Schiff base photo-switching material and preparation method thereof, photochromic material and application in three-dimensional imaging

Abstract

This invention discloses a Schiff base photo-switching material, its preparation method, photochromic material, and its application in three-dimensional imaging. The Schiff base photo-switching material is a compound having the chemical structure shown in general formula (1) or general formula (2): Formula (1) In formula (1), X is a methoxy group; R1 is selected from aromatic hydrocarbon groups or alkyl groups; Formula (2) In formula (2), R2 is a 4-methoxystyryl group; R1 is selected from aromatic hydrocarbon groups. The Schiff base photo-switching material according to this invention can be applied to three-dimensional imaging and has high brightness and high contrast.

Description

Technical Field

[0001] This invention relates to the field of optical materials technology, and in particular to a Schiff base optical switching material and its preparation method, a photochromic material, and its application in three-dimensional imaging. Background Technology

[0002] 3D display technology can be divided into true 3D display and "pseudo-3D" display technology. "Pseudo-3D" displays, such as beam-splitting stereoscopic glasses and automatic beam-splitting stereoscopic displays, generally utilize the principle of "3D parallax" in the human eye to present a 3D visual effect through a 2D display. Because the generated images are unnatural, they can cause serious adverse reactions in observers, such as dizziness and nausea. True 3D display technology can provide complete information about the objective object; the image is an optical real image, interactive, and viewable by multiple people. Static volumetric 3D display technology, as a type of true 3D display technology, works by using two light sources simultaneously to form spatial voxels within the display medium. A spatial 3D image is constructed by scanning or moving these voxels. The resulting 3D image can be viewed from 360 degrees, without distance or angle limitations for the observer, enabling large-screen displays with a greater sense of space and stereoscopic effect. Static volumetric 3D display technology has significant application prospects in medical visualization, military simulation, model building, and everyday displays.

[0003] Limited by the performance of the dielectric materials and the complex optical path design, static volumetric 3D displays have long struggled to achieve satisfactory results. The performance of the dielectric material determines the quality of the volumetric 3D display. Common volumetric 3D display media based on upconversion microcrystalline materials are limited in scale due to manufacturing process constraints, and their low fluorescence efficiency leads to low brightness. The inherent properties of gas display media result in unstable imaging effects. LED array-based 3D display media are costly to manufacture and difficult to achieve large-size, high-transparency displays. Among the many dielectric materials available, organic photochromic materials have gradually attracted researchers' interest. Photochromic materials are materials whose initial state changes in structure or chemical bonds under the excitation of light of a specific wavelength, leading to changes in their conjugated system and optical properties, thus producing a color-changing effect. In addition to changes in their own body color energy, some photochromic isomers can produce fluorescence emission of a different color than their initial structure under the excitation of light of a specific wavelength, i.e., producing a photofluorescent color-changing effect. Organic molecules with photofluorescent effects are also known as organic "light-switching" materials. Organic "light switch" materials can undergo photochromic reactions under the action of a beam of light, producing a photochromic isomer structure. When another light source excites the fluorescent isomer, a spatial point luminescence effect can be produced. That is, "spatial voxel" points can be constructed in a three-dimensional medium. Combined with some basic optical path design, the purpose of three-dimensional display can be achieved.

[0004] Schiff bases, also known as Schiff bases or Schiff's bases, are a class of organic compounds containing imine or methylimine characteristic groups (-CRC=N-). They are generally synthesized by the condensation of amines with activated carbon groups. Due to the lone pair of electrons in the hybrid orbitals of the nitrogen atom, Schiff bases have important applications and research value in chemistry, biology, and other fields. The synthesis of Schiff bases typically involves a condensation reaction between an active group and an amine. Because of its flexible selectivity, slight changes in the groups and chemical environment of the raw materials can produce Schiff base products with different properties and structures, thus offering unique applications. This condensation reaction method can meet the needs of preparing various Schiff bases, such as bidentate Schiff bases (condensation of diamines with radical compounds), monodentate Schiff bases (condensation of mono-base compounds with monoamines), isobis-Schiff bases, asymmetric Schiff bases, etc. Schiff bases and their complexes, due to their excellent catalytic and liquid crystal properties, have significant research value and application potential in molecular catalysis, medicinal chemistry, analytical chemistry, spectroscopy, displays, and other fields. Some types of Schiff base materials exhibit photochromism, meaning they can reversibly change their color under illumination. This is due to an intramolecular proton transfer (ESIPT) process. Taking salicylaldehyde aniline (SA) as an example, under illumination, the initial structure of the SA molecule is excited. Through intramolecular hydrogen bonds, protons in the acidic phenolic hydroxyl group readily transfer to the nearby basic nitrogen atom, resulting in a rapid ESIPT process. This leads to a change in the molecular valence structure and photochromism. This photochromic property of Schiff bases has significant application prospects in information storage, memory simulation, optical computing, anti-counterfeiting, and information display. The isomers of photochromic Schiff base materials before and after the color change exhibit different fluorescence properties; these reversible photofluorescent color-changing materials are also known as "light-switching" materials. Light-switching Schiff base materials can serve as volumetric 3D imaging media for generating spatial voxels, making them highly valuable for research in the field of volumetric 3D display technology.

[0005] In related technologies, Schiff base materials for optical switching have the drawbacks of weak luminescence intensity and limited material variety. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one object of the present invention is to provide a Schiff base optical switching material that can be applied to three-dimensional imaging and exhibits high brightness and high contrast.

[0007] The second objective of this invention is to provide a method for preparing Schiff base photoswitching materials.

[0008] The third objective of this invention is to provide a photochromic material employing the aforementioned Schiff base photoswitching material.

[0009] The fourth objective of this invention is to propose the application of a Schiff base photo-switching material or a photochromic material in three-dimensional imaging.

[0010] According to a first aspect of the present invention, the Schiff base photoswitching material is a compound having the chemical structural formula (1) or the chemical structural formula (2):

[0011] Equation (1) In formula (1), X is a methoxy group; R1 is selected from aromatic hydrocarbon groups or alkyl groups;

[0012] Equation (2) In formula (2), R2 is 4-methoxystyryl; R1 is selected from aromatic hydrocarbon groups.

[0013] The Schiff base photo-switching material according to embodiments of the present invention enriches the types of photo-switching materials and offers higher fluorescence intensity and contrast. Furthermore, it meets the requirements for volumetric 3D display applications, exhibits fast photochromic and luminescence reversible response speeds, and can construct a series of luminescent voxels in space, which can be rapidly switched. Additionally, it possesses significant potential and practical application value. For example, it can be applied in fields such as medicine, photoinitiators, and fluorescent chemical sensors.

[0014] According to some embodiments of the present invention, the Schiff base photoswitching material is any one of the following compounds:

[0015] Equation (1-1) In equation (1-1), R is selected from — (C1-C 30 —X, —OH, —O(CH2) n CH3, —N(CH3)3, —NO2, —CN, —SO3H, —CHO, —COCH3, —COOH, where X is a halogen;

[0016] Equation (1-2)

[0017] Equation (1-3)

[0018] Equation (2-1).

[0019] The method for preparing Schiff base photoswitching material according to a second aspect of the present invention includes the following steps: p-Methoxysalicylaldehyde or 4-methoxystilbenesalicylaldehyde and the corresponding amine were mixed in anhydrous ethanol, refluxed for a first preset time, and then cooled, filtered, washed and dried to obtain the target product.

[0020] According to some embodiments of the present invention, the step of mixing p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde and the corresponding amine with anhydrous ethanol further includes: At a first preset temperature, 4-methoxystyrene and 5-bromosalicylic acid are coupled using palladium metal reagent and organic base catalysis to obtain 4-methoxystilbene salicylaldehyde.

[0021] According to some embodiments of the present invention, the first preset temperature is 50°C to 120°C; and / or, the molar ratio of 4-methoxystyrene to 5-bromosalicylic acid is 1:0.1 to 1:10.

[0022] According to some embodiments of the present invention, when the Schiff base photoswitching material is a compound of formula (2-1), the mixing of p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde with the corresponding amine specifically includes: The 4-methoxystilbene salicylaldehyde and α-phenylethylamine were condensed at a molar ratio of 1:1.0 to 1:10 at 40°C to 100°C to obtain a 4-methoxystilbene salicylaldehyde condensed with α-phenylethylamine Schiff base.

[0023] According to some embodiments of the present invention, when the Schiff base photoswitching material is a compound of formula (1-1), the step of mixing p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde and the corresponding amine in anhydrous ethanol specifically includes: The p-methoxysalicylaldehyde and benzylamine compounds are mixed in anhydrous ethanol at a molar ratio of 1:1.2 to 1:3.0 for a first preset time of 4 to 8 hours; or, when the Schiff base photoswitching material is a compound of formula (1-2), the mixing of p-methoxysalicylaldehyde or 4-methoxystilbene salicylate and the corresponding amine in anhydrous ethanol specifically includes: The p-methoxysalicylic acid and hexamethylenediamine are mixed in anhydrous ethanol at a molar ratio of 1:2.0 to 1:8.0 for a first preset time of 3 h to 24 h; or, when the Schiff base photoswitching material is a compound of formula (1-3), the mixing of p-methoxysalicylic acid or 4-methoxystilbene salicylic acid and the corresponding amine in anhydrous ethanol specifically includes: The p-methoxysalicylaldehyde and heptadecanol are mixed in anhydrous ethanol at a molar ratio of 1:1.2 to 1:3.0 for a first preset time of 1 to 6 hours.

[0024] According to a third aspect of the present invention, the photochromic material is obtained by mixing and curing the Schiff base photoswitch material described in the first aspect of the present invention with a display medium; the mass ratio of the Schiff base photoswitch material to the display medium is 1: (5000~10000), and the display medium includes at least one of acetonitrile, methyl tert-butyl ether, dimethyl sulfoxide, cyclohexane, toluene, dichloromethane and ethyl acetate, or the display medium includes epoxy resin or polymethyl methacrylate.

[0025] Application of Schiff base photo-switching materials or photochromic materials according to the fourth aspect of the present invention in three-dimensional imaging.

[0026] According to some embodiments of the present invention, the material is irradiated with an isomer excitation light source and a color-changing excitation light source, and a photon dot is formed at the intersection of the isomer excitation light source and the color-changing excitation light source; wherein, the color-changing excitation light source is blue visible light with a wavelength of 440nm~470nm, and / or the isomer excitation light source is ultraviolet light with a wavelength of 365nm~410nm; By controlling the scanning path and scanning speed of the isomer excitation source and the color-changing excitation source, three-dimensional imaging can be achieved in the material.

[0027] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a process flow diagram of the preparation of Schiff base photoswitching material according to an embodiment of the present invention; Figure 2 The image shows the 1H NMR spectrum of a Schiff base photoswitch material according to an embodiment of the present invention, wherein the Schiff base photoswitch material is a p-methoxysalicylaldehyde benzylamine Schiff base. Figure 3 The absorption spectrum of a Schiff base photoswitching material according to an embodiment of the present invention is shown, wherein the Schiff base photoswitching material is a p-methoxysalicylaldehyde benzylamine Schiff base. Figure 4 This is a volumetric three-dimensional imaging application of Schiff base optical switching material according to an embodiment of the present invention, specifically, the spatial image effect generated inside a dimethyl sulfoxide solution under the action of two beams of light at 365 nm and 450 nm without any processing; Figure 5The image shows the 1H NMR spectrum of the Schiff base photoswitch material according to the second embodiment of the present invention, wherein the Schiff base photoswitch material is a p-methoxysalicylaldehyde hexamethylenediamine Schiff base. Figure 6 The absorption spectrum of the Schiff base photoswitch material according to the second embodiment of the present invention is a p-methoxysalicylaldehyde hexamethylenediamine Schiff base. Figure 7 This is a volumetric three-dimensional imaging application of Schiff base optical switching material according to the second embodiment of the present invention, specifically, a spatial image effect generated inside a dichloromethane solution under the action of two beams of light at 365 nm and 450 nm without any processing. Figure 8 The image shows the 1H NMR spectrum of the Schiff base photoswitch material according to the third embodiment of the present invention, wherein the Schiff base photoswitch material is a p-methoxysalicylaldehyde heptadecanyl Schiff base. Figure 9 The absorption spectrum of the Schiff base photoswitch material according to the third embodiment of the present invention is a p-methoxysalicylaldehyde heptadecanyl Schiff base. Figure 10 This is a volumetric three-dimensional imaging application of Schiff base optical switching material according to the third embodiment of the present invention, specifically, a spatial image effect generated inside a dimethyl sulfoxide solution under the action of two beams of light at 365 nm and 450 nm without any processing. Figure 11 The image shows the 1H NMR spectrum of the Schiff base photoswitch material according to the fourth embodiment of the present invention, wherein the Schiff base photoswitch material is 4-methoxystilbene salicylaldehyde acetal α-phenylethylamine Schiff base. Figure 12 The absorption spectrum of the Schiff base photoswitching material according to the fourth embodiment of the present invention is shown, wherein the Schiff base photoswitching material is 4-methoxystilbene salicylaldehyde acetal α-phenylethylamine Schiff base. Figure 13 These are fluorescence intensity comparison diagrams of Schiff base photoswitching materials according to embodiments of the present invention, wherein (A) is the Schiff base photoswitching material of Example 5; (B) is the Schiff base photoswitching material of the comparative example; (C) is the Schiff base photoswitching material of Example 7; and (D) is the Schiff base photoswitching material of Example 10. Detailed Implementation

[0029] The embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. The Schiff base photo-switching material according to the first aspect of the present invention is described in detail below.

[0030] According to a first aspect of the present invention, the Schiff base photoswitching material is a compound having the chemical structural formula (1) or the chemical structural formula (2):

[0031] Equation (1) In formula (1), X is a methoxy group; R1 is selected from aromatic hydrocarbon groups or alkyl groups;

[0032] Equation (2) In formula (2), R2 is 4-methoxystyryl; R1 is selected from aromatic hydrocarbon groups.

[0033] For example, in formula (1), X is a methoxy group (-OCH3). The methoxy group is in the para position and can form a conjugation effect with the π bond on the benzene ring, making the para carbon atom electron-rich and enhancing the reactivity. In addition, the methoxy group is an auxochrome group. When it is connected to the benzene ring, it will form p-π conjugation, increasing the conjugation effect on the benzene ring. This makes the structure of the resulting Schiff base photo-switching material more stable and can improve the fluorescence intensity. In formula (2), R2 is 4-methoxystyryl. Formula (2) has a rigid structure with double bonds connecting two benzene rings, which makes the electron cloud density on salicylaldehyde higher and the conjugation structure larger, which is beneficial to the structural stability of the synthesized material and also has higher fluorescence intensity. Moreover, the contrast is high. In addition, the Schiff base photo-switching material provided by this invention can meet the conditions for volumetric three-dimensional display applications, that is, it can emit light at the intersection of the isomer excitation light source and the color-changing excitation light source. Moreover, the reversible reaction speed of photochromism and luminescence is fast, and a series of luminescent voxels can be constructed in space, and the luminescent voxels can be switched quickly. Therefore, utilizing the persistence of human vision to achieve three-dimensional volumetric display (i.e., three-dimensional imaging) has great potential and practical application value. For example, it can be applied in fields such as medicine, photoinitiators, and fluorescent chemical sensors.

[0034] The Schiff base photo-switching material according to embodiments of the present invention enriches the types of photo-switching materials and offers higher fluorescence intensity and contrast. Furthermore, it meets the requirements for volumetric 3D display applications, exhibits fast photochromic and luminescence reversible response speeds, and can construct a series of luminescent voxels in space, which can be rapidly switched. Additionally, it possesses significant potential and practical application value. For example, it can be applied in fields such as medicine, photoinitiators, and fluorescent chemical sensors.

[0035] According to some embodiments of the present invention, the Schiff base photoswitching material is any one of the following compounds:

[0036] Equation (1-1) In equation (1-1), R is selected from — (C1-C30 —X, —OH, —O(CH2) n CH3, —N(CH3)3, —NO2, —CN, —SO3H, —CHO, —COCH3, —COOH, where X is a halogen;

[0037] Equation (1-2)

[0038] Equation (1-3)

[0039] Equation (2-1).

[0040] For example, formula (1-1) is the general structural formula of Schiff bases of the p-methoxysalicylaldehyde benzylamine class. In this series of compounds, the R group in the benzylamine class is an electron-donating group, which recovers much faster than the electron-withdrawing group, and its brightness remains basically unchanged. Its performance enhancement is proportional to the electron-donating ability of benzylamine. In addition, the raw materials are readily available, the process is simple with low equipment requirements, the yield is high, and purification is convenient, enabling large-scale production.

[0041] Formula (1-2) is a Schiff base compound of p-methoxysalicylic acid hexamethylenediamine, with the molecular formula C. 22 H 28 N₂O₄, a relatively inexpensive Schiff base of p-methoxysalicylic acid acetal hexamethylenediamine, can meet the requirements for rapid reversible photochromism and cross-point luminescence in volumetric 3D displays, which is beneficial for the application of Schiff base photo-switching materials in 3D imaging. Furthermore, the preparation process is simple, with high yield and low production cost, allowing for large-scale commercial production. Additionally, the p-methoxysalicylic acid acetal hexamethylenediamine Schiff base compound exhibits high transparency and good stability in display media such as dichloromethane, cyclohexane, ethyl acetate, acetonitrile, toluene solution, epoxy resin, and polymethyl methacrylate, which is conducive to commercial applications.

[0042] Formula (1-3) represents a p-methoxysalicylic acid acetyl heptadecanyl Schiff base. Its unique long-chain amine structure makes the Schiff base photo-switching material easily soluble in other materials and able to disperse uniformly, avoiding interference caused by molecular clusters. Moreover, it has a strong electron-donating ability, and the C=N double bond and the p-π conjugation of the benzene ring further increase the overall molecular conjugation system, making the enol structure in the whole system more likely to gain electrons. This not only lays a good structural foundation for the generation of ESIPT (Excited-State Intramolecular Proton Transfer), but also provides favorable conditions for the intersection of the isomer excitation source and the color-changing excitation source (i.e., voxel point emission) in the application of Schiff base photo-switching material in three-dimensional imaging, further improving its contrast, luminous intensity and recovery speed, and also improving its fatigue resistance.

[0043] Formula (2-1) is a Schiff base of 4-methoxystilbene salicylaldehyde condensed with α-phenylethylamine, that is, the condensation of 4-methoxystilbene salicylaldehyde and α-phenylethylamine yields the Schiff base of 4-methoxystilbene salicylaldehyde condensed with α-phenylethylamine. The methoxy group in the structure of 4-methoxystilbene salicylaldehyde is an electron-donating group, and it has a rigid structure with a double bond connecting two benzene rings, resulting in a high electron cloud density and a large conjugated structure on the salicylaldehyde. This makes the enol structure of the 4-methoxystilbene salicylaldehyde condensed with α-phenylethylamine Schiff base more stable, and also results in higher fluorescence intensity.

[0044] With this setup, the four Schiff base photoswitching materials listed above all have the advantages of readily available raw materials, simple preparation methods, and the ability to achieve large-scale production, and they also have strong application prospects in the field of three-dimensional imaging.

[0045] A method for preparing a Schiff base photoswitching material according to a second aspect of the present invention includes the following steps: p-Methoxysalicylaldehyde or 4-methoxystilbenesalicylaldehyde and the corresponding amine were mixed in anhydrous ethanol, refluxed for a first preset time, and then cooled, filtered, washed and dried to obtain the target product.

[0046] The preparation method of Schiff base photoswitching material according to a specific embodiment of the present invention is simple and easy to operate, with a high yield and low cost of synthesized materials, which is conducive to large-scale production. Furthermore, cooling after the reaction is performed lowers the temperature of the reaction system, allowing the product and any unreacted raw materials to gradually precipitate or condense from the solution state, facilitating subsequent separation operations. Filtration separates the precipitated solids (mainly the target product and possibly a small amount of unreacted solid raw materials) from the solution (containing unreacted soluble impurities, solvents, etc.), achieving preliminary solid-liquid separation and obtaining a relatively enriched solid fraction of the target product. The filtered solid is washed with a suitable washing solvent (e.g., cold anhydrous ethanol) to remove some soluble impurities adsorbed on the solid surface, further improving the purity of the product. Finally, drying is performed to remove any residual solvent and moisture, obtaining a dry and pure target product, facilitating subsequent storage, analysis, and further applications.

[0047] According to some embodiments of the present invention, the above-mentioned mixing of p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde and the corresponding amine with anhydrous ethanol further includes: At a first preset temperature, 4-methoxystyrene was coupled with 5-bromosalicylic acid to obtain 4-methoxystilbene salicylaldehyde by catalysis with palladium metal reagent and organic base.

[0048] The reaction equation for 4-methoxystyrene and 5-bromosalicylic acid is as follows:

[0049] Palladium, as an excellent catalyst for coupling reactions, exhibits high tolerance to various functional groups and typically provides excellent stereo and regio specificity, avoiding the introduction of protecting groups. Organic bases, as catalysts for coupling reactions, can react with aromatic amines to form intermediate ammonium salts, and can also undergo nucleophilic substitution reactions with haloalkanes to form intermediate N-arylamines. Finally, the intermediate N-arylamine undergoes dearomatization under the action of a catalyst to generate the target product. This setup effectively improves reaction efficiency, avoids the introduction of protecting groups, and facilitates the formation of the target product.

[0050] According to some embodiments of the present invention, the first preset temperature is 50°C to 120°C. And / or, the molar ratio of 4-methoxystyrene to 5-bromosalicylic acid is 1:0.1 to 1:10. Preferably, the first preset temperature is 70°C to 100°C. For example, the molar ratio of 4-methoxystyrene to 5-bromosalicylic acid can be 1:0.1, 1:0.5, 1:1.0, 1:2.0, 1:3.0, 1:4.0, 1:5.0, 1:6.0, 1:7.0, 1:8.0, 1:9.0, 1:10, etc., but is not limited thereto.

[0051] Therefore, when the first preset temperature is below 50℃, the thermal motion of the reacting molecules is relatively slow, resulting in a slower reaction rate. However, this helps to avoid some side reactions caused by high temperatures, such as potentially reducing the decomposition of raw materials or products due to overheating. As the reaction temperature increases, the frequency of intermolecular collisions accelerates, promoting the reaction and increasing the reaction rate. However, excessively high temperatures, if not properly controlled, can also lead to problems such as decreased reaction selectivity. Within the aforementioned first preset temperature range, adding 4-methoxystyrene and 5-bromosalicylic acid according to the specified molar ratio allows for optimization based on actual conditions to find the most suitable reaction temperature point, balancing key factors such as reaction rate and product selectivity.

[0052] When the relative amount of 5-bromosalicylaldehyde is low (approximately a molar ratio of 1:0.1), it means that 4-methoxystyrene is in excess. This excess 4-methoxystyrene allows 5-bromosalicylaldehyde to react as completely as possible, increasing its conversion rate. However, more separation operations may be needed to remove the excess 4-methoxystyrene feedstock. Conversely, when the relative amount of 5-bromosalicylaldehyde is high (approximately a molar ratio of 1:10), 4-methoxystyrene participates more fully in the reaction, reducing feedstock loss due to side reactions such as self-polymerization. However, this also leads to waste of 5-bromosalicylaldehyde and increases the difficulty of separating and purifying the product from the large excess. Therefore, setting the optimal molar ratio can achieve a balance between good reaction performance and ease of subsequent operations.

[0053] According to some embodiments of the present invention, when the Schiff base photoswitching material is a compound of formula (2-1), mixing p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde with the corresponding amine specifically includes: 4-Methoxystilbene salicylaldehyde and α-phenylethylamine are condensed in a molar ratio of 1:1.0 to 1:10 at 40°C to 100°C to obtain a 4-methoxystilbene salicylaldehyde condensed into an α-phenylethylamine Schiff base. Preferably, the first preset temperature is 70 to 80°C.

[0054] The reaction equations for the above-mentioned 4-methoxystilbene salicylaldehyde and α-phenylethylamine are as follows:

[0055] The reactant 4-methoxystilbene salicylaldehyde has a melting point of approximately 40°C. When the first preset temperature is below 40°C, the reactants are in a solid state, and the two reactants cannot fully fuse, which is not conducive to the reaction. When the first preset temperature is above 40°C, but the temperature is relatively low, the reactants are all in a liquid state, allowing for full fusion and reaction. At this temperature, the thermal motion of the reactant molecules is relatively mild, resulting in a slower reaction rate, but this helps to avoid some side reactions caused by high temperatures. When the first preset temperature is above 100°C, the frequency of intermolecular collisions is high, and the reactant molecules are prone to thermal decomposition due to excessive temperature, thus affecting the product yield and purity. Within the aforementioned first preset temperature range, adding 4-methoxystilbene salicylaldehyde and α-phenylethylamine according to the above molar ratio allows for optimization based on actual conditions to find the most suitable reaction temperature point, balancing key factors such as reaction rate and product selectivity.

[0056] When the relative amount of 4-methoxystilbene salicylaldehyde is low (approximately a molar ratio of 1:1.0), it means that α-phenylethylamine is in excess. This excess 4-methoxystilbene salicylaldehyde allows for more complete reaction of α-phenylethylamine, increasing its conversion rate. However, more separation operations may be needed to remove the excess 4-methoxystilbene salicylaldehyde feedstock. Conversely, when the relative amount of α-phenylethylamine is high (approximately a molar ratio of 1:10), 4-methoxystilbene salicylaldehyde participates more fully in the reaction, reducing feedstock loss due to side reactions such as self-polymerization. However, this also leads to waste of α-phenylethylamine and increases the difficulty of separating and purifying the product from the large excess α-phenylethylamine. Therefore, setting the optimal molar ratio can achieve a balance between good reaction performance and ease of subsequent operations.

[0057] According to some embodiments of the present invention, when the Schiff base photoswitching material is a compound of formula (1-1), mixing p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde and the corresponding amine in anhydrous ethanol specifically includes: p-Methoxysalicylaldehyde and benzylamine compounds were mixed in anhydrous ethanol at a molar ratio of 1:1.2 to 1:3.0 for a first preset time of 4 to 8 hours.

[0058] The reaction time for Schiff base reactions typically needs to be controlled based on the specific reactants and their ratios, generally ranging from several hours to several days. Too short a reaction time may result in incomplete reaction, leading to low yield and waste of reactants. Conversely, too long a reaction time can incur unnecessary production costs or trigger other side reactions, resulting in decreased production efficiency or product purity. Therefore, in actual production, the optimal reaction time must be selected based on the specific circumstances. When the reaction time is within the aforementioned preset time, adding p-methoxysalicylaldehyde and benzylamine compounds according to the specified molar ratio facilitates optimization to find the most suitable reaction time, balancing key factors such as product yield and production cost.

[0059] According to other embodiments of the present invention, when the Schiff base photoswitching material is a compound of formula (1-2), mixing p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde and the corresponding amine in anhydrous ethanol specifically includes: p-Methoxysalicylaldehyde and hexamethylenediamine are mixed in anhydrous ethanol at a molar ratio of 1:2.0 to 1:8.0 for a first preset time of 3 to 24 hours.

[0060] During the reaction process, the proper setting of conditions such as the properties of reactants, the molar ratio between reactants, and the reaction time is extremely important for the occurrence of the reaction and the yield of the products. Therefore, in actual production, it is essential to select the optimal reaction conditions through numerous controlled variable experiments. When the reaction time is within the aforementioned preset time, p-methoxysalicylaldehyde and hexamethylenediamine are added according to the specified molar ratio, which facilitates optimization to find the most suitable reaction time based on actual conditions. For example, the molar ratio of p-methoxysalicylaldehyde to hexamethylenediamine can be 1:2.0, 1:2.5, 1:3.0, 1:4.0, 1:5.0, 1:6.0, 1:7.0, 1:8.0, etc., but is not limited to these.

[0061] According to some embodiments of the present invention, when the Schiff base photoswitching material is a compound of formula (1-3), mixing p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde and the corresponding amine in anhydrous ethanol specifically includes: p-Methoxysalicylaldehyde and heptadecanol were mixed in anhydrous ethanol at a molar ratio of 1:1.2 to 1:3.0 for a first preset time of 1 to 6 hours.

[0062] When the molar ratio of reactants is limited to a small range, the optimal reaction time can be found through controlled variable experiments based on actual conditions. When the molar ratio of reactants is within the above range, p-methoxysalicylaldehyde and heptadecanylamine are added according to the above molar ratio limits. Through continuous optimization, the optimal first preset time is precisely selected to balance key factors such as product yield and production cost.

[0063] The formation of Schiff bases through the addition reaction of aldehydes and amines is a common type of organic chemical reaction. The main reaction conditions include reaction temperature, reaction time, and solvent. The reaction temperature of aldehydes and amines is generally set within the range of room temperature to the boiling point of the reactants. Within this temperature range, the reaction rate is relatively fast and the system is relatively stable, which is conducive to the formation of Schiff bases. In the specific reaction process, the optimal reaction conditions can be achieved by adjusting the reaction time according to the properties of different reactants. In organic reactions, the choice of reaction time has a certain influence on the properties, morphology, and reaction efficiency of the products. Therefore, it is crucial to select the optimal reaction time through extensive experimental screening. Furthermore, the choice of solvent also plays a vital role in the reaction. Anhydrous ethanol, as a commonly used solvent in organic chemical reactions, can fully dissolve the reactants without affecting the reaction process and is therefore selected as the reaction solvent for preparing Schiff base photoswitching materials.

[0064] In other words, when preparing the Schiff base photoswitch material shown in formula (1-1), p-methoxysalicylaldehyde and benzylamine compounds in a molar ratio of 1:1.2 to 1:3.0 are mixed in anhydrous ethanol, refluxed for 4 to 8 hours, and then cooled, filtered, washed, and dried to obtain the target product of formula (1-1). When preparing the Schiff base photoswitch material shown in formula (1-2), hexamethylenediamine and p-methoxysalicylaldehyde in a molar ratio of 1:2.0 to 1:8.0 are mixed in anhydrous ethanol, refluxed for 3 to 24 hours, and then cooled, filtered, washed, and dried to obtain the target product of formula (1-2). When preparing the Schiff base photoswitch material shown in formula (1-3), p-methoxysalicylaldehyde and heptadecanylamine in a molar ratio of 1:1.2 to 1:3.0 are mixed in anhydrous ethanol, refluxed for 1 to 6 hours, and then cooled, filtered, washed, and dried to obtain the target product of formula (1-3). This setup, by limiting the molar ratio of reactants and the reflux reaction time, further limits the reaction temperature, which is conducive to the smooth progress of the reaction and also to the acquisition of the target product.

[0065] According to some embodiments of the present invention, anhydrous ethanol is used as the reaction solvent. The reactants are mixed in anhydrous ethanol and reacted. By controlling the molar ratio of the reactants and conditions such as a first preset time and temperature, various Schiff base photoswitching materials were successfully prepared. Anhydrous ethanol plays an important role as the reaction solvent here. First, it has good solubility for the reactants methoxysalicylaldehyde and benzylamine compounds, enabling the reactants to be uniformly dispersed in the solution, increasing the effective collision frequency between molecules, and facilitating the smooth progress of the reaction. Second, ethanol has a moderate boiling point, and reflux conditions are easy to achieve. During reflux, it provides a relatively stable and suitable reaction environment, promoting the continuous progress of the reaction. Furthermore, ethanol is relatively easy to recover and reuse through conventional methods such as distillation, resulting in lower costs and relatively better environmental performance, which aligns with some of the requirements of green chemistry principles.

[0066] The photochromic material according to a third aspect of the present invention is obtained by mixing and curing the Schiff base photoswitch material of the first aspect embodiment with a display medium. The mass ratio of the Schiff base photoswitch material to the display medium is 1:(5000~10000). This configuration results in a moderate content of the Schiff base photoswitch material in the photochromic material, a colorless photochromic material, and a pronounced photochromic phenomenon. Furthermore, the preparation method of the photochromic material is simple, improving production efficiency. In addition, the display medium plays an important supporting and auxiliary role in this photochromic material system. It needs to possess characteristics such as good transparency, suitable viscosity, and good compatibility with the Schiff base photoswitch material. On the one hand, transparency ensures that the optical signals of the material, both before and after photochromic changes, can be effectively transmitted and observed. On the other hand, a suitable viscosity helps maintain the uniformity of the system during mixing, curing and other operations, and its good compatibility with Schiff base photo-switching materials ensures that the two can be mixed uniformly, so that the photo-switching materials can be evenly dispersed in it, thereby achieving a uniform photochromic effect when illuminated.

[0067] According to embodiments of the present invention, the photochromic material includes at least one of acetonitrile, methyl tert-butyl ether, dimethyl sulfoxide, cyclohexane, toluene, dichloromethane, and ethyl acetate as the display medium, or the display medium includes epoxy resin or polymethyl methacrylate.

[0068] For example, when the medium is one or more organic solvents such as acetonitrile, methyl tert-butyl ether, dimethyl sulfoxide, cyclohexane, toluene, dichloromethane, and ethyl acetate, the Schiff base photoswitch material is dissolved in the aforementioned organic solvent to form a solution of the Schiff base photoswitch material. When the medium is at least one of epoxy resin and polymethyl methacrylate, the Schiff base photoswitch material is dispersed in the polymer of epoxy resin and / or polymethyl methacrylate to form a solid optical material. With this configuration, the Schiff base photoswitch material provided in this invention exhibits high transparency, good stability, and good reversibility in the aforementioned solutions, epoxy resins, polymethyl methacrylate, and other media, which is beneficial for commercial applications.

[0069] Application of Schiff base photo-switching materials or photochromic materials according to the third aspect of the present invention in three-dimensional imaging.

[0070] Schiff bases contain acidic α-protons that undergo proton transfer at different pH values, forming keto and enol forms. Through enol-keto transitions between the ground and excited states, and ESIPT level transitions, these compounds exhibit a large Stokes shift between their absorption and emission spectra. This large Stokes shift eliminates luminescence quenching caused by self-absorption, increasing the possibility of obtaining strongly luminescent organic materials in aggregated or solid-state states. Salicylaldehyde Schiff bases are compounds containing C=N double bonds, some of which can achieve rapid and reversible photochromism and exhibit cross-emission under dual-source excitation. Their raw materials are generally inexpensive and readily available. Applying salicylaldehyde Schiff base materials to volumetric 3D displays is of great significance for improving the resolution, imaging size, and display effect of volumetric 3D displays.

[0071] According to some embodiments of the present invention, an isomer excitation light source and a color-changing excitation light source are used to irradiate the material, forming optical voxel dots at the intersection of the isomer excitation light source and the color-changing excitation light source (for example, two light sources perpendicularly intersect inside the material to generate optical voxel dots). The color-changing excitation light source is blue visible light with a wavelength of 440 nm to 470 nm. This configuration provides a suitable wavelength range and sufficient energy for the blue visible light. The isomer excitation light source is ultraviolet light with a wavelength of 365 nm to 410 nm. This configuration also provides a suitable wavelength range for the ultraviolet light, meeting the requirements for forming optical voxel dots.

[0072] By controlling the scanning paths and speeds of the isomer excitation light source and the color-changing excitation light source, three-dimensional imaging can be achieved within the material. This setup, using the combination of isomer excitation and color-changing light sources, causes the photochromic material to change color, thus forming voxel dots, which can be rapidly switched. Utilizing the persistence of vision, by controlling the scanning paths and speeds of the two light sources illuminating the photochromic material, a three-dimensional image formed by voxel transformation can be obtained, meeting the image and color requirements of three-dimensional imaging.

[0073] In the field of volumetric 3D applications, the solution obtained by dissolving Schiff base optical switching materials in the display medium is colorless and transparent or nearly colorless and transparent, thus avoiding the influence of its own color and exhibiting excellent optical switching performance. Firstly, the isomers generated by ESIPT under the first beam of light are rapid, and the isomers respond quickly under the second beam of light. The luminous intensity at the intersection of the two beams is bright, with high contrast, fast recovery speed, and good fatigue resistance.

[0074] Other configurations and operations of the Schiff base photo-switching material or photochromic material according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0075] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0076] Example 1 A Schiff base photo-switching material has the structure shown in formula (1-1):

[0077] Equation (1-1) The specific preparation method is as follows (taking p-methoxysalicylic acid acetal 2-methylbenzylamine Schiff base as an example): 1.52 g of p-methoxysalicylaldehyde and 1.45 g of benzylamine were mixed in 10 mL of anhydrous ethanol and refluxed for 4 h. After cooling to room temperature, a precipitate was formed. The precipitate was filtered and washed three times with cold ethanol to obtain the target product. Figure 2 and Figure 3 The figures show the 1H NMR spectrum and absorption spectrum of the target product, respectively. 2.29 g of the target product, p-methoxysalicylic acid acetal 2-methylbenzylamine Schiff base, was obtained, with a yield of 95.2%.

[0078] A specific method for applying the above-mentioned Schiff base photo-switching material in volumetric 3D display is as follows (taking p-methoxysalicylic acid acetal 2-methylbenzylamine Schiff base as an example): S1. Prepare a 0.15 mg / mL dimethyl sulfoxide solution of p-methoxysalicylic acid acetal 2-methylbenzylamine Schiff base. The solution is colorless and transparent. Figure 4 As shown in Figure a; S2. Through absorption spectroscopy and continuously tunable laser testing, 365nm ultraviolet light was determined as the optimal wavelength for photochromism, and 450nm blue light was used as the fluorescence excitation source for the isomer. No voxel points were observed when excited alone at 365nm; however, when the two light sources intersected perpendicularly within the material, voxel point luminescence was generated. Figure 4 As shown in b; S3. The scanning path and scanning speed of the two light sources can be controlled by a computer to complete the three-dimensional display.

[0079] Example 2 The main difference from Example 1 is that the reactant was 2-methylbenzylamine, with a mass of 1.82 g, and the volume of anhydrous ethanol was 12 mL. 2.38 g of the target product was obtained, with a yield of 94.0%.

[0080] Example 3 The main difference from Example 2 is that the mass of 2-methylbenzylamine was 3.64 g and the volume of anhydrous ethanol was 15 mL. 2.43 g of the target product was obtained, with a yield of 95.6%.

[0081] Example 4 A Schiff base photo-switching material has the structure shown in formula (1-2):

[0082] Equation (1-2) The specific preparation method is as follows (taking p-methoxysalicylic acid hexamethylenediamine Schiff base as an example): p-Methoxysalicylaldehyde (8 g, 52.58 mmol) and hexamethylenediamine (3.1 g, 26.29 mmol) were mixed in 15 mL of anhydrous ethanol and refluxed at 80 °C for 5 h. Crystals precipitated upon cooling. The mixture was filtered, washed, and dried to give 6.8 g of the target product, with a yield of 67.19%. Figure 5 and Figure 6 The two images are the 1H NMR spectrum and absorption spectrum of the target product, respectively.

[0083] The specific method for applying the p-methoxysalicylic acid hexamethylenediamine Schiff base in in vivo three-dimensional display is as follows: S1. Prepare a 0.15 mg / mL solution of 3-(trifluoromethyl)salicylaldehyde acetonitrile condensate, 1,4-phenylenediamine acetonitrile. The solution is clear and transparent.

[0084] S2. Through absorption spectroscopy and continuously tunable laser testing, 365nm ultraviolet light was determined as the optimal wavelength for photochromism, and 450nm blue light was used as the fluorescence excitation source for the isomers. For example... Figure 7 As shown, two light sources intersect perpendicularly inside the material, emitting light at the point of intersection.

[0085] S3. The scanning path and scanning speed of the two light sources can be controlled by a computer to complete the three-dimensional display.

[0086] Example 5 The main difference from Example 4 is that the mass of p-methoxysalicylaldehyde was 1.3 g (8.61 mmol), the mass of hexamethylenediamine was 0.5 g (4.3 mmol), and the target product was 1.2 g, with a yield of 72.7%.

[0087] Example 6 A Schiff base photo-switching material has the structure shown in formula (1-3):

[0088] Equation (1-3) The specific preparation method is as follows (taking p-methoxysalicylic acid acetal heptadecanylamine Schiff base as an example): 1.52 g of p-methoxysalicylaldehyde and 3.06 g of heptadecanylamine were mixed in 10 mL of anhydrous ethanol and refluxed for 4 h. After cooling to room temperature, a precipitate formed, which was then filtered off and washed three times with cold ethanol to obtain the target product. 3.54 g of the target product, p-methoxysalicylaldehyde heptadecanylamine Schiff base, was obtained, with a yield of 91.2%. Figure 8 and Figure 9 The two images are the 1H NMR spectrum and absorption spectrum of the target product, respectively.

[0089] The specific method for applying p-methoxysalicylic acid acetal heptadecanyl Schiff base in in vivo three-dimensional display is as follows (taking p-methoxysalicylic acid acetal heptadecanyl Schiff base as an example): S1. Prepare a 0.15 mg / mL dimethyl sulfoxide solution of p-methoxysalicylic acid acetyl heptadecanyl Schiff base. The solution is colorless and transparent. Figure 10 As shown in Figure a.

[0090] S2. Through absorption spectroscopy and continuously tunable laser testing, 365nm ultraviolet light was determined as the optimal wavelength for photochromism, and 450nm blue light was used as the fluorescence excitation source for the isomer. No voxel points were observed when excited alone at 365nm; however, when the two light sources intersected perpendicularly within the material, voxel point luminescence was generated. Figure 10 As shown in b.

[0091] S3. The scanning path and scanning speed of the two light sources can be controlled by a computer to complete the three-dimensional display.

[0092] Example 7 The main difference from Example 6 is that the mass of heptadecanine was 3.82 g and the volume of anhydrous ethanol was 12 mL. 3.45 g of the target product was obtained, with a yield of 88.2%.

[0093] Example 8 The main difference from Example 7 is that the mass of heptadecanine was 7.64 g and the volume of anhydrous ethanol was 15 mL. 3.36 g of the target product was obtained, with a yield of 86.4%.

[0094] Example 9 A Schiff base photo-switching material has the structure shown in formula (2-1):

[0095] Equation (2-1) The specific preparation method is as follows (taking 4-methoxystilbene salicylaldehyde condensate α-phenylethylamine Schiff base as an example): Synthesis of compound S1, 4-methoxystilbene salicylaldehyde: Under an inert atmosphere, 4-methoxystyrene (0.8 g, 5.97 mmol), 5-bromosalicylic acid (1 g, 4.97 mmol), DMF (10 mL), triethylamine (5 mL), and tetrakis(triphenylphosphine)palladium (0.1 g, 0.08 mmol) were added to a three-necked flask, and the mixture was heated to 100 °C for 5 h. After the reaction was completed, the reaction solution was cooled to room temperature, poured into 30 mL of deionized water, extracted with ethyl acetate, separated, dried, and subjected to column chromatography to obtain 0.6 g of 4-methoxystilbene salicylic acid, with a yield of 63.5%.

[0096] Synthesis of S2, α-phenylethylamine Schiff base of compound 4-methoxystilbene salicylaldehyde: To a round-bottom flask, add 0.5 g (1.97 mmol) of 4-methoxystilbene salicylaldehyde and 10 mL of anhydrous ethanol, and stir to dissolve. Then add 0.28 g (2.36 mmol) of α-phenylethylamine to the reaction mixture. Set up a reflux condenser and raise the reaction temperature to 75 °C, stirring and refluxing for 5 hours. After the reaction is complete, cool the reaction mixture to room temperature; a large amount of yellow-green solid precipitates. Filter under reduced pressure, and wash the solid with 5 mL × 3 of ice-cold ethanol. Dry under reduced pressure to obtain 0.56 g of 4-methoxystilbene salicylaldehyde condensate α-phenylethylamine Schiff base, yield 79.8%. Figure 11 and Figure 12 The two images are the 1H NMR spectrum and absorption spectrum of the target product, respectively.

[0097] Example 10 The main difference from Example 9 is that in step S1, the mass of 4-methoxystyrene was 4 g (29.85 mmol), the mass of 5-bromosalicylic acid was 5 g (24.87 mmol), the volume of DMF was 40 mL, the volume of triethylamine was 20 mL, and the mass of tetrakis(triphenylphosphine)palladium was 0.5 g (0.4 mmol). The heating temperature was 95 °C, and the reaction time was 16 h. The cooled solution after the reaction was poured into 60 mL of deionized water to obtain 5.2 g of 4-methoxystilbene salicylic acid, with a yield of 82.2%.

[0098] In step S2, the mass of 4-methoxystilbene salicylaldehyde was 5 g (19.7 mmol), the volume of anhydrous ethanol was 25 mL, the mass of α-phenylethylamine was 4.7 g (39.3 mmol), and the stirring and reflux time was 7 hours. 5.1 g of 4-methoxystilbene salicylaldehyde condensed into α-phenylethylamine Schiff base was obtained, with a yield of 72.5%.

[0099] Fluorescence intensity test of Schiff base photoswitching materials: The luminescence intensity of the Schiff base photoswitching materials prepared in some embodiments was tested using a self-made dual-excitation optical path. The excitation sources were 405 nm and 450 nm. Fluorescence intensity data were recorded using a fiber optic spectrometer and processed and output on a computer. The fluorescence intensity test results for the four Schiff base photoswitching materials are shown below. Figure 13 As shown.

[0100] Depend on Figure 13 It can be seen that the Schiff base of p-methoxysalicylic acid acetal hexamethylenediamine (corresponding to Example 5) exhibits the strongest fluorescence intensity at a wavelength of 500 nm, specifically 0.3. The fluorescence intensities of the Schiff base of p-methoxysalicylic acid acetal heptadecanylamine (corresponding to Example 7) and the Schiff base of 4-methoxystilbene salicylate acetal α-phenylethylamine (corresponding to Example 10) are similar, at 0.23 and 0.21, respectively. Figure 13 In the patent CN202410223656.3, the naphthaleneimide Schiff base with a fluorescence intensity of 0.18 at 500 nm is described as B.

[0101] Because the Schiff base molecule of p-methoxysalicylic acid acetal hexadecimal contains two p-methoxy groups, while the Schiff base molecules of p-methoxysalicylic acid acetal heptadecimal and naphthalimide Schiff bases contain only one p-methoxy group, and the luminescence intensity is related to the number of p-methoxy groups—an increase in the number of p-methoxy groups results in increased luminescence intensity—under the same testing conditions, the fluorescence intensity of the p-methoxysalicylic acid acetal heptadecimal and naphthalimide Schiff bases is relatively lower compared to that of the p-methoxysalicylic acid acetal hexadecimal Schiff base. In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the 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. Therefore, they should not be construed as limitations on this invention.

[0102] In the description of this invention, "a plurality of" means two or more.

[0103] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0104] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A Schiff base photo-switching material, characterized in that, It is a compound having the general chemical structural formula (1) or (2): Equation (1) In formula (1), X is a methoxy group; R1 is selected from aromatic hydrocarbon groups or alkyl groups; Equation (2) In formula (2), R2 is 4-methoxystyryl; R1 is selected from aromatic hydrocarbon groups.

2. The Schiff base photoswitching material according to claim 1, characterized in that, The Schiff base photoswitching material is any one of the following compounds: Equation (1-1) In equation (1-1), R is selected from — (C1-C 30 —X, —OH, —O(CH2) n CH3, —N(CH3)3, —NO2, —CN, —SO3H, —CHO, —COCH3, —COOH, where X is a halogen; Equation (1-2) Equation (1-3) Equation (2-1).

3. The method for preparing the Schiff base photoswitching material according to claim 1 or 2, characterized in that, Includes the following steps: p-Methoxysalicylaldehyde or 4-methoxystilbenesalicylaldehyde and the corresponding amine were mixed in anhydrous ethanol, refluxed for a first preset time, and then cooled, filtered, washed and dried to obtain the target product.

4. The preparation method according to claim 3, characterized in that, The step of mixing p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde and the corresponding amine in anhydrous ethanol further includes: At a first preset temperature, 4-methoxystyrene and 5-bromosalicylic acid are coupled using palladium metal reagent and organic base catalysis to obtain 4-methoxystilbene salicylaldehyde.

5. The preparation method according to claim 4, characterized in that, The first preset temperature is 50℃~120℃; and / or, The molar ratio of 4-methoxystyrene to 5-bromosalicylic acid is 1:0.1 to 1:

10.

6. The preparation method according to claim 4, characterized in that, When the Schiff base photoswitching material is a compound of formula (2-1), the mixing of p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde with the corresponding amine specifically includes: The 4-methoxystilbene salicylaldehyde and α-phenylethylamine were condensed at a molar ratio of 1:1.0 to 1:10 at 40°C to 100°C to obtain a 4-methoxystilbene salicylaldehyde condensed with α-phenylethylamine Schiff base.

7. The preparation method according to claim 3, characterized in that, When the Schiff base photoswitching material is a compound of formula (1-1), the step of mixing p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde and the corresponding amine in anhydrous ethanol specifically includes: The p-methoxysalicylaldehyde and benzylamine compounds are mixed in anhydrous ethanol at a molar ratio of 1:1.2 to 1:3.0 for a first preset time of 4 to 8 hours; or, When the Schiff base photoswitching material is a compound of formula (1-2), the step of mixing p-methoxysalicylic acid aldehyde or 4-methoxystilbene salicylic acid aldehyde and the corresponding amine in anhydrous ethanol specifically includes: The p-methoxysalicylaldehyde and hexamethylenediamine are mixed in anhydrous ethanol at a molar ratio of 1:2.0 to 1:8.0 for a first preset time of 3 to 24 hours; or, When the Schiff base photoswitching material is a compound of formula (1-3), the step of mixing p-methoxysalicylic acid or 4-methoxystilbene salicylic acid and the corresponding amine in anhydrous ethanol specifically includes: The p-methoxysalicylaldehyde and heptadecanol are mixed in anhydrous ethanol at a molar ratio of 1:1.2 to 1:3.0 for a first preset time of 1 to 6 hours.

8. A photochromic material, characterized in that, It is obtained by mixing and curing the Schiff base photoswitch material as described in claim 1 or 2 with a display medium; the mass ratio of the Schiff base photoswitch material to the display medium is 1:(5000~10000), and the display medium includes at least one of acetonitrile, methyl tert-butyl ether, dimethyl sulfoxide, cyclohexane, toluene, dichloromethane, and ethyl acetate, or... The display medium includes epoxy resin or polymethyl methacrylate.

9. The application of the Schiff base photo-switching material according to claim 1 or 2 or the photochromic material according to claim 8 in three-dimensional imaging.

10. The application according to claim 9, characterized in that, The material is irradiated with an isomer excitation light source and a color-changing excitation light source, forming a photobulk point at the intersection of the isomer excitation light source and the color-changing excitation light source; wherein, the color-changing excitation light source is blue visible light with a wavelength of 440nm~470nm, and / or the isomer excitation light source is ultraviolet light with a wavelength of 365nm~410nm; By controlling the scanning path and scanning speed of the isomer excitation source and the color-changing excitation source, three-dimensional imaging can be achieved in the material.

Images