Viologen derivative, preparation method thereof and electrochromic device

Abstract

The invention discloses a viologen derivative, a preparation method thereof and an electrochromic device. The structural formula of the viologen derivative provided by the invention is as shown in the following formula I: # imgabs0 #, wherein R1, R2, R3 and R 4 are respectively and independently selected from substituted or unsubstituted C1-C15 alkyl, C1-C15 alkoxy, C1-C15 cycloalkyl, C1-C15 aryl, C1-C15 alkenyl and C1-C15 alkynyl, and X <-> is any one of I <->, Br <->, Cl <->, ClO4 <->, BF4 <->, PF6 <->, SbF6 <-> or TFSI <->. According to the viologen derivative provided by the invention, a fluorenyl derivative is introduced into a viologen structure to prepare fluorenyl viologen, and the structure has multiple coloring states and can realize color conversion under different voltages.

Description

Technical Field

[0001] The invention relates to the technical field of electrochromic materials, and in particular to a viologen derivative and a preparation method thereof and an electrochromic device. Background Art

[0002] Viologen (1,1'-disubstituted-4,4'-bipyridine) is a common small organic molecule compound with a bipyridine molecular structure. It exhibits obvious color changes under voltage drive, has good optical contrast, high coloring efficiency and redox stability, and is therefore widely used in the field of electrochromism as an organic photoelectric functional material. Although viologen compounds have good electrochemical properties, their coloring state is relatively single, usually blue. This greatly limits their application in the field of optoelectronics. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the above technical background and provide a viologen derivative and a preparation method thereof and an electrochromic device.

[0004] The present invention provides a viologen derivative, and the structural formula of the viologen derivative is shown in the following formula I:

[0005] Formula I Where: R 1 , R 2 , R 3 and R 4 Each independently selected from substituted or unsubstituted C1-C15 alkyl, C1-C15 alkoxy, C1-C15 cycloalkyl, C1-C15 aryl, C1-C15 alkenyl and C1-C15 alkynyl, X - For I - Br - , Cl - , ClO 4 - , BF 4 - PF 6 - , SbF 6 - or TFSI - Any one of .

[0006] The present invention provides a method for preparing the above-mentioned viologen derivatives, which comprises: preparing the viologen derivatives by single alkylation or multiple alkylation.

[0007] The present invention provides an electrochromic device, wherein the cathode electrochromic material of the electrochromic device comprises the above-mentioned viologen derivative or the viologen derivative prepared by the above-mentioned preparation method.

[0008] The present invention has the following beneficial effects.

[0009] The present invention provides a viologen derivative, a preparation method thereof and an electrochromic device. The viologen derivative provided by the present invention is a "fluorenyl viologen" prepared by introducing "fluorene" into the viologen structure. The compound can show different coloring states under different voltages and has good color-changing properties, so that it shows great application value in the field of electrochromism. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0011] Figure 1 is the cyclic voltammetry curve of compound 3; Figure 2 The UV-visible spectrum of the electrochromic device composed of compound 3 and ferrocene. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0013] A viologen derivative, a preparation method thereof, and an electrochromic device provided in an embodiment of the present invention are described in detail below.

[0014] In a first aspect, an embodiment of the present invention provides a viologen derivative, the structural formula of the viologen derivative is shown in Formula I below:

[0015] Formula I Where: R 1 , R 2 , R 3 and R 4Each independently selected from substituted or unsubstituted C1-C15 alkyl, C1-C15 alkoxy, C1-C15 cycloalkyl, C1-C15 aryl, C1-C15 alkenyl and C1-C15 alkynyl, X - For I - Br - , Cl - , ClO 4 - , BF 4 - PF 6 - , SbF 6 - or TFSI - Any one of .

[0016] Viologen is the most common cathode material in the field of electrochromism. During the preparation process, positive charges are introduced into the pyridine group through an alkylation reaction. Fluorene has been widely used in organic optoelectronic materials due to its excellent photoelectric properties and easy modification. The 9th position of fluorene is an active methylene structure, and the two hydrogens at this position are easily alkylated. Therefore, the "fluorene" group in common organic optoelectronic materials also exists in the form of double alkylation substitution. "Fluorenyl viologen" is prepared by introducing "fluorene" into the viologen structure. This type of compound can show different coloring states under different voltages and has good color-changing properties.

[0017] In some alternative embodiments, R 1 and R 2 Each independently is a C1-C15 alkoxy group or a C1-C15 aryl group.

[0018] In some alternative embodiments, R 1 , R 2 , R 3 and R 4 Same or R 1 , R 2 , R 3 and R 4 different.

[0019] In a second aspect, an embodiment of the present invention provides a method for preparing the above-mentioned viologen derivatives, which comprises: preparing the viologen derivatives by single alkylation or multiple alkylation.

[0020] In some optional embodiments, the synthetic route of the one-step alkylation method is as follows: .

[0021] The so-called one-step alkylation method refers to the simultaneous introduction of the R groups on fluorene and pyridine into the skeleton, that is, the R 1 =R 2 =R 3 =R 4 Compared with the multiple alkylation method, the single alkylation method for preparing "fluorenyl viologen" shortens the synthesis route and thus saves the preparation cost.

[0022] In some optional implementations, the reaction material input amounts are as follows: During the coupling process, the amount of pyridine-4-boronic acid used was 2 eq~2.2 eq, K 2 CO 3 The dosage is 2 eq, and the dosage of palladium catalyst is 0.01eq~0.02 eq; During N-alkylation, X - Cl - Br - or I - , RX dosage is 4eq~5eq, when X - for ClO 4 - , BF 4 - PF 6 - , SbF 6 - or TFSI - When the product is dissolved in water, an excess of LiClO is added. 4 , LiBF 4 、LiPF 6 、NaSbF 6 Or an aqueous solution of LiTFSI, and then filter and dry the precipitated precipitate.

[0023] In some optional embodiments, the synthesis route of the multiple alkylation method is as follows: .

[0024] The so-called multiple alkylation is to introduce alkyl groups into the "fluorene" and "pyridine" units respectively. Multiple alkylation can achieve R 1 , R 2 With R 3 , R 4 The separate regulation of these two pairs of combinations yields more diverse types and properties of fluorenyl viologens.

[0025] In some optional implementations, the reaction material input amounts are as follows: In the alkylation process of C, X' is Cl, Br or I, the amount of NaOH used is 2eq~2.2eq, R 1 X' dosage is 1eq, R2 The dosage of X' is 1 eq~1.05 eq; During the coupling process, the amount of pyridine-4-boronic acid used was 2 eq~2.2 eq, K 2 CO 3 The dosage is 2 eq, and the dosage of palladium catalyst is 0.01eq~0.02 eq; During N-alkylation, X - Cl - Br - or I - , R 3 The dosage of X is 1eq~1.05eq, R 4 The dosage of X is 1eq~1.05eq. - for ClO 4 - , BF 4 - PF 6 - , SbF 6 - or TFSI - When the product is dissolved in water, an excess of LiClO is added. 4 , LiBF 4 、LiPF 6 、NaSbF 6 Or an aqueous solution of LiTFSI, and then filter and dry the precipitated precipitate.

[0026] In a third aspect, an embodiment of the present invention provides an electrochromic device, wherein the cathode electrochromic material of the electrochromic device includes the above-mentioned viologen derivative or the viologen derivative prepared by the above-mentioned preparation method.

[0027] In some optional embodiments, the electrochromic device is electrochromic dimming glass.

[0028] The present invention will be further described below in conjunction with the embodiments.

[0029] An embodiment of the present invention provides a viologen derivative, and the structural formula of the viologen derivative is shown in Formula I below:

[0030] Formula I Where: R 1 , R 2 , R 3 and R 4 Each independently selected from substituted or unsubstituted C1-C15 alkyl, C1-C15 alkoxy, C1-C15 cycloalkyl, C1-C15 aryl, C1-C15 alkenyl and C1-C15 alkynyl, X- For I - Br - , Cl - , ClO 4 - , BF 4 - PF 6 - , SbF 6 - or TFSI - Any one of .

[0031] The above-mentioned viologen derivatives can be synthesized by a single alkylation method and a multiple alkylation method. The synthesis route of the multiple alkylation method is as follows: .

[0032] in: In the alkylation process of C, X' is Cl, Br or I, the amount of NaOH used is 2eq~2.2eq, R 1 X' dosage is 1eq, R 2 The dosage of X' is 1eq~1.05eq, R 1 and R 2 One or more selected from the group consisting of C1-C15 alkyl, C1-C15 alkoxy, C1-C15 cycloalkyl, C1-C15 aryl, C1-C15 alkenyl and C1-C15 alkynyl.

[0033] During the coupling process, the amount of pyridine-4-boronic acid used was 2 eq~2.2 eq, K 2 CO 3 The dosage is 2 eq, and the dosage of palladium catalyst is 0.01eq~0.02eq.

[0034] During N-alkylation, X - Cl - Br - or I - , R 3 The dosage of X is 1eq~1.05eq, R 4 The dosage of X is 1eq~1.05eq. - for ClO 4 - , BF 4 - PF 6 - , SbF 6 - or TFSI - When the product in step 3 is dissolved in water, an excess of LiClO 4 , LiBF 4、LiPF 6 、NaSbF 6 Or an aqueous solution of LiTFSI, and then filter and dry the precipitated precipitate.

[0035] The synthetic route of the single alkylation method is as follows: .

[0036] in: During the coupling process, the amount of pyridine-4-boronic acid used was 2 eq~2.2 eq, K 2 CO 3 The dosage is 2 eq, and the dosage of palladium catalyst is 0.01eq~0.02 eq.

[0037] During N-alkylation, X - Cl - Br - or I - , RX usage is 4eq~5eq.

[0038] When X - for ClO 4 - , BF 4 - PF 6 - , SbF 6 - or TFSI - When the product in step 2 is dissolved in water, an excess of LiClO 4 , LiBF 4 、LiPF 6 、NaSbF 6 Or an aqueous solution of LiTFSI, and then filter and dry the precipitated precipitate.

[0039] Example 1: The structural formula of compound 1 is shown below: .

[0040] The multiple alkylation method for synthesizing compound 1 comprises the following steps: Step 1: Synthesis of Intermediate 1 In a two-necked round-bottom flask, 3.24 g of 2,7-dibromofluorene and 0.8 g of sodium hydroxide were dissolved in 100 mL of a mixed solvent of tetrahydrofuran / water = 5:1 and stirred at 60 °C for 1 h. 2.18 g of ethyl bromide was slowly added dropwise, and the reaction progress was monitored by thin layer chromatography. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phase was then distilled under reduced pressure to obtain a crude product, which was purified by column chromatography (mobile phase: petroleum ether) to obtain 2.96 g of intermediate 1 (yield 78%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 7.79 (d, J = 8.3 Hz, 2H), 7.72(s, 2H), 7.55 (d, J = 7.5 Hz, 2H), 1.89 (q, J = 7.3 Hz, 4H), 0.89 (q, J = 6.7Hz, 6H). The structural formula of intermediate 1 is as follows: .

[0041] Step 2: Synthesis of Intermediate 2 In a two-necked round-bottom flask, 3.8 g of intermediate 1 and 2.46 g of pyridine-4-boric acid were dissolved in 100 mL of a mixed solvent of dioxane / water = 5:1. After nitrogen bubbling for 15 min, 116 mg of tetrakistriphenylphosphine palladium was added and reacted at 100 °C for 12 h. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phase was then distilled under reduced pressure to obtain a crude product, which was purified by column chromatography (mobile phase: dichloromethane / ethyl acetate = 8 / 1) to obtain 2.67 g of intermediate 2 (yield 71%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 8.71 (d, J = 8.2 Hz, 4H), 8.09-7.89 (m, 8H), 7.78 (d, J = 7.3 Hz, 2H), 1.91 (q, J = 7.1 Hz, 4H), 0.92 (q, J = 6.6 Hz, 6H). The structural formula of intermediate 2 is as follows: .

[0042] Step 3: Synthesis of Intermediate 3 In a two-necked round-bottom flask, 3.77 g of intermediate 2 and 2.84 g of iodomethane were dissolved in 50 mL of DMF and reacted at 80°C for 12 h. When the raw materials reacted completely, the reaction was cooled to room temperature and 200 mL of dichloromethane was added to precipitate a large amount of powder. The powder was filtered and washed to obtain 4.88 g of intermediate 3 (yield 74%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 9.08 (d, J = 6.9 Hz, 4H), 8.96 (d, J = 7.1 Hz, 4H), 8.09-7.78 (m, 6H), 4.39 (s, 6H),1.94 (q, J = 7.2 Hz, 4H), 0.95 (q, J = 6.9 Hz, 6H). The structural formula of intermediate 3 is as follows: .

[0043] Step 4: Synthesis of compound 1 6.6 g of intermediate 3 and 10 g of LiClO 4 The product was dissolved in two 30 mL portions of deionized water, and then the two were mixed to precipitate a large amount of light yellow solid. The precipitate was filtered and washed three times with deionized water to complete the purification of compound 1 (5.32 g, yield 88%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 9.08 (d, J = 6.9 Hz, 4H), 8.96 (d, J = 7.1 Hz, 4H), 8.09-7.78 (m, 6H), 4.39 (s, 6H), 1.94 (q, J = 7.2 Hz,4H), 0.95 (q, J = 6.9 Hz, 6H).

[0044] Example 2: The structural formula of compound 2 is shown below: .

[0045] The multiple alkylation method for synthesizing compound 2 comprises the following steps: Step 1: Synthesis of intermediate 4 In a two-necked round-bottom flask, 3.24 g of 2,7-dibromofluorene and 0.8 g of sodium hydroxide were dissolved in 100 mL of a mixed solvent of tetrahydrofuran / water = 5:1 and stirred at 60 °C for 1 h. 2.84 g of iodomethane was slowly added dropwise, and the reaction progress was monitored by thin layer chromatography. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phase was then distilled under reduced pressure to obtain a crude product, which was purified by column chromatography (mobile phase: petroleum ether) to obtain 2.85 g of intermediate 4 (yield 81%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 7.79 (d, J = 8.3 Hz, 2H), 7.72(s, 2H), 7.55 (d, J = 7.5 Hz, 2H), 1.69 (s, 6H). The structural formula of intermediate 4 is as follows: .

[0046] Step 2: Synthesis of intermediate 5 In a two-necked round-bottom flask, 3.52 g of intermediate 4 and 2.46 g of pyridine-4-boric acid were dissolved in 100 mL of a mixed solvent of dioxane / water = 5:1. After nitrogen bubbling for 15 min, 116 mg of tetrakistriphenylphosphine palladium was added and reacted at 100 °C for 12 h. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phase was then distilled under reduced pressure to obtain a crude product, which was purified by column chromatography (mobile phase: dichloromethane / ethyl acetate = 8 / 1) to obtain 2.40 g of intermediate 5 (yield 69%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 8.71 (d, J = 8.2 Hz, 4H), 8.09-7.89 (m, 8H), 7.78 (d, J = 7.3 Hz, 2H), 1.69 (s, 6H). The structural formula of intermediate 5 is as follows: .

[0047] Step 3: Synthesis of intermediate 6 In a two-necked round-bottom flask, 3.48 g of intermediate 5 and 2.84 bromoethane were dissolved in 50 mL of DMF and reacted at 80°C for 12 h. When the raw materials reacted completely, the reaction was cooled to room temperature and 200 mL of dichloromethane was added to precipitate a large amount of powder. The powder was filtered and washed to obtain 4.75 g of intermediate 6 (yield 84%). 1H NMR (500 MHz, DMSO-d 6 ): δ 9.08 (d, J = 6.9 Hz, 4H), 8.96 (d, J = 7.1 Hz, 4H), 8.09-7.78 (m, 6H), 4.51 (q, J = 6.6Hz, 4H), 1.69 (s, 6H), 1.53 (q, J = 6.9 Hz, 6H). The structural formula of intermediate 6 is as follows: .

[0048] Step 4: Synthesis of compound 2 5.66 g of intermediate 6 and 10 g of LiTFSI were dissolved in two 30 mL portions of deionized water, respectively. The two were then mixed to precipitate a large amount of light yellow solid. The precipitate was filtered and washed three times with deionized water to complete the purification of compound 1 (8.04 g, yield 81%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 9.08 (d, J = 6.9 Hz, 4H), 8.96 (d, J = 7.1 Hz, 4H), 8.09-7.78 (m, 6H), 4.51 (q, J = 6.6 Hz, 4H), 1.69 (s,6H), 1.53 (q, J = 6.9 Hz, 6H).

[0049] Example 3: The structural formula of compound 3 is shown below: .

[0050] The first two steps of preparing compound 3 by multiple alkylation method are the same as those of preparing compound 1, and the synthesis can be continued directly based on intermediate 2.

[0051] Step 1: Synthesis of intermediate 1 (same as Step 1 in Example 1).

[0052] Step 2: Synthesis of intermediate 2 (same as Step 1 in Example 1).

[0053] Step 3: Synthesis of intermediate 7 In a two-necked round-bottom flask, 3.77 g of intermediate 2 and 2.84 bromoethane were dissolved in 50 mL of DMF and reacted at 80°C for 12 h. When the raw materials reacted completely, the reaction was cooled to room temperature and 200 mL of dichloromethane was added to precipitate a large amount of powder. The powder was filtered and washed to obtain 4.46 g of intermediate 7 (yield 75%). 1H NMR (500 MHz, DMSO-d 6 ): δ 9.08 (d, J = 6.9 Hz, 4H), 8.96 (d, J = 7.1 Hz, 4H), 8.09-7.78 (m, 6H), 4.51 (q, J = 6.6Hz, 4H), 1.89 (q, J = 6.2 Hz, 4H), 1.53 (t, J = 6.9 Hz, 6H), 0.89 (t, J = 7.1Hz, 6H). The structural formula of intermediate 7 is shown below: .

[0054] Step 4: Synthesis of compound 3 5.94 g of intermediate 7 and 10 g of LiPF 6 The product was dissolved in two 30 mL portions of deionized water, and then the two were mixed to precipitate a large amount of light yellow solid. The precipitate was filtered and washed three times with deionized water to complete the purification of compound 3 (6.23 g, yield 86%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 9.08 (d, J = 6.9 Hz, 4H), 8.96 (d, J =7.1 Hz, 4H), 8.09-7.78 (m, 6H), 4.51 (q, J = 6.6 Hz, 4H), 1.89 (q, J = 6.2Hz, 4H), 1.53 (t, J = 6.9 Hz, 6H), 0.89 (t, J = 7.1 Hz, 6H).

[0055] The cyclic voltammetry curve of compound 3 (concentration of 20 mmol) prepared above in propylene carbonate solution (PC) is shown in Figure 1 It can be seen that the redox properties of the viologen derivative are reversible and non-diffusion controlled, and have good reversible redox activity; two pieces of 40*40*0.4mm ITO-coated glass were glued together at offset points, the device box thickness was 125 microns, compound 3 and ferrocene were mixed into a solution and filled into the prepared electrochromic device by vacuum filling, a voltage was applied at both ends, and the UV-visible spectrum was measured from 1.4 to 1.6V (see Figure 2 ). Since the molar extinction coefficient of ferrocene is very low, Figure 2 It can be basically considered as the chromatogram of compound 3. Figure 2As shown, at 1.4 V, the absorption of compound 3 is mainly distributed around 500 nm. When the voltage continues to increase, the absorption of compound 1 at 660 nm is significantly enhanced, which indicates that the color state of compound 3 changes from red to blue.

[0056] Example 4: The structural formula of compound 3 is shown below: .

[0057] The one-step alkylation method for synthesizing compound 3 comprises the following steps: Step 1: Synthesis of intermediate 8 In a two-necked round-bottom flask, 3.24 g of 2,7-dibromofluorene and 2.46 g of pyridine-4-boric acid were dissolved in 100 mL of a mixed solvent of dioxane / water = 5:1. Nitrogen was bubbled for 15 min, and then 116 mg of tetrakistriphenylphosphine palladium was added. The reaction was allowed to react at 100 °C for 12 h. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phase was then distilled under reduced pressure to obtain a crude product, which was purified by column chromatography (mobile phase: dichloromethane / ethyl acetate = 8 / 1) to obtain 1.82 g of intermediate 8 (yield 57%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 8.71 (d, J = 8.3Hz, 4H), 8.00-7.78 (m, 10H), 4.12 (s, 2H). The structural formula of intermediate 8 is as follows: .

[0058] Step 2: Synthesis of intermediate 9 In a two-necked round-bottom flask, 3.2 g of intermediate 8 and 0.8 g of sodium hydroxide were dissolved in 100 mL of DMF. After reacting at 80°C for 1 h, 4.9 g of ethyl bromide was added and the reaction continued for 12 h. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of dichloromethane was added, and a large amount of powder was precipitated. The powder was filtered and washed to obtain 4.28 g of intermediate 9 (yield 72%). 1 HNMR (500 MHz, DMSO-d 6): δ 9.08 (d, J = 6.9 Hz, 4H), 8.96 (d, J = 7.1 Hz, 4H),8.09-7.78 (m, 6H), 4.51 (q, J = 6.6 Hz, 4H), 1.89 (q, J = 6.2 Hz, 4H), 1.53(t, J = 6.9 Hz, 6H), 0.89 (t, J = 7.1 Hz, 6H). The structural formula of intermediate 9 is as follows: .

[0059] Step 3: Synthesis of compound 3 (same as step 4 in Example 3).

[0060] Example 5: The structural formula of compound 4 is shown below: .

[0061] The one-step alkylation method for synthesizing compound 4 comprises the following steps: Step 1: Synthesis of intermediate 8 (same as Step 1 in Example 4).

[0062] Step 2: Synthesis of intermediate 10 In a two-necked round-bottom flask, 3.2 g of intermediate 8 and 0.8 g of sodium hydroxide were dissolved in 100 mL of DMF. After reacting at 80°C for 1 h, 5.67 g of benzyl chloride was added and the reaction continued for 12 h. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of dichloromethane was added, and a large amount of powder was precipitated. The powder was filtered and washed to obtain 4.28 g of intermediate 9 (yield 72%). 1 HNMR (500 MHz, DMSO-d 6 ): δ 9.03 (d, J = 6.9 Hz, 4H), 8.96 (d, J = 7.1 Hz, 4H),8.09 (d, J = 7.2 Hz, 2H), 7.89 (s, 2H), 7.78 (d, J = 6.6 Hz, 2H), 7.60-7.44(m, 10H), 7.23-7.19 (m, 10H), 5.94 (s, 4H), 3.11 (s, 4H). The structural formula of intermediate 10 is as follows: .

[0063] Step 3: Synthesis of compound 4 7.54 g of intermediate 10 and 10 g of NaSbF 6The product was dissolved in two 30 mL portions of deionized water, and then the two were mixed to precipitate a large amount of light yellow solid. The precipitate was filtered and washed three times with deionized water to complete the purification of compound 3 (9.58 g, yield 83%). 1 H NMR (500 MHz, DMSO-d 6 ): δ 9.03 (d, J = 6.9 Hz, 4H), 8.96 (d, J = 7.1 Hz, 4H), 8.09 (d, J = 7.2 Hz, 2H), 7.89 (s, 2H), 7.78 (d, J = 6.6Hz, 2H), 7.60-7.44 (m, 10H), 7.23-7.19 (m, 10H), 5.94 (s, 4H), 3.11 (s, 4H).

[0064] Comparative Example 1: Synthesis of Intermediate 1 In a two-necked round-bottom flask, 3.24 g of 2,7-dibromofluorene and 0.8 g of sodium hydroxide were dissolved in 100 mL of a mixed solvent of tetrahydrofuran / water = 5:1 and stirred at 60 °C for 20 min. 2.18 g of ethyl bromide was slowly added dropwise, and the reaction progress was monitored by thin layer chromatography. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phase was then distilled under reduced pressure to obtain a crude product, which was purified by column chromatography (mobile phase: petroleum ether) to obtain 1.63 g of intermediate 1 (yield 43%).

[0065] Comparative Example 2: Synthesis of Intermediate 9 In a two-necked round-bottom flask, 3.2 g of intermediate 8 and 0.8 g of sodium hydroxide were dissolved in 100 mL of DMF. After reacting at 80°C for 20 h, 4.9 g of ethyl bromide was added and the reaction continued for 12 h. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of dichloromethane was added, and a large amount of powder was precipitated. The powder was filtered and washed to obtain 1.84 g of intermediate 9 (yield 31%).

[0066] Comparative Example 3: Synthesis of Intermediate 1 In a two-necked round-bottom flask, 3.24 g of 2,7-dibromofluorene and 1.38 g of potassium carbonate were dissolved in 100 mL of a mixed solvent of tetrahydrofuran / water = 5:1 and stirred at 60 °C for 4 h. 2.18 g of ethyl bromide was slowly added dropwise, and the reaction progress was monitored by thin layer chromatography. When the raw materials reacted completely, the reaction was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phase was then distilled under reduced pressure to obtain a crude product, which was purified by column chromatography (mobile phase: petroleum ether) to obtain 0.45 g of intermediate 1 (yield 12%).

[0067] As can be seen from the above, in Examples 1, 2 and 3, 2,7-dibromofluorene is first alkylated, then coupled with a pyridine group, and then a secondary alkylation route is performed to obtain "fluorenyl purple essence". In Example 4-5, 2,7-dibromofluorene is first directly coupled with pyridine, followed by a one-step alkylation reaction, and four alkyl groups are simultaneously introduced into the main structure, and finally "fluorenyl purple essence" is obtained. One alkylation has one less step in the synthesis step than multiple alkylations, saving time and material costs. However, whether it is "fluorenyl purple essence" prepared by multiple alkylations or one alkylation, it can show a coloring state from red to blue under different voltages. In Comparative Examples 1 and 2, insufficient reaction time after adding sodium hydroxide will result in too low a yield. This is because the active hydrogen on fluorene is not fully involved in the reaction. As can be seen from Comparative Example 3, when sodium hydroxide is replaced with potassium carbonate, which has a weaker alkalinity, even if the reaction time is increased to 4 h, the active hydrogen on fluorene cannot be effectively reacted, resulting in an extremely low yield.

[0068] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A viologen derivative, characterized in that: The structural formula of the viologen derivative is shown in Formula I below: Formula I Wherein: R1, R2, R3 and R4 are each independently selected from substituted or unsubstituted C1-C15 alkyl, C1-C15 alkoxy, C1-C15 cycloalkyl, C1-C15 aryl, C1-C15 alkenyl and C1-C15 alkynyl, X - For I - Br - , Cl - 、ClO4 - 、BF4 - PF6 - 、SbF6 - or TFSI - Any one of .

2. The viologen derivative according to claim 1, characterized in that R1 and R2 in the viologen derivative are each independently a C1-C15 alkoxy group or a C1-C15 aryl group.

3. The viologen derivative according to claim 1, characterized in that R1, R2, R3 and R4 in the viologen derivative are the same or R1, R2, R3 and R4 are different.

4. A method for preparing a viologen derivative as claimed in any one of claims 1 to 3, characterized in that: It includes: Viologen derivatives are prepared by single alkylation or multiple alkylation.

5. The preparation method according to claim 4, characterized in that: The synthetic route of the one-step alkylation method is as follows: 。 6. The preparation method according to claim 5, characterized in that: The input amounts of the reaction materials are as follows: during the coupling process, the amount of pyridine-4-boric acid used is 2 eq~2.2 eq, the amount of K2CO3 used is 2 eq, and the amount of palladium catalyst used is 0.01 eq~0.02 eq; During N-alkylation, X - Cl - Br - or I - , RX dosage is 4eq~5eq, when X - For ClO4 - 、BF4 - PF6 - 、SbF6 - or TFSI - When the product is dissolved in water, an excess of LiClO4, LiBF4, LiPF6, NaSbF6 or LiTFSI aqueous solution is added, and the precipitated precipitate is filtered and dried.

7. The preparation method according to claim 4, characterized in that: The synthetic route of the multiple alkylation method is as follows: 。 8. The preparation method according to claim 7, characterized in that: The amount of reaction materials input is as follows: in the C alkylation process, X' is Cl, Br or I, the amount of NaOH used is 2eq~2.2 eq, the amount of R1X' used is 1eq, and the amount of R2X' used is 1eq~1.05 eq; During the coupling process, the amount of pyridine-4-boronic acid used was 2 eq~2.2 eq, the amount of K2CO3 used was 2 eq, and the amount of palladium catalyst used was 0.01 eq~0.02 eq; During N-alkylation, X - Cl - Br - or I - , R3X dosage is 1eq~1.05 eq, R4X dosage is 1eq~1.05 eq, when X - For ClO4 - 、BF4 - PF6 - 、SbF6 - or TFSI - When the product is dissolved in water, an excess of LiClO4, LiBF4, LiPF6, NaSbF6 or LiTFSI aqueous solution is added, and the precipitated precipitate is filtered and dried.

9. An electrochromic device, characterized in that: The cathode electrochromic material of the electrochromic device comprises the viologen derivative described in any one of claims 1 to 3 or the viologen derivative prepared by the preparation method described in any one of claims 4 to 8.

10. The electrochromic device according to claim 9, characterized in that: The electrochromic device is electrochromic dimming glass.

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