Electrochromic polymer and preparation method and application thereof

Abstract

The present application relates to a kind of electrochromic polymer, which is obtained by polymerization of spirobifluorene and monomer containing thiophene structure monocyclic or polycyclic structure, containing obvious porous structure, providing ion transport channel, facilitating ion transport, and the electrochromic polymer has rich multicolor change, is a kind of excellent electrochromic functional layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of organic optoelectronics, in particular to an electrochromic polymer and a preparation method and application thereof. BACKGROUND

[0002] Electrochromic materials refer to a phenomenon that the optical properties (absorbance, reflectance, transmittance) of the materials change reversibly and stably under the action of an applied voltage, which is usually manifested as a change in color and transparency. With the increase of the doping (oxidation) degree, the electrochromic materials can form polaron and bipolaron energy levels with lower band gap between the valence band and the conduction band, and the formation of these new energy levels changes the energy required in the valence electron transition, which is manifested as a change in the absorption edge in spectroelectrochemistry. Such materials show broad commercial prospects in many fields such as military camouflage, low-energy display devices, electronic paper, color-changing skin, information storage and display, and can be used for updating and functional integration of various wearable electronic devices.

[0003] The evaluation of the performance of electrochromic materials is the most important problem, and researchers evaluate the electrochromic performance with the following parameters and indexes:

[0004] (1) Optical contrast (Electrochromic contrast, ΔT): the difference between the optical transmittance (T ox and T neut ) of the oxidized state and the neutral state of the electrochromic material at a single wavelength, which is one of the important parameters for measuring the electrochromic performance of the material. This wavelength is determined according to the absorption spectrum of the material (the same material may also have multiple wavelengths), that is, the wavelength corresponding to the maximum absorption edge of the material in the oxidized state or the neutral state. The absorption spectrum of the material refers to the absorbance or transmittance curve corresponding to different wavelengths, the color change of the material is measured by the size of the absorbance, and the electrochromic performance of the material is measured by the degree of change in transmittance at a specific wavelength. In addition, spectroelectrochemical experiments can also reflect the generation of monopolarons or bipolarons in the material according to different applied voltages.

[0005] (2) Coloration efficiency (Coloration efficiency, CE): refers to the ratio between the change in absorbance of the electrochromic material at a specific wavelength and the charge density generated when a certain amount of charge is injected into the conductive polymer film per unit area. Generally, the coloration efficiency of the same polymer film is fixed and does not change during the oxidation or reduction process, and is also independent of the thickness of the film. The formula for calculating the coloration efficiency is:

[0006] CE=ΔOD / QdΔOD=log(T ox / T ref )

[0007] where ΔOD is the optical density change value, refers to the ratio of the transmittance of the oxidized state and the reduced state of the polymer thin film at a specific wavelength λ max d Q is the charge density, refers to the amount of charge injected per unit area.

[0008] (3) Response time: the time required for the electrochromic material or device to complete an oxidation (colored state) or reduction (bleached state) conversion process, the oxidation (coloring) process corresponds to the coloring response time, and the reduction (bleaching) process corresponds to the bleaching response time. The response time is generally calculated by the time required for the transmittance to change by 95%. The factors affecting the conversion time mainly include: the composition of the electrolyte (the acidity and basicity of the solvent, the ion conductivity of the supporting electrolyte), the applied voltage of the oxidation-reduction process, and the ease of ion diffusion in the electrochromic material, etc.

[0009] (4) Open circuit memory: refers to the ability of the electrochromic material to maintain the oxidized state or reduced state color without applying an external voltage. In operation, the optical transmittance of the polymer is tested under the application of an external voltage for a certain time, then the external voltage is disconnected, and the optical transmittance is tested. The change is the memory degree of the material or device. Related applications are that light-emitting diodes (LEDs) can maintain the displayed content in the case of power failure. It is worth noting that for electrochromic materials or devices that display color in solution, due to ion diffusion or exchange, the color displayed by the electrochromic material or device will quickly fade, while all-solid-state electrochromic devices have good memory effect.

[0010] ​The current requirements for electrochromic materials and devices are mainly high optical contrast, high coloring efficiency, short response time, good memory effect, obvious color change, good stability, etc. Prof. Reynolds of Georgia Institute of Technology, Prof. Toppare of Turkey, Prof. Xu Chunye of Chinese Academy of Sciences, Prof. Meng Hong of Peking University, Prof. Jia Chunyang of University of Electronic Science and Technology of China, and Prof. Xu Jingkun of Jiangxi Science and Technology Normal University have made important contributions in the field of electrochromic materials. Multicolor electrochromic materials have great prospects in military camouflage, electrochromic displays and other fields due to their rich colors. However, most of them use mixed electrochromic materials to adjust color, which can also bring new problems, such as the inconsistency of the oxidation and reduction voltages of the two materials, thereby affecting the service life of the device. To solve this problem, we invented a kind of multicolor electrochromic material, which realizes multicolor change through a single material. The pursuit of high-performance electrochromic materials and devices has always been an important mission for researchers. On the one hand, researchers optimize the performance of existing materials to achieve performance breakthroughs. On the other hand, researchers continuously develop new electrochromic materials to achieve more efficient and stable electrochromic performance. SUMMARY

[0011] Based on the above defects, one object of the present application is to provide an electrochromic polymer which can realize yellow-green-blue-purple multicolor electrochromism with a single material.

[0012] The electrochromic polymer has a general structure as shown in general formula (I),

[0013]

[0014] The general structure includes a spirobifluorene unit and an M unit;

[0015] The M unit is selected from a monocyclic or polycyclic structure containing a thiophene structure;

[0016] The monocyclic or polycyclic structure containing a thiophene structure further has a cycloalkyl chain or a cycloalkylene chain;

[0017] n represents the degree of polymerization, and n is an integer from 1 to 10000.

[0018] Further, the M unit is selected from the following structures:

[0019]

[0020] "*" represents the position of the chemical bond between the M unit and the spirobifluorene unit.

[0021] R1, R2 are independently selected from a C3-C 22 alkyl chain or a C3-C 22 alkoxy chain.

[0022] Another object of the present application is to provide a preparation method of the electrochromic polymer.

[0023] Further, the raw material (II) of the spirobifluorene unit has the following structure:

[0024]

[0025] wherein D is selected from one of fluorine, chlorine, bromine or iodine;

[0026] The raw material (III) of the M unit has the following structure:

[0027]

[0028] wherein -H is the H atom at the beta and epsilon positions of the thiophene ring;

[0029] The preparation method of the electrochromic polymer comprises the following steps:

[0030] Under an inert atmosphere, the raw material (II), the raw material (III), pivalic acid, cesium carbonate and other catalysts are added into a reaction solvent, and after heating reaction, the unreacted raw materials are removed to obtain the electrochromic polymer.

[0031] Further, the molar ratio of the raw material (II) to the raw material (III) is 1:2.

[0032] Further, the heating reaction temperature is 100-120℃, and the time is 6-24h.

[0033] Further, the catalyst is a zero-valent palladium or divalent palladium catalyst.

[0034] Further, the solvent is selected from one or more of dimethylacetamide, formamide, acetonitrile, ethanol, acetone, methanol, diethyl ether, chloroform, dichloromethane, dimethyl sulfoxide and toluene.

[0035] Another object of the present application is to provide the application of the above-mentioned electrochromic polymer in the field of electrochromism.

[0036] The present application has the following beneficial effects:

[0037] 1. The novel electrochromic polymer provided by the present application has a clear porous structure, providing ion transmission channels and being conducive to ion transmission.

[0038] 2. The novel electrochromic polymer provided by the present application has excellent yellow-green-blue-purple multicolor change electrochromic performance, and has great application prospects in the field of dynamic camouflage.

[0039] 3.The novel electrochromic polymer provided by the application has solution processing, good flexibility, and wide application prospects in the field of flexible electronics. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A spectroelectrochemical diagram of an electrochromic polymer thin film in an application example is shown.

[0041] Figure 2 A kinetic stability diagram of an electrochromic polymer thin film in an application example is shown. DETAILED DESCRIPTION

[0042] The application is further described below through specific examples, which aims to help better understand the content of the application, and specifically includes the synthesis of polymers and device preparation methods, but these specific embodiments do not limit the protection scope of the application in any way. The raw materials, reactions and post-treatment methods appearing in the examples are all common raw materials on the market unless otherwise stated.

[0043] The practice of the application can adopt conventional techniques of polymer chemistry within the skill in the art. In the following examples, efforts have been made to ensure the accuracy of the numbers (including amounts, temperature, reaction time, etc.) used, but some experimental errors and deviations should be considered. The temperatures used in the following examples are expressed in ℃, and the pressure is atmospheric pressure or close to atmospheric pressure. The solvents used are purchased as analytical or chromatographic pure, and all reactions are carried out in a nitrogen atmosphere. Unless otherwise indicated, all reagents are commercially available.

[0044] The following raw materials are used in the examples of the application:

[0045] ProDOT: 3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thieno[3,4-B][1,4]dioxepine, purchased from Suzhou Nakai Company.

[0046] N-N-dimethylacetamide (DMAc) purchased from Aladdin Reagent (Shanghai) Co., Ltd.;

[0047] Tris(dibenzylacetone)dipalladium-chloroform adduct (Pd(dba)3-CHCl3), cesium carbonate (Cs2CO3), purchased from Energy Chemical Co., Ltd.;

[0048] 2,2',7,7'-Tetrabromo-9,9'-spirobifluorene, purchased from Suzhou Nakai Company;

[0049] Pivalic acid, purchased from Tokyo Chemical Industry Co., Ltd.

[0050] EXAMPLE

[0051] An electrochromic polymer, the chemical reaction process of which is shown as follows:

[0052]

[0053] The specific reaction steps and reaction conditions are as follows:

[0054] 2,2′,7,7′-tetrabromo-9,9′-spirodifluorene (0.5 mmol), ProDOT (1 mmol), pentovalinic acid (0.15 mmol), palladium catalyst (0.025 mmol), and cesium carbonate (1.25 mmol) were added to a pressure-resistant flask. Nitrogen gas was then introduced into the flask for 20 min to purge air, and the flask was then closed. The flask was magnetically stirred in a constant-temperature oil bath at 120 °C for 12 h to carry out the reaction. After cooling to room temperature, the precipitate was washed with anhydrous ethanol and the precipitate was removed. The precipitate was then washed sequentially with ethanol, acetone, n-hexane, dichloromethane, and chloroform in a Soxhlet extractor until colorless. Finally, rotary evaporation was performed to remove excess solvent, yielding the polymer product in 78% yield with a number-average molecular weight of 11370 Da.

[0055] Application examples

[0056] The material prepared in the example was dissolved in chloroform solution and sprayed onto ITO conductive glass to form a polymer film. The film was then placed in a three-electrode electrolytic cell containing an acetonitrile solution of tetrabutylammonium hexafluoride. The working electrode was ITO conductive glass with the polymer film attached, the counter electrode was a platinum wire, and the reference electrode was an Ag / AgCl electrode.

[0057] Test Example 1

[0058] The polymer thin film in the corresponding use case was subjected to spectroelectrochemical testing.

[0059] Using a potentiostatic method, the voltage applied to the working electrode in the application example was adjusted by an electrochemical workstation, while the change trend of the absorption spectrum of the polymer film in the application example under different voltages was recorded by a UV-Vis spectrometer.

[0060] Figure 1 The spectroelectrochemical spectra of the polymer thin film in the application example are shown.

[0061] Depend on Figure 1 It can be seen that as the voltage increases, the absorption edge intensity weakens and shifts at 430 nm, and new absorption edges generated by polaron absorption gradually appear and shift in the near-infrared region. This shift in absorption edge indicates that the electrochromic polymer of the present invention has multiple color changes with the applied voltage.

[0062] Test Example 2

[0063] The kinetic stability of the polymer film in the corresponding use case was studied.

[0064] A UV-Vis spectrophotometer is used to measure the transmittance of polymer films in their oxidized and reduced states at a specific wavelength under a square wave potential, thereby calculating optical contrast, response time, and other parameters. The UV-Vis spectrophotometer records a time-transmittance curve, while the electrochemical workstation records a time-current curve. The coloring efficiency can also be calculated from these two curves.

[0065] Figure 2 The kinetic stability diagram of the polymer in the application example is shown, with a square wave potential interval of 10 s.

[0066] Depend on Figure 2 It is known that the optical contrast ratio of polymers is about 16% (424nm) and 7% (568nm). Although the optical contrast ratio is not high, the color change is obvious. This is because electrochromic materials with transparent states in oxidized and colored states often have high optical contrast. However, in multicolor materials, the optical contrast ratio is often not high, but their excellent electrochromic performance is undeniable.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0068] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An electrochromic polymer, characterized in that, A structural general formula is shown as general formula (I), The preparation method of the electrochromic polymer comprises the following steps: The raw material (II), the raw material (III), pivalic acid, cesium carbonate and a catalyst are added into a solvent under an inert atmosphere, and a heating reaction is performed to obtain the electrochromic polymer; The raw material (II) has the following structure: D is selected from one of fluorine, chlorine, bromine or iodine; The raw material (III) has the following structure:

2. The electrochromic polymer according to claim 1, characterized in that, The molar ratio of the raw material (II) to the raw material (III) is 1:

2.

3. The electrochromic polymer of claim 1, wherein, The heating reaction is performed at a temperature of 100-120 DEG C for 6-24 hours.

4. The electrochromic polymer of claim 1, wherein, The catalyst is a zero-valent palladium or bivalent palladium catalyst.

5. The electrochromic polymer of claim 1, wherein, The solvent is selected from one or more of dimethylacetamide, formamide, acetonitrile, ethanol, acetone, methanol, diethyl ether, chloroform, dichloromethane, dimethyl sulfoxide and xylene.

6. The electrochromic polymer of claim 1 is applied in the field of electrochromism.

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