Electrochromic polymer, film and preparation method thereof

Abstract

The invention belongs to the technical field of electrochromic polymers, and particularly relates to an electrochromic polymer, a film and a preparation method of the film. The preparation monomer of the electrochromic polymer is 2-(heptan-3-yl)-4, 7-bis (thieno [3, 2-b] thiophen-2-yl) benzo [d] thiazole, the monomer can be directly synthesized through the reaction of 4, 7-dibromo-2-(heptane-3-yl) benzothiazole and (thieno [3, 2-B] thiophene-2-yl) tributyltin, and the steps are simple and convenient. The polymer is yellow in a neutral state and blue in an oxidation state, coloring only needs 0.25 s, fading only needs 0.61 s, and the electrochromic response speed is high. The electrochromic polymer is prepared through a cyclic voltammetry method, and the generated polymer naturally deposits and grows on the surface of an ITO glass electrode and has a film form, so that the preparation steps of an electrochromic film are simplified, and the adhesive force between the film and a transparent conductive substrate is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of electrochromic polymer technology, specifically relating to an electrochromic polymer, a thin film, and a method for preparing the same. Background Technology

[0002] Electrochromism is a phenomenon in which a material's optical properties (such as reflectivity, transmittance, and absorptivity) undergo stable and reversible changes when an external electric field is applied, manifesting as reversible alterations in color and transparency. This physical phenomenon relies on reversible redox reactions within the material, modulating its band structure through the injection or extraction of electrons and ions, thereby altering its absorption characteristics for visible light. In practical applications, to achieve maximum visual contrast, color switching between complementary colors is typically chosen. In the prior art, patent CN 114920910 A proposes a solution-processable yellow-blue electrochromic polymer, its preparation method, and its applications. This polymer film is bright yellow in a neutral state at 0V and turns blue after oxidation at 1.1V, exhibiting a contrast ratio of 40% at 458nm. The drawbacks of this approach are that the resulting polymer requires a separate film-forming step for shaping, which is cumbersome; the coloring time of the resulting film is 1.8s, and the fading time is 0.7s, indicating that the coloring response speed still needs improvement. Summary of the Invention

[0003] This invention aims to provide a polymer material capable of achieving yellow-blue electrochromic properties and its preparation method, thereby solving at least one of the problems in the prior art, such as cumbersome preparation steps and long response time of yellow-blue electrochromic polymer films.

[0004] This invention is achieved through the following technical solution:

[0005] A compound monomer for making electrochromic materials, the structural formula of the compound monomer is shown in formula (I):

[0006] (I).

[0007] The chemical name of this monomer is 2-(heptan-3-yl)-4,7-bis(thieno[3,2-b]thiophen-2-yl)benzo[d]thiazole, abbreviated as BZZBT.

[0008] This invention also proposes a method for preparing the aforementioned compound monomers, comprising the following steps:

[0009] 4,7-Dibromo-2-(heptane-3-yl)benzothiazole, (thieno[3,2-B]thieno-2-yl)tributyltin, and Stille coupling catalyst were mixed in organic solvent A and refluxed at 110℃~130℃ for more than 30 h under an inert gas atmosphere to separate the electrochromic compound monomer.

[0010] Preferably, the molar ratio of 4,7-dibromo-2-(heptane-3-yl)benzothiazole to (thieno[3,2-B]thieno-2-yl)tributyltin is 1:2~2.5;

[0011] And / or, the molar ratio of the 4,7-dibromo-2-(heptane-3-yl)benzothiazole to the Stille coupling catalyst is 1:0.01~0.1;

[0012] And / or, the ratio of the mass of the 4,7-dibromo-2-(heptane-3-yl)benzothiazole to the volume of the organic solvent is 20-40 mg / mL.

[0013] This invention also includes an electrochromic polymer, wherein the monomers used to prepare the electrochromic polymer include the compound monomers described in claim 1, and the polymer is abbreviated as BZZB. The polymer structure is shown in formula (II):

[0014] (II).

[0015] This invention also proposes a method for preparing an electrochromic thin film, characterized by comprising the following steps:

[0016] The monomer of the compound according to claim 1 is dissolved in organic solvent B and subjected to cyclic voltammetry electrochemical polymerization.

[0017] The scanning speed is 90~110mV / s, the scanning voltage range is -0.3 to 1.3V, and the number of aggregated scans is 8~11.

[0018] Preferably, the working electrode of the cyclic voltammetry electrochemical polymerization reaction is a transparent conductive thin-film glass.

[0019] Transparent conductive thin-film glass is itself a working electrode material for electropolymerization reactions and can also serve as a substrate material for electrochromic devices. This method allows for the direct fabrication of the devices.

[0020] Preferably, the concentration of the compound monomer in the organic solvent B is 0.5~1.0 mmol / L.

[0021] Preferably, the electrolyte for the cyclic voltammetric electrochemical polymerization reaction is tetrabutylammonium hexafluorophosphate with a concentration of 0.05~0.10 mol / L.

[0022] Preferably, the organic solvent B is a mixed solution of dichloromethane and acetonitrile, with a volume ratio of 7:3.

[0023] Cyclic voltammetry (CV) is a commonly used electrochemical analysis technique that studies electrochemical systems by applying a cyclic linear potential scan to a working electrode and measuring the resulting current. In this invention, this technique is used as a direct method for preparing polymer thin films. In an electrolyte solution, when a forward scan voltage is applied to the working electrode, monomer molecules near the electrode surface are oxidized and initiate a polymerization reaction. The resulting polymer then deposits and grows on the electrode surface.

[0024] The present invention also includes an electrochromic device, comprising a transparent conductive substrate and an electrochromic film as described in any of the preceding claims, wherein the electrochromic film covers the surface of the transparent conductive substrate.

[0025] This invention proposes an electrochromic thin film directly prepared by electrochemical polymerization of monomer of formula (I). The film is yellow in the neutral state and blue in the oxidized state; these are complementary colors, resulting in a striking color contrast. Driven by a square wave voltage of –0.3 V to 1.3 V, the coloring process takes only 0.25 s, and the fading process takes only 0.61 s, demonstrating a coloring response speed far superior to existing similar materials. Furthermore, the monomer of formula (I) undergoes simultaneous polymerization and film formation on the surface of a transparent conductive glass substrate, simplifying the preparation steps of the electrochromic thin film and significantly improving the adhesion between the film and the substrate. This method can be directly used as a preparation method for electrochromic devices. Attached Figure Description

[0026] Figure 1 The synthetic route for the monomer of the compound shown in formula (Ⅰ) is as follows;

[0027] Figure 2 The 1H NMR spectrum of the monomer of the compound shown in formula (Ⅰ) is shown below.

[0028] Figure 3 The polymerization curve of the electrochromic thin film described in this invention;

[0029] Figure 4 The cyclic voltammetry (CV) curves of the electrochromic thin film described in this invention at different scanning speeds are shown.

[0030] Figure 5 The following are the ultraviolet-visible absorption spectra of the electrochromic thin film described in this invention under different voltages;

[0031] Figure 6 The response time of the electrochromic thin film described in this invention at 680 nm is given. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0033] Example 1: Synthesis of the monomer of the compound shown in formula (Ⅰ)

[0034] Synthetic routes such as Figure 1 As shown.

[0035] Weigh 0.3 g (0.766 mmol) of 4,7-dibromo-2-(heptane-3-yl)benzothiazole, 0.832 g (1.94 mmol) of (thieno[3,2-B]thieno-2-yl)tributyltin(VII), and add an appropriate amount of tetra(triphenylphosphine)palladium to a 35 ml reaction tube; under nitrogen protection, add 10 ml of N,N-dimethylformamide (organic solvent A), and heat and stir under reflux at 120 °C for 36 h.

[0036] The resulting reaction mixture was added to deionized water, extracted with dichloromethane, and washed three times with saturated brine. The extracted organic phases were combined, dried over anhydrous Na₂SO₄, filtered, and concentrated under vacuum. An appropriate amount of 200-300 mesh silica gel was added, and the mixture was concentrated and stirred under vacuum. Using 300-400 mesh fine silica gel as the stationary phase, the mixture was subjected to column chromatography to obtain the target product BZZBT(Ⅰ).

[0037] The 1H NMR spectrum of the target product is shown below. Figure 2 As shown.

[0038] Example 2: Preparation of electrochromic polymer (electrochromic thin film)

[0039] Weigh the monomer obtained in Example 1 and dissolve it in a mixed solvent of dichloromethane and acetonitrile (v:v=7:3) (i.e. organic solvent B) to prepare a monomer solution with a concentration of 0.8 mg / ml.

[0040] Electrochemical polymerization was performed using a Chenhua 660 electrochemical workstation. Instrument parameters were set as follows: CV mode, scan rate 100 mV / s, maximum and minimum scan voltages 1.3 V and -0.3 V respectively, and 10 polymerization cycles. Other reaction conditions were set as follows: a three-electrode system, with a working electrode of transparent conductive thin-film glass (ITO glass), an auxiliary electrode of platinum sheet, and an Ag / AgCl electrode as the reference electrode; the electrolyte was tetrabutylammonium hexafluorophosphate with a concentration of 0.05–0.10 mol / L.

[0041] Aggregation curve as Figure 3 As shown, the horizontal axis represents potential, with numerical changes reflecting the potential scan range (-0.3V to 1.5V). The vertical axis represents current, with positive values ​​representing anodic oxidation current and negative values ​​representing cathodic reduction current. The legend "1st cycle" represents the first cycle curve, and the legend "2-10 cycles" represents the second to tenth cycle curves. As the cycle progresses, the peak value of the curve gradually increases, indicating an increase in reaction rate and active substance content.

[0042] After the reaction is complete, the resulting polymer adheres to the ITO glass surface, forming a thin film. The electrochromic film is then cleaned using the aforementioned organic solvent B.

[0043] Example 3: Electrochemical performance testing of electrochromic polymer (electrochromic thin film)

[0044] 10 mL of acetonitrile and 0.387 g of tetrabutylammonium hexafluorophosphate were added to a 10 mL volumetric flask to prepare a test solution with a concentration of 1 mmol.

[0045] Electrochemical tests were performed using a Chenhua 660 electrochemical workstation and the aforementioned three-electrode system. The electrolyte solution was used as the test solution. Cyclic voltammetry (CV) curves of the electrochromic thin film at different scan rates were obtained by adjusting different scan rates.

[0046] The results of the cyclic voltammetry curves are as follows Figure 4 As shown in the figure, different line shapes correspond to different scan rates (50, 100, 200, 300, 500 mV / s). The peak current increases rapidly with increasing scan rate, and the peak shape does not exhibit severe distortion, indicating that the ion transport and electron transfer processes of the electrochromic film are relatively fast, meaning the film responds quickly to potential changes. This demonstrates that the electrochromic film obtained in this embodiment adheres well to the ITO glass, and the electrochromic device formed by the electrochromic film itself and the composite of the electrochromic film and the transparent conductive substrate ITO glass can be directly used as different types of electrochromic material products.

[0047] Example 4: Optical and electrochromic properties testing of the electrochromic polymer (electrochromic thin film)

[0048] Different voltages were applied using a Chenhua 660 electrochemical workstation, and a UV-Vis spectrophotometer was used to scan the wavelength range of 300~1100nm to obtain UV-Vis absorption spectra at different voltages.

[0049] Experimental results are as follows Figure 5As shown in the figure, the horizontal axis represents wavelength (Wavelength), and the vertical axis represents absorbance (Absorbance). The electrochromic film can switch between yellow and blue. At -0.3V, the absorbance is high near 420 nm (corresponding to the peak of the curve), indicating that the film has strong absorption in the blue-violet region, and the film appears yellow, which is its complementary color. At 1.3V, the absorbance is high near 680 nm (corresponding to the peak of the curve), indicating that the film has strong absorption in the red-orange region, and the film appears blue, which is its complementary color.

[0050] Electrochromic response times were measured by applying step voltages of -0.3V and 1.3V to the electrochromic thin film using an electrochemical workstation.

[0051] Experimental results are as follows Figure 6 As shown in the figure, the vertical axis represents transmittance, with the descending segment of the curve representing the coloring process and the ascending segment representing the fading process. The film exhibits a coloring time of 0.25 s and a fading time of 0.61 s under a step voltage, demonstrating a very sensitive response.

Claims

1. A compound monomer for producing electrochromic materials, characterized in that, The structural formula of the monomer of the compound is shown in formula (I): （I）。 2. The method for preparing the compound monomer according to claim 1, characterized in that, Includes the following steps: 4,7-Dibromo-2-(heptane-3-yl)benzothiazole and (thieno[3,2-B]thieno-2-yl)tributyltin were mixed in organic solvent A and Stille coupling catalyst was added. The mixture was refluxed at 110℃~130℃ for more than 30 h under an inert gas atmosphere to separate the electrochromic compound monomer.

3. The preparation method according to claim 2, characterized in that, The molar ratio of 4,7-dibromo-2-(heptane-3-yl)benzothiazole to (thieno[3,2-B]thieno-2-yl)tributyltin is 1:2~2.5; And / or, the molar ratio of the 4,7-dibromo-2-(heptane-3-yl)benzothiazole to the Stille coupling catalyst is 1:0.01~0.1; And / or, the ratio of the mass of the 4,7-dibromo-2-(heptane-3-yl)benzothiazole to the volume of the organic solvent is 20-40 mg / mL.

4. An electrochromic polymer, characterized in that, The monomers used to prepare the electrochromic polymer include the compound monomers described in claim 1.

5. A method for preparing an electrochromic thin film, characterized in that, Includes the following steps: The monomer of the compound according to claim 1 is dissolved in organic solvent B and subjected to cyclic voltammetry electrochemical polymerization. The scanning speed is 90~110mV / s, the scanning voltage range is -0.3 to 1.3V, and the number of aggregated scans is 8~11.

6. The preparation method according to claim 6, characterized in that, The working electrode for the cyclic voltammetry electrochemical polymerization reaction is a transparent conductive thin-film glass.

7. The preparation method according to claim 6, characterized in that, The concentration of the compound monomer in the organic solvent B is 0.5~1.0 mmol / L.

8. The preparation method according to claim 6, characterized in that, The electrolyte used in the cyclic voltammetric electrochemical polymerization reaction is tetrabutylammonium hexafluorophosphate, with a concentration of 0.05~0.10 mol / L.

9. The preparation method according to claim 6, characterized in that, The organic solvent B is a mixed solution of dichloromethane and acetonitrile, with a volume ratio of 7:

3.

10. An electrochromic device, characterized in that, It includes a transparent conductive substrate and an electrochromic film as described in any one of claims 5 to 9, wherein the electrochromic film covers the surface of the transparent conductive substrate.

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