An absorption-fluorescence dual-mode photochromic gel material and a preparation method and application thereof

Abstract

The application discloses an absorption-fluorescence dual-mode photochromic gel material and a preparation method and application thereof, and belongs to the technical field of intelligent light response materials. The gel material is prepared from a vinyl-functionalized viologen monomer, an acrylic acid salt, divinylbenzene and ammonium persulfate through a polymerization reaction; wherein the vinyl-functionalized viologen monomer is obtained through ion exchange from methyl viologen and the acrylic acid salt. The gel material prepared by the application can change the visible absorption spectrum under ultraviolet light irradiation, leading to a change from yellow to blue, accompanied by a significant quenching of fluorescence intensity, forming an absorption-fluorescence dual-mode photochromic response, and having good cycle stability. The gel material provided by the application has stable structure, intuitive and reliable dual-mode response, and a mild and controllable preparation process, and can be applied to the fields of anti-counterfeiting identification, information display and multi-modal intelligent sensing, and effectively improves the signal identification dimension and use safety.

Description

Technical Field

[0001] This invention belongs to the field of intelligent photoresponsive materials technology, specifically an absorption-fluorescence dual-mode photochromic gel material, its preparation method, and its application. Background Technology

[0002] Photochromic materials are a class of smart materials that undergo reversible color changes under specific wavelengths of light. Their core lies in the reversible transformation of the compound's molecular structure, electronic configuration, or conformation under light radiation, leading to changes in the material's absorption spectrum and macroscopic color. Over the past century, researchers have developed various photochromic systems, including azobenzene, spiropyran, diarylethylene, and viologen, and successfully applied them to fields such as information storage, smart sensing, anti-counterfeiting, and optical devices. With continuous advancements in synthetic chemistry and materials preparation technology, photochromic materials are rapidly developing towards functional diversification, intelligent response, and integrated applications.

[0003] Viologen is a collective term for N,N'-disubstituted-4,4'-bipyridine salts. As a typical electron acceptor, its photochromic mechanism is based on a reversible photoinduced electron transfer process. Under ultraviolet light excitation, the viologen molecule acquires electrons from a neighboring electron donor, changing from a divalent dication state (V... 2+ ) reduced to a monovalent free radical cation state (V + Viologen's color changes from colorless or pale yellow to its characteristic blue or purple. Unlike azobenzene, spiropyran, and diarylethylene compounds, which involve covalent bond breaking and rearrangement, viologen's color change process does not involve chemical bond rearrangement. It is less dependent on the molecular free volume and environmental rigidity, maintaining highly efficient photoresponse characteristics even in confined environments such as thin films, gels, and porous materials. Furthermore, the substituents on the nitrogen atom of viologen can be diversely modified. By controlling the type of substituent, its redox potential, solubility, and intermolecular interactions can be altered, allowing it to function as a functional unit and effectively combine with various materials such as metal-organic frameworks, polymers, and inorganic nanoparticles to construct composite material systems with diverse structures and tunable properties.

[0004] As the performance requirements of fields such as information encryption, intelligent sensing, and anti-counterfeiting labels continue to increase, the limitations of output modes relying solely on single color changes are becoming increasingly apparent. Single signals are easily counterfeited or cracked, lack sufficient recognition dimensions, and cannot meet the urgent needs of advanced information encryption, multi-mode sensing, and advanced anti-counterfeiting for complex response behaviors.

[0005] Therefore, developing novel photochromic materials that combine multiple response signals with excellent stability is crucial for promoting the development of high-security information encryption and multimodal intelligent applications. Summary of the Invention

[0006] The purpose of this invention is to provide an absorption-fluorescence dual-mode photochromic gel material, its preparation method, and its applications. This invention utilizes an ion exchange reaction to transfer methyl viologen cations (MV... 2+ ) and acrylate anions (AA) which also have electron-donating capabilities - By combining these elements, polyvinyl functionalized viologen monomers (MV) were designed and synthesized. 2+ ·Cl - AA - This monomer can achieve a UV-induced dual-mode photochromic response of absorption and fluorescence in solution; further utilizing its polymerizability, MV... 2+ ·Cl - AA - MV-PAA gel was successfully prepared by copolymerizing and crosslinking it into a sodium polyacrylate hydrogel network. Under ultraviolet light irradiation, the MV-PAA gel exhibits a color change from yellow to blue, accompanied by quenching of fluorescence intensity, demonstrating excellent reversibility and cycling stability, and showing promising application potential in anti-counterfeiting labels and information displays.

[0007] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides an absorption-fluorescence dual-mode photochromic gel material, which is prepared by polymerization reaction of raw materials comprising vinyl-functionalized viologen monomer, acrylate, crosslinking agent and initiator; wherein the vinyl-functionalized viologen monomer is formed by ion exchange of methyl viologen and acrylate.

[0008] Preferably, the gel material is a polyacrylic acid hydrogel that achieves a dual-mode response of visible light absorption color change and fluorescence intensity quenching under ultraviolet light irradiation.

[0009] Preferably, the acrylate is sodium acrylate; the crosslinking agent is divinylbenzene; and the initiator is ammonium persulfate.

[0010] Preferably, 3 mL of deionized water is used as the solvent, the amount of vinyl-functionalized viologen monomer is 190~210 mg, preferably 200 mg; the amount of acrylate is 1.7~1.9 g, preferably 1.8 g; the amount of crosslinking agent is 45~55 mg, preferably 50 mg; the initiator is ammonium persulfate, the amount is 8~12 mg, preferably 10 mg; and the molar ratio of methyl viologen to acrylate is 1:(1~3), preferably 1:2.

[0011] Preferably, the ultraviolet light wavelength that triggers photochromism is 200 nm to 400 nm, and more preferably 365 nm.

[0012] Preferably, a characteristic absorption peak appears at 350 nm to 450 nm before illumination, preferably at 400 nm, and a characteristic absorption peak appears at 550 nm to 650 nm after illumination, preferably at 610 nm.

[0013] Preferably, the fluorescence excitation wavelength is 350 nm to 420 nm, more preferably 390 nm, and the fluorescence emission wavelength is 450 nm to 700 nm, more preferably 540 nm.

[0014] Secondly, this invention provides a method for preparing an absorption-fluorescence dual-mode photochromic gel material, comprising the following steps: S1. Methyl viologen and acrylate undergo an ion exchange reaction in a solvent to obtain vinyl-functionalized viologen monomer; S2. Dissolve the vinyl-functionalized viologen monomer, acrylate, crosslinking agent, and initiator in water and mix thoroughly; S3. Heating is used to carry out a polymerization reaction to obtain an absorption-fluorescence dual-mode photochromic gel material.

[0015] Preferably, in step S1, the ion exchange reaction temperature is 15℃~35℃ and the reaction time is 12 h~36 h.

[0016] Preferably, in step S3, the polymerization temperature is 40℃~80℃ and the polymerization time is 4 h~8 h, preferably 60℃ and 6 h.

[0017] Thirdly, the present invention provides an application of an absorption-fluorescence dual-mode photochromic gel material for anti-counterfeiting labels, information storage, smart sensing, information display, or optical devices.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention successfully provides an absorption-fluorescence dual-mode photochromic gel material. This material is copolymerized with vinyl-functionalized viologen monomer and acrylate as the main raw materials, which can fill the functional deficiencies of existing single-signal photochromic materials. It can truly realize a dual-mode response of visible light absorption color change and reversible regulation of fluorescence intensity under ultraviolet light triggering, effectively improving the signal recognition dimension and anti-counterfeiting reliability.

[0019] 2. The gel material prepared by this invention exhibits a distinct color change from yellow to blue under ultraviolet light excitation, accompanied by a significant quenching of fluorescence intensity. The dual-mode signal response is synchronous, intuitive, and stable, and identification and detection can be completed without complex equipment. Furthermore, the viologen units are stably fixed in the hydrogel network in the form of covalent bonds. The material can still maintain good response performance after multiple light-recovery cycles, with outstanding reversibility and cycle stability, which can meet the requirements for repeated use. Attached Figure Description

[0020] Figure 1 MV 2+ ·Cl - AA - Mass spectra; (a) positive ion mode mass spectrum; (b) negative ion mode mass spectrum; Figure 2 MV 2+ ·Cl - AA - In D2O 1 H NMR; Figure 3 Infrared spectrum of MV-PAA gel; Figure 4 XPS spectra of MV-PAA gel; (a) Total spectrum; (b) C 1s; (c) N 1s; (d) O 1s; Figure 5 PXRD of MV-PAA gel; Figure 6 MV 2+ ·Cl - AA - Photoresponse performance spectrum; (a) MV before and after illumination 2+ ·Cl - AA - (a) Visible absorption spectrum and sunlight photograph; (b) MV before and after illumination 2+ ·Cl - AA - Fluorescence spectra and fluorescence photographs; Figure 7 MV 2+ ·Cl - AA - EPR spectra before and after illumination; Figure 8 MV 2+ ·Cl - AA - Cyclic stability performance; (a) Absorption cycle curve; (b) Fluorescence cycle curve; Figure 9 Photoresponse performance spectra of MV-PAA gel; (a) Visible absorption spectrum and sunlight photograph of MV-PAA gel before and after light exposure; (b) Fluorescence spectrum and fluorescence photograph of MV-PAA gel before and after light exposure; Figure 10 EPR spectra of MV-PAA gel before and after light exposure; Figure 11 Cyclic stability of MV-PAA gel; (a) Absorption cycle curve; (b) Fluorescence cycle curve. Detailed Implementation

[0021] 1. Experimental Section 1.1 Reagents and Instruments (1) Reagents required for the experiment (as shown in Table 1): Table 1 Reagents required for the experiment (2) Equipment required for the experiment (as shown in Table 2): Table 2 Experimental Equipment 1.2 Material Synthesis (1) MV 2+ ·Cl - AA - Synthesis Accurately weigh 257 mg of methyl viologen (MVCl2) and place it in a 50 mL single-necked round-bottom flask. Add 15 mL of deionized water and stir magnetically at room temperature until fully dissolved. Then, according to the molar ratio n(MVCl2):n(NaAA) = 1:2, accurately weigh 188 mg of sodium acrylate (NaAA) and add it to the above solution, continuing to stir until completely dissolved. After the system is thoroughly mixed, slowly add 15 mL of methanol and seal the flask. Under a nitrogen atmosphere, react magnetically at room temperature for 24 hours. After the reaction is complete, remove the methanol by rotary evaporation under reduced pressure at 40 °C. The remaining aqueous phase is freeze-dried overnight to completely remove water, finally yielding a brownish-yellow MVCl2. 2+ ·Cl - AA - powder.

[0022] (2) Synthesis of MV-PAA gel Weigh 200 mg of the MV prepared above. 2+ ·Cl - AA - Dissolve the compound in 3 mL of deionized water and stir until completely dissolved. Add 1.8 g of sodium acrylate, 50 mg of divinylbenzene (as a crosslinking agent), and 10 mg of ammonium persulfate (as an initiator) sequentially to the solution. Sonicate the mixture in an ultrasonic cleaner for 1 hour to ensure thorough emulsification and the formation of a uniformly dispersed emulsion. Quickly inject the resulting emulsion into a polytetrafluoroethylene mold and polymerize at 60°C for 6 hours to obtain a yellow MV-PAA gel. Wash the resulting gel repeatedly with flowing deionized water to remove residual unreacted monomers and impurities.

[0023] 1.3 Photochromic properties of materials (1) MV 2+ ·Cl - AA -Photochromic properties To study MV 2+ ·Cl - AA - The absorption mode photochromic behavior was observed by accurately weighing 100 mg MV. 2+ ·Cl - AA - The powder was dissolved in 1 mL of deionized water to prepare a homogeneous solution. An appropriate amount of the solution was placed in a quartz cuvette, and its visible absorption spectrum was recorded using a UV-Vis spectrophotometer without UV irradiation. Simultaneously, an optical photograph of the sample under sunlight was taken. Subsequently, the sample solution was vertically irradiated with a 365 nm UV flashlight for 150 s, and the visible absorption spectrum of the sample after irradiation was immediately recorded again. A photograph of its color change under sunlight was also taken to observe the evolution of the absorption spectrum and color change before and after illumination.

[0024] To further study MV 2+ ·Cl - AA - The photochromic properties of the fluorescence mode were determined by taking 100 mg MV. 2+ ·Cl - AA - Dissolve in 1 mL of deionized water and transfer to a quartz cuvette. Record its fluorescence emission spectrum (excitation wavelength 390 nm) and place it in a dark-box three-in-one UV analyzer to capture its fluorescence image under 365 nm UV excitation. Subsequently, irradiate the sample continuously with a 365 nm UV flashlight for 150 s, immediately record the fluorescence emission spectrum of the sample after irradiation, and capture its fluorescence image again in the dark-box three-in-one UV analyzer to compare the changes in fluorescence intensity before and after irradiation.

[0025] (2) Photochromic properties of MV-PAA gel To investigate the photochromic properties of MV-PAA gel in absorption mode, a thoroughly washed gel block was placed in a solid bath. Under conditions without UV irradiation, its diffuse reflectance absorption spectrum was measured using a UV-Vis-NIR spectrophotometer (equipped with an integrating sphere), and a macroscopic photograph of the gel sample was taken under sunlight. Subsequently, the gel surface was uniformly irradiated with a 365 nm UV flashlight for 5 min, and the UV-Vis diffuse reflectance spectrum of the sample after irradiation was quickly recorded. Simultaneously, a photograph of the gel after color change under sunlight was taken to analyze the influence of the photochromic response on the absorption spectrum and sample appearance.

[0026] To further investigate the photochromic behavior of the gel's fluorescence mode, an MV-PAA gel sample under the same treatment conditions was taken. First, its initial fluorescence emission spectrum was measured, and its fluorescence image was captured under 365 nm UV excitation in a darkroom-type three-way UV analyzer. Then, the sample was irradiated with a 365 nm UV flashlight for 5 minutes, and the fluorescence emission spectrum of the gel after irradiation (excitation wavelength 390 nm) was immediately recorded again, and the corresponding fluorescence image was captured in a darkroom. By comparing the fluorescence spectra and emission images before and after irradiation, the performance of the gel system in terms of fluorescence photochromism was discussed.

[0027] 1.4 Reversibility of photochromism in materials (1) MV 2+ ·Cl - AA - Photochromic reversibility To examine MV 2+ ·Cl - AA - The reversible photochromic properties in absorption mode were measured at 100 mg MV. 2+ ·Cl - AA - Dissolve the sample in deionized water and place it in a quartz cuvette. Record the visible absorption spectrum of the unirradiated monomer solution using a UV-Vis spectrophotometer. Irradiate the sample vertically with a UV flashlight for 150 s, and immediately record its visible absorption spectrum. Subsequently, place the irradiated sample in a dark environment and let it stand for 6 h until the solution color completely returns to its initial state, then measure its visible absorption spectrum again. Repeat the above photochromic-fading cycle 20 times to investigate the reversibility and fatigue resistance of the monomer's photochromic response in the absorption mode.

[0028] To explore MV 2+ ·Cl - AA - The reversible photochromic behavior of the monomer in fluorescence mode was demonstrated by weighing 100 mg MV. 2+ ·Cl - AA - The sample was dissolved in deionized water and transferred to a quartz cuvette. The fluorescence emission spectrum was recorded using an excitation wavelength of 390 nm. Subsequently, the sample was irradiated with a UV flashlight for 150 s, and the fluorescence emission spectrum was immediately measured. The irradiated sample was then placed in the dark for 6 h until the solution color returned to its initial level, at which point the fluorescence emission spectrum was recorded again. This light-recovery cycle was repeated 20 times to examine the reversibility and cyclic stability of the photochromic process of the monomer in fluorescence mode.

[0029] (2) Photochromic reversibility of MV-PAA gel To investigate the reversible photochromic properties of MV-PAA gel in absorption mode, a thoroughly washed gel block was fixed in a solid bath, and its diffuse reflectance absorption spectrum was measured using a UV-Vis-NIR spectrophotometer (integrating sphere mode). The gel sample surface was uniformly irradiated with a UV flashlight for 5 min, and its diffuse reflectance absorption spectrum was immediately recorded using a UV-Vis-NIR spectrophotometer. After irradiation, the gel was placed in a dark environment and allowed to stand for 10 h until the sample color completely recovered to its initial state, and its UV-Vis diffuse reflectance spectrum was recorded again. This irradiation-recovery cycle was repeated 10 times to explore the reversibility and reusability of the photochromic properties of the gel system in absorption mode.

[0030] To investigate the reversible photochromic behavior of MV-PAA gel under fluorescence mode, a gel sample treated under the same conditions was taken. First, its initial fluorescence emission spectrum was measured using 390 nm as the excitation wavelength. Then, the gel surface was irradiated with a UV flashlight for 5 min, and the fluorescence emission spectrum of the irradiated sample was immediately recorded. The irradiated sample was then placed in a dark environment and allowed to stand for 10 h until its appearance returned to its initial state, after which its fluorescence emission spectrum was measured again. This cycle was repeated 10 times. By comparing the changes in the characteristic peak positions and intensities of the fluorescence spectra in each cycle, the reversibility and cycle durability of the gel's photochromic behavior under fluorescence mode were comprehensively evaluated.

[0031] 2. Results and Discussion 2.1 Characterization of materials (1) MV 2+ ·Cl - AA - Characterization of monomers The anions and cations of the product were detected separately by mass spectrometry, and the resulting spectra are shown below. Figure 1 As shown. The mass spectrum of its cation is as follows. Figure 1 As shown in figure a, the base peak is located at m / z 171.0914, which is related to the methyl viologen cation demethylation fragment [C]. 11 H 11 N2] + (Calculated value 171.0917) shows a high degree of agreement. Simultaneously, a series of strong peaks related to the methyl viologen cation skeleton were observed: m / z 185.1071 corresponds to [MV-H]. + (Calculated value 185.1079), m / z 186.1149 corresponds to ion MV + (Calculated value 186.1157), these ions collectively confirm the integrity of the methyl viologen cation skeleton in the product. Furthermore, m / z 256.1291 corresponds to the target molecular ion [C]. 15 H 17 ClN2O2] + (Calculated value 256.0979). Anion mode mass spectrometry as follows: Figure 1 As shown in b, the base peak in the spectrum is located at m / z 71.0124, which corresponds to the acrylate anion (calculated value 71.0133).

[0032] Using nuclear magnetic resonance hydrogen spectroscopy (NMR) 1 H NMR) for MV 2+ ·Cl - AA - Characterization was performed, and the spectrum is shown below. Figure 2 As shown in the figure, using D₂O as solvent, the pyridine ring protons (δ 8.5-9.0 ppm, doublet, 4H; δ 7.8-8.2 ppm, doublet, 4H), N-methyl protons (δ 4.2-4.4 ppm, singlet, 6H), and acrylate protons (δ 5.8-6.5 ppm, multiplet, 3H) were observed in the spectrum, indicating that the acrylate group was successfully introduced. Based on a total proton integral of 14.0 for methyl viologen cations, the proton integral for acrylate was approximately 3.0, corresponding to a molar ratio of approximately 1:1 between methyl viologen cations and acrylate groups, indicating that each methyl viologen cation binds to one acrylate group, with the remaining charge compensated by chloride ions.

[0033] (2) Characterization of MV-PAA gel Uniformly cross-linked MV-PAA gels were prepared by thermally initiated polymerization, and the structure of the gels was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS).

[0034] The results of FT-IR characterization of the chemical structure of MV-PAA gel are as follows: Figure 3 As shown in the image, several characteristic absorption peaks attributable to the methyl viologen cation and the polyacrylic acid gel backbone can be observed in the infrared spectrum. Specifically, at 3508 cm⁻¹... -1 The broad absorption peak at 2918 cm⁻¹ corresponds to the stretching vibration of OH groups after carboxyl protonation in the gel. -1 With 2860 cm -1 The characteristic peaks at this location are attributed to the stretching vibrations of the CH bonds in the alkyl chains of the gel skeleton and the methyl viologen cation, confirming that MV 2+ Successfully introduced gel network; 1655 cm -1 This is the stretching vibration peak of C=O after carboxyl protonation, at 1570 cm⁻¹. -1 With 1406 cm -1 Corresponding to COO - The asymmetric and symmetric stretching vibrations indicate the presence of an acrylic gel skeleton, 1458 cm. -1The peak represents the deformation vibration of CH in the gel backbone and methyl viologen cation; 1315 cm⁻¹ -1 The peak at 862 cm⁻¹ is a characteristic stretching vibration of the CN bond in the methyl viologen cation structure, directly proving that the methyl viologen cation is stably loaded onto the gel. -1 The out-of-plane bending vibration of the CH ring corresponding to the crosslinking agent divinylbenzene confirms the successful construction of the three-dimensional crosslinked network.

[0035] The results of XPS analysis of the surface chemical composition of MV-PAA gel are as follows: Figure 4 As shown. From the full spectrum ( Figure 4 In a), three characteristic photoelectron peaks located at ~284.8 eV, ~399.8 eV, and ~532.0 eV can be observed, belonging to the C 1s, N 1s, and O 1s orbitals, respectively. Among them, the C 1s peak (… Figure 4 b) Derived from the pyridine ring skeleton of the methyl viologen cation and the carbon atoms in the acrylate group and gel skeleton; N 1s peak ( Figure 4 c) mainly corresponds to the nitrogen atom on the pyridine ring of the methyl viologen cation, and its binding energy position is consistent with the characteristics of aromatic nitrogen; O 1s peak ( Figure 4 d) originates from oxygen in the sodium polyacrylate gel network. The characteristic peaks of the above three elements are related to MV. 2+ ·Cl - AA - The organic framework composition is highly consistent, confirming that the methyl viologen cation has been incorporated into the gel network, forming an MV-PAA gel.

[0036] The PXRD pattern of MV-PAA gel is shown below. Figure 5 As shown in the figure, no obvious crystallization diffraction peaks were observed, indicating that it is a network structure of sodium polyacrylate gel, exhibiting an amorphous morphology.

[0037] 2.2MV 2+ ·Cl - AA - Photochromic properties The study of MV 2+ ·Cl - AA - Photochromic properties ( Figure 6 ).like Figure 6 As shown in figure a, MV was measured. 2+ ·Cl - AA - UV-Vis absorption spectra of the aqueous solution before and after light irradiation. Before exposure to UV light, MV... 2+ ·Cl - AA -The aqueous solution exhibits absorption at 400 nm, and correspondingly, it appears yellow under sunlight. Under UV irradiation, MV was observed. 2+ ·Cl - AA - A new absorption peak is observed at 610 nm, and the color changes from yellow to blue under sunlight. Further investigation into the photochromic fluorescence properties of the solution yielded the following results: Figure 6 As shown in b. At an excitation wavelength of 390 nm, MV 2+ ·Cl - AA - The aqueous solution initially exhibits strong yellow-green fluorescence emission. After continuous irradiation with ultraviolet light for 150 seconds, the fluorescence emission intensity significantly decreases, and fluorescence quenching is evident.

[0038] To further investigate the reasons for the color change and fluorescence quenching after illumination, the fluorescence intensity (MV) was measured before and after ultraviolet (UV) lamp stimulation. 2+ ·Cl - AA - Electron paramagnetic resonance spectrum of solution ( Figure 7 It can be observed that MV increases after UV light irradiation. 2+ ·Cl - AA - The generated MV + The signal, with a g-value of approximately 2.003, confirms that UV irradiation caused the MV. 2+ ·Cl - AA - A single-electron transfer reaction produces a methyl viologen free radical cation.

[0039] The reversibility of photochromic materials refers to the material's ability to return to its initial state after the removal of light. For example... Figure 8 As shown, in twenty cycles of UV light / dark testing, MV 2+ ·Cl - AA - It exhibits good reversibility; after each removal of ultraviolet light, its daylight color and fluorescence can be restored to their original state. Figure 8 After twenty cycles, MV 2+ ·Cl - AA - The absorbance at 610 nm and the fluorescence intensity at 540 nm did not change significantly compared with the initial values, indicating that its photochromic behavior has good reversibility. Figure 8 a and Figure 8 b).

[0040] 2.3 Optical properties of MV-PAA gel The photochromic properties of MV-PAA gel were studied. Figure 9 ).like Figure 9 As shown in Figure a, under ultraviolet light irradiation, the gel exhibits a new absorption band at 610 nm, and its sunlight color changes from yellow to deep blue. Correspondingly, the yellow fluorescence emission intensity of the gel at 540 nm significantly decreases. Figure 9 b).

[0041] To further investigate the reasons for the color change and fluorescence quenching of MV-PAA gel after light exposure, the electron paramagnetic resonance spectra of MV-PAA gel before and after UV irradiation were measured. Figure 10 Typical viologen radical signals were observed, confirming the occurrence of UV-induced single-electron transfer reactions, which altered the sunlight and fluorescence colors of the gel.

[0042] The reversibility of photochromic materials is a crucial indicator of their practical performance, directly impacting their stability and reliability during repeated use. To investigate the photochromic reversibility of MV-PAA gel, ten consecutive cycles of UV irradiation / recovery testing were conducted. The results are as follows: Figure 11 As shown, after each UV irradiation, the gel's sunlight color changed from yellow to blue, while the fluorescence intensity significantly decreased; however, after irradiation was stopped and the gel was placed in a dark environment for recovery, both the gel's color and fluorescence reversibly returned to their initial states, indicating its good reversible response capability. After ten cycles, the gel's characteristic absorption intensity at 610 nm and fluorescence emission intensity at 540 nm did not show significant attenuation, maintaining excellent performance levels. Figure 11 a and Figure 11 (b) The above results demonstrate that the MV-PAA gel exhibits good reversibility and cycling stability during multiple photochromic cycles, laying the foundation for its practical application in reusable photoresponse devices.

Claims

1. A dual-mode photochromic gel material based on absorption and fluorescence, characterized in that, It is prepared by polymerization reaction of raw materials containing vinyl-functionalized viologen monomer, acrylate, crosslinking agent and initiator; the vinyl-functionalized viologen monomer is formed by ion exchange of methyl viologen and acrylate.

2. The absorption-fluorescence dual-mode photochromic gel material according to claim 1, characterized in that, The gel material is a polyacrylic acid hydrogel that exhibits a dual-mode response under ultraviolet light irradiation, characterized by reversible changes in visible light absorption color and reversible quenching of fluorescence intensity.

3. The absorption-fluorescence dual-mode photochromic gel material according to claim 1, characterized in that, The acrylate is sodium acrylate; the crosslinking agent is divinylbenzene; and the initiator is ammonium persulfate.

4. The absorption-fluorescence dual-mode photochromic gel material according to claim 1, characterized in that, Using 3 mL of deionized water as solvent, the amount of vinyl-functionalized viologen monomer was 190–210 mg; the amount of acrylate was 1.7–1.9 g; the amount of crosslinking agent was 45–55 mg; the amount of initiator was 8–12 mg; and the molar ratio of methyl viologen to acrylate was 1:(1–3).

5. The absorption-fluorescence dual-mode photochromic gel material according to claim 2, characterized in that, The ultraviolet light that triggers photochromism has a wavelength of 200 nm to 400 nm. Before illumination, a characteristic absorption peak appears at 350 nm to 450 nm, and after illumination, a characteristic absorption peak appears at 550 nm to 650 nm.

6. The absorption-fluorescence dual-mode photochromic gel material according to claim 2, characterized in that, The fluorescence excitation wavelength is 350 nm to 420 nm, and the fluorescence emission wavelength is 450 nm to 700 nm.

7. A method for preparing the absorption-fluorescence dual-mode photochromic gel material according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Methyl viologen and acrylate undergo an ion exchange reaction in a solvent to obtain vinyl-functionalized viologen monomer; S2. Dissolve the vinyl-functionalized viologen monomer, acrylate, crosslinking agent, and initiator in water and mix thoroughly; S3. Heating is used to carry out a polymerization reaction to obtain an absorption-fluorescence dual-mode photochromic gel material.

8. The method for preparing the absorption-fluorescence dual-mode photochromic gel material according to claim 7, characterized in that, In step S1, the ion exchange reaction temperature is 15℃~35℃, and the reaction time is 12 h~36 h.

9. The method for preparing the absorption-fluorescence dual-mode photochromic gel material according to claim 7, characterized in that, In step S3, the polymerization temperature is 40℃~80℃ and the polymerization time is 4 h~8 h.

10. The application of the absorption-fluorescence dual-mode photochromic gel material according to any one of claims 1 to 6, characterized in that, Used for anti-counterfeiting labels, information storage, intelligent sensing, information display, or optical devices.

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