High-refractive-index composition and holographic polymer dispersion grating

Abstract

The invention discloses a high-refractive-index composition which comprises at least one of compounds in a general formula I, at least one of compounds in a general formula II and at least one of compounds in a general formula III. The molecular arrangement mode of the high-refractive-index composition provided by the invention is obviously different from the texture of a conventional liquid crystal nematic phase, and the diffraction efficiency and the refractive index modulation degree of the holographic polymer dispersed grating containing the composition can be improved. The invention also provides a holographic polymer dispersed grating which comprises a photoinitiator system, a polymer system and the high-refractive-index composition. The holographic polymer dispersed grating provided by the invention is obviously different from an existing liquid crystal composition by selecting the high-refractive-index composition, can have relatively high diffraction efficiency on S light and P light, has relatively high intersolubility with a polymer system, has a relatively high refractive index modulation degree, and is convenient for practical application of the grating.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a high refractive index composition and a holographic polymer dispersion grating. Background Technology

[0002] Existing holographic polymer-dispersed liquid crystal gratings (HPDLCs) are formed using the principle of polymerization-induced phase separation under coherent laser light. Specifically, a laser beam is split into two coherent beams of equal intensity, which are then converged to obtain an interference spot with a sinusoidal intensity distribution. In the coherent bright region, the light induces the system to absorb photons, generating active centers that trigger monomer polymerization. The polymerization reaction alters the system's chemical energy, causing monomers to diffuse from the coherent dark region to the coherent bright region, as well as reverse diffusion of the liquid crystal, ultimately producing a holographic grating with a periodic arrangement of polymer-rich and liquid crystal-rich phases. Existing HPDLCs strive to utilize high-refractive-index liquid crystal monomers to provide a wider range of refractive index modulation for the grating device, thereby improving its practical application performance.

[0003] However, in the existing grating formation process, the liquid crystal is oriented along the grating vector direction, which causes the grating to have high diffraction efficiency for only one of the S-rays and P-rays, and very low diffraction efficiency for the other. As a result, when the grating faces an unpolarized light source, the S-rays or P-rays will be directly lost, resulting in a 50% loss of light intensity, which seriously affects the practical application of the grating. Summary of the Invention

[0004] The purpose of this invention is to provide a high refractive index composition and a holographic polymer dispersion grating, so as to provide a high refractive index composition and a grating with high refractive index modulation and high diffraction efficiency.

[0005] The present invention achieves the above-mentioned objectives through the following technical solutions.

[0006] In a first aspect, the present invention provides a high refractive index composition comprising:

[0007] At least one of the compounds of general formula I;

[0008] as well as

[0009] At least one of the compounds of general formula II;

[0010] as well as

[0011] At least one of the compounds of general formula III;

[0012] The compound of general formula I is:

[0013]

[0014] in,

[0015] R1 is selected from any one of alkyl and alkoxy groups having 1-10 carbon atoms;

[0016] Selected independently Any one of them;

[0017] X is independently selected from any one of -H, -F, -Me, and -Cl;

[0018] Y1 is selected from any one of -CN, -CF3, -OCF3, -NCS, and -F;

[0019] n1 and n3 can be 0, 1 or 2 respectively or simultaneously;

[0020] n2 is 1, 2, or 3;

[0021] Furthermore, at least one X in the compound of general formula I is selected from -Cl;

[0022] The compound of general formula II is:

[0023]

[0024] in,

[0025] R2 is selected from any one of alkyl and alkoxy groups having 1-10 carbon atoms;

[0026] Y2 is selected from any one of -CN, -NCS, and -F;

[0027] Z is selected from single bonds, alkyne bonds, or ethane bridging bonds;

[0028] n4 and n5 can be 0, 1, or 2 respectively or simultaneously;

[0029] Furthermore, any H atom on the benzene ring in the compound of general formula II can be independently replaced by -F or -Me;

[0030] The compound of general formula III is:

[0031]

[0032] in,

[0033] Selected independently Any one of them;

[0034] Y3 and Y4 are any one of alkyl and alkoxy groups having 1-10 carbon atoms, -CN, -NCS, -F, and -OCF3;

[0035] n6 and n7 can be 0, 1, or 2, respectively or simultaneously.

[0036] Compared with existing technologies, the high refractive index composition provided by this invention has a higher overall refractive index. The general formula I compound containing chlorinated derivatives significantly improves solubility and noticeably increases the overall refractive index of the high refractive index composition; the general formula II compound further improves the refractive index of the composition; the general formula III compound is a meta-disubstituted benzene ring, which makes the composition more diverse and improves the stability of the entire system. The molecular arrangement of the high refractive index composition provided by this invention differs significantly from the texture of conventional liquid crystal nematic phases, which can improve the diffraction efficiency and refractive index modulation of holographic polymer dispersion gratings containing this composition.

[0037] In a second aspect, the present invention provides a holographic polymer dispersion grating comprising a photoinitiator system, a polymer system, and the high refractive index composition described in the first aspect above.

[0038] Compared with the prior art, the holographic polymer dispersion grating provided by the present invention is significantly different from the existing liquid crystal composition by using the above-mentioned high refractive index composition. It can have high diffraction efficiency for both S-rays and P-rays, and it has high miscibility with polymer systems and high refractive index modulation, which facilitates the practical application of such gratings. Detailed Implementation

[0039] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0040] First Embodiment

[0041] This invention provides a high refractive index composition comprising at least one compound of general formula I, at least one compound of general formula II, and at least one compound of general formula III. In other words, the high refractive index composition provided by this invention comprises compounds of general formula I, general formula II, and general formula III, and the compounds of general formula I, general formula II, and general formula III may be one, two, or more.

[0042] Specifically, the compound of general formula I is: R1 is selected from any one of alkyl and alkoxy groups having 1-10 carbon atoms; Selected independently Any one of the following; X is independently selected from any one of -H, -F, -Me and -Cl; Y1 is selected from any one of -CN, -CF3, -OCF3, -NCS and -F; n1 and n3 may be 0, 1 or 2 respectively or simultaneously; n2 is 1, 2 or 3; and at least one X in the compound of general formula I is selected from -Cl.

[0043] In compounds of general formula I, X represents the presence of X at all four sites on the benzene ring side chain. The X at each site is independently selected from -H, -F, -Me, and -Cl. For example, the four sites may be -H, -F, -Me, and -Cl, or all four sites may be -Cl. At least one X is selected from -Cl, meaning that at least one X on the benzene ring side chain in a compound of general formula I is -Cl. It is understood that if n2 in a compound of general formula I is 2 or 3, then perhaps only one X on the benzene ring side chain is selected from -Cl. The same applies to X1, X2, and X3 in compounds of general formulas I-a to I-j below, except that the selection of substituents differs slightly.

[0044] In the embodiments of the invention, R1 and Y1 are selected. The selection of alkyl chains can effectively reduce molecular polarity and increase the miscibility of high refractive index compositions. The selection of polar groups can make the molecules more orderly arranged, increase the overall refractive index, and at the same time increase the light transmittance of the final optical device. In the compound of general formula I, H on the side chain of benzene ring is replaced by Cl, making general formula I a chlorinated compound, which can significantly improve solubility. Moreover, since Cl has a larger atomic radius, compared with F substitution, it is beneficial to compress the liquid crystal phase of the molecules and lower the temperature of the composition.

[0045] As a further improvement of the embodiments of the present invention, the compound of general formula I may be at least one of the compounds of general formula I-a, general formula I-b, general formula I-c, general formula I-d, general formula I-e, general formula I-f, general formula I-g, general formula I-h, general formula I-i, and general formula I-j.

[0046] Specifically, the compound of general formula I-a is:

[0047] Specifically, the compound of general formula I-b is:

[0048] Specifically, the compound of general formula I-c is:

[0049] Specifically, the compound of general formula I-d is:

[0050] Specifically, the compound of general formula I-e is:

[0051] Specifically, the compounds of general formula I-f are:

[0052] Specifically, the compound of general formula I-g is:

[0053] Specifically, the compound of general formula I-h is:

[0054] Specifically, the compound of general formula I-i is:

[0055] Specifically, the compound of general formula I-j is:

[0056] R1 is selected from any one of alkyl and alkoxy groups having 1-10 carbon atoms; Selected independently Any one of the following; X1 and X2 are independently selected from any one of -H, -F, -Me and -Cl; X3 is independently selected from any one of -H, -F and -Me; Y1 is selected from any one of -CN, -CF3, -OCF3, -NCS and -F; n0 is 1 or 2; n2 is 1, 2 or 3; n8 and n9 are 1 or 2; n10 and n11 are 1 or 2; at least one X1 of any compound of general formula I-a to general formula I-j is selected from -Cl; and n2+n8+n9 in general formula I-g ≥ 4.

[0057] It should be noted that compounds of general formula I-a, general formula I-b, general formula I-c, general formula I-d, general formula I-e, general formula I-f, general formula I-g, general formula I-h, general formula I-i, and general formula I-j are only a part of the examples of compounds of general formula I and should not be construed as limiting the compounds of general formula I.

[0058] As a preferred embodiment of the present invention, the compound of general formula I-a may be at least one of the following compounds:

[0059]

[0060] Compounds of general formula I-b may be at least one of the following compounds:

[0061]

[0062] Compounds of general formula I-c can be at least one of the following compounds:

[0063]

[0064]

[0065] Compounds of general formula I-h can be at least one of the following compounds:

[0066]

[0067] It should be noted that the compounds I-a-1 to I-a-4, I-b-1 to I-b-3, I-c-1 to I-c-6, and I-h-1 to I-h-5 mentioned above are only some examples of compounds of general formula I-a, I-b, I-c, and I-h, and should not be construed as limiting the compounds of general formula I.

[0068] Meanwhile, the compound of general formula II is: Wherein, R2 is selected from any one of alkyl and alkoxy groups having 1-10 carbon atoms; Y2 is selected from any one of -CN, -NCS, and -F; Z is selected from a single bond, an alkyne bond, or an ethane bridge bond; n4 and n5 can be 0, 1, or 2 respectively or simultaneously; and any H atom on the benzene ring in the compound of general formula II can be independently replaced by -F or -Me.

[0069] In this embodiment of the invention, the selection of the R2 alkyl chain allows for diversity in the chain length of the compound, effectively reducing molecular polarity while increasing the miscibility between compounds and between the composition and the polymer; the selection of Z increases the flexibility of the molecule, improves the solubility of the monomer in the composition, and increases the molecular refractive index; the selection of n4 and n5 values ​​provides diverse electronic conjugation systems for the high refractive index composition, which can increase the refractive index and the temperature range of the composition; the selection of the Y2 polar group gives the high refractive index composition a higher dielectric constant, resulting in an ordered final arrangement of the mixture, increasing the refractive index of the composition, and increasing the light transmittance by arranging the molecules in an ordered manner.

[0070] As a preferred embodiment of the present invention, the compound of general formula II can be at least one of the following compounds:

[0071]

[0072]

[0073] It should be noted that the above II-1 to II-11 are only some examples of compounds of general formula II and should not be construed as limiting the compounds of general formula II.

[0074] In a preferred embodiment of the present invention, in the compound of general formula II, n4+n5≠0.

[0075] Meanwhile, the compound of general formula III is: in, Selected independently Any one of the following; Y3 and Y4 are any one of alkyl and alkoxy groups with 1-10 carbon atoms, -CN, -NCS, -F, -OCF3; n6 and n7 can be 0, 1 or 2 respectively or simultaneously.

[0076] In the embodiments of the invention, the selection of Y3 and Y4 is as follows: when alkyl chains are selected, the conjugated system of the entire molecule is larger, resulting in a larger refractive index, but the miscibility between compounds and between the composition and the polymer system will be lost. However, the selection of alkoxy chains, especially with different numbers of carbons, can significantly improve the miscibility between compounds and the solubility between the composition and the polymer system. The selection of polar groups is beneficial to increasing the dielectric constant of the molecule and is more conducive to the orderly arrangement of molecules. On the one hand, it increases the overall refractive index of the composition, and on the other hand, the orderly arrangement of molecules can increase the light transmittance, making the light transmittance of the device higher. The selection of cyclohexyl groups can increase the refractive index of the compound and significantly improve its solubility. Selecting larger conjugated groups, such as benzene rings or fluorinated benzene rings, can increase the conjugation system of the compound and improve the refractive index of the molecule. The introduction of heterocycles such as pyrimidine rings and pyridine rings can increase the lateral forces between molecules, increase the molecular order, and improve both the refractive index and light transmittance.

[0077] In a preferred embodiment of the present invention, the compound of general formula III can be at least one of the following compounds:

[0078]

[0079]

[0080] It should be noted that the above III-1 to III-11 are only some examples of compounds of general formula III and should not be construed as limiting the compounds of general formula III.

[0081] In a preferred embodiment of the present invention, in the compound of general formula III, n6+n7≠0.

[0082] As a further improvement to the embodiments of the present invention, the composition provided by the present invention, by mass percentage, comprises 20%-60% of compound of general formula I, 20%-50% of compound of general formula II, and 20%-60% of compound of general formula III. In preferred embodiments, the proportion of compound of general formula I may be 20%, 30%, 40%, 50%, or 60%; the proportion of compound of general formula II may be 20%, 25%, 30%, 35%, 40%, 45%, or 50%; and the proportion of compound of general formula III may be 20%, 30%, 40%, 50%, or 60%.

[0083] By rationally controlling the proportions of compounds of general formula I, general formula II, and general formula III in the composition, the refractive index of the composition can be precisely controlled, and the diffraction efficiency and refractive index modulation of the holographic polymer dispersion grating containing the composition can be improved.

[0084] The compositions provided in the embodiments of the present invention are described in detail below through several sub-examples.

[0085] Table 1 shows the components and their proportions of the compositions in each sub-example:

[0086] Table 1

[0087]

[0088] It should be noted that the components of the compositions in each sub-example use the example compounds from the compounds of general formula I, general formula II, and general formula III described above, and are represented by the codes to the right of the example compounds to simplify the table examples. For example, sub-example 1 uses example compounds I-a-1, I-b-2, and I-c-1 from general formula I, example compounds II-1, II-5, and II-9 from general formula II, and example compounds III-1, III-4, and III-7 from general formula III. Of course, the above sub-examples do not illustrate all implementation methods, nor do they use all example compounds or other compounds from general formula I, general formula II, and general formula III besides the example compounds. The above six sub-examples are only some examples of the compositions in this invention and should not be construed as limiting the compositions in this invention.

[0089] The compositions provided in sub-examples 1 to 6 of this invention have a higher refractive index compared to the commercially available composition E7. Furthermore, since the molecular arrangement of these compositions differs significantly from the texture of conventional liquid crystal nematic phases, this can improve the diffraction efficiency and refractive index modulation of holographic polymer dispersion gratings containing any of the compositions provided in the above sub-examples (as shown in sub-examples 7 and 8). In particular, the diffraction efficiency of S-rays and P-rays in the fabrication of the gratings is relatively high.

[0090] Compared with existing technologies, the high refractive index composition provided in this embodiment has a higher overall refractive index. The general formula I compound, containing a chlorinated derivative, significantly improves solubility and noticeably increases the overall refractive index of the high refractive index composition. The general formula II compound further increases the refractive index of the composition. The general formula III compound, being a meta-disubstituted benzene ring, makes the composition more diverse and improves the stability of the entire system. The molecular arrangement of the high refractive index composition provided by this invention differs significantly from the texture of conventional liquid crystal nematic phases, which can improve the diffraction efficiency and refractive index modulation of holographic polymer dispersion gratings containing this composition.

[0091] Second Embodiment

[0092] This invention also provides a holographic polymer dispersion grating, which includes a photoinitiator system, a polymer system, and any one of the high refractive index compositions described in the first embodiment above.

[0093] In a preferred embodiment of the present invention, the photoinitiator system includes a photosensitizer and a free radical initiator; the polymer system includes a free radical photopolymerization compound monomer and a chain extender monomer.

[0094] Photosensitizers can accelerate the reaction rate and initially shape the grating, while initiators can reduce polymer shrinkage and increase transmittance. Free radical photopolymerization compounds can be activated into free radicals by photosensitizers and undergo chain polymerization, while chain extender monomers help dissolve solid photoinitiators, reduce droplet size, and improve diffraction efficiency.

[0095] In a preferred embodiment of the present invention, the photosensitizer includes one or more of the following: Bengal rose red, eosin, sodium eosin, camphorquinone, fluorescein diacetate, methylene blue, erythrosine B, methylene blue, and cyanine dye. Preferably, Bengal rose red is selected as the photosensitizer.

[0096] In a preferred embodiment of the present invention, the free radical initiator includes one or more of the following: N-phenylglycine, triethylamine, triethanolamine, and diisopropyl N,N-dicarboxylate-2,6-dioxane. Preferably, N-phenylglycine is selected as the free radical initiator.

[0097] In a preferred embodiment of the present invention, the free radical photopolymerizable compound monomer includes one or more of the following: hydroxyethyl methacrylate, ethylurea methacrylate, dipentaerythritol hexaacrylate, polydipentaerythritol pentaacrylate, hydroxyethyl acrylate, polydipentaerythritol tetraacrylate, glycidyl methacrylate, polyethylene glycol diacrylate, and pentanediol diacrylate. Preferably, the free radical photopolymerizable compound monomer is selected from dipentaerythritol hexaacrylate and hydroxyethyl methacrylate.

[0098] In a preferred embodiment of the present invention, the chain extender monomer includes one or more of dimethylallylamine, acrylonitrile, acrylic acid, acrylamide, DMAA, and NVP. Preferably, the chain extender monomer is dimethylallylamine.

[0099] As a further improvement to the embodiments of the present invention, the composition comprises, by weight, 30-70 parts of polymer system, 0.1-10 parts of photoinitiator system, and 20-60 parts of high refractive index composition. In the photoinitiator system, the weight ratio of free radical initiator to photosensitizer is 2:1-20:1.

[0100] The holographic polymer dispersion grating provided in this embodiment of the invention, by employing a composition with a high refractive index, can achieve higher separation efficiency from the polymer phase, resulting in higher diffraction efficiency for both S-rays and P-rays, as well as a higher refractive index modulation.

[0101] The holographic polymer dispersion grating provided in the embodiments of the present invention will be specifically described below through two sub-examples and one comparative example.

[0102] Sub-example 7

[0103] Table 2 shows the composition and proportions of the holographic polymer dispersion grating in sub-example 7:

[0104] Table 2

[0105] raw material Content (parts by weight) N-Phenylglycine 1 Bengal Rose 0.1 Dipentaerythritol hexaacrylate 30 Hydroxyethyl methacrylate 10 Dimethylallylamine 18.9 Sub-Example 2 Composition 40

[0106] In this sub-example, the free radical photopolymerization compound monomers are dipentaerythritol hexaacrylate and hydroxyethyl methacrylate, the chain extender monomer is dimethylallylamine, the photosensitizer is Bengal rose red, and the free radical initiator is N-phenylglycine. The composition is the same as that in the above sub-example 2, which has good compatibility with the polymer system.

[0107] During grating fabrication, the raw materials with the above-mentioned component ratio were placed in a sample vial and magnetically stirred at 25°C for 30 minutes to mix thoroughly. The mixture was then poured into a 3µm container, and a laser with a wavelength of 532nm and an intensity of 3.5mW / cm² was used. 2 The grating was exposed to coherent laser light for 3.0 min and then bleached with 395 nm ultraviolet light to finally prepare a holographic polymer dispersion grating.

[0108] According to the test results, the holographic polymer dispersion grating prepared in this embodiment has an S-ray diffraction efficiency of 81%, a P-ray diffraction efficiency of 78%, and a refractive index modulation of 0.105.

[0109] Sub-example 8

[0110] Table 3 shows the composition and proportions of the holographic polymer dispersion grating in sub-example 8:

[0111] Table 3

[0112] raw material Content (parts by weight) N-Phenylglycine 1 Bengal Rose 0.1 Dipentaerythritol hexaacrylate 30 Hydroxyethyl methacrylate 10 Dimethylallylamine 18.9 Sub-Example 5 Composition 40

[0113] The difference between this sub-example and sub-example 7 is that the composition used is from sub-example 5, which has good compatibility with the polymer system.

[0114] After the grating was prepared, it was tested and found that the holographic polymer dispersion grating prepared in this example had an S-ray diffraction efficiency of 87%, a P-ray diffraction efficiency of 84%, and a refractive index modulation of 0.13.

[0115] Comparative Examples

[0116] Table 4 shows the composition and proportions of the holographic polymer dispersion grating in the comparative examples:

[0117] Table 4

[0118] raw material Content (parts by weight) N-Phenylglycine 1 Bengal Rose 0.1 Dipentaerythritol hexaacrylate 30 Hydroxyethyl methacrylate 10 Dimethylallylamine 18.9 Composition E7 40

[0119] The difference between this comparative example and sub-examples 7 and 8 is that the composition uses a commonly available composition formulation E7.

[0120] After the grating was prepared, it was tested and found that the holographic polymer dispersion grating prepared in this comparative example had an S-ray diffraction efficiency of 85%, a P-ray diffraction efficiency of 12%, and a refractive index modulation degree of 0.082.

[0121] Compared with the comparative examples, the sub-examples 7 and 8 provided by the present invention, under the same polymer system and the same exposure bleaching conditions, have higher refractive indices, which can promote higher separation efficiency from the polymer phase and significantly improve the diffraction efficiency of the gratings produced after phase separation. For example, the S-ray diffraction efficiency of the grating in sub-example 8 is 87%, and the P-ray diffraction efficiency is 84%. At the same time, because the separation of the composition from the polymer system is more thorough in sub-examples 8 and 9, the refractive index modulation of the grating can be significantly improved. For example, the refractive index modulation of the grating in sub-example 11 reaches 0.13.

[0122] Compared with the prior art, the holographic polymer dispersion grating provided in this embodiment is significantly different from the existing liquid crystal composition by using the above-mentioned high refractive index composition. It can have high diffraction efficiency for both S-rays and P-rays, and it has high miscibility with the polymer system and high refractive index modulation, which facilitates the practical application of this type of grating.

[0123] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A high refractive index composition, characterized in that, include: At least one of the compounds of general formula I; as well as At least one of the compounds of general formula II; as well as At least one of the compounds of general formula III; The compound of general formula I is: in, R1 is selected from any one of alkyl and alkoxy groups having 1-10 carbon atoms; Selected independently Any one of them; X is independently selected from any one of -H, -F, -Me, and -Cl; Y1 is selected from any one of -CN, -CF3, -OCF3, -NCS, and -F; n1 and n3 can be 0, 1 or 2 respectively or simultaneously; n2 is 1, 2, or 3; Furthermore, at least one X in the compound of general formula I is selected from -Cl; The compound of general formula II is: in, R2 is selected from any one of alkyl and alkoxy groups having 1-10 carbon atoms; Y2 is selected from any one of -CN, -NCS, and -F; Z is selected from single bonds, alkyne bonds, or ethane bridge bonds; n4 and n5 can be 0, 1, or 2 respectively or simultaneously; Furthermore, any H atom on the benzene ring in the compound of general formula II can be independently replaced by -F or -Me; The compound of general formula III is: in, Selected independently Any one of them; Y3 and Y4 are any one of alkyl and alkoxy groups having 1-10 carbon atoms, -CN, -NCS, -F, and -OCF3; n6 and n7 can be 0, 1, or 2, respectively or simultaneously.

2. The high refractive index composition according to claim 1, characterized in that, By mass percentage, the compound of general formula I accounts for 20%-60%, the compound of general formula II accounts for 20%-50%, and the compound of general formula III accounts for 20%-60%.

3. The high refractive index composition according to claim 1, characterized in that, The compound of general formula I may be at least one of the following compounds: in, R1 is selected from any one of alkyl and alkoxy groups having 1-10 carbon atoms; Selected independently Any one of them; X1 and X2 are independently selected from any one of -H, -F, -Me, and -Cl; X3 is independently selected from any one of -H, -F, and -Me. Y1 is selected from any one of -CN, -CF3, -OCF3, -NCS, and -F; n0 is 1 or 2; n2 is 1, 2 or 3; n8 and n9 are 1 or 2; n10 and n11 are 1 or 2; At least one X1 in any compound of formula I-a to I-j is selected from -Cl; Furthermore, in general formula I-g, n2+n8+n9≥4.

4. The high refractive index composition according to claim 3, characterized in that, The compound of general formula I-a may be at least one of the following compounds: The compound of general formula I-b may be at least one of the following compounds: The compound of general formula I-c may be at least one of the following compounds: The compound of general formula I-h may be at least one of the following compounds:

5. The high refractive index composition according to claim 1, characterized in that, The compound of general formula II may be at least one of the following compounds:

6. The high refractive index composition according to claim 1, characterized in that, The compound of general formula III may be at least one of the following compounds:

7. A holographic polymer dispersion grating, characterized in that, include: The photoinitiator system, the polymer system, and the high refractive index composition as described in any one of claims 1-6.

8. The holographic polymer dispersion grating according to claim 7, characterized in that, The photoinitiator system includes photosensitizers and free radical initiators; The polymer system includes free radical photopolymerizable compound monomers and chain extender monomers.

9. The holographic polymer dispersion grating according to claim 8, characterized in that, The photosensitizers include one or more of the following: Bengal rose red, eosin, sodium eosin, camphor quinone, fluorescein diacetate, methylene blue, erythrosine B, methylene blue, and anthocyanin dyes. The free radical initiator includes one or more of the following: N-phenylglycine, triethylamine, triethanolamine, and diisopropyl N,N-dicarboxylic acid-2,6-dioxane.

10. The holographic polymer dispersion grating according to claim 8, characterized in that, The free radical photopolymerizable monomers include one or more of the following: hydroxyethyl methacrylate, ethylidene methacrylate, dipentaerythritol hexaacrylate, polydipentaerythritol pentaacrylate, hydroxyethyl acrylate, polydipentaerythritol tetraacrylate, glycidyl methacrylate, polyethylene glycol diacrylate, and pentanediol diacrylate. The chain extender monomers include one or more of dimethylallylamine, acrylonitrile, acrylic acid, acrylamide, DMAA, and NVP.

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