Hydrophilic methacrylate polymer with photo-induced dynamic color change fluorescent function, preparation method and application
By introducing photochromic molecules and fluorescent dyes into hydrophilic methacrylate polymers, a FRET system was constructed and nanoparticles were prepared for use in anti-counterfeiting inks. This solved the problems of easy imitation and insufficient stability of existing materials, and achieved reversible fluorescence changes under ultraviolet and visible light and a cost-effective anti-counterfeiting effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SUZHOU UNIV
- Filing Date
- 2023-09-28
- Publication Date
- 2026-07-14
AI Technical Summary
Existing fluorescent anti-counterfeiting materials are easy to counterfeit, and their fluorescence emission weakens when aggregated, making it difficult to meet complex anti-counterfeiting requirements. Traditional preparation methods are complex and lack stability.
A hydrophilic methacrylate polymer with photochromic fluorescence function was synthesized by reprecipitation method. The FRET system was constructed by covalently introducing the photochromic molecule spiropyran (SP) and the fluorescent dye triphenylvinylphenol ester (TPE), and nanoparticles were prepared for use in anti-counterfeiting ink.
It achieves reversible fluorescence color change under ultraviolet and visible light irradiation, improves the complexity and stability of anti-counterfeiting materials, reduces preparation costs, and is suitable for personalized anti-counterfeiting materials.
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Figure CN117285675B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a methacrylate polymer with hydrophilic photochromic fluorescence properties, its preparation method, and its application, belonging to the field of fluorescent polymer materials technology. Technical Background
[0002] Due to the rapid development of technology in recent years, counterfeit products have become increasingly prevalent in society. Counterfeiting not only infringes on the rights of copyright holders but also causes considerable harm to society and the public. Over the past few decades, various anti-counterfeiting technologies have been developed to combat counterfeiting. These methods range from simple watermarks and holograms to complex QR codes. However, current methods are relatively well-known to counterfeiters. Therefore, there is a strong interest in developing new materials for preventing and identifying counterfeiting. Among these materials, fluorescent anti-counterfeiting materials have received widespread attention in recent years. However, relatively simple and easily imitated monochrome fluorescent anti-counterfeiting materials are no longer sufficient for more complex scenarios. Furthermore, to avoid complex anti-counterfeiting construction and verification operations, developing anti-counterfeiting materials with dynamic multi-color fluorescent responses and ease of operation is of significant practical importance. (See reference:) Macromolecules 2020, 53 , 1613-1622).
[0003] Fluorescence resonance energy transfer (FRET)-based systems have gained popularity among researchers and are widely used in fluorescent anti-counterfeiting. Currently, most commercially available fluorescent anti-counterfeiting technologies are based on traditional fluorescent dyes, which may be well-known to counterfeiters and easily imitated. To achieve more complex and difficult-to-counterfeit anti-counterfeiting technologies, fluorescence resonance energy transfer (FRET)-based strategies have been proposed. In many reported studies, an increasing number of researchers are introducing photochromic molecules into FRET systems, combining the dynamic changes in photochromism with the energy transfer between donors and acceptors in FRET to achieve dynamic switching of dual-color or even multi-color fluorescence (see reference: [reference needed]). Macromolecules 2015, 49Spiropyran (SP) is a photochromic organic molecule with a non-planar closed-ring form that does not emit fluorescence. Ultraviolet light irradiation can convert SP into a planar conjugated open-ring form called cyanoid-like (MC), which emits red fluorescence. Under external stimuli, such as visible light irradiation, heat, or pressure, MC can revert to SP. To construct a FRET system, the emission spectrum of the donor and the absorption spectrum of the acceptor must have as much overlap as possible; therefore, it is necessary to select a spectrally matched fluorescent dye for the MC after SP isomerization. The fluorescence of nanoparticles containing traditional fluorescent dyes can sometimes be weakened or even lost due to aggregation-induced quenching (ACQ). The use of aggregation-induced emission (AIE) molecules can circumvent this problem. Nanoparticles containing AIE molecules have been used as multifunctional nanocarriers and are widely applied in the biological field; however, to our knowledge, few studies have to date combined photochromic polymer nanoparticles with AIE molecules for use in photoreversible multicolor fluorescent anti-counterfeiting inks. Recently, polymer nanoparticles (PNPs) have been frequently used to prepare anti-counterfeiting and encryption inks due to their excellent water solubility and photostability. PNPs typically consist of a hydrophobic core and a hydrophilic shell. The internal core of polymer nanoparticles can provide a microenvironment that restricts molecular rotation / movement, enabling TPE to emit strong fluorescence, and allowing MC to better exert its photochromic properties, thus achieving complex anti-counterfeiting purposes. Some research groups have reported anti-counterfeiting applications of nanoparticles prepared by combining the photochromic molecule SP with FRET. Most related studies have prepared nanoparticles using emulsion polymerization (see literature: ACS Applied Materials & Interfaces 2022, 14 (39384-39395.) However, only a few are prepared by reprecipitation. Reprecipitation can directly prepare polymers into nanoparticles without the need for additional surfactants, which is simpler and more efficient than emulsion polymerization, which requires surfactants and involves complex operations. Generally, nanoparticles prepared from hydrophobic polymers without surfactants via reprecipitation do not have good stability. Some literature reports the preparation of nanoparticles that can exist stably in aqueous solutions without surfactants. Most of these methods involve introducing monomers with hydrophilic groups during polymer preparation to increase the hydrophilicity of the polymer itself, thereby forming a stable colloidal solution after nanoparticles are made. However, most of the methods for preparing photochromic nanoparticles using reprecipitation in the literature involve covalently attaching photochromic molecules to the side chains of hydrophilic general-purpose polymers, and then doping them with hydrophobic fluorescent polymers or small molecules to prepare photochromic nanoparticles. (See literature:) Polymer Chemistry(2013, 4(3), 773-781.) While this doping method may simplify the synthesis steps to some extent, it also leads to dye leakage and insufficient stability.
[0004] Chinese invention patent CN115124647A discloses a fluorescent polymer of methyl methacrylate containing SP and TPE groups, its preparation method, and its application. The method involves copolymerizing functionalized SP monomers, functionalized TPE monomers, and methyl methacrylate using free radical polymerization to obtain a modified polymethyl methacrylate terpolymer with photochromic fluorescent properties. Subsequently, this polymer is electrospun into a fiber film for use in the production of fluorescent anti-counterfeiting labels.
[0005] Fluorescent anti-counterfeiting inks have been widely used in anti-counterfeiting, information encryption, and information storage. Due to the frequent forgery of secure documents, improving the security of anti-counterfeiting inks has become a significant challenge. Through researchers' efforts, high-security anti-counterfeiting inks prepared with photochromic fluorescent nanoparticles have been developed to address counterfeiting issues. These inks possess both photochromic and fluorescent emission properties, enhancing security and preventing forgery in various anti-counterfeiting document applications. For decades, developing photochromic fluorescent nanoparticle inks capable of displaying light patterns on different substrates has been a major challenge. Cellulose paper is one of the most important and widely used substrates, and coating it with photochromic fluorescent nanoparticle inks to create various fluorescent patterns is an effective method for anti-counterfeiting encryption. Due to the diverse material forms, encryption and decryption methods, and increasingly stringent customization requirements, the cost-effectiveness of anti-counterfeiting encryption materials is also a crucial factor. Therefore, developing cost-effective anti-counterfeiting encryption materials that can easily meet customers' personalized customization needs is essential. Summary of the Invention
[0006] This invention addresses the shortcomings of existing technologies by providing a hydrophilic polymer with photosensitive dynamic color-changing fluorescence function that can undergo dynamic fluorescence color change under ultraviolet / visible light irradiation, has simple synthesis conditions, high cost performance, and can be customized into various anti-counterfeiting materials for application in the field of anti-counterfeiting encryption, along with its preparation method and applications.
[0007] The technical solution to achieve the objective of this invention is to provide a hydrophilic methacrylate polymer with photosensitive dynamic color-changing fluorescence function, the structural formula of which is:
[0008] ;
[0009] Where n is the number of repeating units, n=100~120; x=0.01~0.05, y=0.03~0.10, z=0.03~0.10.
[0010] The present invention discloses a method for preparing a hydrophilic methacrylate polymer with photochromic fluorescence function. Methyl methacrylate monomer is designated as M1, triphenylvinylphenol methacrylate monomer as M2, spiropyranyl ethyl methacrylate monomer as M3, and hydroxyethyl methacrylate as M4. Based on the molar proportions, 1-xyz parts of M1, x parts of M2, y parts of M3, and z parts of M4, where x = 0.01–0.05, y = 0.03–0.10, and z = 0.03–0.10, are mixed with 2–5 parts of azobisisobutyronitrile and 300–600 parts of N,N-dimethylformamide and stirred. The mixture is reacted under inert gas protection and at a temperature of 75–85°C for 24–48 hours. After purification and drying, a hydrophilic methacrylate polymer with photochromic fluorescence function is obtained.
[0011] The structural formula of the monomer M1 is:
[0012] ;
[0013] The structural formula of the monomer M2 is:
[0014] ;
[0015] The structural formula of the monomer M3 is:
[0016] ;
[0017] The structural formula of the monomer M4 is:
[0018] .
[0019] The present invention also provides a method for preparing hydrophilic methacrylate polymer nanoparticles with photosensitive dynamic color-changing fluorescence function, comprising the following steps:
[0020] (1) Methyl methacrylate monomer is designated as M1, triphenylvinylphenol methacrylate monomer as M2, spiropyranyl ethyl methacrylate monomer as M3, and hydroxyethyl methacrylate as M4. Based on the molar amounts, 1-xyz parts of M1, x parts of M2, y parts of M3, and z parts of M4, where x = 0.01-0.05, y = 0.03-0.10, and z = 0.03-0.10, are mixed with 2-5 parts of azobisisobutyronitrile and 300-600 parts of N,N-dimethylformamide and stirred. The mixture is reacted for 24-48 hours under inert gas protection and at a temperature of 75-85°C. After purification and drying, a methacrylate polymer is obtained.
[0021] (2) Dissolve the methacrylate polymer obtained in step (1) in tetrahydrofuran solvent at a concentration of 0.05 mg / mL to 0.2 mg / mL to obtain a polymer solution; add the polymer solution to deionized water at a volume ratio of 0.5 to 2: 5 to 20, and under ultrasonic conditions, use the reprecipitation method to obtain a mixed solution. After removing tetrahydrofuran, a hydrophilic methacrylate polymer nanoparticle with photoluminescent dynamic color change function is obtained.
[0022] The hydrophilic methacrylate polymer nanoparticles obtained by the above preparation method are nanoparticle solutions with a polymer concentration of 0.05 to 0.2 mg / mL.
[0023] A preferred approach is to concentrate the polymer concentration of the obtained nanoparticle solution to 1–4 mg / mL.
[0024] A hydrophilic methacrylate nanoparticle with photochromic fluorescence function obtained according to the preparation method of the present invention exhibits stable suspension in water with photochromic fluorescence properties, including an initial state, a color-changing state, and a recovery state.
[0025] In its initial state, the nanoparticles are colorless under natural light; when excited by 365 nm ultraviolet light, the nanoparticles emit blue fluorescence in the range of 400–550 nm.
[0026] The color-changing state refers to the initial state of the nanoparticles being light blue under natural light after continuous irradiation with 365 nm ultraviolet light for 5 minutes; and emitting red fluorescence in the range of 600-700 nm when excited by 365 nm ultraviolet light.
[0027] The recovery state refers to the nanoparticles in the discolored state returning to their initial state after being continuously irradiated with visible light for more than 10 minutes.
[0028] This invention relates to the application of hydrophilic polymer nanoparticles with photochromic fluorescence function, which are used to prepare dynamic fluorescent anti-counterfeiting ink. A solution of hydrophilic polymer nanoparticles with photochromic fluorescence function at a polymer concentration of 1-4 mg / mL is mixed with glycerol and ethanol at a volume ratio of 1:0.25:0.075 to obtain a dynamic fluorescent anti-counterfeiting ink.
[0029] The dynamic fluorescent anti-counterfeiting ink prepared according to the present invention is coated on the surface of a permeable matrix material to obtain a dynamic fluorescent anti-counterfeiting and encryption material.
[0030] The permeable matrix material described in this invention includes cellulose paper and cloth.
[0031] In this invention, a hydrophilic general-purpose polymer is synthesized by directly copolymerizing a fluorescent donor, a fluorescent acceptor, and a hydrophilic monomer. The synthesis method provided by this invention avoids dye leakage problems and, through the selection and optimization of synthesis conditions, provides a relatively simple and feasible synthesis method that achieves both photochromic and fluorescence resonance energy transfer effects. This invention conducts detailed photophysical studies on the photochromic properties of nanoparticles, particularly investigating the reproducibility of the photochromic process, to evaluate the fatigue characteristics of nanoparticles as anti-counterfeiting materials. Therefore, the photochromic properties of nanoparticles can be utilized to make their preparation and application more controllable, better meeting specific anti-counterfeiting needs.
[0032] This invention introduces a fourth hydrophilic monomer to form a quaternary copolymer system, aiming to improve the hydrophilicity of the polymer through molecular design; at the same time, the content of the four monomers in the polymer is adjusted and optimized, so that the polymer can stably suspend in water while exhibiting excellent dynamic photochromic properties; finally, the polymer is prepared into nanoparticles for application in the field of fluorescent anti-counterfeiting ink, hoping to expand the anti-counterfeiting application forms of dynamic photochromic polymers.
[0033] This invention designs and synthesizes a polymethacrylate polymer with certain hydrophilic photochromic fluorescence properties. It constructs a FRET system by combining tetraphenylethylene (TPE), which emits blue fluorescence with AIE characteristics, with spiropyran (SP), which emits red fluorescence under ultraviolet light, to produce an anthocyanin-like (MC) fluorescence. The system achieves dynamic changes in fluorescence color solely through ultraviolet light irradiation, relying on photochromism and FRET, and this change is completely reversible. Based on this, fluorescent anti-counterfeiting technology is developed.
[0034] In this invention, to improve the compatibility of different components in the system, methyl methacrylate (MMA) was chosen as the main monomer because the abundant ester group structure in MMA is beneficial to improving the stability of MC. TPE-MA (TPE-containing methacrylate monomers), SP-MA (SP-containing methacrylate monomers), and HEMA (hydroxyl-containing hydroxyl-containing hydroxyl-containing hydroxyl-containing hydroxyl-containing hydroxyl-containing hydroxyl-containing hydroxyl-containing hydroxyl-containing methyl methacrylate) were used as secondary monomers, as their chemical structures are highly similar to those of MMA. Therefore, it is hoped that random copolymerization can yield copolymers with similar monomer feed ratios. The TPE structure (i.e., triphenylvinylbenzene structure) and SP structure of the side groups are key to achieving a significant photochromic process, while the hydrophilic hydroxyl groups in HEMA allow the nanoparticles to exist stably in aqueous solutions. Furthermore, since the polymer contains only a very small amount of fluorescent chromophores TPE and SP, its cost is not significantly different from that of commercially available general-purpose polymer PMMA, and there are no expensive reagents in the polymer synthesis process and subsequent ink formulation. Therefore, the various anti-counterfeiting materials prepared using nanoparticle inks in this invention have a high cost-performance ratio. In this invention, 3% to 10% molar fraction of HEMA is introduced during polymer synthesis to impart a certain degree of hydrophilicity to the polymer, thereby improving the solubility of nanoparticles in the microenvironment and further exhibiting better photophysical properties. It is worth noting that the HEMA content in the polymer is optimized. Since the hydrophilicity of polymer segments affects the fluorescence emission of TPE and SP groups—for example, excessively high polymer chain hydrophilicity can lead to reduced TPE aggregation and weaker fluorescence intensity, but increased hydrophilicity can also make it more difficult for MC to revert to the SP state—choosing an appropriate HEMA content is crucial to the overall photochromic performance of the polymer.
[0035] The principle of this invention is as follows: Photochromic SP and AIE TPE molecules are covalently introduced into the polymer backbone via free radical polymerization to prepare a quaternary copolymer, which is a polymethacrylate polymer with certain hydrophilic photochromic fluorescence properties. Since there is a large overlap between the fluorescence spectrum of TPE and the absorption spectrum of MC, the MC structure generated by the isomerization reaction of SP groups under ultraviolet light is combined with the TPE structure to establish a "donor-acceptor" relationship for fluorescence resonance energy transfer, thereby achieving the effect of dynamic fluorescence color change, which can be applied in the field of anti-counterfeiting encryption. Next, this polymer is prepared into nanoparticles with photochromic fluorescence properties that are stably suspended in water using a simple and efficient reprecipitation method. In the microenvironment of the polymer nanoparticles, TPE and SP can effectively exert their properties, thus achieving the effect of dynamic fluorescence color change. Subsequently, the nanoparticles are used to prepare anti-counterfeiting encryption ink for application in practical anti-counterfeiting scenarios.
[0036] This invention provides a polymethacrylate polymer with certain hydrophilic photochromic fluorescence properties, which is then prepared into a nanoparticle suspension. Its application in dynamic fluorescent anti-counterfeiting is based on the following principle: Since the SP groups on its side groups do not emit fluorescence, when the polymer is excited with ultraviolet light (365 nm), only the TPE is excited and emits blue fluorescence in the 400 nm–550 nm range. Under continuous ultraviolet irradiation, the closed-ring SP gradually undergoes isomerization, forming an MC structure that produces red fluorescence emission in the 600 nm–700 nm range. The absorption of the ring-opening SP in the 500 nm–650 nm range overlaps with the fluorescence emission of the TPE, thus enabling fluorescence resonance energy transfer between them. Under ultraviolet excitation, due to this energy transfer, the blue fluorescence emission intensity of the TPE (energy donor) gradually decreases, while the red fluorescence emission of the MC (energy acceptor) gradually increases, resulting in an observed change in fluorescence color from blue to red. Under visible light irradiation, the MC structure reverts to the SP structure, thus restoring its initial fluorescence properties, thereby achieving the reverse process of the aforementioned fluorescence change. In summary, this invention achieves dynamic fluorescence emission changes (from blue fluorescence to red fluorescence) under ultraviolet light irradiation by constructing an energy transfer process between TPE and MC, and achieves the reverse process (from red fluorescence to blue fluorescence) by visible light irradiation, thereby realizing the purpose of dynamic fluorescence anti-counterfeiting.
[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0038] 1. The polymethacrylate polymer with hydrophilic photochromic fluorescence properties prepared by this invention can be prepared into nanoparticles that can be stably suspended in water; the nanoparticles can undergo significant fluorescence color change under ultraviolet light irradiation, and this fluorescence color change process is reversible under visible light irradiation. Compared with the single fluorescence color of traditional anti-counterfeiting technology, the anti-counterfeiting mechanism of this invention is complex and difficult to imitate.
[0039] 2. The nanoparticles prepared by this invention have good photochromic properties and light reproducibility; and the nanoparticle ink can also exhibit high stability and dynamic fluorescence color-changing characteristics on cellulose paper.
[0040] 3. This invention personalizes high-performance inks into various anti-counterfeiting materials according to different needs and applies them to the field of anti-counterfeiting and encryption, no longer limiting itself to anti-counterfeiting inks themselves, providing new ideas for the field of anti-counterfeiting and encryption, and has potential application value in the field of anti-counterfeiting and encryption. Attached Figure Description
[0041] Figure 1This is a schematic diagram of the synthetic route of the polymethyl methacrylate polymer (denoted as P(MMA-HEMA-TPEMA-SPMA)) with photoluminescent properties provided by the present invention.
[0042] Figure 2 These are the nuclear magnetic resonance spectra of M1, M2, M3, M4 and P (MMA-HEMA-TPEMA-SPMA) prepared in the embodiments of the present invention;
[0043] Figure 3 These are the infrared absorption spectra of M1, M2, M3, M4 and P (MMA-HEMA-TPEMA-SPMA) prepared in the embodiments of the present invention;
[0044] Figure 4 This is a transmission electron microscope image of the dynamic fluorescent anti-counterfeiting nanoparticles prepared according to an embodiment of the present invention;
[0045] Figure 5 This is a dynamic light scattering pattern of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in the embodiments of the present invention;
[0046] Figure 6 The images show the fluorescence emission patterns of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in this invention under ultraviolet light (365 nm, 12 W) irradiation for different times, with an excitation wavelength of 365 nm.
[0047] Figure 7 The images show the fluorescence emission patterns of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in this embodiment of the invention after irradiation with ultraviolet light (365 nm, 12 W) for 5 min and then irradiated with visible light (white light) for different times, with an excitation wavelength of 365 nm.
[0048] Figure 8 This is the relationship between the fluorescence intensity and the number of cycles of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in this embodiment of the invention during 10 cycles of alternating irradiation with 1 minute of ultraviolet light (365 nm, 12 W) and 5 minutes of visible light (white light);
[0049] Figure 9 These are digital photos of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in the embodiments of the present invention under ultraviolet light (365 nm, 60 W) irradiation for different times.
[0050] Figure 10 The letter "C" written on cellulose paper using a brush dipped in the dynamic fluorescent anti-counterfeiting nanoparticle ink prepared in the embodiments of the present invention is a fluorescent digital photograph under ultraviolet light (365 nm, 60 W) for different times.
[0051] Figure 11The words “SOOCHOW” written with a commercially available blank fountain pen pre-injected with the dynamic fluorescent anti-counterfeiting nanoparticle ink prepared in the embodiments of the present invention are fluorescent digital photographs taken under ultraviolet light (365 nm, 60 W) for different times.
[0052] Figure 12 These are fluorescent digital photographs of rewritable fluorescent anti-counterfeiting label paper prepared by drop coating with dynamic fluorescent anti-counterfeiting nanoparticle ink prepared in the embodiments of the present invention, under ultraviolet light (365 nm, 60 W) irradiation for different times. Implementation
[0053] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. Example 1
[0054] This embodiment provides a method for synthesizing a polymethacrylate polymer with certain hydrophilic photochromic fluorescence properties.
[0055] 1. Preparation of triphenylvinylphenol methacrylate monomer (denoted as M2):
[0056] In this embodiment, monomer M2 is prepared from benzophenone via McMurry coupling and esterification reactions, and its structural formula is:
[0057] ;
[0058] For detailed synthesis steps, please refer to the literature ( Journal of Materials Chemistry 2012, 22 ,15128-15135.). Under argon protection, benzophenone (7.3 g, 40 mmol), 4-hydroxybenzophenone (9.5 g, 48 mmol), and zinc powder (12 g, 185 mmol) were added to a 250 mL flask, followed by 80 mL of tetrahydrofuran. Titanium tetrachloride (10 mL, 90 mmol) was added dropwise under ice-water bath conditions. After the addition was complete, the temperature was raised to 75 °C, and the reaction was allowed to proceed for 10 h. The reaction yielded 4-(1,2,2-triphenylvinyl)phenol. Subsequently, under argon protection, methacrylic acid (0.73 g, 8.5 mmol), 4-dimethylaminopyridine (0.06 g, 0.49 mmol), dicyclohexylcarbodiimide (1.8 g, 8.8 mmol), and dichloromethane (120 mL) were added to a 250 mL flask, and the mixture was stirred under ice-water bath conditions for 30 h. The reaction mixture was then slowly added at 3 min, followed by the slow addition of 4-(1,2,2-triphenylvinyl)phenol (3.2 g, 9.3 mmol). After the addition was complete, the mixture was allowed to return to room temperature for 24 h to give monomer M2 (1.8 g, 45.2% yield).
[0059] 2. Preparation of spiropyranyl ethyl methacrylate monomer (denoted as M3):
[0060] In this embodiment, monomer M3 is obtained from 2,3,3-trimethyl-3H-indole through substitution, addition, and esterification reactions, and its structural formula is:
[0061] ;
[0062] For detailed synthesis steps, please refer to the literature ( Journal of the American Chemical Society 2001, 123 , 4651-4652.). Under argon protection, 2,3,3-trimethylindole (25 g, 15 mmol), 2-bromoethanol (2.46 g, 20 mmol) and acetonitrile (20 mL) were added to a 100 mL flask, heated to 85 °C, and reacted for 24 h. After the reaction was completed, 1-(2-hydroxyethyl)-2,3,3-trimethyl-3H-indole-1-onium was obtained. Next, 1-(2-hydroxyethyl)-2,3,3-trimethyl-3H-indole-1-onium (5.86 g, 20 mmol), potassium hydroxide (1.84 g, 32 mmol), and deionized water (100 mL) were added to a flask and reacted at room temperature for 30 min to obtain 9,9,9a-trimethyl-2,3,9,9a-tetrahydrooxazolo[3,2-a]indole; then, 9,9,9a-trimethyl-2,3,9,9a-tetrahydrooxazolo[3,2-a]indole (3.36 g, 16 mmol), 4-nitrosalicylic acid (4.0 g, 24 mmol), and 50 mL of anhydrous ethanol were added to a 100 mL flask and heated to 85 °C for 3 minutes. After the reaction was complete, 2-(3',3'-dimethyl-6-nitrospiro[chromene-2,2'-dihydroindole]-1'-yl)ethane-1-ol was obtained. Then, under argon protection, methacrylic acid (1.3 g, 15 mmol), 4-dimethylaminopyridine (0.084 g, 0.69 mmol), dicyclohexylcarbodiimide (2.5 g, 12 mmol), and dichloromethane (100 mL) were added to a 250 mL flask. The mixture was stirred in an ice-water bath for 30 min, followed by the slow addition of 2-(3',3'-dimethyl-6-nitrospiro[chromene-2,2'-dihydroindole]-1'-yl)ethane-1-ol (5 g, 14 mmol). After the addition was complete, the mixture was allowed to return to room temperature and reacted for 24 h to obtain monomer M3 (3.4 g, 47% yield).
[0063] 3. Preparation of polymer P (MMA-HEMA-TPEMA-SPMA):
[0064] See appendix Figure 1This diagram illustrates the synthetic route of the polymethyl methacrylate polymer (denoted as P(MMA-HEMA-TPEMA-SPMA)) with photochromic fluorescence properties provided in this embodiment. Specifically, under argon protection, methyl methacrylate monomers (M1, 0.33 g, 3.2 mmol), monomers M2 (0.073 g, 0.17 mmol), M3 (0.03 g, 0.07 mmol), M4 (0.023 g, 0.17 mmol), and the catalyst azobisisobutyronitrile (0.024 g, 0.14 mmol) were sequentially added to a 50 mL two-necked flask. Then, 3 mL of N,N-dimethylformamide was added, and the mixture was heated to 75 °C and stirred for 24 h. After the reaction was complete, the mixture was cooled to room temperature, and the product was added dropwise to 150 mL of methanol to precipitate the product. The product was then placed in a vacuum drying oven to obtain a white solid. Yield: 0.15 g, yield: 34.90%. 1 H NMR (300 MHz, CDCl3) δ8.04 (s, 1H), 7.12 (s, 20H), 7.05 (s, 9H), 6.83 (s, 2H), 5.94 – 4.82 (m, 2H), 4.14 (s, 4H), 3.87 (s, 2H), 3.62 (s, 31H), 3.42 (s, 5H). GPC: `M n = 10.7 kDa; `M w = 1.80 kDa; `M w / `M n = 1.68, n=87.
[0065] The structural formula of polymer P (MMA-HEMA-TPEMA-SPMA) is:
[0066] ,
[0067] Where n is the number of repeating units, n=80~90; x=0.01~0.05, y=0.03~0.10, z=0.03~0.10 (according to the claim, "by the amount of substance, 1-xy parts M1, x parts M2, y parts M3, z parts M4, in the structural formula of the embodiment, 1-x-y=0.88, x=0.05, y=0.02, z=0.05 should be a definite value").
[0068] See appendix Figure 2It is the nuclear magnetic resonance spectrum of monomers M1, M2, M3, M4 and polymer P (MMA-HEMA-TPEMA-SPMA) provided in this embodiment, by Figure 2 It can be seen that M1, M2, M3, M4 and P (MMA-HEMA-TPEMA-SPMA) are consistent with the structures shown in the synthesis roadmap.
[0069] See appendix Figure 3 It is the infrared spectrum of monomers M1, M2, M3, M4 and polymer P (MMA-HEMA-TPEMA-SPMA) provided in this embodiment, by Figure 3 It can be further confirmed that M1, M2, M3, M4 and P (MMA-HEMA-TPEMA-SPMA) are identical to the structures shown in the synthetic route diagram. Example 2
[0070] This embodiment provides a dynamic fluorescent anti-counterfeiting nanoparticle of polymethacrylate polymer with certain hydrophilic photosensitive dynamic color-changing fluorescence properties and its preparation.
[0071] The photochromic polymethacrylate polymer P (MMA-HEMA-TPEMA-SPMA) synthesized in Example 1 was dissolved in tetrahydrofuran (5 mL) at a concentration of 1 mg / mL. Then, under strong ultrasonication, 1 mL of the solution was rapidly injected into 10 mL of water, and the mixture was ultrasonicated for 5 minutes. The mixture was then placed in a vacuum environment (21 kPa) at 40°C to remove the tetrahydrofuran, yielding dynamic fluorescent anti-counterfeiting nanoparticles of the photochromic polymethacrylate polymer.
[0072] See appendix Figure 4 This is a transmission electron microscope image of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in this embodiment. The prepared nanoparticles have a uniform particle size distribution and are granular.
[0073] See appendix Figure 5 This is the hydrated particle size distribution map of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in this embodiment, which was measured by dynamic light scattering. The average particle size of the prepared nanoparticles is 45 nm, and the particle size distribution index is 0.039.
[0074] See appendix Figure 6This figure shows the fluorescence emission of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in this embodiment under ultraviolet light (365 nm, 12 W) irradiation for different times (excitation wavelength: 365 nm). As can be seen from the figure, in the initial state (t = 0 s), the nanoparticles emit blue fluorescence in the range of 400 nm to 550 nm under 365 nm ultraviolet light excitation, corresponding to the fluorescence emission of TPE. With increasing ultraviolet light irradiation time, the fluorescence emission in the range of 400 nm to 550 nm (corresponding to TPE) gradually decreases. Simultaneously, the fluorescence emission in the range of 600 nm to 700 nm increases, with a slight redshift (within 10 nm). This position corresponds to the fluorescence emission of MC (the isomerization product of SP under ultraviolet irradiation). The decrease in fluorescence intensity in the range of 400 nm to 550 nm is attributed to the fluorescence resonance energy transfer between TPE and MC, a process that lasts for approximately 5 minutes until a stable state is reached. It can be seen that the nanoparticles in the initial state become discolored nanoparticles after being continuously irradiated with 365 nm ultraviolet light for more than 5 minutes. Under the excitation of 365 nm ultraviolet light, the nanoparticles emit red fluorescence in the range of 600 nm to 700 nm.
[0075] See appendix Figure 7 This is a fluorescence emission spectrum of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in this embodiment after irradiation with ultraviolet light for 5 min, followed by irradiation with visible light (white light) for different times (excitation wavelength of 365 nm). The spectrum shows that as the irradiation time with visible light increases, the fluorescence emission in the 400 nm–550 nm range gradually recovers, while the fluorescence emission peak in the 600 nm–700 nm range gradually decreases. This is because under visible light irradiation, the MC recovers to the closed-loop SP structure, the energy transfer process gradually disappears, and the TPE fluorescence recovers. This recovery process lasts for 10 min. Therefore, it can be concluded that after continuous irradiation with visible light for more than 10 min, the discolored nanoparticles obtain recovered nanoparticles, and their fluorescence emission under 365 nm ultraviolet light excitation almost recovers to the initial state of the nanoparticles.
[0076] See appendix Figure 8 The figure shows the relationship between the fluorescence intensity and the number of cycles of the dynamic fluorescent anti-counterfeiting nanoparticles prepared in this embodiment under 10 cycles of alternating ultraviolet light (1 minute) and visible light (5 minutes). As can be seen from the figure, the fluorescence intensity fluctuates significantly in the first cycle (<20%). However, it exhibits good resistance to light fatigue and stability after the subsequent nine cycles, and demonstrates excellent photochromic properties after 10 consecutive ultraviolet-visible light irradiation cycles, making it suitable for multi-layered anti-counterfeiting verification and encryption. Example 3
[0077] This embodiment provides a method for applying dynamic fluorescent anti-counterfeiting using fluorescent nanoparticles prepared in Example 2. The specific steps are as follows: A digital camera is used to record the fluorescence color of the nanoparticles under ultraviolet light (365 nm, 60 W) irradiation for different times (0 s, 5 s, 10 s). The results show that the dynamic fluorescent anti-counterfeiting nanoparticles exhibit dynamic changes in fluorescence color after ultraviolet irradiation. Specifically, as the ultraviolet irradiation time increases, the fluorescence generated by the nanoparticles after excitation gradually changes from blue to light purple and finally to red.
[0078] See appendix Figure 9 The figures show digital fluorescence images of the nanoparticles prepared in Example 2 under different UV irradiation times. The images show that before UV irradiation, the initial fluorescence color of the nanoparticles is (blue); after 5 seconds of UV irradiation, the fluorescence color is (pale purple), indicating that the nanoparticles are in an intermediate state between the initial and color-changing states, with a fluorescence color between red and blue; after 10 seconds of UV irradiation, the fluorescence color is (red), showing a significant change, indicating that the nanoparticles are in a color-changing state. Therefore, the prepared polymethyl methacrylate polymer nanoparticles with photochromic dynamic fluorescence properties possess excellent photochromic performance and have significant application value in dynamic fluorescent anti-counterfeiting. Example 4
[0079] This embodiment provides a dynamic fluorescent anti-counterfeiting nanoparticle ink and its preparation.
[0080] The dynamic fluorescent anti-counterfeiting nanoparticles synthesized in Example 2 were concentrated to a polymer concentration of 1 mg / mL to 4 mg / mL to obtain a nanoparticle concentration of 0.05 mg / mL to 0.2 mg / mL. Then, 1 mL of the above concentrated nanoparticle solution was mixed with 250 μL of glycerol and 75 μL of ethanol to obtain dynamic fluorescent anti-counterfeiting nanoparticle ink. Example 5
[0081] This embodiment provides several application methods for the dynamic fluorescent anti-counterfeiting nanoparticle ink prepared in Example 4. The specific steps are as follows: the concentrated nanoparticle ink is applied to brush lettering, label paper, and pen handwriting. Brush lettering is prepared by directly using a commercially available brush (1 cm wide) to dip into the ink and write on qualitative filter paper; label paper is prepared by uniformly dripping ink onto the qualitative filter paper and allowing it to air dry naturally; pen handwriting is prepared by filling a commercially available pen with ink and writing on the qualitative filter paper.
[0082] See appendix Figure 10The figures show the fluorescence of the letter "C" written on cellulose paper using a brush dipped in the nanoparticle ink prepared in Example 5, under ultraviolet (365 nm, 60 W) light for different durations. The figures show that before ultraviolet irradiation, the letter is essentially invisible under natural light; however, under ultraviolet light, the fluorescence of the letter on the paper is clearly visible. As the irradiation time increases, the fluorescence color changes from blue to pinkish-white, and finally to bright red, and the letter also shows a faint purple tinge under natural light. These changes are completely reversible under alternating ultraviolet and visible light irradiation.
[0083] See appendix Figure 11 The figures show digital fluorescence images of the word "SOOCHOW" written with a commercially available blank fountain pen pre-filled with the nanoparticle ink prepared in Example 5, under UV (365 nm, 60 W) irradiation for different times. The figures show that "SOOCHOW" exhibits strong blue fluorescence under 365 nm UV light. After 60 s of UV irradiation, the fluorescence color gradually changes from blue to red.
[0084] See appendix Figure 12 The figures show digital fluorescence photographs of rewritable fluorescent anti-counterfeiting labels prepared using the nanoparticle ink prepared in Example 5, after being irradiated with ultraviolet light (365 nm, 60 W) for different durations. The figures show that, using a common 365 nm ultraviolet lamp as the instrument, the fluorescent color of the label changes from blue to pale purple and finally to red after irradiation for 0 s, 10 s, and 60 s. Therefore, as described above, the fluorescence intensity and color of various forms of anti-counterfeiting materials prepared using nanoparticle ink can be finely adjusted, and the decryption method and encryption pattern can also be changed, easily meeting customers' personalized customization requirements and showing great potential in the field of anti-counterfeiting encryption.
Claims
1. A hydrophilic methacrylate polymer with photochromic fluorescence function, characterized in that... Its structural formula is: ； Where n is the number of repeating units, n=100~120; x=0.01~0.05, y=0.03~0.10, z=0.03~0.
10.
2. A method for preparing a hydrophilic methacrylate polymer with photosensitive dynamic color-changing fluorescence function, characterized in that: Methyl methacrylate monomer is designated as M1, triphenylvinylphenol methacrylate monomer as M2, spiropyranyl ethyl methacrylate monomer as M3, and hydroxyethyl methacrylate as M4. These monomers are added in the following proportions: M1 3.2 mmol, M2 0.17 mmol, M3 0.07 mmol, M4 0.17 mmol, azobisisobutyronitrile 0.14 mmol, and N,N-dimethylformamide 3 mL. The mixture of M1, M2, M3, M4, azobisisobutyronitrile, and N,N-dimethylformamide is stirred and reacted under inert gas protection at 75–85 °C for 24–48 h. After purification and drying, a hydrophilic methacrylate polymer with photosensitive dynamic color-changing fluorescence is obtained. The structural formula of the monomer M1 is: ； The structural formula of the monomer M2 is: ； The structural formula of the monomer M3 is: ； The structural formula of the monomer M4 is: 。 3. A method for preparing hydrophilic methacrylate polymer nanoparticles with photochromic fluorescence function, characterized in that... Includes the following steps: (1) Methyl methacrylate monomer is designated as M1, triphenylvinylphenol methacrylate monomer as M2, spiropyranyl ethyl methacrylate monomer as M3, and hydroxyethyl methacrylate as M4. The monomers are added in the following proportions: M1 is 3.2 mmol, M2 is 0.17 mmol, M3 is 0.07 mmol, M4 is 0.17 mmol, azobisisobutyronitrile is 0.14 mmol, and N,N-dimethylformamide is 3 mL. M1, M2, M3, M4, azobisisobutyronitrile, and N,N-dimethylformamide are mixed and stirred. The mixture is reacted for 24 to 48 h under inert gas protection and at a temperature of 75 to 85 °C. After purification and drying, a methacrylate polymer is obtained. (2) Dissolve the methacrylate polymer obtained in step (1) in tetrahydrofuran solvent at a concentration of 0.05 mg / mL to 0.2 mg / mL to obtain a polymer solution; add the polymer solution to deionized water at a volume ratio of 0.5 to 2:5 to 20, and under ultrasonic conditions, use the reprecipitation method to obtain a mixed solution. After removing tetrahydrofuran, a hydrophilic methacrylate polymer nanoparticle with photoluminescent dynamic color change function is obtained.
4. The method for preparing hydrophilic methacrylate polymer nanoparticles with photochromic fluorescence function according to claim 3, characterized in that: The obtained hydrophilic methacrylate polymer nanoparticles were nanoparticle solutions with a polymer concentration of 0.05–0.2 mg / mL.
5. A method for preparing hydrophilic methacrylate polymer nanoparticles with photochromic fluorescence function according to claim 4, characterized in that: The polymer concentration of the obtained nanoparticle solution was concentrated to 1–4 mg / mL.
6. A hydrophilic methacrylate nanoparticle with photochromic fluorescence function obtained by the preparation method according to claim 3, characterized in that: In water, it exhibits stable suspension and photochromic fluorescence properties, including the initial state, the color-changing state, and the recovery state: In its initial state, the nanoparticles are colorless under natural light; when excited by 365 nm ultraviolet light, the nanoparticles emit blue fluorescence in the range of 400–550 nm. The color-changing state refers to the initial state of the nanoparticles being light blue under natural light after continuous irradiation with 365 nm ultraviolet light for 5 minutes; and emitting red fluorescence in the range of 600-700 nm when excited by 365 nm ultraviolet light. The recovery state refers to the nanoparticles in the discolored state returning to their initial state after being continuously irradiated with visible light for more than 10 minutes.
7. The application of the hydrophilic polymer nanoparticles with photochromic fluorescence function as described in claim 6, characterized in that... For the preparation of dynamic fluorescent anti-counterfeiting ink; a solution of hydrophilic polymer nanoparticles with photoluminescent dynamic color-changing function at a polymer concentration of 1-4 mg / mL is mixed with glycerol and ethanol at a volume ratio of 1:0.25:0.075 to obtain a dynamic fluorescent anti-counterfeiting ink.
8. The application of the hydrophilic polymer nanoparticles with photochromic fluorescence function according to claim 7, characterized in that: The prepared dynamic fluorescent anti-counterfeiting ink is coated onto the surface of a permeable matrix material to obtain dynamic fluorescent anti-counterfeiting material or dynamic fluorescent encryption material.
9. The application of the hydrophilic polymer nanoparticles with photochromic fluorescence function according to claim 8, characterized in that: The permeable matrix material includes cellulose paper and cloth.