Rare earth metal polymer with multiple stimulation responsiveness and preparation method thereof

Abstract

The invention discloses a rare earth metal polymer with multiple stimulation responsiveness and a preparation method thereof, two monomers SP and VTPY are mixed with methyl methacrylate (MMA) according to a certain proportion, a polymer skeleton Poly (VTPY-co-SP-co-MMA) is prepared through a free radical polymerization reaction, the polymer and Tb (Com) 3.2 H2O are further subjected to a coordination reaction according to a specific proportion, and the rare earth metal polymer with multiple stimulation responsiveness is obtained. The Poly-Tb (Coum) 3 with the stimuli-responsive discoloration characteristic is prepared by the aid of the method. The rare earth metal polymer with methyl methacrylate as a framework and rare earth terbium ions and spiropyran monomers as double emission centers is synthesized, has multiple stimulation response characteristics, provides a brand new strategy and possibility for development of rare earth-based multifunctional intelligent materials, and has wide application prospects. An innovative solution is provided for development of a thermal enhanced rare earth luminescent material, the thermosensitive fluorescence response performance of the material is greatly improved, and a new thought is provided for design of an intelligent temperature response type rare earth luminescent material.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials, and more particularly to a rare earth metal polymer with multiple stimulus responsiveness and a preparation method thereof. Background Art

[0002] Rare earth metal ions, due to their unique 4f electron shell structures, exhibit properties such as large Stokes shifts, long fluorescence lifetimes, and excellent photostability, holding significant potential for applications in fields such as anti-counterfeiting and encryption, data storage, sensors, and bioimaging. Spiropyrans are multi-stimuli-responsive compounds that can reversibly transform from a closed-ring SP structure to an open-ring MC structure, accompanied by significant changes in UV absorption, in response to external stimuli such as light, temperature, pH, metal ions, and mechanical stress. This property holds great promise for applications in smart materials, molecular electronics, nanomechanics, environmental and biosensing, and photopharmacology.

[0003] By employing fluorescence resonance energy transfer (FRET) technology to covalently bind rare earth ions to spiropyran molecules, a novel multi-stimulus-responsive material can be constructed. In this system, the rare earth ions act as energy donors, while the spiropyran molecules act as energy acceptors. When the rare earth ions are excited, the light energy they emit is transferred to the spiropyran molecules through the FRET process, triggering structural changes in the spiropyran molecules and, in turn, causing color changes. This FRET-based multi-stimulus-responsive composite material is capable of responding not only to light stimuli but also to other external stimuli, such as temperature and pH, achieving multi-stimulus-responsive functionality. By precisely regulating the material's structure and external environmental conditions, the FRET efficiency can be precisely controlled, thereby adjusting the material's luminescence properties. The design and preparation of this composite material provides innovative insights into the development of new intelligent luminescent materials and is expected to play an important role in the field of smart materials.

[0004] Because spiropyran molecules tend to accumulate tightly under solid conditions, affecting their color-changing efficiency, this remains a challenge in improving the photochromic performance of solids. Li (Li Y, Yang Y, Guo X, et al. Achieving enhanced photochromism of spiropyran in pretreated nanoporous lanthanide metal–organic frameworks for information storage applications [J]. ACS applied nano materials, 2023, 6 (7): 5817-5825.) et al. proposed a method for loading spiropyran into pretreated lanthanide metal–organic frameworks (MOFs) to improve their photoresponsiveness. The lanthanide metal–organic frameworks (MOFs) were pretreated by methanol activation and calcination at 330°C, respectively, to remove unnecessary ligands and unreacted byproducts in the MOF pores. This pretreatment technique effectively enlarged the pore size of the MOF, thereby increasing the loading amount of spiropyran and improving its photoresponsiveness. The disadvantage of spiropyran molecules being easily and tightly accumulated under solid-state conditions can be solved by pre-treating the MOF framework. However, the disadvantages of doped materials are obvious, such as uneven distribution and weak material stability. Covalently embedding spiropyran into rare earth metal polymers can effectively solve this problem.

[0005] Zhao (Zhao D, Li X, Li Q, et al. Self-healing photoluminescent polymers with photosensitive behavior for information storage and multiple-level dynamic encryption [J]. Chemical science (Cambridge), 2024, 15 (33): 1336-13312.) et al. designed and synthesized a series of photoresponsive fluorescent metal polymers (SP-Tb-IPU). By adjusting the feed ratio of SP and Tb-Bpy components, a variety of light-controlled fluorescence behaviors were obtained. These polymers exhibited excellent processing properties, outstanding mechanical properties, and self-healing properties at room temperature. The color changes of the products before and after 365nm ultraviolet light irradiation were studied, and the color changes were confirmed by UV-visible absorption spectroscopy. Zhao (Zhao D, Yue C, Li Z, et al. Photostimuli-responsive terbium metallopolymers for dynamic dual-level information encryption [J]. ACS applied polymer materials, 2024, 6 (23): 14590-14597.) et al. synthesized a photoluminescent elastomer that combines visible light and ultraviolet light-driven light stimulation response, good mechanical properties and self-healing ability. By adjusting the ratio of raw materials, the stimulation response and luminescence color of the material can be precisely controlled. The photoPU material has excellent processability, light weight, fatigue resistance, transparency, colorlessness, good mechanical properties and rapid room temperature self-healing properties. In addition, the color (absorption) and fluorescence (emission) of the material can be changed simultaneously under external light stimulation, showing broad application prospects in the field of multiple information anti-counterfeiting.

[0006] In summary, the introduction of spiropyran functional groups into rare earth polymers can significantly enhance their multi-stimulus responsiveness, endowing rare earth ions with synergistic responses to external stimuli such as light, acid, and base. However, current related systems generally suffer from technical bottlenecks such as unclear response mechanisms, uncontrollable interactions between stimuli, and irreversible response processes. Summary of the Invention

[0007] In view of this, the present invention conducts research on the key issues existing in the multiple stimulus response and light color regulation of rare earth luminescent materials. By adopting the fluorescence resonance energy transfer (FRET) technology, rare earth ions and spiropyran molecules are covalently bonded to construct a new type of multiple stimulus response material, so as to achieve accurate sensing and efficient distinction of stimulus type, sequence and intensity, breaking through its application limitations in intelligent recognition and information encryption.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] First, the present invention provides a method for preparing a rare earth metal polymer with multiple stimulus responsiveness, comprising the following steps:

[0010] Step 1: Synthesis of polymer backbone Poly(VTPY-co-SP-co-MMA)

[0011] VTPY, SP, and MMA were mixed and dispersed in DMF and completely dissolved. AIBN initiator was added under nitrogen protection, and the temperature was raised to 80°C and refluxed for 48 hours. After the reaction, the solution was diluted with dichloromethane to twice the volume of the original solution, and then icy anhydrous methanol was added to obtain a light yellow precipitate. The solution was freeze-dried in vacuo to a constant weight to obtain a light yellow powder, namely Poly(VTPY-co-SP-co-MMA);

[0012] Step 2: Synthesis of rare earth metal complexes

[0013] (2.1) 3-Acetyl-4-hydroxy-2H-chromen-2-one was dissolved in acetic acid, followed by addition of phosphorus oxychloride. The mixture was refluxed at 117-119°C for 30 min, followed by addition of phosphorus oxychloride and continued to reflux for 30 min. A precipitate was generated, which was filtered and then added with ethanol to obtain a clear, transparent solution. The solution was allowed to stand for three days until a white solid precipitated. The solution was filtered and dried at 45°C to obtain a white solid powder (Coum).

[0014] (2.2) Coum was dissolved in anhydrous ethanol and terbium chloride hexahydrate was dissolved in water. After mixing, the solution was adjusted to pH 6 with NaOH. The solution was heated to 60°C and stirred under reflux for 6 h. The solution was filtered and dried to obtain a white solid, which was Tb(Coum)3·2H2O.

[0015] Step 3: Synthesis of rare earth metal polymers

[0016] After mixing Poly(VTPY-co-SP-co-MMA) and Tb(Coum)3·2H2O, tetrahydrofuran was added to fully dissolve the mixture. The solution became clear and transparent. The mixture was heated to 60°C and refluxed for 6 hours. After the reaction, n-hexane was added to obtain a white precipitate. After filtration, the mixture was dried at a constant temperature of 45°C to obtain a white solid powder Poly-Tb(Coum)3, which is a rare earth metal polymer with multiple stimulus responsiveness.

[0017] Preferably, in step 1, the molar ratio of VTPY, SP, and MMA is 1:4:100; and the amount of the initiator added is 1.5% of the total molar mass of the mixture.

[0018] Preferably, in step (2.1), the ratio of 3-acetyl-4-hydroxy-2H-benzopyran-2-one, acetic acid, and phosphorus oxychloride is 3 g:20 mL:6.6 mL, and the volume ratio of phosphorus oxychloride added twice in sequence is 5.6:1.

[0019] Preferably, the molar ratio of Coum to terbium chloride hexahydrate in step (2.2) is 3:1.

[0020] Preferably, in step (3.1), the mass ratio of Poly(VTPY-co-SP-co-MMA) to Tb(Coum)3·2H2O is 14:1.

[0021] The present invention also provides a rare earth metal polymer Poly-Tb(Coum)3 with multiple stimulus responsiveness prepared by the method described in the above technical solution.

[0022] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a rare earth metal polymer with multiple stimulus responsiveness and a preparation method thereof, which has the following beneficial effects:

[0023] A rare earth metal polymer with a methyl methacrylate backbone and rare earth terbium ions and spiropyran monomers as dual emission centers was synthesized. The polymer exhibits multiple stimulus-responsive properties, providing new ideas and implementation paths for the design and development of rare earth-based multifunctional smart materials.

[0024] By precisely controlling the energy level matching between rare earth ligands and rare earth ions, combined with the energy transfer control between spiropyran and rare earth ions, this invention successfully achieves a negative thermal quenching effect in which the luminescence intensity of rare earth ions abnormally increases with increasing temperature. This overcomes the limitation of traditional rare earth luminescent materials that their luminescence performance decays under high temperature conditions, and provides an innovative solution for the development of thermally enhanced rare earth luminescent materials.

[0025] Based on the synergistic mechanism of the positive and negative thermal quenching effects of rare earth ions and spiropyran dual emission centers, the range of thermoluminescence color change has been significantly expanded, and the thermosensitive fluorescence response performance of the material has been significantly improved, providing a new idea for the design and application of intelligent temperature-responsive rare earth fluorescent materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0027] Figure 1 The synthetic route of Poly(VTPY-co-SP-co-MMA) and Poly-Tb(Coum)3;

[0028] Figure 2 H NMR spectra of Poly(VTPY-co-SP-co-MMA), VTPY, and SP;

[0029] Figure 3 The infrared spectra of Poly(VTPY-co-SP-co-MMA) and Poly-Tb(Coum)3;

[0030] Figure 4 This is the photochromic spectrum of Poly-Tb(Coum)3;

[0031] Figure 5 This is the acid stimulation response spectrum of Poly-Tb(Coum)3;

[0032] Figure 6 This is the acid-base stimulus response cyclicity diagram of Poly-Tb(Coum)3;

[0033] Figure 7 This is the temperature stimulus response spectrum of Poly-Tb(Coum)3. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] Example 1

[0036] Synthesis of monomers:

[0037] The preparation of VTPY includes the following steps:

[0038] First, the intermediate product TPY-OH was synthesized by weighing 2-acetylpyridine (2.42 g, 20 mmol) and p-hydroxybenzaldehyde (1.22 g, 10 mmol), placing them in a 100-mL round-bottom flask, and dissolving them in 16 mL of ethanol. Potassium hydroxide (1.21 g, 21 mmol) was then added, followed by NH3·H2O, and stirring at room temperature for 24 h. After the reaction, the solution turned reddish-brown. Glacial acetic acid was slowly added until no more precipitate formed. The precipitate was washed three times with anhydrous ethanol to obtain the crude product TPY-OH.

[0039] The crude product TPY-OH (0.24 g, 0.74 mmol) and 4-(p-chloromethyl)styrene (0.22 g, 1.44 mmol) were then dissolved in a 100 mL round-bottom flask with 10 mL of DMF. Potassium hydroxide (0.08 g, 1.45 mmol) was added and stirred at room temperature for 24 h. The solution turned from red to yellow. After the reaction was completed, distilled water was added until no precipitate was produced. The precipitate was filtered, washed with anhydrous ethanol, and dried at a constant temperature to obtain the product.

[0040] The preparation of SP includes the following steps:

[0041] Dicyclohexylcarbodiimide (1.8 g, 8.74 mmol), 4-dimethylaminopyridine (0.05 g, 0.41 mmol), and SP-OH (3 g, 8.5 mmol) were dissolved in 30 mL of dichloromethane in a 100 mL round-bottom flask, stirred in an ice-water bath under a nitrogen atmosphere for 30 min, and then methacrylic acid (0.75 g, 8.72 mmol) was added. Stirring in an ice-water bath under a nitrogen atmosphere for 30 min was continued. After returning to room temperature, stirring was continued for 48 h. After the reaction was completed, a large amount of precipitate was produced. The filtrate was filtered and dried, and then purified by column chromatography with ethyl acetate: petroleum ether (1:4) as the eluent. The product was dried at a constant temperature to obtain a light yellow powder.

[0042] Synthesis of polymer backbone Poly(VTPY-co-SP-co-MMA):

[0043] like Figure 1As shown, VTPY (44.1 mg, 0.1 mmol), SP (168 mg, 0.4 mmol), and MMA (1 g, 10 mmol) were added to a 100 mL round-bottom flask at a molar ratio of 1:4:100 and completely dissolved with DMF. AIBN initiator (1.5 mol%) was added under nitrogen protection, and the temperature was gradually raised to 80 ° C. and heated under reflux for 48 h. After the reaction, a transparent solution was obtained. After dilution with dichloromethane, icy anhydrous methanol was added to obtain a light yellow precipitate, which was placed in a vacuum freeze dryer and dried to constant weight to obtain a light yellow powder, which is the product polymer skeleton Poly (VTPY-co-SP-co-MMA).

[0044] Example 2

[0045] Preparation of rare earth metal polymer Poly-Tb(Coum)3 with multiple stimulus responsiveness:

[0046] Synthesis of rare earth metal complexes: 3-acetyl-4-hydroxy-2H-benzopyran-2-one (3 g, 18.6 mmol) was dissolved in 20 mL of acetic acid in a 100 mL round-bottom flask. Then, phosphorus oxychloride (5.6 mL) was added and refluxed at 117-119°C for 30 min. Then, 1 mL of phosphorus oxychloride was added and refluxed for another 30 min. A large amount of precipitation was generated. After filtration, an appropriate amount of ethanol was added to obtain a clear and transparent solution. After standing for three days, a white solid precipitated and was filtered. The mixture was then dried at a constant temperature of 45°C to obtain a white solid powder of Coum. Coum (0.918 g, 4.5 mmol) was then dissolved in 5 mL of anhydrous ethanol. Terbium chloride hexahydrate (0.56 g, 1.5 mmol) was completely dissolved in water and added to a 50 mL round-bottom flask. The pH of the solution was adjusted to 6 with an aqueous NaOH solution. The solution was heated to 60°C and stirred under reflux for 6 h to produce a large amount of precipitation. After filtration, the mixture was dried at a constant temperature to obtain a white solid, which was Tb(Coum)3·2H2O.

[0047] In a 100 mL round-bottom flask, 100 mg of Poly(VTPY-co-SP-co-MMA) and Tb(Coum)3·2H2O (0.024 mmol, 20 mg) were added, and 10 mL of tetrahydrofuran was added to fully dissolve the mixture. The solution became clear and transparent. The temperature was gradually raised to 60 ° C and refluxed for 6 h. After the reaction, n-hexane was added to precipitate a white precipitate. After filtration, the white solid powder Poly-Tb(Coum)3 was obtained by constant temperature drying at 45 ° C.

[0048] Experimental Example 1

[0049] The intermediates and products in the preparation process of Examples 1-2 were characterized, and the process and results are as follows:

[0050] The H NMR spectra of the polymer backbone Poly(VTPY-co-SP-co-MMA), VTPY and spiropyran SP monomers were analyzed, such as Figure 2 As shown in the figure, there is no proton peak of olefin double bond in the polymer backbone, which proves that the polymerization reaction has occurred successfully.

[0051] The Fourier transform infrared spectra of the polymer skeleton Poly(VTPY-co-SP-co-MMA) and the rare earth metal polymer Poly-Tb(Coum)3 were analyzed. Figure 3 As shown, it is confirmed that the coordination between Tb(Coum)3·2H2O and the N atom in VTPY successfully occurred, and the successful synthesis of rare earth metal polymer Poly-Tb(Coum)3 was also verified.

[0052] Photoresponsiveness of rare earth metal polymers:

[0053] The photochromic behavior of rare earth metal polymer Poly-Tb(Coum)3 was studied. Figure 4 As shown in the figure, under solid-state conditions, the luminescence intensity of rare earth metal ions gradually decreases under 365nm ultraviolet light, while the luminescence intensity of spiropyran at 670nm gradually increases, and the color of Poly-Tb(Coum)3 changes from Tb 3+ The green fluorescence emitted gradually turns into the red fluorescence of the spiropyran MC structure, showing obvious photochromic properties.

[0054] Acid-base stimulus responsiveness of rare earth metal polymers:

[0055] The fluorescence response of rare earth metal polymer Poly-Tb(Coum)3 to acid and base stimulation was studied. It was treated with ultraviolet light and then fumigated with hydrochloric acid gas. The changes in fluorescence spectrum before and after fumigation were recorded. The results are as follows Figure 5 As shown in the emission spectrum, it can be clearly observed that after hydrochloric acid fumigation, the emission peak of spiropyran at around 670nm disappears, while the emission peak of rare earth metal ions is significantly enhanced, and the luminescence color of rare earth metal polymer changes from red to green, which further indicates that the acid gas protonates MC and blocks Tb 3+ The fluorescence resonance energy transfer to the MC structure causes more excitation light energy to be dissipated in the form of green fluorescence.

[0056] After the Poly-Tb(Coum)3 was fumigated with hydrochloric acid, it was further fumigated with ammonia gas and its energy transfer changes were studied by monitoring the changes in the fluorescence spectrum. By repeating this acid-base alternating stimulation process many times, the stimulus response cyclicity of the material was explored, such as Figure 6The results show that the SP structure can be converted into the MC structure by fumigation with alkaline gas, indicating that the rare earth metal polymer Poly-Tb(Coum)3 has good acid-base stimulation reversibility, and in multiple acid-base stimulation cycles, Tb 3+ The ratio of the emission peak intensity at 545 nm to the emission peak intensity of MC at 670 nm showed good cyclicity, indicating that the rare earth metal polymer has good cyclic stability in response to acid-base stimulation.

[0057] Temperature stimulus responsiveness of rare earth metal polymer Poly-Tb(Coum)3:

[0058] The rare earth metal polymer Poly-Tb(Coum)3 was irradiated with ultraviolet light of 365nm wavelength to transform the closed ring structure SP of its spiropyran into an open ring structure MC. Then, the fluorescence emission spectrum of Poly-Tb(Coum)3 in the open ring state was tested under a series of different temperature conditions, such as Figure 7 As shown in the figure, as the temperature increases, the spiropyran transforms from the open-ring state MC back to the closed-ring structure SP, and the luminescence intensity at 670nm gradually decreases. The luminescence intensity of terbium metal ions shows an abnormal negative thermal quenching effect as the temperature increases, and the fluorescence color of the rare earth metal polymer changes from red back to green as the temperature increases.

[0059] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other. The above description of the disclosed embodiments enables professionals and technicians in this field to implement or use the present invention. Various modifications to these embodiments will be apparent to professionals and technicians in this field, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a rare earth metal polymer with multiple stimulus responsiveness, characterized in that: The following steps are involved: Step 1: Synthesis of polymer backbone Poly(VTPY-co-SP-co-MMA) VTPY, SP, and MMA were mixed and dispersed in DMF and completely dissolved. AIBN initiator was added under nitrogen protection, and the temperature was raised to 80°C and refluxed for 48 hours. After the reaction, the solution was diluted with dichloromethane to twice the volume of the original solution, and then icy anhydrous methanol was added to obtain a light yellow precipitate. The solution was freeze-dried in vacuo to a constant weight to obtain a light yellow powder, namely Poly(VTPY-co-SP-co-MMA); Step 2: Synthesis of rare earth metal complexes (2.1) 3-Acetyl-4-hydroxy-2H-chromen-2-one was dissolved in acetic acid, followed by addition of phosphorus oxychloride. The mixture was refluxed at 117-119°C for 30 min, followed by addition of phosphorus oxychloride and continued to reflux for 30 min. A precipitate was generated, which was filtered and then added with ethanol to obtain a clear, transparent solution. The solution was allowed to stand for three days until a white solid precipitated. The solution was filtered and dried at 45°C to obtain a white solid powder (Coum). (2.2) Coum was dissolved in anhydrous ethanol and terbium chloride hexahydrate was dissolved in water. After mixing, the solution was adjusted to pH 6 with NaOH. The solution was heated to 60°C and stirred under reflux for 6 h. The solution was filtered and dried to obtain a white solid, which was Tb(Coum)3·2H2O. Step 3: Synthesis of rare earth metal polymers After mixing Poly(VTPY-co-SP-co-MMA) and Tb(Coum)3·2H2O, tetrahydrofuran was added to fully dissolve the mixture. The solution became clear and transparent. The mixture was heated to 60°C and refluxed for 6 hours. After the reaction, n-hexane was added to obtain a white precipitate. After filtration, the mixture was dried at a constant temperature of 45°C to obtain a white solid powder Poly-Tb(Coum)3, which is a rare earth metal polymer with multiple stimulus responsiveness.

2. The method for preparing a rare earth metal polymer with multiple stimulus responsiveness according to claim 1, characterized in that: In step 1, the molar ratio of VTPY, SP, and MMA is 1:4:100; and the amount of the initiator added is 1.5% of the total molar mass of the mixture.

3. The method for preparing a rare earth metal polymer with multiple stimulus responsiveness according to claim 1, characterized in that: In step (2.1), the ratio of 3-acetyl-4-hydroxy-2H-benzopyran-2-one, acetic acid, and phosphorus oxychloride is 3 g:20 mL:6.6 mL. The volume ratio of phosphorus oxychloride added twice in this order is 5.6:

1.

4. The method for preparing a rare earth metal polymer with multiple stimulus responsiveness according to claim 1, wherein: The molar ratio of Coum to terbium chloride hexahydrate in step (2.2) is 3:

1.

5. The method for preparing a rare earth metal polymer with multiple stimulus responsiveness according to claim 1, characterized in that: In step 3, the mass ratio of Poly(VTPY-co-SP-co-MMA) to Tb(Coum)3·2H2O is 13:

1.

6. A rare earth metal polymer Poly-Tb(Coum)3 with multiple stimulus responsiveness prepared by the preparation method according to any one of claims 1 to 5.

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