Transparent-green electrochromic hydrogel based on viologen derivative as well as preparation and application of transparent-green electrochromic hydrogel
A novel electrochromic hydrogel was prepared by modifying viologen derivatives with specific substituents, which solved the problems of complex structure and lack of materials in existing electrochromic devices, and achieved high transparency-green reversible electrochromic performance, which can be applied to electrochromic display devices.
Patent Information
- Application Number
- CN202511625470.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-07
- Publication Date
- 2026-02-10
AI Technical Summary
Existing electrochromic devices have complex structures, are cumbersome to manufacture, and lack green and safe electrochromic materials.
A novel viologen derivative was synthesized by modifying the N-site of viologen with specific substituents using a transparent-green electrochromic hydrogel based on viologen derivatives. This derivative was then applied to electrochromic hydrogels and display devices, and the devices were assembled using conductive ITO glass and sodium carboxymethyl cellulose as polymer electrolyte matrices.
It achieves a reversible change from a high-transmittance state in the neutral state to a green state under an applied voltage, and then back to a transparent state when the voltage is reduced. This demonstrates good electrochromic performance and stability, enriching the applications of electrochromic materials.
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Figure CN121494777A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrochromic materials technology, specifically relating to a transparent-green electrochromic hydrogel based on viologen derivatives, its preparation method, and its application in display devices. Background Technology
[0002] Electrochromism (EC) refers to the phenomenon that the optical properties (reflectivity, transmittance, absorptivity, etc.) of a material undergo stable and reversible changes under the influence of an external electric field, which manifests as reversible changes in color and transparency in appearance.
[0003] Viologen compounds are a class of small organic molecules with a bipyridine backbone. As a typical electron-deficient system, they undergo significant intramolecular electron transfer under voltage-driven conditions, resulting in distinct color changes. These materials possess excellent optical contrast, high coloring efficiency, and good redox stability, thus finding wide application in the field of electrochromism. Viologen exists in three redox states: neutral, monovalent cationic, and divalent cationic, each corresponding to different color characteristics.
[0004] Electrochromic devices typically employ a five-layer sandwich structure, consisting of a first transparent conductive electrode, an electrolyte layer, an electrochromic layer, an ion storage layer, and a second transparent conductive electrode, making their fabrication quite complex and cumbersome. Therefore, from a green and safe perspective, providing an integrated, environmentally friendly electrochromic hydrogel and electrochromic device is of significant importance. Summary of the Invention
[0005] This invention proposes a transparent-green electrochromic hydrogel based on viologen derivatives, its preparation, and its application. Display devices assembled from this electrochromic hydrogel exhibit high transparency in the neutral state and display green in the reduced state, thus enriching the variety of electrochromic materials.
[0006] The technical solution of the present invention is as follows: A viologen derivative, as shown in formula (I): (I) In formula (I), X - Halogens, for example: Br - I - Cl - Any one of them, preferably Br - .
[0007] The method for preparing the viologen derivative shown in formula (I) of the present invention includes the following steps: (1) 2,7-dibromo-9,9-diethylfluorene, 4-pyridineboronic acid, tetra(triphenylphosphine)palladium, potassium carbonate and 1,4-dioxane were mixed and heated to 90-100°C (preferably 100°C) under N2 protection and refluxed for 45-60 h (preferably 48 h). The reaction solution was then post-treated to obtain the compound shown in formula (II). (II) The molar ratio of 2,7-dibromo-9,9-diethylfluorene to 4-pyridineboronic acid is 1:1.5~3, preferably 1:2~3, and more preferably 1:3; The recommended catalyst dosage is tetra(triphenylphosphine)palladium, which is 0.01% to 0.1% of the molar amount of 2,7-dibromo-9,9-diethylfluorene. Potassium carbonate serves as an alkaline balancing agent to enhance the catalytic activity of the catalyst; the molar ratio of 2,7-dibromo-9,9-diethylfluorene to potassium carbonate is 1:1.5~3, preferably 1:2~3, and more preferably 1:3; 1,4-Dioxane is used as the reaction solvent; the volume-to-mass ratio of 1,4-dioxane to 2,7-dibromo-9,9-diethylfluorene is 27-30:1, mL / g; preferably 28-30:1, mL / g; more preferably 29:1, mL / g; The specific post-processing method is as follows: After the reaction is completed, the reaction solution is cooled to room temperature, water and dichloromethane are added for extraction, the organic phase is dehydrated with anhydrous sodium sulfate, concentrated under reduced pressure and separated by column chromatography, using a mixture of dichloromethane and ethyl acetate in a volume ratio of 20:1 as the eluent, the eluent containing the target compound is collected, and the solvent is removed by rotary evaporation to obtain the compound shown in formula (II). (2) The compound shown in formula (II), 3-bromopropyltrimethylammonium bromide and N,N-dimethylformamide (DMF) were mixed and heated to 110~130℃ under N2 protection and refluxed for 15~24h. The reaction solution was then post-treated to obtain the viologen derivative shown in formula (I). The molar ratio of the compound shown in formula (II) to 3-bromopropyltrimethylammonium bromide is 1:2 to 4, preferably 1:2 to 3, and more preferably 1:3; N,N-dimethylformamide is used as the reaction solvent; the volume-to-mass ratio of N,N-dimethylformamide to the compound shown in formula (II) is 27-30:1, mL / g; preferably 28-30:1, mL / g; more preferably 29:1, mL / g; The specific post-processing method is as follows: After the reaction is completed, wait for the reaction solution to cool to room temperature, and a precipitate will form in the system. Filter and collect the precipitate, wash it with acetonitrile and N,N-dimethylformamide, and dry it at 50°C to obtain the viologen derivative shown in formula (I).
[0008] An electrochromic hydrogel was prepared by the following method: At room temperature, the viologen derivative shown in formula (I), 1,1'-ferrocene dimethyl alcohol and deionized water are mixed and dissolved by sonication. Then, sodium carboxymethyl cellulose (CMC-Na) is added and stirred until a uniform and transparent gel-like substance is formed, thus obtaining an electrochromic hydrogel (initially pale yellow). The preferred formula (I) contains viologen derivative, 1,1'-ferrocene dimethylethanol, sodium carboxymethyl cellulose, and deionized water in a mass ratio of 2:1:17:200.
[0009] An electrochromic display device is assembled according to the following method: 3M double-sided tape is attached to the periphery of the conductive surface of the conductive ITO glass to form an insulating frame. The electrochromic hydrogel of the present invention is evenly coated on the area enclosed by the frame. Another piece of conductive ITO glass is taken and its conductive surface is covered on the hydrogel layer. The frame is pressed to bond the two pieces of conductive ITO glass together to form an electrochromic display device.
[0010] This invention uses conductive ITO glass as the conductive layer, 1,1'-ferrocene dimethyl methanol as the anode supplement material, sodium carboxymethyl cellulose as the polymer electrolyte matrix, and viologen derivatives as shown in formula (I) as electrochromic materials to assemble a transparent-green electrochromic hydrogel display device based on viologen derivatives.
[0011] The technical principles include: This invention synthesizes a novel viologen derivative by using 9,9-diethylfluorene as a bridging structure, breaking the original 4,4'-bipyridine structure, and adjusting the original band gap of viologen, thereby shifting the absorption of viologen in the visible light region. The solubility of the viologen derivative in water can be enhanced by introducing 3-bromopropyltrimethylammonium bromide and modifying it at the N-positions on both sides.
[0012] As an electrochromic material, this viologen derivative exhibits high transmittance in the neutral state, with its absorption peak increasing with the applied negative voltage. In the reduced state, it displays a green color; and as the voltage decreases, the color gradually transitions from green to transparent, repeating this process. The ultraviolet absorption spectrum of this viologen derivative was measured using an electrochemical workstation coupled with a UV-Vis spectrophotometer, revealing high contrast and excellent electrochromic properties.
[0013] The beneficial effects of this invention are as follows: This invention synthesizes a novel viologen derivative electrochromic material by modifying the N-position of viologen with specific substituents, and applies it to electrochromic hydrogels and display devices. The resulting device exhibits high transmittance in the neutral state. When an applied voltage of 1.2 V is applied, the absorption peak shows a significant increase, and the device is green in the reduced state. Furthermore, as the voltage decreases, the color gradually changes from green to transparent, repeating this process. Electrochemical performance tests demonstrate excellent reversible and diffusion-controlled redox properties. The novel viologen derivative provided by this invention enriches the electrochromic material market and has broad application prospects in the field of electrochromism. Attached Figure Description
[0014] Figure 1 : The proton NMR spectrum of formula (I).
[0015] Figure 2 : The proton NMR spectrum of formula (II).
[0016] Figure 3 Example 3: Cyclic voltammetry curves of electrochromic derivatives at different scan rates.
[0017] Figure 4 Example 4: Ultraviolet-visible absorption spectra of the electrochromic device at different voltages.
[0018] Figure 5 Example 5: Response time of electrochromic device at 701nm wavelength.
[0019] Figure 6 Example 5: Stability diagram of electrochromic device at 701nm wavelength. Detailed Implementation
[0020] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.
[0021] In the embodiments of the present invention, unless otherwise specified, all methods used are conventional methods, and all reagents used are commercially available.
[0022] Example 1: Synthesis of Viologen Derivatives
[0023] (1) Under N2 environment, 4-pyridineboronic acid (1.1 g, 9 mmol), 2,7-dibromo-9,9-diethylfluorene (1.14 g, 3 mmol), and tetra(triphenylphosphine)palladium (20 mg) were added to a 50 mL two-necked round-bottom flask, followed by 1,4-dioxane (20 mL) and K2CO3 solution (5.0 M, 10 mL). The mixture was heated to 100 °C and reacted for 48 h. After the reaction cooled, saturated brine and dichloromethane were added for extraction three times. The mixture was then dehydrated with anhydrous Na2SO4, and the solution was evaporated to dryness after adding crude silica gel. A light yellow residue was obtained, which was purified by column chromatography (dichloromethane / ethyl acetate = 20 / 1) to give 0.82 g of the compound shown in formula (II), with a yield of 72.5%. Its 1H NMR characterization is as follows: 1 H NMR (400 MHz, CDCl3) δ 8.73 (d, 4H), δ 8.04 (d, 4H), δ7.89 (s, 2H), δ 7.68 (d, 2H), δ 1.88 (m, 4H), δ 0.79 (t, 6H).
[0024] (2) Under N2 conditions, the compound shown in formula (II) (0.38 g, 1.00 mmol) and 3-bromopropyltrimethylammonium bromide (0.78 g, 3.00 mmol) were added to a 50 mL two-necked round-bottom flask, and DMF (15 mL) was added. The mixture was heated to 130 °C and reacted for 24 h. After cooling to room temperature, a pale yellow product was formed. The product was filtered and washed three times with DMF and anhydrous acetonitrile. Finally, it was dried in a vacuum oven at 50 °C to obtain 0.37 g of the viologen derivative shown in formula (I), with a yield of 64%. Its proton NMR characterization is as follows: 1 H NMR (400 MHz, DMSO-d6): δ 9.35 (q, J = 7.3, 6.6 Hz, 4H), 8.35 (d, J =6.5 Hz, 4H), 8.01 (dd, J=8.1, 1.8 Hz, 1H), 7.84 (d, J = 8.0 Hz, 1H), 7.51 –7.25 (m, 2H), 7.11–6.68 (m, 2H), 4.23 (q, J = 7.0 Hz, 4H), 4.01 (s, 1H), 3.96 (t, J = 6.1 Hz, 1H), 3.56 (m, 22H), 2.36-1.96 (m, 4H), 1.55(s, 6H).
[0025] Example 2 Assembly of electrochromic device
[0026] (1) Dissolve water-soluble viologen derivative (0.02 g, 0.01 mmol) and 1,1'-ferrocene diethanol (0.01 g, 0.04 mmol) in 2 mL of deionized water and sonicate until the 1,1'-ferrocene diethanol is completely dissolved. Then slowly add sodium carboxymethyl cellulose (0.17 g, 0.2 mmol) and stir until homogeneous and transparent, and the gel color is pale yellow.
[0027] (2) Assemble the electrochromic hydrogel into an electrochromic device. Apply 3M tape around the conductive surface of the conductive ITO glass. Apply the electrochromic hydrogel evenly to the frame with a thickness of 3mm. Then cover the frame with the conductive surface of another piece of conductive ITO glass to obtain the electrochromic device.
[0028] Example 3: Electrochemical property testing of electrochromic derivatives
[0029] The redox properties of the viologen derivative shown in formula (I) prepared in Example 1 were studied using a three-electrode system. An aqueous solution of the viologen derivative containing LiCl (0.1 M) (0.1 mmol / L) was used as the electrolyte solution. The working electrode was ITO glass, the counter electrode was platinum wire, and the reference electrode was an Ag / AgCl electrode. Cyclic voltammetry (CV) was used to test the properties at different scan rates.
[0030] The results are as follows Figure 3 As shown, Figure 3 The graph shows the electrochemical properties. It can be seen from the graph that Equation (I) has a pair of obvious redox peaks. As the voltage decreases, the color of the device changes from high transmittance to green. The device can achieve a green color change at 1.2 V.
[0031] Example 4: Spectroelectrochemical Testing of Electrochromic Devices
[0032] The device prepared in Example 2 was tested using a combination of an electrochemical workstation and an ultraviolet spectrometer. The electrochemical workstation was set to constant potential electrolysis, and the ultraviolet spectrometer was set to full-band absorption rate with a scanning range of 400–1100 nm.
[0033] The results are as follows Figure 4 As shown, Figure 4 The visible-ultraviolet spectrum shows almost no absorption in the 400–1100 nm range at the neutral state of 0 V. At 1.2 V, a broad absorption peak appears at 701 nm, indicating that the electrochromic device has completed the colorless to green transition. As the voltage increases further, the absorption peak becomes stronger, and the color of the electrochromic device (ECD) deepens.
[0034] Example 5: Testing the response speed and stability of electrochromic devices
[0035] The device prepared in Example 2 was tested using a combination of an electrochemical workstation and a UV spectrometer. The electrochemical workstation was configured with a multi-potential step method: initial potential of 0V, termination potential of 1.2V, potential pulse width of 10s, and scan time of 12000s. The UV spectrometer was configured with spectral kinetics and a wavelength of 701 nm.
[0036] The final data obtained is as follows Figure 5 , Figure 6 As shown, the coloring time of the electrochromic device is 8.2 s, the fading time is 1.3 s, and the film retains 96.79% contrast after 1000 cycles. The results demonstrate that the electrochromic device provided by this invention exhibits good stability under multiple cycles.
[0037] The ultraviolet absorption spectrum of this device was measured using an electrochemical workstation coupled with a UV-Vis spectrophotometer, revealing high contrast and excellent electrochromic performance. This novel electrochromic device combines electrochromic properties with superior electrochemical performance, showing broad application prospects in the field of electrochromism.
Claims
1. A viologen derivative, as shown in formula (I): (I) In formula (I), X - For Br - I - Cl - Any one of them.
2. The method for preparing the viologen derivative as shown in formula (I) according to claim 1, characterized in that, Includes the following steps: (1) 2,7-dibromo-9,9-diethylfluorene, 4-pyridineboronic acid, tetra(triphenylphosphine)palladium, potassium carbonate and 1,4-dioxane were mixed and heated to 90-100℃ under N2 protection and refluxed for 45-60h. The reaction solution was then post-treated to obtain the compound shown in formula (II). (II) (2) The compound shown in formula (II), 3-bromopropyltrimethylammonium bromide and N,N-dimethylformamide were mixed and heated to 110~130℃ under N2 protection and refluxed for 15~24h. After the reaction solution was post-treated, the viologen derivative shown in formula (I) was obtained.
3. The preparation method according to claim 2, characterized in that, In step (1), the molar ratio of 2,7-dibromo-9,9-diethylfluorene to 4-pyridineboronic acid is 1:1.5~3.
4. The preparation method according to claim 2, characterized in that, In step (1), the amount of tetra(triphenylphosphine)palladium used is 0.01~0.1% of the molar amount of 2,7-dibromo-9,9-diethylfluorene.
5. The preparation method according to claim 2, characterized in that, In step (1), the molar ratio of 2,7-dibromo-9,9-diethylfluorene to potassium carbonate is 1:1.5~3.
6. The preparation method according to claim 2, characterized in that, In step (1), the volume-to-mass ratio of 1,4-dioxane to 2,7-dibromo-9,9-diethylfluorene is 27-30:1, mL / g.
7. The preparation method according to claim 2, characterized in that, In step (2), the molar ratio of the compound shown in formula (II) to 3-bromopropyltrimethylammonium bromide is 1:2~4.
8. The preparation method according to claim 2, characterized in that, In step (2), the volume-to-mass ratio of N,N-dimethylformamide to the compound shown in formula (II) is 27-30:1, mL / g.
9. An electrochromic hydrogel, characterized in that, It is prepared according to the following method: At room temperature, the viologen derivative shown in formula (I) of claim 1, 1'-ferrocene dimethyl alcohol, and deionized water are mixed and dissolved by ultrasonication. Then, sodium carboxymethyl cellulose is added and stirred until a uniform and transparent gel-like substance is formed, thus obtaining an electrochromic hydrogel.
10. An electrochromic display device, characterized in that, It is assembled as follows: 3M double-sided tape is attached to the periphery of the conductive surface of the conductive ITO glass to form an insulating frame. The electrochromic hydrogel described in claim 9 is uniformly coated on the area enclosed by the frame. Another piece of conductive ITO glass is taken and its conductive surface is covered on the hydrogel layer. The frame is pressed together to bond the two pieces of conductive ITO glass to form an electrochromic display device.