A free radical crystalline porous organic salt and its preparation method and photocatalytic application

Abstract

The present invention discloses a free radical type crystalline porous organic salt and its preparation method and photocatalytic application, wherein the chemical structure is shown in Formula 3, and the preparation method comprises the following steps: (1) using 1,5-naphthalenedisulfonic acid shown in Formula 1 and N,N,N',N'-tetra(p-aminophenyl)-p-phenylenediamine shown in Formula 2 as raw materials through charge-assisted hydrogen bond self-assembly, at different temperatures, a series of free radical type crystalline porous organic salts (RPOSs) are synthesized. The crystalline porous organic salt prepared by the present invention has the advantages of simple process, mild reaction conditions and short reaction time. The typical photoactive crystalline porous organic salt RPOS-80 is used as a photocatalyst in the blue light photocatalytic benzylamine coupling reaction, showing excellent heterogeneous photocatalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of novel functional porous organic solid materials, and in particular to a photoactive free radical type crystalline porous organic salt and a preparation method and photocatalytic application thereof. Background Art

[0002] As important pharmaceutical intermediates, imines and their derivatives are widely used in fine chemicals, pharmaceuticals, biological reagents and other fields. With the widespread application of imine compounds in various fields, the direct synthesis of imines through the oxidative coupling process of primary amines has the advantages of low energy consumption and simple process. The selective oxidative coupling of amines to synthesize imines by photocatalysis has gradually become an important research topic. However, the photocatalysts used in this reaction often involve expensive precious metals such as Au, Ru and Pd, and there is also the problem that homogeneous catalysts are difficult to recycle. Therefore, from the perspective of green chemistry, it is of great research significance to develop metal-free or non-precious metal heterogeneous catalysts to achieve the selective oxidation of amines to synthesize imines under solvent-free conditions using air or O2 as oxidants. With the development of visible light photocatalytic technology, the development of photocatalysts with high catalytic activity is crucial.

[0003] Crystalline porous organic salts (POSs) are a novel class of porous organic materials synthesized through self-assembly of organic acids and bases via charge-assisted hydrogen bonding. Their unique directional hydrogen bonding effectively inhibits close packing of building blocks, resulting in significant porosity within the crystal. The unique ionic bonding imparts high polarity to the pores, distinguishing POSs from other organic framework materials. POSs have achieved remarkable progress in proton conductivity, gas separation and adsorption, and separation sensing. However, POSs as heterogeneous photocatalysts are rarely reported, necessitating the design and synthesis of photocatalytically active crystalline porous organic salts. Triphenylamine (TPA) and its derivatives are renowned for their excellent photoelectric properties. TPA and its derivatives also possess excellent redox activity and have been used to construct photoactive free radical polymer materials. Therefore, the development of free radical-type crystalline porous organic salts with both photoactivity and redox activity for photocatalytic oxidation reactions holds great promise. The key lies in a simple strategy to introduce triphenylamine radicals into crystalline porous organic salts. Summary of the Invention

[0004] The present invention aims to provide a free radical crystalline porous organic salt, a preparation method thereof, and photocatalytic applications. The preparation process of the method is simple, requiring only a one-step reaction self-assembly to prepare a tetraphenyl-p-phenylenediamine free radical crystalline porous organic salt. The prepared heterogeneous catalyst is used in a photocatalytic benzylamine coupling reaction and has excellent photocatalytic activity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a functionalized free radical crystalline porous organic salt RPOSs, whose chemical structure is shown in Formula 3:

[0006]

[0007] The present invention also provides a method for preparing the above-mentioned free radical type crystalline porous organic salt, comprising the following steps:

[0008] (1) Radical crystalline porous organic salt RPOSs were synthesized by charge-assisted hydrogen bond self-assembly using 1,5-naphthalene disulfonic acid (Formula 1) and N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine (Formula 2) as raw materials.

[0009] The structural formula of 1,5-naphthalene disulfonic acid shown in Formula 1 is The structural formula of N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine shown in Formula 2 is

[0010] Furthermore, the method specifically includes the following steps:

[0011] S1: Add 1,5-naphthalene disulfonic acid shown in Formula 1 into a container containing an organic solvent DMF, and stir to completely dissolve it to obtain a uniform solution;

[0012] S2: Add N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine shown in Formula 2 into a container containing an organic solvent DMF, and stir to completely dissolve it to obtain a uniform solution;

[0013] S3: transferring the uniform solution obtained in step S1 to a reaction tube, adding the uniform solution obtained in step S2, placing the mixed solution in a reaction tube, placing the reaction tube on a reaction module, and performing an acid-base neutralization reaction at a certain reaction temperature for a period of time. After the reaction is completed, washing, filtering, and drying to obtain free radical-type crystalline porous organic salts RPOSs;

[0014] Preferably, in step S3, the molar ratio between the 1,5-naphthalene disulfonic acid shown in Formula 1 and the N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine shown in Formula 2 is 2:1.

[0015] Preferably, in step S3, the reaction temperature is 20-80°C and the reaction time is 12 hours. A series of free radical crystalline porous organic salts RPOS-20, RPOS-40, RPOS-60 and RPOS-80 were prepared at 20°C, 40°C, 60°C and 80°C.

[0016] The present invention also investigates the application of the free radical type crystalline porous organic salt in the photocatalytic benzylamine coupling reaction.

[0017] Furthermore, the method specifically comprises: using benzylamine as a substrate, using the RPOSs according to claim 1 as a heterogeneous catalyst, in an atmosphere of normal pressure air, using blue light LEDs as a light source, and performing a photocatalytic benzylamine coupling reaction to prepare imine at room temperature.

[0018] The structural formula of the benzylamine is Wherein, R is an unsubstituted group, or one of a methyl group, a methoxy group, a fluoro group, a chloro group, a bromo group, a tert-butyl group and a trifluoromethyl group.

[0019] The present invention prepares free radical crystalline porous organic salts (RPOSs) through a simple self-assembly strategy. The entire process involves using 1,5-naphthalene disulfonic acid and N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine as raw materials, and preparing a series of free radical crystalline porous organic salts RPOSs through charge-assisted hydrogen bond self-assembly at 20-80°C. The free radical crystalline porous organic salts RPOSs are characterized by being rich in stable free radicals, highly crystalline structure and high specific surface area. Among them, the RPOS-80 photocatalyst prepared at 80°C exhibits excellent heterogeneous catalytic performance in the blue light photocatalytic benzylamine coupling reaction to produce imines under mild conditions of room temperature and pressure. Therefore, the present invention develops functionalized free radical crystalline porous organic salts RPOSs based on the charge-assisted hydrogen bond self-assembly strategy, which are used as heterogeneous photocatalysts, using blue light LED as the light source, and achieving efficient conversion of photocatalytic benzylamine coupling to produce imines under room temperature and air atmosphere.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) The preparation process of the present invention requires only one step of reaction, mild reaction conditions, and simple equipment, and has broad prospects for industrial and large-scale application;

[0022] (2) Through a simple charge-assisted hydrogen bond self-assembly strategy, photoactive units were successfully introduced. The catalyst is rich in stable free radicals, highly crystalline, and has a high specific surface area, resulting in the prepared crystalline porous organic salt having excellent photocatalytic activity.

[0023] (3) The functionalized free radical crystalline porous organic salt of the present invention exhibits excellent photocatalytic performance in the blue light photocatalytic benzylamine coupling reaction under normal temperature and pressure conditions, and the photocatalyst also has the advantages of being easy to separate and recycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1Infrared (FTIR) spectra of the raw materials 1,5-naphthalenedisulfonic acid (abbreviated as NDSA), N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine (abbreviated as TAPDA) and the prepared RPOS-80 used in this Example 1, X-ray photoelectron spectroscopy (XPS) spectrum of RPOS-80, and electron paramagnetic resonance (EPR) spectra of TAPDA, RPOS-20, RPOS-40, RPOS-60 and RPOS-80 in Example 1, in the figure, (A) FTIR spectrum, (B) XPS full spectrum, (C) C 1s, (D) N 1s, (E) S2p and (F) EPR spectrum;

[0025] Figure 2 The X-ray powder diffraction (XRD) spectra of the raw materials NDSA, TAPDA and the prepared RPOS-80 used in this Example 1, and the XRD spectra of RPOS-20, RPOS-40, RPOS-60 and RPOS-80 prepared at different temperatures;

[0026] Figure 3 The scanning electron microscope (SEM) images of RPOS-80 prepared in Example 1 are shown in Figures 1 and 250 nm, respectively.

[0027] Figure 4 N2 adsorption-desorption curves and NLDFT pore size distribution diagrams of RPOS-20, RPOS-40, RPOS-60 and RPOS-80 prepared in Example 1 at 77K, in which (A) N2 adsorption-desorption curves and (B) NLDFT pore size distribution diagrams are shown;

[0028] Figure 5 This is the H NMR spectrum of RPOS-80 prepared in Example 1;

[0029] Figure 6 The UV-visible absorption spectra (UV-vis) of the raw materials NDSA and TAPDA and the prepared RPOS-80 used in this Example 1 and the Tauc plots obtained by using the Kubelka-Munk function and optical band gap linear fitting, wherein (A) UV-vis spectra and (B) Tauc plots;

[0030] Figure 7 The photocurrent density responses and impedance spectra represented by Nyquist plots of RPOS-20, RPOS-40, RPOS-60, and RPOS-80 prepared in Example 1, including (A) photocurrent density responses and (B) impedance spectra;

[0031] Figure 8This is a study on the substrate applicability of RPOS-80 prepared in Example 1 in the photocatalytic benzylamine coupling reaction;

[0032] Figure 9-17 is the product of each reaction in this embodiment 3 1 HNMR spectrum. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to the embodiments.

[0034] Example 1: Preparation of free radical crystalline porous organic salt RPOSs

[0035] Synthesis route:

[0036]

[0037] 1,5-Naphthalenedisulfonic acid (0.4 mmol, 0.1152 g) and N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine (0.2 mmol, 0.0946 g) were dissolved in 10 mL of DMF, mixed, and placed in a 50 mL reaction tube. Stirred at room temperature for 20 minutes, the mixture was then reacted at 80°C for 12 hours. After the reaction, the resulting precipitate was dispersed in 20 mL of tetrahydrofuran (THF) and stirred for 2 hours. The precipitate was then filtered and thoroughly washed with THF and ethanol. Finally, the filtered solid was placed in a vacuum drying oven at 80°C for 12 hours to obtain the free radical crystalline porous organic salt RPOS-80. RPOS-20, RPOS-40, and RPOS-60 were prepared using the same method by controlling the temperature at 20°C, 40°C, and 60°C.

[0038] Structural and compositional characterization:

[0039] Figure 1 A is the infrared spectrum of the raw materials NDSA, TAPDA and the prepared RPOS-80 used in this Example 1. As can be seen from the figure, the 1247cm -1 and 3450~3380cm -1 The infrared characteristic peaks at 1215~1030cm are attributed to the stretching vibration of the CN bond on TAPDA and the primary amine NH. -1 The characteristic diffraction peak of sulfonic acid group appeared at 1215-1130cm -1 The corresponding asymmetric stretching vibration of sulfonate anion is 1130-1030cm -1 It can be attributed to the symmetric stretching vibration of the sulfonate anion, which comes from NDSA. -1The primary amine (-NH2) bending vibration peak at 3420 cm is affected by the skeleton vibration of the aromatic ring, and the peak intensity is weakened. -1 The broad peak at 400 nm could be attributed to the presence of partially adsorbed water in the ionic salt or to the presence of hydrogen bonds. The infrared spectrum showed that the two monomers were successfully combined to prepare RPOS-80 through the self-assembly strategy.

[0040] Figure 1 B is the total XPS spectrum of RPOS-80. The complete XPS spectrum provides the detailed atomic concentrations of the elements in RPOS-80: C (69.31 at%), N (9.72 at%), O (16.06 at%), and S (4.92 at%). Figure 1 In the N1s spectrum (C), the three binding energy (BE) peaks of RPOS-80 at 284.5 eV, 284.9 eV, and 285.8 eV are attributed to the C-S bond in the aromatic sulfonic acid, the C-C / C=C bond in the aromatic ring, and the C-N bond in the triphenylamine derivative, respectively. Figure 1 D), the characteristic peaks at 401.9eV and 399.8eV appeared, which were attributed to -NH3 + and -NH2 groups, and the characteristic peak at 400.4 eV is attributed to the tetraphenyl-p-phenylenediamine radical (TPA-N +· ) in the N atom, the signal peak at 399.1eV belongs to the CN bond in the structure. In order to further determine the bonding configuration of the S atom, the S2p spectrum ( Figure 1 E), the S2p peaks at 167.9eV and 168.9eV are attributed to the characteristic peaks of SO. 3 / 2 ) and 169.0eV(S2p 1 / 2 The peak at ) is attributed to -SO3 in RPOS-80 - Anions and residual -SO3H groups. According to the above spectrum results, there are two connection modes of sulfonic acid groups and amino groups in RPOS-80 material. One is the connection mode of -SO3- and -NH3 + The strong charge interaction between anions and cations formed by acid-base neutralization reactions, and the hydrogen bonding between -SO₃H and -NH₂, are another. The bond formed between sulfonic acid and amine is a charge-assisted, directional hydrogen bond. This hydrogen bond is highly ionized, possessing characteristics of both hydrogen and ionic bonds, enhancing the stability and rigidity of the backbone structure. The OH groups in the O 1s spectrum may be partially due to adsorbed water and partially due to intramolecular hydrogen bonding. Figure 1F is the EPR spectra of TAPDA, RPOS-20, RPOS-40, RPOS-60 and RPOS-80. It can be seen from the figure that RPOS-20, RPOS-40, RPOS-60 and RPOS-80 show signals of different intensities respectively, indicating the successful introduction of stable tetraphenyl-p-phenylenediamine radicals. Among them, the radical signal of RPOS-80 is the strongest, corresponding to a g value of 2.0036. It is worth noting that the higher the synthesis temperature, the stronger the radical signal in the obtained RPOSs materials, indicating that high temperature is beneficial to the formation of more radicals in the materials. These characterizations fully demonstrate that in this embodiment, the radical-type crystalline porous organic salts RPOSs have been successfully prepared through simple charge-assisted hydrogen bond interactions.

[0041] Figure 2 XRD spectra of the raw materials NDSA, TAPDA used in Example 1 and the prepared RPOS-80 ( Figure 2 A) and XRD spectra of the prepared RPOS-20, RPOS-40, RPOS-60 and RPOS-80 ( Figure 2 B); it shows that all RPOSs samples have high crystallinity and present a crystalline structure. The higher the synthesis temperature, the higher the crystallinity of the corresponding RPOSs, which may be due to the promotion of the full progress of the reaction at high temperature.

[0042] Figure 3 SEM image of RPOS-80 shows that the polymer has a fluffy morphology stacked by nanorod-like shapes.

[0043] The porous structures of RPOS-20, RPOS-40, RPOS-60 and RPOS-80 are confirmed by nitrogen adsorption-desorption tests at 77K. As Figure 4 shown in A, all RPOSs show type II adsorption isotherms and have significant N2 absorption at high relative pressures of 0.70 < P / P0 < 0.99, indicating the existence of a large number of mesoporous pores in RPOSs. The BET specific surface areas of RPOS-20, RPOS-40, RPOS-60 and RPOS-80 are 7m 2 g -1 、11m 2 g -1 、64m 2 g -1 and 174m 2 g -1Among them, the crystalline porous organic salt RPOS-80 synthesized at 80 ° C has the highest specific surface area, which is also the highest specific surface area of ​​crystalline porous organic salts reported so far measured under N2. The specific surface areas of RPOSs synthesized at different temperatures vary greatly, indicating that high temperature may be conducive to the formation of microporous structure. In addition, the pore size distribution of RPOSs was calculated using the NLDFT model, as shown in Figure 2. Figure 4 As shown in Figure B, RPOS-20, RPOS-40, RPOS-60 and RPOS-80 have a narrow micro-mesopore distribution in the range of 1.47 to 4.75 nm, which is consistent with the type of N2 adsorption-desorption isotherms.

[0044] RPOS-80 was directly dissolved in d6-DMSO and tested for H NMR spectrum. The spectrum obtained was as follows: Figure 5 The three peaks at 8.87ppm, 7.95ppm, and 7.42ppm correspond to the three hydrogen atoms on the naphthalene ring in the structure, and the three multiple peaks at 7.24ppm, 7.07ppm, and 7.01ppm correspond to the three hydrogen atoms on the benzene ring of RPOS-80. Through integration calculation, the stoichiometric ratio of the raw materials TAPDA and NDSA in the structure is 1:2, which is consistent with the predicted structure.

[0045] Figure 6 A is the UV-visible absorption spectrum of the raw materials NDSA, TAPDA and the prepared RPOS-80. It can be seen from the figure that compared with NDSA, the RPOS-80 material has significantly enhanced absorption in the visible light part, but compared with TAPDA, the visible light absorption capacity has decreased. This shows that the successful combination of the two building blocks can enhance the visible light absorption capacity of RPOSs. This is also the result of the interaction between the charge-assisted hydrogen bond and the π-conjugated system of the polyaromatic ring extension. According to the Kubelka-Munk formula and the optical band gap linear fitting ( Figure 6 B), the band gaps of NDSA, TAPDA, and RPOS-80 are 3.54 eV, 2.61 eV, and 3.02 eV, respectively. RPOS-80 has a wide visible light absorption range and a narrow optical band gap, which endows it with excellent light-harvesting ability and semiconductor properties.

[0046] In addition, the photoelectrochemical performance test method was used to evaluate the photoelectric performance of RPOSs. First, the photocurrent density response experiment was carried out on the sample to test its separation and migration efficiency of photoinduced charge carriers. Figure 7 As shown in A, in the 5-cycle visible light-driven intermittent switching irradiation experiment, RPOS-80 showed a higher transient photocurrent response than other samples. In the Nyquist plot of the electrochemical impedance spectroscopy (EIS) Figure 7In Figure 2 (B), RPOS-80 exhibits a smaller arc radius, indicating lower interfacial resistance and higher electron-hole separation efficiency. These characterizations demonstrate that RPOS-80 possesses excellent photogenerated carrier separation and transfer capabilities, thus enabling the successful catalytic reaction under visible light irradiation.

[0047] Example 2: Comparison of catalytic performance and reusability of photocatalytic benzylamine oxidative coupling reaction

[0048] The RPOSs obtained in Example 1 were used in the blue light photocatalytic benzylamine coupling reaction. The reaction conditions were as follows: benzylamine (0.5 mmol, 53.5 mg), the RPOSs catalyst (5 mg) prepared in Example 1 was placed in a 20 mL glass tube, and blue light LEDs (5 W) were used as the light source. The tube was kept connected to the air to supply the required oxygen during the experiment. The reaction mixture was stirred continuously at a speed of 500 rpm and kept at room temperature. After the reaction was completed, a certain amount of solvent CDCl3 was directly added to the reaction system, and the mixture was stirred for 0.5 h. Finally, the product containing CDCl3 was obtained by filtration. 1 The conversion and selectivity were determined by HNMR spectral analysis. The solid catalyst was isolated, washed with ethyl acetate for more than 12 h, dried under vacuum, and then directly reused in the next run.

[0049] As shown in Table 1, when RPOS-20, RPOS-40, and RPOS-60, synthesized at different temperatures in an air atmosphere using blue light as the light source, were used as heterogeneous photocatalysts, achieving benzylamine conversions of 27%, 29%, and 41% after a 6-hour reaction. However, when RPOS-80 was used as the photocatalyst, the benzylamine conversion reached 99% after a 6-hour reaction. These experimental results demonstrate that RPOS-80 exhibits the highest photocatalytic activity among these crystalline porous organic salts. Characterization analysis reveals that RPOS-80 possesses a high specific surface area, a rich pore structure, and stable free radicals. The photocatalytic performance of a catalyst is also related to its photoelectric properties. RPOS-80 exhibits excellent light absorption and a higher separation and migration efficiency of photogenerated charge carriers. Therefore, RPOS-80 exhibits superior photocatalytic activity.

[0050] Table 1 Results of blue light photocatalytic oxidative coupling reaction of benzylamine under different catalysts

[0051]

[0052] Reaction conditions: benzylamine (0.5 mmol), photocatalyst (5 mg), blue light LEDs (5 W), no solvent, room temperature, air atmosphere (1 atm), reaction time: 6 h.

[0053] Recycling experiments were conducted on the photocatalyst RPOS-80 to verify its reusability and structural stability. Five blue-light photocatalytic benzylamine coupling reactions were conducted under the same conditions described above. The experimental results are shown in Table 2. As can be seen from Table 2, the catalyst RPOS-80 has excellent reusability, maintaining high conversion (>92%) and selectivity (>98%) after five reuses.

[0054] Table 2 Recyclability of RPOS-80 in photocatalytic oxidative coupling of benzylamine

[0055]

[0056] Reaction conditions: benzylamine (0.5 mmol), photocatalyst RPOS-80 (5 mg), blue light LEDs (5 W), no solvent, room temperature, air atmosphere (1 atm), reaction time is 6 h.

[0057] Example 3: Substrate Applicability of Catalyst RPOS-80

[0058] In this example, the RPOS-80 prepared in Example 1 was used as a catalyst and various substituted benzylamines were used as substrates to conduct activity comparison and substrate extensibility studies of the RPOS-80 catalyst.

[0059] Under similar reaction conditions, the catalytic performance of RPOS-80 in the photocatalytic oxidative coupling reaction of benzylamines with different substituents was tested by varying the reaction time (6-12h) while keeping other conditions unchanged, using 4-methylbenzylamine, 3-methylbenzylamine, 4-methoxybenzylamine, 4-fluorobenzylamine, 4-chlorobenzylamine, 4-bromobenzylamine, 4-tert-butylbenzylamine, and 4-trifluoromethylbenzylamine.

[0060] The experimental results are as follows Figure 8 As shown. The reaction products are: N-benzyl-1-phenylmethylamine, N-(4-methylbenzyl)-1-(4-methylbenzyl)methylamine, N-(3-methylbenzyl)-1-(3-methylbenzyl)methylamine, N-(4-methoxybenzyl)-1-(4-methoxyphenyl)methylamine, N-(4-fluorobenzyl)-1-(4-fluorophenyl)methylamine, N-(4-chlorobenzyl)-1-(4-chlorophenyl)methylamine, N-(4-bromobenzyl)-1-(4-bromophenyl)methylamine, N-(4-(tert-butyl)benzyl)-1-(4-(tert-butyl)phenyl)methylamine and N-(4-trifluoromethylbenzyl)-1-(4-trifluoromethylphenyl)methylamine. Its 1 The HNMR spectra are as follows Figure 9-17 As shown, the reaction product 1 The HNMR spectrum data are as follows:

[0061] Figure 9For N-benzyl-1-phenylmethylamine (2a) 1 H NMR (400MHz, CDCl3): δ=8.41 (s, 1H), 7.83~7.78 (m, 2H), 7.44 (d, 3H), 7.37 (d, 4H), 7.30~7.25 (m, 1H), 4.85ppm (s, 2H).

[0062] Figure 10 N-(4-methylbenzyl)-1-(4-methylbenzyl)methanamine (2b) 1 H NMR (400MHz, CDCl3): δ = 8.41 (s, 1H), 7.74 (d, 2H), 7.29 (t, 4H), 7.22 (d, 2H), 4.84 (s, 2H), 2.45 (s, 3H), 2.41ppm (s, 3H).

[0063] Figure 11 N-(3-methylbenzyl)-1-(3-methylbenzyl)methanamine (2c) 1 H NMR (400MHz, CDCl3): δ = 8.38 (s, 1H), 7.70 ~ 7.55 (m, 2H), 7.36 ~ 7.22 (m, 3H), 7.14 (d, 3H), 4.81 (s, 2H), 2.41 (s, 3H), 2.38ppm (s, 3H).

[0064] Figure 12 N-(4-methoxybenzyl)-1-(4-methoxyphenyl)methanamine (2d) 1 H NMR (400MHz, CDCl3): δ = 8.30 (s, 1H), 7.72 (d, 2H), 7.25 (d, 2H), 6.90 (d, 4H), 4.73 (s, 2H), 3.83 (s, 3H), 3.79ppm (s, 3H).

[0065] Figure 13 N-(4-fluorobenzyl)-1-(4-fluorophenyl)-methylamine (2e) 1 H NMR (400MHz, CDCl3): δ = 8.35 (s, 1H), 7.77 (s, 2H), 7.30 (t, 2H), 7.10 (t, 2H), 7.02 (d, 2H), 4.77ppm (s, 2H).

[0066] Figure 14 For N-(4-chlorobenzyl)-1-(4-chlorophenyl)methanamine (2f) 1H NMR (400MHz, CDCl3): δ = 8.35 (s, 1H), 7.78 (s, 2H), 7.45 (d, 2H), 7.37 (d, 2H), 7.32 (d, 2H), 4.82ppm (s, 2H).

[0067] Figure 15 For N-(4-bromobenzyl)-1-(4-bromophenyl)methanamine (2g) 1 HNMR (400MHz, CDCl3): δ = 8.36 (d, 1H), 7.80 ~ 7.62 (m, 2H), 7.57 ~ 7.47 (m, 2H), 7.45 (d, 2H), 7.24 ~ 7.18 (m, 2H), 4.75ppm (d, 2H).

[0068] Figure 16 For N-(4-(tert-butyl)benzyl)-1-(4-(tert-butyl)phenyl)methanamine (2h) 1 H NMR (400MHz, CDCl3): δ = 8.39 (s, 1H), 7.74 (d, 2H), 7.46 (d, 2H), 7.39 (d, 2H), 7.29 (d, 2H), 4.81 (s, 2H), 1.35ppm (d, 18H).

[0069] Figure 17 N-(4-trifluoromethylbenzyl)-1-(4-trifluoromethylphenyl)methanamine (2i) 1 HNMR (400MHz, CDCl3): δ = 8.35 (s, 1H), 7.72 (d, 2H), 7.40 (d, 2H), 7.32 (dd, 2H), 7.27 (d, 2H), 4.77ppm (s, 2H).

[0070] from Figure 8 The data show that the catalyst RPOS-80 has excellent photocatalytic activity and good substrate applicability for different reactants. It can be used as an efficient heterogeneous photocatalyst to realize the photocatalytic oxidative coupling reaction of benzylamine under mild conditions.

Claims

1. A free radical crystalline porous organic salt, characterized in that: Typical polymer organic salts are free radical crystalline porous organic salts RPOSs prepared by charge-assisted hydrogen bond self-assembly, and their chemical structure is shown in Formula 3:

2. A method for preparing the free radical type crystalline porous organic salt according to claim 1, characterized in that: The following steps are involved: A series of free radical-type crystalline porous organic salt RPOSs were synthesized by charge-assisted hydrogen bonding self-assembly using 1,5-naphthalene disulfonic acid (Formula 1) and N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine (Formula 2) as raw materials. The structural formula of 1,5-naphthalene disulfonic acid shown in Formula 1 is The structural formula of N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine is shown in Formula 2.

3. The method for preparing a free radical type crystalline porous organic salt according to claim 2, characterized in that: The specific steps include: S1: Add 1,5-naphthalene disulfonic acid represented by Formula 1 into a container containing an organic solvent, N,N-dimethylformamide (DMF), and stir to completely dissolve it to obtain a uniform solution; S2: Add N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine shown in Formula 2 into a container containing an organic solvent DMF, and stir to completely dissolve it to obtain a uniform solution; S3: The uniform solution obtained in step S1 is transferred to a reaction tube, and after being added to the uniform solution obtained in step S2, the mixed solution is placed in a reaction tube, and the reaction tube is placed on a reaction module. An acid-base neutralization reaction is carried out at a certain reaction temperature for a period of time. After the reaction is completed, free radical-type crystalline porous organic salts RPOSs are obtained by washing, filtering, and drying.

4. The method for preparing a free radical type crystalline porous organic salt according to claim 3, characterized in that: In step S3, the molar ratio of 1,5-naphthalene disulfonic acid represented by Formula 1 to N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine represented by Formula 2 is 2:

1.

5. The method for preparing a free radical type crystalline porous organic salt according to claim 3, characterized in that: In step S3, the reaction temperature is 20-80° C., and the reaction time is 12 h. The samples prepared at different temperatures are named RPOS-20, RPOS-40, RPOS-60, and RPOS-80.

6. Use of the free radical crystalline porous organic salt according to claim 1 in a photocatalytic benzylamine coupling reaction.

7. The use according to claim 6, characterized in that Specifically include: Benzylamine is used as a substrate, the RPOSs described in claim 1 are used as a heterogeneous photocatalyst, blue light LEDs are used as a light source, and a photocatalytic benzylamine coupling reaction to prepare imine is carried out at room temperature in an atmosphere of normal pressure and air.

8. The use according to claim 7, characterized in that The structural formula of the benzylamine is Wherein, R is an unsubstituted group, or one of a methyl group, a methoxy group, a fluoro group, a chloro group, a bromo group, a tert-butyl group and a trifluoromethyl group.

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