N-ortho-position modified viologen electrochromic material, preparation method and application

Abstract

The invention discloses an N-ortho-position modified viologen electrochromic material, which is characterized in that an n-butyl or phenyl substituent group is introduced to the N-ortho position of a pyridine ring of ethyl viologen, so that the viologen electrochromic material is formed; the structural general formula of the viologen electrochromic material is as follows: 2, 2 ', 6, 6'-tetrasubstituted (R)-1, 1 '-diethyl-[4, 4'-bipyridyl]-1, 1 '-dionium hexafluorophosphate, wherein R is n-butyl or phenyl. The invention further discloses a preparation method and application of the N-ortho-position modified viologen electrochromic material. By introducing an n-butyl or phenyl substituent to the N-ortho position of a pyridine ring of ethyl viologen, the electrochemical cycle stability of the material is remarkably improved, and the key problem that the viologen material is prone to photooxidative degradation in long-term electrochemical cycle is solved.

Description

Technical Field

[0001] This invention belongs to the field of electrochromic materials technology, specifically an N-ortho modified viologen electrochromic material, its preparation method, and its application. Background Technology

[0002] Electrochromic materials reversibly alter optical properties (such as transmittance or reflectance) when a voltage is applied, and are widely used in energy-saving smart windows, low-power displays, and sensors. Viologen derivatives have become core materials due to their high coloring efficiency, fast response, and low cost, but their poor cycling stability (especially their susceptibility to oxidative degradation in air or water environments) severely restricts their commercialization. This invention focuses on the molecular structure optimization of ethyl viologen, solving the bottleneck problem of performance degradation in long-term electrochemical cycling of existing materials through precise modification of the N-ortho position.

[0003] Electrochromic technology relies on the reversible color change of materials during redox processes. Ethyl viologen (1,1'-diethyl-4,4'-bipyridine dihexafluorophosphate), as a typical viologen material, possesses a high molar absorptivity and rapid response characteristics, but its cycling stability has significant drawbacks: in conventional electrochemical cycling (e.g., ±3.0 V), unmodified ethyl viologen is susceptible to irreversible side reactions (such as CN bond breaking or dimerization) due to nucleophilic attack or free radical oxidation at the 2,2'-position of the 4,4'-bipyridine ring. The cycle life of viologen-chromatic materials is typically <500 cycles (modulation depth decay >40%), and the half-life in humid air is <100 hours. Existing technologies attempt to improve stability by adding antioxidants, but this sacrifices the material's response speed and color clarity.

[0004] Therefore, this paper provides an N-ortho modified viologen electrochromic material, its preparation method, and its application. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides an N-ortho modified viologen electrochromic material, its preparation method, and its application. By introducing n-butyl or phenyl substituents at the N-ortho position of the pyridine ring of ethyl viologen, the electrochemical cycling stability of the material is significantly improved, solving the key problem of viologen-based materials being prone to photo-oxidative degradation during long-term electrochemical cycling.

[0006] The technical solution to achieve the above objectives is: One of the present inventions is an N-ortho modified viologen electrochromic material, wherein an n-butyl or phenyl substituent is introduced at the N-ortho position of the pyridine ring of ethyl viologen to form the viologen electrochromic material; The general structural formula of the viola electrochromic material is: 2,2',6,6'-tetrasubstituted (R)-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate; in, R is n-butyl or phenyl.

[0007] A method for preparing an N-ortho-modified viologen electrochromic material according to the second aspect of the present invention includes: Step S1: 2,2',6,6'-tetrasubstituted (R)-4,4'-bipyridine was dissolved in acetonitrile with bromoethane and refluxed at 80°C with stirring for 24 h. Step S2: After the reaction is complete, cool to room temperature and a large amount of light yellow solid will precipitate. Collect the precipitate by filtration, wash three times with a small amount of cold acetonitrile, and dry under vacuum to obtain crude quaternary ammonium salt product. Step S3: Recrystallize the crude product with a mixed solvent to obtain a pale yellow quaternary ammonium salt product; Step S4: Dissolve the obtained quaternary ammonium salt in deionized water or hot water and heat to 50 °C to aid dissolution; In step S5, ammonium hexafluorophosphate is dissolved in water and slowly added dropwise to the above solution while stirring. As the PF6⁻ exchange is completed, the target product gradually precipitates out as a white to light yellow precipitate. Step S6: After stirring for 1 h, filter the mixture, wash it with water and ether in sequence, and dry it under vacuum to obtain the target product 2,2',6,6'-tetrasubstituted (R)-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate.

[0008] Preferably, in step S1, R is n-butyl or phenyl.

[0009] Preferably, in step S3, if the prepared product is 2,2',6,6'-tetrabutyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, recrystallization is performed using a mixed solvent of ethanol and n-hexane; if the prepared product is 2,2',6,6'-tetraphenyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, recrystallization is performed using a mixed solvent of methanol and ethyl acetate. The mixing ratio of ethanol and n-hexane is 1:3.

[0010] Preferably, in step S4, if the prepared quaternary ammonium salt is 2,2',6,6'-tetrabutyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, the obtained quaternary ammonium salt is dissolved in deionized water; if the prepared quaternary ammonium salt is 2,2',6,6'-tetraphenyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, the obtained quaternary ammonium salt is dissolved in hot water.

[0011] The third invention relates to the application of a viologen electrochromic material prepared according to a method for preparing N-ortho modified viologen electrochromic material in electrochromic devices.

[0012] Preferably, the violet electrochromic material is used as the active layer, and the active layer is loaded onto two conductive substrates by a roll-up method.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention introduces a bulky substituent (n-butyl or phenyl) with steric hindrance effect into the N atom ortho position (i.e., the 2,2', 6,6' position) of the bipyridine ring, which effectively shields the active nitrogen center and π-conjugated system, significantly inhibiting the attack of water molecules, oxygen and other nucleophiles on the viologen cation radical intermediate, thereby improving the chemical stability and photo-oxidation resistance of the material in redox cycles. The alkyl or aryl groups introduced in this invention do not significantly affect the solubility of the material in polar solvents (such as water, alcohols, carbonates, etc.) and can still meet the requirements of solution processing. At the same time, since the substituents are located on non-conjugated pathways, the electronic delocalization characteristics of the 4,4'-bipyridine core are not destroyed, thus maintaining a high molar absorptivity and fast electron transfer kinetics. Attached Figure Description

[0014] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is the molecular structural formula of an N-ortho modified viologen electrochromic material of the present invention; Figure 2 This is a flowchart of a method for preparing an N-ortho-modified viologen electrochromic material according to the present invention; Figure 3 This is a schematic diagram of the optical modulation depth changing with the number of cycles in an embodiment of the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] An N-ortho modified viologen electrochromic material is formed by introducing an n-butyl or phenyl substituent at the N-ortho position of the pyridine ring of ethyl viologen. The general structural formula of the violet electrochromic material is: 2,2',6,6'-tetrasubstituted (R)-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate; in, R is n-butyl or phenyl, such as Figure 1 As shown, the molecular structure on the left is 2,2',6,6'-tetrabutyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate (TBBEVP·2PF6); the molecular structure on the right is 2,2',6,6'-tetraphenyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate (TPPEVP·2PF6).

[0017] In the embodiments, the modulation depth decay rate of the violet electrochromic material is ≤5% after 500 ± 3.0 V constant current cycles in 0.5 mol / L Na2SO4 electrolyte at a wavelength of 633 nm.

[0018] like Figure 2 As shown, a method for preparing an N-ortho-modified viologen electrochromic material includes: In step S1, 2,2',6,6'-tetrasubstituted (R)-4,4'-bipyridine was dissolved in acetonitrile with bromoethane and refluxed at 80°C for 24 h.

[0019] In the examples, R is n-butyl or phenyl.

[0020] Step S2: After the reaction is complete, cool to room temperature and a large amount of light yellow solid will precipitate. Collect the precipitate by filtration, wash three times with a small amount of cold acetonitrile, and dry under vacuum to obtain crude quaternary ammonium salt product.

[0021] Step S3: The crude product is recrystallized with a mixed solvent to obtain a pale yellow quaternary ammonium salt product.

[0022] In the examples, if the prepared product is 2,2',6,6'-tetrabutyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, recrystallization is performed using a mixed solvent of ethanol and n-hexane; if the prepared product is 2,2',6,6'-tetraphenyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, recrystallization is performed using a mixed solvent of methanol and ethyl acetate. The mixing ratio of ethanol and n-hexane is 1:3.

[0023] Step S4: Dissolve the obtained quaternary ammonium salt in deionized water or hot water and heat to 50 °C to aid dissolution.

[0024] In the examples, if the prepared quaternary ammonium salt is 2,2',6,6'-tetrabutyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, the obtained quaternary ammonium salt is dissolved in deionized water; if the prepared quaternary ammonium salt is 2,2',6,6'-tetraphenyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, the obtained quaternary ammonium salt is dissolved in hot water.

[0025] In step S5, ammonium hexafluorophosphate is dissolved in water and slowly added dropwise to the above solution while stirring. As the PF6⁻ exchange is completed, the target product gradually precipitates as a white to light yellow precipitate.

[0026] Step S6: After stirring for 1 h, filter the mixture, wash it with water and ether in sequence, and dry it under vacuum to obtain the target product 2,2',6,6'-tetrasubstituted (R)-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate.

[0027] The violet electrochromic material prepared according to the preparation method of N-ortho modified violet electrochromic material is applied to electrochromic devices. When the electrochromic device is applied in smart glass (> 10 cm × 10 cm), the cycle life is ≥ 1000 times and the coloring / fading response time is ≤ 5 s.

[0028] In this embodiment, the violet electrochromic material is used as the active layer, which is loaded onto two conductive substrates in a roll-up manner.

[0029] The present invention will be further described below with reference to specific embodiments. Example 1: Preparation of 2,2',6,6'-Tetra-n-butyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate (TBBEVP·2PF6) Step S1: Dissolve 20 mmol of 2,2',6,6'-tetra-n-butyl-4,4'-bipyridine (TB-bpy) in 100 mL of anhydrous acetonitrile, add 44 mmol of bromoethane (in excess to ensure complete quaternization), and reflux at 80 °C for 24 h under nitrogen protection.

[0030] Step S2: After the reaction is complete, cool to room temperature and a large amount of light yellow solid will precipitate. Collect the precipitate by filtration, wash three times with a small amount of cold acetonitrile, and dry under vacuum to obtain crude quaternary ammonium salt product.

[0031] Step S3: The crude product is recrystallized with a mixed solvent of ethanol and n-hexane (volume ratio 1:3) to obtain a pale yellow quaternary ammonium salt product.

[0032] In step S4, the obtained quaternary ammonium salt (approximately 10 mmol) is dissolved in 50 mL of deionized water and heated to 50 °C to aid dissolution.

[0033] In step S5, 22 mmol of ammonium hexafluorophosphate (NH4PF6) was dissolved in 20 mL of water and slowly added dropwise to the above solution while stirring. As the PF6⁻ exchange was completed, the target product gradually precipitated as a white to light yellow precipitate.

[0034] Step S6: After stirring for another 1 h, filter the mixture, wash it with water and ether in sequence, and dry it under vacuum to obtain the target product TBBEVP·2PF6, which is a white to light yellow powder with a yield of about 78% and a purity of >99% as determined by HPLC.

[0035] Example 2: Preparation of 2,2',6,6'-tetraphenyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate (TPPEVP·2PF6) The steps are the same as in Example 1, except that 2,2',6,6'-tetraphenyl-4,4'-bipyridine is used as the starting material.

[0036] The specific steps are as follows: Step S1: Dissolve 15 mmol of 2,2',6,6'-tetraphenyl-4,4'-bipyridine (TP-bpy) in 80 mL of anhydrous acetonitrile, add 33 mmol of bromoethane (in excess to ensure complete quaternization), and reflux at 80 °C for 24 h under nitrogen protection.

[0037] Step S2: After the reaction is complete, cool to room temperature and a large amount of light yellow solid will precipitate. Collect the precipitate by filtration, wash three times with a small amount of cold acetonitrile, and dry under vacuum to obtain crude quaternary ammonium salt product.

[0038] Step S3: The crude product is recrystallized using a mixed solvent of methanol and ethyl acetate to obtain a pale yellow quaternary ammonium salt product.

[0039] Step S4: Dissolve the obtained quaternary ammonium salt in 40 mL of hot water and heat to 50 °C to aid dissolution.

[0040] In step S5, ammonium hexafluorophosphate (NH4PF6) is dissolved in 20 mL of water, and 18 mmol of an aqueous solution of NH4PF6 is slowly added dropwise to the above solution while stirring. As the PF6⁻ exchange is completed, the target product gradually precipitates out as a white to light yellow precipitate.

[0041] Step S6: After stirring for 1 h, filter the mixture, wash it with water and ether in sequence, and dry it under vacuum to obtain the target TPPEVP·2PF6 with a yield of about 75%, which is a deep yellow crystal.

[0042] Example 3: Electrochromic Performance Test The TBBEVP·2PF6 obtained in Example 1 was prepared into a 0.1 M aqueous solution, and 0.5 mol / L Na2SO4 was added as a supporting electrolyte. A three-electrode system (ITO glass as the working electrode, platinum wire as the counter electrode, and Ag / AgCl as the reference electrode) was used for cyclic voltammetry (CV) and chronoamperometry tests on a CHI660E electrochemical workstation. The CV scan range was −1.0 V to +2.0 V vs. Ag / AgCl, and the scan rate was 50 mV / s. The results showed a pair of clear and reversible redox peaks, corresponding to V... 2 The ⁺ / V⁺ transition, ΔEp < 80 mV, indicates excellent electrochemical reversibility. A film (approximately 300 nm thick) was spin-coated into a bilayer ITO sandwich structure, and a ±2.5 V step voltage was applied. The initial transmittance at 633 nm was measured to be 78%, the colored state decreased to 22%, and the optical modulation depth reached 56%. After 500 cycles of galvanostatic cycling (±3.0 V, 10 mA / cm²), the film showed excellent electrochemical reversibility. 2 After that, the modulation depth retention rate was 96.2%; the coloring / fading response times were 2.8 s and 3.2 s, respectively.

[0043] This invention, after 500 cycles of ±3.0 V constant current charge-discharge testing in a 0.5 mol / L Na₂SO₄ aqueous electrolyte, exhibits an optical modulation depth retention rate >95%, significantly higher than the <80% of traditional ethyl viologen. Figure 3 As shown.

[0044] This invention operates at a relative humidity of 85% and a light intensity of 100 mW / cm². 2 After 168 hours of exposure under the given conditions, the color response performance decreased by ≤5%, and the half-life was extended to >500 hours.

[0045] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A viologen electrochromic material modified at the N-ortho position, characterized in that, A n-butyl or phenyl substituent is introduced at the N-ortho position of the pyridine ring of ethyl viologen to form the viologen electrochromic material; The general structural formula of the viola electrochromic material is: 2,2',6,6'-tetrasubstituted (R)-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate; in, R is n-butyl or phenyl.

2. A method for preparing an N-ortho-modified viologen electrochromic material, characterized in that, include: Step S1: 2,2',6,6'-tetrasubstituted (R)-4,4'-bipyridine was dissolved in acetonitrile with bromoethane and refluxed at 80°C with stirring for 24 h. Step S2: After the reaction is complete, cool to room temperature and a large amount of light yellow solid will precipitate. Collect the precipitate by filtration, wash three times with a small amount of cold acetonitrile, and dry under vacuum to obtain crude quaternary ammonium salt product. Step S3: Recrystallize the crude product with a mixed solvent to obtain a pale yellow quaternary ammonium salt product; Step S4: Dissolve the obtained quaternary ammonium salt in deionized water or hot water and heat to 50 °C to aid dissolution; In step S5, ammonium hexafluorophosphate is dissolved in water and slowly added dropwise to the above solution while stirring. As the PF6⁻ exchange is completed, the target product gradually precipitates out as a white to light yellow precipitate. Step S6: After stirring for 1 h, filter the mixture, wash it with water and ether in sequence, and dry it under vacuum to obtain the target product 2,2',6,6'-tetrasubstituted (R)-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate.

3. The method for preparing an N-ortho-modified viologen electrochromic material according to claim 2, characterized in that, In step S1, R is n-butyl or phenyl.

4. The method for preparing an N-ortho-modified viologen electrochromic material according to claim 2, characterized in that, In step S3, if the prepared product is 2,2',6,6'-tetrabutyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, recrystallization is performed using a mixed solvent of ethanol and n-hexane; if the prepared product is 2,2',6,6'-tetraphenyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, recrystallization is performed using a mixed solvent of methanol and ethyl acetate. The mixing ratio of ethanol and n-hexane is 1:

3.

5. The method for preparing an N-ortho-modified viologen electrochromic material according to claim 2, characterized in that, In step S4, if the prepared quaternary ammonium salt is 2,2',6,6'-tetrabutyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, the obtained quaternary ammonium salt is dissolved in deionized water; if the prepared quaternary ammonium salt is 2,2',6,6'-tetraphenyl-1,1'-diethyl-[4,4'-bipyridine]-1,1'-dionium hexafluorophosphate, the obtained quaternary ammonium salt is dissolved in hot water.

6. The application of a viologen electrochromic material prepared by the method for preparing N-ortho modified viologen electrochromic material according to claims 2-5 in electrochromic devices.

7. The application according to claim 6, characterized in that, Violet electrochromic material is used as the active layer, which is loaded onto two conductive substrates in a roll-up manner.

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