Schiff base optical switch material, preparation method thereof and static body three-dimensional display system

Abstract

The invention provides a Schiff base optical switch material, the molecular structural formula of which is at least one of the following: # imgabs0. The Schiff base optical switch material has the advantages that the voxel generation and disappearance speeds are both smaller than the limit resolution of human eyes, the response speed is high, and the dynamic refreshing of a three-dimensional image can be realized. Under independent excitation of ultraviolet light or visible light, the luminous intensity of the Schiff base photoswitch material is low, the luminous intensity at the intersection point of the ultraviolet light and the visible light is high, and a formed three-dimensional image is high in brightness and high in contrast ratio. The Schiff base photoswitch material can still be stably switched on and off under multiple excitation of ultraviolet light and visible light, and is good in fatigue resistance and high in stability. The invention also provides a preparation method of the Schiff base optical switch material and a static body three-dimensional display system comprising the Schiff base optical switch material.

Description

Technical Field

[0001] The present application relates to a Schiff base photoswitch material and a preparation method thereof, and a static volumetric three-dimensional display system containing the Schiff base photoswitch material. Background Art

[0002] Static volumetric imaging is one of the true three-dimensional stereoscopic display technologies. The principle of static volumetric imaging is based on a special luminescent material. When two light beams intersect at a point inside the luminescent material, the smallest constituent unit in three-dimensional space - a voxel is generated. When the light beams move rapidly, multiple intersection points are formed in three-dimensional space, thus forming a three-dimensional pattern composed of multiple voxel points. In current research, rare-earth doped materials based on the upconversion principle or organic dyes based on the photoswitch principle can be used as this special luminescent material. However, rare-earth doped materials based on the upconversion principle require expensive high-energy light beams as excitation light sources, which have relatively large safety hazards. At the same time, the small material volume limits the volume of three-dimensional images. The development of organic dyes based on the photoswitch principle is not yet mature, but the light source used for this material has low energy and is not limited by the material volume, and has the potential to develop into the mainstream material for static volumetric imaging. Summary of the Invention

[0003] In view of this, in the first aspect of the present application, a Schiff base photoswitch material is provided, and the molecular structural formula is at least one of the following:

[0004]

[0005] For this Schiff base photoswitch material, the generation and disappearance speeds of voxel points are both less than the limit resolution of the human eye, the response speed is fast, and dynamic refreshing of three-dimensional images can be achieved. Under the excitation of ultraviolet light or visible light alone, the luminescence intensity of this Schiff base photoswitch material is low, and the luminescence intensity at the intersection of ultraviolet light and visible light is high, forming a three-dimensional image with high brightness and high contrast. This Schiff base photoswitch material can still stably switch under multiple excitations of ultraviolet light and visible light, has good anti-fatigue performance and high stability.

[0006] In the second aspect of the present application, a static volumetric three-dimensional display system is provided, including the above-mentioned Schiff base photoswitch material.

[0007] In the third aspect of the present application, a preparation method of a Schiff base photoswitch material is provided, including:

[0008] Step S1: Mix 4-bromo-1,8-naphthalic anhydride and aniline in an organic solvent, and react to obtain Compound I, and this Compound I is

[0009] Step S2: Mix this Compound I, sodium methoxide and a catalyst in an organic solvent, and react to obtain Compound II, and this Compound II is

[0010] Step S3: React the compound II with hydroiodic acid to obtain compound III, and the compound III is

[0011] Step S4: Mix the compound III with hexamine in an organic solvent and react to obtain compound IV, and the compound IV is

[0012] Step S5: Mix at least one of (S)-1-(4-methylphenyl)ethylamine and (R)-1-(4-methylphenyl)ethylamine with the compound IV in an organic solvent and react to obtain the target compound

[0013] at least one of

[0014] In this application, 1,8-naphthalimide is used as a raw material to prepare an aldehyde with an adjacent hydroxyl group, and then the synthesis of the Schiff base photoswitch material is further carried out, which can greatly improve the luminescence intensity of the keto structure of the Schiff base and enhance the voxel point luminescence efficiency of the Schiff base photoswitch in the volumetric three-dimensional display system. Description of the Drawings

[0015] Figure 1 is the 1H NMR spectrum of the Schiff base photoswitch material in Example 1 of this application.

[0016] Figure 2 is the absorption spectrum of the Schiff base photoswitch material in Example 1 of this application.

[0017] Figure 3 is the application schematic diagram of the Schiff base photoswitch material in Example 1 of this application in the static volumetric three-dimensional display system.

[0018] Main Element Symbol Description:

[0019] Static volumetric three-dimensional display system 100

[0020] Imaging space 10

[0021] Container 30

[0022] Ultraviolet light 21

[0023] Visible light 22 Detailed Embodiments

[0024] The embodiments of this application will be described below with reference to the drawings in the embodiments of this application. The data ranges involved in this application should include the end values unless otherwise specified.

[0025] When salicylaldehyde primary amine Schiff base molecules are excited, intramolecular rapid proton transfer occurs, resulting in photochromism and thermochromism phenomena. They are a type of representative optical switch materials. However, the luminescence efficiency of Schiff bases is relatively low, which affects display parameters such as brightness and resolution in static volume three-dimensional displays. To improve the luminescence efficiency of Schiff bases, it is necessary to introduce luminescent groups with high luminescence intensity. 1,8-Naphthalimide fluorescent compounds are a type of compounds with strong fluorescence. In recent years, studies have found that this type of compound has excellent photochemical stability and relatively high quantum efficiency, and can be applied to high-tech fields such as optoelectronic sensitive materials, solar collectors, liquid crystal materials, DNA intercalators, and chemical fluorescence probes.

[0026] Therefore, in this application, 1,8-naphthalimide is used as a raw material to prepare an aldehyde with adjacent hydroxyl groups, and then further synthesize Schiff base optical switch materials, which can greatly improve the luminescence intensity of the keto structure of Schiff bases and enhance the voxel point luminescence efficiency of Schiff base optical switches in the volume three-dimensional display system.

[0027] This application provides a novel Schiff base optical switch material, and its molecular structural formula is:

[0028]

[0029] The above two molecular structural formulas (1) and (2) are two different stereoisomers of the Schiff base optical switch material. Among them, the molecular structural formulas both include chiral carbon atoms connecting four different groups. In molecular structural formula (1), the four different groups are arranged in a clockwise direction, and in molecular structural formula (2), the four different groups are arranged in a counterclockwise direction.

[0030] Please refer to Figure 3 , this application also provides a static volume three-dimensional display system 100, including the above-mentioned Schiff base optical switch material. The Schiff base optical switch material is dispersed in a suitable organic solvent to form a transparent solution, and the transparent solution serves as the imaging space 10 for static volume three-dimensional display. Figure 3 The solution is placed in a transparent container 30. In one embodiment, the organic solvent is cyclohexane, but not limited thereto. For example, the concentration of the Schiff base optical switch material in the organic solvent can be 0.03 - 0.07 mmol / L. The static volume three-dimensional display system 100 also includes an excitation light source (not shown in the figure) for irradiating the imaging space. The excitation light source includes ultraviolet light 21 and visible light 22, and the two light sources intersect at a point in the imaging space to generate a luminescent voxel point. When the excitation light source 20 moves quickly, multiple intersection points are formed in the imaging space 10, serving as voxels to form a three-dimensional stereoscopic image.

[0031] Based on the principle of excited-state proton transfer, this Schiff base photoswitchable material can rapidly transform from the enol form to the keto form under ultraviolet light irradiation. After the ultraviolet light irradiation is removed, at room temperature, the keto form of this Schiff base photoswitchable material will transform into the enol form, that is, the enol form and the keto form are interconvertible, as shown in the following reaction formula. When another beam of visible light intersects with the ultraviolet light, it excites the keto isomer in the imaging space to generate voxel point luminescence; when multiple voxel point arrays are present, a three-dimensional stereoscopic image is displayed inside the Schiff base photoswitchable material.

[0032]

[0033] For this Schiff base photoswitchable material, the speeds of generation and disappearance of voxel points are both less than the limit resolution of the human eye, and it has a fast response speed, enabling dynamic refreshing of three-dimensional images.

[0034] For this Schiff base photoswitchable material, when excited by ultraviolet light or visible light alone, the luminescence intensity is low. At the intersection of ultraviolet light (wavelength 400 ± 5 nm, such as 405 nm) and visible light (wavelength approximately 485 ± 5 nm, such as 488 nm), the luminescence intensity is high, and the three-dimensional image formed has a high brightness and a high contrast. This Schiff base photoswitchable material can still stably switch under multiple excitations of ultraviolet light and visible light, has good anti-fatigue performance, and high stability.

[0035] The preparation method of this Schiff base photoswitchable material includes the following steps S1 to S5.

[0036] Step S1: Mix 4-bromo-1,8-naphthalic anhydride and aniline in an organic solvent and react to obtain compound I, where the molar ratio of 4-bromo-1,8-naphthalic anhydride to aniline is 1:(1.5 - 3.5).

[0037] The organic solvent used in step S1 is at least one of organic solvents such as glacial acetic acid, formic acid, acetic acid, dimethyl sulfoxide, dimethylformamide, acetonitrile, methanol, ethanol, tetrahydrofuran, toluene, dichloroethane, etc.

[0038] In this step S1, the reaction temperature can be controlled at 100 - 130 °C, and reflux for 4 - 8 h under the protection of an inert gas to obtain compound I. The protection of the inert gas can increase the reaction rate. Compound I is Taking glacial acetic acid as the organic solvent as an example, the reaction formula for this step S1 is as follows.

[0039]

[0040] Step S2: Mix compound I, sodium methoxide, and a catalyst in an organic solvent and react to obtain compound II. Among them, compound I and sodium methoxide are used as reactants, the catalyst is copper sulfate, and the molar ratio of compound I, sodium methoxide, and copper sulfate is 1:(7 - 8):(0.1 - 0.3).

[0041] The organic solvent used in step S2 is at least one of alcohol organic solvents such as methanol, ethanol, isopropanol, and ethylene glycol.

[0042] In this step S2, the reaction temperature can be controlled at 50 - 75 °C, and it can reflux for 6 - 10 h under the protection of an inert gas to obtain compound II. The protection of the inert gas can increase the reaction rate. The organic solvent in step S2 is methanol. Compound II is Taking the organic solvent as methanol as an example, the reaction formula of this step S2 is as follows.

[0043]

[0044] Step S3: React compound II with hydroiodic acid to obtain compound III. Among them, the molar ratio of compound II to hydroiodic acid is 1:(75 - 125).

[0045] The reaction of this step S3 can reflux for 8 - 12 h under the protection of an inert gas to obtain compound III. The protection of the inert gas can increase the reaction rate. Compound III is The reaction formula of this step S3 is as follows.

[0046]

[0047] In one embodiment, compound II is mixed with hydroiodic acid with a concentration of 57 wt% (aqueous solution of HI), and among them, the concentration of compound II in hydroiodic acid is 60 - 100 mmol / L.

[0048] Step S4: Mix compound III and hexamethylenetetramine (HMTA) in an organic solvent and react to obtain compound IV. Among them, the molar ratio of compound III to hexamethylenetetramine is 1:(1 - 3).

[0049] The organic solvent in this step S4 is at least one of trifluoroacetic acid (TFA), acetic acid, polyphosphoric acid, dimethyl sulfoxide, methanol, ethanol, and acetone. The reaction reflux time is 8 - 12 h to obtain compound IV. Compound IV is Taking the organic solvent as trifluoroacetic acid (TFA) as an example, the reaction formula of this step S4 is as follows.

[0050]

[0051] Step S5: Mix compound IV and (S)-1-(4-methylphenyl)ethylamine or (R)-1-(4-methylphenyl)ethylamine in an organic solvent for reaction to obtain the target compound. Among them, the molar ratio of compound IV to 1-(4-methylphenyl)ethylamine is 1:(0.9 - 1.1). The reactant 1-(4-methylphenyl)ethylamine in step S5 can have two different stereoconformations. The expression of the stereoconfiguration in organic chemistry is: (R)- indicates that the stereoconformation of the chiral molecule is that the priority order of substituents is arranged in a clockwise direction; (S)- indicates that the stereoconformation of the chiral molecule is that the priority order of substituents is arranged in a counterclockwise direction.

[0052] The organic solvent in this step S5 is various commonly used organic solvents, such as at least one of methanol, ethanol, dichloromethane, dichloroethane, toluene, xylene, dimethyl sulfoxide, and tetrahydrofuran. The reaction reflux time is 2 - 6 h to obtain the target compound. Taking ethanol as an example of the organic solvent, the reaction formula of this step S5 is as follows.

[0053]

[0054] In this application, 4-bromo-1,8-naphthalic anhydride is used as a raw material to synthesize 3-formyl-4-hydroxy-1,8-naphthalimide, and then condensed with chiral 1-(4-methylphenyl)ethylamine to prepare a Schiff base photoswitch. The preparation method of this Schiff base photoswitch material has a simple process, convenient operation, and is convenient for large-scale industrial production.

[0055] The preparation of the Schiff base photoswitch material will be specifically described below through Examples 1 to 3.

[0056] Example 1

[0057] Mix 4-bromo-1,8-naphthalic anhydride (30.5 g, 0.11 mol) and aniline (20.5 g, 0.22 mol) in 300 mL of glacial acetic acid CH3COOH, reflux at 120 °C for 6.5 h under nitrogen protection. After cooling, pour the mixture into water to produce a yellow precipitate. After filtration and recrystallization, a pale yellow crystal, namely compound I, is obtained.

[0058] Mix compound I (24.6 g, 0.07 mol), sodium methoxide (29.6 g, 0.55 mol), and copper sulfate (2.4 g, 0.015 mol) and disperse them in 250 mL of dry methanol solution. Reflux at 65 °C for 8 h under nitrogen protection. Cool the solution to room temperature and filter to obtain a pale yellow solid. Then wash it with 10% hydrochloric acid (30 mL * 3) and water (20 mL * 3) to obtain compound II.

[0059] Compound II (15.0 g, 0.05 mol) was mixed with 400 mL of 57 wt% hydroiodic acid and refluxed for 12 h under nitrogen protection. The solution was cooled to room temperature, filtered, and the crude product was washed with water (50 mL * 3) to obtain a yellow-green solid. The crude product was purified by column chromatography to obtain Compound III.

[0060] A mixture of Compound III (8.7 g, 0.03 mol) and hexamethylenetetramine (8.4 g, 0.06 mol) was refluxed in trifluoroacetic acid for 8 h, and then the solution was cooled to room temperature. The reaction mixture was diluted with distilled water, and the formed precipitate was filtered. The precipitate was washed several times with distilled water and dried. Subsequently, it was dissolved in dichloromethane and purified using a short silica plug to obtain Compound IV.

[0061] Compound IV (0.63 g, 2 mmol) and (S)-1-(4-methylphenyl)ethylamine (0.30 g, 2.2 mmol) were mixed in 20 mL of ethanol, refluxed for 4 h, filtered and washed to obtain the target compound.

[0062] Example 2

[0063] The steps and parameters of Example 2 were basically the same as those of Example 1, and the difference from Example 1 was only that: in the step of synthesizing Compound I, the molar ratio of 4-bromo-1,8-naphthalic anhydride to aniline was 1:3.5.

[0064] Example 3

[0065] The steps and parameters of Example 3 were basically the same as those of Example 1, and the difference from Example 1 was that in the step of synthesizing Compound II, the molar ratio of Compound I, sodium methoxide and copper sulfate was 1:7.14:0.15.

[0066] Example 4

[0067] The steps and parameters of Example 4 were basically the same as those of Example 1, and the difference from Example 1 was that in the step of synthesizing Compound IV, the molar ratio of Compound III to hexamethylenetetramine was 1:3.

[0068] Example 5

[0069] The steps and parameters of Example 5 were basically the same as those of Example 1, and the difference from Example 1 was that Compound IV reacted with (R)-1-(4-methylphenyl)ethylamine.

[0070] Compound IV (0.63 g, 2 mmol) synthesized in Example 1 and (R)-1-(4-methylphenyl)ethylamine (0.3 g, 2.2 mmol) were mixed in 20 mL of ethanol, refluxed for 4 h, filtered and washed to obtain the target compound with a yield of 91%.

[0071] Application Example 1

[0072] The Schiff base photoswitch material synthesized in Example 1 was mixed with cyclohexane to prepare a cyclohexane solution with a concentration of 0.05 mmol / L, and it was placed in a transparent quartz vessel for standby. The excitation light sources, a 405 nm laser and a 488 nm laser, were selected to intersect vertically, as Figure 3 shown. The computer controlled the movement of the laser inside the cyclohexane solution, and volumetric three-dimensional display could be completed.

[0073] Application Example 2

[0074] The Schiff base photoswitch material synthesized in Example 5 was mixed with cyclohexane to prepare a cyclohexane solution with a concentration of 0.05 mmol / L, and it was placed in a quartz vessel for standby. The excitation light sources, a 405 nm laser and a 488 nm laser, were selected to intersect vertically, and the computer controlled the movement of the laser inside the solution, then volumetric three-dimensional display could be completed.

[0075] The structure of the Schiff base photoswitch material, the product of Example 1, was characterized by 1H NMR, and the results were as Figure 1 . According to Figure 1 the positions (chemical shifts) and areas (number of hydrogen atoms) of the peaks in Figure 1 , the peaks of hydrogen in

[0076] Figure 2 could be corresponded to the hydrogen-containing functional groups in the molecular structural formula of the Schiff base photoswitch material, verifying that the Schiff base photoswitch material with this molecular structural formula was formed.

[0077] In this application, 1,8-naphthalimide was used as a raw material to prepare an aldehyde with adjacent hydroxyl groups, and further the synthesis of the Schiff base photoswitch material was carried out, which could greatly improve the luminescence intensity of the Schiff base keto structure and enhance the voxel point luminescence efficiency of the Schiff base photoswitch in the volumetric three-dimensional display system.

[0078] The above embodiments are only used to illustrate the technical solutions of this application and not to limit them. Although the above preferred embodiments have been described in detail for this application, those of ordinary skill in the art should understand that the technical solutions of this application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of this application.

Claims

1. A Schiff base photoswitching material, characterized in that, the molecular structural formula of the Schiff base photoswitching material is:

2. The Schiff base photoswitching material according to claim 1, characterized in that, the Schiff base photoswitching material absorbs light with a wavelength of 350 - 450 nm.

3. A static volumetric 3D display system, characterized in that, it includes the Schiff base photoswitching material according to claim 1 or 2.

4. The static volumetric 3D display system according to claim 3, characterized in that, the Schiff base photoswitching material is dispersed in an organic solvent to form a transparent solution, and the solution serves as the imaging space of the static volumetric 3D display system; the static volumetric 3D display system further includes an excitation light source for emitting excitation light that irradiates the imaging space, and the excitation light includes ultraviolet light and visible light.

5. The static volumetric 3D display system according to claim 4, characterized in that, the wavelength of the ultraviolet light is 400 ± 5 nm, and the wavelength of the visible light is 485 ± 5 nm.

6. A preparation method of a Schiff base photoswitching material, characterized in that, it includes: Step S1: Mix 4-bromo-1,8-naphthalic anhydride and aniline in an organic solvent and react to obtain Compound I, which is Step S2: Mix the compound I, sodium methoxide and a catalyst in an organic solvent, and react to obtain compound II, which is Step S3: React the compound II with hydroiodic acid to obtain compound III, which is Step S4: Mix the compound III and hexamethylenetetramine in an organic solvent and react to obtain compound IV, and the compound IV is Step S5: Mix at least one of (S)-1-(4-methylphenyl)ethylamine and (R)-1-(4-methylphenyl)ethylamine with the compound IV in an organic solvent and react to obtain the target compound at least one of 7. The preparation method of the Schiff base photoswitching material according to claim 6, characterized in that, in the step S1, the molar ratio of 4-bromo-1,8-naphthalic anhydride to aniline is 1:(1.5 - 3.5).

8. The preparation method of the Schiff base photoswitching material according to claim 6, characterized in that, in the step S2, the catalyst is copper sulfate, and the molar ratio of the compound I, sodium methoxide and copper sulfate is 1:(7 - 8):(0.1 - 0.3).

9. The preparation method of the Schiff base photoswitching material according to claim 6, characterized in that, in the step S3, the molar ratio of the compound II to hydroiodic acid is 1:(75 - 125).

10. The preparation method of the Schiff base photoswitching material according to claim 6, characterized in that, in the step S4, the molar ratio of the compound III to hexamine is 1:(1 - 3).

11. The preparation method of the Schiff base photoswitching material according to claim 6, characterized in that, in the step S5, the molar ratio of the compound IV to 1-(4-methylphenyl)ethylamine is 1:(0.9 - 1.1).

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