A rare earth coordination type force-induced multi-fluorescent color variable gel, a preparation method and application thereof

Abstract

The application discloses a preparation method of a rare earth coordination type force-induced multi-fluorescent color variable gel, and comprises the following steps: dissolving a Schiff base ligand molecule, a monomer, an initiator and a crosslinking agent in deionized water, and stirring uniformly to obtain a stable solution, wherein the monomer is at least one of acrylamide, ethyl acrylate, methyl acrylate and methacrylic acid; adding a rare earth compound into the stable solution to obtain a prepolymer solution, and obtaining the rare earth coordination type force-induced multi-fluorescent color variable gel through free radical polymerization; the method has mild conditions, simple steps and is easy to realize. The application further discloses the force-induced multi-fluorescent color variable gel prepared through the preparation method; the types of the rare earth ions and the Schiff base ligand molecules are adjusted to obtain a multi-color fluorescent gel, and the visual fluorescent color change is realized under the action of external force. The force-induced multi-fluorescent color variable gel is combined with other functional materials to realize the integration of multiple functions, and can be applied to multiple fields such as optical devices and mechanical sensors.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of intelligent polymer materials, in particular to a rare earth coordination type force-induced multi-fluorescent color-changing gel, a preparation method and applications. BACKGROUND

[0002] Force-induced fluorescent color-changing gel is a kind of intelligent polymer soft material that can change visible fluorescence color under external stress. Due to the high sensitivity and high color saturation of fluorescence means in the display of external stress changes, force-induced fluorescent color-changing gel materials have good application value in pressure sensing, visual monitoring, material damage indication, optical perception, etc. and have received extensive attention from researchers in recent years.

[0003] Traditional force-induced color-changing gel mainly introduces force-sensitive fluorophores (such as 1,2-dioxetane derivatives, spiropyrans and rhodamines, etc.) into the hydrogel matrix to achieve force-induced fluorescence color change through covalent bond breaking under mechanical force stimulation. However, the covalent bond usually has high bond energy, and the energy required for breaking is relatively high, so the sensitivity of the system to force sensing is not enough. The force-induced color-changing gel of rare earth coordination type mainly realizes fluorescence emission through the coordination bond formed by rare earth ions. Since the coordination bond has low bond energy, the force-induced color-changing gel of rare earth coordination type is expected to realize significant change in fluorescence color under the action of small force, so it has important research value to develop force-induced color-changing gel of rare earth coordination type. However, previous studies have mainly focused on the construction of stable luminescent rare earth coordination gel materials through coordination of rare earth ions, without further research on their force-induced color-changing properties.

[0004] Publication No. CN113929928A discloses a self-healing force-induced color-changing intelligent hydrogel and a preparation method thereof. First, functional fluorescent monomers, methyl acrylate and sodium chloride solution of sodium dodecyl sulfate are mixed to obtain a micelle solution, then acrylamide and initiator are uniformly mixed with the micelle solution to obtain a pre-polymer solution, and the pre-polymer solution is heat-cured to obtain a self-healing force-induced color-changing hydrogel. However, the force sensing sensitivity of the hydrogel prepared by the present application is general.

[0005] Publication No. CN115337876A discloses a porous structure luminescent hydrogel material, its preparation and application. The rare earth europium complex formed by rare earth europium ions and 2-thiophene formyl trifluoroacetone sodium salt is uniformly distributed in the hydrogel formed by microfibrillated cellulose and 2,3-pyridine dicarboxylic acid chitosan. The present application uses the coordination action of rare earth europium ions and carboxyl functional groups to construct a luminescent hydrogel, but further research is needed on the force-induced fluorescent color-changing properties of the luminescent hydrogel material. SUMMARY

[0006] In order to solve the above technical problems, the application provides a preparation method of a rare earth coordination type force-induced multi-fluorescent color variable gel, which is mild in method conditions, simple in steps and easy to realize.

[0007] A preparation method of a rare earth coordination type force-induced multi-fluorescent color variable gel, comprising the following steps:

[0008] (1) dissolving a Schiff base ligand molecule, a monomer, an initiator and a crosslinking agent in deionized water to obtain a stable solution after uniform stirring, 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 the rare earth coordination type force-induced multi-fluorescent color variable gel through free radical polymerization.

[0010] The rare earth element has a unique 4f electron structure, and the 4f electron shows strong coordination and chemical reactivity in chemical reactions. The Schiff base ligand molecule can coordinate with most metal ions due to the imine or methyleneimine characteristic group containing carbon-nitrogen double bonds. Therefore, the rare earth ion can form a stable complex with the Schiff base ligand molecule, and the stable photoluminescence phenomenon in the gel system can be realized through the complex effect.

[0011] In the application, the Schiff base ligand molecule forms a dynamic coordination with the rare earth ion, and the gel system prepared can show sensitive fluorescence color change under external force stimulation due to the weak strength of the coordination bond. When no external force is applied, the dynamic coordination between the rare earth metal ion and the Schiff base ligand molecule can be utilized, and the gel shows fluorescence; when external force (such as stretching) is applied, the dynamic coordination bond between the rare earth metal ion and the Schiff base ligand molecule is destroyed, leading to the change of the gel molecular structure, and then inducing the fluorescence of the gel to change into the fluorescence of the Schiff base ligand molecule itself, realizing the force-induced fluorescence color change.

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

[0013]

[0014]

[0015] In the application, the above Schiff base ligand molecules all contain a pyridine-dicarbon hydrazone organic group, which can promote the original blue fluorescence in the gel system. When the Schiff base ligand molecule forms a dynamic coordination with a rare earth ion such as europium (Eu 3+ ), the color of the Schiff base ligand molecule itself can be changed, and the gel system can show sensitive fluorescence color change under external force stimulation due to the weak strength of the coordination bond.

[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, dicumyl peroxide, diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate.

[0018] Preferably, in step (1), the crosslinking agent is at least one of N,N'-methylene bisacrylamide, sodium tripolyphosphate, glutaraldehyde, ethylene glycol dimethacrylate, divinylbenzene, diisocyanate or triallylisocyanurate.

[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] Further preferably, the monomer is acrylamide, the initiator is potassium persulfate, and the crosslinking agent is N,N'-methylene bisacrylamide.

[0021] Preferably, in an aqueous solution, the acrylamide monomer is polymerized under the initiation of potassium persulfate to obtain polyacrylamide. N,N'-methylene bisacrylamide reacts with the active groups on the polyacrylamide chain obtained by initiation polymerization to form crosslinking points, thereby connecting 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 the rare earth compound added is too small, the rare earth coordination type of gel prepared cannot be observed to have obvious fluorescence without external force; when the amount of the rare earth compound added is too large, the rare earth coordination type of gel prepared cannot achieve obvious mechanoluminescence color change when stretched by external force.

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

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

[0027] The application also provides the rare earth coordination type force-induced multi-fluorescent color change gel prepared by the preparation method, which not only has high force sensitivity, but also can obtain multi-color fluorescent gel by adjusting the types of rare earth ions and Schiff base ligand molecules, and further realizes visual fluorescent color change under external force, that is, realizes real-time visual detection of stress.

[0028] The application also provides application of the rare earth coordination type force-induced multi-fluorescent color change gel in force sensing, material damage detection, material damage indicator, optical switch and flexible device field. The type of rare earth fluorescent compound added in the force-induced multi-fluorescent color change gel provided by the application can be adjusted, and further, due to coordination between the rare earth ions and the Schiff base ligand molecules, the color of the gel changes due to stress adjustment of the coordination bond in the gel system, and the specific fluorescent color can be adjusted according to the actual application requirement. Since the coordination bond is easy to break, the system has high mechanical sensitivity, and can realize response to small stress change, so that the system can be used for real-time monitoring and feedback of stress change in actual application.

[0029] Compared with the prior art, the application has the following beneficial effects:

[0030] (1) The stable complex of the rare earth ions and the Schiff base ligand molecules is formed in the application, and then stable photoluminescence in the gel system is realized; the gel prepared in the application can cause color change of the gel under the action of small external force, and realize force-induced fluorescent color change.

[0031] (2) The type of the rare earth compound and the Schiff base ligand molecule added in the force-induced multi-fluorescent color change gel provided by the application can be adjusted, so that the color of the force-induced multi-fluorescent color change gel can meet the requirements of different environments and applications. Further, the force-induced multi-fluorescent color change gel can be combined with other functional materials to realize integration of multiple functions, so that the gel can be used in optical devices, mechanical sensors and other fields.

[0032] (3) The preparation process of the application is simple, and the universality of the preparation method is strong. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a preparation process schematic diagram of the rare earth coordination type force-induced multi-fluorescent color change gel.

[0034] Figure 2 It is a molecular structure schematic diagram of the rare earth coordination type force-induced multi-fluorescent color change gel prepared in Example 1.

[0035] Figure 3 It is a photo of the rare earth coordination type force-induced multi-fluorescent color change gel prepared in Example 1 under natural light.

[0036] Figure 4Fluorescence spectra of the prepared rare earth coordination type of mechano-chromic polyfluorescent gel 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 Fluorescence spectra of the prepared rare earth coordination type of mechano-chromic polyfluorescent gel 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.

[0038] Figure 6 Fluorescence spectra of the prepared rare earth coordination type of mechano-chromic polyfluorescent gel 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.

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

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

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

[0042] Example 1: The preparation process is shown in Figure 1 .

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

[0044] (2) 0.03 mmol of Eu(NO3)3·6H2O was added to the stable solution obtained in step (1), stirred until uniform, then stirred in an ice water bath for 5 min, and then injected into a covered petri dish. Radical polymerization was carried out at 60°C for 8 h. After the reaction was completed, the hydrogel was taken out of the mold to obtain a rare earth coordination type of mechano-chromic polyfluorescent gel.

[0045] Figure 2 The molecular structure of the prepared rare earth coordination type of mechano-chromic polyfluorescent gel is shown in the figure, wherein the Schiff base ligand molecule forms a complex with the rare earth metal ion Eu 3+ , which is uniformly distributed on the hydrogel network formed by acrylamide. The picture of the prepared rare earth coordination type of mechano-chromic polyfluorescent gel under natural light is shown in Figure 3 .

[0046] Mechano-fluorescent color change performance test

[0047] Figure 4 The images show the fluorescence spectra of the rare-earth coordination-type mechanosensitive polyfluorescent color-changing gel prepared in Example 1 before and after stretching. Fluorescence emission spectroscopy was performed in the 400-700 nm range using 365 nm as the excitation wavelength. Figure 4 As shown in the right figure, before stretching, the prepared mechanotropic multifluorescent color-changing gel exhibits strong fluorescence intensity in the wavelength range of 580-660 nm, with the emission peaks attributed to... 5 D0- 7 F1 (590nm) 5 D0- 7 The F2 (620nm) transition occurs, with the emission peak at 590nm exhibiting the strongest intensity and narrowest peak shape, similar to Eu. 3+ It is related to its location. The multi-fluorescent color-changing gel has a significant emission peak in the 580-660nm range, which is within the orange-red light region. The rare earth complex exhibits strong and stable red fluorescence under ultraviolet light irradiation.

[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 rare earth metal ions and Schiff base ligand molecules are disrupted, leading to changes in molecular structure and a weakening of fluorescence resonance energy transfer. This results in a strong emission peak at 420 nm, which is located in the blue light region. Ultimately, the Schiff base ligand molecules themselves exhibit blue fluorescence, achieving mechanotropic 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 to 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 homogeneous, stir in an ice-water bath for 5 min, and then pour into a covered petri dish. Perform free radical polymerization at 60 °C for 8 h. After the reaction is complete, remove the hydrogel from the mold to obtain a rare earth coordination type mechanotropic fluorescent color-changing gel.

[0052] Figure 5 The images show the fluorescence spectra of the rare-earth coordination-type mechanosensitive multifluorescent gel prepared in Example 2 before and after stretching. The left image shows the fluorescence spectrum before stretching, and the right image shows the fluorescence spectrum after stretching to 1.2 times its original size. As shown in the left image, the successfully prepared rare-earth coordination-type mechanosensitive multifluorescent gel, when not subjected to external force, exhibits fluorescence due to the presence of rare-earth metal ions (Eu...). 3+The dynamic coordination between the gel and the Schiff base ligand molecule results in a strong and stable red fluorescence under ultraviolet light irradiation. As shown in the right figure, when the gel is stretched to about 1.2 times its original size by an external force, the dynamic coordination bond between the two is disrupted, leading to changes in the molecular structure and a weakening of the fluorescence resonance energy transfer. Consequently, the force-dependent red fluorescence weakens, and the blue fluorescence from the Schiff base ligand molecule itself is finally revealed, achieving mechanotropic fluorescence color change.

[0053] Example 3

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

[0055] The successfully prepared rare-earth coordination-type mechanosensitive multifluorescent gel exhibits fluorescence even without external force due to the presence of rare-earth metal ions (Tb). 3+ The dynamic coordination between the gel and the Schiff base ligand molecule results in a strong and stable green fluorescence under ultraviolet light irradiation. However, when the gel is stretched to about 1.2 times its original size by an external force, the dynamic coordination bond between the two is disrupted, leading to changes in the molecular structure and a weakening of the fluorescence resonance energy transfer. Consequently, the force-dependent green fluorescence weakens, and the gel eventually exhibits the blue fluorescence brought by the Schiff base ligand molecule itself, achieving mechanotropic fluorescence color change.

[0056] Example 4

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

[0058] The successfully prepared rare-earth coordination-type mechanosensitive multifluorescent gel exhibits fluorescence even without external force due to the presence of rare-earth metal ions (Tb). 3+ The dynamic coordination between the gel and the Schiff base ligand molecule results in a strong and stable green fluorescence under ultraviolet light irradiation. However, when the gel is stretched to about 1.2 times its original size by an external force, the dynamic coordination bond between the two is disrupted, leading to changes in the molecular structure and a weakening of the fluorescence resonance energy transfer. Consequently, the force-dependent green fluorescence weakens, and the gel eventually exhibits the blue fluorescence brought by the Schiff base ligand molecule itself, achieving mechanotropic fluorescence color change.

[0059] Example 5

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

[0061] Figure 6 Fluorescence spectra of the prepared rare earth coordination type mechanochromic polyfluorescent gel 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 mechanochromic polyfluorescent gel, under the action of external force, due to the dynamic coordination between the rare earth metal ions (Eu 3+ ) and the Schiff base ligand molecules, the gel presents strong and stable red fluorescence under ultraviolet light irradiation; as shown in the right figure, when stretched to about 1.2 times the original by external force, the dynamic coordination between the two is destroyed, leading to changes in molecular structure and weakening of the degree of fluorescence resonance energy transfer, and then presenting the external force-dependent weakening of red fluorescence, and finally showing the blue fluorescence brought by the Schiff base ligand molecules themselves, realizing the mechanochromic fluorescence.

[0062] Example 6

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

[0064] The successfully prepared rare earth coordination type mechanochromic polyfluorescent gel, under the action of external force, due to the dynamic coordination between the rare earth metal ions (Tb 3+ ) and the Schiff base ligand molecules, the gel presents strong and stable green fluorescence under ultraviolet light irradiation; and when stretched to about 1.2 times the original by external force, the dynamic coordination between the two is destroyed, leading to changes in molecular structure and weakening of the degree of fluorescence resonance energy transfer, and then presenting the external force-dependent weakening of green fluorescence, and finally showing the blue fluorescence brought by the Schiff base ligand molecules themselves, realizing the mechanochromic fluorescence.

[0065] Example 7

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

[0067] The successfully prepared rare earth coordination type mechanochromic polyfluorescent gel, under the action of external force, due to the dynamic coordination between the rare earth metal ions (Eu 3+) and the dynamic coordination between the rare earth metal ions (Eu

[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 successfully prepared rare earth coordination type force-induced multi-fluorescent color-changing gel, when not subjected to external force, presents a strong and stable red fluorescence under ultraviolet light irradiation due to the dynamic coordination between the rare earth metal ions (Eu 3+ ) and the Schiff base ligand molecules. When subjected to external force stretching to about 1.2 times the original, the dynamic coordination bond between the two is destroyed, leading to changes in the molecular structure and weakening of the fluorescence resonance energy transfer, and further presenting force-dependent weakening of the red fluorescence, finally showing the blue fluorescence brought by the Schiff base ligand molecules themselves, realizing 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 The fluorescence spectrum of the polymer gel prepared in Comparative Example 1 and not containing rare earth elements, when not subjected to external force, presents the blue fluorescence of the Schiff base ligand molecules themselves.

[0074] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a rare-earth coordination-type mechanosensitive multifluorescent color-changing gel, characterized in that, Includes the following steps: (1) The Schiff base ligand molecule, monomer, initiator and crosslinking agent are dissolved in deionized water and stirred until homogeneous to obtain a stable solution. The monomer is at least one of acrylamide, ethyl acrylate, methyl acrylate and methacrylic acid. The Schiff base ligand molecule is selected from any of the following structures: 、 、 、 、 ； (2) Add rare earth compounds to the stable solution obtained in step (1) to obtain a prepolymer solution, and obtain rare earth coordination type mechanoluminescent color change gel by free radical polymerization.

2. The method for preparing the rare-earth coordination-type mechanosensitive multifluorescent 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.

3. The method for preparing the rare-earth coordination-type mechanosensitive multifluorescent 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, dicumyl peroxide, diisopropyl peroxide, and dicyclohexyl peroxide; the crosslinking agent is at least one of N,N'-methylenebisacrylamide, sodium tripolyphosphate, glutaraldehyde, ethylene glycol dimethacrylate, divinylbenzene, diisocyanate, or triallyl isocyanate.

4. The method for preparing the rare-earth coordination-type mechanosensitive multifluorescent color-changing gel according to claim 1 or 3, 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.

5. The method for preparing the rare-earth coordination-type mechanosensitive multifluorescent color-changing gel according to claim 1, characterized in that, In step (2), the rare earth compound contains at least one rare earth element, namely europium, terbium, gadolinium, lanthanum, or neodymium.

6. The method for preparing the rare-earth coordination-type mechanosensitive multifluorescent 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.

7. The method for preparing the rare-earth coordination-type mechanosensitive multifluorescent color-changing gel according to claim 1, characterized in that, In step (2), the reaction temperature of the free radical polymerization is 40-80℃.

8. A rare-earth coordination-type mechanosensitive color-changing gel prepared by any one of the preparation methods according to claims 1-7.

9. The application of the rare-earth coordination type mechanosensitive polyfluorescent color-changing gel according to claim 8 in the fields of force sensing, material damage detection, material damage indicator, optical switch, and flexible device.

Images