A viologen-anthraquinone-based porous ionic framework and its preparation method and photocatalytic application

Abstract

This invention discloses a viologen-anthraquinone-based porous ionic framework, its preparation method, and its photocatalytic application. Its chemical structure is shown in Formula 1. The preparation method includes the following steps: (1) using 4,4'-bis(2-bromoacetyl)biphenyl and 4,4'-bipyridine as raw materials, a viologen ionic linear polymer precursor VIP-Br is synthesized via a quaternization reaction; (2) using the above VIP-Br and disodium anthraquinone-2,6-disulfonate as raw materials, a viologen-anthraquinone-based porous ionic framework VAQ-PIN is prepared by ionic self-assembly in an aqueous phase at room temperature. This method is green, simple, and operates under mild conditions. The obtained VAQ-PIN can be used as a heterogeneous photocatalyst, exhibiting excellent photocatalytic activity in the photocatalytic oxidative coupling reaction of benzylamine. Formula 1

Description

Technical Field

[0001] This invention relates to the field of functionalized porous materials preparation technology, specifically to a viologen-anthraquinone-based porous ionic framework with photocatalytic activity, its preparation method, and its application in photocatalytic reactions. Background Technology

[0002] Imines and their derivatives are key intermediates in the synthesis of pharmaceuticals, fine chemicals, and bioactive molecules, and their efficient and green synthetic methods have attracted much attention. Among them, visible light photocatalysis-driven amine oxidative coupling reactions have become one of the ideal routes for the preparation of imine compounds due to their mild conditions and environmental friendliness. However, this field still faces significant challenges: most efficient photocatalysts rely on precious metals, which are costly and resource-limited; at the same time, traditional homogeneous catalytic systems suffer from problems such as difficulty in catalyst separation and recovery and poor recyclability, which restrict their large-scale application. Therefore, developing novel heterogeneous organic photocatalysts that combine high activity, high stability, easy recovery, and metal-free properties is of great significance for promoting the development of this technology.

[0003] Porous ionic frameworks (PINs) are a class of novel porous functional materials formed by the self-assembly of organic cations and anions through strong electrostatic interactions. Their ionicly bond-dominated construction not only endows the materials with excellent chemical stability and structural tunability but also allows for the formation of regular, designable pore structures, demonstrating potential in ion exchange, adsorption separation, and sensing. However, research on designing PINs as highly efficient heterogeneous photocatalysts is still in its early stages, and strategies for the synergistic regulation of their photophysical properties and catalytic functions urgently need to be explored.

[0004] Viologen compounds possess excellent photoelectric response, tunable redox potential, and stable free radical chemistry, making them common modules for constructing photoresponsive materials. Anthraquinone derivatives exhibit broad-spectrum visible light absorption and reversible redox properties, making them ideal photosensitizing and catalytic units. Integrating these two functional units into a single porous ionic framework through rational molecular design holds promise for achieving efficient light capture, charge separation, and substrate activation, thereby constructing high-performance heterogeneous photocatalytic materials. Currently, how to simultaneously introduce viologen and anthraquinone active centers into the PINs framework using a simple and green self-assembly strategy and optimize their photocatalytic performance remains a challenging research direction with significant scientific value and application prospects. Summary of the Invention

[0005] The purpose of this invention is to provide a viologen-anthraquinone-based porous ionic framework, its preparation method, and its photocatalytic application. The preparation method is simple, and the target material can be obtained through a one-step ionic self-assembly strategy. The obtained material, when used as a heterogeneous photocatalyst in the photocatalytic benzylamine oxidative coupling reaction, exhibits excellent photocatalytic activity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A functionalized viologen-anthraquinone-based porous ionic framework, denoted as VAQ-PIN, has the chemical structure shown in Formula 1:

[0008]

[0009] This invention also provides a method for preparing the above-mentioned viologen-anthraquinone-based porous ionic framework, comprising the following steps:

[0010] Using viologen ionic linear polymer VIP-Br (as shown in Formula 2) and anthraquinone-2,6-disulfonic acid (as shown in Formula 3) as raw materials, the viologen-anthraquinone-based porous ionic framework VAQ-PIN was synthesized through an ionic self-assembly reaction.

[0011] The structural formula of VIP-Br shown in Equation 2 is as follows: The structural formula of anthraquinone-2,6-disulfonic acid shown in Formula 3 is as follows: .

[0012] Furthermore, the preparation method specifically includes the following steps:

[0013] S1: Dissolve 4,4'-bis(2-bromoacetyl)biphenyl in acetonitrile, an organic solvent, and stir until completely dissolved to obtain solution A; S2: Dissolve 4,4'-bipyridine in acetonitrile, an organic solvent, and stir until completely dissolved to obtain solution B;

[0014] S3: Mix solution A and solution B, transfer to a reaction vessel, and carry out a quaternization reaction under heating conditions; after the reaction is completed, wash, filter and dry to obtain the viologen ionic linear polymer VIP-Br as shown in Formula 2;

[0015] S4: Dissolve the above-mentioned viologen ionic linear polymer in water and stir until completely dissolved to obtain solution C;

[0016] S5: Dissolve disodium anthraquinone-2,6-disulfonic acid in water and stir until completely dissolved to obtain solution D;

[0017] S6: Mix solution C with solution D and carry out ion self-assembly reaction at room temperature; after the reaction is completed, wash, filter and dry to obtain the viologen-anthraquinone-based porous ionic framework VAQ-PIN.

[0018] Preferably, in step S6, the molar ratio of the viologen ionic linear polymer to anthraquinone-2,6-disulfonic acid disodium is 1:1.

[0019] Preferably, in step S6, the ion self-assembly reaction is carried out in an aqueous phase at room temperature for 24 hours.

[0020] This invention also provides the application of the above-mentioned viologen-anthraquinone-based porous ionic framework VAQ-PIN in the photocatalytic oxidative coupling reaction of benzylamine.

[0021] Furthermore, the specific method of the application is as follows: using benzylamine or its derivatives as the reaction substrate, using the VAQ-PIN as the heterogeneous photocatalyst, and using blue LEDs as the light source in an atmospheric pressure air atmosphere, a photocatalytic reaction is carried out at room temperature to prepare the corresponding imine compounds.

[0022] The general structural formula of the benzylamine or its derivatives is: R is selected from hydrogen, methyl, methoxy, fluorine, chlorine, bromine, tert-butyl or trifluoromethyl.

[0023] In summary, this invention successfully constructed a viologen-anthraquinone-based porous ionic framework, VAQ-PIN, possessing both photoactivity and redox functions through a simple ion self-assembly strategy. Under mild conditions of room temperature and ambient pressure, this material can efficiently catalyze the blue light-driven oxidative coupling reaction of benzylamine to generate the target imine product, exhibiting excellent heterogeneous photocatalytic performance and good cycling stability.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The synthesis process is green and simple: the whole preparation process is mild, water is used as solvent, no high temperature and high pressure or complex post-treatment is required, the operation is simple, and it has good potential for large-scale application.

[0026] (2) Unique catalyst structure and function: Through an ionic self-assembly strategy, photoactive anthraquinone units and redox-active viologen units are synergistically integrated into the same porous ionic framework. This structure not only provides efficient light absorption and charge separation capabilities, but its ionic cross-linking characteristics also endow the material with excellent chemical stability.

[0027] (3) Outstanding catalytic performance and practicality: VAQ-PIN exhibits high activity and high selectivity for the oxidative coupling reaction of benzylamine under visible light (blue light) irradiation. At the same time, the catalyst is a solid multiphase material, which can be separated and recovered through simple filtration, and its catalytic activity remains good after recycling, which is in line with the concept of green and sustainable synthesis. Attached Figure Description

[0028] Figure 1 The X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR) spectra of the raw materials anthraquinone-2,6-disulfonic acid disodium (AQ), viologen ionic linear polymer (VIP-Br), and the prepared VAQ-PIN in Example 2 are shown, where (A) is the XRD spectrum and (B) is the FTIR spectrum.

[0029] Figure 2 The X-ray photoelectron spectroscopy (XPS) of VAQ-PIN prepared in Example 2 and the electron paramagnetic resonance (EPR) spectra of VIP-Br and VAQ-PIN are shown, where: (A) XPS full spectrum; (B) C 1s fine spectrum; (C) N 1s fine spectrum; (D) O 1s fine spectrum; (E) S 2p fine spectrum; (F) EPR spectrum.

[0030] Figure 3 The images shown are scanning electron microscope (SEM) images of the VAQ-PIN prepared in Example 2, where: (A) low-magnification SEM image (scale bar: 2.5 μm); (B) high-magnification SEM image (scale bar: 500 nm).

[0031] Figure 4 The N2 adsorption-desorption isotherm of the VAQ-PIN prepared in Example 2 at 77K and the pore size distribution diagram calculated based on the BJH model, wherein: (A) N2 adsorption-desorption curve; (B) BJH pore size distribution curve.

[0032] Figure 5 The images show the UV-Vis absorption spectra of the raw materials AQ, VIP-Br, and the prepared VAQ-PIN in Example 2, as well as the optical bandgap diagrams obtained using the Kubelka-Munk function and Tauc plotting method, where: (A) UV-Vis spectrum; (B) Tauc plot; (C) XPS valence band (VB) spectrum of VAQ-PIN; (D) band structure of VAQ-PIN; and the photoelectrochemical performance test results of the raw materials AQ, VIP-Br, and the prepared VAQ-PIN, where: (E) transient photocurrent response curve; and (F) electrochemical impedance spectroscopy (EIS) Nyquist plot.

[0033] Figure 6 The results show the substrate suitability of the VAQ-PIN prepared in Example 2 in the photocatalytic benzylamine oxidative coupling reaction. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the embodiments.

[0035] Example 1: Preparation of Viologen Ionic Linear Polymer VIP-Br

[0036] Synthesis route:

[0037]

[0038] 4,4'-bis(2-bromoacetyl)biphenyl (BDBP, 0.4 mmol, 0.1636 g) and 4,4'-bipyridine (Bpy, 0.4 mmol, 0.0624 g) were dissolved separately in 5 mL of N,N-dimethylformamide (DMF). The two solutions were mixed and transferred to a 25 mL reaction vessel, and stirred at room temperature for 15 minutes. The reaction vessel was then placed at 100 °C and reacted for 48 hours. After the reaction was complete, the precipitate was collected by vacuum filtration and washed thoroughly with acetonitrile and ethanol, respectively. Finally, the solid product was dried in a vacuum oven at 80 °C for 12 hours to obtain the viologen ionic linear polymer VIP-Br.

[0039] Example 2: Preparation of viologen-anthraquinone-based porous ionic framework VAQ-PIN

[0040] The viologen ionic linear polymer VIP-Br (0.4 mmol, 0.2260 g) prepared in Example 1 and anthraquinone-2,6-disulfonic acid disodium AQ (0.4 mmol, 0.1648 g) were dissolved separately in 5 mL of deionized water. The VIP-Br aqueous solution was added dropwise to the AQ aqueous solution, resulting in immediate precipitation. The suspension was stirred and reacted at room temperature for 24 hours. After the reaction was complete, the precipitate was collected by vacuum filtration and washed thoroughly with water and ethanol sequentially. Finally, the solid product was dried in a vacuum drying oven at 80 °C for 12 hours to obtain the viologen-anthraquinone-based porous ionic framework VAQ-PIN.

[0041]

[0042] Structural and compositional characterization:

[0043] Figure 1 A shows the XRD patterns of the raw materials AQ, VIP-Br, and the prepared VAQ-PIN used in Example 2. This indicates that VAQ-PIN has a higher crystallinity than the crystalline precursors VIP-Br and AQ, exhibiting a crystalline ordered structure.

[0044] Figure 1 A shows the X-ray diffraction (XRD) patterns of the raw materials AQ, VIP-Br, and the prepared VAQ-PIN. Compared with the two precursors AQ and VIP-Br, VAQ-PIN has characteristic diffraction peaks (e.g., 18.8). o 20.1 o 25.7 o 31.6 o 33.2 o 37.9 o 40.8 o The sharper edges indicate that the synthesized material has good crystallinity and an ordered structure.

[0045] Figure 1 B represents the Fourier Transmission Infrared (FTIR) spectra of the raw materials AQ, VIP-Br, and the prepared VAQ-PIN in Example 2. In the FTIR spectrum of VAQ-PIN, at 1600 cm⁻¹... -1 and 1710 cm -1 The characteristic peaks at 738 cm⁻¹ are attributed to the stretching vibrations of C=C and C=O bonds in the VIP-Br framework, respectively. -1 930 cm -1 and 1324 cm -1 The peaks appearing at [insert peak values ​​here] can be attributed to the stretching vibrations of the SO bond, CS bond, and S=O bond in the sulfonic acid group, respectively, and these signals originate from the AQ unit. Furthermore, the broad peak at 3420 cm⁻¹ can be attributed to the presence of adsorbed water or hydrogen bonding interactions in the material. These infrared spectral characteristics indicate that VAQ-PIN materials were successfully prepared by combining VIP-Br with AQ units via an ionic self-assembly strategy.

[0046] Figure 2 A is the full X-ray photoelectron spectroscopy (XPS) spectrum of VAQ-PIN, and its elemental quantitative analysis results show the atomic percentages as follows: C (76.13 at%), N (4.83 at%), O (15.40 at%), and S (2.55 at%). C 1s fine spectrum ( Figure 2 B) can be resolved into four peaks with binding energies at 284.4 eV, 284.8 eV, 285.6 eV, and 287.1 eV, which are respectively attributed to the C / C=C bond in the aromatic ring, the CS bond in the aromatic sulfonic acid, the CN / C=N bond in the viologen group, and the C=O bond. N 1s fine spectrum ( Figure 2 In C), the main peak at 401.9 eV is attributed to viologen dinitrogen cation (VN). ++ The peak at 400.7 eV is attributed to viologen radicals (VN). +• The nitrogen atom in the viologen group, and the peak at 398.9 eV, are attributed to the neutral nitrogen (VN) in the viologen group. 0 O 1s fine spectrum ( Figure 2 In D), the peaks at 530.8 eV, 531.0 eV, 531.8 eV, and 532.8 eV are attributed to adsorbed water, -SO bonds in sulfonic acid groups, -S=O bonds in sulfonic acid groups, and C=O bonds, respectively. S 2p fine spectrum ( Figure 2 E) at 167.4 eV (S 2p 3 / 2 ) and 168.6 eV (S 2p 1 / 2 The double peak at point ) belongs to -SO3 in the material. -Anions. Figure 2 F shows the electron paramagnetic resonance (EPR) spectra of VIP-Br and VAQ-PIN. Compared with VIP-Br, VAQ-PIN exhibits a significantly enhanced radical signal intensity, with a g-value of 2.0041, indicating that the introduction of the anthraquinone anion effectively enhances the radical properties of the viologen cation. These characterization results fully confirm that a radical-type viologen-anthraquinone-based porous ionic framework, VAQ-PIN, was successfully prepared through ionic self-assembly.

[0047] Figure 3 The image shows a scanning electron microscope (SEM) image of VAQ-PIN, revealing a loose, porous morphology composed of sheet-like aggregates. To clarify the pore structure properties of VAQ-PIN, nitrogen adsorption-desorption tests were performed at 77 K. Figure 4 As shown in Figure A, VAQ-PIN exhibits a typical Type IV adsorption isotherm, with a significant jump in nitrogen adsorption in the high relative pressure region (0.80 < P / P0 < 0.99), indicating the presence of abundant mesoporous structures within the material. Calculations using the BET model yield a specific surface area of ​​6 m². 2 g -1 Aperture distribution map calculated based on the BJH model ( Figure 4 B) shows that the pore size of VAQ-PIN is mainly concentrated in the range of 3.71-6.27 nm, exhibiting a narrow mesopore distribution characteristic, which is consistent with the results of the type IV isotherm, confirming the porosity of the material.

[0048] Figure 5 A comparison was made of the UV-Vis absorption spectra of the raw materials VIP-Br, AQ, and the prepared VAQ-PIN. VAQ-PIN showed significantly stronger absorption in the visible light region (400-800 nm) than the two raw materials, indicating that the successful combination of the two building blocks effectively extended the conjugated system of the VAQ-PIN material, significantly enhancing its visible light absorption capability. Based on the Kubelka-Munk equation and the Tauc plot method (…),… Figure 5 B) The optical band gaps (E) of VIP-Br, AQ, and VAQ-PIN were calculated. g The voltage band gaps are 1.97 eV, 1.84 eV, and 1.16 eV, respectively. The narrower band gap of the VAQ-PIN, along with its enhanced visible light absorption capability, contributes to its excellent semiconductor light absorption characteristics. Based on the XPS valence band (VB) spectrum... Figure 5 C), the calculated valence band peak (VBM) of VAQ-PIN is 1.01 eV. Converting this to the hydrogen electrode potential, the VBM of VAQ-PIN-1 is 0.77 eV. According to formula (E CB = E VB (vs. NHE) -E gThe conduction band bottom (CBM) of the VAQ-PIN was found to be -0.39 eV, and the band gap structure was given. Figure 5 (D) It can be observed that the CBM of VAQ-PIN is more negative than the reduction band (-0.35 eV) of the superoxide anion radical. Furthermore, the photogenerated charge behavior of the VAQ-PIN material was evaluated by photoelectrochemical testing. Transient photocurrent response testing ( Figure 5 The E-plot shows that, over five visible light switching cycles, VAQ-PIN exhibits a stronger photocurrent response than VIP-Br and AQ, indicating superior photogenerated carrier separation and migration efficiency. The Nyquist plot of the electrochemical impedance spectroscopy (EIS) is also shown. Figure 5 F) shows that VAQ-PIN has the smallest impedance radius, indicating the lowest charge transfer resistance and the fastest interfacial charge transport kinetics. These results demonstrate that VAQ-PIN possesses excellent photogenerated charge separation and transport capabilities, providing a foundation for its highly efficient photocatalytic performance.

[0049] Example 3: Comparison of catalytic performance and reusability of photocatalytic benzylamine oxidative coupling reaction

[0050] The VAQ-PIN prepared in Example 2 was used for the blue light-catalyzed oxidative coupling reaction of benzylamine. The specific steps are as follows: Benzylamine (0.5 mmol, 53.5 mg) and VAQ-PIN catalyst (5 mg) were added sequentially to a 20 mL glass reaction tube. The reaction was carried out under 5 W blue LED irradiation, with the system kept in contact with air to provide the oxygen required for the reaction. The reaction mixture was continuously stirred at 500 rpm at room temperature. After the reaction was complete, an appropriate amount of deuterated chloroform (CDCl3) was added directly to the system, and stirring was continued for 0.5 hours before filtration. The CDCl3 filtrate containing the product was collected and processed... 1 ¹H NMR spectroscopy analysis determined the conversion and selectivity of the reaction. The solid catalyst after the reaction was thoroughly washed with ethyl acetate (≥12 hours), filtered, and dried under vacuum before being directly used in the next catalytic cycle.

[0051] Table 1 Results of blue light photocatalytic oxidative coupling reaction of benzylamine under different catalysts

[0052] Serial Number catalyst Time (h) Conversion rate (%) Selectivity (%) 1 VAQ-PIN 4 96 99 2 VIP-Br 4 31 99 3 AQ 4 32 98

[0053] Reaction conditions: benzylamine (0.5 mmol), photocatalyst (5 mg), blue LEDs (5 W), solvent-free, room temperature, air atmosphere (1 atm), reaction time 4 h.

[0054] Table 2. Recyclability of VAQ-PIN in photocatalytic benzylamine oxidative coupling reaction

[0055] Number of times to reuse Time (h) Conversion rate (%) Selectivity (%) 1 4 96 99 2 4 96 99 3 4 95 99 4 4 93 99 5 4 92 99

[0056] Reaction conditions: benzylamine (0.5 mmol), photocatalyst VAQ-PIN (5 mg), blue LEDs (5 W), solvent-free, room temperature, air atmosphere (1 atm), reaction time 4 h.

[0057] As shown in Table 1, under blue light irradiation and in an air atmosphere, using VAQ-PIN as a heterogeneous photocatalyst, the conversion rate of benzylamine reached 96% and the selectivity was 99% after 4 hours of reaction. In contrast, when using single-raw material VIP-Br or AQ as catalysts, the conversion rates were only 31% and 32%, respectively, under the same conditions. Combined with photoelectric performance characterization analysis, the excellent photocatalytic activity of VAQ-PIN is attributed to its stable free radical properties, enhanced visible light absorption capacity, and highly efficient photogenerated carrier separation and migration.

[0058] The stability and reusability of the VAQ-PIN catalyst were evaluated through cyclic experiments. Five consecutive reactions were conducted under the same conditions, and the results are shown in Table 2. After five cycles, the catalyst maintained a conversion rate of over 92% and a selectivity of 99%, indicating that VAQ-PIN possesses good structural stability and recyclability.

[0059] Example 4: Substrate suitability of the catalyst VAQ-PIN

[0060] This example uses the VAQ-PIN prepared in Example 2 as a catalyst to investigate its photocatalytic oxidative coupling activity for a series of benzylamine derivatives with different substituents. The selected substrates include: benzylamine, 4-cyanobenzylamine, 4-methylbenzylamine, 4-methoxybenzylamine, 4-fluorobenzylamine, 4-chlorobenzylamine, 4-bromobenzylamine, 4-tert-butylbenzylamine, and 4-trifluoromethylbenzylamine. The reaction conditions are basically the same as in Example 3, except that the reaction time (6-12 hours) was adjusted according to the substrate activity. The photocatalytic performance results are as follows: Figure 6 As shown, VAQ-PIN exhibits excellent catalytic activity and high selectivity for various benzylamine derivatives. The structure of the obtained imine product was confirmed by ¹H NMR, and the specific data are as follows:

[0061] N-Benzyl-1-phenylmethylamine (2a) 1 H NMR (400 MHz, CDCl3): δ=8.42 (s, 1H), 7.83~7.82 (d, 2H), 7.45~7.44 (m, 3H), 7.39~7.29 (m, 5H), 4.86 ppm (s, 2H).

[0062] N-(4-fluorobenzyl)-1-(4-fluorophenyl)-methylamine (2b) 1H NMR (400 MHz, CDCl3): δ=8.43 (s,1H), 7.84~7.81 (m, 2H), 7.36~7.33 (m,2H), 7.17~7.07 (m, 4H), 4.82 ppm (s,2H).

[0063] N-(4-chlorobenzyl)-1-(4-chlorophenyl)-methylamine (2c) 1 H NMR (400 MHz, CDCl3): δ=8.34 (s,1H), 7.73~7.70 (d, 2H), 7.40~7.39 (d,2H), 7.33~7.31 (d, 2H), 7.28~7.26 (d,2H), 4.77 ppm (s, 2H).

[0064] N-(4-bromobenzyl)-1-(4-bromophenyl)methylamine (2d) 1 H NMR (400 MHz, CDCl3): δ=8.37 (s,1H), 7.70~7.68 (d, 2H), 7.61~7.59 (d, 2H), 7.53~7.51 (d, 2H), 7.27~7.25 (d,2H), 4.79 ppm (s, 2H).

[0065] N-(4-cyanobenzyl)-1-(4-cyanobenzyl)methylamine (2e) 1 H NMR (400 MHz, CDCl3): δ=8.50(s, 1H), 7.96~7.93 (d, 2H), 7.77~7.75 (d, 2H), 7.69~7.67 (d, 2H), 7.53~7.51(d, 2H), 4.95 ppm (s, 1H).

[0066] N-(4-methylbenzyl)-1-(4-methylbenzyl)methylamine (2f) 1 H NMR (400 MHz, CDCl3): δ= 8.41(s, 1H), 7.76 ~7.74 (d, 2H), 7.31~7.30 (d, 4H), 7.28~7.22 (d, 2H), 4.85 (s, 2H), 2.46 (s, 3H), 2.31 ppm (s, 3H).

[0067] N-(4-methoxybenzyl)-1-(4-methoxyphenyl)methylamine (2g) 1H NMR (400 MHz, CDCl3): δ=8.35 (s, 1H), 7.78~7.76 (d, 2H), 7.32~7.30 (d, 2H), 6.99~6.97 (d, 2H), 6.95~6.93 (d, 2H), 4.78 (s, 2H), 3.89 (s, 3H), 3.85 ppm (s, 3H).

[0068] N-(4-(tert-butyl)benzyl)-1-(4-(tert-butyl)phenyl)methylamine (2h) 1 H NMR (400 MHz, CDCl3): δ=8.46 (s, 1H), 7.83~7.78 (d, 2H), 7.54~7.52 (d, 2H), 7.47~7.45 (d, 2H), 7.37~7.34 (d, 2H), 4.88 (s, 2H), 1.43~1.38 ppm (d, 18H).

[0069] N-(4-trifluoromethylbenzyl)-1-(4-trifluoromethylphenyl)methylamine (2i) 1 H NMR (400 MHz, CDCl3): δ=8.52 (s, 1H), 7.97~7.95 (d, 2H), 7.75~7.73 (d, 2H), 7.68~7.66 (d, 2H), 7.54~7.52 (d, 2H), 4.95 ppm (s, 2H).

[0070] The above results indicate that the VAQ-PIN catalyst exhibits excellent catalytic activity and substrate applicability for various benzylamines with electron-donating or electron-withdrawing substituents, and can serve as a highly efficient heterogeneous photocatalyst for the oxidative coupling reaction of benzylamines.

Claims

1. A viologen-anthraquinone-based porous ionic framework, characterized in that, It is a porous ionic framework prepared by an ionic self-assembly strategy, denoted as VAQ-PIN, and its chemical structure is shown in Formula 1. .

2. A method for preparing the viologen-anthraquinone-based porous ionic framework according to claim 1, characterized in that, Includes the following steps: Using viologen ionic linear polymer VIP-Br (as shown in Formula 2) and anthraquinone-2,6-disulfonic acid (as shown in Formula 3) as raw materials, the viologen-anthraquinone-based porous ionic framework VAQ-PIN was synthesized through an ionic self-assembly strategy. The structural formula of VIP-Br shown in Equation 2 is as follows: Formula 3 shows the structural formula of anthraquinone-2,6-disulfonic acid. .

3. The preparation method according to claim 2, characterized in that, Specifically, the following steps are included: S1: Dissolve the raw material 4,4'-bis(2-bromoacetyl)biphenyl in acetonitrile and stir until completely dissolved to obtain solution A; S2: Dissolve the raw material 4,4'-bipyridine in acetonitrile and stir until completely dissolved to obtain solution B; S3: Mix solution A and solution B evenly, transfer to a reaction vessel, and carry out a quaternization reaction at a certain temperature; after the reaction is completed, wash, filter and dry to obtain the viologen ionic linear polymer VIP-Br as shown in Formula 2; S4: Dissolve VIP-Br in water and stir until completely dissolved to obtain solution C; S5: Dissolve disodium anthraquinone-2,6-disulfonic acid in water and stir until completely dissolved to obtain solution D; S6: Mix solution C with solution D and carry out ion exchange and self-assembly reaction at room temperature; after the reaction is completed, wash, filter and dry to obtain the viologen-anthraquinone-based porous ionic framework VAQ-PIN.

4. The preparation method according to claim 3, characterized in that, In step S6, the molar ratio of the viologen cationic linear polymer VIP-Br to anthraquinone-2,6-disulfonic acid disodium is 1:

1.

5. The preparation method according to claim 3 or 4, characterized in that, In step S6, the ion self-assembly reaction is carried out in an aqueous phase at room temperature for 24 hours.

6. According to claim 3, the VAQ-PIN prepared in step S6 has significant free radical properties at room temperature.

7. The application of the viologen-anthraquinone-based porous ionic framework VAQ-PIN as described in claim 1 in the photocatalytic oxidative coupling reaction of benzylamine.

8. The application according to claim 6, characterized in that, include: Using benzylamine or its derivatives as the reaction substrate and the VAQ-PIN described in claim 1 as the heterogeneous photocatalyst, a photocatalytic oxidative coupling reaction of benzylamine is carried out at room temperature under normal pressure air atmosphere and blue LED irradiation to prepare the corresponding imine compounds.

9. The application according to claim 7, characterized in that, The structural formula of the benzylamine and its derivatives is as follows: , wherein R is selected from any one of hydrogen, methyl, methoxy, fluorine, chloro, bromo, tert-butyl and trifluoromethyl.

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