Electrochromic covalent organic framework material and its application in smart windows

Abstract

This invention discloses an electrochromic covalent organic framework material and its application in smart windows, belonging to the technical field of electrochromic functional materials. The material possesses a gradient-tunable band structure and redox potential. The preparation method involves mixing a monomer containing tris(4-aminophenyl)amine with monomers containing linker units with different numbers of nitrogen atoms and an organic solvent, ultrasonically dispersing the mixture, and then adding a catalyst to form a mixture. A cleaned ITO glass is immersed in the mixture. The mixture undergoes cryogenic degassing, followed by in-situ polymerization under heating conditions. After the reaction, the product is washed and dried to obtain an electrochromic COF film. This invention achieves a positive shift in the oxidation potential system and an expansion of the charge delocalization range through the modulation of the electronic structure of the linker units. The material exhibits high optical contrast, fast response, low driving voltage, and good cycling stability.

Description

Technical Field

[0001] This invention relates to the field of electrochromic materials technology, specifically to a covalent organic framework material with tunable electrochromic properties, its preparation method, performance testing method, and applications. Particularly, it relates to an NX material whose band structure and redox behavior are systematically controlled by adjusting the number of nitrogen atoms in the connecting units. COF material system. Background Technology

[0002] Electrochromic materials can undergo reversible changes in optical properties under the influence of an electric field, and they hold significant promise for applications in smart windows, low-power displays, anti-glare rearview mirrors, and dynamic thermal management systems. Among numerous electrochromic systems, polymers and framework materials based on triphenylamine units have attracted considerable attention due to their good redox reversibility, high coloring efficiency, and ease of functionalization.

[0003] Covalent organic frameworks (COFs) are a class of crystalline porous materials formed by organic units linked by covalent bonds, possessing high specific surface area, designable pore structures, and good chemical stability. Introducing electroactive triphenylamine units as structural nodes into the COF framework is expected to synergize its electrochemical activity with the structural advantages of COFs, providing a new platform for the development of high-performance electrochromic materials.

[0004] However, current research in this field largely focuses on the modification of the triphenylamine nodes themselves or the performance demonstration of single materials. There is a lack of in-depth mechanistic studies and quantitative summaries regarding how the electronic properties of the connecting units systematically regulate the band structure, redox potential, and electrochromic behavior of COFs. In particular, the possibility of the connecting units transforming from "electronic bridges" into "active centers" and their paradigmatic impact on the electrochromic mechanism have not yet been systematically explored and experimentally verified.

[0005] Therefore, designing a series of model COF systems with gradient changes in the electronic properties of the connecting units and revealing the structure-property relationship and mechanism evolution path for regulating electrochromic properties is of great scientific significance and application value for realizing the rational design of high-performance electrochromic materials. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a covalent organic framework material system with tunable electrochromic properties and a clear mechanism. This system can solve the problems in the prior art where the influence mechanism of the electronic structure of the connecting unit on the electrochromic behavior of COF is unclear and there is a lack of systematic control strategies.

[0007] To solve the above problems, the present invention adopts the following technical solution:

[0008] A method for preparing an electrochromic covalent organic framework material, characterized by comprising the following steps: S1: will contain three (4) The monomers of aminophenylamine are mixed with monomers containing linking units with different numbers of nitrogen atoms and organic solvents, and after being ultrasonically dispersed evenly, a catalyst is added to prepare a mixture. S2: Immerse the cleaned conductive substrate in the mixture; S3: Freeze the mixture The gas is degassed, and then in-situ polymerization is carried out under heating conditions; S4: After the reaction is complete, the product is washed and dried to obtain an electrochromic COF film grown on a conductive substrate.

[0009] Preferably, the linker monomer is a nitrogen-containing aromatic heterocyclic compound, wherein the number of nitrogen atoms in the central benzene ring is 0, 1, 2 or 3.

[0010] More preferably, the connecting unit monomer is selected from at least one of the following compounds: 1, 3, 5 3(4) (aminophenyl)benzene; 4 (4 (aminophenyl) 2,6 2(4) (aminophenyl)pyridine; 4,4',4'' (pyrimidine) 2,4,6 Triphenylamine (trimethyl) 2,4,6 3(4) (aminophenyl) 1,3,5 Triazine.

[0011] Preferably, the organic solvent is a mixture of o-dichlorobenzene and n-butanol in a volume ratio of 1:1; the catalyst is acetic acid with a concentration of 4%. 8M, added at a rate of 0.1 0.3 mL per 2 mL solvent system.

[0012] Preferably, the conductive substrate is ITO glass, FTO glass, or IZO glass.

[0013] Preferably, the freezing The degassing process uses a freeze-thaw cycle method, with 2 cycles. Five times; the temperature of the heating reaction is 100. 140℃, for 48 hours 96 hours.

[0014] Preferably, the washing process includes: filtration of the reaction mixture under reduced pressure using 0.22 μm filter paper; and repeated soaking and washing of the solid product with tetrahydrofuran, each soaking time being 4 hours. 8 hours, total washing time is 24 72 hours.

[0015] The present invention also provides an electrochromic covalent organic framework material prepared by the above preparation method, which has a gradient-tunable band structure and redox potential.

[0016] Preferably, in-situ spectroelectrochemical methods are used to monitor the optical changes of the electrochromic covalent organic framework material at different potentials; combined with valence band X-ray photoelectron spectroscopy and Mott spectroscopy. Schottky tests and density functional theory calculations were used to analyze its band structure, charge storage mechanism, and electrochromic behavior; the optimal connection unit type was selected based on parameters such as optical contrast, response time, and cycle stability.

[0017] The present invention also provides an application of the above-mentioned electrochromic covalent organic framework material in smart windows, displays, anti-glare lenses or thermal management devices.

[0018] The electrochromic properties and mechanisms of the NX-COF materials prepared by the above methods can be revealed through systematic characterization: the dynamic color-changing process is monitored by in-situ spectroelectrochemical methods to obtain optical contrast and response time; combined with valence band XPS, Mott-Schottky tests and DFT calculations, its band structure, charge storage and transfer pathways are analyzed; thus, a complete quantitative structure-activity relationship of "nitrogen content of connecting units (electron-withdrawing ability) → material band structure and oxidation potential → electrochromic behavior and mechanism" is established.

[0019] Through the above technical solution, the present invention achieves the following technical objectives: 1. Provide a series of electrochromic COF materials with different numbers of nitrogen in the connecting units and gradual changes in electronic properties; 2. Elucidate the influence of the electron-withdrawing ability of the connecting units on the material's band structure, oxidation potential, and charge storage mechanism; 3. To achieve a leap from "gradual evolution" to "paradigm shift" in the electrochromic mechanism, and to obtain preferred materials with high optical contrast, fast response and good cycling stability; 4. Provide the preparation method and testing method of the material, as well as its application solutions in fields such as smart windows and displays.

[0020] Compared with the prior art, the electrochromic COF material and its preparation method provided by the present invention have the following beneficial effects: 1. Profound Mechanism Revealed: For the first time, through the systematic regulation of the electronic structure of the connecting unit, the complete mechanism evolution of electrochromic behavior from local oxidation of nodes to full framework charge delocalization and n-type doping was realized, providing a clear blueprint for rational design.

[0021] 2. Excellent overall performance: The preferred embodiment of N3-COF has an optical contrast ratio of up to 95.5% at 503nm, a coloring / fading time as fast as 8.9s / 4.6s, and also has low driving voltage and cycle stability.

[0022] 3. Significant structural advantages: The material is a crystalline COF with ordered channels, which facilitates rapid ion transport; the film is grown in situ, has a strong bond with the substrate, and has good process repeatability.

[0023] 4. Broad application prospects: Based on its high contrast and fast response characteristics, this material has important application value in fields such as smart windows, low-power displays, anti-glare mirrors and dynamic thermal management. Attached Figure Description

[0024] Figure 1 HRTEM and AFM morphology characterization images of the NO, N1, N2, and N3-COFs prepared in Examples 1-4; Figure 2 The XRD patterns and structural simulation diagrams of the NX-COFs prepared in Examples 1-4 are shown. Figure 3 The solid-state carbon NMR spectra of NX-COF prepared in Examples 1-4; Figure 4 The UV-Vis diffuse reflectance spectra and band gap diagrams of the NX-COF prepared in Examples 1-4 are shown. Figure 5 The valence band XPS spectra of NX-COF prepared in Examples 1-4 are shown. Figure 6 This is a schematic diagram of the band structure of the NX-COF prepared in Examples 1-4; Figure 7 The graphs show the Mott-Schottky curves of the NX-COF prepared in Examples 1-4. Figure 8 The image shows the DFT calculation front-line trajectory distribution of the NX-COF prepared in Examples 1-4; Figure 9 The above are three-dimensional in-situ spectroelectrochemical spectra of the NX-COF prepared in Examples 1-4. Figure 10 The optical contrast (ΔT) diagrams of the NX-COFs prepared in Examples 1-4 at characteristic wavelengths are shown. Figure 11The graphs show the coloring and fading response time curves of the NX-COF prepared in Examples 1-4. Figure 12 CIE chromaticity coordinate diagrams of the NX-COF electrochromic process prepared in Examples 1-4; Figure 13 Photographs showing the color changes of actual N1-COF and N3-COF electrochromic devices; Figure 14 The graph shows the stability of NX-COF prepared in Examples 1-4 after 50 CV cycles. Detailed Implementation

[0025] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0026] This invention provides an electrochromic covalent organic framework material, denoted as NX. COF, where X represents the number of nitrogen atoms in the central aromatic ring of the connecting unit, and X is 0, 1, 2 or 3; the material is in the form of tri(4) Aminophenylamine is a constant node that is covalently linked with linking units of different nitrogen contents through Schiff base condensation reaction to form a crystalline two-dimensional layered structure. During the synthesis process, it is grown in situ on ITO conductive glass to form a uniform and dense film.

[0027] Furthermore, the connection unit is selected from the following structures: When X=0, the connection units are 1, 3, and 5. 3(4) (aminophenyl)benzene; When X=1, the number of connection units is 4. (4 (aminophenyl) 2,6 2(4) (aminophenyl)pyridine; When X=2, the connection unit is 4,4',4'' (pyrimidine) 2,4,6 (Triphenylamine) When X=3, the connection units are 2, 4, and 6. 3(4) (aminophenyl) 1,3,5 Triazine.

[0028] The preparation method of the above-mentioned electrochromic covalent organic framework material includes the following steps: S1. Weigh the tris(4-aminophenyl)amine monomer and the selected linker monomer in an equimolar ratio, with a total mass ranging from 80 mg to 150 mg. Add the monomer to a mixed solvent consisting of o-dichlorobenzene and n-butanol, wherein the volume ratio of o-dichlorobenzene to n-butanol is 0.8:1 to 1.2:1, and the total volume of the mixed solvent is 1.5 mL to 3 mL. Sonicate for 10 to 30 minutes to allow the monomer to be fully dispersed and initially dissolved.

[0029] S2. Add an aqueous acetic acid solution with a concentration of 4M to 8M as a catalyst to the above mixture. The volume of the catalyst added is 8% to 15% of the total volume of the mixed solvent. Stir again or briefly sonicate to ensure uniform mixing.

[0030] S3. Immerse or place the indium tin oxide conductive glass, which has been ultrasonically cleaned and dried in sequence with acetone, ethanol and deionized water, in the mixed reaction solution obtained in step S2 with the conductive side facing up.

[0031] S4. Freeze the container containing the mixture and substrate in liquid nitrogen until the solution is completely solidified. Then connect a vacuum pump to evacuate the system to a pressure below 10 Pa. Maintain this pressure for 1-3 minutes, then turn off the vacuum and allow the system to thaw naturally. Repeat this "freeze-evacuate-thaw" cycle 2 to 5 times to thoroughly remove dissolved oxygen from the system.

[0032] S5. Place the sealed container treated in step S4 in an oven or heating table and react at a temperature of 100°C to 140°C for 60 to 96 hours. During this process, the monomer undergoes a polycondensation reaction on the substrate surface, forming a crystalline NX-COF film in situ.

[0033] S6. After the reaction is complete, allow it to cool naturally to room temperature. Remove the conductive glass substrate covered with the COF film. First, use 0.22 μm pore size filter paper to filter the remaining reaction solution under reduced pressure to separate the solid product. Then, immerse the film product in tetrahydrofuran solvent for washing for 24 to 72 hours, replacing the tetrahydrofuran solvent with fresh solvent every 4-12 hours to thoroughly remove unreacted monomers, oligomers, and catalyst. Finally, dry it under vacuum at 50°C to 80°C for 4 to 12 hours to obtain a firmly adhered and uniform NX-COF electrochromic thin film electrode.

[0034] Example 1: Fabrication of NO-COF thin film electrode Weigh 43.6 mg of tris(4-aminophenyl)amine monomer and 58.57 mg of 1,3,5-tris(4-aminophenyl)benzene (NO monomer), and place them together in a mixed solvent containing 1.0 mL of o-dichlorobenzene and 1.0 mL of n-butanol. Sonicate for 20 minutes to form a homogeneous dispersion. Add 0.2 mL of 6M acetic acid aqueous solution as a catalyst to the mixture and stir until homogeneous. Subsequently, immerse a piece of indium tin oxide (ITO) conductive glass (size: 1 cm × 3 cm, conductive side up), which has been pre-sonicated and dried with acetone, ethanol, and deionized water, into the reaction solution.

[0035] The reaction vessel was rapidly frozen in liquid nitrogen until the solution was completely solidified. A vacuum pump was then connected to evacuate the system until the pressure dropped below 10 Pa. This vacuum was maintained for 2 minutes before being shut off, allowing the system to thaw naturally to room temperature. This "freezing-vacuuming-thawing" process was repeated three times to thoroughly remove dissolved oxygen. Afterward, the sealed reaction vessel was placed in an oven preheated to 120°C and reacted at this temperature for 72 hours.

[0036] After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The ITO glass coated with a pale yellow film was removed. The remaining reaction mixture was filtered under reduced pressure using a 0.22-micron pore size polytetrafluoroethylene (PTFE) filter membrane. The resulting solid material (adhered to the ITO glass) was immersed in fresh tetrahydrofuran solvent for washing, with the solvent changed every 6 hours for a total of 48 hours. Finally, the product was dried in a vacuum drying oven at 60°C for 6 hours to obtain the NO-COF thin-film electrode.

[0037] Example 2: Fabrication of N1-COF thin film electrode The preparation method was exactly the same as in Example 1, except that the monomer of the linker unit was replaced with 58.71 mg of 4-(4-aminophenyl)-2,6-bis(4-aminophenyl)pyridine (N1 monomer). The N1-COF thin-film electrode was finally obtained.

[0038] Example 3: Fabrication of N2-COF thin film electrode The preparation method was exactly the same as in Example 1, except that the monomer of the linker unit was replaced with 58.86 mg of 4,4',4''-(pyrimidine-2,4,6-trimethyl)triphenylamine (N2 monomer). The final product was an N2-COF thin-film electrode.

[0039] Example 4: Fabrication of N3-COF thin film electrode The preparation method was exactly the same as in Example 1, except that the monomer of the linker unit was replaced with 59.00 mg of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (N3 monomer). The final product was an N3-COF thin-film electrode.

[0040] Example 5: Material Structure, Morphology and Crystallographic Characterization The four NX-COF thin film electrodes obtained in Examples 1-4 were systematically characterized: 1. Results of high-resolution transmission electron microscopy and atomic force microscopy analysis: such as Figure 1 As shown, HRTEM images reveal clear lattice fringes in N1-COF and N3-COF, with interplanar spacings of 0.875 nm and 1.037 nm, respectively, confirming their crystallinity. AFM measurements show that the four COF films have uniform thicknesses, approximately 67.6 nm (N0), 72.6 nm (N1), 54.2 nm (N2), and 73.2 nm (N3), indicating that COF was successfully grown in situ as a uniform film on the ITO substrate.

[0041] 2. Powder X-ray diffraction analysis results: such as Figure 2 As shown, all four materials exhibit characteristic diffraction peaks near 4.6°, 8°, and 12°, with the main peak at 4.6° corresponding to the (100) crystal plane. The experimental spectra are in high agreement with the simulated spectra based on the AA stacking mode, confirming that the synthesized NX-COF has a pre-defined two-dimensional hexagonal lattice and a long-range ordered structure.

[0042] 3. Solid-state carbon NMR spectroscopy analysis results: such as Figure 3 As shown, the characteristic peak appearing in the 156-162 ppm range is attributed to the carbon atom in the imine bond (C=N), proving that the monomers successfully polymerized via a Schiff base reaction. With the increase in the number of nitrogen atoms in the linking unit, the peak position systematically shifts towards a lower field, indicating a continuous change in the framework electronic environment.

[0043] Example 6: Characterization of band structure and electronic properties 1. Optical band gap and valence band analysis results: Ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS) and Tauc plotting method were used. Figure 4 The calculated optical band gaps (Eg) of N0, N1, N2, and N3-COF are 2.26 eV, 2.11 eV, 2.06 eV, and 1.98 eV, respectively, showing a narrowing trend in the system. Valence band X-ray photoelectron spectroscopy (VB-XPS) was then used to further refine the band gaps. Figure 5 The valence band peaks (Ev) of the four materials were measured to be 2.51 eV, 2.45 eV, 2.17 eV, and 1.86 eV, respectively.

[0044] 2. Mott-Schottky test results: The Mott-Schottky curve of the thin film was tested in 0.1M Na2SO4 electrolyte ( Figure 7 The flat band potentials were obtained by extrapolating the linear intervals, and the conduction band bottom (Ec) positions were calculated to be -0.21V, -0.10V, -0.33V, and -0.56V (vs. Ag / AgCl). Based on the above data, the following plots were generated: Figure 6The band structure evolution diagram shown intuitively demonstrates the systemic regulatory effect of the enhanced electron-withdrawing ability of the connecting units on the COF energy level.

[0045] 3. Theoretical Calculation Verification Results: Periodic models of four COFs were calculated using density functional theory. For example... Figure 8 As shown, the highest occupied molecular orbital (HOMO) is mainly localized at the triphenylamine node, while the lowest unoccupied molecular orbital (LUMO) is localized at the corresponding connecting unit, confirming that the material has a donor-acceptor type π-conjugated structure. The calculated density of states variation trend is consistent with the experimentally measured band evolution.

[0046] Example 7: Study on Electrochromic Properties and Mechanism 1. In-situ spectroelectrochemical analysis results: Using the thin films obtained in Examples 1-4 as the working electrode, Ag / AgCl as the reference electrode, a platinum sheet as the counter electrode, and 0.1M LiClO4 / propylene carbonate solution as the electrolyte, a three-electrode system was constructed. An electrochemical workstation coupled with a UV-Vis spectrometer was used to record the changes in absorption spectra while a step voltage was applied. Figure 9 The results show that all materials exhibit significant electrochromic behavior, but the response mode evolves with the value of X: N0-COF exhibits a unipolar gradient color change from light yellow to blue-black; N1 and N2-COF show more diverse color changes; while N3-COF exhibits a striking contrast change from orange-red to nearly colorless under positive pressure, and obvious n-type doping behavior (color turns dark) is observed under negative pressure, demonstrating bipolar electrochromic potential.

[0047] 2. Performance Quantitative Analysis Results: The optical contrast (ΔT) of the material at characteristic wavelengths was calculated based on the spectral data. Figure 10 ) and response time ( Figure 11 N3-COF achieved the highest ΔT (95.5%) at 503 nm, with coloring and fading times of 8.9 seconds and 4.6 seconds, respectively, making it the material with the best overall performance among the four. Figure 12 The CIE chromaticity diagram visually demonstrates the wide color gamut covered by the four materials during the color change process.

[0048] 3. Summary of Mechanism Evolution: Based on all the characterization data above, this invention clearly reveals the complete evolution path of the electrochromic mechanism: from the "gradual evolution" mechanism of N0-COF based on the local oxidation of triphenylamine nodes, as the electron-withdrawing ability of the connecting units increases, it gradually transitions to the expansion of charge delocalization to the entire π framework. In N3-COF, the strongly electron-withdrawing triazine ring becomes a new charge storage and reaction center, dominating the continuous multi-electron transfer process, achieving a leap to a "paradigm shift" mechanism.

[0049] Example 8: Assembly and Demonstration of Electrochromic Devices Using the N3-COF thin-film ITO glass prepared in Example 4 as the working electrode and another blank ITO glass as the counter electrode, they were separated by a 100 μm thick transparent insulating gasket, and sealed with epoxy resin around the perimeter with a pre-existing injection port. After injecting 0.1 mL of iClO4 / propylene carbonate electrolyte solution into the cavity, the injection port was sealed, thus fabricating a simple electrochromic device. Figure 13 As shown, when a step voltage of +1.5V and -1.5V is applied to the device, a rapid and high-contrast reversible change in the device's color between orange-red and near-colorless states can be observed, which intuitively verifies the feasibility and potential of this material in practical applications such as smart windows and displays.

[0050] Example 9: Cyclic stability test of thin film electrode Using the thin films obtained in Examples 1-4 as the working electrode, Ag / AgCl as the reference electrode, a platinum sheet as the counter electrode, and a 0.1M LiClO4 / propylene carbonate solution as the electrolyte, a three-electrode system was constructed. The thin films were subjected to 50 consecutive cyclic voltammetry (CV) scans (scan range -3 V to 3 V) using an electrochemical workstation. Figure 14 As shown, after 50 high-voltage wide-range charge-discharge cycles, the post-cycle CV curves (red line) of the N0-COF to N3-COF films almost perfectly overlap with the initial original curve (blue line). The positions of their redox characteristic peaks and the integral area enclosed by the curves (i.e., energy storage capacity) showed no significant shift or attenuation. This highly consistent test result demonstrates that all four COF films possess excellent electrochemical reversibility and outstanding cycling stability. This strongly confirms that the strong interfacial bonding constructed by the in-situ growth process can effectively resist the lattice stress caused by frequent ion insertion / extraction during wide-potential scanning, completely avoiding the pulverization and peeling of the active layer, and providing a solid physical guarantee for the long-term stable operation of the device.

[0051] Example 10: Application Scheme 1. Smart Window Application Solution 1) Device structure design: The device adopts a sandwich structure of "transparent conductive layer (ITO glass) - COF electrochromic layer - electrolyte layer - transparent conductive layer (ITO glass)", referring to the typical structure design of smart windows.

[0052] 2) Preparation process: The N3-COF thin film obtained in Example 4 was used as an electrochromic layer and prepared on the surface of ITO glass by in-situ solvothermal synthesis process. It was then laminated layer by layer with the ion conduction layer and the ion storage layer, and encapsulated to obtain the prototype of the smart window.

[0053] 3) Performance advantages: The transparent and colored states can be quickly switched by adjusting the driving voltage (0~1.2V) (fading 4.6s, coloring 8.9s), with an optical contrast of 95.5% and the ability to effectively adjust the sunlight transmittance (8%~60%); it has excellent cycle stability and can meet the long-term use requirements of buildings; the ordered pore structure improves ion transport efficiency and reduces energy consumption.

[0054] 4) Application scenarios: office buildings, residences, high-end shopping malls, etc. It can realize intelligent dimming, energy saving and consumption reduction, and also has adjustable color characteristics.

[0055] 2. Low-power display application solutions 1) Device structure design: Flexible N3-COF electrochromic film is prepared using a flexible ITO substrate (e.g., PET-ITO). Combined with organic electrolyte, a flexible display unit is designed to achieve multi-color switching (based on the synergistic effect of n-type and p-type doping).

[0056] 2) Fabrication process: Using the traditional coating method, N3-COF film is uniformly coated on the flexible PET-ITO substrate, and the film thickness is controlled (50~100 nm) to ensure that it does not fall off when the flexible is bent and that the performance is stable; after encapsulation, a flexible display prototype is obtained.

[0057] 3) Performance advantages: Low driving voltage (≤1.2V), fast response (8.9s coloring, 4.6s fading), and display state switching; flexible and bendable, suitable for wearable devices, flexible terminals and other scenarios; high optical contrast, excellent display clarity, and high contrast display.

[0058] 4) Application scenarios: Low-power, flexible display products such as flexible wristbands, electronic paper, and portable displays.

Claims

1. A method for preparing an electrochromic covalent organic framework material, characterized in that, Includes the following steps: S1: will contain three (4) The monomers of aminophenylamine are mixed with monomers containing linking units with different numbers of nitrogen atoms and organic solvents, and after being ultrasonically dispersed evenly, a catalyst is added to prepare a mixture. S2: Place the cleaned conductive substrate in the mixture; S3: Freeze the mixture The gas is degassed, and then in-situ polymerization is carried out under heating conditions; S4: After the reaction is complete, the product is washed and dried to obtain an electrochromic COF film grown on a conductive substrate.

2. The preparation method according to claim 1, characterized in that, The connecting unit monomer is a nitrogen-containing aromatic heterocyclic compound, and the number of nitrogen atoms in its central benzene ring is 0, 1, 2 or 3.

3. The preparation method according to claim 2, characterized in that, The connecting unit monomer is selected from at least one of the following compounds: 1, 3, 5 3(4) (aminophenyl)benzene; 4 (4 (aminophenyl) 2,6 2(4) (aminophenyl)pyridine; 4,4',4'' (pyrimidine) 2,4,6 (trimethyl)triphenylamine; 2,4,6 3(4) (aminophenyl) 1,3,5 Triazine.

4. The preparation method according to claim 1, characterized in that, The organic solvent is a mixture of o-dichlorobenzene and n-butanol in a volume ratio of 1:1; the catalyst is acetic acid at a concentration of 4%. 8M, added at a rate of 0.1 0.3 mL per 2 mL solvent system.

5. The preparation method according to claim 1, characterized in that, The conductive substrate is ITO glass, FTO glass, or IZO glass.

6. The preparation method according to claim 1, characterized in that, The freezing The degassing process uses a freeze-thaw cycle method, with 2 cycles. Five times; the temperature of the heating reaction is 100. 140℃, for 48 hours 96 hours.

7. The preparation method according to claim 1, characterized in that, The washing process includes: filtration of the reaction mixture under reduced pressure using 0.22 μm filter paper; and repeated immersion washing of the solid product with tetrahydrofuran, each immersion time being 4 hours. 8 hours, total washing time is 24 72 hours.

8. A claim 1 7. An electrochromic covalent organic framework material prepared by any one of the preparation methods described in claim 7, characterized in that, The material is composed of three (4) The aminophenylamine unit is formed by connecting nitrogen-containing linking units through imine bonds, and has a gradient-tunable band structure and redox potential.

9. The application of the electrochromic covalent organic framework material of claim 8 in smart windows, displays, anti-glare lenses, or dynamic thermal management devices.

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