Violet derivatives, their preparation methods, and electrochromic devices

Abstract

This invention discloses a violet derivative, its preparation method, and an electrochromic device. The violet derivative provided by this invention has the following structural formula I: Formula I Wherein: R1, R2, R3, and R 4 Each is 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 groups, X ‑ For I ‑ ,Br ‑ Cl ‑ ClO4 ‑ BF4 ‑ PF6 ‑ SbF6 ‑ or TFSI ‑ Any one of the following. The violet derivative provided by this invention, by introducing a fluorenyl derivative into the violet structure, prepares "fluorenyl violet". This type of structure has multiple color states and can achieve color change under different voltages.

Description

Technical Field

[0001] This invention relates to the field of electrochromic materials technology, and more specifically, to a violet derivative, its preparation method, and an electrochromic device. Background Technology

[0002] Violetine (1,1'-disubstituted-4,4'-bipyridine) is a common small organic molecule compound with a bipyridine molecular structure. It exhibits a significant color change under voltage-driven conditions, possessing good optical contrast, high coloring efficiency, and redox stability. Therefore, it is widely used as an organic optoelectronic functional material in the field of electrochromism. Although violetine compounds have excellent electrochemical properties, their color state is relatively singular, typically blue. This greatly limits their application in optoelectronic fields. Summary of the Invention

[0003] The purpose of this invention is to overcome the defects in the above-mentioned technical background by providing a violet derivative, its preparation method, and an electrochromic device.

[0004] This invention provides a violet derivative, the structural formula of which is shown in Formula I below:

[0005]

[0006] Formula I

[0007] 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 groups, X - For I - ,Br - Cl - ClO4 - BF4 - PF6 - SbF6 - or TFSI - Any one of them.

[0008] The present invention provides a method for preparing the above-mentioned violet derivative, which includes: preparing the violet derivative by one-time alkylation or multiple alkylation.

[0009] The present invention provides an electrochromic device, wherein the cathode electrochromic material of the electrochromic device includes the above-mentioned violet derivative or the violet derivative prepared by the above-mentioned preparation method.

[0010] The present invention has the following beneficial effects.

[0011] This invention provides a violet derivative, its preparation method, and an electrochromic device. The violet derivative provided by this invention is "fluorene-based violet" prepared by introducing "fluorene" into the violet structure. This type of compound can exhibit different color states under different voltages and has good color-changing properties, making it of great application value in the field of electrochromism. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 The cyclic voltammetry curves for compound 3 are shown.

[0014] Figure 2 The image shows the UV-Vis spectrum of an electrochromic device composed of compound 3 and ferrocene. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0016] The following is a detailed description of a violet derivative, its preparation method, and an electrochromic device provided by embodiments of the present invention.

[0017] In a first aspect, embodiments of the present invention provide a violetin derivative, the structural formula of which is shown in Formula I below:

[0018]

[0019] Formula I

[0020] 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 groups, X - For I - ,Br - Cl - ClO4 - BF4 - PF6 -SbF6 - or TFSI - Any one of them.

[0021] Violet is the most common cathode material in the field of electrochromic applications. During its preparation, a positive charge is introduced into the pyridine group via an alkylation reaction. Fluorene, due to its excellent photoelectric properties and ease of modification, has been widely used in organic optoelectronic materials. The 9-position of fluorene is a reactive methylene structure, and the two hydrogens at this position are easily alkylated; therefore, the fluorene group in common organic optoelectronic materials is usually in the form of dialkylated substitution. "Fluorenylviolet," prepared by introducing fluorene into the violet structure, exhibits different color states under different voltages and possesses excellent color-changing properties.

[0022] In some alternative embodiments, R1 and R2 in the violet derivative are each independently C1-C15 alkoxy or C1-C15 aryl groups.

[0023] In some alternative embodiments, R1, R2, R3, and R4 in the violet derivative are the same or different.

[0024] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned violet derivative, which includes: preparing the violet derivative by one-time alkylation or multiple alkylation.

[0025] In some alternative embodiments, the synthetic route of the single alkylation method is as follows:

[0026] .

[0027] The so-called one-time alkylation method refers to the simultaneous introduction of the R groups on fluorene and pyridine into the skeleton, that is, in the prepared "fluorenyl viologen", R1=R2=R3=R4. Compared with the multiple alkylation method, the one-time alkylation method for preparing "fluorenyl viologen" shortens the synthetic route and thus saves preparation costs.

[0028] In some alternative implementations, the amounts of reactants added are as follows:

[0029] During the coupling process, the amount of pyridine-4-boronic acid used was 2 eq to 2.2 eq, the amount of K2CO3 used was 2 eq, and the amount of palladium catalyst used was 0.01 eq to 0.02 eq;

[0030] During N-alkylation, X - For Cl - ,Br - Or I - The amount of RX used is 4eq~5eq, when X - ClO4 -BF4 - PF6 - SbF6 - or TFSI - When preparing the product, it is necessary to dissolve it in water and add an excess of aqueous solution of LiClO4, LiBF4, LiPF6, NaSbF6 or LiTFSI. Then, filter and dry the precipitate.

[0031] In some alternative embodiments, the synthetic route of the multiple alkylation method is as follows:

[0032] .

[0033] Multiple alkylation involves introducing alkyl groups into the "fluorene" and "pyridine" units respectively. Multiple alkylation can achieve separate control of the two pairs of combinations, R1, R2 and R3, R4, resulting in fluorene viologens with more diverse types and properties.

[0034] In some alternative implementations, the amounts of reactants added are as follows:

[0035] During C alkylation, X' is Cl, Br, or I, the amount of NaOH used is 2 eq to 2.2 eq, the amount of R1X' is 1 eq, and the amount of R2X' is 1 eq to 1.05 eq;

[0036] During the coupling process, the amount of pyridine-4-boronic acid used was 2 eq to 2.2 eq, the amount of K2CO3 used was 2 eq, and the amount of palladium catalyst used was 0.01 eq to 0.02 eq;

[0037] During N-alkylation, X - For Cl - ,Br - Or I - The dosage of R3X is 1 eq to 1.05 eq, and the dosage of R4X is 1 eq to 1.05 eq. When X - ClO4 - BF4 - PF6 - SbF6 - or TFSI - When preparing the product, it is necessary to dissolve it in water and add an excess of aqueous solution of LiClO4, LiBF4, LiPF6, NaSbF6 or LiTFSI. Then, filter and dry the precipitate.

[0038] Thirdly, embodiments of the present invention provide an electrochromic device, wherein the cathode electrochromic material of the electrochromic device includes the above-mentioned violet derivative or a violet derivative prepared by the above-mentioned preparation method.

[0039] In some alternative implementations, the electrochromic device is an electrochromic color-changing glass.

[0040] The present invention will be further described below with reference to embodiments.

[0041] This invention provides a violet derivative, the structural formula of which is shown in Formula I below:

[0042]

[0043] Formula I

[0044] 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 groups, X - For I - ,Br - Cl - ClO4 - BF4 - PF6 - SbF6 - or TFSI - Any one of them.

[0045] The above-mentioned violet derivatives can be synthesized using a single alkylation method and a multiple alkylation method. The synthetic route for the multiple alkylation method is shown below:

[0046] .

[0047] in:

[0048] In the C-alkylation process, X' is Cl, Br, or I, the amount of NaOH used is 2 eq to 2.2 eq, the amount of R1X' is 1 eq, the amount of R2X' is 1 eq to 1.05 eq, and R1 and R2 are derived from one or more of the following: C1-C15 alkyl, C1-C15 alkoxy, C1-C15 cycloalkyl, C1-C15 aryl, C1-C15 alkenyl, and C1-C15 alkynyl.

[0049] During the coupling process, the amount of pyridine-4-boronic acid used was 2 eq to 2.2 eq, the amount of K2CO3 used was 2 eq, and the amount of palladium catalyst used was 0.01 eq to 0.02 eq.

[0050] During N-alkylation, X - For Cl - ,Br - Or I - The dosage of R3X is 1 eq to 1.05 eq, and the dosage of R4X is 1 eq to 1.05 eq. When X- ClO4 - BF4 - PF6 - SbF6 - or TFSI - In this process, the product from step 3 needs to be dissolved in water, and an excess of aqueous solution of LiClO4, LiBF4, LiPF6, NaSbF6 or LiTFSI needs to be added. The precipitated precipitate is then filtered and dried.

[0051] The synthetic route for the single alkylation method is shown below:

[0052] .

[0053] in:

[0054] During the coupling process, the amount of pyridine-4-boronic acid used was 2 eq to 2.2 eq, the amount of K2CO3 used was 2 eq, and the amount of palladium catalyst used was 0.01 eq to 0.02 eq.

[0055] During N-alkylation, X - For Cl - ,Br - Or I - The amount of RX used is 4eq~5eq.

[0056] When X - ClO4 - BF4 - PF6 - SbF6 - or TFSI - When doing this, the product from step 2 needs to be dissolved in water, and an excess of aqueous solution of LiClO4, LiBF4, LiPF6, NaSbF6 or LiTFSI needs to be added. Then the precipitated precipitate is filtered and dried.

[0057] Example 1: The structural formula of compound 1 is shown below:

[0058] .

[0059] The synthesis of compound 1 via multiple alkylation methods includes the following steps:

[0060] Step 1: Synthesis of Intermediate 1

[0061] 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 tetrahydrofuran / water mixture (5:1) and stirred at 60 °C for 1 h. 2.18 g of bromoethane was slowly added dropwise, and the reaction progress was monitored by thin-layer chromatography. After the reactants had reacted completely, the reaction mixture was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phases were then distilled under reduced pressure to obtain the crude product, which was purified by column chromatography (mobile phase: petroleum ether) to give 2.96 g of intermediate 1 (78% yield). 1 ¹H NMR (500 MHz, DMSO-d⁶): 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 = 6.7 Hz, 6H). The structural formula of intermediate 1 is shown below:

[0062] .

[0063] Step 2: Synthesis of Intermediate 2

[0064] In a two-necked round-bottom flask, 3.8 g of intermediate 1 and 2.46 g of pyridine-4-boronic acid were dissolved in 100 mL of a 5:1 mixture of dioxane and water. After bubbling under nitrogen for 15 min, 116 mg of tetraphenylphosphine palladium was added, and the reaction was carried out at 100 °C for 12 h. After the starting material had reacted completely, the reaction mixture was cooled to room temperature, 200 mL of water was added, and the mixture was extracted with dichloromethane and the organic phases were combined. The organic phase was then distilled under reduced pressure to obtain the crude product, which was purified by column chromatography (mobile phase: dichloromethane / ethyl acetate = 8 / 1) to give 2.67 g of intermediate 2 (yield 71%). 1 ¹H NMR (500 MHz, DMSO-d⁶): 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 shown below:

[0065] .

[0066] Step 3: Synthesis of Intermediate 3

[0067] 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. After the starting material had reacted completely, the reaction mixture was cooled to room temperature, and 200 mL of dichloromethane was added, resulting in the precipitation of a large amount of powder. The powder was filtered, washed, and yielded 4.88 g of intermediate 3 (yield 74%). 1 ¹H NMR (500 MHz, DMSO-d⁶): 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 shown below:

[0068] .

[0069] Step 4: Synthesis of Compound 1

[0070] 6.6 g of intermediate 3 and 10 g of LiClO4 were dissolved in two 30 mL portions of deionized water, respectively. After mixing the two, a large amount of pale yellow solid precipitated. The precipitate was then 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-d6): 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).

[0071] Example 2: The structural formula of compound 2 is shown below:

[0072] .

[0073] The synthesis of compound 2 via multiple alkylation methods includes the following steps:

[0074] Step 1: Synthesis of Intermediate 4

[0075] 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 tetrahydrofuran / water mixture (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. After the reactants had reacted completely, the reaction mixture was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phases were then distilled under reduced pressure to obtain the crude product, which was purified by column chromatography (mobile phase: petroleum ether) to give 2.85 g of intermediate 4 (yield 81%). 1 ¹H NMR (500 MHz, DMSO-d⁶): 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 shown below:

[0076] .

[0077] Step 2: Synthesis of Intermediate 5

[0078] In a two-necked round-bottom flask, 3.52 g of intermediate 4 and 2.46 g of pyridine-4-boronic acid were dissolved in 100 mL of a 5:1 mixture of dioxane and water. After bubbling with nitrogen for 15 min, 116 mg of tetraphenylphosphine palladium was added, and the reaction was carried out at 100 °C for 12 h. After the starting material had reacted completely, the reaction mixture was cooled to room temperature, 200 mL of water was added, and the mixture was extracted with dichloromethane and the organic phases were combined. The organic phase was then distilled under reduced pressure to obtain the crude product, which was purified by column chromatography (mobile phase: dichloromethane / ethyl acetate = 8 / 1) to give 2.40 g of intermediate 5 (yield 69%). 1 ¹H NMR (500 MHz, DMSO-d⁶): 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 shown below:

[0079] .

[0080] Step 3: Synthesis of Intermediate 6

[0081] 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. After the starting material had reacted completely, the reaction mixture was cooled to room temperature, and 200 mL of dichloromethane was added, resulting in the precipitation of a large amount of powder. The powder was filtered, washed, and yielded 4.75 g of intermediate 6 (yield 84%).1 ¹H NMR (500 MHz, DMSO-d⁶): 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). The structural formula of intermediate 6 is shown below:

[0082] .

[0083] Step 4: Synthesis of Compound 2

[0084] 5.66 g of intermediate 6 and 10 g of LiTFSI were dissolved in two 30 mL portions of deionized water, respectively. After mixing the two solutions, a large amount of pale yellow solid precipitated. The precipitate was then 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-d6): 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).

[0085] Example 3: The structural formula of compound 3 is shown below:

[0086] .

[0087] The first two steps of preparing compound 3 by the multiple alkylation method are the same as those for preparing compound 1, and it can be synthesized directly from intermediate 2.

[0088] Step 1: Synthesis of intermediate 1 (same as step 1 in Example 1).

[0089] Step 2: Synthesis of intermediate 2 (same as step 1 in Example 1).

[0090] Step 3: Synthesis of Intermediate 7

[0091] 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. After the starting material had reacted completely, the reaction mixture was cooled to room temperature, and 200 mL of dichloromethane was added, resulting in the precipitation of a large amount of powder. The powder was filtered, washed, and yielded 4.46 g of intermediate 7 (75% yield). 1 ¹H NMR (500 MHz, DMSO-d⁶): 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 7 is shown below:

[0092] .

[0093] Step 4: Synthesis of Compound 3

[0094] 5.94 g of intermediate 7 and 10 g of LiPF6 were dissolved in two 30 mL portions of deionized water, respectively. After mixing the two solutions, a large amount of pale yellow solid precipitated. The precipitate was then 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-d6): 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).

[0095] The cyclic voltammetry curves of compound 3 (concentration 20 mmol) prepared above in propylene carbonate solution (PC) are shown below. Figure 1 It can be seen that the redox properties of this violet derivative are reversible and diffusion-controlled, exhibiting good reversible redox activity. Two 40*40*0.4mm ITO-plated glass sheets were bonded together using misaligned adhesive, with a device cell thickness of 125 micrometers. Compound 3 and ferrocene were mixed into a solution and filled into the prepared electrochromic device using a vacuum filling method. A voltage was applied across the two ends, and its UV-Vis spectrum from 1.4 to 1.6 V was measured (see...). Figure 2 Because ferrocene has a very low molar extinction coefficient, Figure 2 This can be considered essentially the chromatogram of compound 3. For example... Figure 2 As shown, at 1.4V, 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 has changed from red to blue.

[0096] Example 4: The structural formula of compound 3 is shown below:

[0097] .

[0098] The synthesis of compound 3 via a single alkylation method includes the following steps:

[0099] Step 1: Synthesis of Intermediate 8

[0100] In a two-necked round-bottom flask, 3.24 g of 2,7-dibromofluorene and 2.46 g of pyridine-4-boronic acid were dissolved in 100 mL of a 5:1 dioxane / water mixture. After bubbling under nitrogen for 15 min, 116 mg of tetraphenylphosphine palladium was added, and the reaction was carried out at 100 °C for 12 h. Once the starting material had reacted completely, the reaction mixture was cooled to room temperature, 200 mL of water was added, and the mixture was extracted with dichloromethane. The organic phases were then combined. The organic phase was subsequently distilled under reduced pressure to obtain the crude product, which was purified by column chromatography (mobile phase: dichloromethane / ethyl acetate = 8 / 1) to give 1.82 g of intermediate 8 (yield 57%). 1 ¹H NMR (500 MHz, DMSO-d⁶): δ 8.71 (d, J = 8.3 Hz, 4H), 8.00–7.78 (m, 10H), 4.12 (s, 2H). The structural formula of intermediate 8 is shown below:

[0101] .

[0102] Step 2: Synthesis of Intermediate 9

[0103] 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 and reacted at 80 °C for 1 h. Then, 4.9 g of bromoethane was added, and the reaction continued for 12 h. After the starting material had reacted completely, the reaction mixture was cooled to room temperature, and 200 mL of dichloromethane was added, resulting in the precipitation of a large amount of powder. The powder was filtered, washed, and yielded 4.28 g of intermediate 9 (yield 72%). 1HNMR (500 MHz, DMSO-d6): 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 shown below:

[0104] .

[0105] Step 3: Synthesis of compound 3 (same as step 4 in Example 3).

[0106] Example 5: The structural formula of compound 4 is shown below:

[0107] .

[0108] The synthesis of compound 4 via a single alkylation method includes the following steps:

[0109] Step 1: Synthesis of intermediate 8 (same as step 1 in Example 4).

[0110] Step 2: Synthesis of Intermediate 10

[0111] 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 and reacted at 80 °C for 1 h. Then, 5.67 g of benzyl chloride was added, and the reaction continued for 12 h. After the starting materials had reacted completely, the reaction mixture was cooled to room temperature, and 200 mL of dichloromethane was added, resulting in the precipitation of a large amount of powder. The powder was filtered, washed, and yielded 4.28 g of intermediate 9 (yield 72%). 1 HNMR (500 MHz, DMSO-d6): 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 shown below:

[0112] .

[0113] Step 3: Synthesis of Compound 4

[0114] 7.54 g of intermediate 10 and 10 g of NaSbF6 were dissolved in two 30 mL portions of deionized water, respectively. After mixing the two solutions, a large amount of pale yellow solid precipitated. The precipitate was then 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-d6): 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).

[0115] Comparative Example 1: Synthesis of Intermediate 1

[0116] 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 tetrahydrofuran / water mixture (5:1) and stirred at 60 °C for 20 min. 2.18 g of bromoethane was slowly added dropwise, and the reaction progress was monitored by thin-layer chromatography. After the reactants had reacted completely, the reaction mixture was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phases were then distilled under reduced pressure to obtain the crude product, which was purified by column chromatography (mobile phase: petroleum ether) to give 1.63 g of intermediate 1 (yield 43%).

[0117] Comparative Example 2: Synthesis of Intermediate 9

[0118] 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 and reacted at 80 °C for 20 h. Then, 4.9 g of bromoethane was added, and the reaction continued for another 12 h. After the starting material had reacted completely, the reaction mixture was cooled to room temperature, and 200 mL of dichloromethane was added, resulting in the precipitation of a large amount of powder. The powder was filtered, washed, and yielded 1.84 g of intermediate 9 (yield 31%).

[0119] Comparative Example 3: Synthesis of Intermediate 1

[0120] 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 tetrahydrofuran / water mixture (5:1) and stirred at 60 °C for 4 h. 2.18 g of bromoethane was slowly added dropwise, and the reaction progress was monitored by thin-layer chromatography. After the reactants had reacted completely, the reaction mixture was cooled to room temperature, 200 mL of water was added, and the organic phases were extracted with dichloromethane and combined. The organic phases were then distilled under reduced pressure to obtain the crude product, which was purified by column chromatography (mobile phase: petroleum ether) to give 0.45 g of intermediate 1 (yield 12%).

[0121] As can be seen above, Examples 1, 2, and 3 all involve alkylating 2,7-dibromofluorene first, then coupling it with a pyridine group, followed by a secondary alkylation to obtain "fluorenyl viologen". Examples 4-5, however, involve directly coupling 2,7-dibromofluorene with pyridine, followed by a one-step alkylation reaction, simultaneously introducing four alkyl groups into the main structure to finally obtain "fluorenyl viologen". This single alkylation step is one less step than multiple alkylation, saving time and material costs. However, regardless of whether the "fluorenyl viologen" is prepared by multiple alkylation or single alkylation, it exhibits a color ranging from red to blue under different voltages. In Comparative Examples 1 and 2, insufficient reaction time after adding sodium hydroxide leads to excessively low yields. This is because the active hydrogen on fluorene does not fully participate in the reaction. Comparative Example 3 shows that when sodium hydroxide is replaced with the weaker basic potassium carbonate, even increasing the reaction time to 4 hours cannot effectively react the active hydrogen on fluorene, resulting in extremely low yields.

[0122] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a violanthron derivative, characterized by, It comprises: Step 1: synthesis of intermediate 1 In two round-bottom flasks, 3.24 g of 2,7-dibromofluorene and 0.8 g of sodium hydroxide were dissolved in 100 mL of a mixture of tetrahydrofuran / water=5:1 and stirred at 60°C for 1 h; 2.18 g of bromoethane was slowly added, and the reaction progress was monitored by thin layer chromatography; when the raw material was completely reacted, the reaction was cooled to room temperature, 200 mL of water was added, and the organic phase was extracted with dichloromethane and combined; then the organic phase was distilled under reduced pressure to obtain the crude product, which was purified by column chromatography, and the mobile phase of column chromatography was petroleum ether, to obtain 2.96 g of intermediate 1; The structural formula of intermediate 1 is as follows: ； Step 2: synthesis of intermediate 2 In two round-bottom flasks, 3.8 g of intermediate 1 and 2.46 g of pyridine-4-boric acid were dissolved in 100 mL of a mixture of dioxane / water=5:1, and 116 mg of tetrakis triphenylphosphine palladium was added after nitrogen bubbling for 15 min, and the reaction was carried out at 100°C for 12 h; when the raw material was completely reacted, the reaction was cooled to room temperature, 200 mL of water was added, and the organic phase was extracted with dichloromethane and combined; then the organic phase was distilled under reduced pressure to obtain the crude product, which was purified by column chromatography, and the mobile phase of column chromatography was dichloromethane / ethyl acetate=8 / 1; 2.67 g of intermediate 2 was obtained; The structural formula of intermediate 2 is as follows: ； Step 3: synthesis of intermediate 7 In two round-bottom flasks, 3.77 g of intermediate 2 and 2.84 g of bromoethane were dissolved in 50 mL of DMF and reacted at 80°C for 12 h; when the raw material was completely reacted, 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 4.46 g of intermediate 7; The structural formula of intermediate 7 is as follows: ； Step 4: synthesis of compound 3 5.94 g of intermediate 7 and 10 g of LiPF6 were dissolved in two portions of 30 mL of deionized water, respectively, then mixed to precipitate a large amount of light yellow solid, and the precipitate was filtered and washed with deionized water for 3 times to complete the purification of compound 3, to obtain 6.23 g of compound 3; The structure of compound 3 is as follows: 。

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