Construction method and application of NaYF4: Ln < 3 + > reversible photochromic polymer core-shell nanoparticles

Abstract

The invention discloses a construction method and application of NaYF4: Ln < 3 + > reversible photochromic polymer core-shell nanoparticles, and relates to the technical field of material preparation, and the technical key points are as follows: the NaYF4: Ln < 3 + > reversible photochromic polymer core-shell nanoparticles are prepared by utilizing the characteristics of luminescence concealment of rare earth doped NaYF4: Ln < 3 + > up-conversion nanoparticles (UCNPs) and dynamic fluorescence of a reversible photochromic polymer; the near-infrared / ultraviolet light dual-mode reversible photochromic fluorescent material is constructed, and the synergistic luminescence mechanism of the near-infrared / ultraviolet light dual-mode reversible photochromic fluorescent material is ascertained so as to realize the application of the near-infrared / ultraviolet light dual-mode reversible photochromic fluorescent material in multi-mode fluorescent anti-counterfeiting coding.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, in particular to NaYF4:Ln 3+ @Construction method and application of reversible photochromic polymer core-shell nanoparticles. Background Art

[0002] Traditional anti-counterfeiting technologies currently in commercial use include watermarks, barcodes, and QR codes. However, their single-pattern nature and ease of counterfeiting make them difficult to achieve effective anti-counterfeiting effectiveness in practice. With the continuous advancement of anti-counterfeiting technology, more advanced and effective technologies such as radio frequency identification, laser holography, and nuclear dual-card anti-counterfeiting technology are also being developed. However, these anti-counterfeiting technologies typically require complex and expensive equipment for preparation or testing, resulting in high costs that significantly limit their application areas. Consequently, fluorescent anti-counterfeiting technology, with its advantages of high concealment, excellent fluorescence intensity, and complex coding patterns, has begun to attract widespread attention and has gradually become one of the most commonly used anti-counterfeiting technologies.

[0003] Typical optical materials, such as organic dyes, semiconductor quantum dots, rare earth complexes, and rare earth-doped upconversion fluorescent materials, have been demonstrated to be applicable to the development of fluorescent anti-counterfeiting technologies. Organic fluorescent dyes, quantum dots, and rare earth complexes are down-conversion luminescent materials, emitting light by absorbing higher-energy ultraviolet light and emitting one or more lower-energy photons. However, these traditional fluorescent materials often suffer from drawbacks such as high toxicity, susceptibility to photobleaching, and broad fluorescence emission peaks, limiting their application in fluorescent anti-counterfeiting applications.

[0004] To this end, the present invention aims to provide NaYF4:Ln 3+ @Construction method and application of reversible photochromic polymer core-shell nanoparticles to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems and provide NaYF4:Ln 3+ @Construction method and application of reversible photochromic polymer core-shell nanoparticles, using rare earth doped NaYF4:Ln 3+ Based on the characteristics of the concealed luminescence of upconversion nanoparticles (UCNPs) and the dynamic fluorescence of reversible photochromic polymers, NaYF4:Ln3+@ reversible photochromic polymer core-shell nanoparticles were prepared, and near-infrared / ultraviolet dual-mode reversible photochromic fluorescent materials were constructed. The synergistic luminescence mechanism was explored in order to realize its application in multimodal fluorescent anti-counterfeiting coding.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides NaYF4:Ln 3+@Reversible photochromic polymer core-shell nanoparticle construction method and application, the method comprises the following steps:

[0008] S1, preparing spiropyran monomer SPMA;

[0009] S2. Synthesis of CSNPs with high upconversion fluorescence intensity by a two-step oleic acid-mediated thermal decomposition method;

[0010] S3, using tetraethyl orthosilicate (TEOS) and KH-550 aminosilane (MPS) as silicon sources, SiO2 containing amino functional groups was coated on the surface of CSNPs by sol-gel technology to obtain CSNPs@SiO2-NH2 particles;

[0011] S4, utilizing the esterification reaction between the amino groups on the surface of CSNPs@SiO2-NH2 particles and the carboxyl groups on the RAFT agent CDTPA, CDTPA is grafted onto the surface of CSNPs@SiO2-NH2 particles to obtain CSNPs@SiO2-CDTPA particles;

[0012] S5. Using GMA and SPMA as functional monomers, P(GMA-co-SPMA) reversible photochromic polymer was grafted onto CSNPs@SiO2-CDTPA particles through surface RAFT polymerization to obtain CSNPs@p(GMA-co-SPMA) nanoparticles.

[0013] The CDTPA is 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid.

[0014] The preparation method of the SPMA is as follows:

[0015] S101, using 2,3,3-trimethyl-3H-indole as a raw material to react with bromoethanol to synthesize the intermediate 1-(2-hydroxyethyl)-2,3,3-trimethyl-3H-bromoindole;

[0016] S102, reacting the synthesized bromide with 2-hydroxy-5-nitrobenzaldehyde to obtain a spiropyran compound (2-(3,3-dimethyl-6-nitro-3H-spiro(chromene-2,2-dihydroindole)-1-ethanol));

[0017] S103. The hydroxyl group of the synthetic spiropyran compound is reacted with acryloyl chloride to introduce a polymerizable double bond to prepare SPMA with double bond modification.

[0018] The CSNPs@p(GMA-co-SPMA) nanoparticles are used to prepare infrared / ultraviolet dual-mode reversible photochromic fluorescent anti-counterfeiting inks. The CSNPs@p(GMA-co-SPMA) nanoparticles are dispersed in a 1,4-dioxane solvent to prepare fluorescent inks, which are then used to construct fluorescent anti-counterfeiting patterns.

[0019] Compared with the existing technology, this solution has the following beneficial effects:

[0020] The present invention synthesizes UCNPs with enhanced fluorescence by a two-step thermal decomposition method regulated by oleic acid ligands. By developing a feasible route for the controllable preparation of functional polymer-coated UCNPs nanomaterials, the synergistic luminescence mechanism of UCNPs and reversible photochromic polymers is revealed, promoting the application of functional polymer-coated rare earth-doped NaYF4 nanoparticles in fields such as fluorescent anti-counterfeiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The NaYF4:Ln 3+ @Flowchart of reversible photochromic polymer core-shell nanoparticles;

[0022] Figure 2 is a structural diagram of a spiropyran small molecule in an embodiment of the present invention;

[0023] Figure 3 Schematic diagram of the synthesis and amino modification of NaYF4 upconversion nanoparticles in an embodiment of the present invention;

[0024] Figure 4 Schematic diagram of NaYF4 upconversion nanoparticles grafted with RAFT agent CDTPA in an embodiment of the present invention;

[0025] Figure 5 Schematic diagram of rare earth-doped NaYF4 upconversion nanoparticles coated with spiropyran polymer having a core-shell structure according to an embodiment of the present invention;

[0026] Figure 6 This is a technical roadmap for the synthesis and fluorescent anti-counterfeiting application of CSNPs@p(GMA-co-SPMA) particles in the embodiment of the present invention;

[0027] Figure 7 Schematic diagram of the synthesis of spiropyran small molecules in an embodiment of the present invention;

[0028] Figure 8 This is the SPOH and SPMA H NMR spectra of (2-hydroxyethyl)-2,3,3-trimethyl-3H-bromoindole in the examples of the present invention. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described in detail below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0030] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0031] Example:

[0032] 1. Synthesis of reversible photochromic spiropyran compounds

[0033] Spiropyran compounds (SP) are a class of organic color-changing molecules composed of two aromatic heterocycles (one of which is a pyran ring) connected by a spiro carbon atom. By designing and synthesizing spiropyran compounds with special structures, they can be given some special properties, such as photochromism, mechanochromism and electrochromism. The synthesis of spiropyran compounds is usually in anhydrous ethanol and benzene, under weak base catalysis, by condensing indoline salt compounds and salicylaldehyde compounds. By connecting different types of substituents to salicylaldehyde and modifying different substituents on indoline, spiropyran compounds with various active groups at different positions can be synthesized. By introducing different types of substituents into the spiropyran parent structure, spiropyran compounds can be divided into three special structures of spiropyran small molecules: SP1, SP2 and SP3. The present invention adopts the spiropyran small molecule with the special structure of SP2 to prepare a polymer shell with photochromic properties.

[0034] SP2-structured spiropyran small molecules are synthesized by the condensation of indolinium salts and salicylaldehydes. The side chains of these synthesized SP2-spiropyran small molecules bear active hydroxyl groups, which can be further introduced into polymerizable double bonds through acyl chlorination. The synthesis of SP2-spiropyran small molecules is simple, and double bond modification is easily achieved using inexpensive reagents. SP2-spiropyran small molecules are representative spiropyran compounds with rapid photochromic changes.

[0035] 2. Synthesis of rare earth-doped NaYF4 upconversion nanoparticles and surface modification with RAFT agents

[0036] Thermal decomposition and hydrothermal methods are widely reported in the literature for the synthesis of rare-earth-doped NaYF4 upconversion fluorescent materials. The hydrothermal method is capable of synthesizing rare-earth-doped NaYF4 upconversion fluorescent materials with a variety of morphologies, but its reaction cycle is relatively long, time-consuming, and energy-intensive, and the resulting upconversion fluorescent materials are generally on the micrometer scale. Compared to the hydrothermal method, the thermal decomposition method has a shorter reaction cycle and produces nanoscale upconversion fluorescent materials with uniform particle size and high crystallinity. However, the fluorescence intensity of upconversion fluorescent nanomaterials synthesized by the thermal decomposition method is currently weak. To address this issue, an optically inert shell layer is coated on the surface of the upconversion fluorescent nanomaterial, separating the surface groups from the internal core and achieving fluorescence enhancement. The surface silanization modification of NaYF4 upconversion nanoparticles usually adopts the traditional Stober method or microemulsion method. The basic principle is to hydrolyze the silane coupling agent in an alkaline environment and coat the surface of the upconversion fluorescent nanoparticles with a layer of SiO2 shell, thereby effectively improving the water solubility of the particles. Then, by hydrolyzing the silane containing special functional groups, the functional groups are further modified on the surface to functionalize the surface of the nanoparticles. Since the Stober method or microemulsion method requires hydrolysis in an alkaline aqueous solution, the hydrolysis reaction rate is difficult to control, resulting in uneven thickness of the SiO2 shell, which affects the fluorescence properties of the upconversion particles. In response to the above problems, a SiO2 shell is coated on the surface of the upconversion fluorescent nanomaterial by the reverse microemulsion method, and then KH-550 aminosilane (3-aminopropyltriethoxysilane) containing amino functional groups is hydrolyzed in order to synthesize upconversion nanoparticles modified with amino groups, such as Figure 3 shown.

[0037] In traditional free radical polymerization, the chain transfer reaction is irreversible, which can easily lead to a decrease in the degree of polymerization and uncontrollable reactions. When a chain transfer agent with a large chain transfer constant is selected and its concentration is large enough, free radical polymerization can be converted into controllable / active free radical polymerization. Therefore, the key to the successful implementation of reversible addition-fragmentation chain transfer (RAFT) polymerization lies in whether a suitable compound with a high chain transfer constant and a specific structure can be found as a RAFT chain transfer agent. The RAFT agent selected in the present invention is 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDTPA). The end of the RAFT agent contains a trithiocarbonate group, which can further undergo a reversible addition-fragmentation chain transfer (RAFT) polymerization reaction; the other end of the RAFT agent has an active carboxyl group, which can react with the amino group on the surface of the NaYF4 upconversion nanoparticles under certain conditions, so that the surface of the NaYF4 upconversion nanoparticles is successfully grafted with the RAFT agent CDTPA that can control the polymerization reaction, such as Figure 4 shown.

[0038] 3.NaYF4:Ln 3+Synthesis and synergistic luminescence mechanism of reversibly photochromic polymer core-shell nanoparticles

[0039] Polymer coating on the surface of NaYF4 upconversion nanoparticles is an effective method to give them good water solubility and functionality. By using NaYF4 upconversion nanoparticles grafted with synthetic RAFT agents as seeds and using emulsion RAFT polymerization, the following can be controlled to prepare Figure 5 The core-shell polymer-coated NaYF4 upconversion nanoparticles are shown. By adding spiropyran monomers, the NaYF4 upconversion nanoparticles are endowed with environmental responsiveness.

[0040] 4. Inkjet printing of NaYF4:Ln 3+ Spiropyran core-shell nanoparticles construct multimodal optical anti-counterfeiting codes

[0041] Inkjet printing has high precision, fast speed, and no need for plate making, which is more in line with the development trend of digital printing and flexible production. It is also a common method for patterning fluorescent inks. 3+ Using spiropyran core-shell nanoparticles, researchers have developed an ink formula that maintains all optical properties. By optimizing the pigment-to-binder ratio, they have created a near-infrared / ultraviolet dual-mode reversible photochromic fluorescent anti-counterfeiting ink, producing a highly accurate fluorescent coded anti-counterfeiting pattern. Using tunable upconversion fluorescence color, fluorescence emission under UV irradiation, and color changes in response to light stimulation as encoding units, they have compiled a trimodal information encoding table. By capturing images of the coded anti-counterfeiting pattern under different excitation light states and decoding them according to the encoding table, they achieve multimodal optical encryption and decryption of the anti-counterfeiting information.

[0042] 5. Conclusion

[0043] The technical route and basic principle of the present invention are as follows: first, CSNPs with high upconversion fluorescence intensity are synthesized by a two-step thermal decomposition method mediated by oleic acid; then, tetraethyl orthosilicate (TEOS) and KH-550 aminosilane (MPS) are used as silicon sources, and SiO2 containing amino functional groups is coated on the surface of CSNPs by sol-gel technology to obtain CSNPs@SiO2-NH2 particles; then, CDTPA is grafted onto the CSNPs@SiO2-NH2 particles by the esterification reaction between the amino groups on the surface of CSNPs@SiO2-NH2 particles and the carboxyl groups on the RAFT reagent CDTPA. The researchers then coated the surface of O2-NH2 particles to obtain CSNPs@SiO2-CDTPA particles. Subsequently, using GMA and SPMA as functional monomers, they grafted P(GMA-co-SPMA), a reversible photochromic polymer, onto the CSNPs@SiO2-CDTPA particles via surface RAFT polymerization, yielding CSNPs@p(GMA-co-SPMA) nanoparticles. Finally, the CSNPs@p(GMA-co-SPMA) nanoparticles were dispersed in a 1,4-dioxane solvent to prepare a fluorescent ink, which was then inkjet-printed onto paper to create an advanced fluorescent anti-counterfeiting pattern. The pattern exhibits dual-mode fluorescence, exhibiting green fluorescence under 980nm laser irradiation and red fluorescence under 365nm UV light. Furthermore, after the UV light is removed, the pattern does not disappear immediately, but instead displays a purple pattern under natural light. Furthermore, the pattern exhibits reversible photochromic properties. Under different exposure times to ultraviolet light, the pattern gradually changes from colorless to purple. Under different exposure times to white light, the pattern gradually reverts from purple to its original colorless state. This fluorescent anti-counterfeiting technology is significantly advanced and has broad application prospects in the future of high-level anti-counterfeiting.

[0044] The synthetic route for the spiropyran monomer is as follows: 2,3,3-trimethyl-3H-indole is first reacted with bromoethanol to form a salt, resulting in the synthesis of the intermediate 1-(2-hydroxyethyl)-2,3,3-trimethyl-3H-bromoindole. Subsequently, the synthesized bromide is reacted with 2-hydroxy-5-nitrobenzaldehyde to obtain the spiropyran compound (2-(3,3-dimethyl-6-nitro-3H-spiro(chromene-2,2-dihydroindole)-1-ethanol)). Finally, the hydroxyl group of the synthesized spiropyran compound is reacted with acryloyl chloride to introduce a polymerizable double bond, resulting in the preparation of a double-bond-modified spiropyran monomer.

[0045] A SiO2 shell was coated on the surface of an upconversion fluorescent nanomaterial via a reverse microemulsion method. Amino-modified upconversion nanoparticles were synthesized by hydrolyzing KH-550 aminosilane (3-aminopropyltriethoxysilane), which contains amino functional groups. Oxalyl chloride reacted with the RAFT agent CDTPA in anhydrous dichloromethane, and the solvent was removed by rotary evaporation to obtain chlorinated CDTPA. The chlorinated CDTPA was then reacted with amino-modified upconversion nanoparticles in anhydrous dichloromethane, and the solvent was removed by rotary evaporation to obtain NaYF4 upconversion nanoparticles with the RAFT agent grafted onto their surfaces. The amount of RAFT agent grafted onto the surface of the NaYF4 upconversion nanoparticles can be controlled by controlling the amount of amino groups on the surface, which can be regulated by hydrolysis of the aminosilane.

[0046] NaYF4:Ln 3+ In the synthesis of reversibly photochromic polymer core-shell nanoparticles, NaYF4 upconversion nanoparticles grafted with a synthetic RAFT agent were used as seeds, and emulsion RAFT polymerization was employed to prepare polymer-coated NaYF4 upconversion nanoparticles with a controllable core-shell structure. Using NaYF4 upconversion nanoparticles with a specific surface-grafted RAFT agent as seeds, the polymerization was carried out using hydrophobic monomers such as glycidyl methacrylate, acrylate monomers, and functional spiropyran monomers in an oxygen-free 1,4-dioxane system. Optimization of polymerization conditions: Using NaYF4 upconversion nanoparticles with a specific surface-grafted RAFT agent as seeds, glycidyl methacrylate and photochromic spiropyran monomers were used to synthesize responsive polymer-coated upconversion nanoparticles with a core-shell structure via seeded emulsion RAFT polymerization.

[0047] The NaYF4 and spiropyran reversible photochromic polymer core-shell nanoparticles of the present invention are used as fluorescent anti-counterfeiting materials, which not only utilize the luminescence concealment characteristics of rare earth upconversion nanoparticles, but also combine the characteristics of dynamic fluorescence of reversible photochromic polymers, thereby developing upconversion core-shell nanoparticles with multiple anti-counterfeiting functions.

[0048] The above specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the embodiments as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. NaYF4:Ln 3+ @Reversible photochromic polymer core-shell nanoparticle construction method and application, characterized by: The method comprises the following steps: S1, preparing spiropyran monomer SPMA; S2. Synthesis of CSNPs with high upconversion fluorescence intensity by a two-step oleic acid-mediated thermal decomposition method; S3, using tetraethyl orthosilicate and KH-550 aminosilane as silicon sources, SiO2 containing amino functional groups was coated on the surface of CSNPs by sol-gel technology to obtain CSNPs@SiO2-NH2 particles; S4, utilizing the esterification reaction between the amino groups on the surface of CSNPs@SiO2-NH2 particles and the carboxyl groups on the RAFT agent CDTPA, CDTPA is grafted onto the surface of CSNPs@SiO2-NH2 particles to obtain CSNPs@SiO2-CDTPA particles; S5. Using GMA and SPMA as functional monomers, P(GMA-co-SPMA) reversible photochromic polymer was grafted onto CSNPs@SiO2-CDTPA particles through surface RAFT polymerization to obtain CSNPs@p(GMA-co-SPMA) nanoparticles.

2. NaYF4:Ln as claimed in claim 1 3+ @Reversible photochromic polymer core-shell nanoparticle construction method and application, characterized by: The CDTPA is 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid.

3. NaYF4:Ln as claimed in claim 1 3+ @Reversible photochromic polymer core-shell nanoparticle construction method and application, characterized by: The preparation method of the SPMA is as follows: S101, using 2,3,3-trimethyl-3H-indole as a raw material to react with bromoethanol to synthesize the intermediate 1-(2-hydroxyethyl)-2,3,3-trimethyl-3H-bromoindole; S102, reacting the synthesized bromide with 2-hydroxy-5-nitrobenzaldehyde to obtain a spiropyran compound (2-(3,3-dimethyl-6-nitro-3H-spiro(chromene-2,2-dihydroindole)-1-ethanol)); S103. The hydroxyl group of the synthetic spiropyran compound is reacted with acryloyl chloride to introduce a polymerizable double bond to prepare SPMA with double bond modification.

4. NaYF4:Ln as claimed in claim 1 3+ @Reversible photochromic polymer core-shell nanoparticle construction method and application, characterized by: The CSNPs@p(GMA-co-SPMA) nanoparticles are used to prepare infrared / ultraviolet dual-mode reversible photochromic fluorescent anti-counterfeiting ink.

5. NaYF4:Ln as claimed in claim 4 3+ @Reversible photochromic polymer core-shell nanoparticle construction method and application, characterized by: The CSNPs@p(GMA-co-SPMA) nanoparticles are dispersed in a 1,4-dioxane solvent to prepare a fluorescent ink, which is used to construct a fluorescent anti-counterfeiting pattern.

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