A solution-processable electrochromic polymer, a method for preparing the same, and applications thereof

Abstract

The application relates to the technical field of organic chemistry and organic photoelectric functional materials, and provides a solution-processable electrochromic polymer, a preparation method thereof and application thereof. The solution-processable electrochromic polymer provided by the application has the following characteristics: the structural formula of the electrochromic polymer is as shown in formula (I): (I). The electrochromic polymer provided by the application has the following characteristics: quinacridone is used as a conjugated main chain, a non-conjugated solubilizing group with t-Boc as N-position substitution is introduced, a soluble polymer is prepared by chemical polymerization, a film can be processed by solution processing, the operation is simple, a high-stability electrochromic film based on a hydrogen bond crosslinking network and a high-performance electrochromic device can be prepared on a large scale, and the electrochromic film and the electrochromic device have excellent performance and strong cycle stability.

Description

Technical Field

[0001] This invention relates to the fields of organic chemistry and organic optoelectronic functional materials, specifically to a solution-processable electrochromic polymer, its preparation method, and its applications. Background Technology

[0002] Electrochromic polymers are a special type of polymer material with reversible electrochromic properties. Their optical properties can be controlled by an electric field to achieve controlled color changes. Electrochromic polymers typically consist of an organic polymer matrix, an electrolyte, electrodes, and dyes. The organic polymer matrix is ​​the main component of electrochromic polymers; it possesses good processability and controllability, and its molecular structure and properties can be controlled by adjusting the polymerization reaction conditions.

[0003] In the prior art, electrochromic polymers are commonly used as electrochromic materials. For example, patent CN114409647 B discloses a bifunctional electrochromic material based on quinacridone. This method uses electrochemical polymerization to directly polymerize a polymer film on ITO conductive glass. However, this method must be operated on ITO conductive glass and cannot prepare polymers in solution alone. It is also impossible to prepare thin films through solution processing, making it difficult to achieve large-scale application. Therefore, it is necessary to study a method for preparing electrochromic materials that can be industrialized and mass-produced.

[0004] To achieve large-scale industrial production of electrochromic materials, researchers have focused on conjugated polymers with easily modifiable structures and tunable band gaps. Their research aims to develop low-cost, scalable, solution-processable conjugated polymers to prepare attractive electrochromic materials. To improve the solubility of conjugated polymers and obtain solution-processable polymers, the introduction of solubilizing groups (such as long alkyl or alkoxy chains) is commonly employed. However, while increased polymer solubility can lead to poor adhesion of the film to a conductive substrate, it also affects the film's morphology and photochemical stability. This is currently the main challenge in developing solution-processable polymers.

[0005] Therefore, in order to achieve large-scale industrial production of electrochromic materials and manufacture high-performance electrochromic devices, it is crucial to study a solution-processable polymer and a corresponding solvent-resistant polymer film. Summary of the Invention

[0006] This invention is made to solve the above-mentioned problems, and aims to provide a mass-producible, solution-processable electrochromic polymer, and to prepare a high-stability electrochromic film with excellent performance and strong cycling stability based on a hydrogen bond cross-linking network using this electrochromic polymer, so as to prepare high-performance electrochromic devices.

[0007] During the research, the inventors discovered that using tert-butyloxycarbonyl (t-Boc) as the N-position protecting group not only increases the polymer's solubility in organic solvents but also allows for the formation of an amine at the N-position through thermal decomposition. This amine then forms intermolecular hydrogen bonds with the C=O groups in the adjacent polymer, thereby efficiently cleaving the t-Boc solubilizing group under mild conditions. Furthermore, only gas is generated during thermal decomposition, with no other residual groups. Therefore, the inventors attempted to obtain a stable solvent-resistant electrochromic polymer film through the cleavage of the t-Boc group and the formation of crosslinking hydrogen bonds.

[0008] After extensive experimentation, the inventors discovered that the quinacridone molecule is a π-conjugated system composed of NH and C=O groups, which can provide multiple substitution sites for N-position protection of t-Boc and the formation of intermolecular hydrogen bonds. Simultaneously, the quinacridone molecule also exhibits excellent electrochemical properties. Therefore, the inventors attempted to design a novel solution-processable electrochromic polymer, P1-Boc, by using quinacridone as the conjugated backbone and t-Boc as the solubilizing group for N-position substitution.

[0009] Furthermore, the inventors prepared the electrochromic polymer P1-Boc into a P1-Boc thin film. Through thermal annealing, they promoted the cleavage of t-Boc groups and the formation of a hydrogen-bonded cross-linking network between polymers, transforming the soluble P1-Boc thin film into a solvent-resistant P1 thin film. Due to the formation of a hydrogen-bonded cross-linking network between the polymers in the P1 thin film, it exhibits excellent cycling stability, significantly improved compared to the P1-Boc thin film, and a markedly increased contrast. The electrochromic device based on the P1 thin film still maintains high contrast after 100,000 cycles, with a coloring time of 0.56 s and a fading time of 0.80 s, representing the highest level reported to date for organic electrochromic devices.

[0010] A first aspect of the present invention provides a solution-processable electrochromic polymer, characterized in that the electrochromic polymer has the structural formula of formula (I):

[0011]

[0012] The electrochromic polymer provided by this invention can be dissolved in organic solvents and can be processed into films using solutions. The operation is simple and can be used to mass-produce high-stability electrochromic films with excellent performance and strong cycle stability based on hydrogen bond cross-linking networks.

[0013] A second aspect of the present invention provides a method for preparing a solution-processable electrochromic polymer, characterized by comprising: dissolving compounds a, b, and c in a reaction solvent and obtaining them by Stille coupling polymerization; wherein the structural formula of compound a is as shown in formula (II); the structural formula of compound b is as shown in formula (III); and the structural formula of compound c is as shown in formula (IV).

[0014]

[0015] This invention uses chemical polymerization to prepare a soluble electrochromic polymer. The reaction experiment is simple to operate and facilitates the subsequent large-scale preparation of thin films.

[0016] The method for preparing the solution-processable electrochromic polymer provided by the present invention may also have the following feature: wherein the sum of the amounts of compounds a and b is equal to the amount of compound c, and the ratio of the amounts of compounds a and b is 1:(1 to 1.5).

[0017] This invention limits the molar ratio of the reaction raw materials to ensure that the generated polymer has moderate solubility, high degree of polymerization, and that the film after heat treatment is insoluble in organic solvents.

[0018] The method for preparing the solution-processable electrochromic polymer provided by the present invention may also have the following feature: wherein the reaction solvent is a mixed solution of toluene and tetrahydrofuran, and the volume ratio of toluene to tetrahydrofuran is 1:0.3 to 0.6.

[0019] This invention restricts the reaction solvent, ensuring high reactivity, strong solubility of the reactants, fast reaction rate, and high degree of polymerization of the prepared polymer.

[0020] A third aspect of the present invention provides an application of a solution-processable electrochromic polymer, characterized in that the electrochromic polymer is used to prepare an electrochromic film based on a hydrogen-bonded crosslinking network.

[0021] The electrochromic polymer described in this invention can be used to prepare highly stable electrochromic films with excellent performance and strong cycling stability based on hydrogen bond crosslinking networks.

[0022] A fourth aspect of the present invention provides a method for preparing an electrochromic thin film based on a hydrogen-bonded cross-linked network, characterized by comprising the following preparation steps:

[0023] (1) Dissolve the electrochromic polymer in an organic solvent to obtain a P1-Boc solution, and spray the P1-Boc solution onto FTO conductive glass to form a P1-Boc film.

[0024] (2) The P1-Boc film is subjected to thermal annealing to obtain the electrochromic film, the structural formula of which is shown in formula (V):

[0025]

[0026] This invention utilizes chemical polymerization to prepare a soluble polymer, which is then sprayed onto FTO conductive glass to form a film, enabling large-area film fabrication. After film preparation, thermal annealing removes the t-Boc solubilizing groups and forms a hydrogen-bonded cross-linked network within the film, transforming it from soluble to insoluble. This effectively prevents dissolution and detachment of the film in the solvent due to repeated redox reactions during testing, ensuring the film's chemical stability. Simultaneously, the formation of the hydrogen-bonded cross-linked network further enhances structural stability.

[0027] The method for preparing electrochromic thin films provided by the present invention may also have the following feature: wherein the organic solvent in step (1) is dichloromethane or trichloromethane.

[0028] This invention limits the reaction solvent to ensure that the electrochromic polymer is fully dissolved.

[0029] The method for preparing the electrochromic thin film provided by the present invention may also have the following characteristics: the concentration of the P1-Boc solution is 0.3 to 2.1 mmol / L; the thermal annealing temperature is 170 to 200°C, and the time is 15 to 30 min.

[0030] This invention limits the concentration of the P1-Boc solution, avoiding the problem of uneven film caused by too many coating layers due to too low a concentration, while also avoiding the situation where the polymer is insoluble and clogs the nozzle due to too high a concentration.

[0031] This invention limits the temperature and time of thermal annealing, avoiding incomplete removal of the t-Boc solubilizing groups due to excessively low annealing temperature or short annealing time, which would prevent the formation of intermolecular hydrogen bonds and the production of insoluble films. At the same time, it also avoids damage to the film as a whole due to excessively high annealing temperature or long annealing time, which would affect the electrochromic properties.

[0032] In applications of the solution-processable electrochromic polymer provided by this invention, it can also have the following characteristics: it can be used to prepare electrochromic devices.

[0033] The electrochromic polymer described in this invention can be used to prepare high-performance electrochromic devices.

[0034] A fifth aspect of the present invention provides a method for preparing an electrochromic device, characterized by comprising: fabricating the electrochromic polymer into an electrochromic layer and bonding it to an ion storage layer, and drying the resulting electrochromic device.

[0035] The electrochromic layer made from the electrochromic thin film of the present invention has a tight bond between the thin film and the conductive substrate FTO, which ensures its morphology and photochemical stability.

[0036] By implementing the above technical solution, the present invention has the following beneficial effects:

[0037] The electrochromic polymer provided by this invention uses quinacridone as the conjugated main chain and introduces t-Boc as an N-position substituted non-conjugated solubilizing group. It is prepared by chemical polymerization and can be processed into films using solutions. The operation is simple and can be used to mass-produce high-stability electrochromic films with excellent performance and strong cycle stability based on hydrogen bond cross-linking networks.

[0038] The method for preparing electrochromic polymers provided by this invention restricts the reaction conditions, ensuring high reactivity, strong solubility of the reactants, fast reaction rate, moderate solubility of the generated polymer, high degree of polymerization, and that the film after heat treatment is insoluble in organic solvents.

[0039] The electrochromic polymer provided by this invention is applied to FTO conductive glass by spraying to form a film. The film-forming method is simple and easy to operate, and can realize the large-scale preparation of thin films. Then, the t-Boc solubilizing groups are removed by thermal annealing to form a hydrogen bond cross-linking network, which makes the film change from soluble to insoluble. A highly stable electrochromic thin film based on the hydrogen bond cross-linking network is prepared, and high-performance electrochromic devices can also be prepared. Attached Figure Description

[0040] Figure 1 This is the 1H NMR spectrum of the soluble polymer P1-Boc in Example 1 of the present invention;

[0041] Figure 2 The synthetic route of the soluble polymer P1-Boc in Example 1 of the present invention;

[0042] Figure 3 These are the cyclic voltammetry curves of the soluble P1-Boc film and the solvent-resistant P1 film in Example 9 of the present invention;

[0043] Figure 4 These are the UV-Vis absorption spectra of the soluble P1-Boc film and the solvent-resistant P1 film in Example 10 of the present invention;

[0044] Figure 5This is a comparison of the cycle stability of the soluble P1-Boc film and the solvent-resistant P1 film in Example 11 of the present invention;

[0045] Figure 6 This refers to the cycling stability of the highly stable electrochromic device based on P1 thin film in Embodiment 12 of the present invention. Detailed Implementation

[0046] To make the technical means, creative features, objectives and effects of this invention easy to understand, the invention will be specifically described below in conjunction with embodiments and accompanying drawings.

[0047] Example 1: Preparation of Electrochromic Polymers

[0048] Under N2 protection, a mixed solvent of toluene and tetrahydrofuran (10 mL) was added to the reaction vessel, along with 1 mmol of compound c, 0.5 mmol of compound a, 0.5 mmol of compound b, and 0.05 mmol of Pd(PPh3)4. The reaction was carried out at 90 °C for 72 h. The reaction mixture was poured into 200 mL of methanol and filtered to obtain a solid product. The solid product was extracted sequentially with acetone, n-hexane, and dichloromethane using a Soxhlet extractor. The dichloromethane extract, i.e., the black solid P1-Boc, was collected. The 1H NMR spectrum is shown below. Figure 1 As shown, the spectral peaks at δH 8.76–8.54 belong to the proton signals on the benzene ring of quinacridone in compound b, the spectral peak at δH 6.96 belongs to the proton signals on the thiophene ring of compound c, and the spectral peaks at δH 4.10–3.30 belong to the proton signals on the methylene group connected to oxygen in compound a. This indicates that P1-Boc is a three-component polymer composed of compounds a, b, and c.

[0049] Synthetic routes such as Figure 2 As shown, the structural formula of compound a is as shown in formula (II); the structural formula of compound b is as shown in formula (III); the structural formula of compound c is as shown in formula (IV); and the structural formula of P1-Boc is as shown in formula (I).

[0050]

[0051] Example 2: Preparation of electrochromic thin films based on hydrogen-bonded cross-linked networks

[0052] The P1-Boc polymer obtained in Example 1 was dissolved in dichloromethane to prepare a solution with a concentration of 0.5 mmol / L. Simultaneously, FTO conductive glass was sequentially sonicated in distilled water, ethanol, acetone, toluene, and acetone for 15 min each. The P1-Boc solution was then sprayed onto the washed FTO conductive glass to obtain a P1-Boc film. The P1-Boc film was then heat-annealed in a muffle furnace at 180°C for 15 min to obtain an insoluble P1 film with a hydrogen-bonded crosslinked network.

[0053] Example 3: Fabrication of Electrochromic Devices

[0054] A P1 thin film was used as the electrochromic layer, which was then bonded to the electrochromic layer using a 3M adhesive frame and filled with a gel electrolyte. Poly(3,4-ethylenedioxythiophene) was then prepared as an ion storage layer on another FTO conductive glass substrate via constant-potential polymerization at a polymerization charge of 0.1C and a polymerization potential of 1.6V. Finally, the electrochromic layer and the ion storage layer were bonded face-to-face and vacuum-dried at 60°C for 6 hours to obtain an all-solid-state electrochromic device.

[0055] Example 4: Screening of substrate ratios for electrochromic polymer reactions

[0056] In this embodiment, an electrochromic polymer was prepared according to the method in Example 1, and the ratio of reaction substrates was further screened.

[0057] Table 1. Changes in reaction efficiency with varying substrate ratio.

[0058]

[0059] As shown in Table 1, the reaction can proceed smoothly only when the sum of the amounts of compounds a and b is equal to the amount of compound c. At the same time, the polymer produced has moderate solubility and high degree of polymerization when the ratio of the amounts of compounds a and b is 1:(1 to 1.5), and the heat-treated P1 film is insoluble in organic solvents.

[0060] Example 5: Screening of Solvent Ratios for Electrochromic Polymer Reactions

[0061] In this embodiment, an electrochromic polymer was prepared according to the method in Example 1, and the ratio of the reaction solvent was further screened.

[0062] Table 2 shows the changes in reaction efficiency with varying solvent ratios.

[0063]

[0064] As shown in Table 2, an excessively high volume ratio of toluene to tetrahydrofuran will cause the substrate to become insoluble and the reaction to fail. An excessively low volume ratio will result in low reactivity and a low degree of polymerization of the prepared polymer. When the volume ratio of toluene to tetrahydrofuran is 1:(0.3-0.6), the reactants have strong solubility, the reaction rate is fast, the reactivity is high, and the degree of polymerization of the prepared polymer is high.

[0065] Example 6: Solvent Screening for Electrochromic Thin Films Based on Hydrogen-Bonded Crosslinking Networks

[0066] In this embodiment, an electrochromic film was prepared according to the method in Example 2, and the solvents for the P1-Boc polymer during the reaction process were further screened.

[0067] Table 3 shows the changes in reaction effect with P1-Boc polymer solvent.

[0068] Serial Number solvent reaction effect 1 dichloromethane P1-Boc polymer dissolution 2 chloroform P1-Boc polymer dissolution 3 petroleum ether P1-Boc polymer is insoluble 4 ethanol P1-Boc polymer is insoluble

[0069] As shown in Table 3, the P1-Boc polymer has good solubility when the solvent is dichloromethane or trichloromethane, which facilitates experimental operation.

[0070] Example 7: Polymer concentration screening for electrochromic thin films based on hydrogen-bonded cross-linked networks

[0071] In this embodiment, an electrochromic film was prepared according to the method in Example 2, and the concentration of the P1-Boc polymer solution during the reaction process was further screened.

[0072] Table 4. Variation of preparation effect with P1-Boc polymer solution concentration.

[0073]

[0074] As shown in Table 4, too low a concentration of P1-Boc solution leads to a higher number of coating layers, resulting in uneven thickness of the prepared P1-Boc film. Too high a concentration causes polymer insolubility and nozzle clogging. Therefore, the concentration of P1-Boc solution should be limited to 0.3–2.1 mmol / L to ensure successful P1-Boc film preparation.

[0075] Example 8: Screening of annealing conditions for electrochromic thin films based on hydrogen-bonded cross-linked networks

[0076] In this embodiment, an electrochromic thin film was prepared according to the method in Example 2, and the annealing conditions were further screened.

[0077] Table 5. Changes in preparation effect with annealing conditions

[0078] Serial Number Annealing temperature (°C) Annealing time (min) Preparation effect 1 160 15 At excessively low temperatures, the t-Boc solubilizing groups are not completely removed. 2 170 15 At lower temperatures, the t-Boc solubilizing groups are largely removed. 3 180 15 At a suitable temperature, the t-Boc solubilizing group is completely removed. 4 190 15 At a suitable temperature, the t-Boc solubilizing group is completely removed. 5 200 15 At higher temperatures, the t-Boc solubilizing groups are completely removed. 6 210 15 Excessive annealing temperature can damage the film. 7 180 10 If the time is too short, the t-Boc solubilizing group will not be completely removed. 8 180 15 In a short time, the t-Boc solubilizing groups are basically removed. 9 180 20 With appropriate time, the t-Boc solubilizing group is completely removed. 10 180 25 With appropriate time, the t-Boc solubilizing group is completely removed. 11 180 30 Over time, the t-Boc solubilizing group is completely removed. 12 180 35 Over time, the membrane will be damaged.

[0079] As shown in Table 5, annealing temperatures that are too low or annealing times that are too short will result in incomplete removal of the t-Boc solubilizing groups, preventing the formation of intermolecular hydrogen bonds and the production of insoluble P1 films. Conversely, annealing temperatures that are too high or annealing times that are too long will damage the P1 film as a whole, affecting its electrochromic properties. Therefore, the annealing temperature should be limited to 170–200℃ and the annealing time to 15–30 min to ensure the performance of the P1 film.

[0080] Example 9: Electrochemical performance testing of P1-Boc thin films and P1 thin films

[0081] The tests were conducted in a three-electrode system using a 0.15 mol / L tetrabutylammonium hexafluorophosphate acetonitrile solution as the supporting electrolyte. Specifically, the thin film was used as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode. The cyclic voltammetry curves of the P1-Boc thin film and the P1 thin film were measured at a scan rate of 100 mV / s.

[0082] like Figure 3 As shown, the initial oxidation potential of the P1-Boc film is 0.33 V, and that of the P1 film is 0.22 V. The redox peaks of the P1-Boc and P1 films are located at 0.78 and 0.52 V, and 0.70 and 0.46 V, respectively. This may be due to the removal of the strong electron acceptor t-Boc group, which lowers the oxidation potential. The peak current ratios of the P1 film and the P1-Boc film are 1.15 and 1.46, respectively, indicating that the P1 film has better redox reversibility than the P1-Boc film.

[0083] Example 10: Spectroelectrochemical properties of P1-Boc thin films and P1 thin films.

[0084] The spectroelectrochemical properties of the thin film were tested using an electrochemical workstation coupled with a UV-Vis spectrophotometer. A 0.15 mol / L tetrabutylammonium hexafluorophosphate acetonitrile solution was used as the supporting electrolyte in a three-electrode system, with the thin film as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode. UV absorption curves of the thin film in the range of 0–1 V were collected.

[0085] like Figure 4 As shown, in the neutral state, the P1-Boc film and the P1 film exhibit similar broad and strong absorption peaks near 520 nm. As the potential increases from 0 to 1.0 V, new absorption peaks appear successively in the 800–1000 nm and 1100 nm regions. Therefore, the breaking of the t-Boc group and the formation of the hydrogen bond crosslinking network have almost no effect on the spectroelectrochemical behavior of the polymer film.

[0086] Example 11: Kinetic testing of P1-Boc thin films and P1 thin films

[0087] The kinetic properties of the thin film were tested using an electrochemical workstation coupled with a UV-Vis spectrophotometer. A 0.15 mol / L tetrabutylammonium hexafluorophosphate acetonitrile solution was used as the supporting electrolyte in a three-electrode system, with the thin film as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode. The step time was 2 s and the step voltage was 0–1 V. The stability of the film at the maximum absorption wavelength was tested.

[0088] like Figure 5 As shown, after 1000 cycles, the P1-Boc film retained only 58.0% of its initial contrast, while the P1 film retained 88.7% of its initial contrast. Therefore, the stability of the heat-treated P1 film is greatly improved compared to that of the P1-Boc film.

[0089] Example 12: Stability Testing of Electrochromic Devices Based on P1 Thin Films

[0090] The stability of the P1 thin film-based electrochromic device was tested using an electrochemical workstation coupled with a UV-Vis spectrophotometer. The electrochromic layer was used as the working electrode, and the ion storage layer as the counter and reference electrodes. The step time was 2 s and the step voltage ranged from -0.3 to 0.7 V.

[0091] like Figure 6 As shown, after 100,000 cycles, the device still retains 88.4% of its contrast, thus demonstrating the excellent stability of the P1 thin film-based electrochromic device.

[0092] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

Claims

1. A method for preparing a solution-processable electrochromic polymer, characterized in that, The electrochromic polymer has the structural formula as shown in formula (I): Compounds a, b, and c were dissolved in a reaction solvent and obtained by Stille coupling polymerization; the structural formula of compound a is shown in formula (II); the structural formula of compound b is shown in formula (III); and the structural formula of compound c is shown in formula (IV). The sum of the amounts of compounds a and b is equal to the amount of compound c, and the ratio of the amounts of compounds a and b is 1:(1 to 1.5).

2. The method for preparing the solution-processable electrochromic polymer according to claim 1, characterized in that, The reaction solvent is a mixed solution of toluene and tetrahydrofuran, with a volume ratio of toluene to tetrahydrofuran of 1:0.3 to 0.

6.

3. An application of the electrochromic polymer prepared by the method for preparing a solution-processable electrochromic polymer as described in claim 1, characterized in that, The electrochromic polymer was used to prepare electrochromic films based on hydrogen-bonded cross-linked networks.

4. A method for preparing an electrochromic thin film based on a hydrogen-bonded cross-linked network, characterized in that, The preparation steps include the following: (1) The electrochromic polymer prepared by the method of preparing a solution-processable electrochromic polymer as described in claim 1 is dissolved in an organic solvent to obtain a P1-Boc solution, and the P1-Boc solution is sprayed onto FTO conductive glass to form a P1-Boc thin film. (2) The P1-Boc film is subjected to thermal annealing to obtain the electrochromic film, the structural formula of which is shown in formula (V):

5. The method for preparing the electrochromic thin film according to claim 4, characterized in that, The organic solvent in step (1) is dichloromethane or trichloromethane.

6. The method for preparing the electrochromic thin film according to claim 4, characterized in that, The concentration of the P1-Boc solution is 0.3–2.1 mmol / L; the thermal annealing temperature is 170–200 °C, and the time is 15–30 min.

7. The application of the electrochromic polymer prepared by the method for preparing a solution-processable electrochromic polymer as described in claim 1, characterized in that, Used to prepare electrochromic devices.

8. A method for preparing an electrochromic device, characterized in that, The electrochromic polymer prepared by the method of preparing a solution-processable electrochromic polymer according to claim 1 is used to fabricate an electrochromic layer and bond it with an ion storage layer. After drying, the electrochromic device is obtained.

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