Cyclohexanone-based photosensitizers, methods of making, mixed photosensitizers, and photopolymer films

Abstract

The application provides a cyclohexanone photosensitizer shown in a formula I, a preparation method of the cyclohexanone photosensitizer, a mixed photosensitizer containing the cyclohexanone photosensitizer, a photopolymerization composition and a photopolymer film, wherein the cyclohexanone photosensitizer has the structural formula shown in the formula I, wherein R1 and R2 are each independently selected from hydrogen or C1-C4 alkyl. The cyclohexanone photosensitizer provided by the application replaces a benzene ring with thiophene, shows excellent absorption performance in a green laser wavelength range, is well matched with a 532nm laser, and provides more candidate photosensitizers for the development of green photosensitive polymer films.

Description

Technical Field

[0001] This invention relates to the field of holographic storage materials, and more specifically, to a cyclohexanone photosensitizer, its preparation method, a mixed photosensitizer, and a photopolymer film. Background Technology

[0002] Holography has wide applications in many fields, including data storage, microscopy, photolithography, head-up displays, 3D imaging, interferometry, and anti-counterfeiting. In recent years, holographic storage has attracted considerable attention. It can be used to record and reproduce the amplitude and phase information of light, possessing three-dimensional spatial recording and two-dimensional data access capabilities, meeting the demands of the information age for large-capacity data storage and rapid transmission. Currently, storage materials are the key factor restricting the application of holographic storage technology. Traditional holographic recording materials use silver halide emulsions and dichromate gelatin. Silver halide exhibits particle noise, while dichromate gelatin is subject to harsh humidification conditions and has poor environmental resistance. The growth of inorganic photorefractive crystal holographic storage materials such as LiNb and SBN typically requires strict control over doping, temperature, and environmental conditions, making it difficult to produce large-sized materials and resulting in high costs, hindering commercialization in the short term.

[0003] In comparison, photopolymers offer numerous advantages: high photosensitivity, high resolution, high diffraction efficiency, high signal-to-noise ratio, low cost, ease of processing, and the ability to be processed using a completely dry method and developed rapidly. The resulting holographic images exhibit high geometric fidelity, making them a research hotspot in recent years. Cyclic ketone photosensitizers are a common class of dyes with good photosensitizing properties in the visible light region. Various commercially available lasers with matching wavelengths can be selected within a wide wavelength range of 400-600 nm as the information recording light source to initiate the polymerization of acrylate or olefin monomers. Further utilization of angle multiplexing and / or wavelength multiplexing techniques can achieve massive information storage. DuPont, Inc. in the United States, was the first to release a series of bis(p-dialkyl-amino-phenyl)-α,β-unsaturated ketone / cyclic ketone photosensitizers. These photosensitizers are suitable for the red band, and their combination with the initiator HABI expands the wavelength range of photopolymers.

[0004] Patent US5470662A discloses photopolymerizable film materials, including chlorofluoropolymer monomers as binders, and also discloses the use of HABI initiators.

[0005] Patent US5759721A discloses the use of 5,12-bis(phenylethynyl)naphthalene as a photosensitizer, wherein the holographic recording medium comprises an acid-generating agent capable of generating acid upon exposure to photochemical radiation, a binder, and at least one monomer or oligomer capable of undergoing cationic polymerization initiated by the acid generated by the acid-generating agent.

[0006] None of the aforementioned patents disclose the photosensitizer itself or its preparation method, nor do they provide any technical insights.

[0007] In view of the above technical problems, this invention is hereby introduced. Summary of the Invention

[0008] The main objective of this invention is to provide a cyclohexanone photosensitizer, its preparation method, a mixed photosensitizer and a photopolymer film, which is simple to prepare, has good compatibility with 532nm lasers, and has high photosensitivity.

[0009] To achieve the above objectives, the present invention provides a cyclohexanone photosensitizer of Formula I:

[0010]

[0011] R1 and R2 are each independently selected from hydrogen or C1-C4 alkyl groups.

[0012] Preferably, R1 and R2 are each independently selected from methyl, ethyl, n-propyl and isopropyl.

[0013] Preferably, the compounds are selected from those of formula II or formula III, or combinations thereof:

[0014]

[0015] <Form III>.

[0016] In another aspect, this invention provides a method for preparing a cyclohexanone photosensitizer represented by Formula I, comprising the following steps:

[0017] In step S1, 5-halogen-2-thiophenecarboxaldehyde is mixed with dialkylamine or ammonia and reacted at 80-110°C for 3-20 hours to obtain the intermediate shown in Formula IV.

[0018]

[0019] R3 and R4 are each independently selected from hydrogen or C1-C4 alkyl groups, and the dialkylamine is selected from dimethylamine, diethylamine, di-n-propylamine, and diisopropylamine. Preferably, 5-halogen-2-thiophenecarboxaldehyde is 5-bromo-2-thiophenecarboxaldehyde.

[0020] Step S2: Mix the intermediate shown in Formula IV with cyclohexanone, add an alkaline catalyst, and react at 80-110℃ for 3-20 h to obtain the cyclohexanone photosensitizer shown in Formula I.

[0021] Preferably, in step S1, the molar ratio of 5-bromo-2-thiophene carboxaldehyde to dialkylamine or ammonia is 1:2.5 to 4.

[0022] Preferably, in step S2, the mass ratio of cyclohexanone to the intermediate shown in Formula IV is 1:4 to 6.

[0023] In addition, the present invention also proposes a mixed photosensitizer, comprising cyclohexanone photosensitizer and purslane.

[0024] Preferably, the mass ratio of purslane to cyclohexanone photosensitizer is 1:0.6 to 1.2, and more preferably, the mass ratio is 1:1.

[0025] In addition, this application also proposes a photopolymerization composition comprising a mixed photosensitizer.

[0026] Preferably, it also includes photopolymerizable monomers, wherein the monomers are selected from one or more combinations of vinyl monomers, acrylic monomers and acrylate monomers;

[0027] It also includes an initiator selected from hexaarylbisimidazole initiators, preferably o-chlorohexaarylbisimidazole.

[0028] The cyclohexanone photosensitizer, its preparation method, mixed photosensitizer, and photopolymer film proposed in this invention achieve the following technical effects:

[0029] 1. Cyclohexanone photosensitizers, by replacing the benzene ring with thiophene, exhibit excellent absorption performance in the green laser wavelength range and show good matching with 532nm lasers, providing more candidate photosensitizers for the development of green-sensitive photopolymer films.

[0030] 2. By mixing cyclohexanone photosensitizers with purpureus and adjusting the ratio of their components, the diffraction efficiency of the film can be improved.

[0031] 3. By adjusting the composition of the photopolymerization composition, the components are highly compatible, resulting in more stable film performance.

[0032] 4. By controlling the film thickness and incident light intensity, the diffraction efficiency of the film can be further improved. Attached Figure Description

[0033] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0034] Figure 1 The normalized ultraviolet absorption spectra of photosensitizers DYE-1 and DYE-2 are shown.

[0035] Figure 2 The diffraction efficiency of photopolymer films obtained with different DYE-1 dosages is shown under the condition of maintaining a dosage of 5 mg of gentian violet;

[0036] Figure 3 The diffraction efficiency of photopolymer films obtained with different amounts of gentian violet (DYE-1) is shown under the condition of maintaining a DYE-1 dosage of 5 mg.

[0037] Figure 4 A schematic diagram of the exposure circuitry in this embodiment is shown;

[0038] Figure 5 Example 5 and the comparative example are shown with an incident light intensity of 1.5 mw / cm. 2 Diffraction efficiency under the given conditions;

[0039] Figure 6 This shows the effect when the incident light intensity is 5 mw / cm. 2 Under the given conditions, the exposure diffraction efficiency of photopolymer films of different thicknesses;

[0040] Figure 7 The diffraction efficiency of the photopolymer film prepared with a DYE-1:Berberis = 1:1 ratio is shown at different incident light intensities.

[0041] The above figures include the following reference numerals:

[0042] 1. Laser; 2. Pinhole; 3. Lens; 4. Aperture stop; 5. Beam splitter; 6. First reflecting mirror; 7. Second reflecting mirror; 8. Sample box. Detailed Implementation

[0043] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0044] The present invention will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention. The term "comprising" indicates the presence of a feature, but does not exclude the presence or addition of one or more other features. The terms "lateral," "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the purpose of description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0045] In this description, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0046] This application proposes a novel cyclohexanone photosensitizer, and a method for preparing the cyclohexanone photosensitizer, including a mixed photosensitizer of the cyclohexanone photosensitizer and a photopolymer film.

[0047] This application conducts optical performance tests on the obtained photopolymer film, including diffraction efficiency, refractive index modulation, and photosensitivity. Diffraction efficiency affects the information storage density per unit volume and, more importantly, the brightness of the holographic image; therefore, it is crucial for characterizing the film's performance. The aforementioned performance parameters were tested using methods conventional in the art. The diffraction efficiency was calculated using the following formula:

[0048]

[0049] Where I1 is the diffracted light intensity and I2 is the incident light intensity. The diffracted light intensity I1 and the incident light intensity I2 transmitted through the photopolymer film are measured using a power meter.

[0050] The refractive index modulation Δn is obtained by the following formula:

[0051]

[0052] Where λ is the wavelength of the detection light source, θ is the incident angle of the recording reference light, and η max d represents the maximum diffraction efficiency, and d represents the film thickness.

[0053] The photosensitivity S is obtained by the following formula:

[0054]

[0055] Where, η max denoted as the maximum diffraction efficiency, E is the exposure amount when the diffraction efficiency reaches its maximum, and d is the film thickness.

[0056] This application proposes cyclohexanone photosensitizers, the molecular structure of which is shown in Formula I below.

[0057]

[0058] Wherein, R1 and R2 are each independently selected from hydrogen or C1-C4 alkyl groups. Preferably, R1 and R2 are each independently selected from methyl, ethyl, n-propyl, and isopropyl. Cyclohexanone photosensitizers are selected from the following... wait.

[0059] The following will provide a detailed explanation of two cyclohexanone photosensitizers, R1 and R2, which are methyl and ethyl, respectively.

[0060] Example 1

[0061] In one embodiment of this application, the cyclohexanone photosensitizer is shown in the following formula (hereinafter collectively referred to as DYE-1).

[0062]

[0063] The preparation method involves uniformly mixing 5-bromo-2-thiophenecarboxaldehyde and dimethylamine, then adding deionized water and refluxing the mixture at 80-110°C for 3-20 hours to obtain crude product 1. Preferably, reacting at 100°C for 12 hours yields a higher intermediate yield. The molar ratio of 5-bromo-2-thiophenecarboxaldehyde to dimethylamine is 1:2.5-4, preferably 1:3. Besides 5-bromo-2-thiophenecarboxaldehyde, other 5-halogenated 2-thiophenecarboxaldehydes, such as 5-chloro-2-thiophenecarboxaldehyde, can also be used.

[0064] Furthermore, the crude product 1 was separated and purified by the following method to obtain the 5-(dimethylamino)-2-thiophene carboxaldehyde intermediate 1 shown in the following formula.

[0065]

[0066] Specifically, the crude product is extracted with chloroform and deionized water. The chloroform layer is dried with anhydrous sodium sulfate, and the solvent is evaporated. Further purification is performed by column chromatography to obtain a solid phase containing intermediate 1. The solid phase is then eluted with a combination of ethyl acetate and n-hexane, and the solvent is evaporated to obtain the purified intermediate 1. Preferably, the molar ratio of ethyl acetate to n-hexane in the combined solvent is 1:1.

[0067] The above-mentioned 5-(dimethylamino)-2-thiophenecarboxaldehyde intermediate 1 was mixed with cyclohexanone, and an alkaline catalyst was added. The mixture was heated under reflux and stirred at 80-110°C for 3-20 hours. The resulting reaction solution was cooled, filtered, washed with ice water, and dried to obtain DYE-1. Sodium hydroxide is preferred as the alkaline catalyst in this reaction, and the reaction is carried out in an ethanol solvent. The mass ratio of cyclohexanone to 5-(dimethylamino)-2-thiophenecarboxaldehyde is 1:4-6, preferably 1:4.9.

[0068] The final product was characterized by proton NMR spectroscopy, and the molecular formula and structure of the product were confirmed as shown above. 1 ¹H NMR (600MHz, DMSO-d6): δ (ppm) data are: 7.63 (s, 2H); 7.22 (d, J = 4.2Hz, 2H); 6.03 (d, J = 4.2Hz, 2H); 2.97 (s, 12H); 2.72 (t, J = 5.4Hz, 4H); 1.79 (p, J = 6.6Hz, 2H).

[0069] Example 2

[0070] In one embodiment of this application, the cyclohexanone photosensitizer is shown in the following formula (hereinafter referred to as DYE-2).

[0071]

[0072] The preparation method is as follows: 5-bromo-2-thiophene carboxaldehyde and diethylamine are mixed evenly, then N,N-dimethylformamide and methyltrioctylammonium chloride are added and stirred evenly. The reactants are refluxed at a temperature range of 80-110℃ for 3-20 hours to obtain crude product 2.

[0073] Crude product 2 was extracted with diethyl ether and deionized water. The ether layer was collected, dried over anhydrous sodium sulfate, and the solvent was evaporated. Further purification was performed using column chromatography to obtain a solid phase containing the intermediate. The solid phase was eluted with a combination of ethyl acetate and n-hexane, and the solvent was evaporated to obtain 5-(diethylamino)-2-thiophenecarboxaldehyde intermediate 2 as shown in the following formula. The molar ratio of ethyl acetate to n-hexane in the combined solvent was 1:3.

[0074]

[0075] The above-mentioned 5-(diethylamino)-2-thiophene carboxaldehyde intermediate 2 was mixed with cyclohexanone, and an alkaline catalyst was added. The mixture was heated under reflux and stirred at 80-110°C for 3-20 hours. The resulting reaction solution was cooled, filtered, washed with ice water, and dried to obtain DYE-2. Sodium hydroxide is preferred as the alkaline catalyst in this reaction, and the reaction is carried out in an ethanol solvent. The mass ratio of cyclohexanone to 5-(diethylamino)-2-thiophene carboxaldehyde is 1:4-6, preferably 1:4.1.

[0076] This application not only limits the reaction of 5-bromo-2-thiophene carboxaldehyde with dimethylamine or diethylamine, but also extends it to the preparation of the intermediate shown in Formula IV with 5-halogen-2-thiophene carboxaldehyde and dialkylamine or ammonia, and the reaction of the intermediate shown in Formula IV with cyclohexanone to prepare Formula I.

[0077]

[0078] R3 and R4 are each independently selected from hydrogen or C1-C4 alkyl groups, and the dialkylamine is selected from dimethylamine, diethylamine, di-n-propylamine, and diisopropylamine.

[0079] The final product was characterized by 1H NMR spectroscopy, confirming its molecular formula and structure as shown above. 1H NMR (600 MHz, Chloroform-d): δ (ppm) data were: 7.86 (s, 2H); 7.10 (d, J = 4.2 Hz, 2H); 5.87 (d, J = 4.2 Hz, 2H); 3.37 (q, J = 7.2 Hz, 8H); 2.82 (t, J = 5.4 Hz, 4H); 1.90 (p, J = 6.1 Hz, 2H); 1.22 (t, J = 7.1 Hz, 12H).

[0080] This application conducts photophysical performance tests on the DYE-1 and DYE-2 photosensitizers obtained in Examples 1 and 2 above, and the results are shown in the table below.

[0081] Table 1. Photophysical performance test results of DYE-1 and DYE-2

[0082]

[0083] Based on the photophysical performance test results, the synthesized DYE-1 and DYE-2 have relatively large molar extinction coefficients, which to some extent indicates that DYE-1 and DYE-2 have good light absorption, high photosensitivity, and high diffraction efficiency.

[0084] Combining Table 1 and Figure 1 As shown, DYE-1 and DYE-2 exhibit strong absorption around 500 nm, therefore, a wavelength around 500 nm can be used to expose photopolymer films containing DYE-1 and DYE-2. DYE-1 and DYE-2 can be used to prepare green-sensitive photopolymer films and have good compatibility with 532 nm lasers.

[0085] The two typical cyclohexanone photosensitizers prepared by the above method achieved the following technical effects:

[0086] 1. Cyclohexanone photosensitizers, by replacing the benzene ring with thiophene, exhibit excellent absorption performance in the green laser wavelength range and show good matching with 532nm lasers, providing more candidate photosensitizers for the development of green-sensitive photopolymer films.

[0087] 2. Cyclohexanone photosensitizers have simple molecular structures, simple preparation methods, and high product yields.

[0088] 3. Multiple separation technologies are used to achieve high product precision.

[0089] Example 3

[0090] In another aspect, this application also proposes a mixed photosensitizer comprising a cyclohexanone photosensitizer prepared by the above method and a purslane. The absorption wavelength of the purslane is close to that of the synthesized cyclohexanone photosensitizer, which has an absorption wavelength less than 532 nm, while the absorption wavelength of the purslane is greater than 532 nm. The combination of the two results in a mixed photosensitizer with a greater absorption effect at 532 nm.

[0091] This application investigates the effect of different ratios of mixed photosensitizers on the diffraction efficiency of photopolymer films. Figure 2 , 3 As shown, the diffraction efficiency is high when the mass ratio of *Begonia solani* to cyclohexanone photosensitizer is in the range of 1:0.6 to 1.2, and the diffraction efficiency increases rapidly with the extension of exposure time. Furthermore, while keeping the amount of *Begonia solani* at 5 mg, the photopolymer film obtained using 5 mg of the cyclohexanone photosensitizer described in this application exhibits significantly better diffraction efficiency than other ratios, and this advantage becomes more pronounced with the extension of exposure time. Similarly, while keeping the amount of cyclohexanone photosensitizer at 5 mg, the photopolymer film obtained using 5 mg of *Begonia solani* exhibits better diffraction efficiency than other ratios. Therefore, when the composition ratio of *Begonia solani* to cyclohexanone photosensitizer is 1:1, the diffraction efficiency of the photopolymer film is even higher.

[0092] This application uses a mixed photosensitizer, achieving the following technical effects:

[0093] 1. Combining cyclohexanone photosensitizers with purslane improves the light absorption effect at 532nm, making it more compatible with 532nm lasers.

[0094] 2. The diffraction efficiency was further optimized by adjusting the ratio of cyclohexanone photosensitizer to purslane.

[0095] Example 4

[0096] This application also proposes a photopolymerization composition in which the aforementioned mixed photosensitizer is applied, wherein the mass percentage of the mixed photosensitizer in the photopolymerization composition is 0.1% to 1%. In addition to the mixed photosensitizer, the photopolymerization composition also includes photopolymerizable monomers, film-forming agents, initiators, and chain transfer agents. The photopolymerizable monomers can combine with free radicals generated by the initiator and form polymer chains through chain growth. The photosensitizer has strong absorption in a specific region of the visible light wavelength range; after absorbing light energy, it transfers energy to the initiator through electron transfer or simple energy transfer, thereby causing the initiator to generate free radicals. The film-forming agent supports the other components, promoting the formation of a geometrically stable photopolymer film.

[0097] The photopolymerization monomer is selected from one or more combinations of vinyl monomers, acrylic monomers, and acrylate monomers, and the monomer accounts for 10% to 50 wt% of the photopolymerization composition. The initiator is selected from hexaarylbisimidazole photoinitiators, preferably o-chlorohexaarylbisimidazole. These initiators have good compatibility with cyclic ketone photosensitizers, and the range of usable wavelengths is expanded by using commercially available initiators. The initiator accounts for 0.5% to 5% of the mass of the photopolymerization composition.

[0098] The film-forming agent is selected from one or more of polyvinyl acetate, polymethyl methacrylate, epoxy resin, and fluorinated resin, and the mass percentage of the film-forming agent in the photopolymerization composition is 30% to 90%.

[0099] The chain transfer agent is a nitrogen-containing aromatic heterocyclic thiol compound, accounting for 0.5% to 3% by mass in the photopolymerization composition. It is preferably one or more of 4-methyl-4H-3-thiol-1,2,4-triazole, 4-amino-1,2,4-triazole-3-thiol, and 4-methylthiol-2-thiol. This type of chain transfer agent has strong electron transfer function, which can improve the polymerization rate of the active monomer. It can also control the viscosity by controlling the chain growth reaction of the polymer, thereby improving the uniformity, transparency, and resolution of the photopolymer. It also has good thermal stability, which is beneficial for the preservation of photosensitive materials.

[0100] In addition, the photopolymerization composition also includes a certain amount of solvent, which can be selected from alcohol solvents, such as methanol, ethanol, n-butanol, isobutanol, etc.; halogenated alkane solvents, such as dichloromethane, trichloromethane, etc.; ketone solvents, such as acetone, butanone, etc.; ester solvents, such as methyl acetate, ethyl acetate, etc. The solvent selected in this application is a composite solvent composed of multiple solvents with different polarities, using a compound solvent of dichloromethane and N,N-dimethylformamide. Considering that dichloromethane is highly volatile, an excessively high proportion of dichloromethane is not conducive to membrane leveling; an excessively low proportion of dichloromethane makes the membrane difficult to dry and susceptible to environmental influences. This application, through experimental adjustment, determined that a composite solvent mixed at a volume ratio of 9:1 provides better film-forming performance.

[0101] Example 5

[0102] The following detailed description of the composition of the photopolymer composition and the preparation process of the photopolymer film will be provided with specific examples.

[0103] Table 2. Composition of the photopolymerization composition

[0104]

[0105] Methods for preparing photopolymer films include:

[0106] (1) Add the film-forming agent polyvinyl acetate to the mixed solvent of dichloromethane and N,N-dimethylformamide, stir evenly to form a transparent solution.

[0107] (2) In a dark room with a red safety light, the monomer, chain transfer agent and initiator are added to the solution obtained in step (1) in sequence and stirred until completely dissolved.

[0108] (3) In a dark room and under a red safety light, dissolve the photosensitizer in a small amount of solvent and add it to the mixed solution obtained in step (2). Stir until completely dissolved to form a mixed photosensitive liquid.

[0109] (4) The mixed photosensitive solution prepared in step (3) is passed through a filter under a red safety lamp to remove dust and other impurities, resulting in a uniform, bubble-free mixed photosensitive solution. Before use, the mixed photosensitive solution is stored in a dark box. Preferably, the pore size of the filter is 0.45 μm.

[0110] (5) Take the mixed photosensitive solution and apply it to a glass substrate using a wet film coating machine. After drying in a dark room, a photopolymer film is obtained. Since the photopolymer film is highly sensitive to light, the prepared photopolymer film is stored in a dark box.

[0111] The prepared photopolymer film was placed on the sample stage, and a 532nm laser was used as the exposure light source. Figure 4 As shown, the laser exposure optical path includes a laser beam expander system, an aperture stop, a half-wave plate, a polarizing beam splitter, and a mirror. The laser emitted from laser 1 is expanded by a small hole 2 and a lens 3 in the beam expander system, then passes through an aperture stop 4 and is split into two beams by a beam splitter 5, maintaining a 1:1 intensity ratio. The two beams are reflected by a first mirror 6 and a second mirror 7, and then converge to irradiate the photopolymer film sample box 8, forming interference fringes. The angle between the two beams is 135°. During the test, the intensity of each 532nm green light beam was 5mW / cm². 2 The exposure time was 1 second. In addition, the intensity of transmitted light and diffracted light of the photopolymer film after exposure was detected by two probes, respectively, to further obtain the optical parameters of the photopolymer film.

[0112] The optical performance test results of the above-mentioned photopolymer film, such as diffraction efficiency and refractive index modulation, are as follows.

[0113] <![CDATA[η max ]]> Transmission rate Refractive index modulation Photosensitivity 69％ 83％ 0.0019 <![CDATA[1.94cm 2 ·mJ -1 ]]>

[0114] To compare its performance with existing photopolymer films, this application sets up a comparative example, testing the diffraction efficiency of films of the same thickness under identical conditions. For example... Figure 5As shown, the photopolymer film prepared in this application exhibits better diffraction efficiency under exposure conditions of more than 4 seconds, and the diffraction efficiency advantage becomes more prominent with the extension of exposure time.

[0115] Example 6

[0116] Since film thickness has a significant impact on performance parameters such as diffraction efficiency, refractive index modulation, and photosensitivity, this application uses film thickness as a variable to study the effect of film thickness on diffraction efficiency of photopolymer films. Figure 6 As shown, when the incident light intensity is 5mw / cm 2 Under the condition of exposure time ≥ 1 second, the diffraction efficiency of a 60 μm thick film is higher than that of a thicker film.

[0117] Example 7

[0118] This application investigates the effect of incident light intensity on the diffraction efficiency of photopolymer films.

[0119] like Figure 7 As shown, photopolymer films were synthesized by controlling the mass ratio of cyclohexanone photosensitizer to cyanobacteria at 1:1, with different incident light intensities as variables, and the effect of different incident light intensities on the diffraction efficiency of the photopolymer film was studied. The results show that using 5 mW / cm² light is effective. 2 The diffraction efficiency of photopolymer films obtained with shorter exposure times of 1 to 2 seconds is higher.

[0120] In summary, the photopolymer film proposed in this embodiment achieves the following technical effects:

[0121] 1. The optical performance is improved by using the mixed photosensitizer containing cyclohexanone proposed in this application.

[0122] 2. By adjusting the composition of the photopolymerization composition, the components are highly compatible, resulting in more stable film performance.

[0123] 3. By controlling the film thickness and incident light intensity, the diffraction efficiency of the film can be further improved.

[0124] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cyclohexanone photosensitizer of formula I: ###0001### wherein, R1, R2 are each independently selected from C1-C4 alkyl. R1, R2 are each independently selected from methyl, ethyl, n-propyl and i-propyl.

3. The cyclohexanone photosensitizer of claim 1, selected from the following formula II or formula III: ###0002### or a combination thereof.

2. The cyclohexanone-based photosensitizer according to claim 1, wherein 4. A method for preparing the cyclohexanone photosensitizer of claim 1, comprising the following steps: Step S1, mixing 5-halogen-2-thiophene formaldehyde and dialkylamine or ammonia gas, and reacting at 80-110°C for 3-20h to obtain an intermediate of formula IV, ###0003### wherein, R3, R4 are each independently selected from C1-C4 alkyl, and the dialkylamine is selected from dimethylamine, diethylamine, di-n-propylamine, di-i-propylamine; Step S2, mixing the intermediate of formula IV with cyclohexanone, adding a basic catalyst, and reacting at 80-110°C for 3-20h to obtain the cyclohexanone photosensitizer of formula I.

5. The method for preparing the cyclohexanone photosensitizer of claim 4, wherein the reaction temperature is 100°C.

4. A process for the preparation of the cyclohexanone-based photosensitizer represented by the formula I in claim 1, characterized by, 6. The method for preparing the cyclohexanone photosensitizer of claim 4, wherein the 5-halogen-2-thiophene formaldehyde is 5-bromo-2-thiophene formaldehyde. In step S1, the molar ratio of 5-bromo-2-thiophene formaldehyde to dialkylamine or ammonia gas is 1:2.5-4. <Formula IV> In step S2, the mass ratio of cyclohexanone to the intermediate of formula IV is 1:4-6.

7. A composition comprising the cyclohexanone photosensitizer of any one of claims 1-3 and a phthalocyanine.

8. The composition of claim 7, wherein the mass ratio of the phthalocyanine to the cyclohexanone photosensitizer is 1:0.6-1.

2.

9. The composition of claim 7, wherein the mass ratio of the phthalocyanine to the cyclohexanone photosensitizer is 1:

1.

7. The method of claim 4, wherein the cyclohexanone-based photosensitizer is prepared by the reaction of cyclohexanone and the compound of formula (I) in the presence of a base.

10. The composition of claim 7, further comprising a mixed photosensitizer.

8. The method for preparing cyclohexanone photosensitizers according to claim 4, characterized in that, 11. The composition of claim 10, wherein the mixed photosensitizer is selected from the group consisting of a cyclohexanone photosensitizer and a phthalocyanine.

9. A hybrid photosensitizer, characterized in that, 12. The composition of claim 10, further comprising a photopolymerization monomer selected from the group consisting of a vinyl monomer, an acrylic monomer and an acrylate monomer.

10. The hybrid photosensitizer of claim 9, wherein 13. The composition of claim 10, further comprising an initiator selected from the group consisting of hexaarylbiimidazole initiators.

11. The hybrid photosensitizer of claim 10, wherein 14. The composition of claim 13, wherein the initiator is ortho-chlorinated hexaarylbiimidazole.

12. A photopolymerizable composition characterized in that, ​ 13. The photopolymerizable composition of claim 12, wherein ​ ​ 14. The photopolymerizable composition of claim 13, wherein ​

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