A pH-responsive rosin-based Schiff base AIE surfactant, its preparation method and its uses

Abstract

This invention discloses a pH-responsive rosin-based Schiff base AIE surfactant, its preparation method, and its applications. The molecular structure of the pH-responsive rosin-based Schiff base AIE surfactant is as follows: Rosin is used as a raw material, and maleic amylopectin is obtained through D-A addition. Then, imidization and condensation reactions are performed to obtain the pH-responsive rosin-based Schiff base AIE surfactant. This surfactant exhibits good AIE performance and biocompatibility. In the solid state, this surfactant displays photochromic properties, while in aqueous solution, it exhibits good pH responsiveness. It can be used for cell imaging, anti-counterfeiting, and information encryption, expanding the range of rosin-based surfactants. This surfactant can also be used to prepare pH-responsive AIE supramolecular hydrogels. The hydrogels prepared from this surfactant possess excellent mechanical properties, temperature resistance, pH responsiveness, shear recovery, and fluorescence. Furthermore, they are injectable and malleable, and can be applied in anti-counterfeiting materials, biomimetic materials, tissue engineering, and other fields.

Description

Technical Field

[0001] This invention relates to a pH-responsive rosin-based Schiff base aggregation-induced emission (AIE) surfactant, its preparation method, and its uses, belonging to the technical fields of surfactants and fluorescent nanomaterials. Background Technology

[0002] Traditional organic dyes typically exhibit strong fluorescence in dilute solutions, but their fluorescence drops sharply or even ceases to glow in concentrated solutions or in the solid state—a phenomenon known as aggregation-induced quenching. In 2001, Tang Benzhong's research group proposed the "aggregation-induced emission effect (AIE)," which describes compounds that exhibit no or weak fluorescence in dilute solutions, but strong fluorescence in aggregated or solid states. The discovery of AIE successfully solved the fluorescence quenching problem inherent in traditional dyes and holds immense application potential. However, AIE compounds often possess highly distorted chemical structures, resulting in relatively loose aggregation in solution. Furthermore, AIE compounds typically have poor water solubility, requiring organic solvents for dissolution in practical applications, which somewhat limits their applicability.

[0003] Rosin is a natural and renewable resource that is abundant and inexpensive, and it has been widely used in adhesives, coatings, inks, rubber, papermaking, food, metal processing and other fields.

[0004] This invention modifies rosin while introducing AIE groups to obtain surfactants with good surface activity and fluorescence properties. It significantly improves water solubility and aggregation ability, expands the types of rosin-based surfactants, and promotes the high-value application of rosin-based surfactants in fields such as anti-counterfeiting, information encryption, and biomimicry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a pH-responsive rosin-based Schiff base AIE surfactant, its preparation method, and its applications. This invention uses maleic acridinium as a raw material, undergoes an imidization reaction with p-phenylenediamine to obtain an intermediate, and then condenses it with different substituted salicylaldehydes to obtain a pH-responsive rosin-based Schiff base AIE surfactant, which exhibits good surface activity and fluorescence properties.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A pH-responsive rosin-based Schiff base AIE surfactant has the following molecular structure:

[0008]

[0009] When pH ≥ 7, the pH-responsive rosin-based Schiff base AIE surfactant aggregates in the aqueous solution and emits green fluorescence; when pH < 7, the pH-responsive rosin-based Schiff base AIE surfactant precipitates from the aqueous solution and emits yellow fluorescence; by adjusting the pH value of the system, the fluorescence intensity cycles with the pH cycle and is consistent with the fluorescence intensity corresponding to the pH before the cycle.

[0010] In other words, during the cycle, when pH ≥ 7, the pH-responsive rosin-based Schiff base AIE surfactant aggregates in the aqueous solution and emits green fluorescence; when pH < 7, the pH-responsive rosin-based Schiff base AIE surfactant precipitates from the aqueous solution and emits yellow fluorescence. "The fluorescence intensity is consistent with the pH before the cycle," meaning that after multiple cycles, the fluorescence intensity at each pH is consistent with the fluorescence intensity at the same pH after the solution was initially prepared. For example, after multiple cycles, the fluorescence intensity at pH 9 is consistent with the fluorescence intensity at pH 9 after the solution was initially prepared.

[0011] The aforementioned pH-responsive rosin-based Schiff base AIE surfactant exhibits good pH responsiveness in aqueous solution. When the pH-responsive rosin-based Schiff base AIE surfactant is dissolved in water and the pH of the solution is adjusted to 12, and then the pH is successively decreased to 11, 10, 9, 8, 7, 6, 5, 4, and 3, the fluorescence intensity of the solution first decreases, then increases, and then decreases again. After multiple cycles between pH=12 and pH=3, the fluorescence intensity of the pH-responsive rosin-based Schiff base AIE surfactant solution remains unchanged.

[0012] The pH-responsive rosin-based Schiff base AIE surfactant of this application is soluble in water at pH ≥ 7, but insoluble in water at pH < 7.

[0013] R1 is H or Cl. When R1 is H, R2 is H, Cl, Br or NO2; when R1 is Cl, R2 is H.

[0014] This application presents a pH-responsive rosin-based Schiff base AIE surfactant, exhibiting excellent AIE performance and biocompatibility. It displays photochromic properties in the solid state and good pH responsiveness in aqueous solution, making it suitable for cell imaging, anti-counterfeiting, and information encryption, thus expanding the range of rosin-based surfactants. This surfactant can also be used to prepare pH-responsive AIE supramolecular hydrogels. The hydrogels prepared from this surfactant possess excellent mechanical properties, temperature resistance, pH responsiveness, shear recovery, and fluorescence. Furthermore, they are injectable and malleable, making them applicable to anti-counterfeiting materials, biomimetic materials, tissue engineering, and other fields. The preparation method of the aforementioned pH-responsive rosin-based Schiff base AIE surfactant is as follows: N-(4-aminophenyl)imide maleic acridinium and salicylaldehydes with different substituents are added to an organic solvent for an aldehyde-amine condensation reaction to obtain the pH-responsive rosin-based Schiff base AIE surfactant; wherein the different substituent salicylaldehydes are compound I, compound II, compound III, compound IV, or compound V.

[0015]

[0016] To improve product yield, the organic solvent used is methanol or ethanol; the molar ratio of N-(4-aminophenyl)imide maleic acridinium to different substituted salicylaldehydes is 1:(1.05-1.15); the condensation reaction temperature is 65-85℃ and the time is 4-6h.

[0017] The preparation method of the above-mentioned N-(4-aminophenyl)imide maleopause acid is as follows: maleopause acid is dissolved in an organic solvent and added dropwise to an organic solvent of p-phenylenediamine to carry out an imidization reaction, thereby obtaining N-(4-aminophenyl)imide maleopause acid.

[0018] The molar ratio of maleic acridinium to p-phenylenediamine is 1:(1.05-1.15); the organic solvent is N,N-dimethylformamide; the imidization reaction conditions are: the dropping temperature is 75-85℃, after the dropping is completed, the reaction continues at 75-85℃ for 1.5-2.5h, and then the temperature is raised to 140-150℃ to continue the reaction for 4-5h to obtain N-(4-aminophenyl)imide maleic acridinium.

[0019] The aforementioned maleic anhydride was prepared by a DA addition reaction of rosin and maleic anhydride in an acidic solvent. The molar ratio of rosin to maleic anhydride was 1:(1.10–1.20); the acidic solvent was glacial acetic acid; the temperature of the DA addition reaction was 140–150 °C, and the time was 4–5 h.

[0020] The synthetic route for the above-mentioned pH-responsive rosin-based Schiff base AIE surfactant using rosin as a raw material is as follows:

[0021]

[0022] The pH-responsive rosin-based Schiff base AIE surfactant was prepared by introducing Schiff base groups into rosin as a raw material through DA addition, imidization and condensation reactions.

[0023] The above-mentioned pH-responsive rosin-based Schiff base AIE surfactant was prepared at a concentration of 0.1–0.3 mmol·L⁻¹. -1 An aqueous solution of the substance is used as an aqueous anti-counterfeiting ink or information encryption. It emits green fluorescence at pH=12. When the pH value of the system is lowered, the pH-responsive rosin-based Schiff base AIE surfactant is precipitated. The precipitated pH-responsive rosin-based Schiff base AIE surfactant solid emits yellow fluorescence.

[0024] When an aqueous solution of the pH-responsive rosin-based Schiff base AIE surfactant (pH=12) is written on black cardstock, it emits green fluorescence. After drying, the fluorescence disappears. Upon spraying with hydrochloric acid solution, the pH-responsive rosin-based Schiff base AIE surfactant precipitates and emits yellow fluorescence.

[0025] The pH-responsive rosin-based Schiff base AIE surfactant described above can be used for the detection of aluminum ions. Under a 365 nm UV lamp, SA emits yellow fluorescence in a 50% water / tetrahydrofuran solution. Upon the addition of aluminum ions, the fluorescence emission shifts to blue, emitting blue fluorescence.

[0026] The aforementioned pH-responsive rosin-based Schiff base AIE surfactant can also be used to prepare pH-responsive AIE supramolecular hydrogels. The preparation method of pH-responsive AIE supramolecular hydrogels is as follows: add the pH-responsive rosin-based Schiff base AIE surfactant to ultrapure water, adjust the pH of the system to ≥11, heat until the solution is clear and transparent, and let it stand at a constant temperature of 20-30℃ for 30-48 hours to obtain pH-responsive AIE supramolecular hydrogels.

[0027] In the aforementioned pH-responsive AIE supramolecular hydrogels, the concentration of the pH-responsive rosin-based Schiff base AIE surfactant is 10–80 mmol·L⁻¹. -1 The surfactant in this application can form a supramolecular hydrogel at 10 mM, with the aggregates being nanofibers, an effect that ordinary AIE surfactants cannot achieve.

[0028] In the aforementioned pH-responsive AIE supramolecular hydrogels, the pH-responsive rosin-based Schiff base AIE surfactant molecules contain carboxyl, phenolic hydroxyl, and imine groups, making them highly sensitive to changes in external pH. Adjusting the pH value of the system can alter the mechanical properties and fluorescence intensity of the gel. When the pH ≥ 11, the pH-responsive AIE supramolecular hydrogel exhibits good mechanical properties and fluorescence. When 7 ≤ pH < 11, the solubility of the pH-responsive rosin-based Schiff base AIE surfactant in water decreases, causing it to precipitate from the aqueous solution. Within this pH range, the surfactant's solubility decreases, resulting in a small amount of precipitate, but macroscopically, the gel remains, and the mechanical properties and fluorescence of the pH-responsive AIE supramolecular hydrogel decrease. When pH < 7, the pH-responsive rosin-based Schiff base AIE surfactant precipitates from the water, and the solution changes from green fluorescence emission to yellow fluorescence emission.

[0029] The pH adjustment method for the above gel is as follows: Dilute hydrochloric acid solution or dilute sodium hydroxide solution is added to the gel using a capillary tube, heated and stirred until the solution becomes clear and transparent, and the pH value of the gel is measured after cooling.

[0030] The aforementioned pH-responsive AIE supramolecular hydrogels exhibit good temperature resistance; their mechanical strength, including elastic modulus and viscous modulus, remains essentially unchanged within the temperature range of 25-95℃, with an elastic modulus greater than 1*10⁻⁶. 3 At Pa, the fluorescence intensity only decreased by half, making it possible for the gel to be used for bioassays at high temperatures.

[0031] The aforementioned pH-responsive AIE supramolecular hydrogels exhibit good mechanical properties, with an elastic modulus greater than 1*10. 3 Pa.

[0032] The pH-responsive AIE supramolecular hydrogels described above exhibit shear recovery properties, and can achieve interconversion from gel to liquid as strain changes.

[0033] The pH-responsive AIE supramolecular hydrogels described above are injectable and malleable, and can be used as injectable fluorescent hydrogels. They can be molded into different shapes and can be used in anti-counterfeiting materials, biomimetic materials, tissue engineering, etc.

[0034] The aforementioned pH-responsive rosin-based Schiff base AIE surfactant can also be used as a yellow dye and for cell imaging.

[0035] The aforementioned pH-responsive rosin-based Schiff base AIE surfactant can also be used as an emulsifier, solubilizer, or dispersant, and can also be used for the detection of aluminum ions.

[0036] Any techniques not mentioned in this invention are based on existing technologies.

[0037] The present invention achieves the following technical effects:

[0038] 1. This invention combines the superhydrophobicity of the rigid tricyclic diterpenoid structure of rosin, and uses rosin as the starting material to prepare a pH-responsive rosin-based Schiff base AIE surfactant through DA addition, imidization, and condensation reaction. This pH-responsive rosin-based Schiff base AIE surfactant has good pH responsiveness, expands the types of rosin-based surfactants, and broadens the application of rosin in fluorescent probes, anti-counterfeiting, information encryption, bioimaging, and other fields.

[0039] 2. This invention utilizes the strong aggregation ability of the rigid framework of rosin to promote the self-assembly of pH-responsive rosin-based Schiff base AIE surfactants to prepare pH-responsive AIE supramolecular hydrogels. These hydrogels exhibit good fluorescence, and their aggregates are chiral nanofibers. The pH-responsive AIE supramolecular hydrogels possess excellent pH responsiveness and shear recovery, and exhibit strong temperature resistance within the range of 25–95°C. They are injection-producible and malleable, thus broadening their applications in various fields.

[0040] 3. The pH-responsive rosin-based Schiff base AIE surfactant prepared from biomass resources in this invention exhibits good biocompatibility and biodegradability. The presence of the Schiff base group endows it with strong bioactivity and fluorescence properties. The development of this surfactant expands the application of rosin-based surfactants in fluorescence and also provides a foundation for the high-value utilization of rosin.

[0041] 4. The pH-responsive rosin-based Schiff base AIE surfactant in this invention can be used to prepare pH-responsive AIE supramolecular hydrogels, as well as as a yellow dye, emulsifier, solubilizer or dispersant, and can also be used for aluminum ion detection and cell imaging. Attached Figure Description

[0042] Figure 1 The pH-responsive rosin-based Schiff base AIE surfactant MPASA prepared in Example 1 1 HNMR image.

[0043] Figure 2 This is a solid-state fluorescence emission diagram of the pH-responsive rosin-based Schiff base AIE surfactant prepared in Example 1.

[0044] Figure 3 The fluorescence emission diagram of the pH-responsive rosin-based Schiff base AIE surfactant prepared in Example 1 in a water / tetrahydrofuran mixed solution is shown.

[0045] Figure 4 The images show fluorescence photographs and spectra of the pH-responsive rosin-based Schiff base AIE surfactant in aqueous solutions at different pH values, as well as fluorescence spectra before and after pH response in Example 4.

[0046] Figure 5 This is an anti-counterfeiting application diagram of the pH-responsive rosin-based Schiff base AIE surfactant solution (pH=12) prepared in Example 5.

[0047] Figure 6 The fluorescence emission diagram of the pH-responsive rosin-based Schiff base AIE surfactant prepared in Example 1 in acetone / water at pH=12.

[0048] Figure 7 The surface tension diagram is shown for the pH-responsive rosin-based Schiff base AIE surfactant MPASA prepared in Example 1.

[0049] Figure 8 The image shows the fluorescence spectrum of different metal ions detected by the pH-responsive rosin-based Schiff base AIE surfactant MPASA prepared in Example 1.

[0050] Figure 9 Macroscopic images and fluorescence spectra of pH-responsive AIE supramolecular hydrogels of different concentrations prepared in Example 9.

[0051] Figure 10 The pH-responsive AIE supramolecular hydrogel (50 mmol·L⁻¹) prepared in Example 9 -1 Shear recovery rheology plot of ).

[0052] Figure 11 Example 9 shows the pH-responsive AIE supramolecular hydrogel (50 mmol·L⁻¹) prepared. -1 Rheological diagram of temperature resistance.

[0053] Figure 12 Example 9 shows the pH-responsive AIE supramolecular hydrogel (50 mmol·L⁻¹) prepared. -1 The macroscopic diagram of plasticity. Detailed Implementation

[0054] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0055] Example 1

[0056] The preparation of pH-responsive rosin-based Schiff base AIE surfactants includes the following steps:

[0057] (1) Synthesis of maleic acrid acid: Accurately weigh 800.00 g (2.64 mol) of ordinary rosin (Guangdong Weida Chemical Co., Ltd., Grade 1 rosin), maleic anhydride (282.8 g, 2.9 mol), and 320 g of glacial acetic acid into a four-necked flask equipped with a mechanical stirrer, and add a reflux condenser. Raise the temperature to 140℃ and react for 5 h. After cooling the reaction solution to room temperature, add 800 g of glacial acetic acid to induce crystallization. Filter to obtain crude maleic acrid acid, recrystallize three times with glacial acetic acid to obtain a white solid, which is maleic acrid acid with a purity of 96%.

[0058] (2) Synthesis of N-(4-aminophenyl)imide maleic acridinium: p-phenylenediamine (8.92 g, 0.0825 mol) and 100 mL of N,N-dimethylformamide were added to a four-necked flask. A magnetic stir bar was added, a reflux purging device was connected, and nitrogen gas was introduced for protection. After heating to 80 °C, 100 mL of DMF solution containing maleic acridinium (30 g, 0.075 mol) was slowly added dropwise to the reaction mixture (N,N-dimethylformamide solution of p-phenylenediamine) using a constant-pressure dropping funnel over a period of 1 hour. After the addition was complete, the reaction was continued at 80 °C for 2 hours, then the temperature was increased to 145 °C and the reaction was continued for 4 hours until completion. After the reaction mixture cooled to room temperature, a pink solid precipitated. After filtration and drying, the mixture was recrystallized twice with N,N-dimethylformamide and water (volume ratio 9:1) to obtain a light pink solid, namely the synthesis of N-(4-aminophenyl)imide maleic acridinary acid (25.6 g), yield: 69.6%.

[0059] (3) pH-responsive rosin-based Schiff base AIE surfactant (MPASA): Accurately weigh N-(4-aminophenyl)imide maleic acridinium (0.01 mol, 4.906 g) and salicylaldehyde (0.011 mol, 1.343 g) into a single-necked flask, add 150 mL of methanol, add a stir bar, and connect a reflux condenser. Heat the reaction to 75 °C and react for 4 h. After the reaction solution cools to room temperature, filter and wash with hot methanol (65 °C) to obtain a yellow solid powder, which is compound MPASA (5.2 g), with a yield of 87.4%. Figure 1 To prepare a pH-responsive rosin-based Schiff base AIE surfactant MPASA 1 H NMR spectrum.

[0060] (4) pH-responsive rosin-based Schiff base AIE surfactant (MPASA-4Cl): Accurately weigh N-(4-aminophenyl)imide maleic acridinium (0.01 mol, 4.906 g) and 4-chlorosalicylaldehyde (0.011 mol, 1.723 g) into a single-necked flask, add 150 mL of methanol, add a stir bar, and connect a reflux condenser. Heat the reaction to 65 °C and react for 4 h. After the reaction solution cools to room temperature, filter, and wash with hot methanol (65 °C) to obtain a yellow powder, which is compound MPASA-4Cl (4.95 g), with a yield of 78.7%.

[0061] (5) pH-responsive rosin-based Schiff base AIE surfactant (MPASA-5Cl): Accurately weigh N-(4-aminophenyl)imide maleic acridinium (0.01 mol, 4.906 g) and 5-chlorosalicylaldehyde (0.011 mol, 1.723 g) into a single-necked flask, add 120 mL of methanol, add a stir bar, and connect a reflux condenser. Heat the reaction to 70 °C and react for 4 h. After the reaction solution cools to room temperature, filter, and recrystallize from methanol to obtain a yellow powder, which is compound MPASA-5Cl (4.41 g), with a yield of 70.0%.

[0062] (6) pH-responsive rosin-based Schiff base AIE surfactant (MPASA-5Br): Accurately weigh N-(4-aminophenyl)imide maleic acridinium (0.01 mol, 4.906 g) and 5-bromosalicylic acid (0.011 mol, 2.211 g) into a single-necked flask, add 120 mL of methanol, add a stir bar, and connect a reflux condenser. Heat the reaction to 80 °C and react for 4 h. After the reaction solution cools to room temperature, filter, and recrystallize from methanol to obtain a yellow powder, which is compound MPASA-5Br (4.72 g), with a yield of 70.1%.

[0063] (7) pH-responsive rosin-based Schiff base AIE surfactant (MPASA-5NO2): Accurately weigh N-(4-aminophenyl)imide maleic acridinium (0.01 mol, 4.906 g) and 5-nitrosalicylic acid (0.011 mol, 1.838 g) into a single-necked flask, add 150 mL of methanol, add a stir bar, and connect a reflux condenser. Heat the reaction to 85 °C and react for 4 h. After the reaction solution cools to room temperature, filter and wash with hot methanol to obtain a light yellow powder, which is compound MPASA-5NO2 (5.6 g), with a yield of 87.5%.

[0064] Example 2

[0065] Determination of AIE properties of pH-responsive rosin-based Schiff base AIE surfactants:

[0066] A pH-responsive rosin-based Schiff base AIE surfactant solid was packed into a solid fluorescence measuring dish, and the full spectrum was scanned to determine the maximum excitation wavelength. The maximum excitation wavelength was selected as 380 nm, the scanning range was 300-700 nm, and the scanning speed was 1000 nm·min. -1 .like Figure 2 As shown, the five compounds exhibited distinct emission peaks in the 500-700 nm range, displaying yellow fluorescence emission.

[0067] Example 3

[0068] Determination of AIE properties of pH-responsive rosin-based Schiff base AIE surfactants in water / organic solvents:

[0069] pH-responsive rosin-based Schiff base AIE surfactant MPASA was added to water / tetrahydrofuran mixed solvents at different ratios. The concentration of MPASA was 2*10. -5 mmol·L -1 The fluorescence properties of the solution were tested using a fluorescence spectrometer, with a maximum excitation wavelength of 380 nm selected. The results are as follows: Figure 3 As shown, compound MPASA exhibits excited-state intramolecular proton transfer (ESIPT) characteristics, displaying two emission peaks in water / tetrahydrofuran solution: an enol fluorescence emission peak at 433 nm and a keto fluorescence emission peak at 545 nm. With increasing water content in the water / tetrahydrofuran solvent, the emission intensity of the enol structure decreases, while the intensity of the keto structure emission peak significantly increases when the water content is greater than 90%, emitting strong yellow fluorescence, indicating that compound MPASA possesses AIE characteristics. Figure 3 The percentage indicates the volume content of water in the solvent; for example, 10% means that the volume content of water in the solvent is 10%.

[0070] Example 4

[0071] pH-responsive rosin-based Schiff base AIE surfactant (pH=12) pH responsiveness

[0072] Weigh a certain amount of surfactant MPASA and prepare a solution with a concentration of 0.2 mmol·L⁻¹. -1 An aqueous solution was prepared, and the pH of the solution was adjusted to 12. The pH of the solution was then gradually adjusted to 11, 10, 9, 8, 7, 6, 5, 4, and 3 using dilute hydrochloric acid solution. The fluorescence spectra of the solutions at different pH values ​​were measured using a fluorescence spectrometer. Simultaneously, the fluorescence spectra of the solution at pH = 12 were measured before and after five pH cycles. The maximum excitation wavelength was selected as 380 nm, the scan range as 300-700 nm, and the scan rate as 1000 nm·min. -1Fluorescence images of solutions at different pH levels and after five pH cycles were captured using a camera, with a 365nm UV lamp as the light source. Figure 4 It was found that the pH-responsive rosin-based Schiff base AIE surfactant solution emitted green fluorescence at pH ≥ 7, and the fluorescence intensity gradually decreased as the solution pH decreased. At pH < 7, the solution emitted yellow fluorescence, indicating that the surfactant gradually precipitated from the solution. After cycling the pH-responsive rosin-based Schiff base AIE surfactant solution five times between pH = 12 and pH = 3, the fluorescence intensity and emission peak position remained unchanged, indicating that the surfactant has good pH responsiveness. Figure 4 In the left image, the pH values ​​of the solutions in the upper left corner are 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 from left to right; in the right image, the solutions in the upper left corner are the first prepared solution and the solution after 5 cycles from left to right.

[0073] Example 5

[0074] Application of information encryption and anti-counterfeiting technology for pH-responsive rosin-based Schiff base AIE surfactants (pH=12):

[0075] Weigh a certain amount of surfactant MPASA and prepare a solution with a concentration of 0.2 mmol·L⁻¹. -1 Adjust the pH of the aqueous solution to 12. Pour the solution into a writing pen and write "CAF" on black cardstock. Figure 5 As shown, green fluorescence emission can be observed under 365nm ultraviolet light irradiation; the fluorescence disappears after the cardboard dries. When a dilute hydrochloric acid solution is sprayed onto the cardboard, a pH-responsive rosin-based Schiff base AIE surfactant precipitates; after drying, the cardboard exhibits yellow fluorescence emission. In conclusion, the pH-responsive rosin-based Schiff base AIE surfactant solution (pH=12) can be used as an information encryption and water-based anti-counterfeiting ink.

[0076] Example 6

[0077] AIE performance of pH-responsive rosin-based Schiff base AIE surfactant (pH=12):

[0078] Prepare an MPASA aqueous solution of a certain concentration, adjust the pH to 12, and then dissolve the above solution in acetone / water solutions of different ratios to achieve an MPASA concentration of 2*10. -5 mmol·L -1 Its fluorescence performance was tested using a fluorescence spectrometer, with a maximum excitation wavelength of 380 nm, a scanning range of 300-700 nm, and a scanning speed of 1000 nm·min. -1 .like Figure 6As shown, MPASA has a strong emission peak at 480 nm at pH=12, and its fluorescence intensity gradually increases with the increase of acetone content, indicating that MPASA has AIE characteristics at pH=12. Figure 6 In the diagram, 0-95 indicates the volume content of acetone in the solution, such as 10 indicating that the volume content of acetone in the solution is 10%.

[0079] Example 7

[0080] The critical micelle concentration (cmc) of the sample solution at different pH values ​​and the surface tension (γ) at the critical micelle concentration were determined using the surface tension method. cmc The method is as follows:

[0081] The critical micelle concentration and surface tension of surfactants were determined using a Sigma 701 surface tension meter via the Wilhelmy plate method. The measurement temperature was 25℃. The Wilhelmy plate was 19.44 mm wide, 0.1 mm thick, and 65 mm high. Each measurement was repeated three times, and the measurement error for each point was set to 0.05 mN·m. -1 Plot the surface tension versus concentration curves of pH-responsive rosin-based Schiff base AIE surfactants (taking MPASA as an example), as shown below. Figure 7 As shown. The CMC value of this surfactant is 1.71 mmol·L⁻¹. -1 The corresponding γ cmc 50.95 mN·m -1 It can be used as an emulsifier, solubilizer or dispersant.

[0082] Example 8

[0083] Application of pH-responsive rosin-based Schiff base AIE surfactants in aluminum ion detection:

[0084] ZnCl2, AlCl3, ZnCl2, CuCl2, MgCl2, FeCl3, PbCl2, NiCl2, CrCl3, SnCl2, BaCl2, LiCl, and CaCl2 powders were weighed out, dissolved in ultrapure water, and diluted to obtain a 200 μM metal ion mother liquor. 0.0238 g of MPASA compound was weighed out, dissolved in 20 mL of tetrahydrofuran, and diluted 100 times to obtain a 20 μM MPASA tetrahydrofuran solution. Equal volumes of the metal ion mother liquor and MPASA solution were mixed thoroughly and added to a cuvette. The fluorescence properties of the solution were tested using a fluorescence spectrometer, with a maximum excitation wavelength of 380 nm. The results are as follows: Figure 8 As shown. By Figure 8It was found that MPASA exhibits two emission peaks in a water / tetrahydrofuran (1:1 volume ratio) solution: an enol fluorescence emission peak at 433 nm and a keto fluorescence emission peak at 545 nm. Upon the addition of aluminum ions, the keto peak shifts to an emission peak at 468 nm, emitting blue fluorescence. No significant peak shift changes were observed upon the addition of other metal ions, indicating that the MPASA water / tetrahydrofuran solution demonstrates good selectivity for aluminum ions.

[0085] Example 9

[0086] Preparation of pH-responsive AIE supramolecular hydrogels:

[0087] Accurately weigh 0.0356 g of the pH-responsive rosin-based Schiff base AIE surfactant MPASA and 6 g of ultrapure water obtained in Example 1 into a glass vial. Adjust the pH of the solution to 12. Heat the solution at 75°C until it becomes clear and transparent. Then, place it in a 25°C incubator and let it stand for 48 hours to obtain the pH-responsive AIE supramolecular hydrogel (10 mmol·L⁻¹). -1 Alternatively, 15, 20, 25, 30, 35, 40, 45, and 50 mmol·L can be prepared using this method. -1 Gel samples. Gel samples at concentrations below 30 mmol·L⁻¹. -1 The intensity is relatively low at low concentrations, but increases significantly at concentrations ≥30 mmol·L⁻¹. -1 The fluorescence intensity increases over time, and the vial can be inverted. It exhibits photoluminescence under 365 nm ultraviolet light, and the fluorescence intensity of the gel increases with increasing surfactant concentration. Fluorescence spectroscopy was performed using a maximum excitation wavelength of 380 nm, a scanning range of 300-700 nm, and a scanning speed of 1000 nm / min. -1 The gel sample was exposed to natural light (upper left image; values ​​in the image represent concentrations in mmol·L⁻¹). -1 ) and ultraviolet light (lower layer of the left image; the values ​​in the image are concentrations, in mmol·L). -1 Macroscopic photographs and fluorescence emission spectra shown below. Figure 9 As shown.

[0088] The pH adjustment method for pH-responsive AIE supramolecular hydrogels is as follows: Dilute hydrochloric acid solution or dilute sodium hydroxide solution is added to the gel using a capillary tube, heated and stirred until the solution becomes clear and transparent, and the pH value of the gel is measured after cooling.

[0089] The pH-responsive properties of the above-mentioned hydrogels can be used for anti-counterfeiting, information storage, and drug encapsulation and release. Hydrogels with a pH ≥ 11 can be used in biomimetic materials or tissue engineering, etc.

[0090] Example 10

[0091] pH-responsive AIE supramolecular hydrogel shear-restoring rheological testing method is as follows:

[0092] Using a rotational rheometer to study 50 mmol·L -1 Shear recovery tests were performed on MPASAAIE supramolecular hydrogels with the frequency f fixed at 1 Hz and strains of 0.5% and 10%. The results are as follows: Figure 10 As shown, when the strain is 0.5%, the elastic modulus (G') of the sample is much greater than the viscous modulus (G”), exhibiting gel properties. When the strain is 10%, the viscous modulus (G”) is greater than the elastic modulus (G'), exhibiting liquid properties, indicating that the three-dimensional structure of the gel is destroyed at this point. When the strain is restored to 0.5%, the elastic modulus and viscous modulus of the hydrogel return to their pre-test values, indicating that this MPASA AIE supramolecular hydrogel has good shear recovery properties and can be used for tissue engineering or drug delivery.

[0093] Example 11

[0094] The method for studying the temperature resistance of pH-responsive AIE supramolecular hydrogels is as follows:

[0095] Following the method described in Example 9, prepare 50 mmol·L -1 The elastic modulus and viscous modulus of MPASA supramolecular hydrogels were measured using a rotational rheometer at 25-95℃ as a function of temperature. During the test, the frequency f was fixed at 1 Hz, and the strain was fixed at 1%. Figure 11 As shown, within the temperature range of 25-95℃, the elastic modulus of the gel sample is always greater than the viscous modulus, and both the elastic modulus and viscous modulus remain unchanged with temperature changes, indicating that the pH-responsive AIE supramolecular hydrogel has strong temperature resistance.

[0096] Example 12

[0097] The study on the injectable and shaping applications of pH-responsive AIE supramolecular hydrogels was conducted using the following methods:

[0098] Following the method described in Example 8, prepare 50 mmol·L -1 The MPASA supramolecular hydrogel was prepared by drawing a certain amount of the gel using a disposable syringe, gently pushing the syringe until the gel overflowed, and then photographing the sample under white light and ultraviolet light. The gel was then injected into a custom-made four-leaf clover mold using a syringe, and photographed again under white light and ultraviolet light. Figure 12 As shown, this pH-responsive AIE supramolecular hydrogel exhibits excellent injectability and plasticity, allowing it to be molded into any shape. Under ultraviolet light, the gel sample displays green fluorescence, suggesting its potential applications in organ scaffolds, biomimetic materials, and more.

[0099] Comparative Example 1

[0100] Using rosin as a raw material, N-(4-aminophenyl)imide maleic aspirin intermediate is obtained through DA addition and imidization. Further coupling with phenol and acid-base neutralization reaction yields a pH-responsive rosin-based rigid surfactant, as detailed below:

[0101] The preparation of N-(4-aminophenyl)imide maleic acridinium was carried out according to Example 1;

[0102] In a 600 mL beaker, add N-(4-aminophenyl)imide maleic acrid acid (30.0 g, 0.061 mol), 40 mL of water, and 45.0 g of concentrated hydrochloric acid. Stir until homogeneous. After cooling, the system becomes a paste and is placed in an ice-salt bath. Dissolve sodium nitrite (5.59 g, 0.81 mol) in 20 mL of water. At below 0 °C, add the sodium nitrite solution dropwise to the N-(4-aminophenyl)imide maleic acrid acid and concentrated hydrochloric acid system. The system gradually becomes clear, forming a yellow solution. During the reaction, use pH paper to ensure the reaction system is acidic. In an 800 mL beaker, add phenol (5.90 g, 0.063 mol), add 100 mL of water, and adjust the pH of the solution to 11 with concentrated sodium hydroxide solution. Slowly add the diazonium salt solution described above, maintaining the temperature below 0°C (the pH of the system is maintained at 9-11 by adding sodium hydroxide solution during the addition). After a short time, a brownish-yellow precipitate forms in the solution. After the addition is complete, continue stirring for 1 hour to finish the reaction. Add HCl dropwise to make the system acidic. Filter the reaction solution and wash twice with distilled water to obtain a light yellow powder. Recrystallize twice with ethanol and water to obtain an orange-yellow solid, namely 4-maleiporic acid-based azophenol (23.7 g).

[0103] 8.0 g (0.014 mol) of 4-maleopyric acid-based azophenol, 0.60 g (0.015 mol) of sodium hydroxide, and 80 g of anhydrous ethanol were added to a 250 mL single-necked flask equipped with a magnetic rotor and connected to a reflux flask. The temperature was raised to 40 °C and the reaction was carried out for 6 h. After the reaction solution was cooled to room temperature, the ethanol was removed by rotary evaporation. The solution was recrystallized twice with ethanol and acetone to obtain an orange-yellow solid, which was a pH-responsive rosin-based rigid anionic surfactant (6.13 g) with the following structure:

[0104] Experiments showed that this structure does not have gelling properties (it cannot form a gel) and fluorescent properties.

[0105] Comparative Example 2

[0106] Using rosin as a raw material, N-(4-aminophenyl)imide maleic azobenzene intermediate was obtained through DA addition and imidization. Maleic azobenzene monomer was then prepared via coupling with phenol and halogenated hydrocarbon substitution reaction, as detailed below:

[0107] The preparation of N-(4-aminophenyl)imide maleic acridinium was carried out according to Example 1;

[0108] Weigh 25g of N-(4-aminophenyl)imide maleic azophenol and dissolve it in 100mL of 12% dilute hydrochloric acid; dissolve 4.70g of sodium nitrite in 15mL of water and add it dropwise at 0-5℃, continuing the reaction for 1h; then, dissolve 4.95g of phenol in 20mL of 10% sodium hydroxide solution, add the phenol / sodium hydroxide solution dropwise to the reaction system, and adjust the pH of the reaction to 9-11 using sodium hydroxide aqueous solution, reacting for 2h; finally, adjust the pH to 4-6 using 12% dilute hydrochloric acid, filter, and recrystallize using ethanol to obtain maleic azophenol.

[0109] 5.96 g of maleic azophenol, 18.5 g of epichlorohydrin, and 0.24 g of benzyltributylammonium chloride were weighed into a flask and reacted at 117 °C for 3 h. The temperature was then lowered to 80 °C, and 1.68 g of potassium hydroxide was added, with the reaction continuing for another 3 h. After the reaction was complete, excess epichlorohydrin was distilled off under reduced pressure to obtain the maleic azophenyl epoxy monomer with the following structure:

[0110] R is Experiments have shown that this structure is insoluble in water, lacks surface activity, and does not exhibit gelling or fluorescent properties.

[0111] Comparative Example 3

[0112] Using rosin as a raw material, N-(4-aminophenyl)imide maleic acridinium intermediate is obtained through DA addition and imidization. Rosin-based rigid anionic surfactants can be prepared by coupling with phenol, methyl esterification, and haloalkane substitution reactions, as detailed below:

[0113] The preparation of N-(4-aminophenyl)imide maleic acridinium was carried out according to Example 1.

[0114] (1) In a 600 mL beaker, add N-(4-aminophenyl)imide maleic acrid acid (30.0 g, 0.061 mol), 40 mL of water, and 45.0 g of concentrated hydrochloric acid. Stir until well mixed. After cooling, the system becomes a paste. Place it in an ice-salt bath. Dissolve sodium nitrite (5.59 g, 0.81 mol) in 20 mL of water. At below 0 °C, add the sodium nitrite solution dropwise to the above N-(4-aminophenyl)imide maleic acrid acid and concentrated hydrochloric acid system. The system gradually becomes clear, forming a yellow solution. During the reaction, use pH paper to ensure that the reaction system is acidic.

[0115] Add phenol (5.90 g, 0.063 mol) to an 800 mL beaker, then add 100 mL of water. Adjust the pH of the solution to 11 using concentrated sodium hydroxide solution. Slowly add the diazonium salt solution mentioned above, maintaining the temperature below 0°C (the pH of the system is maintained at 9-11 by adding sodium hydroxide solution during the addition). After a short time, a brownish-yellow precipitate forms in the solution. After the addition is complete, continue stirring for 1 hour. Once the reaction is complete, add HCl to make the system acidic. Filter the reaction solution and wash twice with distilled water to obtain a light yellow powder. Recrystallize twice with ethanol and water to obtain an orange-yellow solid, namely 4-maleiporinosyl azophenol (23.7 g).

[0116] (2) Under N2 protection, K2CO3 (26.58 g, 0.19 mol) and 100 mL DMF were added to a 500 mL three-necked flask equipped with a magnetic rotor, and a reflux reflux device was connected. After stirring for 0.5 h, a DMF solution of 4-maleicopteroyl ethyl azophenol (19.2 g, 0.032 mol) was added, and the temperature was raised to 80 °C. Then, a DMF solution of bromoethane (3.67 g, 0.034 mol) was added in a single batch, and the reaction was stirred for 24 h until the reaction was complete. After cooling to room temperature, the mixture was filtered, and the filtrate was collected. 100 mL of ice water was added to the filtrate with stirring, and the mixture was extracted three times (with dichloromethane). The organic layer was collected and washed three times with deionized water. The mixture was dried over anhydrous MgSO4, filtered, and the filtrate was collected and distilled (to remove dichloromethane) to obtain a brown solid. The product was recrystallized three times with petroleum ether and ethyl acetate to obtain an orange-yellow solid, namely 4-maleicopteroyl ethyl azophenol (13.6 g).

[0117] (3) Synthesis of Rosin-based Rigid Anionic Surfactant: 10.0 g (0.016 mol) of 4-maleicopterinyl ethyl azophenol, 0.67 g (0.017 mol) of sodium hydroxide, and 80 g of anhydrous ethanol were added to a 250 mL flask equipped with a magnetic rotor and connected to a reflux apparatus. The temperature was raised to 70 °C and the reaction was allowed to proceed for 12 h. After the reaction was complete, the reaction solution was cooled to room temperature, and the ethanol was removed by rotary evaporation. The solution was recrystallized twice with ethanol and acetone to obtain an orange-yellow solid, which was the rosin-based rigid anionic surfactant (7.5 g), with the following structure:

[0118] Experiments showed that this structure does not possess gelling or fluorescent properties.

[0119] Comparative Example 4

[0120] Take 2.4 g of maleicopterinic azophenol (0.004 mol) into a three-necked flask, heat to 60 °C, and slowly add SOCl2 (1.92 g, 0.016 mol) at a rate of 30 drops / min. Bubbles are generated. React for 30 min until no bubbles are in the flask. Add anhydrous methanol (5 g, 0.016 mol) and continue reflux for 5 h. After the reaction is complete, remove methanol by rotary evaporation. Recrystallize the methanol and obtain a brownish-yellow solid powder by column chromatography, which is methylmaleicopterinic azophenol.

[0121] p-Toluenesulfonyl polyethylene glycol monomethyl ether (n = 69, 16.62 g, 0.004 mol) and methylmaleic anhydride-based azophenol (0.61 g, 0.001 mol) were dissolved in 50 mL LMF and 0.55 g, 0.004 mol of K₂CO₃, respectively, in round-bottom flasks. The reaction mixture was stirred in a preheated oil bath at 60 °C for 36 h, and then the reaction was stopped. The product was precipitated in excess cold diethyl ether and recrystallized in ethanol. After drying for 48 h, it was dialyzed in water for 2 days, and dried to obtain a photoresponsive rosin-based azophenyl polymer.

[0122] Where n is 69, experiments have shown that this structure does not possess gelation or fluorescence properties.

Claims

1. A pH-responsive rosin-based Schiff base AIE surfactant, characterized in that: Its molecular structure is as follows: ； When pH ≥ 7, the pH-responsive rosin-based Schiff base AIE surfactant aggregates in the aqueous solution and emits green fluorescence; when pH < 7, the pH-responsive rosin-based Schiff base AIE surfactant precipitates from the aqueous solution and emits yellow fluorescence; by adjusting the pH value of the system, the fluorescence intensity cycles with the pH cycle and is consistent with the fluorescence intensity corresponding to the pH before the cycle.

2. A method for preparing the pH-responsive rosin-based Schiff base AIE surfactant according to claim 1, characterized in that: N-(4-aminophenyl)imide maleic acridinium and salicylaldehydes with different substituents were added to an organic solvent for an aldehyde-amine condensation reaction to prepare a pH-responsive rosin-based Schiff base AIE surfactant; wherein the different substituents of salicylaldehyde are compound I, compound II, compound III, compound IV or compound V: 。 3. The preparation method according to claim 2, characterized in that: The organic solvent is methanol or ethanol; the molar ratio of N-(4-aminophenyl)imide maleic acridinium to different substituted salicylaldehydes is 1:(1.05~1.15); the condensation reaction temperature is 65~85℃ and the time is 4~6h.

4. The preparation method according to claim 2 or 3, characterized in that: The preparation method of N-(4-aminophenyl)imide maleiperic acid is as follows: maleiperic acid is dissolved in an organic solvent and added dropwise to an organic solvent of p-phenylenediamine to carry out an imidization reaction, thereby obtaining N-(4-aminophenyl)imide maleiperic acid; the molar ratio of maleiperic acid to p-phenylenediamine is 1:(1.05~1.15); the organic solvent is N,N-dimethylformamide; the imidization reaction conditions are: the dropwise addition temperature is 75~85℃, after the dropwise addition is completed, the reaction is continued at 75~85℃ for 1.5~2.5h, and then the temperature is raised to 140~150℃ to continue the reaction for 4~5h to obtain N-(4-aminophenyl)imide maleiperic acid.

5. The use of the pH-responsive rosin-based Schiff base AIE surfactant according to claim 1, characterized in that: The pH-responsive rosin-based Schiff base AIE surfactant was prepared at a concentration of 0.1–0.3 mmol·L⁻¹. -1 An aqueous solution of the substance is used as an aqueous anti-counterfeiting ink or information encryption. It emits green fluorescence when the pH value is ≥7. When the pH value of the system is reduced, the pH-responsive rosin-based Schiff base AIE surfactant is precipitated. The precipitated pH-responsive rosin-based Schiff base AIE surfactant solid emits yellow fluorescence.

6. The use of the pH-responsive rosin-based Schiff base AIE surfactant according to claim 1, characterized in that: The method for preparing pH-responsive AIE supramolecular hydrogels is as follows: pH-responsive rosin-based Schiff base AIE surfactant is added to ultrapure water, the pH of the system is adjusted to ≥11, the solution is heated until it is clear and transparent, and then kept at a constant temperature of 20~30℃ for 30~48 h to obtain pH-responsive AIE supramolecular hydrogels.

7. The use according to claim 6, characterized in that: In pH-responsive AIE supramolecular hydrogels, the concentration of pH-responsive rosin-based Schiff base AIE surfactant is 10–80 mmol·L⁻¹. -1 .

8. The use according to claim 7, characterized in that: When pH ≥ 11, the pH-responsive AIE supramolecular hydrogel exhibits good mechanical properties and fluorescence, with no pH-responsive rosin-based Schiff base AIE surfactant precipitating. When pH ≤ 11, some pH-responsive rosin-based Schiff base AIE surfactant precipitates, and the mechanical properties and fluorescence of the pH-responsive AIE supramolecular hydrogel decrease. When pH < 7, pH-responsive rosin-based Schiff base AIE surfactant precipitates, and the solution changes from green fluorescence emission to yellow fluorescence emission.

9. The use according to any one of claims 6-8, characterized in that: pH-responsive AIE supramolecular hydrogels exhibit temperature resistance; their elastic modulus and viscous modulus remain unchanged within the temperature range of 25-95 °C, with an elastic modulus greater than 1. 10 3 Pa; pH-responsive AIE supramolecular hydrogels exhibit shear recovery properties, and as strain changes, pH-responsive AIE supramolecular hydrogels interconvert from gel to liquid. pH-responsive AIE supramolecular hydrogels are injectable and malleable.

10. The use of the pH-responsive rosin-based Schiff base AIE surfactant according to claim 1, characterized in that: It can be used as a yellow dye; or for cell imaging; or as an emulsifier, solubilizer or dispersant; or for the detection of aluminum ions.

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