Photoresponse azobenzene covalent organic framework material and preparation method thereof

Abstract

The invention discloses a photoresponse azobenzene covalent organic framework material and a preparation method thereof, and belongs to the technical field of covalent organic framework materials. According to the invention, 2, 5-dihydroxy terephthalaldehyde and a C3 symmetric amino monomer are taken as monomers, a hydroxylated covalent organic framework is synthesized through a solvothermal method, p-phenylazo benzoyl chloride is introduced into a hydroxyl site through an acyl chloride post-modification method, a branched chain type covalent organic framework with a suspended azobenzene unit is formed, and light-operated dynamic response is realized; the rigid or flexible framework type azobenzene covalent organic framework is directly synthesized by taking p-diaminoazobenzene as a construction unit, C3 symmetrical aldehyde group monomers with different sizes and flexible monomers through a solvothermal method. Through structural design regulation, the azobenzene covalent organic framework with photoresponse characteristics can be prepared, and a new strategy is provided for development of light-operated functional materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of covalent organic framework materials, and in particular relates to a photoresponsive azobenzene covalent organic framework material and a preparation method thereof. Background Art

[0002] In recent years, various new porous materials have been widely used as separation media in complex sample analysis. In order to increase the selective separation or recognition ability of the medium for the target, it is often necessary to functionalize the medium and introduce forces that are specific to the target. However, these specific forces are usually difficult to control. While increasing the selectivity of the medium, it also increases the difficulty of dissociating or eluting the target from the medium surface.

[0003] Stimuli-responsive materials are a special class of materials with intelligent behavior. They can receive external stimulus signals (such as light, heat, electric field, magnetic field, pH, humidity, etc.) to cause reversible or irreversible changes in the physical and chemical properties of the material itself (phase state, polarity and luminescence, etc.), thereby producing corresponding functions. Among various stimuli, light is the most attractive and environmentally friendly stimulus, with the advantages of remote and instant control. Due to its unique photoinduced cis-trans isomerization properties, the azobenzene group can reversibly regulate the molecular configuration and polarity through ultraviolet / visible light irradiation, providing an ideal platform for the construction of light-responsive smart materials. However, traditional azobenzene photoresponsive materials are mostly small molecules or polymers, with problems such as poor stability, low response efficiency, and difficulty in integration, which limit their practical applications.

[0004] Covalent organic frameworks (COFs) are a class of crystalline materials with highly ordered porous structures formed by organic building blocks connected by strong covalent bonds. Due to their high specific surface area, excellent chemical stability, and designable structural functions, COFs have shown broad application prospects in adsorption, separation, catalysis, energy storage, and other fields. Embedding photoresponsive azobenzene units into the ordered COF pores not only improves the mass transfer rate and interaction probability between the responsive units and the target, but also modulates the physicochemical properties of the COF, such as conformation and polarity, through light stimulation, thereby regulating the adsorption / desorption behavior of the target on the COF and enabling controlled intelligent separation and analysis of the target. However, related research is still in its preliminary exploratory stage, and limitations in synthetic strategies result in low-density loading and disordered distribution of azobenzene groups, which impairs the material's orderliness, mass transfer efficiency, and photoresponsiveness. Therefore, developing novel synthetic strategies to achieve high-density integration and controllable distribution of azobenzene groups in COFs and revealing their structure-activity relationship are of great significance for promoting the development of light-controlled smart materials. Summary of the Invention

[0005] To address these challenges, the present invention proposes two strategies for preparing photoresponsive azobenzene COFs through innovative molecular design: A branched structure precisely introduces dangling azobenzene units through post-modification, endowing the material with high-degree-of-freedom photoisomerization capabilities; a backbone structure utilizes topological matching of p-diaminoazobenzene monomers with aldehyde monomers of varying sizes to enable the controllable construction of rigid or flexible backbones. This innovative technique, which incorporates photoresponsive azobenzene units into COFs, provides new insights into the development of efficient, stable, and functionally tunable light-controlled smart materials.

[0006] The present invention provides a method for preparing a photoresponsive azobenzene covalent organic framework material, comprising the following steps:

[0007] Under the action of a catalyst, 2,5-dihydroxyterephthalaldehyde and a C3 symmetrical amino monomer undergo a condensation reaction to synthesize a hydroxylated covalent organic skeleton, which is then subjected to an acyl chloride post-modification reaction with p-phenylazobenzoyl chloride to form a branched azobenzene covalent organic skeleton having a dangling azobenzene unit; alternatively, under the action of a catalyst, p-diaminoazobenzene is used as an amino monomer and directly condensed with a C3 symmetrical aldehyde monomer or a flexible monomer through a solvent thermal method to form a skeleton-type azobenzene covalent organic skeleton.

[0008] In an embodiment of the present invention, a method for preparing a branched azobenzene covalent organic skeleton specifically includes: in the presence of a catalyst, using 2,5-dihydroxyterephthalaldehyde and a C3 symmetrical amino monomer as monomers, performing a condensation reaction by a solvent thermal method in a first reaction solvent to synthesize a hydroxylated covalent organic skeleton; and subjecting the obtained hydroxylated covalent organic skeleton to an acyl chloride post-modification reaction with p-phenylazobenzoyl chloride in a second reaction solvent to introduce an azobenzene group into the hydroxyl site to form a branched azobenzene covalent organic skeleton having a dangling azobenzene unit.

[0009] In an embodiment of the present invention, in the preparation method of the branched azobenzene covalent organic skeleton, the C3 symmetrical amino monomer is one or more of 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 1,3,5-tris(4-aminophenoxy)benzene, and tris(4-aminophenyl)amine.

[0010] In an embodiment of the present invention, in the preparation method of the branched azobenzene covalent organic skeleton, the molar ratio of 2,5-dihydroxyterephthalaldehyde to C3 symmetrical amino monomer is (1-5):1; the first reaction solvent is one or more of acetonitrile, dimethyl sulfoxide, dichloromethane, mesitylene, 1,4-dioxane, o-dichlorobenzene, n-butanol, and chloroform; the catalyst is acetic acid and / or scandium trifluoromethanesulfonate, and the total molar ratio of the catalyst to 2,5-dihydroxyterephthalaldehyde and C3 symmetrical amino monomer is 0.6:0.25-0.5; the condensation reaction temperature is 25-120°C, and the reaction time is 6-72h.

[0011] In an embodiment of the present invention, the method for preparing a branched azobenzene covalent organic framework further includes washing, centrifugation, and drying steps after the condensation reaction; the washing solvent is one or more of tetrahydrofuran, ethanol, and ultrapure water; and unreacted monomers are washed away by washing.

[0012] In an embodiment of the present invention, in the method for preparing a branched azobenzene covalent organic framework, the amount of p-phenylazobenzoyl chloride added is 1-3 times the total mass of the hydroxylated covalent organic framework.

[0013] In an embodiment of the present invention, in the method for preparing a branched azobenzene covalent organic framework, the solvent for the acyl chloride post-modification reaction is selected from one or more of anhydrous triethylamine, anhydrous tetrahydrofuran, dichloromethane, diethyl ether, and toluene, the reaction temperature is 25-60°C, and the reaction time is 12-24h.

[0014] In an embodiment of the present invention, the method for preparing a branched azobenzene covalent organic framework further includes washing, centrifugation, and drying steps after the acyl chloride post-modification reaction; the washing solvent is one or more of tetrahydrofuran, ethanol, dichloromethane, and ultrapure water; and unreacted monomers are washed away by washing.

[0015] In an embodiment of the present invention, in the preparation method of the skeleton-type azobenzene covalent organic skeleton, the C3 symmetrical aldehyde monomer is one or more of trimesicaldehyde, 1,3,5-tris(p-formylphenyl)benzene, and 1,3,5-tris(4'-formyl[1,1'-biphenyl]-4-yl)benzene; the flexible monomer is one or more of 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine, 4,4',4"-(benzene-1,3,5-triyltris(oxy))tribenzaldehyde, and 4,4',4",4"-((benzene-1,2,4,5-tetrayltetra(methylene))tetra(oxy)tetrabenzaldehyde.

[0016] In an embodiment of the present invention, in the preparation method of the skeleton-type azobenzene covalent organic skeleton, the molar ratio of p-diaminoazobenzene to the C3 symmetrical aldehyde monomer or the flexible monomer is (1-5):1, the solvent is selected from one or more of acetonitrile, dimethyl sulfoxide, dichloromethane, mesitylene, dioxane, o-dichlorobenzene, n-butanol and chloroform, the catalyst is selected from acetic acid and / or scandium trifluoromethanesulfonate, the condensation reaction temperature is 25-120°C, and the reaction time is 6-72h.

[0017] In an embodiment of the present invention, in the method for preparing a skeleton-type azobenzene covalent organic framework, the total molar ratio of the catalyst to p-diaminoazobenzene and C3 symmetrical aldehyde monomer is 0.6:0.25-0.5.

[0018] In an embodiment of the present invention, in the method for preparing a skeleton-type azobenzene covalent organic framework, the total molar ratio of the catalyst to p-diaminoazobenzene and the flexible monomer is 0.6:0.25-0.5.

[0019] In an embodiment of the present invention, the method for preparing a skeleton-type azobenzene covalent organic framework further includes washing, centrifugation, and drying steps after the condensation reaction; the washing solvent is one or more of tetrahydrofuran, ethanol, and ultrapure water; and unreacted monomers are washed away by washing.

[0020] In an embodiment of the present invention, in the method for preparing a skeleton-type azobenzene covalent organic framework, when a flexible monomer is used, the obtained material has dynamically adjustable framework flexibility.

[0021] The present invention provides a photoresponsive azobenzene covalent organic framework material prepared by the method described above.

[0022] The present invention provides application of the above-mentioned photoresponsive azobenzene covalent organic framework material in light-controlled functional devices.

[0023] The present invention provides applications of the above-mentioned photoresponsive azobenzene covalent organic framework material in the fields of photoresponsive adsorption separation, light-driven molecular switching, and light-controlled catalysis.

[0024] The technical solution of the present invention has the following advantages over the prior art:

[0025] (1) Both azobenzene covalent organic framework materials designed in the present invention have unique photoresponse properties. Branched COFs: The introduction of dangling azobenzene units through post-modification avoids the problem of easy decomposition or structural instability of azobenzene monomers in direct synthesis. The dangling branches reduce steric hindrance, making the cis-trans isomerization of azobenzene more efficient, and improving the photoresponse speed and reversibility. Skeleton-type COFs: Directly using para-diaminoazobenzene as the skeleton unit, it ensures that the photoresponse groups are evenly distributed in the main chain, enhancing structural stability and light energy transfer efficiency. Combining rigid and flexible aldehyde monomers, the pore size, interlayer spacing and mechanical properties of the material can be adjusted to meet the needs of different application scenarios.

[0026] (2) The synthesis methods of the two azobenzene covalent organic framework materials described in the present invention are flexible and controllable. The branched type adopts the acyl chloride post-modification method to accurately introduce azobenzene groups on the pre-synthesized hydroxylated COFs, which solves the problem of mismatch between the reactivity of azobenzene monomers and aldehyde groups in the traditional co-condensation method. The skeleton type is synthesized in one step by the solvent thermal method, and high crystallinity is achieved by dynamic covalent chemistry. By selecting aldehyde monomers of different sizes, the material topology (such as pore size, specific surface area) can be controlled without the need for complex templates or post-processing.

[0027] (3) The open channels of branched COFs are combined with photoresponsive sites to achieve photocontrolled adsorption / desorption and selective catalysis simultaneously. The high specific surface area and periodic π-conjugated structure of skeleton-type COFs are suitable for photocatalytic degradation or photoelectric sensing. By adjusting the monomer combination (such as introducing flexible units), the material can have both photoresponsiveness and stimulus-responsive elasticity, achieving high dynamic responsiveness, structural adjustability and multifunctional integration, providing a new paradigm for the application of intelligent photocontrolled materials in energy, environment, biomedicine and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the synthesis of branched and backbone azobenzene COFs in Examples 1 to 5 of the present invention;

[0029] Figure 2 The X-ray diffraction patterns (PXRD) of DHPA-TAPB and DHPA-TAPB@PAzo in Example 1 of the present invention are shown in FIG.

[0030] Figure 3 FT-IR spectra of DHPA-TAPB and DHPA-TAPB@PAzo in Example 1 of the present invention; wherein, a is the FT-IR spectra of DHPA-TAPB, and b is the FT-IR spectra of DHPA-TAPB@PAzo;

[0031] Figure 4: are scanning electron micrographs of DHPA-TAPB and DHPA-TAPB@PAzo in Example 1 of the present invention; wherein, a is a scanning electron micrograph of DHPA-TAPB, and b is a scanning electron micrograph of DHPA-TAPB@PAzo;

[0032] Figure 5 These are the test results of the light response performance of the branched azobenzene COF DHPA-TAPB@PAzo according to Example 1 of the present invention; wherein, a is the UV-visible absorption spectrum of DHPA-TAPB@PAzo under 365 nm light irradiation, and b is the UV-visible absorption spectrum of DHPA-TAPB@PAzo under 405 nm light irradiation;

[0033] Figure 6 The PXRD patterns of the skeleton-type azobenzene covalent organic framework materials in Examples 2 to 5 of the present invention are as follows;

[0034] Among them, a is the PXRD pattern of Tb-Azo, b is the PXRD pattern of Tfpb-Azo; c is the PXRD pattern of Tpp-Azo; d is the PXRD pattern of Tfpt-Azo;

[0035] Figure 7 FT-IR images of the skeleton-type azobenzene covalent organic framework materials in Examples 2 to 5 of the present invention;

[0036] Among them, a is the FT-IR image of Tb-Azo, b is the FT-IR image of Tfpb-Azo; c is the FT-IR image of Tpp-Azo; d is the FT-IR image of Tfpt-Azo;

[0037] Figure 8 This is a scanning electron microscope image of the skeleton-type azobenzene covalent organic framework material in Examples 2 to 5 of the present invention;

[0038] Among them, a is the scanning electron microscopy image of Tb-Azo, b is the scanning electron microscopy image of Tfpb-Azo; c is the scanning electron microscopy image of Tpp-Azo; d is the scanning electron microscopy image of Tfpt-Azo;

[0039] Figure 9 The light response performance test results of the skeleton-type azobenzene COF Tb-Azo in Example 2 of the present invention are shown in FIG. 1 , wherein a is the UV-visible absorption spectrum of Tb-Azo under 405 nm light irradiation, and b is the UV-visible absorption spectrum of Tb-Azo under 520 nm light irradiation.

[0040] Figure 10The light response performance test results of the skeleton-type azobenzene COF Tfpb-Azo in Example 3 of the present invention are shown in FIG. 1 , wherein a is the UV-visible absorption spectrum of Tfpb-Azo under 405 nm light irradiation, and b is the UV-visible absorption spectrum of Tfpb-Azo under 520 nm light irradiation;

[0041] Figure 11 The light response performance test results of the skeleton-type azobenzene COF Tpp-Azo in Example 4 of the present invention are shown in FIG. 1 , wherein a is the UV-visible absorption spectrum of Tpp-Azo under 405 nm light irradiation, and b is the UV-visible absorption spectrum of Tpp-Azo under 520 nm light irradiation.

[0042] Figure 12 The light response performance test results of the skeleton-type azobenzene COF Tfpt-Azo in Example 5 of the present invention are shown in FIG. 5 , wherein a is the UV-visible absorption spectrum of Tfpt-Azo under 405 nm light irradiation, and b is the UV-visible absorption spectrum of Tfpt-Azo under 520 nm light irradiation;

[0043] Figure 13 The light-responsive pore changes of the skeleton-type azobenzene COF Tfpt-Azo in Example 5 of the present invention are shown in FIG. 1 , where a is the nitrogen adsorption-desorption isotherm of Tfpt-Azo before and after 405 nm light irradiation, and b is the pore size distribution before and after 405 nm light irradiation.

[0044] Figure 14 The photoresponsive contact angle change results of the skeleton-type azobenzene COF Tfpt-Azo in Example 5 of the present invention; wherein a is the contact angle image of Tfpt-Azo before 405 nm light irradiation, and b is the contact angle image after 405 nm light irradiation;

[0045] Figure 15 The photoresponsive adsorption of different iodine substances by the skeleton-type azobenzene COF Tfpt-Azo in Example 5 of the present invention; wherein, a is the static adsorption performance of Tfpt-Azo for CH3I in the cis-trans isomerization form, and b is the static adsorption performance of Tfpt-Azo for I2 in the cis-trans isomerization form. DETAILED DESCRIPTION

[0046] The present invention will be further described below with reference to specific embodiments so that those skilled in the art can better understand and implement the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. It should be understood that the specific embodiments are only used to illustrate the present invention, and the embodiments are not intended to limit the present invention.

[0047] In the present invention, unless otherwise defined, technical and scientific terms used herein have the same meanings as commonly understood by one skilled in the art to which the present invention belongs.

[0048] In the present invention, unless stated otherwise, the term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0049] In the present invention, unless otherwise stated, the experimental methods used in the examples of the present invention are conventional methods unless otherwise stated, and the materials, reagents, etc. used are all commercially available unless otherwise stated.

[0050] Example 1

[0051] Reference Figure 1 As shown, the branched azobenzene covalent organic framework material (DHPA-TAPB@PAzo) and the preparation method thereof of this embodiment specifically include the following steps:

[0052] S1. Weigh 2,5-dihydroxyterephthalaldehyde (DHPA) (0.15 mmol, 24.9 mg) and 1,3,5-tris(4-aminophenyl)benzene (TAPB) (0.1 mmol, 35.1 mg) into a 35 mL Schlenk tube. Add 0.5 mL of mesitylene and 0.5 mL of 1,4-dioxane. Ultrasonicate for 5 min to evenly disperse the two monomers in the solution.

[0053] S2. Under ultrasound, 6 mol / L acetic acid (0.1 mL) was slowly added dropwise to the mixed solution. After continuing ultrasound for 10 min, the mixture was degassed using three freeze-pump-thaw cycles. The mixture was condensed at 120°C for 72 h to obtain an orange-yellow precipitate.

[0054] S3. Wash the orange-yellow precipitate with tetrahydrofuran, collect the precipitate by centrifugation, and dry it in a vacuum oven at 60° C. for 12 h to obtain an orange-yellow solid hydroxylated covalent organic framework (DHPA-TAPB).

[0055] S4. Disperse 25 mg of DHPA-TAPB in a Schlenk tube containing 3 mL of anhydrous tetrahydrofuran and add 50 μL of anhydrous triethylamine as a deacidifying agent. Dissolve 40 mg of phenylazobenzoyl chloride (PAzo) in 2 mL of anhydrous tetrahydrofuran and add dropwise to the DHPA-TAPB suspension with stirring. Stir the reaction at room temperature (25°C) for 12 h to obtain a reddish-brown precipitate.

[0056] S5. The reddish-brown precipitate was washed with tetrahydrofuran, the precipitate was collected by centrifugation and dried in a vacuum oven at 60° C. for 12 h to obtain a branched azobenzene covalent organic framework material (DHPA-TAPB@PAzo).

[0057] Example 2

[0058] Reference Figure 1 As shown, the skeleton-type azobenzene covalent organic framework material (Tb-Azo) and the preparation method thereof of this embodiment specifically include the following steps:

[0059] S1. Weigh trimesaldehyde Tb (0.2 mmol, 32.4 mg) and p-diaminoazobenzene Azo (0.3 mmol, 63.7 mg) into a 35 mL Schlenk tube. Add 0.75 mL of mesitylene and 0.25 mL of 1,4-dioxane. Ultrasonicate for 5 min to evenly disperse the two monomers in the solution.

[0060] S2. Under ultrasound, 6 mol / L acetic acid (0.1 mL) was slowly added dropwise to the mixed solution. After continuing ultrasound for 10 min, the mixture was degassed using three freeze-pump-thaw cycles. The mixture was condensed at 120°C for 72 h to obtain a yellow-brown precipitate.

[0061] S3. Wash the yellow-brown precipitate with tetrahydrofuran, collect the precipitate by centrifugation, and dry it in a vacuum oven at 60° C. for 12 h to obtain a skeleton-type azobenzene covalent organic framework (Tb-Azo).

[0062] Example 3

[0063] Reference Figure 1 As shown, the skeleton-type azobenzene covalent organic framework material (Tfpb-Azo) and its preparation method of this embodiment are basically the same as those of Example 2, except that:

[0064] (1) Trimellitic acid Tb (0.2 mmol, 32.4 mg) was replaced with 1,3,5-tris(p-formylphenyl)benzene Tfpb (0.2 mmol, 78.7 mg);

[0065] (2) Replace 0.75 mL of mesitylene and 0.25 mL of 1,4-dioxane with 1.5 mL of mesitylene and 0.5 mL of 1,4-dioxane;

[0066] (3) Replace 6 mol / L acetic acid (0.1 mL) with 6 mol / L acetic acid (0.2 mL).

[0067] Example 4

[0068] Reference Figure 1 As shown, the skeleton-type azobenzene covalent organic framework material (Tpp-Azo) and its preparation method of this embodiment are basically the same as those of Example 2, except that:

[0069] (1) Replace trimesaldehyde Tb (0.2 mmol, 32.4 mg) with 1,3,5-tris(4'-formyl[1,1'-biphenyl]-4-yl)benzene (CAS No.: 805246-78-0) Tpp (0.1 mmol, 61.9 mg); replace p-diaminoazobenzene Azo (0.3 mmol, 63.7 mg) with p-diaminoazobenzene Azo (0.15 mmol, 31.9 mg);

[0070] (2) The condensation reaction at 120°C for 72 hours was replaced by the condensation reaction at 120°C for 48 hours.

[0071] Example 5

[0072] Reference Figure 1 As shown, the skeleton-type azobenzene covalent organic framework material (Tfpt-Azo) and its preparation method of this embodiment are basically the same as those of Example 2, except that:

[0073] (1) Trimellitic acid Tb (0.2 mmol, 32.4 mg) was replaced with the flexible monomer 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine (CAS No.: 3140-75-8) (Tfpt) (0.1 mmol, 44.2 mg); p-diaminoazobenzene Azo (0.3 mmol, 63.7 mg) was replaced with p-diaminoazobenzene Azo (0.15 mmol, 31.9 mg);

[0074] (2) Replace 0.75 mL of mesitylene and 0.25 mL of 1,4-dioxane with 0.1 mL of n-butanol and 0.9 mL of o-dichlorobenzene;

[0075] (3) The condensation reaction at 120°C for 72 hours was replaced by a condensation reaction at 120°C for 24 hours.

[0076] Test Example 1

[0077] The branched azobenzene covalent organic framework material DHPA-TAPB@PAzo prepared in Example 1 was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, etc. The results are as follows: Figure 1-Figure 3 As shown. Figure 2 The hydroxylated covalent organic framework DHPA-TAPB exhibits characteristic PXRD diffraction peaks at 2.8°, 4.8°, 5.5°, and 7.4°, demonstrating the successful synthesis of DHPA-TAPB. The branched azobenzene COF DHPA-TAPB@PAzo, obtained after post-acyl chloride modification, also exhibits characteristic PXRD diffraction peaks at 2.9° and 5.7°. Compared to DHPA-TAPB, the diffraction peaks exhibit reduced intensity and shifted angles, further confirming the successful synthesis of DHPA-TAPB@PAzo.

[0078] from Figure 3 As can be seen from the infrared spectrum, DHPA-TAPB has a peak at 1617 cm -1 The characteristic peak of imine C=N appeared at the same time as the characteristic peak of DHPA aldehyde group (1693cm -1 ) obviously decayed, which again showed that DHPA and TAPB were successfully condensed through Schiff base reaction. Figure 3 In b, compared with the precursor COF DHPA-TAPB, the infrared spectrum of DHPA-TAPB@PAzo prepared by acyl chloride reaction showed that the imine C=N (1617 cm -1 ) retention and N=N(1479cm -1 ) characteristic peaks indicate the successful synthesis of branched azobenzene COF.

[0079] from Figure 4 a As can be seen from the figure, the hydroxylated COF DHPA-TAPB has a smooth spherical morphology. Figure 4 b It can be seen that the surface of the branched azobenzene COF DHPA-TAPB@PAzo prepared by acyl chloride reaction becomes rough.

[0080] Test Example 2: Photoresponse Performance Test of Branched Azobenzene COFs

[0081] Reference Figure 5 As shown in the figure, the photoresponse performance of the branched azobenzene COF DHPA-TAPB@PAzo was investigated by UV-visible absorption spectrum changes. When irradiated with 365nm and 405nm light alternately, DHPA-TAPB@PAzo exhibited photoreversible cis / trans isomerization in DMF solution. Figure 5 As shown in Figure a, under 365 nm light irradiation, DHPA-TAPB@PAzo undergoes trans-to-cis isomerization, resulting in a gradual decrease in absorbance at 328 nm over time. Subsequently, upon irradiation with 405 nm light, DHPA-TAPB@PAzo undergoes cis-to-trans isomerization, with the absorbance at 327 nm gradually increasing over time and reaching a photostable state within approximately 50 s. This photoisomerization behavior demonstrates the excellent photoresponsiveness of DHPA-TAPB@PAzo, providing important evidence for its application in photoresponsive and smart materials.

[0082] Test Example 3

[0083] The skeleton-type azobenzene covalent organic framework materials (Tb-Azo, Tfpb-azo, Tpp-Azo and Tfpt-Azo) prepared in Examples 2-5 were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, etc. The results are as follows Figure 6-Figure 8 shown.

[0084] from Figure 6 It can be seen that in the skeleton-type azobenzene COF, the PXRD spectra of Tb-Azo, Tfpb-azo, Tpp-Azo and Tfpt-Azo show main characteristic diffraction peaks at 3.3°, 2.2°, 1.7° and 2.1°, respectively, indicating that the skeleton-type azobenzene COFs with ordered crystal structure were successfully synthesized.

[0085] from Figure 7 It can be seen that the C=N characteristic peak (1617cm -1 ) and the characteristic peaks of aldehyde-CHO (1686 cm -1 ), which confirmed the successful formation of imine bonds between structural units through the Schiff base condensation reaction, and further verified the successful synthesis of all skeleton-type azobenzene COFs.

[0086] Figure 8 The morphologies of the backbone azobenzene COFs were characterized using scanning electron microscopy. Tb-Azo exhibited a wood-block-like stacking structure, Tfpb-Azo exhibited a rod-like stacking structure, and Tpp-Azo exhibited a pole-like stacking structure. Tfpt-Azo exhibited an irregular spherical shape.

[0087] Test Example 4: Photoresponse Performance Test of Skeleton-type Azobenzene COFs

[0088] Reference Figure 9-12 As shown in the figure, the photoresponse properties of skeleton-type azobenzene COFs (Tb-Azo, Tfpb-azo, Tpp-Azo and Tfpt-Azo) were investigated by changes in UV-visible absorption spectra. Figure 9-11 It can be seen that when 405nm and 520nm light are alternately irradiated, all rigid skeleton azobenzene COFs (Tb-Azo, Tfpb-azo, Tpp-Azo) also exhibit photoreversible cis / trans isomerization in DMF solution, and the azobenzene photoisomerization ability is not lost due to the introduction of the rigid skeleton. Under the irradiation of 405nm light, Tb-Azo, Tfpb-azo and Tpp-Azo undergo trans to cis isomerization, resulting in a gradual decrease in the absorbance at 410nm over time. Subsequently, when irradiated with 520nm light, Tb-Azo, Tfpb-azo and Tpp-Azo undergo cis to trans isomerization, and the absorbance at 410nm gradually increases over time and reaches a photostable state within about 10s. From Figure 12It can be seen that compared to the rigid skeleton structures of Tb-Azo, Tfpb-Azo, and Tpp-Azo, the addition of the flexible unit Tfpt in Tfpt-Azo increases the isomerization freedom of its Azo and makes the cis-trans isomerization deformation more pronounced, thereby further enhancing the material's photoresponsiveness, dynamic reversibility, and mechanical adaptability. At the same time, the position of the absorption peak blue-shifts. Under irradiation with 405nm light, Tfpt-Azo undergoes trans-to-cis isomerization, resulting in a gradual decrease in absorbance at 395nm over time. Subsequently, when irradiated with 520nm light, Tfpt-Azo undergoes cis-to-trans isomerization, and the absorbance at 395nm gradually increases over time, reaching a photostable state within approximately 10s.

[0089] Test Example 5: Changes in the pore structure of flexible azobenzene COF Tfpt-Azo

[0090] like Figure 13 As shown in the figure, 100 mg of Tfpt-Azo powder material was taken and divided into two equal parts. One group served as the control group, and the other group was irradiated with 405 nm light for 12 hours, degassed at room temperature, and nitrogen adsorption experiments were performed to explore the changes in pore size and specific surface area of ​​the Tfpt-Azo sample before and after illumination. The experimental results showed that the specific surface area of ​​Tfpt-Azo increased significantly after illumination, reaching 180.377 m 2 g-1, much higher than the 99.408m before illumination 2 g -1 In addition, the main aperture after illumination is 4.08 nm, which is smaller than 4.22 nm before illumination.

[0091] Test Example 6: Contact Angle Change of Flexible Azobenzene COF Tfpt-Azo

[0092] like Figure 14 As shown in the figure, when not irradiated, the contact angle of a water droplet on the glass surface coated with trans-Tfpt-Azo is 124.8°, indicating that the material surface exhibits typical hydrophobic properties. When the coated surface is irradiated with 405nm light for 30 minutes, the contact angle drops to 108.9°, confirming that its surface wettability is enhanced. This significant decrease in contact angle is attributed to the trans-to-cis photoisomerization of the azobenzene group. The trans-to-cis isomerization of azobenzene is accompanied by a significant change in its dipole moment. The dipole moment of the cis isomer is significantly higher than that of the trans isomer, resulting in an increase in surface polarity and a decrease in surface free energy, thereby making the Tfpt-Azo surface more hydrophilic.

[0093] Test Example 7: Application of the photoresponsive adsorption of different iodine substances by the flexible azobenzene COF Tfpt-Azo

[0094] like Figure 15As shown, upon irradiation with 405 nm light, Tfpt-Azo changes from its original trans configuration (trans) to its cis configuration (cis). The adsorption of gaseous CHI and I2 by both trans-Tfpt-Azo and cis-Tfpt-Azo increases over time, but exhibits different adsorption rates and capacities at different stages. For polar CHI, the adsorption capacity of trans-Tfpt-Azo is 3.12 g g⁻¹. After irradiation with 405 nm light, this capacity increases to 3.45 g g⁻¹ due to increased polarity and increased specific surface area. For non-polar I2, the adsorption capacity decreases from 5.61 g g⁻¹ to 4.93 g g⁻¹ due to the increased polarity of the cis configuration and the weakening of the π-π stacking effect.

[0095] The embodiments provided above are not intended to limit the scope of the present invention, nor are the steps described to limit their execution order. Any obvious improvements to the present invention made by those skilled in the art in combination with existing common knowledge shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a photoresponsive azobenzene covalent organic framework material, characterized in that: The following steps are involved: Under the action of a catalyst, 2,5-dihydroxyterephthalaldehyde and a C3 symmetrical amino monomer undergo a condensation reaction to synthesize a hydroxylated covalent organic skeleton, which is then subjected to an acyl chloride post-modification reaction with p-phenylazobenzoyl chloride to form a branched azobenzene covalent organic skeleton having a dangling azobenzene unit; alternatively, under the action of a catalyst, p-diaminoazobenzene is used as an amino monomer and directly condensed with a C3 symmetrical aldehyde monomer or a flexible monomer through a solvent thermal method to form a skeleton-type azobenzene covalent organic skeleton.

2. The method according to claim 1, characterized in that The preparation method of a branched azobenzene covalent organic skeleton specifically comprises: under the action of a catalyst, using 2,5-dihydroxyterephthalaldehyde and a C3 symmetrical amino monomer as monomers, performing a condensation reaction by a solvent thermal method in a first reaction solvent to synthesize a hydroxylated covalent organic skeleton; performing an acyl chloride post-modification reaction on the obtained hydroxylated covalent organic skeleton and p-phenylazobenzoyl chloride in a second reaction solvent to introduce azobenzene groups into the hydroxyl sites to form a branched azobenzene covalent organic skeleton with dangling azobenzene units; wherein the C3 symmetrical amino monomer is one or more of 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 1,3,5-tris(4-aminophenoxy)benzene, and tris(4-aminophenyl)amine.

3. The method according to claim 2, characterized in that The molar ratio of 2,5-dihydroxyterephthalaldehyde to C3 symmetrical amino monomer is 1-5:1; the catalyst is acetic acid and / or scandium trifluoromethanesulfonate, and the total molar ratio of the catalyst to 2,5-dihydroxyterephthalaldehyde and C3 symmetrical amino monomer is 0.6:0.25-0.

5.

4. The method according to claim 1, wherein The added amount of p-phenylazobenzoyl chloride is 1-3 times the total mass of the hydroxylated covalent organic framework.

5. The method according to claim 1, wherein The C3 symmetrical aldehyde monomer is one or more of trimesaldehyde, 1,3,5-tris(p-formylphenyl)benzene, and 1,3,5-tris(4'-formyl[1,1'-biphenyl]-4-yl)benzene; the flexible monomer is one or more of 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine, 4,4',4"-(benzene-1,3,5-triyltri(oxy))tribenzaldehyde, and 4,4',4",4"-((benzene-1,2,4,5-tetrayltetra(methylene))tetra(oxy)tetrabenzaldehyde.

6. The method according to claim 1, characterized in that The molar ratio of p-diaminoazobenzene to the C3 symmetrical aldehyde monomer or the flexible monomer is 1-5:

1.

7. The method according to claim 1, characterized in that In the preparation of the skeleton-type azobenzene covalent organic framework, the total molar ratio of the catalyst to the two reaction substrates is 0.6:0.25-0.

5.

8. A photoresponsive azobenzene covalent organic framework material prepared by the method according to any one of claims 1 to 7.

9. Use of the photoresponsive azobenzene covalent organic framework material according to claim 8 in a light-controlled functional device.

10. Use of the photoresponsive azobenzene covalent organic framework material according to claim 8 in the fields of photoresponsive adsorption separation, light-driven molecular switching, and light-controlled catalysis.

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