Preparation and application of AIE-based high-stretching sp / h8ettb double-network reversible color-changing hydrogel

Abstract

The present application relates to the preparation field of fluorescent hydrogel, in particular to a kind of preparation and application of high tensile SP / H8ETTB double-network reversible color-changing hydrogel based on AIE, which is prepared by using polyvinyl alcohol, carboxymethyl chitosan, spiropyran and tetra [4-(3,5-dicarboxyphenyl)] tetraphenyl ethylene as raw material, first, biodegradable polyvinyl alcohol / carboxymethyl chitosan network skeleton is obtained by physical crosslinking, and spiropyran with multi-stimulus response characteristics and tetra [4-(3,5-dicarboxyphenyl)] tetraphenyl ethylene with aggregation-induced emission characteristics are used as luminescent filler, and polyvinyl alcohol / carboxymethyl chitosan gel network is constructed to construct high tensile hydrogel with photoluminescence and reversible color change.The preparation process of the present application is simple, and a new idea is provided for obtaining high tensile hydrogel with excellent reversible color-changing performance.

Description

Technical Field

[0001] This invention relates to the field of fluorescent hydrogel preparation, specifically to the preparation and application of a highly stretched SP / H8ETTB dual-network reversible color-changing hydrogel based on AIE, which exhibits photoluminescence, reversible photochromism, and high stretching properties. Background Technology

[0002] Fluorescent gels, besides possessing the inherent soft tissue-inspired biomimetic structure, excellent biocompatibility, and good mechanical properties of gel structures, also exhibit additional luminescent properties, making them highly attractive in fields such as biomedicine, optical anti-counterfeiting, and information encryption. However, the application of traditional fluorescent materials is largely limited by aggregation-induced quenching (ACQ). But in 2001, Academician Tang Benzhong's team discovered aggregation-induced emission (AIE), the complete opposite of ACQ. At high concentrations, intramolecular motion is restricted, limiting non-radiative transitions and promoting radiative transitions, leading to enhanced fluorescence. Therefore, AIE hydrogels have been extensively studied in recent years. AIE molecules possess high emission efficiency, excellent photostability and sensitivity, and exhibit enhanced fluorescence properties in the aggregated state. Therefore, compared to traditional fluorescent groups, introducing AIE molecules into a gel network is more likely to form stable fluorescent gels with enhanced light intensity, even at high concentrations. The restricted intramolecular motion of AIE molecules embedded in the gel network, physically or chemically, leads to enhanced emission of AIE hydrogels.

[0003] In recent years, through continuous exploration by researchers, an increasing number of AIE hydrogels have been developed. These AIE hydrogels can respond to stimuli such as light, pH, temperature, and solvents. However, AIE hydrogels that integrate multiple stimuli are still relatively rare. Among them, tetraphenylethylene, phenyl-substituted thiophene, and phenylvinyl anthracene are commonly used AIE molecules. Tetraphenylethylene has attracted widespread attention due to its simple synthesis, easy derivatization, and good stability. Here, we choose tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene (H8ETTB) as the AIE molecule. As a derivative of tetraphenylethylene, it is a typical aggregation-induced emission molecule, exhibiting high luminescence intensity at high concentrations.

[0004] We selected spiropyran (SP) as the functional fluorescent filler. Spiropyran is a fluorescent molecule that responds to various stimuli such as light, pH, and temperature. Under ultraviolet light irradiation or heating, it can transform from a colorless closed-ring SP structure to a colored open-ring anthocyanin structure MC. Under visible light, the open-ring structure can revert back to the closed-ring structure. Because the MC structure is extremely unstable, it quickly transforms into the SP structure, which gives spiropyran an extremely fast color-changing speed.

[0005] By introducing spiropyran molecules with multiple stimulus responses into the AIE hydrogel network, it is hoped that a reversible color-changing hydrogel based on AIE can be constructed, thus broadening the application of AIE hydrogels in fields such as biomedicine, optical anti-counterfeiting, and information encryption. Summary of the Invention

[0006] To address the problem that there are still relatively few AIE hydrogels that integrate multiple stimuli, this invention provides a method for preparing and applying a highly tensile SP / H8ETTB dual-network reversible color-changing hydrogel based on AIE.

[0007] This invention is achieved through the following technical solution: a method for preparing a highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE, comprising the following steps: (1) Preparation of polyvinyl alcohol / carboxymethyl chitosan hydrogel concentrate Polyvinyl alcohol was dissolved in deionized water by stirring and allowed to stand until no bubbles were present. Carboxymethyl chitosan was dissolved in deionized water by stirring. The carboxymethyl chitosan solution was then poured into the polyvinyl alcohol solution. The mixture was heated and stirred to evaporate the water. After standing to remove the bubbles, a concentrated solution was obtained. (2) Preparation of polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene concentrate Tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran were added to N,N-diethylformamide and ultrasonically mixed to obtain a mixed solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran; the mixed solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran was added to the concentrate in step (1), stirred at room temperature, and allowed to stand to remove bubbles to obtain a concentrated solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran; (3) Preparation of polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel A concentrated solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran was extruded into a mold, and the mold was frozen at -40°C for 12 hours. Then it was thawed at room temperature for 12 hours. The freezing and thawing process was repeated three times to obtain polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel.

[0008] As a further improvement to the preparation method of the present invention, step (3) can be replaced by: A concentrated solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran was coated onto a plate to form a thin film, which was then placed at room temperature to obtain a polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel.

[0009] As a further improvement to the preparation method of the present invention, the feeding ratio of polyvinyl alcohol, carboxymethyl chitosan, tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran is 10000:2500:5:5-15.

[0010] As a further improvement to the preparation method of the present invention, the amount of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene is calculated in mg, the amount of N,N-diethylformamide is calculated in ml, and the ratio of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene to N,N-diethylformamide is 5 mg: 2 ml.

[0011] As a further improvement to the preparation method of the present invention, in step (1), polyvinyl alcohol is stirred and dissolved in deionized water at 95°C, and carboxymethyl chitosan is stirred and dissolved in deionized water at 60°C.

[0012] As a further improvement to the preparation method of the present invention, in step (1), the mixture obtained by pouring the carboxymethyl chitosan solution into the polyvinyl alcohol solution is stirred at 60°C to evaporate the water.

[0013] This invention also provides a method for preparing a highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible photochromic hydrogel based on AIE, and the application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel prepared therein in reversible photochromism.

[0014] This invention further provides a method for preparing a highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE, and the application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel in pH color change.

[0015] This invention further provides a method for preparing a highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE, and the application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel that changes color in water / DEF solutions with different water fractions.

[0016] This invention further provides a method for preparing a highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE, and the resulting polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel can be used as an anti-counterfeiting label.

[0017] This invention possesses significant advantages over prior art. Using polyvinyl alcohol (PVA), carboxymethyl chitosan, spiropyran, and tetratetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene as raw materials, a biodegradable PVA / carboxymethyl chitosan network framework is first obtained through physical cross-linking. Spiopyran, with its multi-stimulus responsive properties, and tetratetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene, with its aggregation-induced emission properties, are used as luminescent fillers to construct a photoluminescent, reversibly color-changing, highly tensile hydrogel with the PVA / carboxymethyl chitosan gel network. The preparation process of this invention is simple, providing a new approach to obtaining hydrogels with high tensile strength and excellent reversible color-changing properties. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of the preparation process of polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel.

[0021] Figure 2 The Fourier transform infrared (FTIR) spectra of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel film in Example 2 and the polyvinyl alcohol / carboxymethyl chitosan hydrogel film in the comparative example are shown. Comparing the two FTIR curves reveals that the stretching vibration peak of OH decreases from 3275 cm⁻¹. -1 Redshifted to 3248cm -1 This indicates that the added spiropyran and tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene form a certain number of hydrogen bonds with polyvinyl alcohol and carboxymethyl chitosan; and the increase in the half-peak width after the addition of the filler indicates that the amount of OH increases.

[0022] Figure 3The photoluminescence of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel film in Example 2 under 365nm UV light irradiation and its reversible photochromic properties between 365nm and white light are shown in Figure a). Figure a) shows that the gel film is purplish-pink under 365nm UV light irradiation, demonstrating its photoluminescence properties. Figures b) and c) show that the gel film is pale purple after irradiation with 365nm UV light; after irradiation with white light, the pale purple color fades to pale yellow; this property is maintained even after 10 repetitions, demonstrating the reversible photochromic properties of the gel film.

[0023] Figure 4 Images of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel samples from Example 2 after treatment with hydrochloric acid / sodium hydroxide solutions of different pH values ​​under 365 nm UV light. a) Image shows the hydrogel immediately after treatment with different pH solutions; b) Image shows the hydrogel immediately after treatment with different pH solutions for 1 minute. From the images, we can see that the film exhibits bright yellow fluorescence under UV light after treatment with solutions at pH=5 and 9. After one minute, the bright yellow fluorescence fades, and the film changes to pink fluorescence. This demonstrates the pH-changing color-changing properties of the film.

[0024] Figure 5 Stress-strain curves of polyvinyl alcohol / carboxymethyl chitosan hydrogel (PVA / CMCS hydrogel, comparative example) and polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel samples (Examples 1-3) are shown in the figures. As can be seen from the figures, the tensile strength of the polyvinyl alcohol / carboxymethyl chitosan hydrogel is 11.36 MPa, and the elongation at break is 511%. After adding spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene, the tensile strength is between 6 and 11 MPa, and the elongation at break is between 410% and 600%. This demonstrates the high tensile strength of the polyvinyl alcohol / carboxymethyl chitosan hydrogel. While the addition of spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene slightly reduces the tensile strength, it still retains high tensile strength.

[0025] Figure 6The images show the photoexcitation spectrum (PLE, EM: 375 nm), photoemission spectrum (PL, EX: 300 nm), and images under 365 nm UV light illumination of a polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel film. The left side shows the PLE, with stronger fluorescence intensity around 300 nm and 370 nm. To compare fluorescence intensity under uniform testing conditions, the PL spectrum was measured at an excitation wavelength of 300 nm. The figures show strong emission peaks at 420 nm and 620 nm, with higher emission intensity at a H8ETTB:SP ratio of 1:2.

[0026] Figure 7 Images of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene in water / DEF solutions with different water fractions (volume percentages) were captured under sunlight and 365 nm UV light. In Figure a), the mixed solution is colorless and transparent as the water fraction increases from 10% to 60%. At 70% water fraction, it is a transparent pale green, gradually changing to a cloudy whitish-green as the water fraction increases to 95%. Figure b) shows that under 365 nm UV light, the solution is pale yellow-green with a low aggregation-induced emission (AIE) effect as the water fraction decreases from 10% to 50%. At 80% water fraction, the solution becomes a bright yellow-green, and at 95% water fraction, it becomes a glaring green. This is due to the AIE effect of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene molecules. Detailed Implementation

[0027] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0029] This invention provides a specific embodiment of a method for preparing a highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE, comprising the following steps: (1) Preparation of polyvinyl alcohol / carboxymethyl chitosan hydrogel concentrate Polyvinyl alcohol was dissolved in deionized water by stirring and allowed to stand until no bubbles were present. Carboxymethyl chitosan was dissolved in deionized water by stirring. The carboxymethyl chitosan solution was then poured into the polyvinyl alcohol solution. The mixture was heated and stirred to evaporate the water. After standing to remove the bubbles, a concentrated solution was obtained. (2) Preparation of polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene concentrate Tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran were added to N,N-diethylformamide and ultrasonically mixed to obtain a mixed solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran; the mixed solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran was added to the concentrate in step (1), stirred at room temperature, and allowed to stand to remove bubbles to obtain a concentrated solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran; (3) Preparation of polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel A concentrated solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran was extruded into a mold, and the mold was frozen at -40°C for 12 hours. Then it was thawed at room temperature for 12 hours. The freezing and thawing process was repeated three times to obtain polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel.

[0030] In the above embodiments, hydrogel strips were prepared by freeze-thaw molding. In the embodiments provided by the present invention, the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel strips obtained after freeze-thaw molding have a thickness of approximately 1.2 mm and a width of approximately 10 mm.

[0031] In another embodiment of the present invention, step (3) can be replaced by: coating a concentrated solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran into a thin film on a plate and placing it at room temperature to obtain a polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel. Specifically, the plate is a glass plate, but those skilled in the art can also use other plates with planar structures as the coating surface of the concentrated solution.

[0032] In the above embodiments, the hydrogel film prepared by coating into a thin film is obtained.

[0033] In this invention, spiropyran and tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene are used as fluorescent fillers. N,N-diethylformamide is used to dissolve the fluorescent fillers, and the fillers are added to the hydrogel system through physical blending. Biodegradable polyvinyl alcohol and carboxymethyl chitosan are used as the network framework. A photoluminescent, reversibly color-changing, highly tensile hydrogel is constructed through physical cross-linking caused by stirring. In the polyvinyl alcohol / carboxymethyl chitosan solution, numerous hydrogen bonds can form between the hydroxyl groups on polyvinyl alcohol and carboxymethyl chitosan and between them and water molecules. Thus, a flexible network framework of polyvinyl alcohol / carboxymethyl chitosan solution is obtained through physical cross-linking. Spiropyran and tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene are uniformly dispersed in the polyvinyl alcohol / carboxymethyl chitosan concentrate. The hydroxyl groups on spiropyran and the carboxyl groups on tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene can also form hydrogen bonds with polyvinyl alcohol and carboxymethyl chitosan, resulting in physical cross-linking and a toughening effect.

[0034] In one embodiment of the present invention, the feed ratio of polyvinyl alcohol, carboxymethyl chitosan, tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran is 10000:2500:5:5-15. In one embodiment of the present invention, the mass ratio of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene to spiropyran is 5:5 (1:1). In another embodiment of the present invention, the mass ratio of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene to spiropyran is 5:10 (1:2). In yet another embodiment of the present invention, the mass ratio of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene to spiropyran is 5:15 (1:3).

[0035] In another embodiment of the present invention, the amount of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene is in mg and the amount of N,N-diethylformamide is in ml, and the ratio of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene to N,N-diethylformamide is 5 mg: 2 ml.

[0036] In one embodiment of the present invention, in step (1), polyvinyl alcohol is stirred and dissolved in deionized water at 95°C, and carboxymethyl chitosan is stirred and dissolved in deionized water at 60°C.

[0037] In another embodiment of the present invention, in step (1), the mixture obtained by pouring the carboxymethyl chitosan solution into the polyvinyl alcohol solution is stirred at 60°C to evaporate the water.

[0038] This invention also provides the application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel prepared by the above-mentioned method based on AIE in reversible photochromism.

[0039] This invention further provides the application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel prepared by the above-mentioned method based on AIE in pH color change.

[0040] This invention further provides the application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel prepared by the above-mentioned method based on AIE to change color in water / DEF solutions with different water fractions.

[0041] This invention further provides the application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel prepared by the above-mentioned method based on AIE as an anti-counterfeiting label. Furthermore, when the hydrogel provided by this invention is used as an anti-counterfeiting label, the label exhibits high tensile strength.

[0042] The specific embodiments of the present invention will be described in detail below.

[0043] For clarity, the technical solution of the present invention will be described in detail below through the following examples and comparative examples, and the volume ratio of polyvinyl alcohol / carboxymethyl chitosan concentrate to spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene solution used in the following examples and comparative examples is 10 ml: 2 ml.

[0044] Examples 1-3

[0045] The chemical materials used in this invention are: polyvinyl alcohol, carboxymethyl chitosan, spiropyran, tetrakis[4-(3,5-dicarboxyphenyl)]tetraphenylethylene, N,N-diethylformamide, and deionized water, with quality purity and precision controlled. The combined amounts are as follows: measured in grams, milliliters, and milligrams.

[0046] Polyvinyl alcohol (PVA), solid, 99.5%, 100g ± 0.001g Carboxymethyl chitosan: CMCS, solid, 99.5%, 50g ± 0.001g Spiropyran: SP, solid, 93%, 1g ± 0.001g Tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene: H8ETTB Solid content 98%, 100mg ± 0.1mg N,N-Diethylformamide: DEF, liquid, 99%, 100mL ± 0.001mL Deionized water: H2O, liquid, 99.99%, 5000mL ± 50mL The preparation method of AIE-based high-strength spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel includes the following steps: (a) Preparation of polyvinyl alcohol / carboxymethyl chitosan hydrogel concentrate ① Preparation of polyvinyl alcohol / carboxymethyl chitosan mixed solution Accurately weigh 10g ± 0.001g of polyvinyl alcohol and 2.5g ± 0.001g of carboxymethyl chitosan using an analytical balance. Accurately measure 100ml and 30ml of deionized water using a graduated cylinder, respectively. Then, add 10g of polyvinyl alcohol to 100ml of deionized water while stirring at 95℃, and stir for 1 hour. After the polyvinyl alcohol dissolves, cool the solution to room temperature, cover with plastic wrap, and let it stand until no bubbles remain. Next, add 2.5g of carboxymethyl chitosan to 30ml of deionized water while stirring at 60℃, and stir for 30 minutes to obtain a carboxymethyl chitosan solution.

[0047] ② Preparation of polyvinyl alcohol / carboxymethyl chitosan hydrogel concentrate Slowly pour the carboxymethyl chitosan solution into the polyvinyl alcohol solution. Stir the mixture at 60°C to evaporate the water, concentrate to 50 ml, and let stand to remove air bubbles before use.

[0048] (II) Preparation of polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel ① Preparation of spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene solution Accurately weigh 5 mg ± 0.1 mg of tetrakis[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and 5 mg ± 0.1 mg, 10 mg ± 0.1 mg, and 15 mg ± 0.1 mg of spiropyran using an analytical balance. Accurately measure 2 ml ± 0.001 ml of N,N-diethylformamide liquid using a pipette. Add 5 mg ± 0.1 mg of tetrakis[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and 5 mg ± 0.1 mg (Example 1), 10 mg ± 0.1 mg (Example 2), and 15 mg ± 0.1 mg (Example 3) of spiropyran to the corresponding 2 ml ± 0.001 ml of N,N-diethylformamide solution, respectively. Sonicate for 10 min to obtain a spiropyran / tetrakis[4-(3,5-dicarboxyphenyl)]tetraphenylethylene solution.

[0049] ② Physical blending Take 10 ml of polyvinyl alcohol / carboxymethyl chitosan hydrogel concentrate in a beaker, add the obtained spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene solution to the concentrate, stir at room temperature for 2 h, let stand to remove trace bubbles for later use, and obtain a concentrate of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran.

[0050] ③ Freeze-thaw molded hydrogel strips Using a disposable syringe, slowly squeeze 2 ml of the concentrated solution of tetrakis[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran into a 60mm*10mm*2mm mold, avoiding the formation of air bubbles. Freeze the mold at -40℃ for 12 hours, then thaw at room temperature for 12 hours. Repeat this cycle three times to obtain a polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetrakis[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel strip. The hydrogel strip has a thickness of 1.2mm, a width of 10mm, and a length of 60mm.

[0051] ④ Room temperature forming of hydrogel films The concentrated solution containing tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran was placed on a glass plate, taking care not to generate air bubbles. Then, a thin film was slowly and evenly coated onto the glass plate using a coater. After standing at room temperature for 4 hours, a polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel film was obtained.

[0052] (III) Detection, testing, analysis, and characterization The optical and mechanical properties of the prepared polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel were detected, analyzed, and characterized. Optical property analysis of hydrogels using Edinburgh FLS1000; Mechanical property analysis of hydrogels using a digital multi-dimensional tensile testing machine; Conclusion: The polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel has excellent optical and mechanical properties and can be used for the subsequent preparation of anti-counterfeiting labels. Comparative Example

[0053] A method for preparing a polyvinyl alcohol / carboxymethyl chitosan hydrogel includes the following steps: (1) Preparation of polyvinyl alcohol / carboxymethyl chitosan hydrogel concentrate Accurately weigh 10g ± 0.001g of polyvinyl alcohol and 2.5g ± 0.001g of carboxymethyl chitosan using an analytical balance. Accurately measure 100ml and 30ml of deionized water using a graduated cylinder, respectively. Then, add 10g of polyvinyl alcohol to 100ml of deionized water while stirring at 95℃, and stir for 1 hour until the polyvinyl alcohol dissolves. Afterward, cool the solution to room temperature, cover with plastic wrap, and let it stand until no air bubbles remain. Next, add 2.5g of carboxymethyl chitosan to 30ml of deionized water while stirring at 60℃, and stir for 30 minutes until the carboxymethyl chitosan dissolves. Slowly pour this solution into the polyvinyl alcohol solution. Stir the mixture at 60℃ to evaporate water, concentrate to 50ml, and let it stand to remove air bubbles before use.

[0054] (2) Preparation of polyvinyl alcohol / carboxymethyl chitosan hydrogel Using a disposable syringe, slowly squeeze 2 ml of polyvinyl alcohol / carboxymethyl chitosan concentrate into a 60 mm * 10 mm * 2 mm mold, avoiding the formation of air bubbles. Freeze the mold at -40℃ for 12 hours, then thaw at room temperature for 12 hours. Repeat this cycle three times to obtain polyvinyl alcohol / carboxymethyl chitosan hydrogel strips with a thickness of 1.2 mm, a width of 10 mm, and a length of 60 mm.

[0055] Place the polyvinyl alcohol / carboxymethyl chitosan concentrate onto a glass plate, taking care not to generate air bubbles. Then, use a coater to slowly and evenly coat a thin film onto the glass plate. After standing at room temperature for 4 hours, a polyvinyl alcohol / carboxymethyl chitosan hydrogel film will be obtained.

[0056] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A method for preparing a highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE, characterized in that, Includes the following steps: (1) Preparation of polyvinyl alcohol / carboxymethyl chitosan hydrogel concentrate Polyvinyl alcohol was dissolved in deionized water by stirring and allowed to stand until no bubbles were present. Carboxymethyl chitosan was dissolved in deionized water by stirring. The carboxymethyl chitosan solution was then poured into the polyvinyl alcohol solution. The mixture was heated and stirred to evaporate the water. After standing to remove the bubbles, a concentrated solution was obtained. (2) Preparation of polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene concentrate Tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran were added to N,N-diethylformamide and ultrasonically mixed to obtain a mixed solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran; the mixed solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran was added to the concentrate in step (1), stirred at room temperature, and allowed to stand to remove bubbles to obtain a concentrated solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran; (3) Preparation of polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel A concentrated solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran was extruded into a mold, and the mold was frozen at -40°C for 12 hours. Then it was thawed at room temperature for 12 hours. The freezing and thawing process was repeated three times to obtain polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel.

2. The method for preparing the highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE according to claim 1, characterized in that, Step (3) can be replaced by: A concentrated solution of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran was coated onto a plate to form a thin film, which was then placed at room temperature to obtain a polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel.

3. The method for preparing the highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE according to claim 1 or 2, characterized in that, The feed ratio of polyvinyl alcohol, carboxymethyl chitosan, tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene and spiropyran is 10000:2500:5:5-15.

4. The method for preparing the highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE according to claim 1 or 2, characterized in that, The amount of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene is expressed in mg, and the amount of N,N-diethylformamide is expressed in mL. The ratio of tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene to N,N-diethylformamide is 5 mg: 2 mL.

5. The method for preparing the highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE according to claim 1 or 2, characterized in that, In step (1), polyvinyl alcohol is dissolved in deionized water at 95°C and carboxymethyl chitosan is dissolved in deionized water at 60°C.

6. The method for preparing the highly stretched spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel based on AIE according to claim 1 or 2, characterized in that, In step (1), the mixture obtained by pouring the carboxymethyl chitosan solution into the polyvinyl alcohol solution is stirred at 60°C to evaporate the water.

7. The application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible photochromic hydrogel prepared by the method of AIE-based high-stretch spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel according to claim 1 or 2 in reversible photochromism.

8. The application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel prepared by the method of AIE-based high-stretch spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel according to claim 1 or 2 in pH color change.

9. The application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel prepared by the method of claim 1 or 2, which is based on AIE, to change color in water / N,N-diethylformamide solutions with different water fractions.

10. The application of the polyvinyl alcohol / carboxymethyl chitosan / spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene dual-network reversible color-changing hydrogel prepared by the method of AIE-based high-stretch spiropyran / tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene hydrogel as an anti-counterfeiting label.

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