A red-transparent display electrochromic polymer and a preparation method thereof

Abstract

The application belongs to the technical field of electrochromic materials, and provides a red-transparent display electrochromic polymer and a preparation method thereof.The method comprises the following steps: N-(2,5-dibromophenyl)-2-ethylhexylthioamide, potassium hexacyanoferrate and sodium hydroxide are subjected to ring formation reaction to obtain 4,7-dibromo-2-(heptane-3-yl)benzothiazole; EDOT, n-butyllithium and tributyltin chloride are subjected to substitution reaction to obtain EDOT-Sn; 4,7-dibromo-2-(heptane-3-yl)benzothiazole and EDOT-Sn are subjected to Stille coupling reaction and then electrochemical polymerization reaction to obtain the electrochromic polymer.The method obtains a pure donor (D) type organic molecule, and the corresponding electrochromic film is prepared by electrochemical polymerization, reversible switching between red and transparent is realized, and good cycle stability and relatively fast color change response speed are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochromic materials, and particularly relates to a red-transparent display electrochromic polymer and a preparation method thereof. BACKGROUND

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

[0003] Red is a basic component color of the additive three primary colors (red, green, and blue), and plays a very important role in color regulation and rich display effects. Red in the neutral state of the conducting polymer needs to meet the optical absorption of high energy band, which is manifested as single absorption in the visible light band. Donor (D) type polymers are conducive to realizing red due to their wide energy gap. In recent years, there have been more studies on the electro-polymerization method for preparing “green-transparent” and “blue-transparent” materials, but due to the lack of suitable donor structures, there are relatively few studies on the electro-polymerization method for preparing “red-transparent” materials. The Gunbas research group prepared a red-transparent electrochromic film by electrochemical polymerization through structural modification of phenanthrocarbazole, but there are many absorption residues in the oxidized state, which cannot completely achieve transparency, and the cycle stability of the film is not ideal. Therefore, it is an urgent problem to be solved to find a suitable donor structure and prepare an electrochromic material that is red in the neutral state, completely transparent in the oxidized state, and has high cycle stability by the electro-polymerization method.

[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 display electrochromic polymer based on benzothiazole derivatives and a preparation method thereof. SUMMARY

[0005] The present application relates to the technical field of electrochromic materials, and particularly relates to a red-transparent display electrochromic polymer and a preparation method thereof.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

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

[0008]

[0009] wherein n is an average polymerization degree, and n is 100-2000;

[0010] The red-transparent display electrochromic polymer is obtained by electrochemical polymerization of a red-transparent display electrochromic monomer compound, and a structural formula of the electrochromic monomer compound is:

[0011]

[0012] The present application also provides a preparation method of the red-transparent display electrochromic polymer, comprising the following steps:

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

[0014] 2) N-(2,5-dibromophenyl)-2-ethylhexanamide and phosphorus pentasulfide are subjected to sulfuration reaction to obtain N-(2,5-dibromophenyl)-2-ethylhexylthioamide;

[0015] 3) N-(2,5-dibromophenyl)-2-ethylhexylthioamide, potassium ferricyanide and sodium hydroxide are subjected to ring formation reaction to obtain 4,7-dibromo-2-(heptane-3-yl)benzothiazole;

[0016] 4) 3,4-vinyldioxothiophene, n-butyllithium and tributyltin chloride are mixed and subjected to substitution reaction to obtain tin-substituted EDOT derivative EDOT-Sn;

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

[0018] 6) The electrochromic monomer compound is subjected to electrochemical polymerization reaction to obtain the red-transparent display electrochromic polymer.

[0019] Preferably, the molar ratio of 2,5-dibromoaniline to 2-ethylhexanoyl chloride in step 1) 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 1.5-2.5h;

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

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

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

[0023] As preferred, the molar ratio of N-(2,5-dibromophenyl)-2-ethylhexanethioamide, potassium ferricyanide and sodium hydroxide in step 3) is 1:3.7-4.3:7-9; the temperature of the ring-forming reaction is 85-105℃, and the time of the ring-forming reaction is 2.5-3.5h;

[0024] The solvent of the ring-forming reaction is 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] As preferred, the molar ratio of 3,4-vinylenedithiophene, n-butyllithium and tributyltin chloride in step 4) is 1:1-1.2:1-1.6, the temperature of the mixing is -80--75℃, and the substitution reaction is carried out at room temperature.

[0026] As preferred, the n-butyllithium in step 4) is n-butyllithium solution, and the concentration of the n-butyllithium solution is 1-3mol / L; the tributyltin chloride is tributyltin chloride solution, and the concentration of the tributyltin chloride solution is 1-5g / mL;

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

[0028] As preferred, the molar ratio of 4,7-dibromo-2-(heptane-3-yl)benzothiazole, EDOT-Sn and palladium catalyst in step 5) is 1:2-6:0.01-0.1; the time of the Stille coupling reaction is 45-50h; and 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 1g:30-40mL.

[0030] Preferably, the substitution reaction in step 1), the sulfuration reaction in step 2), the ring formation 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 for the electrochemical polymerization reaction in step 6) is acetonitrile, the electrolyte is tetra-n-butylammonium hexafluorophosphate, the concentration of the electrochromic monomer compound is 0.5-1 mmol / L, and the concentration of the tetra-n-butylammonium hexafluorophosphate is 0.05-0.1 mol / L.

[0032] The electrochemical polymerization reaction is a cyclic voltammetry electrochemical polymerization reaction, and 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 cycle number is 10 cycles.

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

[0034] 1) The electrochromic material of the present application has a new structure representative which has not been involved in the current research, takes benzothiazole derivative (PBTZ-2Br) as a conjugated core, 3,4-ethylenedioxythiophene (EDOT) as an electroactive polymerization unit monomer compound, designs and synthesizes a pure donor (D) type organic molecule, forms a uniform and smooth polymer film (PBTZ-EDOT) through electrochemical polymerization, is simple and effective in preparation, and the polymer film shows good electrochromic performance, can realize reversible switching between red and transparent, has good cycle stability and relatively fast color change response speed.

[0035] 2) The polymer film prepared by the present application can realize reversible switching from red to transparent under different voltage windows; the film is pure red in a neutral state, has almost no absorption residue in an oxidized state, and presents high transparency. The optical contrast is 25.2% under a 535 nm waveband, and the optical contrast of the film is 21.26% after 1000 cycles, without obvious attenuation, showing very excellent electrochemical stability. In addition to the stable color change behavior, the film has a relatively fast response time of 0.6s / 0.26s under a 535 nm waveband, and the PBTZ-EDOT of the present application is an excellent new type of electrochromic material, which has potential research prospects in the display field of electronic paper, electronic tags and the like. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is a synthesis route map of the electrochromic monomer compound (PBTZ-EDOT) of the present application.

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

[0038] Figure 3 Cyclic voltammogram of the electrochromic polymer thin film of Example 1 at different current scan rates;

[0039] Figure 4 UV-Vis absorption spectrum of the electrochromic polymer thin film of Example 1 at a voltage of -0.2-0.7V;

[0040] Figure 5 Contrast and spectral dynamic stability diagram of the electrochromic polymer thin film of Example 1 at a wavelength of 535nm;

[0041] Figure 6 Response time diagram of the electrochromic polymer thin film of Example 1 at a wavelength of 535nm;

[0042] Figure 7 Colorimetric curve of the electrochromic polymer thin film of Example 1 at different voltages. DETAILED DESCRIPTION

[0043] The present application provides a red-transparent display electrochromic polymer, and a structural formula of the electrochromic polymer is as follows:

[0044]

[0045] wherein n is an average polymerization degree, and the value of n is 100-2000;

[0046] The red-transparent display electrochromic polymer is obtained by electrochemical polymerization of a red-transparent display electrochromic monomer compound, and a structural formula of the electrochromic monomer compound is as follows:

[0047]

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

[0049] The present application further provides a preparation method of the red-transparent display electrochromic polymer, and the method comprises the following steps:

[0050] 1) Substitution reaction of 2,5-dibromoaniline and 2-ethylhexanoyl chloride to obtain N-(2,5-dibromophenyl)-2-ethylhexanamide;

[0051] 2) Sulfuration reaction of N-(2,5-dibromophenyl)-2-ethylhexanamide and phosphorus pentasulfide to obtain N-(2,5-dibromophenyl)-2-ethylhexylthioamide;

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

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

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

[0055] 6) The electrochromic monomer compound is subjected to an electrochemical polymerization reaction to obtain an electrochromic polymer with red-transparent display.

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

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

[0058] In the present application, the molar ratio of N-(2,5-dibromophenyl)-2-ethylhexanethioamide and phosphorus pentasulfide in step 2) is preferably 1.8-2.5: 1, further preferably 2-2.3: 1, and more preferably 2.1-2.2: 1; the temperature of the sulfuration reaction is preferably 100-120°C, further preferably 105-115°C, and more preferably 110°C; and the time of the sulfuration reaction is preferably 2.5-3.5h, further preferably 3h.

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

[0060] In the present application, the molar ratio of N-(2,5-dibromophenyl)-2-ethylhexylthioamide, potassium ferricyanide and sodium hydroxide in step 3) is preferably 1:3.7-4.3:7-9, further preferably 1:3.8-4.2:7.5-8.5, and more preferably 1:4:8; the temperature of the ring-forming reaction is preferably 85-105℃, further preferably 90-100℃, and more preferably 95℃; and the time of the ring-forming reaction is preferably 2.5-3.5h, further preferably 3h.

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

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

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

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

[0065] In the present application, 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, further 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, further preferably 46-49h, and more preferably 47-48h; and the palladium catalyst is preferably palladium acetate, tetrakis(triphenylphosphine)palladium or dichlorobis(triphenylphosphine)palladium.

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

[0067] In the present application, the substitution reaction of step 1), the sulfurization reaction of step 2), the ring-forming reaction of step 3), the substitution reaction of step 4), and the Stille coupling reaction of step 5) are preferably carried out under a nitrogen atmosphere.

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

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

[0070] In the present application, the structural formulas of 2,5-dibromoaniline and N-(2,5-dibromo-phenyl)-2-ethylhexanamide are as follows:

[0071]

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

[0073]

[0074] The technical solutions provided by the present application will be described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

[0075] Example 1

[0076] Synthesis of N-(2,5-dibromophenyl)-2-ethylhexanamide: 12.1 mmol of 2,5-dibromoaniline was dissolved in 45 mL of pyridine, 12.1 mmol of 2-ethylhexanoyl chloride was slowly added to the pyridine solution of 2,5-dibromoaniline under nitrogen atmosphere, and heated to reflux at 110°C for 2 h. The cooled solution was poured into 200 mL of ice water, and 100 mL of ethyl acetate was added. The aqueous layer was extracted with 200 mL of ethyl acetate. The organic layer was dried over anhydrous MgS04, filtered, and concentrated by vacuum evaporation. White solid compound N-(2,5-dibromophenyl)-2-ethylhexanamide (4.0 g, 80%) was obtained by rotary evaporation.

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

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

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

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

[0081] Synthesis of electrochromic polymer for red-transparent display: The monomer PBTZ-EDOT was dissolved in chromatographic grade acetonitrile, and the concentration of PBTZ-EDOT was 1 mmol / L. Then, tetra-n-butylammonium hexafluorophosphate with a concentration of 0.1 mol / L was added as an electrolyte. Electrochemical polymerization was carried out by cyclic voltammetry 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), and an electrochromic polymer film was obtained attached to the ITO glass. The scan rate of the cyclic voltammetry was 100 mV / s, the voltage was -0.2-1.1 V, and the number of cycles was 10.

[0082] Example 2

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

[0084] Synthesis of N-(2,5-dibromophenyl)-2-ethylhexanethioamide: 5.08 mmol of N-(2,5-dibromophenyl)-2-ethylhexanamide was added to a mixture of 2.21 mmol of phosphorus pentasulfide and 40 mL of anhydrous toluene, and the light yellow suspension was heated under nitrogen protection at 115°C for 3 h. The solution was then cooled to 0°C and filtered, and the insoluble portion was dissolved in 60 mL of ethyl acetate and extracted with water three times. The organic phase was collected and concentrated, and column chromatography was performed using silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether (1:4 by volume) as the mobile phase. The eluate containing the target compound was collected, and the compound N-(2,5-dibromophenyl)-2-ethylhexanethioamide was obtained as an orange solid after drying.

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

[0086] Synthesis of EDOT-Sn: 7.03 mmol of EDOT was dissolved in 18 mL of anhydrous tetrahydrofuran under nitrogen protection, then 3.9 mL of n-butyllithium hexane solution (the concentration of n-butyllithium was 2 mol / L) was added dropwise by needle tube at -80℃, after stirring for 1 h at this temperature, 1 mL of tributyltin chloride solution (the concentration of tributyltin chloride was 2.5 g / mL) was added, and after the addition of the tributyltin chloride solution was completed, it was restored to room temperature and stirred for 24 h, after the reaction was completed, the obtained reaction solution was separated and purified by an alumina chromatographic column to obtain the crude product of compound EDOT-Sn.

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

[0088] Synthesis of electrochromic polymer for red-transparent display: the monomer PBTZ-EDOT was dissolved in chromatographic grade acetonitrile, the concentration of PBTZ-EDOT was 0.8 mmol / L, then tetra-n-butylammonium hexafluorophosphate with a concentration of 0.08 mol / L was added as an electrolyte, and cyclic voltammetry 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 electrochemically polymerize to obtain an electrochromic polymer film attached to the ITO glass, the scan rate of the cyclic voltammetry was 100 mV / s, the voltage was -0.2-1.1 V, and the number of cycles was 10.

[0089] Example 3

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

[0091] Synthesis of N-(2,5-dibromophenyl)-2-ethylhexanethioamide: 5.08 mmol of N-(2,5-dibromophenyl)-2-ethylhexanamide was added to a mixture of 2.32 mmol of phosphorus pentasulfide and 35 mL of anhydrous toluene, and the light yellow suspension was heated under nitrogen protection at 105°C for gentle reflux for 3.5 h. Then the solution was cooled to 0°C and filtered, and the insoluble part was dissolved with 50 mL of ethyl acetate and then extracted with water three times. The organic phase was collected and concentrated, and column chromatography was performed for purification with silica gel as the stationary phase and a mixture of dichloromethane and petroleum ether (1:4 by volume) as the mobile phase. The eluate containing the target compound was collected, and the compound N-(2,5-dibromophenyl)-2-ethylhexanethioamide was obtained as an orange solid after drying.

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

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

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

[0095] Synthesis of electrochromic polymer for red-transparent display: The monomer PBTZ-EDOT was dissolved in chromatographic grade acetonitrile to obtain a solution with a concentration of 0.7 mmol / L. Then, tetra-n-butylammonium hexafluorophosphate with a concentration of 0.06 mol / L was added as an electrolyte. The electrochemical polymerization was performed by cyclic voltammetry 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 scan rate of the cyclic voltammetry was 100 mV / s, the voltage was -0.2-1.1 V, and the number of cycles was 10.

[0096] Application Example: Performance Test of Red-to-Transparent Electrochromic Material

[0097] The CV curve of the film prepared in Example 1 was tested in a 0.1 mol / L tetra-n-butylammonium hexafluorophosphate acetonitrile solution using an electrochemical workstation combined with a UV- visible spectrophotometer. The UV-visible light absorption at different voltages, the bleaching time and coloring time of the film at a specific wavelength, the transmittance at a specific wavelength and the relationship with time, and the film stability at a step voltage were measured. The color and relative brightness of the film at different voltages were measured using an electrochemical workstation combined with a colorimeter.

[0098] The electrochemical polymerization curve of the electrochromic monomer compound (PBTZ-EDOT) of Example 1 is shown in FIG. 1; the cyclic voltammetry curve of the electrochromic polymer film of Example 1 at different current scan rates is shown in FIG. 2; the UV-visible absorption spectrum of the electrochromic polymer film of Example 1 at a voltage of -0.2-0.7 V is shown in FIG. 3; the contrast and spectral kinetic stability of the electrochromic polymer film of Example 1 at a wavelength of 535 nm are shown in FIG. 4; and the response time of the electrochromic polymer film of Example 1 at a wavelength of 535 nm is shown in FIG. 5. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 ​​​​As shown; the chromaticity curves of the electrochromic polymer film of Example 1 at different voltages are 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 UV-visible absorption spectrum of -0.2 to 0.7 V shows 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 in the 535nm band is 25.2%. After 1000 cycles, the optical contrast ratio of the film is 21.26%, with no obvious attenuation, showing excellent electrochemical stability. In addition to the stable color change behavior, 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 graph, the positive x-axis, positive y-axis, negative x-axis, and negative y-axis are colored red, yellow, green, and blue, respectively. Colors falling on the coordinate axes are pure colors, and the colors decrease as they approach the origin, with the origin being colorless. The figure shows that the polymer film is pure red in its neutral state and exhibits almost no absorption residue in its oxidized state, demonstrating high transparency. 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.

[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 principles of the present invention. These improvements and modifications should also be regarded as within 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 ranges from 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-ethylhexanoamide; 2) N-(2,5-dibromophenyl)-2-ethylhexanamide and phosphorus pentasulfide undergo sulfurization reaction to obtain N-(2,5-dibromophenyl)-2-ethylhexanthioamide; 3) N-(2,5-dibromophenyl)-2-ethylhexanethioamide, potassium ferricyanide and sodium hydroxide undergo cyclization reaction to obtain 4,7-dibromo-2-(heptane-3-yl)benzothiazole; 4) 3,4-ethylenedioxythiophene, n-butyllithium and tributyltin chloride are mixed and subjected to a substitution reaction to obtain a tin-containing EDOT derivative EDOT-Sn; 5) Stille coupling reaction of 4,7-dibromo-2-(heptane-3-yl)benzothiazole and EDOT-Sn in the presence 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 sulfurization reaction time 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-ethylhexanamide 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 cyclization reaction time 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 In step 4), the molar ratio of 3,4-ethylenedioxythiophene, n-butyllithium and tributyltin chloride is 1:1-1.2:1-1.6, the mixing temperature is -80--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 for 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 for 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 to 110 mV / s, the voltage is -0.2 to 1.1 V, and the number of cycles is 10.

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