An isoindigo-based viologen-based electroactive material and its synthesis and application

Abstract

The present invention discloses an isoindigo-based viologen electroactive material and its synthesis and application, belonging to the technical field of organic semiconductor materials. The technical scheme is: by modifying the isoindigo skeleton and introducing a flexible chain, the solubility and charge transfer performance of the isoindigo-based viologen electroactive material are effectively improved, solving the problem that the traditional isoindigo molecule has poor solubility and the dihedral angle is not conducive to charge transfer; the isoindigo-based viologen electroactive material combines the redox properties of viologen compounds and the charge transfer advantages of isoindigo, showing fast electrochromic response and high efficiency; the isoindigo-based viologen electroactive material shows excellent electrochromic performance in the visible and near-infrared bands, providing new ideas for the development of related devices; it is applied to the preparation of electrochromic devices, showing obvious advantages, and has broad application prospects and commercial value.

Description

Technical Field

[0001] The invention belongs to the technical field of organic semiconductor materials, and specifically relates to an isoindigo-based viologen-based electroactive material and its synthesis and application in the preparation of electrochromic devices. Background Art

[0002] Near-infrared electrochromic materials are a type of material that can change its light absorption characteristics in the near-infrared region when subjected to an electric field. These materials have important application prospects in optoelectronic devices such as adjustable light and thermal management, smart windows, displays, and sensors. There are four main categories of common near-infrared electrochromic materials, including: (1) Oxide materials: such as tungsten oxide, vanadium oxide, etc., which usually need to be prepared at high temperature, and due to their slow ion diffusion kinetics, it takes a long time to reach a stable color change state after the electric field is applied, thus limiting their application range; (2) Metal nanoparticles: such as gold nanoparticles, silver nanoparticles, etc. Metal nanoparticles have excellent electrochromic properties, but their cost is high and their stability is limited; (3) Composite materials: a class of materials with excellent electrochromic properties formed by combining organic materials and inorganic materials, but the preparation process of such composite materials is relatively complicated; (4) Organic small molecules and polymer materials: such as polythiophene, polyaniline, etc. Among them, organic small molecules have great potential in the application of near-infrared electrochromic materials due to their designability.

[0003] Isoindigo is an organic small molecule with a unique structure. It is an isomer of the famous dye indigo and has potential application value in the field of electrochromic materials. However, the isoindigo skeleton itself has factors that are not conducive to electrochromic performance. First, as a rigid planar molecule, isoindigo has poor solubility in conventional solvents, which limits its processability and application range. In order to improve its solubility, it is usually necessary to introduce flexible chains for modification to increase solubility. In addition, the two indigo units in isoindigo have a certain degree of dihedral angle, which is not conducive to the transfer of charge between molecules, thus affecting its electrochromic performance. Therefore, it is of great significance to modify the traditional isoindigo skeleton and design and synthesize a new type of near-infrared electrochromic material containing the isoindigo skeleton. Summary of the invention

[0004] In view of the problem that traditional iso-indigo materials have poor solubility, limited charge transfer and poor electrochromic performance due to their structural characteristics, thus limiting their application in the field of electrochromism, the present invention aims to provide an iso-indigo-based viologen-based electroactive material and its synthesis and application in the preparation of electrochromic devices.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides an isoindigo-based viologen-based electroactive material, the structural formula of which is shown in Formula 1 below:

[0007] ;

[0008] Among them, R 1 Any one selected from a methyl group, an ethyl group, a hydrogen atom and a cyclobutyl group; R 2 Selected from benzyl or ethyl.

[0009] Further, it includes any one of the structural formulas shown in Formula 2 to Formula 5:

[0010] .

[0011] A method for synthesizing an isoindigo-based viologen-based electroactive material is characterized by comprising the following steps:

[0012] (1) Under an inert atmosphere, compound 1 and 4-pyridine boronic acid are mixed and refluxed for coupling reaction, the reaction is quenched with distilled water, extracted, dried, and purified to obtain an intermediate compound;

[0013] The structural formula of the compound 1 is: , where R 1 Any one selected from a methyl group, an ethyl group, a hydrogen atom and a cyclobutyl group;

[0014] The structural formula of the intermediate compound is: ; Among them, R 1 Any one selected from a methyl group, an ethyl group, a hydrogen atom and a cyclobutyl group;

[0015] (2) The intermediate compound and excess R 2 -Br reaction, the reaction is completed, the precipitate is separated by vacuum filtration, washed, and dried to obtain an isoindigo-based viologen-based electroactive material, wherein R 2 Selected from benzyl or ethyl.

[0016] The compound 1 is obtained by reacting the compound 2 with 6-bromoindol-2-one. The structural formula of the compound 2 is , where R 1 Any one selected from a methyl group, an ethyl group, a hydrogen atom and a cyclobutyl group.

[0017] The molar ratio of the compound 2 to 6-bromoindol-2-one is 1:1-1.5, and the reaction conditions are 110-130° C. and reflux reaction for 8-10 h.

[0018] In step (1), the molar ratio of compound 1 to 4-pyridineboronic acid is 1:2-4.

[0019] In step (1), the temperature of the coupling reaction is 80°C to 120°C, and the reaction time is 2 d to 4 d; the catalyst used in the coupling reaction is any one of tetrakis(triphenylphosphine)palladium, palladium acetate and bis(tri-tert-butylphosphine)palladium.

[0020] Furthermore, the catalyst used in the coupling reaction is tetrakis(triphenylphosphine)palladium.

[0021] Furthermore, the molar ratio of the catalyst to compound 1 is 0.04-0.06:1.

[0022] Furthermore, the reaction solvent used in the coupling reaction is a mixed solvent of toluene, water and ethanol in a volume ratio of 15:2:1.

[0023] In step (1), the eluent used for purification is a mixed solvent prepared by mixing dichloromethane and ethyl acetate in a volume ratio of 1:1 to 3.

[0024] Furthermore, the eluent used in the purification is a mixed solvent prepared by dichloromethane and ethyl acetate in a volume ratio of 1:2.

[0025] In step (2), the reaction conditions are 80°C to 100°C and the reaction time is 10 h to 14 h.

[0026] The isoindigo-based viologen electroactive material is used in the preparation of an electrochromic device, wherein the electrochromic device uses the isoindigo-based viologen electroactive material as an electrochromic layer.

[0027] Furthermore, the concentration of the isoindigo-based viologen electroactive material is 2.0×10 -3 mol / L~1×10 -5 mol / L.

[0028] Furthermore, the solvent used in the isoindigo-based viologen electroactive material is a 0.1 mol / L to 0.5 mol / L acetonitrile solution of tetrabutylammonium hexafluorophosphonate.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The isoindigo-based viologen electroactive material provided by the present invention not only increases the solubility of the isoindigo-based viologen electroactive material in a solvent, but also improves its processing performance by introducing a flexible chain modification into the isoindigo skeleton, so that the material is easier to prepare into devices of various shapes and sizes, thereby broadening the scope of application; the viologen compound has excellent redox performance, and after combining with isoindigo, the formed novel material performs well in charge transfer, and the presence of hydrogen bonds within the isoindigo molecule is conducive to the coplanarity of the skeleton, further promoting the transfer of charge, so that the material responds faster and has higher efficiency in the electrochromic process; since isoindigo has two lactam structures and is an excellent electron acceptor, after combining with the viologen compound, the isoindigo-based viologen electroactive material formed can produce significant color changes in the redox process, and by adjusting the molecular structure and substituents, its electrochromic performance can be further adjusted to meet the needs of different application scenarios; the isoindigo-based viologen electroactive material exhibits excellent electrochromic performance in the near-infrared band, providing a new idea and method for the development of near-infrared electrochromic devices. It can be seen that the isoindigo-based viologen-based electroactive materials provided by the present invention have excellent solubility, charge transfer performance, electrochromic performance and near-infrared electrochromic performance, and have broad application prospects in the fields of smart windows, low-energy consumption displays, automobile rearview mirrors, military camouflage, etc.

[0031] The synthesis method of the isoindigo-based viologen electroactive material provided by the present invention is simple to operate and suitable for large-scale production. The synthesis method successfully overcomes the unfavorable factors existing in the isoindigo skeleton itself through strategies such as structural modification, molecular design, introduction of functional groups, and optimization of the synthesis method, and achieves comprehensive improvement in solubility, charge transfer performance, electrochromic performance, and near-infrared electrochromic performance.

[0032] The invention provides an application of the isoindigo-based viologen-based electroactive material in the preparation of an electrochromic device. The isoindigo-based viologen-based electroactive material is used as a color-changing layer of the electrochromic device, and exhibits advantages such as obvious color change, enhanced absorption in the near-infrared region, moderate coloring and fading time, high transmittance, and good cycle stability. This makes the isoindigo-based viologen-based electroactive material have broad application prospects and commercial value in the field of electrochromic devices, and provides new solutions for the fields of smart windows, military camouflage, and smart building sunshade systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the intermediate compound molecule of Example 1 of the present invention;

[0034] Figure 2 This is a hydrogen nuclear magnetic resonance spectrum of the isoindigo-based viologen electroactive material (Formula 2) molecule of Example 1 of the present invention;

[0035] Figure 3 The UV-visible cyclic voltammogram of the isoindigo-based viologen electroactive material (Formula 2) and the intermediate compound molecule of Example 1 of the present invention;

[0036] Figure 4 1 is the cyclic voltammogram of the isoindigo-based viologen-based electroactive material (Formula 2) of Example 1 of the present invention;

[0037] Figure 5 This is a color change test spectrum of a liquid electrochromic device prepared from the isoindigo-based viologen-based electroactive material (Formula 2) of Example 1 of the present invention;

[0038] Figure 6 This is a graph showing the coloring time (Tc) and fading time (Tb) of a liquid electrochromic device prepared from the isoindigo-based viologen-based electroactive material (Formula 2) of Example 1 of the present invention;

[0039] Figure 7 This is a test chart of the cyclic stability of a liquid electrochromic device prepared from the isoindigo-based viologen-based electroactive material (Formula 2) according to Example 1 of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0041] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0043] 1. Implementation

[0044] Example 1

[0045] This embodiment provides an isoindigo-based viologen-based electroactive material, and the specific preparation process includes the following steps:

[0046] (1) Preparation of compound 1 (1,1'-bis(methylcyclobutyl)-6,6'-dibromoisoindigo)

[0047] 1-Cyclobutylmethyl-dihydroindole-2,3-dione (1.63 g, 7.5 mmol) and 6-bromoindole-2-one (1.59 g, 7.5 mmol, 1 eq.) were weighed as starting materials, and the two raw materials were dissolved in acetic acid (30 mL). Concentrated hydrochloric acid (0.3 mL) was added to the solution, and the mixture was refluxed at 120°C for 9 h to obtain a reaction mixture. After the reaction was completed, the reaction mixture was cooled to room temperature, poured into 500 mL of saturated sodium chloride solution, and the solid was precipitated. The solid was washed with distilled water for 3 times and filtered to obtain a preliminary product and a by-product 1-bromomethylcyclobutane (983.6 mg, 6.6 mmol, 6.6 eq.). The preliminary product was dissolved in N,N'-dimethylformamide (DMF, 30 mL) and reacted at 100°C for 10 h. After the reaction was completed, the mixture was cooled to room temperature and poured into 500 mL of saturated sodium chloride solution. mL saturated sodium chloride solution, solid precipitated, washed with distilled water 3 times, and filtered to obtain a solid product; the solid product was vacuum dried at 80 ° C for 6 h and purified by silica gel column chromatography (developing solvent: dichloromethane) to obtain 2.80 g of compound 1 (1,1'-(methylcyclobutyl)-6,6'-dibromoisoindigo) as bright red linear crystals with a yield of 84%.

[0048] The structural formula of compound 1 is: .

[0049] (2) Preparation of intermediate compound (1,1'-bis(methylcyclobutyl)-6,6'-di(4-pyridyl)isoindigo)

[0050] The compound 1 (557 mg, 1.0 mmol), 4-pyridineboronic acid (369 mg, 3.0 mmol, 3 eq.), potassium carbonate (691 mg, 5.0 mmol, 5 eq.) and tetrakis(triphenylphosphine)palladium (58 mg, 0.05 mmol, 0.05 eq.) obtained in step (1) were weighed respectively, and the above raw materials were dissolved in a mixed solvent (toluene, water and ethanol in a volume ratio of 15 mL:2 mL:1 mL), and refluxed at 80°C for 3 days to obtain a reaction solution; after the reaction solution was cooled to room temperature, the reaction solution was poured into distilled water (50 mL) to quench the reaction; the aqueous phase was extracted with dichloromethane (30 mL×3), and the organic phases were combined; then dried with anhydrous sodium sulfate for 5 h to remove water in the organic phase, and the organic solvent was removed by rotary evaporation to obtain a crude product; the crude product was purified by silica gel column chromatography, and the eluent was a mixed solvent of dichloromethane and ethyl acetate in a volume ratio of 1:2, and finally 40 mg of black-red crystalline intermediate compound (1,1'-bis(methylcyclobutyl)-6,6'-dibromoisoindigo), with a yield of 11.1%.

[0051] The physicochemical identification of the above intermediate compounds is shown in the attached Figure 1 , the data looks like this:

[0052] 1 H NMR (600 MHz, CDCl 3 ) δ : 9.29 (d, J = 7.5 Hz, 2H), 8.72 (s, 4H), 7.55(s, 4H), 7.32 (d, J = 7.7 Hz, 2H), 7.02 (s, 2H), 3.91 (d, J = 6.2 Hz, 2H), 2.83(s, 2H), 2.10 (s, 4H), 1.92 (s, 8H).

[0053] 13 C NMR (151 MHz, CDCl 3 ) δ : 168.27, 150.39, 147.63, 145.99, 142.13,133.14, 130.61, 122.26, 121.48, 120.99, 106.40, 45.16, 34.08, 26.39, 18.34.

[0054] HRMS-APCI: m / z [M+H] + Theory: [C36 H 33 N 4 O 2 ] + : 553.25980, Experimental: 553.25834.

[0055] The structural formula of the intermediate compound is confirmed as follows:

[0056] .

[0057] (3) Preparation of isoindigo-based viologen-based electroactive materials

[0058] Under nitrogen protection, the intermediate compound (1.0 mmol, 0.553 g) obtained in step (2) was weighed as a substrate, benzyl bromide (5.5 mL, excess) was added and mixed, and DMF was used as a solvent. The mixture was heated and stirred at 90° C. for 12 hours to obtain a reaction mixture. During the reaction, stirring was performed to ensure that the reaction was uniform. The progress of the reaction was monitored regularly by observing the color change of the reaction solution or taking samples for thin layer chromatography (TLC) analysis. After the reaction was completed, the reaction mixture was cooled to room temperature, and the precipitate was separated by vacuum filtration. The precipitate was washed three times with a mixed solvent (ether, methanol and chloroform in a volume ratio of 10:1:1); the washed precipitate was placed in a high vacuum drying oven and dried until the product reached a constant weight, thereby obtaining 380 mg of a khaki-colored isoindigo-based viologen electroactive material with a yield of 77%.

[0059] The physical and chemical identification of the corresponding khaki isoindigo-based viologen-based electroactive materials is shown in the attached Figure 2 , the data is as follows:

[0060] 1 H NMR (400 MHz, CDCl 3 ) δ : 9.31 (m, 6H), 7.79 (m, 4H), 7.60 (m, 4H), 7.48 (m, 6H), 5.89 (m, 4H), 3.98 (m, 4H), 2.8 (m, 2H), 2.0 (m, 4H), 1.85 (m,8H);

[0061] HRMS-ESI: m / z [M+H] + Theory: [C 50 H 46 Br 2 O 2 N 4 ] + : 894.1967, Experimental: 894.1988.

[0062] The structural formula of the isoindigo-based viologen-based electroactive material is confirmed to be as follows:

[0063] .

[0064] The solution UV-visible spectra of the intermediate compound in this example and the finally prepared isoindigo-based viologen electroactive material (Formula 2) are as follows: Figure 3 As shown, the maximum absorption wavelength λ of the isoindigo-based viologen-based electroactive material (Formula 2) prepared in this embodiment is max is 663 nm, and the maximum absorption wavelength of the intermediate compound in dichloromethane is λ max The maximum absorption wavelength of isoindigo-based viologen-based electroactive materials is 643 nm, which is due to the absorption caused by the intramolecular charge transfer. Compared with the intermediate compound, the maximum absorption wavelength of isoindigo-based viologen-based electroactive materials has shifted 20 nm to the low energy absorption region (i.e., the direction of longer wavelength). This change indicates that after the formation of viologen salt, the charge transfer characteristics of the molecule have changed, resulting in the red shift of the absorption spectrum. In the wavelength range of 550-575 nm, both the intermediate compound and the isoindigo-based viologen-based electroactive materials (Formula 2) show obvious absorption. This absorption band is attributed to π-π* transition absorption, that is, the absorption caused by the transition of π electrons in the molecule from the ground state to the excited state. Compared with the intermediate compound, the molecular structure of isoindigo-based viologen-based electroactive materials (Formula 2) has increased the degree of conjugation. The enhancement of the conjugation effect makes the electron cloud distribution of the molecule more extensive, and the energy required for the electron transition is reduced. This change directly leads to the maximum absorption wavelength shifting to the low energy absorption region, i.e., a red shift of 20 nm. The enhancement of the conjugation effect not only affects the electron cloud distribution of the molecule, but also further affects its spectral characteristics.

[0065] Example 2

[0066] This embodiment provides an isoindigo-based viologen-based electroactive material, and the specific preparation process includes the following steps:

[0067] (1) Preparation of compound 1 (1,1'-dimethyl-6,6'-dibromoisoindigo)

[0068] 1-Methyl-dihydroindole-2,3-dione (1.2089 g, 7.5 mmol) and 6-bromoindole-2-one (1.59 g, 7.5 mmol, 1 eq.) were weighed as starting materials, the two raw materials were dissolved in acetic acid (30 mL), and concentrated hydrochloric acid (0.3 mL) was added, and the reaction mixture was refluxed at 120°C for 9 h to obtain a reaction mixture; after the reaction was completed, the reaction mixture was cooled to room temperature and poured into 500 mL of saturated sodium chloride solution to precipitate a solid, which was washed with distilled water 3 times and filtered to obtain a preliminary product and a by-product 1-bromomethylcyclobutane (983.6 mg, 6.6 mmol, 6.6 eq.), the preliminary product was dissolved in N,N'-dimethylformamide (DMF, 30 mL), and the reaction was carried out at 100°C for 10 h; after the reaction was completed, the reaction mixture was cooled to room temperature and poured into 500 mL of saturated sodium chloride solution to precipitate a solid. mL saturated sodium chloride solution, solid precipitated, washed with distilled water 3 times, and filtered to obtain a solid product; the solid product was vacuum dried at 80 ° C for 6 h, and purified by silica gel column chromatography (developing solvent: dichloromethane) to obtain 2.60 g of compound 1 (1,1'-dimethyl-6,6'-dibromoisoindigo), compound 1 was bright red linear crystals, and the yield was 80%.

[0069] The structural formula of compound 1 is: .

[0070] (2) Preparation of intermediate compound (1,1'-dimethyl-6,6'-di(4-pyridyl)isoindigo)

[0071] The compound 1 (447 mg, 1.0 mmol), 4-pyridineboronic acid (369 mg, 3.0 mmol, 3 eq.), potassium carbonate (691 mg, 5.0 mmol, 5 eq.) and tetrakis(triphenylphosphine)palladium (58 mg, 0.05 mmol, 0.05 eq.) obtained in step (1) were weighed respectively, and the above raw materials were dissolved in a mixed solvent (toluene, water and ethanol in a volume ratio of 15 mL:2 mL:1 mL), and refluxed at 80°C for 3 days to obtain a reaction solution; after the reaction solution was cooled to room temperature, the reaction solution was poured into distilled water (50 mL) to quench the reaction; the aqueous phase was extracted with dichloromethane (30 mL×3), and the organic phases were combined; then dried with anhydrous sodium sulfate for 5 h to remove water in the organic phase, and the organic solvent was removed by rotary evaporation to obtain a crude product; the crude product was purified by silica gel column chromatography, and the eluent was a mixed solvent of dichloromethane and ethyl acetate in a volume ratio of 1:2, and finally 54 mg of black-red crystalline intermediate compound (1,1'-dimethyl-6,6'-di(4-pyridyl)isoindigo), with a yield of 15%.

[0072] The intermediate compound is: .

[0073] (3) Preparation of isoindigo-based viologen-based electroactive materials

[0074] Under nitrogen protection, the intermediate compound (1.0 mmol, 0.3905 g) obtained in step (2) was weighed as a substrate, benzyl bromide (5.5 mL, excess) was added and mixed, and DMF was used as a solvent. The mixture was heated at 90° C. for 12 hours to obtain a reaction mixture. During the reaction, stirring was performed to ensure that the reaction proceeded evenly. The progress of the reaction was monitored regularly by observing the color change of the reaction solution or taking samples for thin layer chromatography (TLC) analysis. After the reaction was completed, the reaction mixture was cooled to room temperature, and the precipitate was separated by vacuum filtration. The precipitate was washed three times with a mixed solvent (ether, methanol and chloroform in a volume ratio of 10:1:1); the washed precipitate was placed in a high vacuum drying oven and dried until the product reached a constant weight, thereby obtaining 390 mg of a khaki-colored isoindigo-based viologen-based electroactive material with a yield of 80%.

[0075] The physicochemical identification data of the corresponding isoindigo-based viologen-based electroactive materials are shown below:

[0076] 1 H NMR (400 MHz, CDCl 3 ) δ : 9.31 (m, 6H), 7.79 (m, 4H), 7.60 (m, 4H), 7.48 (m, 6H), 5.89 (m, 4H), 3.98 (m, 6H);

[0077] HRMS-ESI: m / z [M+H] + Theory: [C 42 H 35 Br 2 O 2 N 4 ] + : 785.1127, Experimental: 785.1252.

[0078] The structural formula of the isoindigo-based viologen-based electroactive material is confirmed to be as follows:

[0079] .

[0080] Example 3

[0081] This embodiment provides an isoindigo-based viologen-based electroactive material, and the specific preparation process includes the following steps:

[0082] (1) Preparation of compound 1 (1,1'-diethyl-6,6'-dibromoisoindigo)

[0083] 1-Ethyl-dihydroindole-2,3-dione (7.5 mmol, 1.344 g) and 6-bromoindole-2-one (1.59 g, 7.5 mmol, 1 eq.) were weighed as starting materials, and the two raw materials were dissolved in acetic acid (30 mL). Concentrated hydrochloric acid (0.3 mL) was added to the solution, and the mixture was refluxed at 120 °C for 9 h to obtain a reaction mixture. After the reaction was completed, the mixture was cooled to room temperature and poured into 500 mL of saturated sodium chloride solution to precipitate a solid, which was washed with distilled water three times and filtered to obtain a preliminary product and a by-product 1-bromomethylcyclobutane (983.6 mg, 6.6 mmol, 6.6 eq.). The preliminary product was dissolved in N,N'-dimethylformamide (DMF, 30 mL) and reacted at 100 °C for 10 h. After the reaction was completed, the mixture was cooled to room temperature and poured into 500 mL of saturated sodium chloride solution to obtain a solid. mL saturated sodium chloride solution, solid precipitated, washed with distilled water 3 times, filtered to obtain a solid product, the solid product was vacuum dried at 80 ° C for 6 h, purified by silica gel column chromatography (developing solvent: dichloromethane), and 2.40 g of compound 1 (1,1'-diethyl-6,6'-dibromoisoindigo) was obtained as bright red linear crystals with a yield of 66%;

[0084] The structural formula of compound 1 is: .

[0085] (2) Preparation of intermediate compounds

[0086] The compound 1 (1.0 mmol, 0.4908 g) obtained in step (1), 4-pyridineboronic acid (369 mg, 3.0 mmol, 3 eq.), potassium carbonate (691 mg, 5.0 mmol, 5 eq.) and tetrakis(triphenylphosphine)palladium (58 mg, 0.05 mmol, 0.05 eq.) obtained in step (1) were weighed respectively, and the above raw materials were dissolved in a mixed solvent (toluene, water and ethanol in a volume ratio of 15 mL:2 mL:1 mL), and refluxed at 80°C for 3 days to obtain a reaction solution; after the reaction solution was cooled to room temperature, the reaction solution was poured into distilled water (50 mL) to quench the reaction; the aqueous phase was extracted with dichloromethane (30 mL×3), and the organic phases were combined; then dried with anhydrous sodium sulfate for 5 h to remove water in the organic phase, and the organic solvent was removed by rotary evaporation to obtain a crude product; the crude product was purified by silica gel column chromatography, and the eluent was a mixed solvent of dichloromethane and ethyl acetate in a volume ratio of 1:2, and finally 40 mg black-red crystalline intermediate compound (1,1'-diethyl-6,6'-di(4-pyridyl)isoindigo), with a yield of 20%.

[0087] The structural formula of the intermediate compound is: .

[0088] (3) Preparation of isoindigo-based viologen-based electroactive materials

[0089] Under nitrogen protection, the intermediate compound (1,1'-diethyl-6,6'-di(4-pyridyl)isoindigo, 1.0 mmol, 0.4185 g) obtained in step (2) and benzyl bromide (5.5 mL, excess) were weighed and mixed, and DMF was used as a solvent. The mixture was heated and stirred at 90°C for 12 hours to obtain a reaction mixture. During the reaction, stirring was performed to ensure that the reaction proceeded evenly. The progress of the reaction was monitored regularly by observing the color change of the reaction solution or taking samples for thin layer chromatography (TLC) analysis. After the reaction was completed, the reaction mixture was cooled to room temperature, and the precipitate was separated by vacuum filtration. The precipitate was washed three times with a mixed solvent (ether, methanol and chloroform in a volume ratio of 10:1:1); the washed precipitate was placed in a high vacuum drying oven and dried until the product reached a constant weight, thereby obtaining a khaki-colored isoindigo-based viologen electroactive material with a yield of 70%.

[0090] The physicochemical identification data of the corresponding isoindigo-based viologen-based electroactive materials are shown below:

[0091] 1 H NMR (400 MHz, CDCl 3 ) δ : 9.31 (m, 6H), 7.79 (m, 4H), 7.60 (m, 4H), 7.48 (m, 6H), 5.89 (m, 4H), 3.98 (m, 4H), 2.8 (m, 6H);

[0092] HRMS-ESI: m / z [M+H] + Theory: [C 44 H 39 Br 2 O 2 N 4 ] + : 813.1440, Experimental: 813.1487.

[0093] The structural formula of the isoindigo-based viologen-based electroactive material prepared in this example is confirmed to be:

[0094] .

[0095] Example 4

[0096] This embodiment provides an isoindigo-based viologen-based electroactive material, and the specific preparation process includes the following steps:

[0097] (1) Preparation of compound 1 (1,1'-bis(methylcyclobutyl)-6,6'-dibromoisoindigo)

[0098] 1-Cyclobutylmethyl-dihydroindole-2,3-dione (1.63 g, 7.5 mmol) and 6-bromoindole-2-one (1.59 g, 7.5 mmol, 1 eq.) were weighed as starting materials, the two raw materials were dissolved in acetic acid (30 mL), and concentrated hydrochloric acid (0.3 mL) was added, and the mixture was refluxed at 120 °C for 9 h to obtain a reaction mixture; after the reaction was completed, the reaction mixture was cooled to room temperature, poured into 500 mL of saturated sodium chloride solution, and the solid was precipitated. The solid was washed with distilled water for 3 times and filtered to obtain a preliminary product and a by-product 1-bromomethylcyclobutane (983.6 mg, 6.6 mmol, 6.6 eq.), and the preliminary product was dissolved in N,N'-dimethylformamide (DMF, 30 mL) and reacted at 100 °C for 10 h; after the reaction was completed, the mixture was cooled to room temperature and poured into 500 mL of saturated sodium chloride solution to precipitate a solid, which was washed with distilled water three times and filtered. The solid product was vacuum dried at 80 °C for 6 h and purified by silica gel column chromatography (developing solvent: dichloromethane) to obtain 2.80 g of bright red linear crystal compound 1 (1,1'-(methylcyclobutyl)-6,6'-dibromoisoindigo), with a yield of 84%;

[0099] The structural formula of compound 1 is: .

[0100] (2) Preparation of intermediate compound (1,1'-bis(methylcyclobutyl)-6,6'-di(4-pyridyl)isoindigo)

[0101] The compound 1 (1,1'-bis(methylcyclobutyl)-6,6'-dibromoisoindigo, 507 mg, 1.0 mmol), 4-pyridineboronic acid (369 mg, 3.0 mmol, 3 eq.), potassium carbonate (691 mg, 5.0 mmol, 5 eq.) and tetrakis(triphenylphosphine)palladium (58 mg, 0.05 mmol, 0.05 eq.) obtained in step (1) were weighed respectively, and the above raw materials were dissolved in a mixed solvent (toluene, water and ethanol in a volume ratio of 15 mL:2 mL:1 mL), and refluxed at 80°C for 3 days to obtain a reaction solution; after the reaction solution was cooled to room temperature, the reaction solution was poured into distilled water (50 mL) to quench the reaction; the aqueous phase was extracted with dichloromethane (30 mL×3), and the organic phases were combined; and then dried over anhydrous sodium sulfate for 5 min. h, to remove water from the organic phase, and then remove the organic solvent by rotary evaporation to obtain a crude product; the crude product was purified by silica gel column chromatography, and the eluent was a mixed solvent of dichloromethane and ethyl acetate in a volume ratio of 1:2, and finally 40 mg of a black-red crystalline intermediate compound (1,1'-bis(methylcyclobutyl)-6,6'-di(4-pyridyl)isoindigo) was obtained, with a yield of 11.1%.

[0102] The structural formula of the intermediate compound is: .

[0103] (3) Preparation of isoindigo-based viologen-based electroactive materials

[0104] Under nitrogen protection, the intermediate compound (0.4505 g, 1.0 mmol) obtained in step (2) was weighed as a substrate, ethyl bromide (5.5 mL, excess) was added and mixed, and DMF was used as a solvent. The mixture was heated and stirred at 90° C. for 12 hours to obtain a reaction mixture. During the reaction, stirring was performed to ensure that the reaction was uniform. The progress of the reaction was monitored regularly by observing the color change of the reaction solution or taking samples for thin layer chromatography (TLC) analysis. After the reaction was completed, the reaction mixture was cooled to room temperature, and the precipitate was separated by vacuum filtration. The precipitate was washed three times with a mixed solvent (ether, methanol and chloroform in a volume ratio of 10:1:1); the washed precipitate was placed in a high vacuum drying oven and dried until the product reached a constant weight, thereby obtaining a khaki-colored isoindigo-based viologen electroactive material with a yield of 65%.

[0105] The physicochemical identification data of the corresponding isoindigo-based viologen-based electroactive materials are shown below:

[0106] 1 H NMR (400 MHz, CDCl 3 ) δ : 9.31 (m, 6H), 7.79 (m, 4H), 5.89 (m, 4H), 3.98 (m, 4H), 3.9 (m, 4H), 2.8 (m, 2H), 2.0 (m, 4H), 1.85 (m, 8H), 1.8 (m,6H);

[0107] HRMS-ESI: m / z [M+H] + Theory: [C 40 H 43 Br 2 O 2 N 4 ] + : 769.1753, Experimental: 769.1898.

[0108] The structural formula of the isoindigo-based viologen-based electroactive material is confirmed to be as follows:

[0109] .

[0110] 2. Electrochemical properties test

[0111] On the basis of Examples 1 to 4, the electrochemical properties of the isoindigo-based viologen-based electroactive materials prepared by the present invention were investigated, and the isoindigo-based viologen-based electroactive materials of the present invention were tested by cyclic voltammetry, and the change of current with voltage was observed by applying a periodically changing voltage.

[0112] In DMF solution, tetrabutylammonium hexafluorophosphate was used as electrolyte (concentration: 0.1 mol / L), a three-electrode system (Pt wire as working electrode, Pt sheet as auxiliary electrode, Ag / AgCl as reference electrode) and ferrocene as reference substance were used, and the scanning rate was 100 mV / s. The isoindigo-based viologen electroactive material of Example 1 was tested (concentration: 1.0×10 -3 mol / L), the cyclic voltammetry curve of the isoindigo-based viologen electroactive material (Formula 2) prepared in Example 1 is as follows Figure 4 shown.

[0113] By the attached Figure 4 From the data, it can be seen that the isoindigo-based viologen-based electroactive material (Formula 2) prepared in Example 1 produced two pairs of redox peaks, located at -0.28 V and -0.07 V, respectively. The first oxidation peak at -0.28 V is a reversible redox peak, and the second oxidation peak at -0.07 V is an irreversible redox peak, indicating that the isoindigo-based viologen-based electroactive material prepared in Example 1 has two pairs of redox peaks, one of which is reversible and the other is irreversible.

[0114] 3. Application Examples

[0115] An electrochromic device was prepared using the isoindigo-based viologen electroactive material (Formula 2) prepared in Example 1 of the present invention. The electrochromic device adopted a sandwich structure, and a liquid cavity was constructed between two layers of ITO-covered glass plates, and the electrochromic active material was placed in the interlayer cavity to obtain an electrochromic device. The ITO glass (2.0 cm×4.0 cm, resistance of 10 Ω / square) was ultrasonically cleaned in acetone for thirty minutes, and purged with nitrogen to ensure that there was no residual acetone on the surface of the ITO glass; a liquid groove was constructed on one of the ITO glasses using 3M double-sided tape, and another ITO glass was combined with the ITO glass with the groove to form an ITO interlayer containing a liquid cavity structure; a liquid containing a concentration of 2.0×10 -3 mol / L solution of isoindigo-based viologen-based electroactive material (Formula 2) is injected into the liquid cavity, and the solvent of the isoindigo-based viologen-based electroactive material (Formula 2) solution is 0.1 mol / L acetonitrile solution of tetrabutylammonium hexafluorophosphonate; the sealing of the ITO interlayer is checked to ensure that there is no leakage, and a liquid electrochromic device is obtained.

[0116] The performance test of the prepared liquid electrochromic device is as follows:

[0117] 1. Spectral test of color change phenomenon of liquid electrochromic device

[0118] The electrochemical workstation is connected in series with the in-situ UV-visible absorption spectroscopy to monitor the absorption spectrum changes of the liquid electrochromic device at different voltages in real time, such as Figure 5 shown.

[0119] By the attached Figure 5 The data show that when positive voltages of different magnitudes are applied to the liquid electrochromic device, a new maximum absorption peak is generated at 807 nm, and as the voltage increases, the intensity of the absorption peak continues to increase, indicating that the optical properties of the isoindigo-based viologen electroactive material of electrochromic material Example 1 are changing; when a voltage of 2.5 V is applied to the liquid electrochromic device, the liquid electrochromic device changes from its original brick red state to a dark green state; as time increases, the absorption peak intensity continues to increase, indicating that the electrochromic reaction is ongoing and the degree of reaction deepens with time; when a voltage of -0.1 V is applied to the liquid electrochromic device, the liquid electrochromic device recovers from the dark green state to the original brick red state, indicating that the electrochromic reaction is reversible and the original color state of the device can be restored by changing the voltage direction. The results show that when the isoindigo-based viologen-based electroactive material of the present invention is used as an electrochromic active material, a new absorption peak will be generated and accompanied by a color change when a positive voltage is applied, and this color change is reversible. The original color can be restored by changing the voltage direction, which provides an important basis for the further research and application of electrochromic devices and demonstrates the potential of isoindigo-based viologen-based electroactive materials in the field of electrochromism.

[0120] 2. Color change performance test of liquid electrochromic device

[0121] This experiment aims to comprehensively evaluate the color-changing performance of liquid electrochromic devices, including coloring time (Tc), fading time (Tb) and cycle stability, and to provide performance parameters and evaluation basis for the application of the isoindigo-based viologen electroactive materials provided by the present invention in the field of electrochromism. Coloring time refers to the time required for the color-changing material to change from a neutral state to a colored state. A voltage is applied to change the device, and the time required for the transmittance to reach 90% of the maximum transmittance difference before and after the color change is recorded; while fading time refers to the time required for the color-changing material to recover from the colored state to the neutral state; the voltage is removed to fade the device, and the time required for the transmittance to reach 90% of the maximum transmittance difference before and after the color change is recorded; cycle stability refers to the number of cycles of the device between the colored state and the faded state. Through multiple cycle tests, the stability of the color-changing performance of the device is observed. The coloring time (Tc) and fading time (Tb) of the liquid electrochromic device prepared using the isoindigo-based viologen electroactive material (Formula 2) of Example 1 were tested. For specific results, see the attached. Figures 6 and 7 shown.

[0122] By the attached Figure 6 From the data, it can be seen from the electrochemical spectrum that the maximum absorption wavelength produced by the color change of the liquid electrochromic device is 807 nm. At this wavelength, the maximum transmittance of the liquid electrochromic device is 64.41%. The voltage is applied to change the liquid electrochromic device from the neutral state to the colored state. The time required for the transmittance to reach 90% difference is 9.3s, that is, the coloring time is 9.3s; the voltage is removed to restore the liquid electrochromic device from the colored state to the neutral state. The time required for the transmittance to reach 90% difference is 25.1s, and the fading time is 25.1s. It shows that the liquid electrochromic device prepared by the isoindigo-based viologen electroactive material (Formula 2) in Example 1 has a faster response speed and is suitable for application scenarios that require rapid color change.

[0123] By the attached Figure 7 The data show that the liquid electrochromic device has a strong cycle stability within 1100s in the cycle stability test, which indicates that the liquid electrochromic device prepared by the isoindigo-based viologen electroactive material (Formula 2) in Example 1 has good durability and reliability, and can maintain stable color-changing performance during long-term use, which provides strong support for the application of the material in the field of near-infrared electrochromic materials. This also shows that the isoindigo-based viologen electroactive material of the present invention has important potential in the application field of near-infrared electrochromic materials.

[0124] The above is only a preferred embodiment of the present invention and is not intended to limit 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 technical principles of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention. The above content is only to illustrate the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention fall within the protection scope of the claims of the present invention.

Claims

1. An isoindigo-based viologen-based electroactive material, characterized in that: The structural formula is shown in Formula 1 below: Wherein, R1 is selected from any one of methyl, ethyl, hydrogen atom and cyclobutyl; R2 is selected from benzyl or ethyl.

2. The isoindigo-based viologen electroactive material according to claim 1, characterized in that: Including any one of the structural formulas shown in Formula 2 to Formula 5: 。 3. A method for synthesizing an isoindigo-based viologen-based electroactive material according to any one of claims 1 to 2, characterized in that: The following steps are involved: (1) Under an inert atmosphere, compound 1 and 4-pyridine boronic acid are mixed and refluxed for coupling reaction, the reaction is quenched with distilled water, extracted, dried, and purified to obtain an intermediate compound; The structural formula of the compound 1 is: , wherein R1 is selected from any one of a methyl group, an ethyl group, a hydrogen atom and a cyclobutyl group; The structural formula of the intermediate compound is: ; Wherein, R1 is selected from any one of a methyl group, an ethyl group, a hydrogen atom and a cyclobutyl group; (2) reacting the intermediate compound with an excess of R2-Br, and after the reaction is completed, separating the precipitate by vacuum filtration, washing, and drying to obtain an isoindigo-based viologen-based electroactive material, wherein R2 is selected from benzyl or ethyl.

4. The method for synthesizing an isoindigo-based viologen-based electroactive material according to claim 3, characterized in that: The compound 1 is obtained by reacting the compound 2 with 6-bromoindol-2-one. The structural formula of the compound 2 is , wherein R1 is selected from any one of a methyl group, an ethyl group, a hydrogen atom and a cyclobutyl group.

5. The method for synthesizing an isoindigo-based viologen-based electroactive material according to claim 4, characterized in that: The molar ratio of the compound 2 to 6-bromoindol-2-one is 1:1-1.5, and the reaction conditions are 110-130° C. and reflux reaction for 8-10 h.

6. The method for synthesizing an isoindigo-based viologen-based electroactive material according to claim 3, characterized in that: In step (1), the molar ratio of compound 1 to 4-pyridineboronic acid is 1:2-4.

7. The method for synthesizing an isoindigo-based viologen-based electroactive material according to claim 3, characterized in that: In step (1), the temperature of the coupling reaction is 80°C to 120°C, and the reaction time is 2 d to 4 d; the catalyst used in the coupling reaction is any one of tetrakis(triphenylphosphine)palladium, palladium acetate and bis(tri-tert-butylphosphine)palladium.

8. The method for synthesizing an isoindigo-based viologen electroactive material according to claim 3, characterized in that: In step (1), the eluent used for purification is a mixed solvent prepared by mixing dichloromethane and ethyl acetate in a volume ratio of 1:1 to 3.

9. The method for synthesizing an isoindigo-based viologen-based electroactive material according to claim 3, characterized in that: In step (2), the reaction conditions are 80°C to 100°C and the reaction time is 10 h to 14 h.

10. Use of an isoindigo-based viologen electroactive material according to any one of claims 1 to 2 in the preparation of an electrochromic device, characterized in that: The electrochromic device uses the isoindigo-based viologen electroactive material as the electrochromic layer.

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