A D-A type photochromic material and its preparation method

Abstract

The present invention provides a D-A type photochromic material and a preparation method thereof. The D-A type photochromic material uses compound 1 as the initial raw material, constructs a methyl-substituted spiropyran molecular skeleton SP-Br through two-step organic reactions, and then couples an aromatic conjugate unit to the spiropyran molecular skeleton through Suzuki coupling to obtain the product. The photochromic material and the preparation method thereof according to the present invention introduce an aromatic conjugate unit into the spiropyran molecular skeleton to construct a series of D-A type conjugate structures, effectively increasing the conjugate length of the molecule, regulating the HOMO / LUMO energy levels and band gap of the molecule, as well as the ring-opening / ring-closing rate of the molecule, thereby effectively regulating the photochromic ability and color change range of the material; the introduction of the conjugate unit can significantly increase the free volume of the material in the solid state, so that a series of D-A type conjugate materials can also produce an obvious photochromic process in the pure solid state.

Description

Technical Field

[0001] The present invention relates to the technical field of camouflage materials, and in particular, to a D-A type photochromic material and a preparation method thereof. Background Art

[0002] The photochromic process refers to the process in which a compound undergoes changes in its chemical structure and electronic energy levels after being irradiated by a radiation light source such as ultraviolet light and visible light, generating another compound. Its absorption spectrum will change significantly, thereby causing a significant change in its color in different states. The radiation light source usually includes ultraviolet light and visible light, etc.; this process is usually reversible. After photochromism occurs, it can return to the initial state under the irradiation of light with another specific wavelength or under the action of heat.

[0003] Spiropyrans were first discovered by Hirshberg in 1952 and achieve the photochromic process through the isomerization of ring-opening and ring-closing. It is one of the materials that have been studied earliest and most extensively among current photochromic materials. There is a spiro carbon atom with an SP3 heterocycle in the colorless spiropyran structure. Under ultraviolet light irradiation, the C-O bond at the spiro ring breaks and opens, the molecular structure rotates, forming a large conjugated plane, and the absorption peak undergoes a red shift, resulting in a significant change in its color; under certain conditions, the colored ring-opening structure can return to the initial spiro ring structure.

[0004]

[0005] A large number of studies have been carried out at home and abroad on this basis. For example, Angiolini et al. successfully prepared a homopolymer of methacrylic acid containing a spiropyran unit. By introducing methyl methacrylate and ethyl cellulose, the fatigue resistance of the material can be effectively improved, and it has good thermal stability and excellent photochromic properties. Alex Julià-López et al. prepared spiropyran-based core-shell microcapsules. The nonanoic acid solution of spiropyran was made into organic phase microcapsules by solvent evaporation method, which has good reverse photochromic properties, and the tunability of photochromism is greatly enhanced. Different colors and color change rates can be adjusted by changing the properties of the solvent. After adding it to the solid matrix, the photochromic and thermochromic properties are not affected. Xu Xiaoming et al. synthesized a series of novel photochromic compounds containing spirocycles and fulgimide. This photochromic material contains an asymmetric double chromophore structure of spiropyran and fulgimide at the same time. After ultraviolet light irradiation, it shows absorption wavelengths different from those of the parent compound, and the stability and fatigue resistance are significantly improved compared with spiropyran. For example, in the Chinese patent with the application number 202111154155.7, a fluorescent conjugated polymer containing a spiropyran side group was prepared by the Sonogashira coupling method, and it was combined with a polymethyl methacrylate matrix. Using the electrospinning process, a fluorescent fiber membrane with photochromic properties was obtained. Most of the existing studies on spiropyran-based photochromic materials are optimized by modifying functional groups or compounding materials on the premise of keeping the molecular skeleton unchanged, and the performance improvement is limited.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] The problem solved by the present invention is that the existing spiropyran-based photochromic materials have poor color change rate, poor reversibility, single color system and poor stability.

[0008] To solve the above problems, the present invention provides a D-A type photochromic material, using compound 1 as the initial raw material, and the compound 1 is

[0009]

[0010] The methyl-substituted spiropyran molecular skeleton SP-Br is constructed through two-step organic reactions, and then the aromatic conjugate unit is coupled to the spiropyran molecular skeleton through Suzuki coupling to obtain it.

[0011] The present invention effectively increases the conjugation length of the molecule by constructing a series of D-A type conjugate structures, regulates the HOMO / LUMO energy levels and band gaps of the molecule and the ring-opening / ring-closing rate of the molecule, and then effectively regulates the photochromic ability and color change range of the material; the introduction of the conjugate unit can significantly increase the free volume of the material in the solid state, so that the series of D-A type conjugate materials can also produce an obvious photochromic process in the pure solid state.

[0012] Preferably, the aromatic conjugate unit is an aromatic heterocyclic conjugate unit. Preferably, the aromatic heterocyclic conjugate unit is any one of thiophene (-T), pyridine (-Py), and benzofuran (-BF) units.

[0013] Preferably, the methyl-substituted spiropyran molecular skeleton SP-Br is prepared through the following reaction:

[0014]

[0015] Preferably, the D-A type photochromic material is prepared through the following reaction:

[0016]

[0017] Preferably, the preparation method of the methyl-substituted spiropyran molecular skeleton SP-Br is as follows:

[0018] 1) Add compound 1 to the reaction vessel, then add methyl iodide in a molar ratio of 2-3:1, add anhydrous chloroform under anhydrous and anaerobic conditions, heat up and stir to reflux; after reacting for 5-8 h, cool to room temperature, extract with an appropriate amount of organic solvent for 1-4 times, collect and combine the organic phases, separate by silica gel column chromatography and dry to obtain a yellow product;

[0019] 2) Feed the above yellow product into the reaction vessel, then add 5-bromosalicylaldehyde in a molar ratio of 0.8-1.2:1, add anhydrous ethanol under anhydrous and anaerobic conditions, then heat up to 50-60 °C, slowly dropwise add piperidine, heat up and stir to reflux; after reacting for 3-8 h, cool to room temperature, extract with an appropriate amount of organic solvent for 1-4 times, collect and combine the organic phases, separate by silica gel column chromatography and dry to obtain the product. Preferably, the temperature corresponding to heating up and stirring to reflux is 75-90 °C.

[0020] Preferably, the preparation method further includes:

[0021] 3) Add SP-Br to the reaction vessel, then add any one of phenylboronic acid, pyridineboronic acid, thiopheneboronic acid, and benzofuranboronic acid and tetrakis(triphenylphosphine)palladium, then add cesium carbonate or potassium carbonate, add an appropriate amount of mixed solvent to the reaction system under anaerobic conditions, heat up to 70-120 °C to the reflux state, after reacting for 4-10 h, cool to room temperature, extract with an appropriate amount of organic solvent for 1-4 times respectively, collect and combine the organic phases, separate by silica gel column chromatography and dry to obtain the product.

[0022] Preferably, the mixed solution is formed by tetrahydrofuran or dioxane and water in a molar ratio of 2-4:1. Preferably, the molar ratio of tetrahydrofuran or dioxane to water is 3:1.

[0023] Preferably, the molar ratio of the phenylboronic acid, pyridineboronic acid, thiopheneboronic acid, or benzofuranboronic acid to SP-Br is 2-4:1, the molar ratio of the tetrakis(triphenylphosphine)palladium to SP-Br is 1:9-12, and the molar ratio of the cesium carbonate or potassium carbonate to SP-Br is 6-10:1.

[0024] Preferably, the molar ratio of the phenylboronic acid, pyridineboronic acid, thiopheneboronic acid, or benzofuranboronic acid to SP-Br is 3:1, the molar ratio of the tetrakis(triphenylphosphine)palladium to SP-Br is 1:10, and the molar ratio of the cesium carbonate or potassium carbonate to SP-Br is 8:1.

[0025] Preferably, in step 3), before the temperature-raising operation, liquid nitrogen freezing and pumping are performed 2-5 times to remove oxygen again.

[0026] The liquid nitrogen freezing and pumping means that the reaction system is placed in a liquid nitrogen environment or liquid nitrogen is introduced into the reaction interlayer to make the reaction system close to the liquid nitrogen temperature for solidification, and then the vacuum is pumped to remove oxygen; then, while maintaining the vacuum state, room temperature water is introduced into the reaction interlayer to make the reaction system return to the liquid state again, and the reaction system is placed in a liquid nitrogen environment or liquid nitrogen is introduced into the reaction interlayer again to make the reaction system close to the liquid nitrogen temperature for solidification, and then the vacuum is pumped again to remove oxygen. Repeat 2-5 times to completely remove oxygen.

[0027] Preferably, the organic solvent in steps 1)-3) is dichloromethane.

[0028] Compared with the prior art, the preparation method of the D-A type photochromic material of the present invention has the following beneficial effects: 1) The absorption spectrum of the prepared D-A type photochromic material is significantly red-shifted after ring-opening, and the molecular free volume is significantly increased; 2) The photochromic ability and reversibility of the material are effectively improved, and then a high-performance photochromic material with a tunable photochromic range and an obvious photochromic process under pure solid state can be obtained, which has broad application prospects and practical values in cutting-edge fields such as camouflage protection, optoelectronic storage, and intelligent sensing. Description of the Drawings

[0029] Figure 1 is the 1 HNMR spectrum of Compound 2 in the examples of the present invention;

[0030] Figure 2 is the 1 HNMR spectrum of SP-Br in the examples of the present invention;

[0031] Figure 3 is the 1 HNMR spectrum of SP-B in Example 1 of the present invention;

[0032] Figure 4 is the1 1H NMR spectrum;

[0033] Figure 5 1H NMR spectrum of SP-Py described in Example 3 of the present invention; 1 1H NMR spectrum;

[0034] Figure 6 1H NMR spectrum of SP-BF described in Example 4 of the present invention; 1 1H NMR spectrum;

[0035] Figure 7 UV-Vis absorption spectrum of the sample prepared in Example of the present invention in dilute acetone solution;

[0036] Figure 8 Color change of different samples before and after direct UV irradiation;

[0037] Figure 9 Color change of SP-B film described in Example 1 of the present invention before and after UV irradiation;

[0038] Figure 10 Color change of SP-T film described in Example 2 of the present invention before and after UV irradiation;

[0039] Figure 11 Color change of SP-Py film described in Example 3 of the present invention before and after UV irradiation. Detailed implementation manners

[0040] To make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of specific embodiments of the present invention will be given with reference to the accompanying drawings. On the premise of no conflict, the features in the embodiments of the present invention can be combined with each other.

[0041] Extensive and in-depth research has been carried out on spiropyran-based photochromic materials at home and abroad. However, most of the research and application development on their photochromic properties are still carried out by modifying functional groups or compounding materials on the premise of keeping their molecular skeletons unchanged. There are still problems that the photochromic rate, the photochromic reversibility in the solid state, and the photostability of spiropyran-based materials need to be improved; the colors after photochromism are also relatively single, and it is difficult to meet the further requirements in the field of intelligent color-changing camouflage.

[0042] However, there are few studies on constructing new spiropyran-based molecular materials from the intrinsic properties of the molecular skeleton and then improving the photochromic properties. Therefore, the photochromic properties of such photochromic materials, such as the photochromic rate, the reversibility of photochromism, and the color system of the ring-opening structure after color change, have not been significantly improved and changed. For this reason, the applicant proposes the following technical solutions:

[0043] Example 1

[0044] A preparation method of a D-A type photochromic material, comprising:

[0045] 1) Preparation of Compound 2

[0046] Add 5.0 g of Compound 1 into a 250 mL two-necked flask, then add methyl iodide with a molar ratio of 2.5:1 to Compound 1. After performing an anhydrous and anaerobic treatment, inject 100 mL of anhydrous chloroform into the reaction system, and heat up to 85 °C and stir until reflux; after reacting for 6 h, cool down to room temperature, extract three times with 100 ml of dichloromethane / water = 1:1 respectively, collect and combine the organic phases. Separate by silica gel column chromatography (petroleum ether / ethyl acetate = 1:1), monitor with TLC thin-layer chromatography for collection, and dry to finally obtain a pale yellow product, Compound 2, 1 The HNMR spectrum is as Figure 1 , and the yield is 80%.

[0047]

[0048] 2) Preparation of SP-Br

[0049] Add 1.6 g of Compound 2 into a 250 mL two-necked flask, then add 5-bromosalicylaldehyde with a molar ratio of 1:1 to Compound 2. After performing an anhydrous and anaerobic treatment, inject 80 mL of anhydrous ethanol into the reaction system, heat up to 55 °C, drop 0.8 mL of piperidine into the reaction system, and continue to heat up to 80 °C and stir until reflux. After reacting for 8 h, cool down to room temperature, extract three times with 50 ml of dichloromethane respectively, collect and combine the organic phases. Separate by silica gel column chromatography (petroleum ether / ethyl acetate = 1:1) to finally obtain a yellow product, SP-Br, 1 The HNMR spectrum is as Figure 2 , and the yield is 75%.

[0050]

[0051] 3) Preparation of SP-B

[0052] Add 250 mg of Compound SP-Br into a 100 mL two-necked flask, then add phenylboronic acid with a molar ratio of 3:1 to SP-Br - that is, 256.7 mg, tetrakis(triphenylphosphine)palladium with a molar ratio of 1:10 to SP-Br - that is, 81.1 mg, and potassium carbonate with a molar ratio of 6:1 to SP-Br - that is, 581.8 mg. Replace with nitrogen for anaerobic treatment, and inject 12 mL of a mixed solvent of anhydrous tetrahydrofuran and water (THF:H 2O = 3:1), and the deoxygenation operation was carried out by freezing and pumping with liquid nitrogen three times. The temperature was raised to 85 °C until reflux, and after reacting for 8 h, it was cooled to room temperature. It was extracted three times with a mixed solution of 50 ml of dichloromethane and 50 ml of water, and the organic phases were collected and combined. Column chromatography separation on silica gel (petroleum ether / ethyl acetate = 80:1) was carried out, and finally a light yellowish-white product SP-B was obtained. 1 The HNMR spectrum is as Figure 3 , and the yield was 65%.

[0053]

[0054] Example 2

[0055] A preparation method of a D-A type photochromic material, comprising:

[0056] 1) Preparation of compound 2

[0057] Compound 2 was prepared by the same method as in Example 1.

[0058] 2) Preparation of SP-Br

[0059] SP-Br was prepared by the same method as in Example 1.

[0060] 3) Preparation of SP-T

[0061] 200 mg of compound SP-Br was added to a 100 mL two-necked flask, and then thiopheneboronic acid with a molar ratio of 3:1 to SP-Br - that is, 215.5 mg, tetrakis(triphenylphosphine)palladium with a molar ratio of 1:10 to SP-Br - that is, 64.9 mg, and potassium carbonate with a molar ratio of 6:1 to SP-Br - that is, 465.5 mg were added. Nitrogen displacement was carried out for anaerobic treatment, and 10 mL of a mixed solvent of anhydrous tetrahydrofuran and water (THF:H 2 O = 3:1) was injected into the reaction system, and the deoxygenation operation was carried out by freezing and pumping with liquid nitrogen three times. The temperature was raised to 85 °C until reflux, and after reacting for 10 h, it was cooled to room temperature. It was extracted three times with 30 ml of extraction solution (the extraction solution was dichloromethane:water = 1:1), and the organic phases were collected and combined. Column chromatography separation on silica gel (petroleum ether / ethyl acetate = 100:1) was carried out, and finally a white-pink product SP-T was obtained. 1 The HNMR spectrum is as Figure 4 , and the yield was 55%.

[0062]

[0063] Example 3

[0064] A preparation method of a D-A type photochromic material, comprising:

[0065] 1) Preparation of compound 2

[0066] Compound 2 was prepared by the same method as in Example 1.

[0067] 2) Preparation of SP-Br

[0068] SP-Br was prepared by the same method as in Example 1.

[0069] 3) Preparation of SP-Py

[0070] 200 mg of compound SP-Br was added to a 100 mL two-necked flask, and then pyridine boronic acid with a molar ratio of 4:1 to SP-Br - that is, 276 mg, tetrakis(triphenylphosphine)palladium with a molar ratio of 1:10 to SP-Br - that is, 64.9 mg, and cesium carbonate with a molar ratio of 8:1 to SP-Br - that is, 1463.1 mg were added. It was purged with nitrogen for anaerobic treatment, and 10 mL of a mixed solvent of anhydrous dioxane and water (dioxane:H 2 O = 3:1) was injected into the reaction system. The deoxygenation operation was performed by freezing and pumping with liquid nitrogen 3 times. The temperature was raised to 105 °C until reflux, and after reacting for 10 h, it was cooled to room temperature. It was extracted three times with 30 ml of extraction solution each time (the extraction solution was dichloromethane:water = 1:1), and the organic phases were collected and combined. It was separated by silica gel column chromatography (petroleum ether:ethyl acetate = 5:1), and finally the white-pink product SP-Py was obtained, 1 The HNMR spectrum was as Figure 5 , and the yield was 45%.

[0071]

[0072] Example 4

[0073] A preparation method of a D-A type photochromic material, comprising:

[0074] 1) Preparation of compound 2

[0075] Compound 2 was prepared by the same method as in Example 1.

[0076] 2) Preparation of SP-Br

[0077] SP-Br was prepared by the same method as in Example 1.

[0078] 3) Preparation of SP-BF

[0079] Add 200 mg of compound SP-Br to a 100 mL two-necked flask, then add 149.4 mg of benzofuranboronic acid with a molar ratio of 3:1 to SP-Br, 64.9 mg of tetrakis(triphenylphosphine)palladium with a molar ratio of 1:10 to SP-Br, and 1463.1 mg of cesium carbonate with a molar ratio of 8:1 to SP-Br. Replace the air with nitrogen for anaerobic treatment, and inject 10 mL of a mixed solvent of anhydrous dioxane and water (dioxane:H 2 O = 3:1) into the reaction system. Perform deoxygenation operations by freezing and pumping with liquid nitrogen three times. Heat up to 105 °C until refluxing, react for 10 h, then cool to room temperature. Extract three times with 30 mL of extraction solution each time (the extraction solution is dichloromethane:water = 1:1), collect and combine the organic phases. Separate by silica gel column chromatography (petroleum ether:ethyl acetate = 150:1), and finally obtain a pale yellow product SP-BF, 1 The HNMR spectrum is as shown in Figure 6 , and the yield is 68%.

[0080]

[0081] Dissolve the above product and SP-Br in acetone respectively to prepare dilute solutions, and perform ultraviolet-visible absorption spectroscopy colorimetry with a scanning range from 320 nm to 500 nm. The maximum absorption peaks of the above product and SP-Br are both around 330 nm, as shown in Figure 7 . This is because the conjugation is poor before the photochemical ring-opening, and the delocalization of π electrons between the spiropyran unit and the connected conjugated unit is poor.

[0082] Select two traditional spiropyran molecules, spiropyran molecule SP-NO 2 (purchased commercially) and SP-Br, as controls, and at the same time select the samples prepared in Examples 1-2 for irradiation tests. Irradiate with 365 nm ultraviolet light for 1 min to compare the photochromic effects. The results are as shown in Figure 8 . Among them, no obvious color change was observed for the spiropyran molecule SP-NO 2 (purchased commercially) and SP-Br, while obvious photochromic phenomena occurred for SP-B and SP-Py, and both turned blue-gray.

[0083] Due to the strong photochromic reversibility of the prepared product, it will return to the closed-ring state within several seconds after irradiation in the solution state. Therefore, it is very difficult to monitor the ultraviolet-visible absorption spectrum of this type of product in the open-ring state in the solution state, which also indirectly shows that the photochromic rate and photochromic reversibility of this type of material have been significantly improved.

[0084] Since the molecules are closely packed in the solid powder state, it is difficult to observe the intrinsic color of the material after photochromism. Therefore, the samples prepared in Examples 1-3 were attached to the inner wall of a round-bottom flask by adding a solvent and then spin-drying to remove the solvent, forming a pure solid film. Further, the photochromic properties were tested. The samples were irradiated with a 365 nm ultraviolet lamp for 15 s, and the irradiation vertical distance was 20 cm. The results are shown in the following table:

[0085] Table 1 Color changes of the prepared samples before and after irradiation

[0086]

[0087] As can be seen from the above table, the samples prepared in the examples all exhibited obvious photochromic properties, changing from yellowish-white or pinkish-white to blue within a few seconds, indicating that introducing a conjugated segment into spiropyran to construct a D-A system can not only broaden the photochromic range of the material, but also increase the free volume of the material by introducing large-volume conjugated units, enabling the ring-opening and ring-closing processes to occur even in the pure solid state, thereby enhancing the photochromic reversibility in the solid state and effectively improving the photochromic performance of the material.

[0088] In addition, the photochromic effect of SP-B is not as obvious as that of SP-T and SP-Py. This is because the dihedral angle between the benzene ring and the adjacent conjugated system is much larger than that between thiophene and pyridine; at the same time, due to the push-pull electron effect, the intramolecular charge transfer (ICT) ability of SP-T and SP-Py is also stronger than that of SP-B. Eventually, the conjugation degree and the π-electron ionization ability of SP-B before and after ring-opening are much weaker than those of SP-T and SP-Py. Therefore, during the irradiation with 365 nm ultraviolet light, the photochromic properties such as the photochromic rate and the degree of color change of SP-T and SP-Py are significantly stronger than those of SP-B. The research results show that introducing a heterocyclic conjugated system can further enhance the photochromic properties of this type of D-A spiropyran molecular material.

[0089] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope defined in the claims.

Claims

1. A D-A type photochromic material, characterized in that, the structure of the material is:

2. The preparation method of the D-A type photochromic material according to claim 1, characterized in that, the material is prepared by the following reaction:

3. The preparation method of the D-A type photochromic material according to claim 1, characterized in that, the preparation method includes: adding SP-Br into a reaction vessel, and the structure of the SP-Br is: Then add pyridine boronic acid and tetrakis(triphenylphosphine)palladium, and then add cesium carbonate or potassium carbonate. Under anaerobic conditions, add an appropriate amount of mixed solvent to the reaction system, heat up to 70-120 °C to the reflux state, react for 4-10 h, then cool to room temperature, extract 1-4 times with an appropriate amount of organic solvent respectively, collect and combine the organic phases, separate by silica gel column chromatography, and dry to obtain the product.

4. The preparation method of the D-A type photochromic material according to claim 2 or 3, characterized in that, the SP-Br is prepared by the following reaction:

5. The preparation method of the D-A type photochromic material according to claim 4, characterized in that, the preparation method of the SP-Br is: 1) Add compound 1 into a reaction vessel, and the structural formula of the compound 1 is: Then add methyl iodide in a molar ratio of 2-3:1, add anhydrous chloroform under anhydrous and anaerobic conditions, heat up and stir to reflux; after reacting for 5-8 h, cool to room temperature, extract 1-4 times with an appropriate amount of organic solvent, collect and combine the organic phases, separate by silica gel column chromatography, and dry to obtain a yellow product; 2) Charge the above yellow product into a reaction vessel, then add 5-bromosalicylaldehyde in a molar ratio of 0.8-1.2:1, add anhydrous ethanol under anhydrous and anaerobic conditions, then heat up to 50-60 °C, slowly dropwise add piperidine, heat up and stir to reflux; after reacting for 3-8 h, cool to room temperature, extract 1-4 times with an appropriate amount of organic solvent, collect and combine the organic phases, separate by silica gel column chromatography, and dry to obtain the product.

6. The preparation method of the D-A type photochromic material according to claim 3, characterized in that, the molar ratio of the pyridine boronic acid to the SP-Br is 3:1, the molar ratio of the tetrakis(triphenylphosphine)palladium to the SP-Br is 1:10, and the molar ratio of the cesium carbonate or potassium carbonate to the SP-Br is 8:

1.

7. The preparation method of the D-A type photochromic material according to claim 3, characterized in that, before the heating operation, freeze-pump with liquid nitrogen 2-5 times to remove oxygen again.

8. The preparation method of the D-A type photochromic material according to claim 5, characterized in that, the organic solvent in steps 1)-2) is dichloromethane.

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