Photoinitiators, holographic polymer dispersed liquid crystal materials, methods of making and using the same

Abstract

The application provides a kind of photoinitiator, holographic polymer dispersed liquid crystal material and its preparation method and application, the above-mentioned photoinitiator is a single-component photoinitiator, which is excited after absorbing photon and homolysis generates carbon radical with initiation polymerization activity;Compared with the holographic polymer dispersed liquid crystal material of the existing multi-component photoinitiating system, the chemical reaction in the molecule of the photoinitiator in the application cannot be disturbed by additive, which is cracked after being excited, effectively improves the generation efficiency of free radical, and can realize the holographic recording process faster, greatly improves the photosensitive sensitivity of holographic polymer material, effectively simplifies the formula of holographic polymer dispersed liquid crystal material, further reduces the production cost of holographic polymer dispersed liquid crystal material.

Description

Technical Field

[0001] This invention relates to the field of optical functional materials technology, and in particular to a photoinitiator, a holographic polymer-dispersed liquid crystal material, its preparation method and application. Background Technology

[0002] Among holographic recording materials, holographic polymer-dispersed liquid crystal materials exhibit high refractive index modulation, good processing suitability, and large information storage capacity, making them suitable for high-end anti-counterfeiting, information storage, virtual reality, and augmented reality applications. Holographic polymer-dispersed liquid crystal materials consist of a photoinitiating system, holographic recording monomers, liquid crystals, and other functional components as precursors. Under irradiation by two coherent beams, the photoinitiating system in the coherent bright region absorbs photons and generates active centers, which in turn trigger the polymerization reaction of the holographic recording monomers. Simultaneously, the liquid crystals are displaced to the coherent dark region. Ultimately, a periodically ordered phase-separated structure is formed in the holographic polymer-dispersed liquid crystal material.

[0003] Currently disclosed photoinitiation systems for preparing holographic polymer-dispersed liquid crystal materials typically consist of photosensitizers and co-initiators, containing at least two chemical components. During coherent light irradiation, the photosensitizer and co-initiator undergo intermolecular photo-redox reactions, generating active centers (usually free radicals). According to the inventors' research, introducing certain functional components into holographic polymer materials can interfere with the intermolecular reactions of traditional photoinitiation systems. Furthermore, the currently disclosed techniques for preparing holographic polymer-dispersed liquid crystal materials involve long holographic coherent exposure times, significantly limiting their preparation efficiency.

[0004] According to existing technology, the photosensitivity (S) of holographic polymer materials is related to the holographic coherence exposure time (t). ind The correlation between the two is negative. Therefore, improving the photosensitivity of holographic polymer materials is of great significance for their large-scale production. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a photoinitiator, a holographic polymer dispersed liquid crystal material, a preparation method thereof, and its application. The purpose is to prepare a holographic polymer dispersed liquid crystal material with high photosensitivity, so as to solve the problems of the photoinitiation system of the prior art for preparing holographic polymer dispersed liquid crystal materials being too complex, easily interfered with, and having low reaction efficiency.

[0006] To address the aforementioned technical problems, the present invention first provides a photoinitiator, which comprises the following chemical structure: ; Wherein, R1 includes any one of methoxy, diethylamino, hydroxymethyl, trifluoromethyl, phenyl, and 4-cyanophenyl; R2 includes any one of hydrogen, methyl, and phenyl; R3 includes any one of hydrogen, bromine, and iodine; R4 includes any one of hydrogen, methyl, phenyl, and styryl; and R5 includes any one of alkyl groups with fewer than 6 carbon atoms and phenyl groups.

[0007] Preferably, the photoinitiator can be excited by visible light with a wavelength of 420 nm to 700 nm; the maximum molar extinction coefficient of the photoinitiator in the 420 nm to 700 nm range is not less than 40000 Lmol. -1 cm -1 .

[0008] Preferably, after the photoinitiator is excited, the boron-carbon bond homolytically breaks and generates R5 initiating radicals, which initiate the polymerization reaction of the holographic recording monomer; the bond dissociation energy of the boron-carbon bond is not greater than 2.54 eV.

[0009] Preferably, the R5 initiating radical includes any one of methyl radical, ethyl radical, n-propyl radical, n-butyl radical, n-hexyl radical, and phenyl radical.

[0010] Accordingly, the present invention also provides a holographic polymer-dispersed liquid crystal material, wherein the raw materials for preparing the holographic polymer-dispersed liquid crystal material include, by weight, 0.01 to 5 parts of photoinitiator as described above, 20 to 80 parts of holographic recording monomer and 15 to 79 parts of inert component.

[0011] Preferably, the holographic recording monomer includes at least one of acrylate monomers, acrylamide monomers, and vinyl monomers.

[0012] Preferably, the raw materials for preparing the holographic polymer-dispersed liquid crystal material further include 0.05 to 5 parts of additives; the additives have photoresponsive functions and include any one of pyrrole methylene 546, Nile Red, Rhodamine B, spiropyran compounds, diarylethylene compounds, and azobenzene compounds.

[0013] Accordingly, the present invention also provides a method for preparing a holographic polymer-dispersed liquid crystal material as described in any of the above claims, the method comprising the following steps: S10, the photoinitiator, holographic recording monomer, additives and inert components are mixed evenly to obtain the first mother liquor; S20, the first mother liquor is injected into the liquid crystal cell by siphon and placed in the dark to obtain the holographic recording medium; S30, the holographic recording medium is placed under a coherent laser for holographic coherent exposure to obtain a high photosensitivity holographic polymer material; S40, the high photosensitivity holographic polymer material is placed under a visible light source until the holographic recording monomer in the high photosensitivity holographic polymer material is completely reacted, while the photoinitiator is bleached to obtain a holographic polymer-dispersed liquid crystal material.

[0014] Preferably, during the holographic coherent exposure process, the holographic coherent exposure time of the high photosensitivity holographic polymer material is 0.01s to 5s, and the exposure dose is 0.1 mJ / cm² to 10 mJ / cm²; the photosensitivity of the high photosensitivity holographic polymer material is greater than 100 cm² / mJ.

[0015] Accordingly, the present invention also provides the application of the holographic polymer-dispersed liquid crystal material prepared by the preparation method of the holographic polymer-dispersed liquid crystal material as described in any of the above claims in the fields of anti-counterfeiting, information storage, virtual reality and augmented reality.

[0016] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a photoinitiator, a holographic polymer-dispersed liquid crystal material, its preparation method, and its applications. The photoinitiator is a single-component photoinitiator that, upon absorbing photons and being excited, directly undergoes homolytic cleavage of boron-carbon chemical bonds, generating carbon free radicals with polymerization initiation activity. Compared to existing multi-component photoinitiation systems for holographic polymer-dispersed liquid crystal materials, the intramolecular chemical reaction of the photoinitiator in this invention is not interfered with by additives. Upon excitation, it undergoes intramolecular cleavage, effectively improving the free radical generation efficiency and enabling faster holographic recording. This significantly enhances the photosensitivity of the holographic polymer material while effectively simplifying the formulation of the holographic polymer-dispersed liquid crystal material, further reducing its production cost. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the preparation method of holographic polymer-dispersed liquid crystal material provided in an embodiment of the present invention; Figure 2 The holographic image of the holographic polymer material for high-end anti-counterfeiting prepared in Example 26 of this invention; Figure 3 The fluorescent image is of the holographic polymer material prepared for high-end anti-counterfeiting in Example 26 of this invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a photoinitiator, a holographic polymer dispersed liquid crystal material, a preparation method thereof, and its application. The purpose is to prepare a holographic polymer dispersed liquid crystal material with high photosensitivity, so as to solve the problems of the photoinitiation system of the prior art for preparing holographic polymer dispersed liquid crystal materials being too complex, easily interfered with, and having low reaction efficiency.

[0020] To address the aforementioned technical problems, the present invention first provides a photoinitiator, which comprises the following chemical structure: ; Wherein, R1 includes any one of methoxy, diethylamino, hydroxymethyl, trifluoromethyl, phenyl, and 4-cyanophenyl; R2 includes any one of hydrogen, methyl, and phenyl; R3 includes any one of hydrogen, bromine, and iodine; R4 includes any one of hydrogen, methyl, phenyl, and styryl; and R5 includes any one of alkyl groups with fewer than 6 carbon atoms and phenyl groups.

[0021] In this embodiment of the invention, the photoinitiator is a single-component photoinitiator that can be excited by visible light with a wavelength of 420 nm to 700 nm. In contrast, existing single-component photoinitiators used for holographic polymer materials are difficult to be excited by visible light in the 420 nm to 700 nm range. The maximum molar extinction coefficient of the aforementioned single-component photoinitiator in the 420 nm to 700 nm range is not less than 40,000 Lmol. -1 cm -1 .

[0022] The molar extinction coefficient, also known as the molar absorptivity coefficient, refers to the absorbance value when the solution concentration is 1 mol / L and the optical path length is 1 cm. It reflects the ability of a substance to absorb light; the larger the value, the stronger the substance's ability to absorb light of a specific wavelength.

[0023] In this embodiment of the invention, the boron-carbon bonds excited by the single-component photoinitiator can homolytically cleave and generate R5-initiated free radicals; the bond dissociation energy of the boron-carbon bond is not greater than 2.54 eV; wherein, the bond dissociation energy of the boron-carbon bond can be calculated using a quantum chemical calculation program of the prior art, the specific method of which is as follows: The enthalpies of reactants and products in the photoreaction process of a single-component photoinitiator were calculated using the Gaussian16 package. Geometric optimization and frequency calculations were performed on all intermediates at the B3LYP-D3 / Def2-TZVP level until no imaginary frequencies were found. Subsequently, higher-precision single-point energy calculations were performed on the optimized structures at the M06-2X / Def2-TZVPP level. An implicit solvation model (SMD, acetonitrile as solvent) was used in all calculations. Finally, the enthalpies of reactants and products were obtained by combining the results from the Shermo program with Gaussian16 calculations. Bond dissociation energy is generally defined as the enthalpy change of the reaction during the breaking of chemical bonds in a molecule, i.e., the enthalpy of the product minus the enthalpy of the reactants.

[0024] Furthermore, the R5-initiating radical includes any one of the following: methyl radical, ethyl radical, n-propyl radical, n-butyl radical, n-hexyl radical, and phenyl radical.

[0025] Unlike previous photoinitiation systems used in holographic polymer materials, the photoinitiation system provided in this invention is a single-component photoinitiator. Upon absorbing photons and being excited, it directly undergoes homolytic cleavage of boron-carbon chemical bonds, generating carbon free radicals with polymerization-initiating activity. Previous photoinitiation systems for holographic polymer materials typically consist of a mixture of one or more photosensitizers and one or more co-initiators. After the photosensitizer absorbs photons and reaches an excited state, it undergoes an intermolecular redox reaction with the co-initiator to generate active species with polymerization-initiating activity. This intermolecular chemical reaction is easily affected by the chemical environment, its efficiency is limited, and the reaction process can be interfered with by additives in the holographic polymer material.

[0026] In this embodiment of the invention, the initiating free radicals generated by the above-mentioned single-component photoinitiator can act on the holographic recording monomer, causing the holographic recording monomer to undergo a polymerization reaction; the chain initiation reaction rate of the polymerization reaction is faster than the chain growth reaction rate, and the polymerization reaction rate can be calculated according to the methods in the published literature (J. Phys. Chem. A2008, 112, 29, 6772–6782).

[0027] Accordingly, the present invention also provides a holographic polymer-dispersed liquid crystal material, which, by weight, comprises: 0.01 to 5 parts of a photoinitiator as claimed in any one of claims 1 to 4, 20 to 80 parts of a holographic recording monomer, and 15 to 79 parts of an inert component.

[0028] Specifically, the homolytic cleavage of boron-carbon bonds and the resulting R5-initiating free radicals generated after the photoinitiator is excited can trigger free radical polymerization of holographic recording monomers; holographic recording monomers include at least one of acrylate monomers, acrylamide monomers, and vinyl monomers.

[0029] Preferably, the holographic recording monomer is one or more of N-vinylpyrrolidone, N-vinylcarbazole, o-phenylphenoxyethyl acrylate, 4-biphenylmethanol acrylate, N,N-dimethylacrylamide, β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, acrylic acid, methacrylic acid, 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, ethylene glycol dimethacrylate, ethoxylated bisphenol A diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and hyperbranched acrylate.

[0030] Furthermore, the raw materials for preparing holographic polymer-dispersed liquid crystal materials also include 0.05 to 5 parts of additives; the additives are a type of photoresponsive molecules that can emit visible light or undergo photoisomerization reactions after being excited by light; the additives include any one of pyrrole methylene 546, Nile red, Rhodamine B, spiropyrans, diarylethylenes, and azobenzenes.

[0031] Accordingly, please refer to Figure 1 The present invention further provides a method for preparing the above-mentioned holographic polymer-dispersed liquid crystal material, the method comprising the following steps: S10, the photoinitiator, holographic recording monomer, additives and inert components are mixed evenly to obtain the first mother liquor; S20, the first mother liquor is injected into the liquid crystal cell by siphon and placed in the dark to obtain the holographic recording medium; S30, the holographic recording medium is placed under a coherent laser for holographic coherent exposure to obtain a high photosensitivity holographic polymer material; S40, the high photosensitivity holographic polymer material is placed under a visible light source (white LED lamp or high-pressure mercury lamp) until the holographic recording monomer in the high photosensitivity holographic polymer material is completely reacted, and the photoinitiator is bleached to obtain a holographic polymer-dispersed liquid crystal material.

[0032] In this embodiment of the invention, the wavelength of the coherent laser in step S30 is 420nm~700nm; for example, the wavelength of the coherent laser is 420nm, 442nm, 460nm, 491nm, 532nm, 577nm, or 640nm.

[0033] In this embodiment of the invention, one of the properties of the high photosensitivity holographic polymer material of the present invention can be described by photosensitivity (S), which can be calculated according to the methods of published materials ("Holographic Polymer Materials", Science Press), as shown in the following formula (1): (1) In formula (1): η The diffraction efficiency of holographic polymer materials. dThe thickness of the holographic polymer material, I To record the total holographic light intensity, t ind The time required to reach maximum diffraction efficiency.

[0034] According to publicly available information (Holographic Polymer Materials, Science Press; Macromolecules 2024, 57, 6, 2557–2573). η The specific testing method is as follows: The intensity of the diffracted light and the intensity of the transmitted light from the holographic polymer material at the Bragg angle are measured using a light intensity meter, and the diffraction efficiency is calculated using the following formula. η : (2) in, and and are the diffraction intensity and transmission intensity of the holographic polymer material at the Bragg angle, respectively.

[0035] In this embodiment of the invention, the holographic coherent exposure time used in the holographic coherent exposure process of the high photosensitivity holographic polymer material is 0.01s to 5s; the exposure dose used in the holographic coherent exposure of the high photosensitivity holographic polymer material is 0.1 mJ / cm² to 10 mJ / cm²; and the photosensitivity of the high photosensitivity holographic polymer material is greater than 100 cm² / mJ.

[0036] Preferably, the photosensitivity of the high photosensitivity holographic polymer material is greater than 300 cm / mJ.

[0037] Accordingly, the present invention also provides the application of the holographic polymer-dispersed liquid crystal material prepared by the preparation method of the holographic polymer-dispersed liquid crystal material as described in any of the above claims in the fields of anti-counterfeiting, information storage, virtual reality and augmented reality.

[0038] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by known methods.

[0039] Comparative Example 1: The holographic polymer material consists of 1 part by weight of 3,3'-carbonylbis(7-diethylamine coumarin) and 4 parts by weight of... N25 parts by weight of phenylglycine, PO616A, and 70 parts by weight of pentaerythritol triacrylate were prepared by laser holographic coherent exposure at a wavelength of 460 nm.

[0040] The specific preparation method is as follows: 3,3'-carbonylbis(7-diethylamine coumarin), N 1-Phenylated glycine, PO616A, and pentaerythritol triacrylate were mixed uniformly to obtain a mother liquor material. This mother liquor material was then poured into a liquid crystal cell with a thickness of 9 micrometers. Subsequently, it was exposed to a 460 nm coherent laser at a power density of 6 mW / cm² for 30 seconds. It was then placed under a white light lamp for 10 minutes to allow the unreacted holographic recording monomers to fully polymerize. The prepared holographic polymer material exhibited a diffraction efficiency of 95% and a photosensitivity of 6 cm / mJ.

[0041] Comparative Example 2: The holographic polymer material consists of 1 part by weight of 3,3'-carbonylbis(7-diethylamine coumarin) and 4 parts by weight of... N The mixture of 25 parts by weight of phenylglycine, 65 parts by weight of pentaerythritol triacrylate, and 5 parts by weight of rhodamine B was prepared by laser holographic coherent exposure at a wavelength of 460 nm.

[0042] The specific preparation method is as follows: 3,3'-carbonylbis(7-diethylamine coumarin), N Phenylated glycine, PO616A, pentaerythritol triacrylate, and rhodamine B were mixed uniformly to obtain a mother liquor material. This mother liquor material was then poured into a liquid crystal cell with a thickness of 9 micrometers. Subsequently, it was exposed to a 460 nm coherent laser at a power density of 6 mW / cm² for 30 seconds. It was then placed under a white light lamp for 10 minutes to allow the unreacted holographic recording monomers to fully polymerize. The prepared holographic polymer material exhibited a diffraction efficiency of 7% and a photosensitivity of 1.6 cm / mJ.

[0043] Comparative Example 3: The holographic polymer material consists of 1 part by weight of safranin O and 2 parts by weight of... N The mixture of 2 parts by weight of phenylglycine, 15 parts by weight of diphenyliodonium hexafluorophosphate, 80 parts by weight of pentaerythritol tetraacrylate was prepared by laser holographic coherent exposure at a wavelength of 532 nm.

[0044] The specific preparation method is as follows: Saffron O, NA mother liquor was prepared by uniformly mixing phenylglycine, diphenyliodonium hexafluorophosphate, PO616A, and pentaerythritol tetraacrylate. This mother liquor was then poured into a 9-micrometer-thick liquid crystal cell. Subsequently, it was exposed to a 532 nm coherent laser at a power density of 6 mW / cm² for 10 seconds. It was then placed under a white light lamp for 10 minutes to allow the unreacted holographic recording monomers to fully polymerize. The prepared holographic polymer material exhibited a diffraction efficiency of 93% and a photosensitivity of 17.9 cm / mJ.

[0045] Comparative Example 4: The holographic polymer material consists of 1 part by weight of safranin O and 2 parts by weight of... N The mixture of 2 parts by weight of phenylglycine, 2 parts by weight of diphenyliodonium hexafluorophosphate, 10 parts by weight of P0616A, 80 parts by weight of pentaerythritol tetraacrylate, and 5 parts by weight of pyrrole methylene 546 was prepared by laser holographic coherent exposure at a wavelength of 532 nm.

[0046] The specific preparation method is as follows: Saffron O, N A mother liquor was prepared by uniformly mixing phenylglycine, diphenyliodonium hexafluorophosphate, PO616A, pentaerythritol tetraacrylate, and pyrrole methylene 546. This mother liquor was then poured into a 9-micrometer-thick liquid crystal cell. Subsequently, it was exposed to a 532 nm coherent laser at a power density of 6 mW / cm² for 10 seconds. It was then placed under a white light lamp for 10 minutes to allow the unreacted holographic recording monomers to fully polymerize. The prepared holographic polymer material exhibited a diffraction efficiency of 5% and a photosensitivity of 4.1 cm / mJ.

[0047] Examples 1 to 26: Specifically, the holographic polymer-dispersed liquid crystal material provided in Example 1 consists of 0.01 parts by weight of photoinitiator, 33.99 parts by weight of P0616A, 26 parts by weight of pentaerythritol triacrylate, and 40 parts by weight of... N,N - Dimethylacrylamide was prepared by laser holographic coherent exposure at a wavelength of 442 nm.

[0048] Specifically, the preparation method provided in Example 1 is as follows: The single-component photoinitiator, P0616A, and pentaerythritol triacrylate are used. N,NDimethylacrylamide was mixed thoroughly to obtain a mother liquor material. This mother liquor material was then poured into a liquid crystal cell with a thickness of 9 micrometers. Subsequently, it was exposed to a 442 nm coherent laser with a total power density of 2 mW / cm² and a holographic coherent exposure time of 5 seconds. It was then placed under a high-pressure mercury lamp and irradiated for 10 minutes to allow the unreacted holographic recording monomers to completely polymerize. The prepared holographic polymer material exhibited a diffraction efficiency of 81% and a photosensitivity of 100 cm / mJ.

[0049] Specifically, the formulations and preparation methods of the holographic polymer-dispersed liquid crystal materials provided in Examples 2 to 26 are generally similar to those in Example 1, with specific differences shown in Tables 1 to 3 below: Table 1: Formulations of holographic polymer-dispersed liquid crystal materials in Examples 1 to 26

[0050] Table 2: Structural formulas or Chinese names of components in Examples 1 to 26

[0051] Table 3: Exposure parameters of coherent laser used in the preparation of holographic polymer-dispersed liquid crystal materials in Examples 1 to 26

[0052] Specifically, the preparation method of photoinitiator 1 provided in Example 1 of Table 2 includes the following steps: One equivalent of phosgene was bubbled into tetrahydrofuran containing two equivalents of pyrrole, and the reaction was carried out at room temperature for 12 hours. Subsequently, three equivalents of triethylamine and five equivalents of boron trifluoride diethyl ether complex were added sequentially, and the reaction was carried out at room temperature for 24 hours to obtain the parent structure A of photoinitiator 1. One equivalent of parent structure A was dissolved in methanol and refluxed for 12 hours to obtain the parent structure B of photoinitiator 1. Then, 10 equivalents of methyllithium were added, and the reaction was carried out at room temperature for 24 hours to obtain photoinitiator 1. The molar extinction coefficient of photoinitiator 1 at a wavelength of 440 nm was 61856 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.54 eV.

[0053] Specifically, the preparation method of photoinitiator 2 provided in Example 2 of Table 2 is largely the same as that of photoinitiator 1, except that the methyl lithium in Example 1 is replaced with ethyl lithium. The molar extinction coefficient of photoinitiator 2 at a wavelength of 439 nm is 64816 Lmol. -1cm -1 The bond dissociation energy of the boron-carbon bond is 2.53 eV.

[0054] Specifically, the preparation method of photoinitiator 3 provided in Example 3 of Table 2 is largely the same as that of photoinitiator 1, except that the methyllithium in Example 1 is replaced with phenyllithium. The molar extinction coefficient of photoinitiator 3 at a wavelength of 443 nm is 59451 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.53 eV.

[0055] Specifically, the preparation method of photoinitiator 4 provided in Example 4 of Table 2 includes the following steps: The parent structure A of photoinitiator 4 was obtained by dissolving 1 equivalent of the parent structure A described in Example 1 in acetonitrile, adding 5 equivalents of diethylamine, and then adding 10 equivalents of methyllithium and reacting at room temperature for 24 hours. The parent structure D of photoinitiator 4 was obtained by reacting 1 equivalent of the parent structure D with 2 equivalents of N-bromosuccinimide in tetrahydrofuran for 24 hours. The molar extinction coefficient of photoinitiator 4 at a wavelength of 457 nm was 61864 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.49 eV.

[0056] Specifically, the preparation method of photoinitiator 5 provided in Example 5 of Table 2 is largely the same as that of photoinitiator 4, except that: methyllithium in Example 4 is replaced with ethyllithium, and N-bromosuccinimide in Example 4 is replaced with N-iodosuccinimide. The molar extinction coefficient of photoinitiator 5 at a wavelength of 459 nm is 68411 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.47 eV.

[0057] Specifically, the preparation method of photoinitiator 6 provided in Example 6 of Table 2 includes the following steps: Photoinitiator 6 was obtained by dissolving 1 equivalent of acetoxyacetyl chloride and 2 equivalents of 2,4-dimethylpyrrole in tetrahydrofuran solvent and refluxing for 24 hours; then adding 3 equivalents of triethylamine and 5 equivalents of boron trifluoride diethyl ether complex and reacting at room temperature for 24 hours; subsequently adding 10 equivalents of phenyllithium and 2 equivalents of N-iodosuccinimide and reacting for 24 hours to obtain photoinitiator 6. Photoinitiator 6 has a molar extinction coefficient of 78912 Lmol at a wavelength of 534 nm. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.05 eV.

[0058] Specifically, the preparation method of photoinitiator 7 provided in Example 7 of Table 2 includes the following steps: One equivalent of benzaldehyde and two equivalents of 2,4-dimethylpyrrole were dissolved in tetrahydrofuran solvent, and the mixture was refluxed for 24 hours with a catalytic amount of concentrated hydrochloric acid. Then, one equivalent of 2,3-dichloro-5,6-dicyanobenzoquinone was added, and the reaction was carried out at room temperature for 24 hours. Finally, three equivalents of triethylamine and five equivalents of a boron trifluoride diethyl ether complex were added, and the reaction was carried out at room temperature for 24 hours to obtain the parent structure E of photoinitiator 7. One equivalent of the parent structure E was reacted with 10 equivalents of ethyllithium in tetrahydrofuran at room temperature for 24 hours to obtain photoinitiator 7. The molar extinction coefficient of photoinitiator 7 at a wavelength of 513 nm is 74512 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.01 eV.

[0059] Specifically, the preparation method of photoinitiator 8 provided in Example 8 of Table 2 includes the following steps: One equivalent of trifluoroacetaldehyde acetal acetate and two equivalents of 2,4-Diphenyl-1H-pyrrole were dissolved in tetrahydrofuran solvent. The mixture was refluxed for 24 hours with a catalytic amount of concentrated hydrochloric acid. Then, one equivalent of 2,3-dichloro-5,6-dicyanobenzoquinone was added, and the reaction was carried out at room temperature for 24 hours. Finally, three equivalents of triethylamine and five equivalents of a boron trifluoride diethyl ether complex were added, and the reaction was carried out at room temperature for 24 hours to obtain the parent structure F of photoinitiator 8. One equivalent of the parent structure F was then reacted with two equivalents of N-iodosuccinimide in tetrahydrofuran for 24 hours. Then, ten equivalents of methyllithium were added, and the reaction was carried out at room temperature for 24 hours to obtain photoinitiator 8. Photoinitiator 8 has a molar extinction coefficient of 89713 Lmol at a wavelength of 651 nm. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 1.52 eV.

[0060] Specifically, the preparation method of photoinitiator 9 provided in Example 9 of Table 2 includes the following steps: Photoinitiator 9 is obtained by refluxing 1 equivalent of photoinitiator 7 and 2 equivalents of benzaldehyde in DMF for 1 hour. Photoinitiator 9 has a molar extinction coefficient of 86428 Lmol at a wavelength of 632 nm. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 1.53 eV.

[0061] Specifically, the preparation method of photoinitiator 10 provided in Example 10 of Table 2 includes the following steps: One equivalent of 4-cyanobenzaldehyde and two equivalents of 2,4-dimethylpyrrole were dissolved in tetrahydrofuran solvent. The mixture was refluxed for 24 hours with a catalytic amount of concentrated hydrochloric acid. Then, one equivalent of 2,3-dichloro-5,6-dicyanobenzoquinone was added and reacted at room temperature for 24 hours. Finally, a complex of triethylamine and boron trifluoride diethyl ether was added and reacted at room temperature for 24 hours to obtain the parent structure G of photoinitiator 10. One equivalent of the parent structure G was reacted with two equivalents of N-iodosuccinimide in tetrahydrofuran for 24 hours. Then, 10 equivalents of ethyllithium were added and reacted at room temperature for 24 hours to obtain photoinitiator 10. Photoinitiator 10 has a molar extinction coefficient of 77143 Lmol at a wavelength of 522 nm. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 1.91 eV.

[0062] Specifically, the preparation method of photoinitiator 11 provided in Example 11 of Table 2 is largely the same as that of photoinitiator 10, except that: trifluoroacetaldehyde acetal succinate is used instead of 4-cyanobenzaldehyde in Example 10, and phenyl lithium is used instead of ethyl lithium in Example 10, to obtain photoinitiator 11. The molar extinction coefficient of photoinitiator 11 at a wavelength of 582 nm is 80588 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 1.71 eV.

[0063] Specifically, the preparation method of photoinitiator 12 provided in Example 12 of Table 2 is largely the same as that of photoinitiator 1, except that: replacing the methyllithium in Example 1 with n-propyllithium yields the parent structure H of photoinitiator 12; reacting 1 equivalent of the parent structure H with 2 equivalents of N-iodosuccinimide in tetrahydrofuran for 24 hours yields photoinitiator 12. The molar extinction coefficient of photoinitiator 12 at a wavelength of 461 nm is 62418 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.47 eV.

[0064] Specifically, the preparation method of photoinitiator 13 provided in Example 13 of Table 2 is largely the same as that of photoinitiator 1, except that: 1 equivalent of the parent structure A from Example 1 is dissolved in acetonitrile, and 5 equivalents of dimethylamine are added, followed by 10 equivalents of positively charged lithium, and the reaction is carried out at room temperature for 24 hours to obtain photoinitiator 13. The molar extinction coefficient of photoinitiator 13 at a wavelength of 436 nm is 61258 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.53 eV.

[0065] Specifically, the preparation method of photoinitiator 14 provided in Example 14 of Table 2 is largely the same as that of photoinitiator 13, except that n-butyllithium is replaced with n-pentyllithium. The molar extinction coefficient of photoinitiator 14 at a wavelength of 437 nm is 61546 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.53 eV.

[0066] Specifically, the preparation method of photoinitiator 15 provided in Example 15 of Table 2 is largely the same as that of photoinitiator 13, except that n-butyllithium is replaced with n-hexyllithium. The molar extinction coefficient of photoinitiator 15 at a wavelength of 437 nm is 62451 Lmol. -1 cm -1 The bond dissociation energy of the boron-carbon bond is 2.53 eV.

[0067] Specifically, in step S30 of the preparation method of holographic polymer dispersed liquid crystal material in Examples 1 to 9, the high photosensitivity holographic polymer material is irradiated under a high-pressure mercury lamp for 10 minutes after holographic coherent exposure; in step S30 of the preparation method of holographic polymer dispersed liquid crystal material in Examples 10 to 26, the high photosensitivity holographic polymer material is irradiated under a white light lamp for 10 minutes after holographic coherent exposure.

[0068] Specifically, the diffraction efficiency and photosensitivity data of the holographic polymer-dispersed liquid crystal materials in Examples 1 to 26 are shown in Table 4: Table 4: Diffraction efficiency and photosensitivity of holographic polymer-dispersed liquid crystal materials in Examples 1 to 26

[0069] Furthermore, according to the data in Table 4, the diffraction efficiency of the holographic polymer-dispersed liquid crystal materials in Examples 1-2 and Examples 4-26 is 81%-99%, and the photosensitivity is 100 cm / mJ-1843 cm / mJ. Compared with the holographic polymer materials provided in Comparative Examples 1-3, the above results show higher diffraction efficiency and higher photosensitivity.

[0070] The holographic polymer-dispersed liquid crystal material prepared in Example 26 has now been applied in the field of high-end anti-counterfeiting. Please refer to... Figure 2 as well as Figure 3 , Figure 2 The holographic image of the holographic polymer material for high-end anti-counterfeiting prepared in Example 26 of this invention; Figure 3The fluorescent image of the holographic polymer material for high-end anti-counterfeiting prepared in Example 26 of this invention is shown below. The image preparation method for Example 26 is as follows: First, in holographic recording, a flower-shaped mask is used to block the object light during holographic exposure, and a flower-shaped holographic grating is recorded, i.e., the holographic image, as shown below. Figure 2 As shown; then bleached with a white LED for 10 minutes; finally, a panda-shaped mask was used to block the holographic polymer-dispersed liquid crystal material, and irradiated under a high-pressure mercury lamp for 10 minutes to degrade the pyrrole methylene 546 in the exposed area, thus producing a fluorescent image with contrast, as shown. Figure 3 As shown.

[0071] In summary, the beneficial effects of the present invention, compared with the prior art, are as follows: (1) This invention provides a single-component photoinitiator for preparing high photosensitivity holographic polymer dispersed liquid crystal materials. After being excited, the single-component photoinitiator directly undergoes homolytic cleavage of boron-carbon bonds, generating initiating free radicals that act on the holographic recording monomer. Compared with the holographic polymer materials that have been disclosed using multi-component photoinitiation systems, this invention effectively simplifies the formulation of holographic polymer materials.

[0072] (2) This invention provides a single-component photoinitiator for preparing high-sensitivity holographic polymer-dispersed liquid crystal materials. Upon excitation, the photoinitiator directly undergoes homolytic cleavage of boron-carbon bonds, generating initiating free radicals that act on the holographic recording monomer. In previously disclosed holographic polymer materials, initiating free radicals are generated through intermolecular photoredox reactions in multi-component photoinitiation systems. Intermolecular chemical reactions depend on effective collisions, which is detrimental to the efficiency of free radical generation. The single-component photoinitiator provided by this invention undergoes intramolecular cleavage upon excitation, effectively improving the efficiency of free radical generation.

[0073] (3) This invention provides a single-component photoinitiator for preparing high-photosensitivity holographic polymer-dispersed liquid crystal materials. Its reaction efficiency is far higher than that of previously disclosed multi-component initiators, enabling faster holographic recording and significantly improving the photosensitivity of the holographic polymer material. The photosensitivity of the high-photosensitivity holographic polymer material is greater than 100 cm / mJ. This effectively improves the processing efficiency of the holographic polymer material.

[0074] (4) The present invention provides a single-component photoinitiator for preparing high photosensitivity holographic polymer-dispersed liquid crystal materials in which the intramolecular chemical reaction is not interfered with by additives. As shown in Comparative Examples 2 and 4, when using multi-component photoinitiators, the diffraction efficiency of holographic polymer materials is significantly affected by functional additives.

[0075] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0076] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A photoinitiator, characterized in that, The photoinitiator comprises the following chemical structure: ； Wherein, R1 includes any one of methoxy, diethylamino, hydroxymethyl, trifluoromethyl, phenyl, and 4-cyanophenyl; R2 includes any one of hydrogen, methyl, and phenyl; R3 includes any one of hydrogen, bromine, and iodine; R4 includes any one of hydrogen, methyl, phenyl, and styryl; and R5 includes any one of alkyl groups with fewer than 6 carbon atoms and phenyl groups.

2. The photoinitiator according to claim 1, characterized in that, The photoinitiator can be excited by visible light with a wavelength of 420 nm to 700 nm; the maximum molar extinction coefficient of the photoinitiator in the 420 nm to 700 nm range is not less than 40000 Lmol. - 1 cm -1 .

3. The photoinitiator according to claim 1 or 2, characterized in that, When the photoinitiator is excited, the boron-carbon bonds are homolytically cleaved to generate R5 initiating radicals, which initiate polymerization of the holographic recording monomers; the bond dissociation energy of the boron-carbon bonds is no greater than 2.54 eV.

4. The photoinitiator according to claim 3, characterized in that, The R5-initiating radical includes any one of methyl radical, ethyl radical, n-propyl radical, n-butyl radical, n-hexyl radical, and phenyl radical.

5. A holographic polymer-dispersed liquid crystal material, characterized in that, The raw materials for preparing the holographic polymer-dispersed liquid crystal material, by weight, include: 0.01 to 5 parts of the photoinitiator as described in any one of claims 1 to 4, 20 to 80 parts of the holographic recording monomer, and 15 to 79 parts of the inert component.

6. The holographic polymer-dispersed liquid crystal material according to claim 5, characterized in that, The holographic recording monomer includes at least one of acrylate monomers, acrylamide monomers, and vinyl monomers.

7. The holographic polymer-dispersed liquid crystal material according to claim 5, characterized in that, The raw materials for preparing the holographic polymer-dispersed liquid crystal material also include 0.05 to 5 parts of additives; the additives have photoresponsive functions and include any one of pyrrole methylene 546, Nile Red, Rhodamine B, spiropyran compounds, diarylethylene compounds, and azobenzene compounds.

8. A method for preparing a holographic polymer-dispersed liquid crystal material as described in any one of claims 5 to 7, characterized in that, The preparation method includes the following steps: S10, the photoinitiator, the holographic recording monomer, the additive and the inert component are mixed evenly to obtain the first mother liquor; S20, the first mother liquor is siphoned into the liquid crystal cell and placed in the dark to obtain a holographic recording medium; S30, the holographic recording medium is placed under a coherent laser for holographic coherent exposure to obtain a high photosensitivity holographic polymer material; S40, the high photosensitivity holographic polymer material is placed under a visible light source until the holographic recording monomers in the high photosensitivity holographic polymer material are completely reacted, while the photoinitiator is bleached to obtain the holographic polymer-dispersed liquid crystal material.

9. The method for preparing the holographic polymer-dispersed liquid crystal material according to claim 8, characterized in that, During the holographic coherent exposure process, the holographic coherent exposure time of the high photosensitivity holographic polymer material is 0.01s to 5s, and the exposure dose is 0.1 mJ / cm² to 10 mJ / cm²; the photosensitivity of the high photosensitivity holographic polymer material is greater than 100 cm² / mJ.

10. The application of a holographic polymer-dispersed liquid crystal material prepared by any one of claims 5 to 7 or any one of claims 8 to 9 in the fields of anti-counterfeiting, information storage, virtual reality, and augmented reality.

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