than 400 nm, effectively reducing the energy required for excitation. Its high maximum extinction coefficient enables efficient absorption at the target wavelength, facilitating initiator cleavage and conversion. Its short-term conversion rate exceeds 80%, shortening the initiator cleavage time, increasing the efficiency of free radical generation, and enhancing the photocuring effect. Its electron spin spectrum parameters (hyperfine coupling constants) are greater than 14.8 (G) and 2.9 (H), and it can achieve a mechanical balance between rigidity and flexibility in the photocured material, indicating that the free radical lifetime is relatively short, the electrons are highly localized, the reactivity is strong, and the curing effect is good, surpassing traditional coumarin oxime ester structures.

[0036] The coumarin oxime ester photoinitiator obtained in the present invention, through a low-energy consumption and low-environmental-load photoinitiator design-preparation route, is superior to similar compounds reported previously in terms of absorption spectrum, initiation efficiency, and curing depth. It has broad application prospects in the fields of photocurable 3D printing, biomedical hydrogel photocuring molding, and so on. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The schematic diagram of the synthesis of the photoinitiator of the present invention shows the synthesis route of the coumarin intermediate A, the oximation intermediate B and the target coumarin oxime ester photoinitiator C using a three-step reaction method.

[0038] Figure 2 UV-Vis absorption spectra (left) and fluorescence emission spectra (right) of photoinitiators C-1-4 in acetonitrile solution. The UV-Vis curves (left) show that C-1-C-3 all have characteristic photoinitiator absorption wavelengths exceeding 400 nm, with C-1 absorbing at approximately 430 nm. The fluorescence emission spectrum (right) shows that C-1 exhibits significant fluorescence emission at the short wavelength of 476 nm. Tauc plot analysis indicates that C-1 has a narrow transition band gap, a short excited state lifetime, and low fluorescence efficiency, suggesting a preference for relaxation dissipation via nonradiative transitions (e.g., intersystem crossing (ISC) to triplet states), which favors fragmentation or free radical formation.

[0039] Figure 3 Steady-state photolysis spectra of photoinitiators C-1–4 in acetonitrile solution under 405 nm irradiation, along with a schematic diagram of the solution color change before and after photolysis of photoinitiator C-1. The steady-state spectra demonstrate that photoinitiator C-1 achieves over 80% conversion within 300 s, exceeding both the conversion rate and conversion rate of the other control groups. The steady-state photolysis photographs confirm that photoinitiator C-1 achieves complete cleavage and conversion within 600 s, with the solution color completely fading.

[0040] Figure 4 Electron spin resonance (ESR) spectra of photoinitiators C-1-4 captured by PBN in a DMSO solution reveal free radical capture. The spin spectrum demonstrates that the free radicals generated by photocleavage of initiators C-1-C-4 are triplet states. Fitted hyperfine coupling constants are large (particularly C1, which has the largest), indicating a relatively short free radical lifetime, highly localized electrons, and strong reactivity.

[0041] Figure 5 Digital photographs showing the visual detection of CO₂ production by the decarboxylation reaction induced by photoinitiators C-1-4 in acetonitrile solution under 405 nm UV irradiation. The left side of each photograph shows a potassium carbonate aqueous solution (pH = 10.5, purple) containing the phenolphthalein indicator, and the right side shows a toluene solution (yellow-green) containing the photoinitiator. Their photochemical activity stems from the photoinduced cleavage of the N−O bond within the molecule and the subsequent decarboxylation reaction to produce CO₂. Upon irradiation with 405 nm UV light, the toluene solution on the right exhibits significant discoloration (yellow-green to pale yellow), confirming N−O bond cleavage and subsequent decarboxylation within the photoinitiator. The color of the solution on the left changes from purple to light pink, confirming that the decarboxylation reaction produces CO₂, which causes discoloration of the indicator solution. Sample C-1 exhibits the most pronounced discoloration, demonstrating the optimal cleavage and decarboxylation performance.

[0042] Figure 6 Photographic images (a, b) of 3D printing of maleic acid-modified gelatin (MAH) and norbornene-modified gelatin (NB) using the present invention's photoinitiator C-1 and the commercially available photoinitiator Irgacure 2959, respectively, along with stress-strain curves (c) and a summary comparison of mechanical property data for each sample (d). The mechanical property statistical histograms show that GelMAH and GelNB samples cured with C-1 exhibit higher elongation at break and maximum tensile stress than those cured with Irgacure 2959, indicating that C-1 induces the formation of a more complete and dense cured cross-linked network, resulting in superior performance. DETAILED DESCRIPTION

[0043] The coumarin oxime ester compounds of the present invention are based on the π-bridge structure of coumarin itself. The substituents are mainly screened at the farthest end of the π-bridge structure, and electron-pushing substituents and electron-withdrawing substituents are added. The electron acceptor and donor functional groups need to be at the diagonal sites of the π-bridge of the coumarin parent nucleus. The electron-pushing substituent (R2) is selected from -NR a R b (e.g. N,N-dimethyl, N,N-diethyl); the electron-withdrawing substituent (R4) is selected from unsubstituted or halogen-substituted phenyl, 5-membered heteroaryl, the 5-membered heteroaryl containing 1, 2 or 3 heteroatoms selected from N, O and S, the 5-membered heteroaryl is unsubstituted or substituted with nitro (e.g. 、 ).

[0044] The present invention discloses a method for preparing coumarin oxime ester compounds. In the first step, a Knoevenagel aldol condensation reaction is performed in which an aromatic aldehyde containing an electron-donating substituent reacts with a β-ketoester compound in the presence of an organic base catalyst, resulting in dehydration, condensation, and cyclization to produce a coumarin core intermediate A bearing an electron-donating substituent. In the second step, intermediate A reacts with a hydroxylamine compound in the presence of an organic base catalyst to undergo a nucleophilic addition-elimination reaction, thereby introducing an oxime hydroxyl group at the acyl position of the coumarin backbone to produce an oxime hydroxyl intermediate B. In the third step, oxime hydroxyl intermediate B reacts with an acyl halide reagent containing an electron-withdrawing group to produce the target coumarin oxime ester photoinitiator. Through esterification condensation between the acyl chloride and the oxime hydroxyl group, an electron-withdrawing group is successfully introduced into the acyl end of the oxime ester bond, thereby producing a coumarin oxime ester product having a push-pull charge distribution.

[0045] The coumarin oxime ester photoinitiator molecules of the present invention incorporate a strong electron-pushing group (R2) on the coumarin backbone and a strong electron-withdrawing group (R4) at the oxime ester acyl end, creating a highly efficient electron-pushing and electron-pulling conjugation effect within the molecule. This significantly red-shifts the maximum absorption wavelength to the visible light region of approximately 450-480 nm. This improves the accessibility of the initiation wavelength compared to unmodified coumarin oxime esters, thereby reducing the energy required for excitation and making it easier to achieve initiation conditions. This reduces curing costs and achieves energy conservation and emission reductions. The photoinitiator of the present invention can be activated by visible light LEDs around 405 nm, meeting the current demand for curing with low-energy LED sources. Furthermore, the introduction of the push-pull electron structure reduces the bond dissociation energy of the oxime ester N-O bond, facilitating N-O bond cleavage under illumination, increasing the quantum yield of the photoinitiator and enabling more rapid free radical generation. Combined with the instantaneous decarboxylation of the oxime ester, the photoinitiator of the present invention achieves photobleaching during polymerization initiation, reducing the self-attenuation of light absorption. This allows for photocuring of thicker materials without incomplete curing. Furthermore, the photoinitiator exhibits excellent thermal stability, remaining stable at conventional storage and processing temperatures and resistant to premature decomposition. The polymer materials formed by its initiation and curing exhibit excellent mechanical properties, demonstrating its suitability for the preparation of high-strength cured products.

[0046] Example 1

[0047] Preparation of 7-N,N-diethyl 3-(1-(hydroxyimino)ethyl)coumarin perfluorobenzoyl chloride oxime ester

[0048]

[0049] The photoinitiator molecule synthesized in this example contains a strong electron-withdrawing perfluoroaromatic acyl group, which can form a strong "push-pull" charge effect with the N,N-diethyl group on the coumarin core.

[0050] First, 4-diethylamino-salicylaldehyde (6.01 g, 31.0 mmol) was added to 80 mL of triethanolamine and stirred for 5 minutes. Ethyl acetoacetate (4.81 mL, 37.0 mmol) and L-proline (0.36 g, 1.69 mmol) were then added. The reaction was carried out under a nitrogen atmosphere. The oil bath was heated to 100°C and refluxed under condensation for 4 hours. After the reaction was complete, the mixture was cooled to 45°C. The reaction solution was added dropwise to 100 mL of ice water and stirred for 30 minutes. The precipitate was vacuum filtered and washed with a large amount of deionized water to obtain a crude yellow solid. The crude product was dried in a vacuum oven at 50°C for 12 hours to remove moisture. The crude product was then purified by silica gel column chromatography (petroleum ether:ethyl acetate = 6:1) to obtain Intermediate A as an orange solid in an approximately 74.32% yield. H NMR spectrum of Intermediate A: 1 H NMR (500 MHz, Chloroform-d), δ = 8.43 (d, 1H), 7.40 (d,1H), 6.63 (dd, 1H), 6.48 (d, 1H), 3.46 (q, 4H), 2.68 (s, 3H), 1.24 (t, 6H).

[0051] Intermediate A (534.2 mg, 2.06 mmol) was then uniformly dissolved in 20 mL of anhydrous ethanol, and piperidine (340 mL, 3.71 mmol) was added. After stirring for 5 minutes, hydroxylamine hydrochloride (300.4 mg, 4.30 mmol) was added. Under a nitrogen atmosphere, the mixture was heated to 80°C in an oil bath and allowed to react for 2 hours. After the reaction solution cooled to 45°C, 10 mL of 5% sodium bicarbonate solution was added and stirred for 5 minutes. The solution was poured into a separatory funnel and extracted with dichloromethane (3 × 15 mL) by vortexing. 10 mL of saturated brine was added and mixed. The organic layer was separated and dehydrated with anhydrous Na2SO4. The solid was filtered to obtain a solution. The dichloromethane was removed by rotary evaporation to obtain the crude product. The crude product was purified by silica gel column chromatography (petroleum ether:ethyl acetate = 6:1) to obtain Intermediate B as a red solid in an approximately 69.74% yield. H NMR spectrum of Intermediate B: 1H NMR (500 MHz, DMSO-d6), δ = 11.12(s, 1H), 7.87 (s, 1H), 7.50 (s, 1H), 6.72 (s, 1H), 6.53 (s, 1H), 3.43 (s,4H), 2.04 (s, 3H), 1.12 (s, 6H).

[0052] Finally, Intermediate B (1.37 g, 5 mmol) was uniformly dissolved in 30 mL of anhydrous dichloromethane. Triethylamine (1.39 mL, 10 mmol) was added and mixed. The mixture was cooled to below 0°C and stirred for 30 minutes. Under a nitrogen atmosphere, perfluorobenzoyl chloride powder (6 mmol) was dissolved in 10 mL of anhydrous dichloromethane and slowly added dropwise to the reaction solution over 10 minutes. The reaction was stirred for 2 hours. 10 mL of 5% sodium bicarbonate solution was added and stirred for 30 minutes. 10 mL of saturated brine was added to the reaction solution, and the organic phase was separated. The organic layer was dehydrated with anhydrous Na2SO4, and the solid was filtered to obtain an organic solution. The dichloromethane solution was removed by rotary evaporation to obtain a crude product. The crude product was purified by silica gel column chromatography (petroleum ether:ethyl acetate = 8:1) to obtain crystalline product C-1 in approximately 60% yield. H NMR spectrum: 1 H NMR (500 MHz, Chloroform-d), δ = 7.47 (s,1H), 7.46 (s, 1H), 6.57 (s, 1H), 6.55 (d, J = 2.5 Hz, 1H), 6.50 (s, 1H), 3.43(d, J = 7.1 Hz, 6H), 3.39 (s, 3H), 1.21 (s, 4H). 13 C NMR (126 MHz, Chloroform-d), δ = 162.31, 155.82, 152.20, 150.82, 146.13, 144.06, 133.25,115.43, 108.51, 106.12, 103.42, 89.44, 43.87, 13.08, 11.20.

[0053] The structural and performance parameters of product C-1 (7-N,N-diethyl 3-(1-(hydroxyimino)ethyl)coumarin perfluorobenzoyl chloride oxime ester) are shown in Table 1; the fluorescence emission spectrum of product C-1 is shown in Figure 2 As shown; the steady-state photolysis spectrum of product C-1 is as shown Figure 3 As shown; the EPR spectrum and hyperfine coupling constant of product C-1 captured by PBN in dimethyl sulfoxide solution are shown as Figure 4As shown in Table 2; the photodecarboxylation picture of product C-1 is as follows Figure 5 Comparison of mechanical properties of maleic acid modified gelatin and norbornene gelatin obtained by solidification of product C-1 Figure 6 As shown in Figure 2 (compared with the commercial photoinitiator Irgacure 2959, BASIF). The elongation at break and the maximum tensile stress of the cured maleic acid-modified gelatin prepolymer are both more than 20% higher than those of the sample cured with Irgacure 2959. Figure 6 shown.

[0054] The photocurable slurry was prepared by weighing an appropriate amount of C-1 and mixing it with 0.5 mL of acetone. The mixture was ultrasonically dissolved in an ultrasonic water bath for 20 minutes to obtain a clear C-1 solution. Simultaneously, an appropriate amount of the diluent polyethylene glycol diacrylate (PEGDA) was added to the pre-prepared modified gelatin prepolymers (GelNB and GelMA). After mechanical stirring for 5 minutes, the dissolved C-1 solution was added and mixed. The mixture was physically stirred for 5 minutes, followed by ultrasonic mixing for 30 minutes to homogenize the diluent and C-1. The mixture was then placed in a fume hood for 3 hours to remove excess solvent. The formulations are shown in the table below.

[0055] Material Mass (g) Mass fraction (wt.%) GelNB / GelMA (oligomer) 1 80 PEGDA (diluent) 0.1 8 C-1 (PI) 0.15 12

[0056] The prepared slurry was then centrifuged for 15 minutes to eliminate bubbles. The defoamed slurry was then injected into the standard syringe barrel of the 3D printing equipment (DIW) and installed in the constant temperature printing hopper. The model file was imported through a computer program, and the platform's movement path was planned using CAD software. The structure and size of the printed object were designed, the distance between the nozzle and the substrate was calibrated, and the Z axis was adjusted to zero using a standard feeler gauge to ensure smooth injection printing and avoid clogging. Before formal printing, a 3 cm × 3 cm single-layer pattern printing test was performed to observe the viscosity of the printing slurry, the movement speed of the platform, and the light curing time of the printed part. After the test, the printing program was started, the air pump pressure and platform stability were observed, and the printing was completed. The printed sample was transferred to the curing station for UV post-treatment (405 nm wavelength, 50 mW / cm² intensity irradiation for 10 minutes). After the light curing was completed, the corresponding cured part was obtained.

[0057] All performance indicators and test methods are currently recognized for photoinitiator testing. Please refer to: 1. Hammoud F, Hijazi A, Schmitt M, et al. A review on recently proposed oximeester photoinitiators[J]. European Polymer Journal, 2023, 188: 111901; 2. A mitochondria-targeted two-photon excited near-infrared emission hydrogen sulfide fluorescent probe and its preparation method and application, CN111635385 A; 3. Li Mengqi. Synthesis and performance study of coumarin-based photoinitiators[D]. Jiangnan University, 2022.

[0058] Comparative Example 1

[0059] Preparation of 7-N,N-diethyl 3-(1-(hydroxyimino)ethyl)coumarin piperic acid chloride oxime ester

[0060]

[0061] Steps 1 and 2 were identical to those in Example 1, except that in step 3, Intermediate B (1.37 g, 5 mmol) was uniformly dissolved in 30 mL of anhydrous dichloromethane, triethylamine (1.39 mL, 10 mmol) was added, the mixture was cooled to below 0°C, and the solution was stirred for 30 minutes. Under a nitrogen atmosphere, piperic acid chloride powder (6 mmol) was dissolved in 10 mL of anhydrous dichloromethane and slowly added dropwise to the reaction solution over 10 minutes. The reaction was stirred for 2 hours, followed by the addition of 10 mL of 5% sodium bicarbonate solution and stirring for 30 minutes. 10 mL of saturated brine was then added to the reaction solution, and the organic phase was separated. The organic layer was dehydrated with anhydrous Na2SO4, and the solid was filtered to obtain an organic solution. The dichloromethane solution was then removed by rotary evaporation to obtain a crude product. The crude product was purified by silica gel column chromatography (petroleum ether:ethyl acetate = 8:1) to obtain green crystalline product C-2 in a yield of 65.81%. H NMR spectrum: 1H NMR (500MHz, Chloroform-d), δ = 8.44 (d, J = 1.2 Hz, 1H), 7.86 (dd, J = 8.2, 1.7 Hz, 1H), 7.63 (d, J = 1.7 Hz, 1H), 7.43 (d, J = 4.9 Hz, 1H), 6.89 (d, J = 8.2 Hz,1H), 6.71 (dd, J = 8.9, 2.2 Hz, 1H), 6.49 (dd, J = 8.9, 2.5 Hz, 1H), 6.06 (s,2H), 3.45-3.40 (m, 4H), 3.37 (d, J = 7.3 Hz, 3H), 1.21-1.19 (m, 6H). NMR carbon spectrum: 13 C NMR (126 MHz, CDCl3), δ = 165.35, 164.04, 154.69, 154.66, 153.01,151.96, 150.28, 148.29, 145.77, 134.30, 127.04, 122.34, 117.54, 110.99, 108.37, 105.09, 102.41, 89.62, 45.30, 12.94, 12.72.

[0062] The structural and performance parameters of product C-2 (7-N,N-diethyl 3-(1-(hydroxyimino)ethyl) coumarin piperic acid chloride oxime ester) are shown in Table 1; the fluorescence emission spectrum of product C-2 is shown in Figure 2 As shown; the steady-state photolysis spectrum of product C-2 is as shown Figure 3 As shown; the EPR spectrum and hyperfine coupling constant of product C-2 captured by PBN in dimethyl sulfoxide solution are shown as Figure 4 As shown in Table 2; the photodecarboxylation picture of product C-2 is as follows Figure 5 shown.

[0063] Comparative Example 2

[0064] Preparation of 7-N,N-diethyl 3-(1-(hydroxyimino)ethyl)coumarin terephthaloyl chloride oxime

[0065]

[0066] This comparative example uses terephthaloyl dichloride (terephthaloyl chloride, also known as terephthaloyl bischloride) as an acylating agent in a reaction with intermediate B to investigate the effect of diacyl substitution on the performance of the photoinitiator. The reaction involves one equivalent of intermediate B and 0.5 equivalents of terephthaloyl chloride (theoretically, one terephthaloyl chloride molecule can react with two molecules of B). Esterification is carried out under otherwise identical conditions, followed by similar extraction and purification steps. The final product, C-3, is obtained as a yellow solid with a yield of approximately 56%, slightly lower than the product with single acyl substitution. The low yield is speculated to be related to the increased side reactions caused by the presence of the second acyl chloride group in terephthaloyl chloride. NMR and IR characterization of the product structure are consistent with the expected monosubstituted product (presumably, the second acyl chloride group is hydrolyzed to a carboxylic acid). Performance testing indicates that, compared to the monoacylcoumarin oxime esters described in the examples, the introduction of the terephthaloyl group results in a more rigid molecular structure and increased steric hindrance, leading to a decrease in photoinitiation efficiency. H NMR spectrum of product C-3: 1 H NMR (500 MHz, Chloroform-d), δ = 9.48 (s, 2H), 8.46-8.42 (m, 1H), 7.45 (d,J = 8.8 Hz, 1H), 6.25 (d, J = 2.4 Hz, 1H), 6.07 (s, 1H), 3.43 (s, 4H), 3.38(s, 3H), 1.19 (s, 6H). 13 C NMR (126 MHz, CDCl3), δ =163.36, 153.18,144.56, 134.36, 120.93, 110.38, 109.63, 103.33, 95.63, 76.26, 76.00, 75.75,43.79, 11.55, 11.38.

[0067] The structural and performance parameters of product C-3 (7-N,N-diethyl 3-(1-(hydroxyimino)ethyl) coumarin phthaloyl chloride oxime ester) are shown in Table 1; the fluorescence emission spectrum of product C-3 is shown in Figure 2 As shown; the steady-state photolysis spectrum of product C-3 is as shown Figure 3 As shown; the EPR spectrum and hyperfine coupling constant of product C-3 captured by PBN in dimethyl sulfoxide solution are shown as Figure 4 As shown in Table 2; the photodecarboxylation picture of product C-3 is as follows Figure 5 shown.

[0068] Comparative Example 3

[0069] Preparation of 7-N,N-diethyl 3-(1-(hydroxyimino)ethyl)coumarin phthaloyl chloride oxime ester

[0070]

[0071] This comparative example is similar to Comparative Example 2, except that the acylating agent is changed to phthaloyl dichloride (PhCl). Intermediate B and PCl are reacted in a 1:0.5 molar ratio. The product is purified to yield 7-N,N-diethyl 3-(1-(hydroxyimino)ethyl)coumarin phthaloyl chloride oxime, designated C-4, in approximately 63% yield. H NMR spectrum: 1 H NMR (500 MHz, Chloroform-d), δ = 8.02 (s, 2H), 7.93 (s, 2H), 7.92 (s, 2H), 7.91 (s, 2H),7.24 (s, 2H), 6.26 (s, 2H), 6.05 (s, 2H), 3.41 (s, 8H), 3.35 (s, 6H), 1.20(s, 12H). 13 C NMR (126 MHz, Chloroform-d), δ = 164.23, 162.64, 154.08,145.47, 135.92, 135.26, 131.17, 125.57, 111.22, 104.24, 96.49, 44.69, 12.43, 12.27.

[0072] The structural and performance parameters of product C-4 (7-N,N-diethyl 3-(1-(hydroxyimino)ethyl) coumarin phthaloyl chloride oxime ester) are shown in Table 1; the fluorescence emission spectrum of product C-4 is shown in Figure 2 As shown; the steady-state photolysis spectrum of product C-4 is as shown Figure 3 As shown; the EPR spectrum and hyperfine coupling constant of product C-4 captured by PBN in dimethyl sulfoxide solution are shown as Figure 4 As shown in Table 2; the photodecarboxylation picture of product C-4 is as follows Figure 5 Similar to Comparative Example 2, this compound is a diacyl-substituted coumarin oxime ester structure. Due to the ortho-diacyl substitution, hydrogen bonds may be formed in the molecule or greater conformational tension may be generated, resulting in a decrease in the efficiency of its N−O bond cleavage to produce active species.

[0073] Table 1 Photophysical properties of C-1~4

[0074] Photoinitiator <![CDATA[λ max (nm)]]> <![CDATA[C r @300 s(%)]]> <![CDATA[ε 405 (M -1 cm -1 )]]> <![CDATA[λ ex (nm)]]> <![CDATA[λ em-max (nm)]]> C-1 424 94.88 8660 438 476 C-2 473 3.97 5130 399 515 C-3 475 56.96 3070 404 515 C-4 361 67.68 3280 395 469

[0075] Table 2 Hyperfine coupling constant values ​​of C1~4 in ESR experiments

[0076] Photoinitiator aN(G) aH(G) C-1 14.94 3.10 C-2 14.81 2.92 C-4 14.48 2.84 C-5 14.65 2.97

[0077] Table 1 Photophysical properties of photoinitiators C-1~4, including maximum absorption wavelength (λ max ), the conversion rate when irradiated with 405nm UV for 300 seconds (C r @300 s), extinction coefficient at 405 nm (ε 405 ), emission wavelength (λ em ) and the maximum wavelength of fluorescence emission (λ em-max The data in Table 1 show that, except for C-4, the other samples have longer absorption wavelengths. The conversion rate of C-1 is the highest at 300s, which can reach more than 90%. At the same time, C-1 has the highest excitation wavelength (λ ex >430 nm) and lower emission wavelengths (λ em-max <480 nm), and C-1 has a high hyperfine coupling constant, indicating that the coumarin oxime ester photoinitiator has good activity and photocuring properties, among which C-1 exceeds the performance of the currently common coumarin oxime ester photoinitiators of the same type.

[0078] Table 2. Specific values ​​of the hyperfine coupling constants (aN, aH) for photoinitiators C-1–4 measured in electron spin resonance (ESR) experiments, which quantitatively characterize the stability and capture efficiency of free radicals. High hyperfine coupling constants demonstrate the high reactivity of the free radicals generated by the developed coumarin oxime ester photoinitiators.

[0079] It should be understood that the present invention is not limited to the above-described specific embodiments. Without departing from the principles of the present invention, skilled artisans may make various modifications and adjustments to the types and positions of the donor and acceptor substituents, the details of the synthesis process, etc., and such modifications shall be deemed to be within the scope of protection of the present invention.

Claims

1. A coumarin oxime ester compound represented by formula (I), Formula (I) in, R1 is selected from H, phenyl; R2 is selected from -NR a R b , R a 、R b Each independently selected from H, C 1-4 Alkyl; R3 is selected from H, C 1-4 Alkyl; R4 is selected from unsubstituted or halogen-substituted phenyl, 5-membered heteroaryl, the 5-membered heteroaryl containing 1, 2 or 3 heteroatoms selected from N, O and S, the 5-membered heteroaryl is unsubstituted or substituted by nitro.

2. The coumarin oxime ester compound according to claim 1, wherein: R2 is selected from -N(Me)2, -N(Et)2.

3. The coumarin oxime ester compound according to claim 1 or 2, characterized in that: R3 is selected from H, methyl, ethyl; preferably R3 is selected from methyl.

4. The coumarin oxime ester compound according to any one of claims 1 to 3, characterized in that: R4 is selected from unsubstituted or halogen-substituted phenyl, 5-membered heteroaryl, the 5-membered heteroaryl containing 1, 2 or 3 N heteroatoms, the 5-membered heteroaryl being unsubstituted or substituted by nitro; Preferably, R4 is selected from fluoro-substituted phenyl, triazole, and the triazole is unsubstituted or substituted by nitro; Preferably, R4 is selected from fluoro-substituted phenyl; Preferably, R4 is selected from 、 ; Most preferably, R4 is selected from .

5. The coumarin oxime ester compound according to claim 1, having the following structure: 。 6. The method for preparing the coumarin oxime ester compound according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) reacting an aromatic aldehyde compound with a β-ketoester compound under the catalysis of an organic base to obtain intermediate A; (2) reacting the intermediate A with a hydroxylamine compound under the catalysis of an organic base to obtain the intermediate B; (3) reacting the intermediate B with an acyl halide reagent to obtain the coumarin oxime ester compound.

7. The method for preparing coumarin oxime ester compounds according to claim 6, wherein: In step (1), the aromatic aldehyde compound is selected from one or more of 4-diethylaminosalicylaldehyde and 4-dimethylaminosalicylaldehyde; the β-ketoester compound is selected from one or more of ethyl acetoacetate and methyl acetoacetate; and the organic base is selected from one or more of L-proline, D-proline, triethanolamine, and piperidine.

8. The method for preparing the coumarin oxime ester compound according to claim 6 or 7, characterized in that: In step (2), the hydroxylamine compound is selected from one or more of hydroxylamine hydrochloride, hydroxylamine sulfate or free hydroxylamine aqueous solution; and the organic base is selected from one or more of piperidine, pyrrolidine, morpholine and triethylamine.

9. The method for preparing the coumarin oxime ester compound according to any one of claims 6 to 8, characterized in that: In step (3), the acyl halide reagent is an acyl chloride reagent; further, the acyl chloride reagent is selected from one of benzoyl chloride, p-fluorobenzoyl chloride, and perfluorobenzoyl chloride.

10. Use of the coumarin oxime ester compound according to any one of claims 1 to 5 as a photoinitiator.

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