Salicylaldehyde hydrazone bridged organic boron photoinitiator as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of organic synthesis, and particularly relates to a salicylaldehyde hydrazone bridged organic boron photoinitiator as well as a preparation method and application thereof. The structural formula of the salicylaldehyde hydrazone bridged organic boron photoinitiator is as shown in formula I, wherein R is H or halogen atom; the salicylaldehyde hydrazone bridged organic boron photoinitiator has a vertical spatial configuration formed by a seven-membered ring and a six-membered ring. A framework of the salicylaldehyde hydrazone bridged organic boron photoinitiator has a unique vertical spatial configuration, generation of a spinning triplet state can be effectively promoted through orbital angular momentum regulation and control, and a more favorable excited state characteristic is provided for a photoinitiation process. The absorption wavelength and the emission spectrum of an LED light source are well overlapped, and high reaction activity can still be kept under the conditions of low irradiation intensity (lt, 60 mW / cm) and short exposure time (lt, 60 s). In addition, the preparation method of the salicylaldehyde hydrazone bridged organic boron photoinitiator is simple and efficient, the raw material cost is low, and the salicylaldehyde hydrazone bridged organic boron photoinitiator has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a salicylaldehyde hydrazone-bridged organic boron photoinitiator, its preparation method, and its application. Background Technology

[0002] Photopolymerization technology, as a cutting-edge technology that transforms liquid resin into solid objects through photoinduced reactions, enables precise control of the reaction time and space. Nature Reviews Materials 2021 6 , 99). The emergence of this revolutionary technology has brought significant breakthroughs to multiple fields such as imaging technology, photolithography, adhesives, coatings, and 3D printing. Advanced Materials 2020 32 , 1903769; Chemical Reviews 2021 121 ,4001). However, the high-energy ultraviolet (UV) light widely used in current photolithography processes has many limitations. On the one hand, high-energy UV light easily leads to material degradation, affecting product performance; on the other hand, its light absorption characteristics are limited, and there are also certain safety hazards during use ( ). ACS Applied Materials&Interfaces 2022 14 In comparison, visible light emitting diodes (LEDs) have gradually become a research hotspot in the field of photopolymerization due to their significant advantages such as low radiation, non-toxicity, high cost-effectiveness, and high efficiency. Advanced Functional Materials 2023 33 , 2214567). This technological shift not only provides new directions for the development of biocompatible materials and lightweight composite materials, but also opens up new avenues for the fabrication of multifunctional 3D / 4D printed objects. Nature Communications 2022 13 , 7321; Science Advances 2023 9 (eadf4561). However, developing high-performance visible light initiators that combine rapid curing (<60 s) and low irradiance requirements (<60 mW / cm²) remains a critical research challenge in this field. Journal of Polymer Science 2022 60 Therefore, it is very necessary to continuously explore new high-performance visible light initiation systems.

[0003] In the field of photoinitiator research, acylphosphine oxides are considered a model of high-performance photoinitiators due to their rapid polymerization kinetics, excellent storage stability, and efficient photobleaching properties. Angewandte Chemie International Edition 2021 60, 12345). Although these compounds exhibit excellent thermal stability and curing efficiency, their limited water solubility and potential toxicity greatly limit their application in the biomedical field. Chemical Society Reviews 2022 51 , 6789). Meanwhile, germanium-based photoinitiators (especially acyl germanium) have begun to attract attention as alternatives to acylphosphine oxides, offering advantages such as lower toxicity and red-shifted absorption. Advanced Science 2023 10 (2205678), however, due to the scarcity of germanium, its cost remains high. In recent years, organoboron compounds such as boron dipyrrole methylene (BODIPY) and aza-BODIPY dyes have attracted much attention due to their high efficiency in inducing polymerization. Journal of the American Chemical Society 2022 144 , 12345). However, the synthetic routes for these compounds are quite complex, often requiring multiple reaction steps to complete ( Angewandte Chemie International Edition 2023 62 , e202301234). Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a salicylaldehyde hydrazone-bridged organoboron photoinitiator, its preparation method, and its applications. The backbone of this salicylaldehyde hydrazone-bridged organoboron photoinitiator possesses a unique vertical spatial configuration, which can effectively promote the generation of spin triplet states through orbital angular momentum modulation, providing more favorable excited-state characteristics for the photoinitiation process. Its absorption wavelength has good overlap with the emission spectrum of LED light sources, and it maintains high reactivity even under low irradiation intensity (<60 mW / cm²) and short exposure time (<60 s). Furthermore, the preparation method of this salicylaldehyde hydrazone-bridged organoboron photoinitiator is simple and efficient, with low raw material costs, and has broad application prospects.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a salicylaldehyde hydrazone-bridged organic boron photoinitiator, the structural formula of which is shown in Formula I: , Wherein, R is a H or a halogen atom; The salicylaldehyde hydrazone-bridged organic boron photoinitiator has a vertical spatial configuration consisting of a seven-membered ring and a six-membered ring.

[0006] Preferably, R is one of H, Br, F, Cl or I.

[0007] Preferably, R is H or Br.

[0008] More preferably, the substitution position of R is at position 3, 4 or 5 of the salicylaldehyde skeleton.

[0009] Preferably, the structure of the organohydrazine-bridged salicylaldehyde hydrazone boron complex is shown in formulas 1a-1e. .

[0010] Secondly, a method for preparing a salicylaldehyde hydrazone-bridged organic boron photoinitiator, the method comprising: 1) In the presence of a solvent, salicylaldehyde and / or salicylaldehyde derivatives, hydrazine hydrate and Lewis acid are mixed and reacted to generate salicylaldehyde hydrazine hydrazone ligand; 2) In the presence of a base, the salicylaldehyde hydrazine hydrazone ligand is subjected to a boron complexation reaction with arylboronic acid.

[0011] Preferably, in step 1), the salicylaldehyde derivative is a brominated salicylaldehyde derivative.

[0012] Preferably, the brominated salicylaldehyde derivative is selected from one or more of 3-bromosubstituted 2-hydroxybenzaldehyde, 4-bromosubstituted 2-hydroxybenzaldehyde, 5-bromosubstituted 2-hydroxybenzaldehyde, and 3,5-dibromo-2-hydroxybenzaldehyde.

[0013] More preferably, in step 1), the Lewis acid is selected from one or more of acetic acid, p-toluenesulfonic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0014] More preferably, in step 1), the solvent is selected from one or more of acetonitrile, 1,4-epoxybicyclohexane, toluene, chlorobenzene, o-dichlorobenzene, p-dichlorobenzene and m-dichlorobenzene.

[0015] More preferably, in step 1), the molar ratio of salicylaldehyde and / or salicylaldehyde derivative to hydrazine hydrate is 1 to 3:1, preferably 2:1.

[0016] More preferably, in step 1), the volume ratio of the Lewis acid to hydrazine hydrate is 0.2~0.5:1.

[0017] More preferably, in step 1), the reaction conditions include: a temperature of 100~150℃, a time of 2~3h, and a stirring rate of 200~500 rpm.

[0018] More preferably, the catalytic reaction is carried out in a metal bath.

[0019] Preferably, in step 2), the alkali is selected from one or more of tripotassium phosphate, sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0020] Preferably, in step 2), the arylboronic acid is selected from phenylboronic acid, 4-bromophenylboronic acid, or 4-trifluoromethylphenylboronic acid.

[0021] More preferably, in step 2), the molar ratio of the base to the arylboronic acid is 1:2 to 20, preferably 1:3.

[0022] More preferably, in step 2), the conditions for the complexation reaction include: a temperature of 140~150℃ and a time of 8~15h.

[0023] Thirdly, the present invention provides a salicylaldehyde hydrazone-bridged organic boron photoinitiator prepared by the preparation method described in the second aspect.

[0024] Fourthly, the present invention provides the application of salicylaldehyde hydrazone-bridged organic boron photoinitiator as described in the first or third aspect in the preparation of photoinitiator materials, photocurable coatings, photocurable adhesives, and photocurable 3D printing.

[0025] Fifthly, the present invention provides a photoinitiator composition comprising a salicylaldehyde hydrazone-bridged organoboron photoinitiator, an iodonium salt, and ethyl 4-dimethylaminobenzoate; wherein, The salicylaldehyde hydrazone-bridged organoboron photoinitiator is the salicylaldehyde hydrazone-bridged organoboron photoinitiator described in the first or third aspect.

[0026] Preferably, the iodonium salt is di-tert-butyldiphenyliodonium hexafluorophosphate.

[0027] In the above technical solution, this invention prepares a novel visible light-activated organoboron complex—a salicylaldehyde hydrazone-bridged organoboron photoinitiator (BOSHY)—using a one-pot method. This salicylaldehyde hydrazone-bridged organoboron photoinitiator is derived from salicylaldehyde acridine ligands and phenylboronic acid, exhibiting a vertical spatial configuration. The axially coordinated boric acid significantly enhances its solubility through apical functionalization. More importantly, the vertical alignment of these components alters orbital angular momentum and couples with spin angular momentum to generate a spin triplet state. Simultaneously, bromination in the BOSHY framework accelerates intersystem crossing rates through the "heavy atom effect," thereby improving spin-orbit coupling and enhancing photopolymerization performance. Based on this design, this invention synthesizes various BOSHY derivatives with different degrees of bromination.

[0028] Furthermore, the visible light-induced system (PIS) based on the BOSHY of this invention can efficiently catalyze the cationic polymerization of epoxy resin under 405 nm LED illumination in a three-component system composed of di-tert-butyldiphenyliodonium hexafluorophosphate (IOD) and ethyl 4-dimethylaminobenzoate (EDB), with a conversion rate as high as 78%.

[0029] Furthermore, the polymerization kinetics induced by the BOSHY dye of this invention were comprehensively and systematically characterized by steady-state photolysis, fluorescence lifetime quenching, and transient absorption spectroscopy. All of these demonstrated that the salicylaldehyde hydrazone-bridged organic boron photoinitiator of this invention has good photophysical properties and good application value in photopolymer materials. It is suitable for fields such as photopolymerization 3D printing and electronic packaging adhesives, and is especially suitable for scenarios with high curing speed requirements.

[0030] Moreover, the preparation method of the salicylaldehyde hydrazone-bridged organic boron photoinitiator of the present invention adopts a one-pot reaction, the synthesis method is simple, the reaction conditions are mild, and the yield is 40%~56%, which is significantly better than the similar photoinitiators synthesized in multiple steps.

[0031] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0032] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 The X-ray crystal structures of salicylaldehyde hydrazone-bridged organic boron photoinitiators 1a-c prepared in Examples 1-3 of this invention are shown in (a), (b), and (c), where H atoms are white, C atoms are light gray, N atoms are blue, O atoms are red, B atoms are pink, and Br atoms are orange. Figure 2 (a) is the front molecular orbital (FMO) distribution and energy level diagram with spin-orbit coupling (SOC) matrix element (ξ) of the salicylaldehyde hydrazone-bridged organic boron photoinitiator 1a prepared in Example 1 of the present invention and the salicylaldehyde hydrazone-bridged organic boron photoinitiator 1e prepared in Example 5 of the present invention; (b) is the absorption spectrum of the salicylaldehyde hydrazone-bridged organic boron photoinitiators 1a-e prepared in Examples 1-5 of the present invention in toluene; (c) is the fluorescence emission spectrum of the salicylaldehyde hydrazone-bridged organic boron photoinitiators 1a-e prepared in Examples 1-5 of the present invention. Figure 3(a) The photopolymerization reaction of EPOX with the salicylaldehyde hydrazone-bridged organic boron photoinitiator of the present invention under 405 nm LED irradiation was monitored by real-time Fourier transform infrared spectroscopy. (b) The photopolymerization curve of EPOX (relationship between epoxy conversion rate and irradiation time) in a 25 μm film of a photoinitiating system composed of IOD and EDB with the salicylaldehyde hydrazone-bridged organic boron photoinitiator 1a-e prepared in Examples 1-5 of the present invention under 405 nm (50 mW / cm²) LED irradiation. (c) The final polymerization efficiency of EPOX in the film when using the salicylaldehyde hydrazone-bridged organic boron photoinitiator 1a-e prepared in Examples 1-5 of the present invention with a photoinitiating system composed of IOD and EDB. (d) The enhanced contrast fluorescence image of a three-dimensional object printed by EPOX in the presence of the 1c / EDB / IOD photoinitiating system, with a scale bar of 5. mm, (e) is an enhanced contrast fluorescence image of a three-dimensional object printed by EPOX in the presence of the 1d / EDB / IOD photoinitiation system, with a scale bar of 5 mm. Detailed Implementation

[0033] The embodiments of the present invention will be described in detail below. The specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention.

[0034] In a first aspect, the present invention provides a salicylaldehyde hydrazone-bridged organoboron photoinitiator, the structural formula of which is shown in Formula I: , Wherein, R is a H or a halogen atom; The salicylaldehyde hydrazone-bridged organic boron photoinitiator has a vertical spatial configuration consisting of a seven-membered ring and a six-membered ring.

[0035] In a preferred embodiment of the present invention, R is one of H, Br, F, Cl or I.

[0036] In a preferred embodiment of the present invention, R is H or Br.

[0037] In a preferred embodiment of the present invention, the substitution position of R is at position 3, 4 or 5 of the salicylaldehyde skeleton.

[0038] In a preferred embodiment of the present invention, the structure of the organohydrazine-bridged salicylaldehyde-boron complex is shown in formulas 1a-1e. .

[0039] Secondly, a method for preparing a salicylaldehyde hydrazone-bridged organic boron photoinitiator, the method comprising: 1) In the presence of a solvent, salicylaldehyde and / or salicylaldehyde derivatives, hydrazine hydrate and Lewis acid are mixed and reacted to generate salicylaldehyde hydrazine hydrazone ligand; 2) In the presence of a base, the salicylaldehyde hydrazine hydrazone ligand is subjected to a boron complexation reaction with arylboronic acid.

[0040] In a preferred embodiment of the present invention, in step 1), the salicylaldehyde derivative is a brominated salicylaldehyde derivative.

[0041] In a preferred embodiment of the present invention, the brominated salicylaldehyde derivative is selected from one or more of 3-bromosubstituted 2-hydroxybenzaldehyde, 4-bromosubstituted 2-hydroxybenzaldehyde, 5-bromosubstituted 2-hydroxybenzaldehyde, and 3,5-dibromo-2-hydroxybenzaldehyde.

[0042] In a preferred embodiment of the present invention, in step 1), the Lewis acid is selected from one or more of acetic acid, p-toluenesulfonic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0043] In a preferred embodiment of the present invention, in step 1), the solvent is selected from one or more of acetonitrile, 1,4-epoxybicyclohexane, toluene, chlorobenzene, o-dichlorobenzene, p-dichlorobenzene and m-dichlorobenzene.

[0044] In a preferred embodiment of the present invention, in step 1), the molar ratio of salicylaldehyde and / or salicylaldehyde derivative to hydrazine hydrate is 1 to 3:1, preferably 2:1.

[0045] In a preferred embodiment of the present invention, in step 1), the volume ratio of the Lewis acid to hydrazine hydrate is 0.2~0.5:1.

[0046] In a preferred embodiment of the present invention, in step 1), the reaction conditions include: a temperature of 100~150℃, a time of 2~3h, and a stirring rate of 200~500 rpm.

[0047] In a preferred embodiment of the present invention, the catalytic reaction is carried out in a metal bath.

[0048] In a preferred embodiment of the present invention, in step 2), the alkali is selected from one or more of tripotassium phosphate, sodium carbonate, sodium bicarbonate and sodium hydroxide.

[0049] In a preferred embodiment of the present invention, in step 2), the arylboronic acid is selected from one of phenylboronic acid, 4-bromophenylboronic acid, or 4-trifluoromethylphenylboronic acid.

[0050] In a preferred embodiment of the present invention, in step 2), the molar ratio of the base to arylboronic acid is 1:2 to 20, preferably 1:3.

[0051] In a preferred embodiment of the present invention, in step 2), the conditions for the complexation reaction include: a temperature of 140~150℃ and a time of 8~15h.

[0052] In a preferred embodiment of the present invention, the preparation method further includes: extraction and drying, separation and purification, wherein the separation is a conventional method in the art, and the purification is performed by silica gel column chromatography to purify the crude product.

[0053] In a preferred embodiment of the present invention, the extraction and drying conditions include: extracting the product multiple times with dichloromethane, drying the product with anhydrous sodium sulfate to remove water, and then removing the solvent by rotary evaporation under reduced pressure.

[0054] In this invention, the eluent used in the silica gel column chromatography is a conventional eluent formulation in the art. For example, it can be obtained by mixing petroleum ether and dichloromethane in a volume ratio of 2:1, or by mixing hexane and ethyl acetate in a volume ratio of 9:1, or by mixing n-hexane and dichloromethane in a volume ratio of 1:1.

[0055] Thirdly, the present invention provides a salicylaldehyde hydrazone-bridged organic boron photoinitiator prepared by the preparation method described in the second aspect.

[0056] Fourthly, the present invention provides the application of salicylaldehyde hydrazone-bridged organic boron photoinitiator as described in the first or third aspect in the preparation of photoinitiator materials, photocurable coatings, photocurable adhesives, and photocurable 3D printing.

[0057] Fifthly, the present invention provides a photoinitiator composition comprising a salicylaldehyde hydrazone-bridged organoboron photoinitiator, an iodonium salt, and ethyl 4-dimethylaminobenzoate; wherein, The salicylaldehyde hydrazone-bridged organoboron photoinitiator is the salicylaldehyde hydrazone-bridged organoboron photoinitiator described in the first or third aspect.

[0058] In a preferred embodiment of the present invention, the iodonium salt is di-tert-butyldiphenyliodonium hexafluorophosphate.

[0059] In a preferred embodiment of the present invention, the initiation conditions of the photoinitiator composition include: an irradiation intensity of 50 mW / cm². 2 The exposure time is 50-60 s, and the visible light wavelength is 405 nm.

[0060] The present invention will be described in detail below through examples. In the following examples, the pharmaceuticals and agents are all conventional commercially available products.

[0061] Salicylic aldehyde hydrazone-bridged organoboron photoinitiators 1a-e were synthesized according to the synthetic routes shown below.

[0062]

[0063] Example 1 This embodiment illustrates the synthesis of salicylaldehyde hydrazone-bridged organic boron photoinitiator 1a. The structural formula and synthesis method of 1a are as follows:

[0064] In a 100 mL pressure-resistant reaction flask, salicylaldehyde (244 mg, 2 mmol) was dissolved in 20 mL of anhydrous chlorobenzene. Hydrazine hydrate (60 μL, 1 mmol) and glacial acetic acid (5 drops) were added sequentially. The reaction mixture was heated and stirred in a metal bath at 105 °C for 2.5 h. After complete conversion of the starting material was confirmed by TLC monitoring, potassium phosphate (K3PO4, 690 mg, 3.0 mmol, 1.5 equivalents) and phenylboronic acid (1.1 g, 9.0 mmol, 4.5 equivalents) were added, and the mixture was refluxed at 145 °C for 12 h. After the reaction was terminated, the system was allowed to cool naturally to room temperature and then extracted multiple times with dichloromethane (3 × 30 mL). After merging the organic phases, the product was dried with anhydrous sodium sulfate, and then the solvent was removed by rotary evaporation under reduced pressure. The crude product was then separated and purified by silica gel column chromatography (eluent: dichloromethane / petroleum ether = 1:1, v / v) to give a yellow solid product 1a (181 mg, 56%).

[0065] The NMR and high-resolution mass spectrometry data for 1a are as follows: 1 H NMR (400 MHz, CDCl3) δ 8.62 (s, 1H), 7.72 (s, 1H), 7.56 (ddd, J =8.7, 7.2, 1.7 Hz, 1H), 7.46 (ddd, J = 8.6, 7.1, 1.8 Hz, 1H), 7.41 (dd, J = 7.8, 1.7 Hz, 1H), 7.34 (dd, J = 8.3, 1.1 Hz, 1H), 7.24 – 7.18 (m, 3H), 7.15 – 7.10(m, 4H), 6.96 (td, J = 7.6, 1.0 Hz, 1H), 6.91 (ddd, J = 8.0, 7.1, 1.2 Hz, 1H). 13CNMR (101 MHz, CDCl3) δ 160.7, 160.2, 159.1, 156.7, 138.2, 135.8, 135.0,131.8, 131.4, 127.3, 127.3, 122.1, 120.4, 119.9, 119.7, 119.7, 113.9. 11 B NMR (128 MHz, CDCl3) δ 4.26. HRMS (ESI) calcd for C 20 H 16 BN2O2[M + H] + : 327.1305, found 327.1308. Example 2 This embodiment illustrates the synthesis of salicylaldehyde hydrazone-bridged organoboron photoinitiator 1b. The structural formula and synthesis method of 1b are as follows:

[0066] In a 100 mL pressure-resistant reaction flask, 3-bromo-2-hydroxybenzaldehyde (402 mg, 2 mmol) was dissolved in 20 mL of anhydrous chlorobenzene, followed by the addition of hydrazine hydrate (60 μL, 1 mmol) and glacial acetic acid (5 drops). The reaction system was heated and stirred in a metal bath at 105 °C for 2.5 h. After complete conversion of the starting material was confirmed by TLC monitoring, potassium phosphate (K3PO4, 690 mg, 3.0 mmol, 1.5 equivalents) and phenylboronic acid (1.1 g, 9.0 mmol, 4.5 equivalents) were added, and the mixture was refluxed at 145 °C for 12 h. After the reaction was terminated, the system was allowed to cool naturally to room temperature and then extracted multiple times with dichloromethane (3 × 30 mL). The combined organic phases were dried over anhydrous sodium sulfate. After removing the solvent by rotary evaporation under reduced pressure, the crude product was separated and purified by silica gel column chromatography (eluent: dichloromethane / petroleum ether = 1:1, v / v) to give a yellow solid product 1b (448 mg, 47%).

[0067] The NMR and high-resolution mass spectrometry data for 1b are as follows: 1 H NMR (500 MHz, CDCl3) δ 8.66 (s, 1H), 7.82 (dd, J = 7.8, 1.6 Hz, 1H),7.78 – 7.74 (m, 2H), 7.39 (dd, J= 7.8, 1.6 Hz, 1H), 7.24 – 7.20 (m, 2H), 7.19– 7.11 (m, 4H), 6.85 (t, J = 7.8 Hz, 1H), 6.79 (t, J = 7.8 Hz, 1H). 13 C NMR (126MHz, CDCl3) δ 159.6, 157.3, 156.4, 156.2, 141.2, 138.3, 135.1, 131.5, 130.8,127.5, 127.4, 121.8, 120.6, 120.5, 117.0, 114.7, 113.9. 11 B NMR (128 MHz, CDCl3) δ 5.24. HRMS (ESI) calcd for C 20 H 13 BBr2N2O2[M + H] + : 482.9515 found481.9437. Example 3 This embodiment illustrates the synthesis of salicylaldehyde hydrazone-bridged organoboron photoinitiator 1c. The structural formula and synthesis method of 1c are as follows:

[0068] In a 100 mL pressure-resistant reaction flask, 4-bromo-2-hydroxybenzaldehyde (402 mg, 2 mmol) was dissolved in 20 mL of anhydrous chlorobenzene, followed by the addition of hydrazine hydrate (60 μL, 1 mmol) and glacial acetic acid (5 drops). The reaction system was heated and stirred in a metal bath at 105 °C for 2.5 h. After complete conversion of the starting material was confirmed by TLC, potassium phosphate (K3PO4, 690 mg, 3.0 mmol, 1.5 equivalents) and phenylboronic acid (1.1 g, 9.0 mmol, 4.5 equivalents) were added, and the mixture was refluxed at 145 °C for 12 h. After the reaction was terminated, the system was allowed to cool naturally to room temperature and then extracted multiple times with dichloromethane (3 × 30 mL). The combined organic phases were dried over anhydrous sodium sulfate. After removing the solvent by rotary evaporation under reduced pressure, the crude product was separated and purified by silica gel column chromatography (eluent: dichloromethane / petroleum ether = 2:3, v / v) to give a yellow solid product 1c (207 mg, 43%).

[0069] The NMR and high-resolution mass spectrometry data for 1C are as follows: 1H NMR (400 MHz, CDCl3) δ 8.59 (s, 1H), 7.67 (s, 1H), 7.50 (s, 1H), 7.33 (d, J = 1.8 Hz, 1H), 7.26 (d, J = 2.0 Hz, 1H), 7.23 – 7.10 (m, 6H), 7.08 –7.00 (m, 2H). 13 C NMR (126 MHz, C DCl3) δ 160.3, 159.8, 159.2, 156.2, 136.5,133.4, 132.0, 131.7, 129.6, 127.6, 127.5, 125.1, 123.8, 123.4, 123.1, 120.6,119.4, 112.8. 11 B NMR (128 MHz, CDCl3) δ 4.20. HRMS (ESI) calcd forC 20 H 14 BBr2N2O2[M + H] + : 482.9215, found 482.9526. Example 4 This embodiment illustrates the synthesis of salicylaldehyde hydrazone-bridged organoboron photoinitiator 1d. The structural formula and synthesis method of 1d are as follows:

[0070] In a 100 mL pressure-resistant reaction flask, 5-bromo-2-hydroxybenzaldehyde (402 mg, 2 mmol) was dissolved in 20 mL of anhydrous chlorobenzene, followed by the addition of hydrazine hydrate (60 μL, 1 mmol) and glacial acetic acid (5 drops). The reaction system was heated and stirred in a metal bath at 105 °C for 2.5 h. After complete conversion of the starting material was confirmed by TLC monitoring, potassium phosphate (K3PO4, 690 mg, 3.0 mmol, 1.5 equivalents) and phenylboronic acid (1.1 g, 9.0 mmol, 4.5 equivalents) were added, and the mixture was refluxed at 145 °C for 12 h. After the reaction was terminated, the system was allowed to cool naturally to room temperature and then extracted multiple times with dichloromethane (3 × 30 mL). The combined organic phases were dried over anhydrous sodium sulfate. After removing the solvent by rotary evaporation under reduced pressure, the crude product was separated and purified by silica gel column chromatography (eluent: dichloromethane / petroleum ether = 1:3, v / v) to give a yellow solid product 1d (228 mg, 47%).

[0071] The 1-day NMR and high-resolution mass spectrometry data are as follows: 1 H NMR (400 MHz, CDCl3) δ 8.57 (d, J = 1.9 Hz, 1H), 7.66 – 7.60 (m, 2H), 7.53 (dd, J = 8.7, 2.5 Hz, 2H), 7.32 (d, J = 1.1 Hz, 1H), 7.21 (d, J = 8.8 Hz, 1H), 7.15 (t, J = 3.2 Hz, 5H), 7.02 (d, J = 8.9 Hz, 1H). 13 C NMR (101 MHz, CDCl3) δ159.6, 159.2, 158.1, 156.0, 140.9, 137.8, 137.5, 133.1, 131.7, 127.7, 127.5,124.0, 121.8, 121.7, 115.3, 111.5, 111.5. 11 B NMR (128 MHz, CDCl3) δ 4.47. HRMS(ESI) calcd for C 20 H 14 BBr2N2O2[M + H] + : 482.9215, found 482.9517. Example 5 This embodiment illustrates the synthesis of salicylaldehyde hydrazone-bridged organoboron photoinitiator 1e. The structural formula and synthesis method of 1e are as follows:

[0072] In a 100 mL pressure-resistant reaction flask, 3,5-dibromosalicylic acid (560 mg, 2 mmol) was dissolved in 20 mL of anhydrous chlorobenzene, followed by the addition of hydrazine hydrate (60 μL, 1 mmol) and glacial acetic acid (5 drops). The reaction system was heated and stirred in a metal bath at 105 °C for 2.5 h. After confirming complete conversion of the starting materials, potassium phosphate (K3PO4, 690 mg, 3.0 mmol, 1.5 equivalents) and phenylboronic acid (1.1 g, 9.0 mmol, 4.5 equivalents) were added, and the mixture was refluxed at 145 °C for 12 h. After the reaction was terminated, the system was allowed to cool naturally to room temperature and then extracted multiple times with dichloromethane (3 × 30 mL). The combined organic phases were dried over anhydrous sodium sulfate. After removing the solvent by rotary evaporation under reduced pressure, the crude product was separated and purified by silica gel column chromatography (eluent: dichloromethane / petroleum ether = 2:3, v / v) to give a yellow solid product 1e (262 mg, 41%).

[0073] The NMR and high-resolution mass spectrometry data for 1e are as follows: 1 H NMR (400 MHz, CDCl3) δ 8.60 (s, 1H), 7.90 (dd, J = 25.1, 2.4 Hz, 2H), 7.73 – 7.49 (m, 2H), 7.32 – 7.16 (m, 6H). 13 C NMR (126 MHz, CDCl3) δ 158.5,156.6, 155.6, 155.3, 143.2, 140.3, 136.9, 132.5, 131.4, 127.8, 127.6, 122.5,118.0, 115.4, 115.0, 111.5, 111.2. 11 B NMR (128 MHz, CDCl3) δ 5.59. HRMS (ESI)calcd for C 20 H 12 BBr4N2O2[M + H] + : 638.7725, found 638.7753. Test Example 1 Single crystals suitable for X-ray diffraction analysis were cultivated using a slow solvent evaporation method. The specific method is as follows: The salicylaldehyde hydrazone-bridged organoboron photoinitiators 1a-1c prepared in Examples 1-3 were dissolved in a dichloromethane / n-hexane (v / v = 1:2) mixed solvent, and high-quality single crystals were obtained by slow evaporation at 25°C. The X-ray single crystals of 1a-c were obtained by slowly diffusing hexane into a dichloromethane solution. The crystal structure data of 1a-c are shown in Table 1 and... Figure 1 As shown.

[0074] Crystal structure data in Tables 11a, 1b and 1c

[0075] Depend on Figure 1 The contents show that there are four types of ring structures in the BOSHY skeleton: a seven-membered ring and a six-membered ring in the central part, and two benzene rings on the periphery.

[0076] As shown in Table 1, the bond lengths of nitrogen-nitrogen (NN) bonds and boron-nitrogen (BN) bonds are approximately 1.41(1) Å and 1.61(1) Å, respectively. Among the two types of BO bonds in each molecule, the BO bond between the boron atom and the oxygen atom in the seven-membered ring is shorter, at 1.45(2) Å, while the other BO bond in the six-membered ring has a bond length of 1.47(2) Å.

[0077] From the data in Table 1 and Figure 1 The contents reveal that the salicylaldehyde hydrazone-bridged organoboron photoinitiator 1a-c exhibits varying degrees of distortion in its central structure. The dihedral angle between the central six-membered ring plane and the seven-membered ring plane ranges from 107.7° to 126.5°, the dihedral angle between the benzene ring on boron and the six-membered ring plane ranges from 95.1° to 107.0°, while the dihedral angle between the benzene ring on boron and the seven-membered ring plane is smaller, ranging from 73.0° to 75.8°. The sp³ hybridization of each boron atom, and its bonding with the four different ligands (including one phenyl, one oxygen, and two nitrogen atoms) in the corresponding six-membered and seven-membered rings, leads to structural asymmetry, thus endowing the fluorophore with chirality. They all crystallize as a 1:1 racemic mixture, with the two crystallographic enantiomers exhibiting opposite orientations at the boron center in each unit cell.

[0078] Test Example 2 To investigate the correlation between molecular structure and excited-state properties, density functional theory (DFT) and time-dependent (TD)-DFT calculations were first performed at the B3LYP / 6-31G(d) theoretical level, such as... Figure 2 As shown in (a).

[0079] Depend on Figure 2As shown in (a), the salicylaldehyde hydrazone-bridged organoboron photoinitiator 1a exhibits a strong ground state (S0)-first excited singlet state (S1) transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), with an oscillator strength of 0.227. The relatively small energy level difference between the S1 / T2 and S1 / T3 states suggests that the salicylaldehyde hydrazone-bridged organoboron photoinitiator 1a may undergo an effective intersystem crossing (ISC) process, further supported by the calculated spin-orbit coupling (SOC) values: 2.69 cm⁻¹ for S1-T1, 2.03 cm⁻¹ for S1-T2, and 2.67 cm⁻¹ for S1-T3.

[0080] To improve the efficiency of intersystem crossing (ISC) in molecules, a series of photosensitizers (1b-1e) containing heavy bromine atoms were derived from the molecular skeleton of compound 1a. For example... Figure 2 As shown in (a), calculations using 1e as an example show that the energy levels and band gaps of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in the bromine-substituted photosensitizer are reduced, and the spin-orbit coupling (SOC) value is significantly increased. These findings are consistent with our molecular design intent, indicating that the heavy atom effect can significantly enhance spin-orbit coupling in organoboron photoinitiators.

[0081] Test Example 3 We systematically studied the photophysical properties of this series of BOSHYs in three solvents with different polarities: toluene, dichloromethane, and acetonitrile. The data are shown in Table 2. The absorption and emission spectra of this series of compounds in toluene are shown below. Figure 2 (b) and 2(c).

[0082] Table 2 Spectral data of 1a-e in organic solvents

[0083] As shown in Table 2, 1a-e exhibit broad and strong absorption and weak emission in common organic solvents. For example, 1a in toluene shows a significant maximum absorption peak at 381 nm and emission at 509 nm, indicating an emission peak at approximately 6600 cm⁻¹. -1 It exhibits a significant Stokes shift, which is larger than that of typical BODIPY dyes, and similar spectral shapes have been observed in other BOSHYs.

[0084] Depend on Figure 2 (b) It is known that bromination causes the absorption peak wavelength to turn red. For example, the maximum absorption wavelengths of 1c, 1d, and 1e in toluene are 398 nm, 400 nm, and 406 nm, respectively, which are red-shifted by 18 to 26 nm compared to 1a in toluene. This red-shift is attributed to the electron-withdrawing effect of the bromine atom.

[0085] These BOSHYs exhibit weak fluorescence, likely due to the free rotation of the benzene ring. Their absorption bands gradually blue-shift with increasing solvent polarity, exhibiting a low solvent-dependent fluorescence solvation colorimetric effect. For example, in toluene, the maximum absorption and emission wavelengths at 1c are 398 nm and 509 nm, respectively. In acetonitrile, these wavelengths shift to 384 nm and 499 nm, respectively. They all exhibit varying degrees of absorption in the visible light region, thus ensuring good overlap with the emission spectrum of the LED light source used in this invention. The triplet lifetime of the BOSHY compounds of this invention is 15.4–23.5 μs, indicating effective intersystem crossing when the BOSHYs of this invention are used as photoinitiators to initiate photopolymerization reactions. This enables efficient energy and electron transfer reactions, making them valuable for applications in photopolymer materials.

[0086] Application Example 1 After the photophysical properties of the BOSHY derivatives prepared in Examples 1-5 of this invention were characterized, their effectiveness as photosensitizers capable of initiating polymerization reactions was evaluated.

[0087] The photopolymerization reaction was carried out using (3,4-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylic acid ester (EPOX, trade name Uvacure 1500) as the reference monomer, and the concentration of the initiator used was calculated based on the monomer content.

[0088] 0.1 wt% of the BOSHY photosensitizer prepared in Examples 1-5, 2.0 wt% of the donor initiator ethyl 4-dimethylaminobenzoate (EDB), and 2.0 wt% of the acceptor initiator bis(4-tert-butylphenyl)iodonium hexafluorophosphate (IOD) were completely dissolved in the monomer. A visible light emitting diode (LED@405 nm) with a maximum emission wavelength of 405 nm was used as the illumination source for the photopolymerization process and photolysis experiment. The diameter of the light spot was approximately 3 cm, and the incident light intensity on the sample surface was approximately 50 mW / cm². −2 (Measured using a Thorlabs PM100D power meter), the experimental procedure is as follows: Figure 3 As shown in (a), the basic formulation for EPOX cationic polymerization is shown in Table 3.

[0089] Note: To avoid prepolymerization, all formulations must be prepared fresh and stored in a dark environment at room temperature before light exposure.

[0090] Table 3

[0091] The cationic polymerization of EPOX was carried out in a thin-film state, in which 1 to 2 drops of the formulation solution were added between two polypropylene films (laminated) with a thickness of approximately 25 μm. All photopolymerization experiments were conducted under mild conditions: at room temperature (15–30 °C) under 405 nm LED visible light irradiation. The photopolymerization reaction was quantitatively characterized by real-time Fourier transform infrared spectroscopy, which continuously tracked the changes in the epoxy group content in EPOX (its characteristic peak is located at approximately 791 cm⁻¹ under thin-film conditions). Figure 3 As shown in (b) and 3(c).

[0092] The final functional group reaction functionality conversion (FC) is determined by measuring the peak area of ​​the relevant characteristic peaks at a specific illumination time according to the formula (1) listed below: Conversion (%) = (A0 − At) / A0 × 100(1) Where A0 is the initial peak area of ​​the epoxy groups before LED illumination (in EPOX), and At is the peak area after a given illumination time.

[0093] In the presence of the BOSHYs / IOD / EDB photoinitiator system (PISs), the curve showing the change in epoxy group conversion rate with illumination time is as follows: Figure 3 As shown in (b), and after 200 s of 405 nm LED illumination, the corresponding final conversion rate of the epoxy groups is as follows: Figure 3 As shown in (c), a significant improvement in polymerization conversion was observed when using halogenated derivatives compared to non-halogenated derivatives. Therefore, we conclude that halogenation via ISC to enhance triplet formation is a general method for improving photoinitiation efficiency.

[0094] When the light source was turned on, the polymerization reaction was rapidly initiated, and the conversion rate of the epoxy groups reached a maximum of approximately 78%. After 200 s of 405 nm LED irradiation, the 1c / IOD / EDB system and the 1d / IOD / EDB system achieved polymerization efficiencies as high as 78% and 73%, respectively. For 1c and 1d, the LED irradiation times required to reach the maximum conversion rates were 52 ± 2 seconds and 55 ± 3 seconds, respectively. Previous studies have shown that BODIPY dyes are not particularly effective in initiating cationic polymerization reactions, with low polymerization rates, typically requiring at least ten minutes to complete the polymerization process, especially under visible light irradiation. In particular, this was achieved at a relatively low light intensity of 50 mW / cm². Under 405 nm visible light LED irradiation (light intensity of 50 mW / cm²), the photoinitiation efficiency of the BOSHYs / IOD / EDB photoinitiation system followed the order: 1c > 1d > 1e > 1b > 1a.

[0095] Through 3D printing experiments, the photopolymerization reaction of EPOX and the fabrication of three-dimensional objects were realized. Since both 1c and 1d photoinitiation systems (PIS) exhibit high efficiency in initiating cationic polymerization reactions, EPOX containing 1c or 1d / IOD / EDB (mass fractions of 0.1% / 2% / 2% respectively) was selected for these experiments. Direct laser writing was performed in air using a 405nm laser diode, thus achieving a highly efficient photopolymerization process limited to the irradiated area. Macroscopic patterns with a thickness exceeding 1.2 mm were generated in a very short time (<1 min for a 1 cm long pattern). LED patterns produced by the 1C system, such as Figure 3 As shown in (d) and the "XYZ" pattern obtained from the 1d system, Figure 3 As shown in (e), these patterns were subsequently observed using a digital camera. The printed 3D patterns exhibited excellent spatial resolution, with a step size of approximately 80 μm between the cured and uncured resins, consistent with the spot size of the laser used. Furthermore, the printed 3D objects emitted a distinct blue-green fluorescence due to the presence of 1c or 1d. In turn, the successful 3D printing validates the high photoinitiation efficiency of BOSHY dyes and potentially broadens their application prospects.

[0096] In summary, the salicylaldehyde hydrazone-bridged organic boron photoinitiator-BOSHY system of this invention is obtained by reacting salicylaldehyde or salicylaldehyde derivatives with hydrazine hydrate under Lewis acid catalysis to generate salicylaldehyde hydrazone ligands. Then, the salicylaldehyde hydrazone ligands undergo a one-pot self-assembly boron complexation reaction with arylboronic acid under an inorganic alkaline environment. The unique vertical spatial configuration of this type of BOSHY framework can effectively promote the generation of spin triplet states through orbital angular momentum modulation, providing more favorable excited-state characteristics for the photoinitiation process. Introducing halogen atoms into the framework utilizes the "heavy atom effect" to significantly enhance intersystem crossing efficiency, thereby optimizing spin-orbit coupling characteristics and improving photopolymerization performance.

[0097] Simultaneously, this invention also developed a novel photoinitiation system, BOSHYs / IOD / EDB, precisely matched to the LED emission wavelength, for rapid cationic polymerization reactions. Utilizing the three-component system of BOSHY compounds, IOD, and EDB of this invention, the polymerization reaction of epoxy compounds can be catalyzed under 405 nm LED light irradiation, with the photopolymerization reaction of the brominated BOSHY compounds being even more rapid. At 50 mW cm⁻¹ −2Under low-intensity light, the conversion rate of epoxy compounds can reach 78% in just 52 seconds. This indicates that the salicylaldehyde hydrazone-bridged organic boron photoinitiator of the present invention can maintain high reactivity under low irradiation intensity (<60 mW / cm²) and short exposure time (<60 s).

[0098] The numerical ranges disclosed in this invention (including endpoint values ​​and their intermediate values) should be understood to include reasonable ranges close to them. All disclosed numerical ranges, individual numerical values, and new numerical ranges formed by any combination thereof are protected by this invention.

[0099] The scope of protection of this invention is not limited to the specific embodiments described. Any reasonable modification or equivalent substitution of technical features based on the technical concept of this invention, as long as it does not depart from the core design idea of ​​this invention, should be regarded as a technical solution covered by this invention.

Claims

1. A salicylaldehyde hydrazone-bridged organic boron photoinitiator, characterized in that, The structural formula of the salicylaldehyde hydrazone-bridged organic boron photoinitiator is shown in Formula I: ， Wherein, R is a H or a halogen atom; The salicylaldehyde hydrazone-bridged organic boron photoinitiator has a vertical spatial configuration consisting of a seven-membered ring and a six-membered ring.

2. The salicylaldehyde hydrazone-bridged organic boron photoinitiator according to claim 1, characterized in that, The R is one of H, Br, F, Cl or I; Preferably, R is H or Br; More preferably, the substitution position of R is at position 3, 4 or 5 of the salicylaldehyde skeleton.

3. The salicylaldehyde hydrazone-bridged organic boron photoinitiator according to claim 1 or 2, characterized in that, The structure of the organohydrazine-bridged salicylaldehyde hydrazone boron complex is shown in formulas 1a-1e. 。 4. A method for preparing a salicylaldehyde hydrazone-bridged organic boron photoinitiator, characterized in that, The preparation method includes: 1) In the presence of a solvent, salicylaldehyde and / or salicylaldehyde derivatives, hydrazine hydrate and Lewis acid are mixed and reacted to generate salicylaldehyde hydrazine hydrazone ligand; 2) In the presence of a base, the salicylaldehyde hydrazine hydrazone ligand is subjected to a boron complexation reaction with arylboronic acid.

5. The preparation method according to claim 4, characterized in that, In step 1), the salicylaldehyde derivative is a brominated salicylaldehyde derivative; Preferably, the brominated salicylaldehyde derivative is selected from one or more of 3-bromosubstituted 2-hydroxybenzaldehyde, 4-bromosubstituted 2-hydroxybenzaldehyde, 5-bromosubstituted 2-hydroxybenzaldehyde, and 3,5-dibromo-2-hydroxybenzaldehyde. More preferably, in step 1), the Lewis acid is selected from one or more of acetic acid, p-toluenesulfonic acid, hydrochloric acid, nitric acid, and sulfuric acid; More preferably, in step 1), the solvent is selected from one or more of acetonitrile, 1,4-epoxybicyclohexane, toluene, chlorobenzene, o-dichlorobenzene, p-dichlorobenzene and m-dichlorobenzene; More preferably, in step 1), the molar ratio of salicylaldehyde and / or salicylaldehyde derivative to hydrazine hydrate is 1 to 3:1, preferably 2:1; More preferably, in step 1), the volume ratio of the Lewis acid to hydrazine hydrate is 0.2~0.5:1; More preferably, in step 1), the reaction conditions include: a temperature of 100~150℃, a time of 2~3h, and a stirring rate of 200~500 rpm; More preferably, the catalytic reaction is carried out in a metal bath.

6. The preparation method according to claim 4 or 5, characterized in that, In step 2), the base is selected from one or more of tripotassium phosphate, sodium carbonate, sodium bicarbonate and sodium hydroxide; Preferably, in step 2), the arylboronic acid is selected from phenylboronic acid, 4-bromophenylboronic acid, or 4-trifluoromethylphenylboronic acid; More preferably, in step 2), the molar ratio of the base to the arylboronic acid is 1:2 to 20, preferably 1:3; More preferably, in step 2), the conditions for the complexation reaction include: a temperature of 140~150℃ and a time of 8~15h.

7. A salicylaldehyde hydrazone-bridged organic boron photoinitiator prepared by the preparation method described in claims 4-6.

8. The application of the salicylaldehyde hydrazone-bridged organic boron photoinitiator as described in claims 1-3 or the salicylaldehyde hydrazone-bridged organic boron photoinitiator as described in claim 7 in the preparation of photoinitiator materials, photocurable coatings, photocurable adhesives, and photocurable 3D printing.

9. A photoinitiator composition, characterized in that, The photoinitiator composition comprises a salicylaldehyde hydrazone-bridged organic boron photoinitiator, an iodonium salt, and ethyl 4-dimethylaminobenzoate; wherein... The salicylaldehyde hydrazone-bridged organoboron photoinitiator is the salicylaldehyde hydrazone-bridged organoboron photoinitiator according to claims 1-3 or the salicylaldehyde hydrazone-bridged organoboron photoinitiator according to claim 7.

10. The photoinitiator composition according to claim 9, characterized in that, The iodonium salt is di-tert-butyldiphenyliodonium hexafluorophosphate.

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