Electrochromic polymer with red-transparent display and preparation method thereof

Abstract

The invention belongs to the technical field of electrochromic materials, and provides a red-transparent display electrochromic polymer and a preparation method thereof. The method disclosed by the invention comprises the following steps: carrying out ring formation reaction on N-(2, 5-dibromophenyl)-2-ethylhexyl thioamide, potassium ferricyanide and sodium hydroxide to obtain 4, 7-dibromo-2-(heptane-3-yl) benzothiazole; the preparation method comprises the following steps: carrying out substitution reaction on EDOT, n-butyllithium and tributyltin chloride to obtain EDOT-Sn; the preparation method comprises the following steps: carrying out Stille coupling reaction on 2, 4, 7-dibromo-2-(heptane-3-yl) benzothiazole and EDOT-Sn, and then carrying out electrochemical polymerization reaction to obtain the electrochromic polymer. A pure donor (D) type organic molecule is obtained by the method, a corresponding electrochromic film is prepared by electrochemical polymerization, reversible switching between red and transparency is realized, and the electrochromic film has good cycle stability and high color change response speed.

Description

Technical Field

[0001] The invention relates to the technical field of electrochromic materials, and in particular to an electrochromic polymer with red-transparent display and a preparation method thereof. Background Art

[0002] Electrochromic materials can be divided into inorganic electrochromic materials and organic electrochromic materials. Conductive polymer electrochromic materials (ECPs) have many advantages over inorganic or organic small molecule materials, including simple structural design, diverse coloring, high coloring efficiency, manufacturing of large-area or flexible devices, etc., and have rapid development potential. Since electrochromic materials for display must include a transparent state, the introduction of 3,4-ethylenedioxythiophene (EDOT) as the D structure is necessary. Literature shows that the enlargement of the substituted ring at the 3 and 4 positions of thiophene and the introduction of additional substituents can not only retain the high transmittance in the oxidized state, but also significantly improve the solubility of the monomer and the electrochromic properties of the polymer.

[0003] Red is the basic component color of the additive tricolor (red, green, and blue), and plays a very important role in color regulation and rich display effects. The realization of red in the neutral state of conductive polymers requires the optical absorption of high energy bands, which is manifested as single absorption in the visible light band. Donor (D) type polymers are conducive to the realization of red due to their wide energy gap. In recent years, there have been many studies on the preparation of "green-transparent" and "blue-transparent" materials by electropolymerization, but due to the lack of suitable donor structures, there are relatively few studies on the preparation of "red-transparent" materials by electropolymerization. The Gunbas research group prepared red-transparent electrochromic films by electrochemical polymerization through structural modification of phenanthrocarbazole, but there are more absorption residues in the oxidized state, which cannot achieve complete transparency, and the cyclic stability of the film is not ideal. Therefore, it is an urgent problem to find a suitable donor structure and prepare electrochromic materials that are red in the neutral state, completely transparent in the oxidized state, and have high cyclic stability by electropolymerization.

[0004] Benzothiazole derivatives are often used to make light-emitting diodes and solar cells due to their excellent photoelectric properties and thermal stability, but there are few reports in the field of electrochromism. Therefore, it is of great significance to study a red-transparent electrochromic polymer based on benzothiazole derivatives and its preparation method. Summary of the invention

[0005] The object of the present invention is to provide a red-transparent electrochromic polymer and a preparation method thereof in order to overcome the deficiencies of the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides an electrochromic polymer with a red-transparent display, and the structural formula of the electrochromic polymer is:

[0008]

[0009] Wherein, n is the average degree of polymerization, and the value of n is 100 to 2000;

[0010] The red-transparent electrochromic polymer is obtained from a red-transparent electrochromic monomer compound through an electrochemical polymerization reaction; the structural formula of the electrochromic monomer compound is:

[0011]

[0012] The present invention also provides a method for preparing the electrochromic polymer with red-transparent display, comprising the following steps:

[0013] 1) 2,5-dibromoaniline and 2-ethylhexanoyl chloride undergo substitution reaction to obtain N-(2,5-dibromophenyl)-2-ethylhexanoylamide;

[0014] 2) N-(2,5-dibromophenyl)-2-ethylhexanamide and phosphorus pentasulfide undergo a sulfurization reaction to obtain N-(2,5-dibromophenyl)-2-ethylhexanthioamide;

[0015] 3) N-(2,5-dibromophenyl)-2-ethylhexanethioamide, potassium ferrocyanide and sodium hydroxide undergo cyclization reaction to obtain 4,7-dibromo-2-(heptane-3-yl)benzothiazole;

[0016] 4) 3,4-ethylenedioxythiophene, n-butyl lithium and tributyltin chloride are mixed and subjected to substitution reaction to obtain a tinated EDOT derivative EDOT-Sn;

[0017] 5) 4,7-dibromo-2-(heptane-3-yl)benzothiazole and EDOT-Sn undergo Stille coupling reaction under the catalysis of a palladium catalyst to obtain an electrochromic monomer compound;

[0018] 6) The electrochromic monomer compound undergoes an electrochemical polymerization reaction to obtain an electrochromic polymer having a red-transparent display.

[0019] Preferably, in step 1), the molar ratio of 2,5-dibromoaniline to 2-ethylhexanoyl chloride is 1-1.2:1-1.2, the temperature of the substitution reaction is 100-120° C., and the time of the substitution reaction is 1.5-2.5 h;

[0020] The solvent for the substitution reaction is pyridine, and the mass volume ratio of 2,5-dibromoaniline to pyridine is 1 g:13-20 mL.

[0021] Preferably, in step 2), the molar ratio of N-(2,5-dibromophenyl)-2-ethylhexanamide to phosphorus pentasulfide is 1.8-2.5:1, the temperature of the sulfurization reaction is 100-120° C., and the time of the sulfurization reaction is 2.5-3.5 h;

[0022] The solvent for the sulfidation reaction is anhydrous toluene, and the mass volume ratio of N-(2,5-dibromophenyl)-2-ethylhexylamide to anhydrous toluene is 1 g:13-20 mL.

[0023] Preferably, in step 3), the molar ratio of N-(2,5-dibromophenyl)-2-ethylhexanethioamide, potassium ferrocyanide and sodium hydroxide is 1:3.7-4.3:7-9; the temperature of the cyclization reaction is 85-105° C., and the time of the cyclization reaction is 2.5-3.5 h;

[0024] The solvents for the cyclization reaction are water and anhydrous ethanol, and the volume ratio of water to anhydrous ethanol is 17-19:1; the mass volume ratio of N-(2,5-dibromophenyl)-2-ethylhexanethioamide to water is 1g:17-20mL.

[0025] Preferably, in step 4), the molar ratio of 3,4-ethylenedioxythiophene, n-butyllithium and tributyltin chloride is 1:1 to 1.2:1 to 1.6, the mixing temperature is -80 to -75°C, and the substitution reaction is carried out at room temperature.

[0026] Preferably, in step 4), the n-butyl lithium is an n-butyl lithium solution having a concentration of 1 to 3 mol / L, and the tributyltin chloride is a tributyltin chloride solution having a concentration of 1 to 5 g / mL;

[0027] Step 4) The solvent for the substitution reaction is tetrahydrofuran, and the mass volume ratio of 3,4-ethylenedioxythiophene to tetrahydrofuran is 1g:15-25mL.

[0028] Preferably, in step 5), the molar ratio of 4,7-dibromo-2-(heptane-3-yl)benzothiazole, EDOT-Sn and palladium catalyst is 1:2-6:0.01-0.1; the Stille coupling reaction time is 45-50 hours; the palladium catalyst is palladium acetate, tetrakis(triphenylphosphine)palladium or dichlorobis(triphenylphosphine)palladium;

[0029] The solvent of the Stille coupling reaction is N,N-dimethylformamide, and the mass volume ratio of 4,7-dibromo-2-(heptane-3-yl)benzothiazole to N,N-dimethylformamide is 1 g:30-40 mL.

[0030] Preferably, the substitution reaction in step 1), the sulfurization reaction in step 2), the cyclization reaction in step 3), the substitution reaction in step 4) and the Stille coupling reaction in step 5) are carried out under a nitrogen atmosphere.

[0031] Preferably, the solvent of the electrochemical polymerization reaction in step 6) is acetonitrile, the electrolyte is tetra-n-butylammonium hexafluorophosphonate, the concentration of the electrochromic monomer compound is 0.5-1 mmol / L, and the concentration of tetra-n-butylammonium hexafluorophosphonate is 0.05-0.1 mol / L;

[0032] The electrochemical polymerization reaction is a cyclic voltammetry electrochemical polymerization reaction, the scanning speed of the cyclic voltammetry electrochemical polymerization reaction is 90-110 mV / s, the voltage is -0.2-1.1 V, and the number of cycles is 10.

[0033] The beneficial effects of the present invention include the following:

[0034] 1) The electrochromic material of the present invention has a new structural representative that has not been involved in current research. A pure donor (D) type organic molecule is designed and synthesized using a benzothiazole derivative (PBTZ-2Br) as a conjugated core and 3,4-ethylenedioxythiophene (EDOT) as a monomer compound of an electroactive polymerization unit. A uniform and smooth polymer film (PBTZ-EDOT) is formed through electrochemical polymerization. The preparation is simple and effective. The polymer film exhibits good electrochromic properties, can achieve reversible switching between red and transparent, and has good cycle stability and a faster color change response speed.

[0035] 2) The polymer film prepared by the present invention can achieve reversible switching from red to transparent under different voltage windows; the film is pure red in the neutral state, and has almost no absorption residue in the oxidized state, showing high transparency. In the 535nm band, the optical contrast is 25.2%. After 1000 cycles, the optical contrast of the film is 21.26%, with no obvious attenuation, showing very excellent electrochemical stability. In addition to the stable color change behavior, the film has a faster response time of 0.6s / 0.26s in the 535nm band. The PBTZ-EDOT of the present invention is an excellent new electrochromic material with potential research prospects in display fields such as electronic paper and electronic tags. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The synthetic route of the electrochromic monomer compound (PBTZ-EDOT) of the present invention;

[0037] Figure 2 is an electrochemical polymerization curve of the electrochromic monomer compound (PBTZ-EDOT) of Example 1;

[0038] Figure 3 The cyclic voltammetry curves of the electrochromic polymer film of Example 1 at different current sweep rates;

[0039] Figure 4 The figure is a UV-visible absorption spectrum of the electrochromic polymer film of Example 1 at a voltage of -0.2 to 0.7 V;

[0040] Figure 5 Graph showing contrast and spectral dynamic stability of the electrochromic polymer film of Example 1 at 535 nm;

[0041] Figure 6 This is a response time diagram of the electrochromic polymer film of Example 1 in the 535nm band;

[0042] Figure 7 : is the chromaticity curve of the electrochromic polymer film of Example 1 at different voltages. DETAILED DESCRIPTION

[0043] The present invention provides an electrochromic polymer with a red-transparent display, and the structural formula of the electrochromic polymer is:

[0044]

[0045] Wherein, n is the average degree of polymerization, and the value of n is 100 to 2000;

[0046] The red-transparent electrochromic polymer is obtained from a red-transparent electrochromic monomer compound through an electrochemical polymerization reaction; the structural formula of the electrochromic monomer compound is:

[0047]

[0048] In the electrochromic polymer of the present invention, the value of n is preferably 300-1500, more preferably 500-1200, and even more preferably 800-1000.

[0049] The present invention also provides a method for preparing the electrochromic polymer with red-transparent display, comprising the following steps:

[0050] 1) 2,5-dibromoaniline and 2-ethylhexanoyl chloride undergo substitution reaction to obtain N-(2,5-dibromophenyl)-2-ethylhexanoylamide;

[0051] 2) N-(2,5-dibromophenyl)-2-ethylhexanamide and phosphorus pentasulfide undergo a sulfurization reaction to obtain N-(2,5-dibromophenyl)-2-ethylhexanthioamide;

[0052] 3) N-(2,5-dibromophenyl)-2-ethylhexanethioamide, potassium ferrocyanide and sodium hydroxide undergo cyclization reaction to obtain 4,7-dibromo-2-(heptane-3-yl)benzothiazole;

[0053] 4) 3,4-ethylenedioxythiophene, n-butyl lithium and tributyltin chloride are mixed and subjected to substitution reaction to obtain a tinated EDOT derivative EDOT-Sn;

[0054] 5) 4,7-dibromo-2-(heptane-3-yl)benzothiazole and EDOT-Sn undergo Stille coupling reaction under the catalysis of a palladium catalyst to obtain an electrochromic monomer compound;

[0055] 6) The electrochromic monomer compound undergoes an electrochemical polymerization reaction to obtain an electrochromic polymer having a red-transparent display.

[0056] In the present invention, the molar ratio of 2,5-dibromoaniline and 2-ethylhexanoyl chloride in step 1) is preferably 1-1.2:1-1.2, more preferably 1-1.1:1-1.1, and more preferably 1:1; the temperature of the substitution reaction is preferably 100-120°C, more preferably 105-115°C, and more preferably 110°C; the time of the substitution reaction is preferably 1.5-2.5h, and more preferably 2h;

[0057] The solvent for the substitution reaction is preferably pyridine, and the mass volume ratio of 2,5-dibromoaniline to pyridine is preferably 1 g:13-20 mL, more preferably 1 g:15-18 mL, and even more preferably 1 g:16-17 mL.

[0058] In the present invention, the molar ratio of N-(2,5-dibromophenyl)-2-ethylhexanamide and phosphorus pentasulfide in step 2) is preferably 1.8 to 2.5:1, more preferably 2 to 2.3:1, and more preferably 2.1 to 2.2:1. The temperature of the sulfurization reaction is preferably 100 to 120°C, more preferably 105 to 115°C, and more preferably 110°C. The sulfurization reaction time is preferably 2.5 to 3.5 hours, and more preferably 3 hours.

[0059] The solvent for the sulfidation reaction is preferably anhydrous toluene, and the mass volume ratio of N-(2,5-dibromophenyl)-2-ethylhexanamide to anhydrous toluene is preferably 1 g:13-20 mL, more preferably 1 g:15-18 mL, and more preferably 1 g:16-17 mL.

[0060] In the present invention, the molar ratio of N-(2,5-dibromophenyl)-2-ethylhexanethioamide, potassium ferrocyanide and sodium hydroxide in step 3) is preferably 1:3.7-4.3:7-9, more preferably 1:3.8-4.2:7.5-8.5, more preferably 1:4:8; the temperature of the cyclization reaction is preferably 85-105°C, more preferably 90-100°C, more preferably 95°C, and the cyclization reaction time is preferably 2.5-3.5h, more preferably 3h;

[0061] The solvent for the cyclization reaction is preferably water and anhydrous ethanol, and the volume ratio of water to anhydrous ethanol is preferably 17 to 19:1, more preferably 17.5 to 18.5:1, and more preferably 18:1; the mass volume ratio of N-(2,5-dibromophenyl)-2-ethylhexanethioamide and water is preferably 1 g:17 to 20 mL, and more preferably 1 g:18 to 19 mL.

[0062] In the present invention, the molar ratio of 3,4-ethylenedioxythiophene, n-butyllithium and tributyltin chloride in step 4) is preferably 1:1-1.2:1-1.6, more preferably 1:1.05-1.15:1.1-1.5, more preferably 1:1.1:1.2-1.3, the mixing temperature is preferably -80--75°C, more preferably -79--76°C, more preferably -78--77°C, and the substitution reaction is preferably carried out at room temperature.

[0063] In the present invention, the n-butyl lithium in step 4) is an n-butyl lithium solution, and the concentration of the n-butyl lithium solution is preferably 1-3 mol / L, more preferably 1.5-2.5 mol / L, and more preferably 2 mol / L; the tributyltin chloride is a tributyltin chloride solution, and the concentration of the tributyltin chloride solution is preferably 1-5 g / mL, more preferably 2-4 g / mL, and more preferably 3 g / mL;

[0064] Step 4) The solvent for the substitution reaction is preferably tetrahydrofuran, and the mass volume ratio of 3,4-ethylenedioxythiophene to tetrahydrofuran is preferably 1 g:15-25 mL, more preferably 1 g:18-22 mL, and more preferably 1 g:20 mL.

[0065] In the present invention, the molar ratio of 4,7-dibromo-2-(heptane-3-yl)benzothiazole, EDOT-Sn and palladium catalyst in step 5) is preferably 1:2-6:0.01-0.1, more preferably 1:3-5:0.02-0.08, and more preferably 1:4:0.04-0.05; the time of the Stille coupling reaction is preferably 45-50h, more preferably 46-49h, and more preferably 47-48h; the palladium catalyst is preferably palladium acetate, tetrakis(triphenylphosphine)palladium or dichlorobis(triphenylphosphine)palladium;

[0066] The solvent for the Stille coupling reaction is preferably N,N-dimethylformamide, and the mass volume ratio of 4,7-dibromo-2-(heptane-3-yl)benzothiazole to N,N-dimethylformamide is preferably 1 g:30-40 mL, more preferably 1 g:33-37 mL, and more preferably 1 g:35 mL.

[0067] In the present invention, the substitution reaction in step 1), the sulfurization reaction in step 2), the cyclization reaction in step 3), the substitution reaction in step 4) and the Stille coupling reaction in step 5) are preferably carried out under a nitrogen atmosphere.

[0068] In the present invention, the solvent of the electrochemical polymerization reaction in step 6) is preferably acetonitrile, the electrolyte is preferably tetra-n-butylammonium hexafluorophosphonate, the concentration of the electrochromic monomer compound is preferably 0.5-1 mmol / L, more preferably 0.6-0.9 mmol / L, more preferably 0.7-0.8 mmol / L, and the concentration of tetra-n-butylammonium hexafluorophosphonate is preferably 0.05-0.1 mol / L, more preferably 0.06-0.09 mol / L, more preferably 0.07-0.08 mol / L;

[0069] The electrochemical polymerization reaction is preferably a cyclic voltammetry electrochemical polymerization reaction. The scan rate of the cyclic voltammetry electrochemical polymerization reaction is preferably 90 to 110 mV / s, further preferably 95 to 105 mV / s, more preferably 100 mV / s, the voltage is preferably -0.2 to 1.1 V, further preferably -0.2 to 0.8 V, more preferably -0.2 to 0.7 V, and the number of cycles is preferably 10.

[0070] In the present invention, the structural formulas of 2,5-dibromoaniline and N-(2,5-dibromophenyl)-2-ethylhexanamide are respectively:

[0071]

[0072] The structural formulas of N-(2,5-dibromophenyl)-2-ethylhexanethioamide, 4,7-dibromo-2-(heptane-3-yl)benzothiazole and EDOT-Sn are:

[0073]

[0074] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0075] Example 1

[0076] Synthesis of N-(2,5-dibromophenyl)-2-ethylhexanamide: 12.1mmol of 2,5-dibromoaniline was dissolved in 45mL of pyridine. Under a nitrogen atmosphere, 12.1mmol of 2-ethylhexanoyl chloride was slowly added to the pyridine solution of 2,5-dibromoaniline. The mixture was heated to reflux at 110°C for 2h. The cooled solution was poured into 200mL of ice water, and 100mL of ethyl acetate was added. The aqueous layer was extracted with 200mL of ethyl acetate. The synthesized organic layer was dried over anhydrous MgSO4, filtered and concentrated by vacuum evaporation. The white solid compound N-(2,5-dibromophenyl)-2-ethylhexanamide (4.0g, 80%) was obtained by rotary evaporation.

[0077] Synthesis of N-(2,5-dibromophenyl)-2-ethylhexylthioamide: 5.08mmol N-(2,5-dibromophenyl)-2-ethylhexylthioamide was added to a mixture of 2.54mmol phosphorus pentasulfide and 30mL anhydrous toluene. Under nitrogen protection, the bright yellow suspension was heated and gently refluxed at 110°C for 3h. The solution was then cooled to 0°C and filtered. The insoluble part was dissolved with 50mL ethyl acetate and then extracted with water three times. The organic phase was collected and concentrated, and purified by column chromatography, with silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether in a volume ratio of 1:4 as the mobile phase. The eluent of the target compound was collected and dried to obtain an orange solid compound N-(2,5-dibromophenyl)-2-ethylhexylthioamide (1.80g, 75%).

[0078] Synthesis of 4,7-dibromo-2-(heptane-3-yl)benzothiazole (PBTZ-2Br): 10.68mmol N-(2,5-dibromophenyl)-2-ethylhexanethioamide, 42.72mmol potassium ferrocyanide, and 85.44mmol sodium hydroxide were added to a mixture of water and ethanol (75.6mL of water and 4.2mL of anhydrous ethanol), and then stirred at 95°C for 3h under nitrogen protection. The mixture was cooled in an ice bath to obtain a precipitate. The precipitate was then filtered and washed with water. After washing with water, ethyl acetate was added to dissolve the precipitate, and the water was removed with anhydrous sodium sulfate and concentrated by vacuum evaporation. The stationary phase was silica gel, and a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:5 was used as the mobile phase. The eluent containing the target compound was collected by thin layer chromatography, and the solvent was removed by thin layer chromatography. The yellow oily monomer 4,7-dibromo-2-(heptane-3-yl)benzothiazole (PBTZ-2Br) (2.1 g, 50%) was obtained by rotary evaporation and drying.

[0079] Synthesis of EDOT-Sn: Under nitrogen protection, 7.03 mmol EDOT was dissolved in 20 mL anhydrous tetrahydrofuran, and then 3.37 mL of n-butyl lithium hexane solution (the concentration of n-butyl lithium was 2.5 mol / L) was added dropwise through a syringe at -78°C. After stirring at this temperature for 1 hour, 1 mL of tributyltin chloride solution (the concentration of tributyltin chloride was 2.97 g / mL) was added. After the addition of the tributyltin chloride solution, the mixture was returned to room temperature and stirred for 24 hours. After the reaction was completed, the obtained reaction solution was separated and purified by an alumina chromatography column to obtain a crude product of the compound EDOT-Sn with a yield of 80%.

[0080] Synthesis of PBTZ-EDOT: Under nitrogen protection, 0.767mmol PBTZ-2Br, 2.3mmol EDOT-Sn, and 0.035mmol tetrakis(triphenylphosphine)palladium were added to a two-necked round-bottom flask in sequence, and then 10mL anhydrous N,N-dimethylformamide (DMF) was added. The reaction was refluxed for 48h under stirring. After the reaction, the obtained reaction solution was poured into 100mL deionized water and mixed, and the precipitate was collected by filtration. The precipitate was then extracted with saturated sodium chloride solution and dichloromethane, the organic phase was collected and dried with anhydrous sodium sulfate, and finally a mixture of petroleum ether and dichloromethane in a volume ratio of 1:5 was used as the mobile phase. The electrochromic monomer compound (PBTZ-EDOT) was purified by silica gel column chromatography.

[0081] Synthesis of electrochromic polymer with red-transparent display: The monomer PBTZ-EDOT was dissolved in chromatographic grade acetonitrile, the concentration of PBTZ-EDOT was 1 mmol / L, and then 0.1 mol / L of tetra-n-butylammonium hexafluorophosphonate was added as an electrolyte. Cyclic voltammetry electrochemical polymerization was carried out in a three-electrode system (ITO conductive glass as the working electrode, platinum wire as the counter electrode, and Ag / AgCl as the reference electrode) to obtain an electrochromic polymer film attached to the ITO glass. The scanning speed of the cyclic voltammetry was 100 mV / s, the voltage was -0.2 to 1.1 V, and the number of cycles was 10.

[0082] Example 2

[0083] Synthesis of N-(2,5-dibromophenyl)-2-ethylhexanamide: 12.1mmol of 2,5-dibromoaniline was dissolved in 55mL of pyridine. Under a nitrogen atmosphere, 14mmol of 2-ethylhexanoyl chloride was slowly added to the pyridine solution of 2,5-dibromoaniline. The mixture was heated to reflux at 115°C for 2.5h. The cooled solution was poured into 200mL of ice water, and 100mL of ethyl acetate was added. The aqueous layer was extracted with 200mL of ethyl acetate. The synthesized organic layer was dried over anhydrous MgSO4, filtered and concentrated by vacuum evaporation. The white solid compound N-(2,5-dibromophenyl)-2-ethylhexanamide was obtained by rotary evaporation.

[0084] Synthesis of N-(2,5-dibromophenyl)-2-ethylhexylthioamide: 5.08mmol N-(2,5-dibromophenyl)-2-ethylhexylthioamide was added to a mixture of 2.21mmol phosphorus pentasulfide and 40mL anhydrous toluene. Under nitrogen protection, the bright yellow suspension was heated and gently refluxed at 115°C for 3h. The solution was then cooled to 0°C and filtered. The insoluble part was dissolved with 60mL ethyl acetate and then extracted with water three times. The organic phase was collected and concentrated, and purified by column chromatography, with silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether in a volume ratio of 1:4 as the mobile phase. The eluent of the target compound was collected and dried to obtain an orange solid compound N-(2,5-dibromophenyl)-2-ethylhexylthioamide.

[0085] Synthesis of 4,7-dibromo-2-(heptane-3-yl)benzothiazole (PBTZ-2Br): 10.68mmol N-(2,5-dibromophenyl)-2-ethylhexanethioamide, 40.6mmol potassium ferrocyanide, and 82.5mmol sodium hydroxide were added to a mixture of water and ethanol (72.5mL of water and 4.2mL of anhydrous ethanol), and then stirred at 90°C for 3.5h under nitrogen protection. The mixture was cooled in an ice bath to obtain a precipitate. The precipitate was then filtered and washed with water. After washing with water, ethyl acetate was added to dissolve the precipitate, and the water was removed with anhydrous sodium sulfate and concentrated by vacuum evaporation. The stationary phase was silica gel, and a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:5 was used as the mobile phase. The eluent containing the target compound was collected by thin layer chromatography, and the solvent was removed by thin layer chromatography. The yellow oily monomer 4,7-dibromo-2-(heptane-3-yl)benzothiazole (PBTZ-2Br) was obtained by rotary evaporation and drying.

[0086] Synthesis of EDOT-Sn: Under nitrogen protection, 7.03 mmol EDOT was dissolved in 18 mL anhydrous tetrahydrofuran, and then 3.9 mL of n-butyl lithium hexane solution (the concentration of n-butyl lithium was 2 mol / L) was added dropwise through a syringe at -80°C. After stirring at this temperature for 1 hour, 1 mL of tributyltin chloride solution (the concentration of tributyltin chloride was 2.5 g / mL) was added. After the addition of the tributyltin chloride solution, the mixture was returned to room temperature and stirred for 24 hours. After the reaction was completed, the obtained reaction solution was separated and purified by an alumina chromatography column to obtain a crude product of the compound EDOT-Sn.

[0087] Synthesis of PBTZ-EDOT: Under nitrogen protection, 0.767mmol PBTZ-2Br, 3.8mmol EDOT-Sn, and 0.04mmol palladium acetate were added to a two-necked round-bottom flask in sequence, and then 10mL anhydrous DMF was added. The reaction was refluxed for 50h under stirring. After the reaction, the obtained reaction solution was poured into 100mL deionized water and mixed, and the precipitate was collected by filtration. The precipitate was then extracted with saturated sodium chloride solution and dichloromethane, the organic phase was collected and dried with anhydrous sodium sulfate, and finally a mixture of petroleum ether and dichloromethane in a volume ratio of 1:5 was used as the mobile phase. The electrochromic monomer compound (PBTZ-EDOT) was purified by silica gel column chromatography.

[0088] Synthesis of electrochromic polymer with red-transparent display: The monomer PBTZ-EDOT was dissolved in chromatographic grade acetonitrile, the concentration of PBTZ-EDOT was 0.8 mmol / L, and then 0.08 mol / L of tetra-n-butylammonium hexafluorophosphonate was added as an electrolyte. Cyclic voltammetry electrochemical polymerization was carried out in a three-electrode system (ITO conductive glass as the working electrode, platinum wire as the counter electrode, and Ag / AgCl as the reference electrode) to obtain an electrochromic polymer film attached to the ITO glass. The scanning speed of the cyclic voltammetry was 100 mV / s, the voltage was -0.2 to 1.1 V, and the number of cycles was 10.

[0089] Example 3

[0090] Synthesis of N-(2,5-dibromophenyl)-2-ethylhexanamide: 12.1mmol of 2,5-dibromoaniline was dissolved in 50mL of pyridine. Under a nitrogen atmosphere, 13.5mmol of 2-ethylhexanoyl chloride was slowly added to the pyridine solution of 2,5-dibromoaniline. The mixture was heated to reflux at 105°C for 2h. The cooled solution was poured into 200mL of ice water, and 100mL of ethyl acetate was added. The aqueous layer was extracted with 200mL of ethyl acetate. The synthesized organic layer was dried over anhydrous MgSO4, filtered and concentrated by vacuum evaporation. The white solid compound N-(2,5-dibromophenyl)-2-ethylhexanamide was obtained by rotary evaporation.

[0091] Synthesis of N-(2,5-dibromophenyl)-2-ethylhexylthioamide: 5.08mmol N-(2,5-dibromophenyl)-2-ethylhexylthioamide was added to a mixture of 2.32mmol phosphorus pentasulfide and 35mL anhydrous toluene. Under nitrogen protection, the bright yellow suspension was heated and gently refluxed at 105°C for 3.5h. The solution was then cooled to 0°C and filtered. The insoluble part was dissolved with 50mL ethyl acetate and then extracted three times with water. The organic phase was collected and concentrated, and purified by column chromatography, with silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether in a volume ratio of 1:4 as the mobile phase. The eluent of the target compound was collected and dried to obtain an orange solid compound N-(2,5-dibromophenyl)-2-ethylhexylthioamide.

[0092] Synthesis of 4,7-dibromo-2-(heptane-3-yl)benzothiazole (PBTZ-2Br): 10.68mmol N-(2,5-dibromophenyl)-2-ethylhexanethioamide, 44.5mmol potassium ferrocyanide, and 89.7mmol sodium hydroxide were added to a mixture of water and ethanol (79.8mL of water and 4.2mL of anhydrous ethanol), and then stirred at 100°C for 3h under nitrogen protection. The mixture was cooled in an ice bath to obtain a precipitate. The precipitate was then filtered and washed with water. After washing with water, ethyl acetate was added to dissolve the precipitate, and the water was removed with anhydrous sodium sulfate and concentrated by vacuum evaporation. The stationary phase was silica gel, and a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:5 was used as the mobile phase. The eluent containing the target compound was collected by thin layer chromatography, and the solvent was removed by thin layer chromatography. The yellow oily monomer 4,7-dibromo-2-(heptane-3-yl)benzothiazole (PBTZ-2Br) was obtained by rotary evaporation and drying.

[0093] Synthesis of EDOT-Sn: Under nitrogen protection, 7.03 mmol EDOT was dissolved in 23 mL anhydrous tetrahydrofuran, and then 2.8 mL of n-butyl lithium hexane solution (the concentration of n-butyl lithium was 3 mol / L) was added dropwise through a syringe at -76°C. After stirring at this temperature for 1 hour, 1 mL of tributyltin chloride solution (the concentration of tributyltin chloride was 3.3 g / mL) was added. After the addition of the tributyltin chloride solution, the mixture was returned to room temperature and stirred for 24 hours. After the reaction was completed, the obtained reaction solution was separated and purified by an alumina chromatography column to obtain a crude product of the compound EDOT-Sn.

[0094] Synthesis of PBTZ-EDOT: Under nitrogen protection, 0.767mmol PBTZ-2Br, 2.8mmol EDOT-Sn, and 0.03mmol dichlorobis(triphenylphosphine)palladium were added to a two-necked round-bottom flask in sequence, and then 10mL anhydrous DMF was added. The reaction was refluxed for 46h under stirring. After the reaction, the obtained reaction solution was poured into 100mL deionized water and mixed, and the precipitate was collected by filtration. The precipitate was then extracted with saturated sodium chloride solution and dichloromethane, the organic phase was collected and dried with anhydrous sodium sulfate, and finally a mixture of petroleum ether and dichloromethane in a volume ratio of 1:5 was used as the mobile phase. The electrochromic monomer compound (PBTZ-EDOT) was purified by silica gel column chromatography.

[0095] Synthesis of electrochromic polymer with red-transparent display: The monomer PBTZ-EDOT was dissolved in chromatographic grade acetonitrile, the concentration of PBTZ-EDOT was 0.7 mmol / L, and then 0.06 mol / L of tetra-n-butylammonium hexafluorophosphonate was added as an electrolyte. Cyclic voltammetry electrochemical polymerization was carried out in a three-electrode system (ITO conductive glass as the working electrode, platinum wire as the counter electrode, and Ag / AgCl as the reference electrode) to obtain an electrochromic polymer film attached to the ITO glass. The scanning speed of the cyclic voltammetry was 100 mV / s, the voltage was -0.2 to 1.1 V, and the number of cycles was 10.

[0096] Application example: Performance testing of electrochromic materials from red to transparent

[0097] Using an electrochemical workstation coupled with an ultraviolet-visible spectrophotometer, the CV curve of the film prepared in Example 1, ultraviolet-visible light absorption at different voltages, fading time and coloring time of the film at a specific wavelength, the relationship between transmittance and time at a specific wavelength, and film stability at a step voltage were tested in an acetonitrile solution of tetra-n-butylammonium hexafluorophosphonate at a concentration of 0.1 mol / L. An electrochemical workstation coupled with a colorimeter was used to measure the color and relative brightness of the film at different voltages.

[0098] The electrochemical polymerization curve of the electrochromic monomer compound (PBTZ-EDOT) of Example 1 is as follows: Figure 2 The cyclic voltammetry curves of the electrochromic polymer film of Example 1 at different current sweep rates are shown in Figure 3 As shown; the UV-visible absorption spectrum of the electrochromic polymer film of Example 1 at a voltage of -0.2 to 0.7 V is as shown Figure 4 As shown; the contrast and spectral dynamic stability of the electrochromic polymer film of Example 1 at 535nm band are as shown Figure 5 As shown; the response time of the electrochromic polymer film of Example 1 in the 535nm band is as follows Figure 6As shown; the chromaticity curve of the electrochromic polymer film of Example 1 at different voltages is as shown Figure 7 shown.

[0099] from Figure 2 From the electropolymerization curve, it can be seen that as the number of polymerization cycles increases, the current density also increases accordingly, indicating that as the electropolymerization process proceeds, the monomer adheres to the ITO glass surface to form a film. Figure 3 The cyclic voltammetry curve shows that the polymer film has two oxidation peaks and one reduction peak, located at 0.55V / 0.89V and 0.61V. Figure 4 The ultraviolet-visible absorption spectrum of -0.2 to 0.7 V found that the electrochromic polymer film based on benzothiazole derivatives can achieve reversible switching from red to transparent. Figure 5 and Figure 6 It can be seen that the contrast ratio at 535nm is 25.2%. After 1000 cycles, the optical contrast ratio of the film is 21.26%, with no obvious attenuation, showing excellent electrochemical stability. Figure 6 It can be seen that the film has a faster response time of 0.6s / 0.26s in the 535nm band. Figure 7 In the figure, the positive half axis of the X axis, the positive half axis of the Y axis, the negative half axis of the X axis, and the negative half axis of the Y axis are red, yellow, green, and blue, respectively. The coordinate axis is pure color, and the closer to the origin, the lighter the color, and the origin is colorless. It can be seen from the figure that the polymer film is pure red in the neutral state, and there is almost no absorption residue in the oxidized state, showing high transparency. The PBTZ-EDOT of the present invention is an excellent new electrochromic material, which has potential research prospects in display fields such as electronic paper and electronic tags.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A red-transparent electrochromic polymer, characterized in that: The structural formula of the electrochromic polymer is: Wherein, n is the average degree of polymerization, and the value of n is 100 to 2000; The red-transparent electrochromic polymer is obtained from a red-transparent electrochromic monomer compound through an electrochemical polymerization reaction; the structural formula of the electrochromic monomer compound is:

2. The method for preparing the red-transparent electrochromic polymer according to claim 1, characterized in that: The following steps are included: 1) 2,5-dibromoaniline and 2-ethylhexanoyl chloride undergo substitution reaction to obtain N-(2,5-dibromophenyl)-2-ethylhexanoylamide; 2) N-(2,5-dibromophenyl)-2-ethylhexanamide and phosphorus pentasulfide undergo a sulfurization reaction to obtain N-(2,5-dibromophenyl)-2-ethylhexanthioamide; 3) N-(2,5-dibromophenyl)-2-ethylhexanethioamide, potassium ferrocyanide and sodium hydroxide undergo cyclization reaction to obtain 4,7-dibromo-2-(heptane-3-yl)benzothiazole; 4) 3,4-ethylenedioxythiophene, n-butyl lithium and tributyltin chloride are mixed and subjected to substitution reaction to obtain a tinated EDOT derivative EDOT-Sn; 5) 4,7-dibromo-2-(heptane-3-yl)benzothiazole and EDOT-Sn undergo Stille coupling reaction under the catalysis of a palladium catalyst to obtain an electrochromic monomer compound; 6) The electrochromic monomer compound undergoes an electrochemical polymerization reaction to obtain an electrochromic polymer having a red-transparent display.

3. The preparation method according to claim 2, characterized in that: Step 1) The molar ratio of 2,5-dibromoaniline to 2-ethylhexanoyl chloride is 1-1.2:1-1.2, the temperature of the substitution reaction is 100-120° C., and the time of the substitution reaction is 1.5-2.5 h; The solvent for the substitution reaction is pyridine, and the mass volume ratio of 2,5-dibromoaniline to pyridine is 1 g:13-20 mL.

4. The preparation method according to claim 2 or 3, characterized in that: Step 2) the molar ratio of N-(2,5-dibromophenyl)-2-ethylhexanamide to phosphorus pentasulfide is 1.8-2.5:1, the temperature of the sulfurization reaction is 100-120° C., and the time of the sulfurization reaction is 2.5-3.5 hours; The solvent for the sulfidation reaction is anhydrous toluene, and the mass volume ratio of N-(2,5-dibromophenyl)-2-ethylhexylamide to anhydrous toluene is 1 g:13-20 mL.

5. The preparation method according to claim 4, characterized in that: Step 3) the molar ratio of N-(2,5-dibromophenyl)-2-ethylhexanethioamide, potassium ferrocyanide and sodium hydroxide is 1:3.7-4.3:7-9; the temperature of the cyclization reaction is 85-105° C., and the time of the cyclization reaction is 2.5-3.5 hours; The solvents for the cyclization reaction are water and anhydrous ethanol, and the volume ratio of water to anhydrous ethanol is 17-19:1; the mass volume ratio of N-(2,5-dibromophenyl)-2-ethylhexanethioamide to water is 1g:17-20mL.

6. The preparation method according to claim 5, characterized in that: Step 4) The molar ratio of 3,4-ethylenedioxythiophene, n-butyl lithium and tributyltin chloride is 1:1 to 1.2:1 to 1.6, the mixing temperature is -80 to -75°C, and the substitution reaction is carried out at room temperature.

7. The preparation method according to claim 5 or 6, characterized in that: Step 4) the n-butyl lithium is an n-butyl lithium solution having a concentration of 1 to 3 mol / L, and the tributyltin chloride is a tributyltin chloride solution having a concentration of 1 to 5 g / mL; Step 4) The solvent for the substitution reaction is tetrahydrofuran, and the mass volume ratio of 3,4-ethylenedioxythiophene to tetrahydrofuran is 1g:15-25mL.

8. The preparation method according to claim 7, characterized in that: Step 5) The molar ratio of 4,7-dibromo-2-(heptane-3-yl)benzothiazole, EDOT-Sn and palladium catalyst is 1:2-6:0.01-0.1; the Stille coupling reaction time is 45-50 hours; the palladium catalyst is palladium acetate, tetrakis(triphenylphosphine)palladium or dichlorobis(triphenylphosphine)palladium; The solvent of the Stille coupling reaction is N,N-dimethylformamide, and the mass volume ratio of 4,7-dibromo-2-(heptane-3-yl)benzothiazole to N,N-dimethylformamide is 1 g:30-40 mL.

9. The preparation method according to claim 8, characterized in that: The substitution reaction in step 1), the sulfurization reaction in step 2), the cyclization reaction in step 3), the substitution reaction in step 4 and the Stille coupling reaction in step 5 are carried out under a nitrogen atmosphere.

10. The preparation method according to claim 9, characterized in that: Step 6) the solvent of the electrochemical polymerization reaction is acetonitrile, the electrolyte is tetra-n-butylammonium hexafluorophosphonate, the concentration of the electrochromic monomer compound is 0.5-1 mmol / L, and the concentration of tetra-n-butylammonium hexafluorophosphonate is 0.05-0.1 mol / L; The electrochemical polymerization reaction is a cyclic voltammetry electrochemical polymerization reaction, the scanning speed of the cyclic voltammetry electrochemical polymerization reaction is 90-110 mV / s, the voltage is -0.2-1.1 V, and the number of cycles is 10.

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