Rare earth coordination type force-induced multi-fluorescence color change gel as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of rare earth coordination type force-induced multi-fluorescence color change gel, which comprises the following steps: dissolving Schiff base ligand molecules, monomers, an initiator and a cross-linking agent in deionized water, and uniformly stirring to obtain a stable solution, the monomer is at least one of acrylamide, ethyl acrylate, methyl acrylate and methacrylic acid; a rare earth compound is added into the stable solution to obtain a pre-polymerized solution, the rare earth coordination type force-induced multi-fluorescence color change gel is obtained through free radical polymerization, and the method is mild in condition, simple in step and easy to implement. The invention also discloses the force-induced multi-fluorescent color change gel prepared by the preparation method, the multi-color fluorescent gel is obtained by adjusting the types of rare earth ions and Schiff base ligand molecules, and visual fluorescent color change is realized under the action of external force. The force-induced multi-fluorescence color change gel is combined with other functional materials, integration of multiple functions is achieved, and the force-induced multi-fluorescence color change gel can be applied to multiple fields of optical devices, mechanical sensors and the like.

Description

Technical Field

[0001] The invention relates to the technical field of intelligent polymer materials, and in particular to a rare earth coordinated force-induced multi-fluorescence color-changing gel, a preparation method and an application thereof. Background Art

[0002] Force-induced fluorescent color-changing gel is a smart polymer soft material that can change visible fluorescent color under external stress. Since the fluorescence method has the characteristics of high sensitivity and high color saturation in displaying external stress changes, force-induced fluorescent color-changing gel material has great application value in pressure sensing, visual monitoring, material damage indication, optical perception, etc., and has received widespread attention from researchers in recent years.

[0003] Traditional mechanochromic gels mainly introduce force-sensitive fluorophores (such as 1,2-dioxetane derivatives, spiropyrans, and rhodamine) into the hydrogel matrix to achieve covalent bond breaking under mechanical force stimulation to achieve mechanochromic color change. However, covalent bonds usually have high bond energies and require more energy to break, so the system is not sensitive enough to force perception. Rare earth coordination mechanochromic gels mainly achieve fluorescence luminescence through the coordination bonds formed by rare earth ions. Due to the low bond energy of the coordination bonds, rare earth coordination mechanochromic gels are expected to achieve significant changes in fluorescence color under the action of small forces. Therefore, the development of rare earth coordination mechanochromic gels has important research value. However, previous studies mostly constructed stable luminescent rare earth coordination gel materials through the coordination of rare earth ions, and did not further study their mechanochromic properties.

[0004] Publication No. CN113929928A discloses a self-healing mechanochromic smart hydrogel and a preparation method thereof, firstly, a functional fluorescent monomer, methyl acrylate and a sodium chloride solution of sodium dodecyl sulfate are mixed to obtain a micelle solution, then acrylamide, an initiator and the micelle solution are mixed to obtain a prepolymer solution, and the prepolymer solution is thermally cured to obtain a self-healing mechanochromic hydrogel. However, the hydrogel prepared by the present invention has a general sensitivity to force perception.

[0005] Publication No. CN115337876A discloses a porous structure luminescent hydrogel material and its preparation and application, wherein a rare earth europium complex formed by rare earth europium ions and 2-thenoyltrifluoroacetone sodium salt is uniformly distributed in a hydrogel formed by microfibrillated cellulose and 2,3-pyridinedicarboxylic acid chitosan. The present invention uses the coordination of rare earth europium ions and carboxyl functional groups to construct a luminescent hydrogel, but in order to further study the mechanoluminescent color change performance of the luminescent hydrogel material. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a rare earth coordinated force-induced multi-fluorescence color-changing gel, which has mild conditions, simple steps and is easy to implement.

[0007] A method for preparing a rare earth coordinated force-induced multi-fluorescence color-changing gel comprises the following steps:

[0008] (1) dissolving Schiff base ligand molecules, monomers, initiators and crosslinking agents in deionized water, stirring evenly to obtain a stable solution, wherein the monomer is at least one of acrylamide, ethyl acrylate, methyl acrylate and methacrylic acid;

[0009] (2) adding a rare earth compound to the stable solution obtained in step (1) to obtain a prepolymer solution, and obtaining a rare earth coordination type mechanochromic multi-fluorescent color-changing gel through free radical polymerization.

[0010] Rare earth elements have a unique 4f electron structure, and their 4f electrons show strong coordination and chemical reactivity in chemical reactions. Schiff base ligand molecules can coordinate with most metal ions because they have imine or azomethine characteristic groups containing carbon-nitrogen double bonds. Therefore, rare earth ions can form stable complexes with Schiff base ligand molecules, and then stable photoluminescence can be achieved in the gel system through the action of the complex.

[0011] In the present invention, the Schiff base ligand molecules form dynamic coordination with the rare earth ions. Since the strength of the coordination bond is relatively weak, the prepared gel system can show sensitive fluorescence color change to external force stimulation. When not subjected to external force, the dynamic coordination effect between the rare earth metal ions and the Schiff base ligand molecules can be utilized to make the gel show fluorescence; when subjected to external force (such as stretching), the dynamic coordination bonds formed between the rare earth metal ions and the Schiff base ligand molecules are destroyed, resulting in changes in the molecular structure of the gel, thereby inducing the fluorescence of the gel to be converted into the fluorescence of the Schiff base ligand molecules themselves, thereby achieving force-induced fluorescence color change.

[0012] Preferably, in step (1), the Schiff base ligand molecule is selected from any of the following structures:

[0013]

[0014]

[0015] In the present invention, the Schiff base ligand molecules all contain pyridine-dicarbonyl groups, which can promote the original blue fluorescence in the gel system. 3+ ) can change its own color by forming dynamic coordination. Since the strength of the coordination bond is weak, the gel system can show sensitive fluorescence color change in response to external force stimulation.

[0016] Preferably, the molar ratio of the Schiff base ligand molecule to the monomer is 1:400-3000.

[0017] Preferably, in step (1), the initiator is at least one of potassium persulfate, azobisisobutyronitrile, ammonium persulfate, dimethyl azobisisobutyrate, azobisisobutylamidine hydrochloride, benzoyl peroxide, diisopropyl peroxydicarbonate, and dicyclohexyl peroxydicarbonate.

[0018] Preferably, in step (1), the cross-linking agent is at least one of N,N'-methylenebisacrylamide, sodium tripolyphosphate, glutaraldehyde, ethylene glycol dimethacrylate, divinylbenzene, diisocyanate or triallyl isocyanurate.

[0019] Preferably, in step (1), the molar ratio of the crosslinking agent to the monomer is 1:400-1500, and the molar ratio of the initiator to the monomer is 1:200-600.

[0020] More preferably, the monomer is acrylamide, the initiator is potassium persulfate, and the cross-linking agent is N,N'-methylenebisacrylamide.

[0021] Preferably, in aqueous solution, acrylamide monomers are polymerized under the initiation of potassium persulfate to obtain polyacrylamide. N,N'-methylenebisacrylamide reacts with the active groups on the polyacrylamide chains obtained by the initiation of polymerization to form crosslinking points, thereby connecting the linear polymer chains to form a hydrogel.

[0022] Preferably, in step (2), the rare earth compound contains at least one rare earth element of europium, terbium, gadolinium, lanthanum and neodymium.

[0023] Preferably, the molar ratio of the rare earth compound to the Schiff base ligand molecule is 1:1-300.

[0024] When the amount of rare earth compound added is too small, the rare earth coordination gel obtained will not show obvious fluorescence when not subjected to external force; when the amount of rare earth compound added is too large, the rare earth coordination gel obtained will not achieve obvious mechano-induced fluorescence color change when subjected to external force stretching.

[0025] Preferably, in step (2), the reaction temperature of the free radical polymerization is 40-80°C.

[0026] Preferably, in step (2), the free radical polymerization time is 4-12 hours.

[0027] The present invention also provides a rare earth coordinated force-induced multi-fluorescent color-changing gel obtained by the above-mentioned preparation method. The gel not only has high force sensitivity, but also can obtain a multi-color fluorescent gel by adjusting the types of rare earth ions and Schiff base ligand molecules. Further, it can realize visual fluorescence color change under the action of external force, that is, realize instant visual detection of stress.

[0028] The present invention also provides the application of rare earth coordinated force-induced multi-fluorescent color-changing gel in the fields of force sensing, material damage detection, material damage indicator, optical switch, and flexible device. In the force-induced multi-fluorescent color-changing gel provided by the present invention, the type of rare earth fluorescent compound added is adjustable. Further, due to the coordination of rare earth ions with Schiff base ligand molecules, the coordination bonds in the gel system are force-adjusted to cause the color of the gel to change, and the specific fluorescent color can be adjusted according to the actual application requirements. Since the coordination bonds are easy to break, the system has a high mechanical sensitivity and can respond to small stress changes, so it can be used for real-time monitoring and feedback of stress changes in practical applications.

[0029] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0030] (1) The present invention forms a stable complex with a rare earth ion and a Schiff base ligand molecule, thereby realizing a stable photoluminescence phenomenon in a gel system; the gel prepared by the present invention can cause the color of the gel to change under the action of a small external force, thereby realizing mechanoluminescence color change.

[0031] (2) In the force-induced multi-fluorescent color-changing gel provided by the present invention, by adjusting the types of rare earth compounds and Schiff base ligand molecules added, the color of the force-induced multi-fluorescent color-changing gel can meet the needs of different environments and applications. Further combining the force-induced multi-fluorescent color-changing gel with other functional materials can achieve the integration of multiple functions, so that it can be used in multiple fields such as optical devices and mechanical sensors.

[0032] (3) The preparation process of the present invention is simple and the preparation method has strong universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the preparation process of rare earth coordinated multi-fluorescent color-changing gel.

[0034] Figure 2 This is a schematic diagram of the molecular structure of the rare earth coordination type mechanochromic fluorescent gel prepared in Example 1.

[0035] Figure 3 This is a photograph of the rare earth coordination type Lizhiduo fluorescent color-changing gel prepared in Example 1 under natural light.

[0036] Figure 4The fluorescence spectra of the rare earth coordination type force-induced multi-fluorescence color-changing gel prepared in Example 1 before and after stretching, wherein the left figure is the fluorescence spectrum after stretching to 1.2 times the original, and the right figure is the fluorescence spectrum before stretching.

[0037] Figure 5 The fluorescence spectra of the rare earth coordination type force-induced multi-fluorescence color-changing gel prepared in Example 2 before and after stretching, wherein the left figure is the fluorescence spectrum before stretching, and the right figure is the fluorescence spectrum after stretching to 1.2 times the original size.

[0038] Figure 6 The fluorescence spectra of the rare earth coordination type force-induced multi-fluorescence color-changing gel prepared in Example 5 before and after stretching, wherein the left figure is the fluorescence spectrum before stretching, and the right figure is the fluorescence spectrum after stretching to 1.2 times the original size.

[0039] Figure 7 This is the fluorescence spectrum of the polymer gel without rare earth elements prepared in Comparative Example 1. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below in conjunction with the examples, but the embodiments of the present invention are not limited to the following examples.

[0041] The raw materials used in the present invention are all commercially available.

[0042] Example 1: Schematic diagram of the preparation process Figure 1 shown.

[0043] (1) Add 2.5 g of acrylamide, 6 mg of N,N'-methylenebisacrylamide, 20 mg of potassium persulfate, 0.03 mmol of Schiff base I and 10 mL of deionized water into a reaction beaker and stir at room temperature for 2 h to obtain a stable solution.

[0044] (2) Add 0.03 mmol of Eu(NO3)3·6H2O to the stable solution obtained in step (1), stir until uniform, stir in an ice water bath for 5 min, inject into a covered petri dish, and perform free radical polymerization at 60°C for 8 h. After the reaction is completed, remove the hydrogel from the mold to obtain a rare earth coordination type multi-fluorescent color-changing gel.

[0045] Figure 2 The molecular structure diagram of the prepared rare earth coordination type multi-fluorescent color-changing gel, in which the Schiff base ligand molecule and the rare earth metal ion Eu 3+ The complex is evenly distributed on the hydrogel network formed by acrylamide. The picture of the prepared rare earth coordination type multi-fluorescent color-changing gel under natural light is as follows: Figure 3 shown.

[0046] Fluorescence color change performance test

[0047] Figure 4 The fluorescence spectrum of the rare earth coordination type mechanochromic fluorescent gel prepared in Example 1 before and after stretching. The fluorescence emission spectrum was scanned at 400-700 nm with 365 nm as the excitation wavelength. Figure 4 As shown in the figure on the right, before stretching, the prepared force-induced multi-fluorescence color-changing gel has a strong fluorescence intensity at a wavelength of 580-660nm, and the emission peaks are respectively attributed to 5 D0- 7 F1(590nm), 5 D0- 7 F2 (620nm) transition, among which the emission peak intensity at 590nm is the largest and the peak shape is the narrowest, which is similar to Eu 3+ The position of the fluorescent color-changing gel has an obvious emission peak at 580-660nm. This wavelength range is located in the orange-red light region. The rare earth complex exhibits strong and stable red fluorescence under ultraviolet light.

[0048] like Figure 4 As shown in the left figure, when the gel is stretched to about 1.2 times its original size by external force, the dynamic coordination bonds between the rare earth metal ions and the Schiff base ligand molecules are destroyed, resulting in changes in the molecular structure and a weakening of the fluorescence resonance energy transfer, showing an intense emission peak at 420nm, which is in the blue light region, and ultimately showing the blue fluorescence of the Schiff base ligand molecules themselves, achieving force-induced fluorescence color change.

[0049] Example 2

[0050] (1) Add 6.0 g of acrylamide, 12 mg of N,N'-methylenebisacrylamide, 40 mg of potassium persulfate, 0.06 mmol of Schiff base I and 20 mL of deionized water into a reaction beaker and stir at room temperature for 2 h to obtain a stable solution.

[0051] (2) Add 0.06 mmol of Eu(NO3)3·6H2O to the stable solution obtained in step (1), stir until uniform, stir in an ice water bath for 5 min, and then inject into a covered petri dish, and free radical polymerize at 60°C for 8 h. After the reaction is completed, remove the hydrogel from the mold to obtain a rare earth coordination type force-induced multi-fluorescence color-changing gel.

[0052] Figure 5 The fluorescence spectra of the rare earth coordination type force-induced multi-fluorescent color-changing gel prepared in Example 2 before and after stretching, wherein the left figure is the fluorescence spectrum before stretching, and the right figure is the fluorescence spectrum after stretching to 1.2 times the original. As shown in the left figure, the successfully prepared rare earth coordination type force-induced multi-fluorescent color-changing gel, when not subjected to external force, due to the rare earth metal ions (Eu 3+) and the Schiff base ligand molecules, the gel exhibits a strong and stable red fluorescence under ultraviolet light; as shown in the right figure, when stretched to about 1.2 times of its original size by external force, the dynamic coordination bond between the two is destroyed, resulting in changes in the molecular structure and a weakening of the fluorescence resonance energy transfer, and then showing a weakening of the red fluorescence that is dependent on the external force, and finally showing the blue fluorescence brought by the Schiff base ligand molecules themselves, realizing force-induced fluorescence color change.

[0053] Example 3

[0054] The preparation method is the same as that of Example 1, except that in step (1), the Schiff base ligand molecule added is 0.04 mmol of Schiff base I; and in step (2), the rare earth compound added is 0.03 mmol of Tb(NO3)3·5H2O.

[0055] The rare earth coordination type force-induced multi-fluorescence color-changing gel successfully prepared, when not subjected to external force, due to the rare earth metal ions (Tb 3+ ) and the Schiff base ligand molecules, the gel exhibits a strong and stable green fluorescence under ultraviolet light; when it is stretched to about 1.2 times its original size by an external force, the dynamic coordination bond between the two is destroyed, resulting in changes in the molecular structure and a weakening of the fluorescence resonance energy transfer, and then showing an external force-dependent weakening of the green fluorescence, and finally showing the blue fluorescence brought by the Schiff base ligand molecules themselves, realizing force-induced fluorescence color change.

[0056] Example 4

[0057] The preparation method is the same as that of Example 2, except that in step (1), the Schiff base ligand molecule added is 0.08 mmol of Schiff base I; and in step (2), the rare earth compound added is 0.04 mmol of Tb(NO3)3·5H2O.

[0058] The rare earth coordination type force-induced multi-fluorescence color-changing gel successfully prepared, when not subjected to external force, due to the rare earth metal ions (Tb 3+ ) and the Schiff base ligand molecules, the gel exhibits a strong and stable green fluorescence under ultraviolet light; when it is stretched to about 1.2 times its original size by an external force, the dynamic coordination bond between the two is destroyed, resulting in changes in the molecular structure and a weakening of the fluorescence resonance energy transfer, and then showing an external force-dependent weakening of the green fluorescence, and finally showing the blue fluorescence brought by the Schiff base ligand molecules themselves, realizing force-induced fluorescence color change.

[0059] Example 5

[0060] The preparation method is the same as that of Example 1, except that in step (1), the Schiff base ligand molecule added is 0.04 mmol of Schiff base III.

[0061] Figure 6 The fluorescence spectra of the rare earth coordination type force-induced multi-fluorescent color-changing gel prepared in Example 5 before and after stretching, wherein the left figure is the fluorescence spectrum before stretching, and the right figure is the fluorescence spectrum after stretching to 1.2 times the original. As shown in the left figure, the successfully prepared rare earth coordination type force-induced multi-fluorescent color-changing gel, when not subjected to external force, due to the rare earth metal ions (Eu 3+ ) and the Schiff base ligand molecules, the gel exhibits a strong and stable red fluorescence under ultraviolet light; as shown in the right figure, when stretched to about 1.2 times of its original size by external force, the dynamic coordination bond between the two is destroyed, resulting in changes in the molecular structure and a weakening of the fluorescence resonance energy transfer, and then showing a weakening of the red fluorescence that is dependent on the external force, and finally showing the blue fluorescence brought by the Schiff base ligand molecules themselves, realizing force-induced fluorescence color change.

[0062] Example 6

[0063] The preparation method is the same as that of Example 1, except that in step (1), the monomer and Schiff base ligand molecule added are 4.0 g of acrylamide and 0.04 mmol of Schiff base I, respectively; and the rare earth compound added in step (2) is 0.0006 mmol of Tb(NO3)3·5H2O.

[0064] The rare earth coordination type force-induced multi-fluorescence color-changing gel successfully prepared, when not subjected to external force, due to the rare earth metal ions (Tb 3+ ) and the Schiff base ligand molecules, the gel exhibits a strong and stable green fluorescence under ultraviolet light; when it is stretched to about 1.2 times its original size by an external force, the dynamic coordination bond between the two is destroyed, resulting in changes in the molecular structure and a weakening of the fluorescence resonance energy transfer, and then showing an external force-dependent weakening of the green fluorescence, and finally showing the blue fluorescence brought by the Schiff base ligand molecules themselves, realizing force-induced fluorescence color change.

[0065] Example 7

[0066] The preparation method is the same as that of Example 1, except that in step (1), the monomer and Schiff base ligand molecule added are 3.0 g acrylamide and 0.09 mmol Schiff base I, respectively; and the rare earth compound added in step (2) is 0.0003 mmol Eu(NO3)3·6H2O.

[0067] The rare earth coordination type force-induced multi-fluorescence color-changing gel successfully prepared, when not subjected to external force, due to the rare earth metal ions (Eu 3+) and the Schiff base ligand molecules, the gel exhibits a strong and stable red fluorescence under ultraviolet light; when it is stretched to about 1.2 times its original size by an external force, the dynamic coordination bond between the two is destroyed, resulting in changes in the molecular structure and a weakening of the fluorescence resonance energy transfer, and then showing an external force-dependent weakening of the red fluorescence, and finally revealing the blue fluorescence brought by the Schiff base ligand molecules themselves, achieving force-induced fluorescence color change.

[0068] Example 8

[0069] The preparation method is the same as that of Example 1, except that in step (1), the Schiff base ligand molecule added is 0.03 mmol of Schiff base V.

[0070] The rare earth coordination type force-induced multi-fluorescence color-changing gel successfully prepared, when not subjected to external force, due to the rare earth metal ions (Eu 3+ ) and the Schiff base ligand molecules, the gel exhibits a strong and stable red fluorescence under ultraviolet light; when it is stretched to about 1.2 times its original size by an external force, the dynamic coordination bond between the two is destroyed, resulting in changes in the molecular structure and a weakening of the fluorescence resonance energy transfer, and then showing an external force-dependent weakening of the red fluorescence, and finally revealing the blue fluorescence brought by the Schiff base ligand molecules themselves, achieving force-induced fluorescence color change.

[0071] Comparative Example 1

[0072] The preparation method is the same as that of Example 1, except that in step (2), no rare earth compound is added.

[0073] Figure 7 This is a fluorescence spectrum of the polymer gel without rare earth elements prepared in Comparative Example 1. When no external force is applied, the blue fluorescence of the Schiff base ligand molecule itself is presented.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a rare earth coordination type multi-fluorescent color-changing gel, characterized in that: The following steps are involved: (1) dissolving Schiff base ligand molecules, monomers, initiators and crosslinking agents in deionized water, stirring evenly to obtain a stable solution, wherein the monomer is at least one of acrylamide, ethyl acrylate, methyl acrylate and methacrylic acid; (2) adding a rare earth compound to the stable solution obtained in step (1) to obtain a prepolymer solution, and obtaining a rare earth coordination type mechanochromic fluorescent gel through free radical polymerization.

2. The method for preparing the rare earth coordination type mechanochromic fluorescent color-changing gel according to claim 1, characterized in that: Preferably, in step (1), the Schiff base ligand molecule is selected from any of the following structures:

3. The method for preparing the rare earth coordination type mechanochromic fluorescent color-changing gel according to claim 1, characterized in that: The molar ratio of the Schiff base ligand molecule to the monomer is 1:400-3000.

4. The method for preparing the rare earth coordination type mechanochromic fluorescent color-changing gel according to claim 1, characterized in that: In step (1), the initiator is at least one of potassium persulfate, azobisisobutyronitrile, ammonium persulfate, dimethyl azobisisobutyrate, azobisisobutylamidine hydrochloride, benzoyl peroxide, diisopropyl peroxydicarbonate, and dicyclohexyl peroxydicarbonate; and the cross-linking agent is at least one of N,N'-methylenebisacrylamide, sodium tripolyphosphate, glutaraldehyde, ethylene glycol dimethacrylate, divinylbenzene, diisocyanate, or triallyl isocyanurate.

5. The method for preparing the rare earth coordination type mechanochromic fluorescent color-changing gel according to claim 1 or 4, characterized in that: In step (1), the molar ratio of the crosslinking agent to the monomer is 1:400-1500, and the molar ratio of the initiator to the monomer is 1:200-600.

6. The method for preparing the rare earth coordination type mechanochromic fluorescent color-changing gel according to claim 1, characterized in that: In step (2), the rare earth compound contains at least one rare earth element of europium, terbium, gadolinium, lanthanum and neodymium.

7. The method for preparing the rare earth coordination type mechanochromic fluorescent color-changing gel according to claim 1, characterized in that: The molar ratio of the rare earth compound to the Schiff base ligand molecule is 1:1-300.

8. The method for preparing the rare earth coordination type mechanochromic fluorescent color-changing gel according to claim 1, characterized in that: In step (2), the reaction temperature of the free radical polymerization is 40-80°C.

9. The rare earth coordination type mechanochromic fluorescent gel prepared by the preparation method according to any one of claims 1 to 8.

10. Application of the rare earth coordinated force-induced multi-fluorescent color-changing gel according to claim 9 in the fields of force sensing, material damage detection, material damage indicator, optical switch, and flexible device.

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