Preparation method and application of temperature-induced dynamic adjustable fluorescent hydrogel

Abstract

The application provides a preparation method and application of a temperature-induced dynamic adjustable fluorescent hydrogel, and belongs to the technical field of fluorescent hydrogels. In a nitrogen atmosphere, 4,5-dibromoresorcinol is reacted with TPE-Bpin having an AIE effect to obtain TPECA, and the TPECA is photopolymerized with MBAA to synthesize a covalently crosslinked polyacrylamide fluorescent hydrogel in one step; the polyacrylamide fluorescent hydrogel is coordinated with Eu 3+ , to obtain a temperature-induced dynamic adjustable fluorescent hydrogel. The hydrogel of the application exhibits excellent thermal stability and response characteristics to temperature stimulation, and a powerful information encryption application is further constructed by synergistic effect of the excellent characteristics, and the application supports on-demand information decryption.

Description

Technical Field

[0001] This application relates to a method for preparing and applying a temperature-induced dynamically tunable fluorescent hydrogel, belonging to the field of fluorescent hydrogel technology. Background Technology

[0002] Chemical-based anti-counterfeiting technologies utilize color-emitting or luminescent materials for information encryption. These materials offer numerous advantages, including easy accessibility and a wide range of adjustable colors. To date, various color-emitting and luminescent materials have been developed into security inks or solid data carriers (such as polymer films).

[0003] However, compared to traditional materials with static color or light emission output, advanced materials with dynamic color or light emission properties offer superior performance and enable higher levels of security or larger amounts of data encoding. Therefore, recent research trends have shifted towards stimulus-responsive materials with multi-mode optical properties, which facilitate ideal on-demand decryption, allowing different information to be displayed under varying conditions.

[0004] In recent years, lanthanide compounds and viable ligands have become popular fluorescent materials due to their superior properties, including high luminescence quantum yield, sharp emission bands, and excellent photochemical stability. Stimulus-responsive fluorescent hydrogels can be flexibly modulated based on their chemical structure and composition, sensitivity to external stimuli, and dynamic fluorescence characteristics. Summary of the Invention

[0005] In view of this, this application provides a method for preparing temperature-induced dynamically tunable fluorescent hydrogels, based on Eu 3+ Due to the dynamic coordination with TPECA, the hydrogel exhibits a good reversible response to temperature stimulation in terms of optical properties.

[0006] Specifically, this application is implemented through the following scheme: A method for preparing a temperature-induced dynamically tunable fluorescent hydrogel, comprising the following steps: Step 1: Under a nitrogen atmosphere, 4,5-dibromocatechol (CABr) reacts with TPE-Bpin, which exhibits the AIE effect, to obtain TPECA.

[0007] The structural formula of the TPE-Bpin is: .

[0008] The structural formula of the TPECA is: .

[0009] Step 2, weigh acrylamide, N , N'-Methylenebisacrylamide (MBAA), 1-hydroxycyclohexylphenyl ketone and TPECA were photoinitiated and polymerized in one step to synthesize a covalently cross-linked polyacrylamide fluorescent hydrogel, denoted as PAM-TPECA.

[0010] Step 3: Under room temperature conditions, the polyacrylamide fluorescent hydrogel reacts with Eu... 3+ After coordination and washing with deionized water, a temperature-induced dynamically tunable fluorescent hydrogel was obtained, denoted as PAM-TPECA-Eu.

[0011] Furthermore, as a preferred option: In step one, The molar ratio of 4,5-dibromocatechol to TPE-Bpin, which has an AIE effect, is 1:2.0 to 2.5.

[0012] Step one also involves adding an alkaline agent, a palladium catalyst, and dioxane. The reaction can be specifically configured as follows: Under a nitrogen atmosphere, the alkaline agent, dioxane, 4,5-dibromocatechol, TPE-Bpin (with AIE effect), and solvent are stirred until homogeneous. Then, the palladium catalyst is added, and the reaction is carried out at 70–80°C. After cooling to room temperature, the reaction is quenched with water and extracted to purify and obtain TPECA. More preferably: The palladium catalyst is either tetra(triphenylphosphine)palladium or 1,1'-bis(diphenylphosphine)ferrocene palladium(II) dichloromethane complex.

[0013] The alkaline agent is either potassium carbonate or potassium acetate.

[0014] The TPE-Bpin is synthesized as follows: under a nitrogen atmosphere, it is obtained by reacting 4,4'4"-(2-(4-bromophenyl)ethylene-1,1,2-triyl)tris(methoxybenzene) with pinacol diboronate in the presence of a palladium catalyst. More preferably: The molar ratio of 4,4'4"-(2-(4-bromophenyl)ethylene-1,1,2-triyl)tri(methoxybenzene) to pinacol diboronic acid ester is 1:2.0 to 2.3.

[0015] The 4,4'4"-(2-(4-bromophenyl)ethylene-1,1,2-triyl)tri(methoxybenzene) was obtained as follows: under a nitrogen atmosphere, zinc granules were added to a reaction vessel, followed by the addition of a solvent (including but not limited to tetrahydrofuran) under a nitrogen stream. The mixture was cooled to approximately 0–5°C, titanium tetrachloride was injected, and the mixture was brought back to room temperature with stirring. The mixture was then heated to 60–80°C and refluxed for 2–5 hours. The resulting mixed reaction solution was cooled to approximately 0–5°C, and 4,4'-dimethoxybenzophenone and 4-bromo-4'-methoxybenzophenone were dissolved in a solvent (including but not limited to tetrahydrofuran) and added to the mixed reaction solution. The mixture was refluxed until complete conversion, quenched with a saturated ammonium chloride aqueous solution, extracted, dried, concentrated by rotary evaporation, and purified to obtain 4,4'4"-(2-(4-bromophenyl)ethylene-1,1,2-triyl)tri(methoxybenzene), denoted as TPE-Br.

[0016] The preparation method of 4-bromo-4'-methoxybenzophenone is as follows: anisole is added to an anhydrous dichloromethane solution of 4-bromobenzoyl chloride and aluminum chloride, the reaction is carried out in a nitrogen atmosphere at 0-5℃, quenched with hydrochloric acid solution, diluted with dichloromethane and separated, the aqueous layer is extracted with dichloromethane, the organic layers are combined, dried, concentrated by rotary evaporation, and purified to obtain 4-bromo-4'-methoxybenzophenone.

[0017] The 4,5-dibromocatechol was synthesized as follows: a solvent (including but not limited to dichloromethane) was added to the catechol, stirred and cooled to 0-5°C, liquid bromine was added dropwise, the mixture was heated to room temperature and stirred continuously, the reaction mixture was washed with saturated sodium bicarbonate solution (until no more bubbles were observed), sodium metabisulfite solution (until no more bubbles were observed) and water, the organic layer was dried and filtered, the solvent was removed under reduced pressure, and the mixture was passed through a column to obtain 4,5-dibromocatechol.

[0018] In step two, the polymerization reaction is initiated by ultraviolet light. More preferably, the wavelength of the ultraviolet light is 350–400 nm.

[0019] In step three, The Eu 3+ It comes from any one of Eu(NO3)3, EuCl3, and Eu2(SO4)3.

[0020] The Eu 3+ The concentration ranges from 0.095 to 0.105 mol / L.

[0021] This application successfully prepared a programmable fluorescent hydrogel, PAM-TPECA-Eu, with multi-state fluorescence switching capability by combining aggregation-induced emission (AIE) mechanism with dynamic lanthanide metal-ligand coordination. The introduction of coordination bonds makes the hydrogel network more compact, while the hydrogel exhibits excellent thermal stability and temperature-responsive characteristics. Heating causes the hydrogel fluorescence color to change from blue to red, and this change is highly reversible.

[0022] Based on the aforementioned excellent optical properties and the change in fluorescence emission color gradient under different ambient temperatures, the fluorescent hydrogel can be applied to fields such as information encryption and ambient temperature monitoring. Therefore, the second objective of this application is to provide the application of the aforementioned dynamically adjustable fluorescent hydrogel in environmental interactive color-changing and dynamic information anti-counterfeiting labels, thereby constructing a powerful information encryption application that supports on-demand information decryption. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application.

[0024] Figure 1 This is a schematic diagram of the synthesis process of this application.

[0025] Figure 2 The figures show the fluorescence emission spectra of different hydrogels (Ex=365 nm). Part (a) of the figure represents PAM-TPECA-Eu and PAM-TPECA hydrogels, and part (b) represents PAM-Eu and PAM hydrogels.

[0026] Figure 3 Fourier transform infrared spectra of PAM-TPECA and PAM-TPECA-Eu hydrogels.

[0027] Figure 4 The XPS spectra of PAM-TPECA and PAM-TPECA-Eu hydrogels are shown. Part (a) in the figure represents O 1s and part (b) represents N 1s.

[0028] Figure 5The images show the SEM morphology of different hydrogels. Part (a) shows PAM-TPECA with a 200µm scale bar, part (b) shows PAM-TPECA (1 mg)-Eu with a 200µm scale bar, part (c) shows PAM-TPECA (5 mg)-Eu with a 200µm scale bar, part (d) shows PAM-TPECA with a 100µm scale bar, part (e) shows PAM-TPECA (1 mg)-Eu with a 100µm scale bar, and part (f) shows PAM-TPECA (5 mg)-Eu with a 100µm scale bar.

[0029] Figure 6 The image shows the EDS mapping spectrum of PAM-TPECA-Eu hydrogel. Part (a) of the image shows PAM-TPECA-Eu with a 50µm scale bar, and part (b) shows the EDS mapping spectrum of europium.

[0030] Figure 7 Tensile stress-strain curves of PAM-TPECA and PAM-TPECA-Eu hydrogels.

[0031] Figure 8 The TGA curve of PAM-TPECA-Eu hydrogel is shown.

[0032] Figure 9 The effect of temperature on the fluorescence of PAM-TPECA-Eu hydrogel (Ex=365 nm) is shown in the figure. Part (a) is a photograph of PAM-TPECA-Eu taken at different temperatures under UV light in a dark environment; part (b) is the fluorescence emission spectrum of PAM-TPECA-Eu at 25℃ and 100℃; and part (c) is the CIE chromaticity diagram of PAM-TPECA (25℃), PAM-TPECA-Eu (25℃) and PAM-TPECA-Eu (100℃) hydrogels after UV-Vis irradiation.

[0033] Figure 10 Photographs of the temperature-induced color change process of PAM-TPECA-Eu hydrogel under dark conditions and 254nm ultraviolet light.

[0034] Figure 11 The PAM-TPECA-Eu hydrogel, used as a digital information encryption tag, displays different encrypted information under dark conditions and under 254 nm and 365 nm ultraviolet light irradiation and heating conditions. Detailed Implementation

[0035] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the technical solutions in the embodiments of this application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit the technical solutions of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0036] Table 1: Raw materials and reagents used in this application .

[0037] Table 2: Characterization and testing instruments used in this application .

[0038] The preparation and application effects are illustrated below with specific examples.

[0039] This embodiment provides a method for preparing a temperature-induced dynamically tunable fluorescent hydrogel. The embodiment of this application is described with reference to Figure 1.

[0040] Step 1: Synthesis of 4,4,5,5-tetramethyl-2-(4-(1,2,2-tris(4-methoxyphenyl)vinyl)phenyl)-1,3,2-dioxoborhecyclopentane Synthesis of S1,4-bromo-4'-methoxybenzophenone Anisole (6.28 g, 58.1 mmol) was added to an anhydrous dichloromethane solution of 4-bromobenzoyl chloride (8.02 g, 36.8 mmol) and aluminum chloride (7.31 g, 55.3 mmol), and the reaction was carried out at 0 °C under a nitrogen atmosphere for 4 h. The reaction was quenched with hydrochloric acid solution (100 ml, 2 M). The solution was diluted with dichloromethane (30 ml) and separated. The aqueous layer was extracted with dichloromethane, and the organic layers were combined, washed with anhydrous magnesium sulfate, dried, concentrated by rotary evaporation, and purified by silica gel column chromatography (petroleum ether:dichloromethane = 1:3, v / v) to give a pure white powder (9.89 g, yield 92.3%). The pure white powder is 4-bromo-4'-methoxybenzophenone.

[0041] Synthesis of S2,4,4'4"-(2-(4-bromophenyl)ethylene-1,1,2-triyl)tris(methoxybenzene) Under a nitrogen atmosphere, zinc granules (6.6 g, 50 mmol) were added to a 250 mL two-necked flask, followed by 60 mL of tetrahydrofuran under a nitrogen stream. The mixture was cooled to 0 °C, and titanium tetrachloride (5 mL, 45 mmol) was slowly added using a syringe. The mixture was then brought back to room temperature and stirred for 0.5 h, followed by reflux at 70 °C for 2.5 h. The mixture was cooled to 0 °C, and 4,4'-dimethoxybenzophenone (8.01 g, 33.1 mmol) and 4-bromo-4'-methoxybenzophenone (10.02 g, 34.4 mmol) dissolved in 60 mL of tetrahydrofuran were added to the mixture. The mixture was refluxed until thin-layer chromatography showed complete conversion. The reaction was quenched with saturated ammonium chloride aqueous solution and extracted with dichloromethane. The organic layer was dried over anhydrous magnesium sulfate for 2 h, concentrated by rotary evaporation, and purified by silica gel column chromatography (petroleum ether: dichloromethane = 1:3, v / v) to give a yellow solid (4.07 g, yield 24.5%). The yellow solid was 4,4'4"-(2-(4-bromophenyl)ethylene-1,1,2-triyl)tris(methoxybenzene) (TPE-Br).

[0042] Synthesis of S3, TPE-Bpin Potassium acetate (0.78 g, 8.0 mmol), pinacol diborate (1.02 g, 4.0 mmol), and TPE-Br (1.01 g, 2.0 mmol) were added to a 250 mL two-necked flask. Under a nitrogen atmosphere, 20 mL of dioxane was added, and the mixture was stirred magnetically for 30 s. Then, 40 mg (0.05 mmol) of a 1,1'-bis(diphenylphosphine)ferrocene palladium(II) dichloromethane complex was added, and the mixture was heated and stirred at 80 °C for 24 h under a nitrogen atmosphere. After the reaction mixture cooled to room temperature, the reaction was quenched with water and extracted with dichloromethane. The organic layer was separated by washing with water, dried over sodium sulfate, and the solvent was removed under reduced pressure. The solution was separated by column chromatography (petroleum ether:dichloromethane = 1:1, v / v) to give a yellow solid (0.81 g, yield 29.92%). The yellow solid is 4,4,5,5-tetramethyl-2-(4-(1,2,2-tris(4-methoxyphenyl)vinyl)phenyl)-1,3,2-dioxoboranecyclopentane (TPE-Bpin).

[0043] Step 2: Synthesis of 4,5-dibromocatechol Weigh 5.02 g (45.6 mmol) of catechol into a 250 mL two-necked flask, add 100 mL of dichloromethane, stir and cool to 0 °C. Then, add dropwise 15 mL of a dichloromethane solution of liquid bromine (15.66 g, 98 mmol). Heat the solution to room temperature and stir continuously for 72 h. Wash the reaction mixture with saturated sodium bicarbonate solution (until no more bubbling is observed), sodium metabisulfite solution (until no more bubbling is observed), and water (100 mL). Dry the organic layer with sodium sulfate and filter, removing the solvent under reduced pressure. Flash column chromatography at 25 °C (petroleum ether:dichloromethane = 1:1) yields a grayish-white solid (0.81 g, yield 30.78%). The grayish-white solid is 4,5-dibromocatechol (CABr).

[0044] Step 3: Synthesis of 4,4"-bis(1,2,2-tris(4-methoxyphenyl)vinyl)-[1,1':2',1"-terphenyl]-4',5'-diol Potassium carbonate (0.078 g, 0.8 mmol), 4,5-dibromocatechol (0.10 g, 0.2 mmol), and TPE-Bpin (0.50 g, 0.46 mmol) were added to a 250 mL two-necked flask. Under a nitrogen atmosphere, 21 mL of dioxane, 21 mL of water, and 7 mL of ethanol were added. After stirring magnetically for 30 s, 1,1'-bis(diphenylphosphine)ferrocene palladium(II) dichloromethane complex (16 mg, 0.02 mmol) was added. The mixture was heated at 85 °C for 24 h under a nitrogen atmosphere. After the reaction solution cooled to room temperature, the reaction was quenched with water and extracted with dichloromethane. Separation was performed by column chromatography (petroleum ether:ethyl acetate = 1:1, v / v) to give a yellow solid (25 mg, yield 13.14%). The yellow solid is 4,4"-bis(1,2,2-tris(4-methoxyphenyl)vinyl)-[1,1':2',1"-terphenyl]-4',5'-diol (TPECA).

[0045] Step 4: Synthesis of PAM-TPECA Weigh out 1.066 g of acrylamide. N , N '-Methylenebisacrylamide (MBAA) (4.5 mg), 1-hydroxycyclohexylphenyl ketone (30.6 mg), and TPECA (1 mg) were dissolved in 2.5 ml of water and 0.5 ml of tetrahydrofuran, respectively, and polymerized under 365 nm UV light for 1.5 min to obtain fluorescent hydrogel PAM-TPECA.

[0046] Step 5: Preparation of PAM-TPECA-Eu PAM-TPECA was soaked in Eu(NO3)3 (0.1M) solution at room temperature for 30 min, and washed three times with deionized water to obtain Eu-containing... 3+ The hydrogel PAM-TPECA-Eu.

[0047] The hydrogels prepared by the above method were subjected to performance testing, and the results are as follows: 1) Fluorescence emission spectrum Fluorescence emission spectroscopy of PAM-TPECA-Eu was performed at Ex=365 nm, with PAM-TPECA, PAM-Eu, and PAM as controls. Figure 2 As shown, AM-TPECA-Eu possesses a typical three-dimensional network structure: a polyacrylamide network cross-linked by chemical bonds and metal coordination. When Eu is coordinated onto the hydrogel... 3+ Subsequently, its emission intensity increased, due to AM-Eu 3+ The cross-linking results in a more compact three-dimensional network (see...). Figure 2 (as shown in part (a) of the document), this can be seen from Figure 2 The phenomenon shown in (b) that the fluorescence intensity of PAM-Eu is much greater than that of PAM indicates that AM-Eu... 3+ The cross-linking makes the PAM clusters more compact, and due to the cluster-induced emission effect and the hydrogen bond-induced emission effect, its fluorescence emission intensity becomes greater, coupled with TPECA-Eu 3+ The formation of these factors leads to more severe aggregation of AIE luminescent groups.

[0048] 2) Fourier transform infrared spectroscopy To further confirm Eu 3+ Successful coordination was achieved, and Fourier transform infrared spectroscopy was performed on freeze-dried PAM-TPECA and PAM-TPECA-Eu hydrogel samples. Figure 3 As shown: The stretching vibration frequency of C=O in AM ranges from 1601 cm⁻¹ -1 Moved to 1598 cm -1 The stretching vibration frequency of C−O in TPECA ranges from 1186 cm⁻¹ -1 Moved to 1183 cm -1 This indicates that Eu 3+ Metal coordination interactions were formed between AM and TPECA.

[0049] 3) X-ray photoelectron spectroscopy X-ray photoelectron spectra of two hydrogels, PAM-TPECA and PAM-TPECA-Eu, after freeze-drying were measured, further revealing the metal-ligand coordination interaction. Figure 4As shown: The O 1s spectrum of the PAM-TPECA hydrogel can be fitted to two peaks, corresponding to C=O and C−O respectively (see...). Figure 4 (a) of the text); the N 1s spectrum can be fitted to a single peak, corresponding to N=O (see part (a)). Figure 4 (part (b) in the text). However, when coordinated with Eu 3+ Subsequently, the appearance of a new peak in the O 1s spectrum indicated the presence of O−Eu, while the N 1s spectrum further supported the formation of N−Eu in the PAM-TPECA-Eu hydrogel. XPS results of O 1s and N 1s confirmed that AM and TPECA were involved in the coordination process.

[0050] 4) Scanning electron microscope images Scanning electron microscopy (SEM) images of freeze-dried PAM-TPECA, PAM-TPECA (1 mg)-Eu, and PAM-TPECA (5 mg)-Eu were determined, respectively. Figure 5 As shown, the PAM-TPECA hydrogel exhibits a loose and porous cross-linked network structure (see Figure 1). Figure 5 In sections (a) and (d), in contrast to the smaller pore structure in PAM-TPECA-Eu, it can be observed that as the TPECA content increases, the pores in the hydrogel become smaller and the pore structure becomes more numerous. This is attributed to the high density of acrylamide and Eu. 3+ And TPECA and Eu 3+ The formation of metal-ligand coordination between them.

[0051] 5) EDS mapping spectrum The EDS mapping spectra of the freeze-dried PAM-TPECA-Eu hydrogel samples were determined, as shown below. Figure 6 As shown, Eu in the sample is uniformly distributed in the hydrogel, further illustrating that Eu... 3+ Successful matching.

[0052] 6) Tensile stress-strain curve The tensile stress-strain curves of PAM-TPECA and PAM-TPECA-Eu hydrogels were measured respectively, and the results are as follows: Figure 7 As shown: Eu coordination on hydrogel 3+ Subsequently, the elongation at break increased from 16% to 73%, and the maximum tensile stress increased from 0.2 MPa to 0.7 MPa, indicating that Eu... 3+ The coordination with the hydrogel enhances its mechanical properties, mainly due to AM-Eu. 3+ The formation of coordination crosslinks leads to a more compact hydrogel network, and this dynamic metal-ligand coordination interaction can dissipate some of the tensile stress, making the hydrogel less prone to breakage.

[0053] 7) Thermogravimetric analysis The thermal stability of the PAM-TPECA-Eu hydrogel was investigated by TGA after drying at 70 ℃. Figure 8 As shown, when the temperature rises from room temperature to 100℃, there is only about 1% mass loss, which may be due to the evaporation of residual solvent in the hydrogel; when the temperature continues to rise to 202℃, the network structure of the hydrogel begins to decompose, indicating that the hydrogel has good thermal stability.

[0054] 8) Temperature-responsiveness of hydrogels The PAM-TPECA-Eu hydrogel was heated at 30 °C in 10 °C increments and then irradiated with a 254 nm UV lamp in the dark. Images of the hydrogel at different temperatures were then captured. The results are as follows: Figure 9 As shown in section (a), the hydrogel exhibits blue fluorescence of TPECA when unheated. When heated to 60 °C, the hydrogel begins to show red fluorescence, and the fluorescence color completely turns red when heated to 100 °C. To verify the reversibility of its temperature-induced color change, the hydrogel temperature was restored to 30 °C. After half an hour, the fluorescence color returned to blue, indicating that the temperature response behavior of PAM-TPECA-Eu is reversible.

[0055] The fluorescence emission spectra of the PAM-TPECA-Eu hydrogel were measured at 25℃ and 100℃ under the condition of Ex=365 nm, and the results are as follows. Figure 9 As shown in section (b): the emission peak intensity at 610 nm increases significantly at 100 °C, which belongs to Eu 3+ The launch peak.

[0056] Under the condition of Ex=365 nm, the CIE colorimetric diagrams of three hydrogels, PAM-TPECA (25℃), PAM-TPECA-Eu (25℃), and PAM-TPECA-Eu (100℃), were measured after UV-Vis irradiation. The results are as follows: Figure 9 As shown in section (c): When the PAM-TPECA-Eu hydrogel is heated from 25 °C to 100 °C, the fluorescence color changes significantly, from blue to red.

[0057] The above results indicate that the PAM-TPECA-Eu hydrogel exhibits excellent color changes upon heating. This is because heating intensifies the molecular thermal motion of TPECA, altering its conformation and the relationship between TPECA and Eu. 3+ The distance or relative orientation of TPECA leads to more Eu 3+Coordination occurs, enhancing the energy transfer efficiency between the two. TPECA, as a UV-absorbing ligand, achieves Eu absorption through a ligand-to-metal energy transfer process, known as the "antenna effect." 3+ It emits red fluorescence. Additionally, water molecules are Eu... 3+ A strong fluorescence quencher, at 100 °C, causes partial evaporation of free or coordinated water within the hydrogel, reducing the influence of water molecules on Eu. 3+ The quenching of luminescence, thus making Eu 3+ The red fluorescence emission was significantly enhanced.

[0058] 9) Information encryption applications of hydrogels Because the PAM-TPECA-Eu hydrogel in this embodiment has temperature-responsive characteristics and unique multicolor fluorescence conversion capabilities, it can be applied in the fields of advanced information encryption and on-demand decryption.

[0059] Figure 10 To demonstrate the application of PAM-TPECA-Eu in environmentally interactive color change: The hydrogel was cut into tulip flower shapes, and leaves were drawn on paper using a commercially available green fluorescent dye. The entire device was then heated. In a dark environment, illuminated with a 254 nm UV lamp, it was observed that at 20 °C, the fluorescence intensity of the flower was very weak, and the fluorescence color was almost invisible. As the temperature increased, the flower color first turned yellow, then orange, and when heated to 100 °C, the fluorescence color turned red, with the fluorescence emission intensity gradually increasing during this process. Furthermore, due to the Eu... 3+ The coordination with TPECA is highly reversible, and the entire process can be repeated multiple times.

[0060] Figure 11 To demonstrate the effectiveness of PAM-TPECA-Eu in dynamic information anti-counterfeiting labels: First, three different hydrogels were prepared and integrated, including PAM-TPECA (green block), PAM-TPECA-Eu (yellow block), and PAM-Eu (red block). Each hydrogel was cut into strips (10×2×2 mm) and programmed with the encrypted information number "888" to obtain the corresponding anti-counterfeiting label. Under visible light, the label displays the number "888". In a dark environment, irradiation with 365 nm and 254 nm ultraviolet light respectively, both display the number "626". Heating the label to 100 ℃ further improved the display. Under 365 nm ultraviolet light, the information remained unchanged as "626", while under 254 nm ultraviolet light, it displayed "254". This shows that irradiation with 254 nm and 365 nm ultraviolet light followed by heating revealed different encrypted information, thus achieving the purpose of on-demand decryption.

[0061] The above process first synthesized the target fluorescent molecule TPECA, then synthesized a covalently cross-linked PAM-TPECA hydrogel using a one-pot method, and finally combined it with Eu... 3+ Coordination was performed to obtain PAM-TPECA-Eu hydrogel, and its structure and properties were characterized by fluorescence emission spectroscopy and Fourier transform infrared spectroscopy, demonstrating that Eu... 3+ Successful coordination of PAM-TPECA-Eu was demonstrated, and its thermal stability was characterized by thermogravimetric analysis. Temperature-responsive experiments showed that the hydrogel exhibited a significant change in fluorescence color upon heating. Utilizing the multicolor fluorescence conversion capability of the designed PAM-TPECA-Eu hydrogel, it demonstrated excellent performance in environmentally interactive color-changing applications and dynamic information anti-counterfeiting label applications.

[0062] The above-described embodiments are merely illustrative of several feasible implementations of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention, nor are the embodiments intended to limit the scope of protection in the claims of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention. All equivalent implementations or changes that do not depart from the present invention should be included in the technology of the present invention.

Claims

1. A method for preparing a temperature-induced dynamically tunable fluorescent hydrogel, characterized in that, The steps are as follows: Step 1: Under a nitrogen atmosphere, 4,5-dibromocatechol reacts with TPE-Bpin, which exhibits the AIE effect, to obtain TPECA. The structural formula of the TPE-Bpin is: , The structural formula of TPECA is: ; Step 2: Photoinitiated polymerization of TPECA, acrylamide, and MBAA to synthesize covalently cross-linked polyacrylamide fluorescent hydrogel in one step; Step 3, polyacrylamide fluorescent hydrogel and Eu 3+ Coordination yields temperature-induced dynamically tunable fluorescent hydrogels.

2. The method for preparing a temperature-induced dynamically tunable fluorescent hydrogel according to claim 1, characterized in that, In step one, the molar ratio of 4,5-dibromocatechol to TPE-Bpin, which has an AIE effect, is 1:2.0 to 2.

5.

3. The method for preparing a temperature-induced dynamically tunable fluorescent hydrogel according to claim 1, characterized in that, In step one, under a nitrogen atmosphere, the alkaline agent, dioxane, 4,5-dibromocatechol, TPE-Bpin with AIE effect, and solvent are stirred evenly, and then a palladium catalyst is added. The reaction is carried out at 70-80℃, cooled to room temperature, the reaction is quenched with water, and extracted to obtain TPECA.

4. The method for preparing a temperature-induced dynamically tunable fluorescent hydrogel according to claim 3, characterized in that: The palladium catalyst is either tetra(triphenylphosphine)palladium or 1,1'-bis(diphenylphosphine)ferrocene palladium(II) dichloromethane complex, and the alkaline agent is either potassium carbonate or potassium acetate.

5. The method for preparing a temperature-induced dynamically tunable fluorescent hydrogel according to claim 1, characterized in that, The TPE-Bpin is synthesized as follows: under a nitrogen atmosphere, it is obtained by reacting 4,4',4"-(2-(4-bromophenyl)ethylene-1,1,2-triyl)tris(methoxybenzene) with pinacol diboronate in the presence of a palladium catalyst.

6. The method for preparing a temperature-induced dynamically tunable fluorescent hydrogel according to claim 5, characterized in that: The molar ratio of 4,4',4"-(2-(4-bromophenyl)ethylene-1,1,2-triyl)tri(methoxybenzene) to pinacol diboronic acid ester is 1:2.0 to 2.

3.

7. The method for preparing a temperature-induced dynamically tunable fluorescent hydrogel according to claim 1, characterized in that: In step two, ultraviolet light is used to initiate the polymerization reaction.

8. The preparation method according to claim 1, characterized in that: The Eu 3+ The concentration is 0.095–0.105 mol / L.

9. The method for preparing a temperature-induced dynamically tunable fluorescent hydrogel according to claim 1, characterized in that: In step three, the Eu 3+ It comes from any one of Eu(NO3)3, EuCl3, and Eu2(SO4)3.

10. The application of a fluorescent hydrogel prepared by the method of claim 1 in an environmentally interactive color-changing and dynamic information anti-counterfeiting label.

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