Tribranched azobenzene compound as well as preparation method and application thereof

Abstract

The invention provides a tribranched azobenzene compound as well as a preparation method and application thereof, and belongs to the technical field of optical functional materials. The tribranched azobenzene compound disclosed by the invention can be subjected to trans-cis configuration transformation under the irradiation of 365nm ultraviolet light, and meanwhile, the compound is transformed into a liquid state from a solid state; the liquid cis-isomer can be subjected to cis-trans configuration conversion under the excitation of 450nm blue light and is converted into a solid state at the same time. Light-induced trans-cis configuration transformation not only can store light energy as chemical energy, but also can store phase change energy through light-controlled solid-liquid phase change, and the stored energy is released in a heat energy mode under blue light irradiation. The tribranched azobenzene compound disclosed by the invention has a photoinduced reversible solid-liquid phase change characteristic, provides a new strategy for developing a novel light-controlled phase change material, a photoinduced phase change heat storage material and a molecular light energy storage material, and has important significance for further developing the photoinduced phase change energy storage material.

Description

Technical Field

[0001] The present invention relates to the technical field of optical functional materials, and particularly to a tribranched azobenzene compound, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing shortage of energy resources, the energy consumption in the modern world has been steadily rising. Therefore, it is urgent to develop sustainable and environmentally friendly technologies to alleviate the energy crisis. Solar energy has attracted much attention because it can provide an infinite and effective energy supply. However, the efficient utilization of solar energy is still hindered by limited storage options and irregular sunlight supply. Therefore, there is an urgent need to develop intelligent, effective, environmentally friendly, and cost-effective solar energy utilization methods.

[0003] Azobenzene compounds are a kind of molecular photoswitch with a highly reversible cis-trans photoisomerization ability, and show great application potential in many technical fields such as light-driven and energy storage. In particular, azobenzene compounds can convert sunlight into heat energy based on the forward isomerization reaction and store it, which is called the charging process. The heat energy is released through heating or light-induced reverse isomerization to reset the switch for recharging, which is called the discharging process. Although azobenzene exhibits excellent isomerization cycles, its energy storage density is relatively low. Summary of the Invention

[0004] The purpose of the present invention is to provide a tribranched azobenzene compound, a preparation method thereof, and an application thereof. The tribranched azobenzene compound has a photoinduced reversible solid-liquid phase transition property and a high energy storage density at the same time.

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

[0006] The present invention provides a tribranched azobenzene compound having the structure shown in Formula I:

[0007]

[0008] In Formula I, R1, R2, and R3 are H; or R1 and R2 are H and R3 is -CH3; or R1 and R2 are -CH3 and R3 is H.

[0009] The present invention provides a preparation method of the tribranched azobenzene compound according to the above technical solution, including the following steps:

[0010] Mix 4-n-butylaniline, a diazotizing reagent, a phenolic compound, and a first solvent, and carry out a diazo coupling reaction to obtain an azophenol compound; the phenolic compound includes phenol, xylenol, or m-cresol;

[0011] Mix the azophenol compound, base reagent, catalyst, 1,1'-dibromododecane and a second solvent to carry out a first substitution reaction to obtain a long-alkyl-substituted azobenzene derivative;

[0012] Mix the long-alkyl-substituted azobenzene derivative, methyl gallate, base reagent, catalyst and a third solvent to carry out a second substitution reaction to obtain a tribranched azobenzene compound having the structure shown in Formula I.

[0013] Preferably, the phenolic compound is separated from coal tar or obtained commercially.

[0014] Preferably, the diazotizing reagent is concentrated hydrochloric acid, sodium nitrite and sodium hydroxide; the molar ratio of 4-n-butylaniline, sodium nitrite, sodium hydroxide to the phenolic compound is 1:1:1:1 to 1:3:3.3:3.

[0015] Preferably, the temperature of the diazo coupling reaction is 0 to 5 °C and the time is 1 to 2 h.

[0016] Preferably, in the step of the first substitution reaction, the base reagent includes potassium carbonate or sodium bicarbonate; the catalyst includes potassium iodide or potassium bromide; the molar ratio of the azophenol compound, base reagent, catalyst to 1,1'-dibromododecane is 1:3:1:1 to 1:5:3:3.

[0017] Preferably, the temperature of the first substitution reaction is 60 to 70 °C and the time is 12 to 48 h.

[0018] Preferably, in the step of the second substitution reaction, the base reagent includes potassium carbonate or sodium bicarbonate; the catalyst includes potassium iodide or potassium bromide; the molar ratio of the long-alkyl-substituted azobenzene derivative, methyl gallate, base reagent to the catalyst is 3:1:2:1 to 9:3:15:3.

[0019] Preferably, the temperature of the second substitution reaction is 60 to 75 °C and the time is 12 to 48 h.

[0020] The present invention provides an application of the tribranched azobenzene compound described in the above technical solution or the tribranched azobenzene compound prepared by the preparation method described in the above technical solution in the field of energy storage.

[0021] Due to the change in bond order of the azo group present in the molecular structure of the tribranched azobenzene compound of the present invention under photoexcitation, the rotational barrier is reduced, enabling the cis and trans isomers to interconvert. Meanwhile, the energy difference between the trans and cis isomers and the driving effect of light ensure the reversibility of this process. Specifically, the tribranched azobenzene compound of the present invention can undergo a trans-cis configuration transformation under 365 nm ultraviolet light irradiation, and simultaneously the compound changes from a solid state to a liquid state; the liquid cis isomer can undergo a cis-trans configuration transformation under the excitation of 450 nm blue light and simultaneously change back to a solid state. The photoinduced trans-cis configuration transformation can not only store light energy as chemical energy, but also the solid-liquid phase change characteristics induced by an external light source can additionally store phase change energy, thereby significantly enhancing the energy density value of the tribranched azobenzene compound. The stored energy is released in the form of heat under blue light irradiation. The tribranched azobenzene compound of the present invention has photoinduced reversible solid-liquid phase change characteristics. The present invention improves the isomerization and charging rates by introducing the characteristic of photoliquefaction (while being irradiated with light, the solid reversibly transforms into an isotropic liquid, and liquefaction will increase the penetration depth of light and thus promote the charging rate), and at the same time uses the additional storage of latent heat to increase the energy storage density, providing a new strategy for the development of new light-controlled phase change materials, photoinduced phase change heat storage, and molecular photoenergy storage materials, which is of great significance for the further development of photoinduced phase change energy storage materials.

[0022] The tribranched azobenzene compound of the present invention can be transformed into the cis isomer under 365 nm ultraviolet light excitation while storing light energy as chemical energy, and the stored energy can be recovered and heat is released simultaneously under the irradiation of 450 nm blue light. The energy storage and release process of this tribranched anthryl compound based on photoinduced reversible isomerization reaction for storing / releasing photothermal energy is cycle-stable.

[0023] The present invention utilizes a photoinduced reversible isomerization reaction to prepare a tribranched azobenzene compound through a diazo coupling reaction and a two-step substitution reaction. The prepared tribranched azobenzene compound can undergo trans-cis isomerization under 365 nm light irradiation and simultaneously change from a solid state to a liquid state to achieve the storage of light energy and phase change energy, and undergo a cis-trans recovery reaction under 450 nm blue light irradiation while changing from a liquid state to a solid state and releasing the stored energy in the form of heat.

[0024] The phenolic compound used as the preparation raw material in the present invention is from commercially available products or products separated from coal tar. The preparation method of this tribranched azobenzene compound can not only further broaden the utilization path of phenolic compounds, but also further enrich the molecular photoheat storage system.

[0025] The synthesis process of the tribranched azobenzene compound of the present invention is simple, has a high yield, is easy to mass-produce, is cycle-stable, and is environmentally friendly during the utilization process. Description of the Drawings

[0026] Figure 1It is the preparation route diagram of the three-branch azobenzene compound in the present invention;

[0027] Figure 2 It is the 1H NMR spectrum (b) of azophenol (a) and long-alkyl-substituted azophenol compounds prepared in Example 1 (deuterated chloroform);

[0028] Figure 3 It is the 1H NMR spectrum (deuterated chloroform) of the three-branch azobenzene compound in Example 2;

[0029] Figure 4 It is the UV-visible absorption spectra of the three-branch azobenzene compound prepared in Example 3 after irradiation with 365 nm ultraviolet light (a) and 450 nm blue light (b) (methanol solution, 1 M, light power 10 mW / cm 2 ) at different times;

[0030] Figure 5 It is the optical photograph of the reversible solid-liquid phase transition of the three-branch azobenzene compound prepared in Example 3 under alternating irradiation with ultraviolet light (365 nm, 60 mW / cm 2 , solid state changes to liquid state) and blue light (450 nm, 60 mW / cm 2 , liquid state changes to solid state);

[0031] Figure 6 It is the energy release curve of the three-branch azobenzene compound prepared in Example 3 after ultraviolet light irradiation. Detailed implementation mode

[0032] In the present invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well-known to those skilled in the art.

[0033] The present invention provides a three-branch azobenzene compound with the structure shown in Formula I:

[0034]

[0035] In Formula I, R1, R2, and R3 are H; or R1 and R2 are H and R3 is -CH3; or R1 and R2 are -CH3 and R3 is H.

[0036] In the present invention, the three-branch azobenzene compound is preferably

[0037]

[0038] As Figure 1 shown, the present invention provides a preparation method of the three-branch azobenzene compound described in the above technical solution, including the following steps:

[0039] Mix 4 - n - butylaniline, a diazotization reagent, a phenolic compound, and a first solvent, and carry out a diazo coupling reaction to obtain an azophenolic compound; the phenolic compound includes phenol, xylenol, or m - cresol;

[0040] Mix the azophenolic compound, a base reagent, a catalyst, 1,12 - dibromododecane, and a second solvent, and carry out a first substitution reaction to obtain a long - alkyl - substituted azobenzene derivative;

[0041] Mix the long - alkyl - substituted azobenzene derivative, methyl gallate, a base reagent, a catalyst, and a third solvent, and carry out a second substitution reaction to obtain a tribranched azobenzene compound with the structure shown in Formula I.

[0042] In the present invention, 4 - n - butylaniline, a diazotization reagent, a phenolic compound, and a first solvent are mixed, and a diazo coupling reaction is carried out to obtain an azophenolic compound.

[0043] In the present invention, the phenolic compound includes phenol, xylenol, or m - cresol; the phenolic compound is preferably a commercially available product or obtained by separating from coal tar; the present invention preferably uses the method for separating phenolic compounds from coal tar disclosed in Patent CN108913195B to extract the phenolic compound.

[0044] In the present invention, the diazotization reagent is preferably concentrated hydrochloric acid, sodium nitrite, and sodium hydroxide; the molar ratio of 4 - n - butylaniline, sodium nitrite, sodium hydroxide to the phenolic compound is preferably 1:1:1:1 to 1:3:3.3:3, more preferably 1:1.1:3.3:1.1.

[0045] In the present invention, the first solvent is preferably deionized water; the mass concentration of the concentrated hydrochloric acid is preferably 37%. The present invention has no special limitation on the total amount of the organic solvent, and it can be adjusted according to actual needs to ensure the smooth progress of the reaction.

[0046] The present invention has no special limitation on the ratio of 4 - n - butylaniline to concentrated hydrochloric acid, and it can be adjusted according to the well - known methods in the art according to actual needs to ensure the smooth progress of the reaction.

[0047] The present invention preferably mixes 4-n-butylaniline, concentrated hydrochloric acid and the first part of the first solvent (the volume ratio of the concentrated hydrochloric acid to the first part of the first solvent is preferably 1:2 to 1:5, more preferably 1:3.6 to 5), stirs at -5 to 0 °C (more preferably -3 °C) for 20 to 30 min to obtain a first mixed solution, dissolves sodium nitrite in the second part of the first solvent to obtain a sodium nitrite solution, drops the sodium nitrite solution into the first mixed solution, and stirs at 0 °C for 20 to 40 min (more preferably 30 min) to obtain a diazonium salt solution; mixes a phenolic compound, sodium hydroxide and the third part of the first solvent, cools to 0 °C, and drops the diazonium salt solution into the obtained mixed solution. During the dropping process, a saturated aqueous sodium carbonate solution is added to maintain the pH value of the mixed solution at 9 to 10, and a diazo coupling reaction is carried out under this alkaline condition.

[0048] In the present invention, the temperature of the diazo coupling reaction is preferably 0 to 5 °C, more preferably 0 °C, the time is preferably 1 to 2 h, more preferably 1 to 1.25 h; the pH value is preferably 9 to 10. During the diazo coupling reaction, the aniline group is first activated to undergo a diazotization reaction and then coupled with the phenolic compound.

[0049] After the diazo coupling reaction ends, the present invention preferably adjusts the pH value to 3 to 5 with 0.5 M hydrochloric acid (to avoid the phenol becoming a salt), continues to stir for 30 to 50 min, then extracts the mixed liquid with dichloromethane, dries the organic layer with anhydrous sodium sulfate for 24 to 48 h, and purifies the obtained crude product by column chromatography (ethyl acetate / n-hexane = 1 / 2, V / V) to obtain an azophenol compound. The present invention has no special limitation on the extraction, drying and column chromatography, and can be carried out according to the processes well-known in the art.

[0050] In the present invention, the structural formula of the azophenol compound is

[0051]

[0052] After obtaining the azophenol compound, the present invention mixes the azophenol compound, a base reagent, a catalyst, 1,2-dibromododecane and a second solvent to carry out a first substitution reaction to obtain a long-alkyl-substituted azobenzene derivative.

[0053] In the step of the first substitution reaction in the present invention, the base reagent preferably includes potassium carbonate or sodium bicarbonate; the catalyst preferably includes potassium iodide or potassium bromide; the molar ratio of the azophenol compound, the base reagent, the catalyst to 1,2-dibromododecane is preferably 1:3:1:1 to 1:5:3:3, more preferably 1:3:1:2.3; the second solvent is preferably acetone; the present invention has no special limitation on the amount of the second solvent used, as long as the reaction proceeds smoothly. The present invention has no special limitation on the mixing of the raw materials for the first substitution reaction, and can be mixed evenly according to the stirring methods well-known in the art.

[0054] In the present invention, the temperature of the first substitution reaction is preferably 60 to 70 °C, more preferably 65 to 68 °C, the time is preferably 12 to 48 h, more preferably 24 to 36 h; the first substitution reaction is preferably carried out under stirring and reflux conditions.

[0055] After completing the substitution reaction, in the present invention, it is preferably cooled to room temperature, the inorganic salts are filtered off, the filtrate is washed with acetone, and the obtained organic filtrate is evaporated to dryness under reduced pressure (40 °C, 30 min, 0.1 MPa, 50 - 100 rpm), and purified by flash chromatography using n-hexane / ethyl acetate (volume ratio 4:1) to obtain the long-alkyl-substituted azobenzene. The present invention has no special limitation on the specific processes of the filtration, washing, evaporation to dryness under reduced pressure and purification, and it can be carried out according to the processes well-known in the art.

[0056] In the present invention, the structural formula of the long-alkyl-substituted azobenzene derivative is

[0057]

[0058] The present invention mixes the long-alkyl-substituted azobenzene derivative, methyl gallate, a base reagent, a catalyst and a third solvent to carry out a second substitution reaction to obtain the tribranched azobenzene compound shown in Formula I.

[0059] The present invention has no special limitation on the mixing of the long-alkyl-substituted azobenzene derivative, methyl gallate, a base reagent, a catalyst and a third solvent, and the materials can be mixed evenly according to the processes well-known in the art.

[0060] In the present invention, in the steps of the second substitution reaction, the base reagent preferably includes potassium carbonate or sodium bicarbonate; the catalyst preferably includes potassium iodide or potassium bromide; the molar ratio of the long-alkyl-substituted azobenzene derivative, methyl gallate, the base reagent to the catalyst is preferably 3:1:2:1 to 9:3:15:3, more preferably 3:1:3:1. In the present invention, the third solvent is preferably acetone; the present invention has no special limitation on the amount of the third solvent, and it can be adjusted according to actual needs to ensure the smooth progress of the reaction.

[0061] In the present invention, the temperature of the second substitution reaction is preferably 60 to 75 °C, more preferably 65 to 75 °C, the time is preferably 12 to 48 h, more preferably 24 to 36 h; the second substitution reaction is preferably carried out under stirring and reflux conditions.

[0062] After completion of the second substitution reaction, the mixture obtained in the present invention is preferably cooled to room temperature, the inorganic salts are removed by filtration, washed with acetone, and the obtained organic filtrate is evaporated to dryness under reduced pressure (40 °C, 30 min, 0.1 MPa, 50 - 100 revolutions per minute). The obtained crude product is purified by a silica gel chromatography column, and the eluent used is ethyl acetate and dichloromethane, and the volume ratio of ethyl acetate to dichloromethane is 1:5, to obtain a tribranched azobenzene compound.

[0063] The present invention provides the application of the tribranched azobenzene compound described in the above technical solution or the tribranched azobenzene compound prepared by the preparation method described in the above technical solution in the energy storage field. The present invention has no special limitation on the application method, and the tribranched azobenzene compound can be directly used as an energy storage material.

[0064] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0065] Example 1

[0066] 1) 4-n-Butylaniline (4.47 g, 30.00 mmol), 10 mL of concentrated hydrochloric acid (37%) and 50 mL of deionized water were successively added to a 250 mL flask and stirred at 0 °C for 20 min, and then an aqueous solution of 10 mL of sodium nitrite (2.27 g, 33.00 mmol) was added dropwise; after the addition was completed, the obtained mixed liquid was continuously stirred at 0 °C for 30 min to obtain a diazonium salt solution;

[0067] Phenol (4.82 g, 33.00 mmol), sodium hydroxide (4.00 g, 100.00 mmol) and 50 mL of deionized water were added to another 250 mL flask, stirred and cooled to 0 °C, and then the above diazonium salt solution was added dropwise. During the addition, a saturated sodium carbonate aqueous solution was added to maintain the pH value of the mixed solution at 9; after the addition was completed, the obtained mixed liquid was continuously stirred and reacted at 0 °C for 2 h. After the reaction was completed, 10 mL of 0.5 M hydrochloric acid was added to adjust the pH value to 5, and after stirring for 30 min, the mixed liquid was extracted with dichloromethane. The organic layer was dried with anhydrous sodium sulfate for 24 h, and the organic layer was concentrated to obtain a crude product. After the crude product was purified by column chromatography (ethyl acetate / n-hexane = 1 / 2, V / V), a high-purity azophenol was obtained;

[0068] 2) Add azophenol (2.0 g, 7.8 mmol), dodecyl dibromide (9 g, 18 mmol), potassium carbonate (3.32 g, 24 mmol) and potassium iodide (12.94 g, 7.8 mmol) successively into a single-necked flask containing 150 mL of acetone, stir, and continuously stir and reflux at 68 °C for 24 h; after the reaction is completed, cool the mixture to room temperature, filter, wash the filter cake with acetone three times, and evaporate and dry the organic filtrate under reduced pressure (40 °C, 30 min, 0.1 MPa, 100 rpm). Purify by flash chromatography using n-hexane / ethyl acetate (volume ratio 4:1) to obtain an orange solid product, the long-alkyl-substituted azobenzene derivative;

[0069] 3) Put the long-alkyl-substituted azobenzene derivative (1.25 g, 3.60 mmol), methyl gallate (0.23 g, 1.2 mmol), potassium carbonate (0.33 g, 2.4 mmol) and potassium iodide (0.19 g, 1.2 mmol) successively into 100 mL of acetone, and continuously stir and reflux at 70 °C for 24 h; after the reaction is completed, cool the mixture to room temperature, filter, wash it with acetone, and evaporate and dry the obtained organic filtrate under reduced pressure (40 °C, 30 min, 0.1 MPa, 100 rpm). Purify the obtained crude product by silica gel column chromatography, and the volume ratio of the eluent ethyl acetate to dichloromethane is 1:5 to obtain the three-branched azobenzene compound.

[0070] Example 2

[0071] 1) Add 4-n-butylaniline (4.47 g, 30.00 mmol), 11 mL of concentrated hydrochloric acid and 40 mL of deionized water successively into a 250 mL flask and stir at -3 °C for 30 min, then add dropwise 10 mL of an aqueous solution of sodium nitrite (2.27 g, 33.00 mmol); after the addition is completed, continue to stir the mixed liquid at 0 °C for 20 min to obtain a diazonium salt solution;

[0072] Add phenol (4.82 g, 33.00 mmol), sodium hydroxide (4.00 g, 100.00 mmol) and 50 mL of deionized water into another 250 mL flask, stir and cool to 0 °C, then add dropwise the above diazonium salt solution; during the addition, add saturated sodium carbonate aqueous solution to maintain the pH value of the mixed solution at 9; after the addition is completed, continue to stir and react the mixed liquid at 0 °C for 1 h; after the reaction is completed, add 10 mL of 0.5 M hydrochloric acid to adjust the pH value of the mixed solution to 5, continue to stir for 50 min, then extract the mixed liquid with dichloromethane, dry the organic layer with anhydrous sodium sulfate for 36 h, and purify the obtained crude product by column chromatography (ethyl acetate / n-hexane = 1 / 2, V / V) to obtain high-purity azophenol;

[0073] 2) Add azophenol (2.0 g, 7.8 mmol), dodecyl dibromide (9 g, 18 mmol), potassium carbonate (3.32 g, 24 mmol) and potassium iodide (12.94 g, 7.8 mmol) into a single-necked flask containing 200 mL of acetone in sequence, stir, and continuously stir and reflux at 70 °C for 36 h; after the reaction is completed, cool the mixture to room temperature, filter, wash the filter cake with acetone twice, and dry the obtained organic filtrate by reduced pressure evaporation (40 °C, 30 min, 0.1 MPa, 100 rpm); purify by flash chromatography using n-hexane / ethyl acetate (volume ratio 4:1) to obtain an orange solid product, the long-alkyl-substituted azobenzene derivative;

[0074] 3) Put the long-alkyl-substituted azobenzene derivative (1.25 g, 3.60 mmol), methyl gallate (0.23 g, 1.20 mmol), potassium carbonate (0.66 g, 4.8 mmol) and potassium iodide (0.19 g, 1.20 mmol) into 150 mL of acetone in sequence, and continuously stir and reflux at 65 °C for 36 h; after the reaction is completed, cool the mixture to room temperature, filter, and wash with acetone; dry the obtained organic filtrate by reduced pressure evaporation (40 °C, 30 min, 0.1 MPa, 100 rpm), and purify the obtained crude product by silica gel column chromatography with the volume ratio of ethyl acetate to dichloromethane being 1:5 to obtain the three-branched azobenzene compound.

[0075] Example 3

[0076] 1) Add 4-butylaniline (4.47 g, 30.00 mmol), 11 mL of concentrated hydrochloric acid and 35 mL of deionized water into a 300 mL flask in sequence and stir at -5 °C for 30 min, then dropwise add 20 mL of an aqueous solution of sodium nitrite (2.27 g, 33.00 mmol). After the addition is completed, continue to stir the mixed liquid at 0 °C for 40 min to obtain a diazonium salt solution;

[0077] Add phenol (4.82 g, 33.00 mmol), sodium hydroxide (4.00 g, 100.00 mmol) and 80 mL of deionized water into another 250 mL flask, stir and cool to 0 °C, and then dropwise add the above diazonium salt solution; during the dropping process, add saturated sodium carbonate aqueous solution to maintain the pH value of the mixed solution at 9; after the addition is completed, continue to stir and react the mixed liquid at 0 °C for 75 min; after the reaction is completed, add 10 mL of 0.5 M hydrochloric acid to adjust the pH value of the mixed solution to 5, continue to stir for 50 min, and then extract the mixed liquid with dichloromethane. The organic layer is dried with anhydrous sodium sulfate for 48 h. After the obtained crude product is purified by column chromatography (ethyl acetate / n-hexane = 1 / 2, V / V), azophenol is obtained;

[0078] 2) Add azophenol (2.0 g, 7.8 mmol), 1,12-dibromododecane (9 g, 18 mmol), potassium carbonate (3.32 g, 24 mmol) and potassium iodide (12.94 g, 7.8 mmol) successively into a single-necked flask containing 180 mL of acetone, stir, and reflux the reaction at 65 °C with continuous stirring for 48 h; after the reaction is completed, cool the mixture to room temperature, filter, wash the filter cake with acetone 5 times, and evaporate and dry the organic filtrate under reduced pressure (40 °C, 30 min, 0.1 MPa, 100 rpm). Purify by flash chromatography using n-hexane / ethyl acetate (volume ratio 4:1) to obtain an orange solid product, a long-alkyl-substituted azobenzene derivative;

[0079] 3) Put the long-alkyl-substituted azobenzene derivative (1.25 g, 3.60 mmol), methyl gallate (0.23 g, 1.2 mmol), potassium carbonate (0.49 g, 3.6 mmol) and potassium iodide (0.19 g, 1.20 mmol) successively into 120 mL of acetone, and reflux the reaction at 75 °C with continuous stirring for 48 h; after the reaction is completed, cool the mixture to room temperature, filter, wash it with acetone, and evaporate and dry the obtained organic filtrate under reduced pressure (40 °C, 30 min, 0.1 MPa, 100 rpm). Purify the obtained crude product by silica gel column chromatography, and the volume ratio of the eluent ethyl acetate to dichloromethane is 1:5 to obtain a tris-azobenzene compound.

[0080] Characterization and performance testing

[0081] Figure 2 1H NMR spectra of azophenol phenols (a) and long-alkyl-substituted azophenol compounds prepared in Example 1 (b) (deuterated chloroform); From Figure 2 it can be seen that the corresponding azophenol compounds have been successfully synthesized.

[0082] Figure 3 1H NMR spectrum of the tris-azobenzene compound in Example 2 (deuterated chloroform), from Figure 3 it can be seen that the tris-azobenzene compound has been successfully synthesized.

[0083] Figure 4 UV-visible absorption spectra of the tris-azobenzene compound prepared in Example 3 after irradiation with 365 nm ultraviolet light (a) and 450 nm blue light (b) (methanol solution, 1 M, light power 10 mW / cm 2 ) at different times. From Figure 3 it can be seen that the tris-azobenzene compound can effectively complete the reversible photoisomerization reaction under ultraviolet light irradiation.

[0084] Figure 5Optical photographs of the reversible solid-liquid phase transition of the ter-branched azobenzene compound prepared in Example 3 under alternating irradiation with ultraviolet light (365 nm, 60 mW / cm 2 , solid to liquid) and blue light (450 nm, 60 mW / cm 2 , liquid to solid). It can be seen from Figure 5 that the ter-branched azobenzene compound has excellent light-controlled reversible solid-liquid phase transition characteristics.

[0085] Figure 6 Energy release curve of the ter-branched azobenzene compound prepared in Example 3 after ultraviolet light irradiation (differential scanning calorimeter, 10 °C / min, -20 to 200 °C). It can be seen from Figure 6 that the energy storage density of the ter-branched azobenzene compound includes the isomerization enthalpy (126 J / g) and the phase transition energy (45 J / g).

[0086] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A three-branched azobenzene compound, characterized in that: It has the structure shown in formula I: In formula I, R1, R2, and R3 are H; or R1 and R2 are H and R3 is -CH3; or R1 and R2 are -CH3 and R3 is H.

2. The method for preparing the three-branched azobenzene compound according to claim 1, characterized in that: The following steps are involved: Mixing 4-n-butylaniline, a diazo reagent, a phenolic compound and a first solvent to perform a diazo coupling reaction to obtain an azophenolic compound; the phenolic compound includes phenol, xylenol or m-cresol; The azophenol compound, the alkaline reagent, the catalyst, dibromododecane and the second solvent are mixed to carry out a first substitution reaction to obtain a long alkyl substituted azobenzene derivative; The long alkyl substituted azobenzene derivative, methyl gallate, an alkali reagent, a catalyst and a third solvent are mixed to carry out a second substitution reaction to obtain a three-branched azobenzene compound having a structure shown in formula I.

3. The preparation method according to claim 2, characterized in that: The phenolic compounds are separated from coal tar or obtained commercially.

4. The preparation method according to claim 2, characterized in that: The diazotizing agent is concentrated hydrochloric acid, sodium nitrite and sodium hydroxide; the molar ratio of 4-n-butylaniline, sodium nitrite, sodium hydroxide and phenolic compound is 1:1:1:1 to 1:3:3.3:

3.

5. The preparation method according to claim 2 or 4, characterized in that: The temperature of the diazo coupling reaction is 0-5°C and the time is 1-2h.

6. The preparation method according to claim 2, characterized in that: In the step of the first substitution reaction, the alkaline reagent includes potassium carbonate or sodium bicarbonate; the catalyst includes potassium iodide or potassium bromide; and the molar ratio of the azophenol compound, the alkaline reagent, the catalyst and dibromododecane is 1:3:1:1 to 1:5:3:

3.

7. The preparation method according to claim 2 or 6, characterized in that: The temperature of the first substitution reaction is 60-70° C. and the time is 12-48 hours.

8. The preparation method according to claim 2, characterized in that: In the step of the second substitution reaction, the alkaline reagent includes potassium carbonate or sodium bicarbonate; the catalyst includes potassium iodide or potassium bromide; and the molar ratio of the long alkyl substituted azobenzene derivative, methyl gallate, alkaline reagent and catalyst is 3:1:2:1 to 9:3:15:

3.

9. The preparation method according to claim 2 or 8, characterized in that: The temperature of the second substitution reaction is 60-75° C. and the time is 12-48 hours.

10. Use of the tris-azobenzene compound according to claim 1 or the tris-azobenzene compound prepared by the preparation method according to any one of claims 2 to 9 in the field of energy storage.

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