A blue to transparent electrochromic polymer and its preparation method and application

Abstract

The present invention relates to a blue to transparent electrochromic polymer, and its structure is as follows: wherein n represents the degree of polymerization, and n is a natural number of 8-100. The polymer can realize the conversion between the blue state and the transparent state, and has the characteristics of low driving voltage (step potential is 0V and 1.0V), high optical contrast (usually above 40%, up to 45%), and high stability (square wave potential scan 200 times still maintains good stability); the polymer is easily soluble in organic solvents such as toluene and dichloromethane for solution treatment, which is convenient for large-area film formation by spraying or scraping, and is conducive to process treatment and application.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochromic polymers, and in particular to a blue to transparent electrochromic polymer and a preparation method and application thereof. Background Art

[0002] Electrochromism refers to the phenomenon that when a material is subjected to an external electric field, it undergoes a redox reaction through the injection or extraction of ions and electrons, causing the material to switch between an oxidized state and a neutral state, and the appearance is manifested as a reversible color change. Electrochromic materials have broad application prospects in the fields of smart windows, military intelligent camouflage, etc. Compared with inorganic metal oxides and organic small molecule electrochromic materials, electrochromic polymers have the advantages of easy molecular structure design, rich color changes, high optical contrast, fast response rate, and high stability. As one of the three primary colors, blue electrochromic polymers that display blue are of great significance to electrochromic display. Therefore, the development of blue to transparent electrochromic materials has always been the research focus in the field of electrochromism.

[0003] Generally, polymer materials such as polyaniline and polythiophene are difficult to dissolve due to their rigid main chain, and the solution treatment makes it difficult to form a large-area film; in addition, electrochromic materials as base colors usually need to be dissolved in order to be compounded with other color-changing materials to exert their color matching performance. In order to achieve the solution treatment of polymers, long-chain alkyl or ionic groups can be introduced into the side chains of polymers to achieve the purpose of dissolving in oily solvents and water. However, polymers soluble in water still have problems such as poor stability, while polymers that can be treated with oily solvents have the advantages of not affecting the color change of the main chain and high stability. However, the types of polymers that can be treated with oily solvents, especially high-performance blue, green, red and other base color polymers, are still relatively small, which seriously limits the industrialization of electrochromic polymers. However, the current soluble blue to transparent electrochromic polymers are mainly based on the main chain structure of propylene dioxythiophene, which not only has a single structure and few types, but also has problems such as low contrast and slow response rate. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a blue to transparent electrochromic polymer and a preparation method thereof, mainly by introducing an ethylenedioxythiophene structure into a thienothiophene derivative, an electrochromic polymer with a blue to transparent conversion and a color change contrast ratio of more than 40% is successfully prepared, and the polymer has the advantages of good stability, low potential required for color change, high response efficiency, etc. The electrochromic polymer of the present invention can be treated in a solution to exert its color matching performance, which is conducive to its process treatment and application, such as large-area film formation or preparation of electrochromic devices.

[0006] (II) Technical solution

[0007] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0008] In a first aspect, the present invention provides a blue to transparent electrochromic polymer, the structural formula of which is as follows:

[0009]

[0010] Wherein, n represents the degree of polymerization, and n is a natural number of 8-100.

[0011] In a second aspect, the present invention provides a method for preparing a blue to transparent electrochromic polymer as shown in Formula I, the method specifically comprising:

[0012] Dissolve one of 2,5-dibromo-3,4-ethylenedioxythiophene, 2,5-dichloro-3,4-ethylenedioxythiophene and 2,5-diiodo-3,4-ethylenedioxythiophene and the compound represented by formula II as synthetic monomers in an organic solvent, add an organic acid, an inorganic weak base and a palladium catalyst, and heat under inert gas protection to cause a polymerization reaction to obtain a blue to transparent electrochromic polymer having a structure represented by formula I;

[0013] The reaction process is as follows, wherein R = Br, Cl or I;

[0014]

[0015] According to a preferred embodiment of the present invention, the organic acid is pivalic acid or tert-decanoic acid; the inorganic weak base is potassium carbonate, cesium carbonate or potassium acetate; and the palladium catalyst is palladium acetate.

[0016] According to a preferred embodiment of the present invention, the organic solvent is N,N-dimethylacetamide or N,N-dimethylpropionamide.

[0017] According to a preferred embodiment of the present invention, the molar ratio of one of 2,5-dibromo-3,4-ethylenedioxythiophene, 2,5-dichloro-3,4-ethylenedioxythiophene and 2,5-diiodo-3,4-ethylenedioxythiophene to the monomer of the compound represented by formula II is 1:1.

[0018] According to a preferred embodiment of the present invention, the molar ratio of the inorganic weak base to the compound represented by formula II is 3-4:1; the molar ratio of the organic acid to the compound represented by formula II is 0.5-1:1; and the molar ratio of the palladium catalyst to the compound represented by formula II is 0.05-0.1:1.

[0019] According to a preferred embodiment of the present invention, the polymerization reaction temperature is 120-140° C., and the reaction time is 36-72 hours.

[0020] According to a preferred embodiment of the present invention, after the reaction is completed, the reaction solution is cooled to room temperature, and the reaction solution is dropped into cold methanol for precipitation, and the precipitate is dried and filtered; then Soxhlet extraction is performed with methanol, n-hexane and chloroform respectively, the chloroform extract is concentrated, and then dropped into cold methanol for precipitation, filtered and dried, to obtain the blue to transparent electrochromic polymer shown in Formula I.

[0021] In a third aspect, the present invention further provides a use of a blue to transparent electrochromic polymer represented by Formula I in the preparation of an electrochromic film and an electrochromic device.

[0022] Preferably, the electrochromic film is prepared by dissolving the condensed ring thiophene electrochromic polymer shown in Formula I in an organic solvent to obtain a mixed solution, coating the mixed solution on the surface of the substrate and drying it, and the film thickness is 80-400 nm. The organic solvent can be a weakly polar solvent such as toluene and chloroform.

[0023] Preferably, the electrochromic device comprises an upper electrode layer, an electrolyte layer, an electrochromic thin film layer and a lower electrode layer stacked in sequence, wherein the electrochromic thin film layer is a thin film layer formed by a condensed ring thiophene type electrochromic polymer as shown in Formula I.

[0024] (III) Beneficial effects

[0025] The invention uses 2,5-dibromo-3,4-ethylenedioxythiophene (or 2,5-dichloro-3,4-ethylenedioxythiophene or 2,5-diiodo-3,4-ethylenedioxythiophene) and a compound shown in Formula II as synthetic monomers to carry out arylation coupling polymerization reaction, thereby introducing 3,4-ethylenedioxythiophene as an embedding unit into the main chain of a thienothiophene derivative, and utilizing the electron-donating property and conjugated planarity of 3,4-ethylenedioxythiophene to red-shift the absorption spectrum of the polymer and display blue in a neutral state; at the same time, combining with the long-chain alkyl group in the side chain structure of the thienothiophene derivative, the interaction between molecules is weakened, and the polymer is easily soluble in organic solvents such as toluene and dichloromethane for solution treatment, so that large-area film formation by spraying or scraping is convenient, thereby facilitating process treatment and application.

[0026] The polymer of the present invention can realize the conversion between the blue state and the transparent state, and has the characteristics of low driving voltage (step potential is 0V and 0.8V), high optical contrast (usually above 40%, and up to 45%), and high stability (square wave potential scans 200 times and still maintains good stability), and is suitable for the assembly application of electrochromic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The hydrogen nuclear magnetic spectrum of the blue to transparent electrochromic polymer of the present invention is shown in FIG.

[0028] Figure 2 The molecular weight and distribution diagram of the polymer represented by formula I determined by gel permeation chromatography, the reference sample is polystyrene, the solvent is tetrahydrofuran, the ordinate in the figure is the detection intensity, and the abscissa is the retention time.

[0029] Figure 3 The spectral absorption curve and color photograph of the blue to transparent electrochromic polymer shown in Formula I dissolved in chloroform.

[0030] Figure 4 The UV-visible absorption spectra and color change photos of the blue to transparent electrochromic polymer film shown in Formula I at different potentials.

[0031] Figure 5 The cyclic voltammetry curve of the blue to transparent electrochromic polymer film shown in Formula I.

[0032] Figure 6 The square wave potential cycling curve of the blue to transparent electrochromic polymer film shown in Formula I.

[0033] Figure 7 : is the thermal stability curve of the blue to transparent electrochromic polymer shown in Formula I. DETAILED DESCRIPTION

[0034] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0035] Example 1

[0036] This embodiment is a method for preparing a blue to transparent electrochromic polymer of the present invention, and the specific process is as follows:

[0037] (1) Synthesis of the compound represented by formula II:

[0038] At -78°C and nitrogen protection, a hexane solution of n-butyl lithium was added dropwise to a THF solution of thieno(3-2-b)thiophene, and then TIPSCl (triisopropylsilyl chloride) was added, and after quenching, extraction, washing and drying, an intermediate product 1 was obtained; at -78°C and nitrogen protection, a hexane solution of n-butyl lithium and a THF solution of trimethyltin chloride were added to the THF solution of the intermediate product 1, and after quenching, extraction, washing and drying, an intermediate product 2 was obtained; the intermediate product 2 was heated to 40 ℃ and then heated to 30 ℃. Under nitrogen protection, the intermediate product 4 is added to a toluene solution containing compound 3 (ethyl 2,5-dibromothieno[3,2-B]thiophene-3,6-dicarboxylate: CAS: 1800376-55-9), Pd2(dba)3 and P(o-tol)3, and then extracted, washed and dried to obtain intermediate product 4; at -78°C and nitrogen protection, intermediate product 4 is added to a THF solution of 4-hexyl-1-bromobenzene and a hexane solution of n-butyllithium, and then extracted, washed and dried to obtain the compound represented by formula II. The detailed synthesis process can be found in Chinese patent application CN201980006127.5 (description

[0245] -

[0255] ).

[0039] (2) The synthesis method of the blue to transparent electrochromic polymer shown in Formula I is as follows:

[0040] 0.1 mmol of 2,5-dibromo-3,4-ethylenedioxythiophene, 0.1 mmol of the compound represented by formula II, 0.006 mmol of palladium acetate, 0.3 mmol of potassium carbonate, and 0.05 mmol of pivalic acid were placed in a 25 mL two-necked bottle, ventilated and injected with nitrogen, 15 mL of anhydrous N,N-dimethylacetamide (DMAC) was injected, ventilated and filled with nitrogen, heated to 120° C. and refluxed for reaction for 72 h, cooled to room temperature after the reaction was completed, and the reaction solution was dripped into cold methanol for precipitation, and the precipitate was filtered and dried; then Soxhlet extraction was performed with methanol, n-hexane and chloroform respectively, each extraction time was 24 h, the chloroform extract was concentrated to 15 mL, and then dripped into cold methanol to precipitate to obtain a black solid, which was filtered and dried to obtain a blue to transparent electrochromic polymer represented by formula I.

[0041] like Figure 1 As shown, it is the nuclear magnetic resonance hydrogen spectrum of the blue to transparent electrochromic polymer shown in formula I. Figure 2 The molecular weight and distribution diagram of the target polymer of the structure shown in Formula I measured by gel permeation chromatography are shown, the reference sample is polystyrene, the solvent is tetrahydrofuran, the ordinate in the figure is the detection intensity, and the abscissa is the retention time. The molecular weight Mn of the polymer shown in Formula I is measured to be 19590 Daltons, Mw is 47973 Daltons, and PDI is 2.44885.

[0042] Example 2

[0043] The blue to transparent electrochromic polymer of formula I obtained in Example 1 was dissolved in chloroform to prepare a solution of 8 mg / ml. The insoluble matter was filtered out through a filter. The solution was placed in a spray gun and the air pressure was controlled to be 2 MPa. The film was sprayed on a conductive glass. The absorbance of the film was about 0.8. After spraying, the film was placed in a vacuum drying oven at 40°C for vacuum drying for standby use.

[0044] The following performance tests were performed on the prepared polymers and polymer films:

[0045] (1) The condensed ring thiophene electrochromic polymer of formula I prepared in Example 1 was tested for solution spectrum:

[0046] The polymer was dissolved in chloroform to a concentration of 2×10 -4 mg / mL solution, the solution absorption curve and photo are as follows Figure 3 As shown, the absorption peak of the polymer is at 560 nm (absorbing yellow-green light), and the polymer solution appears blue-purple.

[0047] (2) Spectroelectrochemical performance test of polymer films at different voltages:

[0048] A three-electrode system was used, with platinum wire as the counter electrode, calibrated silver wire as the reference electrode, the polymer film of Example 1 as the working electrode, and the supporting electrolyte as 0.1 mol / L lithium perchlorate / propylene carbonate solution. The spectroelectrochemical spectra of the copolymer film at different applied voltages and the photos of discoloration (oxidation state) and coloration (neutral state) are shown in Figure 2. Figure 4 As shown, it shows that the polymer film has obvious electrochromic properties.

[0049] (3) Cyclic voltammetry was used to test the initial redox voltage of the prepared polymer film:

[0050] like Figure 5 As shown, the initial redox voltages of the prepared polymer films were approximately 0.2V and 0.15V.

[0051] (4) Spectral response and stability of the prepared polymer film tested by step method:

[0052] like Figure 6 As shown, the step potential of the polymer film prepared in Example 1 is 0 V and 0.8 V, and the maximum transmittance contrast is 45%. The electrochemical stability of the prepared polymer film was tested, and the square wave potential was scanned 200 times and still maintained good stability.

[0053] (5) Testing the thermal stability of electrochromic polymers: Figure 7 As shown, the thermal decomposition temperature of the polymer is greater than 300°C, indicating that it can be used in a working environment with higher temperature.

[0054] It can be seen from the above embodiments and various test results that the color and absorption spectrum of the copolymer film prepared by the present invention can be regulated by the type of copolymer monomer, the copolymer film can achieve a transformation from blue to transparent, and has the characteristics of low driving potential, obvious color change contrast, high coloring efficiency, good stability, etc. The prepared copolymer film can be applied in the fields of electrochromic display, adaptive camouflage, etc.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A blue to transparent electrochromic polymer, characterized in that Its structural formula is as follows: Wherein, n represents the degree of polymerization, and n is a natural number of 8-100.

2. A method for preparing a blue to transparent electrochromic polymer of formula I, characterized in that: The method comprises: dissolving one of 2,5-dibromo-3,4-ethylenedioxythiophene, 2,5-dichloro-3,4-ethylenedioxythiophene and 2,5-diiodo-3,4-ethylenedioxythiophene and a compound shown in formula II as synthetic monomers in an organic solvent, adding an organic acid, an inorganic weak base and a palladium catalyst, and heating under inert gas protection conditions to cause a polymerization reaction, thereby obtaining a blue to transparent electrochromic polymer having a structure shown in formula I; The reaction process is as follows, wherein R = Br, Cl or I; n represents the degree of polymerization, and n is a natural number of 8-100; 3. The preparation method according to claim 2, characterized in that: The organic acid is pivalic acid or tert-decanoic acid; the inorganic weak base is potassium carbonate, cesium carbonate or potassium acetate; and the palladium catalyst is palladium acetate.

4. The preparation method according to claim 2, characterized in that: The organic solvent is N,N-dimethylacetamide or N,N-dimethylpropionamide.

5. The preparation method according to claim 2, characterized in that: The molar ratio of one of 2,5-dibromo-3,4-ethylenedioxythiophene, 2,5-dichloro-3,4-ethylenedioxythiophene and 2,5-diiodo-3,4-ethylenedioxythiophene to the monomer of the compound represented by formula II is 1:

1.

6. The preparation method according to claim 2, characterized in that: The molar ratio of the inorganic weak base to the compound shown in formula II is 3-4:1; the molar ratio of the organic acid to the compound shown in formula II is 0.5-1:1; and the molar ratio of the palladium catalyst to the compound shown in formula II is 0.05-0.1:

1.

7. The preparation method according to claim 2, characterized in that: The polymerization temperature is 120-140°C and the reaction time is 36-72h.

8. The preparation method according to claim 2, characterized in that: After the reaction is completed, the reaction solution is cooled to room temperature, and the reaction solution is dropped into cold methanol for precipitation, and the precipitate is dried and filtered; then Soxhlet extraction is performed with methanol, n-hexane and chloroform respectively, the chloroform extract is concentrated, and then dropped into cold methanol for precipitation, filtered and dried to obtain the blue to transparent electrochromic polymer shown in Formula I.

9. Use of the blue to transparent electrochromic polymer according to claim 1 in the preparation of electrochromic films and electrochromic devices.

10. The use according to claim 9, characterized in that: The electrochromic film is prepared by dissolving the condensed ring thiophene electrochromic polymer shown in formula I in an organic solvent to obtain a mixed solution, coating the mixed solution on the surface of a substrate and drying the mixed solution, and the film thickness is 80-400nm; The electrochromic device comprises an upper electrode layer, an electrolyte layer, an electrochromic thin film layer and a lower electrode layer stacked in sequence, wherein the electrochromic thin film layer is a thin film layer formed by a condensed ring thiophene type electrochromic polymer as shown in Formula I.

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