Thermochromism and fluorescence dual-response porous liquid crystal material as well as preparation method and application thereof

Abstract

The invention discloses a thermochromism and fluorescence dual-response porous liquid crystal material and a preparation method thereof. The preparation method comprises the following steps: synthesizing spiropyrane; preparing a spiropyrane / cyanostyrene derivative / hexadecanoic acid thermochromic material; the preparation method comprises the following steps: preparing Eu-MOF; preparing a thermoluminescence color changing material / Eu-MOF composite material; the porous liquid crystal material with thermochromism and fluorescence dual response is prepared. According to the porous liquid crystal material with thermochromism and fluorescence dual response, the phase change material and the fluorescent material are introduced into the liquid crystal, so that the liquid crystal has different fluorescence display effects above and below the phase change temperature, the color and the shape can be dynamically regulated and controlled, and the porous liquid crystal material is applied to the fields of information storage, camouflage, display and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid crystal materials, and in particular relates to a porous liquid crystal material with dual responses of thermochromism and fluorescence, and a preparation method and application thereof. Background Art

[0002] Stimuli-responsive materials are a type of widely used smart materials that change their structure and properties by changing intermolecular or intramolecular forces, phase transitions, or conformations when exposed to external stimuli, such as light, solvents, force, and heat. Among them, thermochromic fluorescent materials (TFMs) have the advantages of being easily available, low cost, good stability, and suitable for large-scale on-site applications. They have attracted widespread attention and have broad application prospects in the fields of anti-counterfeiting, fluorescent switches, sensors, and the like.

[0003] Liquid crystal has many advantages as a stimulus-responsive material. First, a slight change in the structure of liquid crystal molecules can cause a significant change in its optical properties. Therefore, liquid crystal materials can quickly respond to external stimuli such as electric fields, temperature, and light, and achieve rapid reversible changes. Secondly, liquid crystal materials only require small external stimuli to change, so the power consumption required to drive liquid crystal devices is low. Finally, compared with other stimulus-responsive materials, the preparation process of liquid crystal materials is relatively simple and the cost is low, which is conducive to the large-scale commercial application of liquid crystal technology. In short, liquid crystal materials have the advantages of fast response, low power consumption, flexibility and relatively low cost, making them a widely used stimulus-responsive material.

[0004] Spiropyran (SPBM) is a type of photochromic material that contains pyran rings and spiro rings in its molecular structure, with switchable pigment colors and red fluorescence. Under ultraviolet light, the non-fluorescent V-shaped SP structure molecules will be converted into fluorescent rod-shaped MC structures; when the MC isomers are exposed to visible light, they will be converted back to the original non-fluorescent closed-ring SP structure. Based on the behavior of spiropyran optical configuration conversion, SPBM can be converted between V-shaped colorless SP and rod-shaped dark MC, which makes spiropyran compounds have broad application prospects in the fields of optical switches and optical storage.

[0005] Since a single fluorescent material is usually static, it is easy to copy and imitate. Therefore, another photochromic material, a cyanostyrene derivative (AIE-CSD, 1-(2-cyanostyrene)-4-(4-cyanostyrene)benzene), is introduced to achieve switchable fluorescence. In the composite system, under continuous ultraviolet irradiation at 365nm, the spiropyran and cyanostyrene molecules undergo photoisomerization, the fluorescence intensity of SPBM increases, and the fluorescence of AIE-CSD shows a quenching trend, that is, the blue emission gradually weakens, while the red emission increases, and the fluorescence color gradually changes from short-wavelength blue to long-wavelength red fluorescence. Interestingly, under sufficient visible light irradiation, the red fluorescence gradually weakens and returns to blue fluorescence. On this basis, time-varying information encryption can be achieved.

[0006] However, spiropyran and cyanostyrene derivatives have planar conjugated structures and are prone to agglomeration through π-π stacking, which affects the photochromic efficiency. In addition, the rod-shaped MC isomer is unstable. At room temperature, the MC isomer will spontaneously return to the more stable SP form, resulting in poor thermal stability of spiropyran molecules. Summary of the invention

[0007] In order to solve the above technical problems, the present invention uses hexadecanoic acid as a matrix, spiropyran and cyanostyrene derivatives as fluorophores, and prepares a thermochromic material with good reversibility and obvious fluorescence emission changes. The self-crystallization phase change characteristics of the phase change material are used to drive the aggregation state change of the fluorophore to regulate the change of its fluorescence behavior, thereby obtaining a thermochromic material. Subsequently, based on liquid crystal as a thermal response emission source, combined with a thermosensitive long-chain carboxylic acid with self-crystallization properties, a porous liquid crystal material with dual responses of thermochromic and fluorescence with tunable fluorescence and temperature color change characteristics is obtained.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is: a method for preparing a porous liquid crystal material with dual responses of thermochromism and fluorescence, comprising the following steps:

[0009] Step 1, synthesis of spiropyran, under nitrogen protection, add a certain amount of 2-bromoethanol and a certain amount of 2,3,3-trimethyl-2H-indole, and a certain amount of dichloromethane into a flask equipped with a reflux condenser, stir, heat to a certain temperature, and reflux for a period of time; after stopping the reaction, remove dichloromethane by distillation, add a certain amount of n-hexane, filter, recrystallize and purify with a certain amount of ethyl acetate, and dry under vacuum to obtain pink purple granular crystals;

[0010] Under nitrogen protection, a certain amount of sodium hydroxide solution was added dropwise to a flask containing a certain amount of the above-mentioned purple granular crystals, and the mixture was stirred to obtain a yellow solution, which was extracted with ethyl acetate. The organic layer was dried with anhydrous MgSO4 for a period of time, filtered, and the ethyl acetate was removed by rotary evaporation to obtain a yellow oily substance.

[0011] Under light-proof conditions, a certain amount of the yellow oil and a certain amount of 2-hydroxy-5-nitrobenzaldehyde are placed in a reaction container, a certain amount of anhydrous ethanol is added, nitrogen is introduced for protection, the reaction is heated to a certain temperature, refluxed for a period of time, cooled to room temperature, the solvent is removed by rotary evaporation, and recrystallized with acetone to obtain purple crystals, namely spiropyran;

[0012] Step 2, preparing a spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color-changing material, respectively weighing a certain amount of hexadecanoic acid solid, spiropyran and 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene, mixing and magnetically stirring for a period of time in a constant temperature oil bath environment, so that the spiropyran and 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene are fully dissolved in the hexadecanoic acid liquid, and the spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color-changing material is obtained;

[0013] Step 3: Prepare Eu-MOF. Take a certain amount of isophthalic acid, europium nitrate and hexadecyltrimethylammonium bromide, dissolve them in a certain amount of dimethylformamide solution, stir at room temperature for a period of time, let stand, centrifuge, wash with ethanol and distilled water respectively, and finally freeze-dry to obtain a white solid powder, which is Eu-MOF.

[0014] Step 4, preparing a thermofluorescent color-changing material / Eu-MOF composite material, mixing a certain amount of Eu-MOF and spiropyran / cyanostyrene derivative / hexadecanoic acid thermofluorescent color-changing material, adding the mixture to an aqueous solution containing isophthalic acid and a benzimidazole ligand, stirring the mixture for reaction, standing the mixture at room temperature, centrifuging the mixture, washing the mixture with distilled water, and freeze-drying the mixture to obtain a thermofluorescent color-changing material / Eu-MOF composite material;

[0015] Step 5. Prepare a porous liquid crystal material with dual responses of thermochromism and fluorescence. Take a certain amount of the above-mentioned thermochromic fluorescent material / Eu-MOF composite material, add it into the nematic liquid crystal 1717 together with the ultraviolet polymerizable monomer 6301 and the photoinitiator UV-329, place the mixture in a magnetic stirring constant temperature oil bath, continue to heat and magnetically stir at a certain temperature, and obtain a porous liquid crystal material with dual responses of thermochromism and fluorescence.

[0016] As a preferred embodiment of the above technical solution, in the step 1, 7.6 g of 2-bromoethanol and 8.0 g of 2,3,3-trimethyl-2H-indole, and 50 mL of dichloromethane are added to a flask equipped with a reflux condenser, stirred, heated to 90° C., and refluxed for 12 hours; after stopping the reaction, dichloromethane is removed by distillation, 60 mL of n-hexane is added, filtered, and purified by recrystallization with 80 mL of ethyl acetate, and dried under vacuum for 6 hours to obtain pink-purple granular crystals;

[0017] Under nitrogen protection, 200 mL of 10% sodium hydroxide solution was added dropwise to a flask containing 13.9 g of the above-mentioned purple granular crystals, and the mixture was stirred to obtain a yellow solution, which was extracted with ethyl acetate. The organic layer was dried over anhydrous MgSO4 for 24 h, filtered, and the ethyl acetate was removed by rotary evaporation to obtain a yellow oil.

[0018] Under light-proof conditions, 6.6 g of the above yellow oil and 5.5 g of 2-hydroxy-5-nitrobenzaldehyde were placed in a reaction container, 50 mL of anhydrous ethanol was added, nitrogen was introduced for protection, the reaction was heated to 80° C., refluxed for 6 h, cooled to room temperature, the solvent was removed by rotary evaporation, and recrystallized with acetone to obtain purple crystals, namely spiropyran.

[0019] As a preferred embodiment of the above technical solution, in the step 2, 2.8 g of hexadecanoic acid solid, 5.6 mg of spiropyran and 5.6 mg of 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene are weighed respectively, mixed and magnetically stirred for 3 hours in a constant temperature oil bath environment at 80°C to allow the spiropyran and 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene to be fully dissolved in the hexadecanoic acid liquid to obtain the spiropyran / cyanostyryl derivative / hexadecanoic acid thermoluminescent color-changing material.

[0020] As a preferred embodiment of the above technical scheme, in the step three, 21 mg of isophthalic acid, 56 mg of europium nitrate and 58 mg of hexadecyltrimethylammonium bromide are taken and dissolved in 50 mL of dimethylformamide solution. The mixture is stirred at room temperature for 30 min and then allowed to stand for 2 h. The mixture is centrifuged and washed with ethanol and distilled water respectively, and finally freeze-dried to obtain a white solid powder, namely Eu-MOF.

[0021] As a preferred embodiment of the above technical solution, in the step 4, 18 mg of Eu-MOF and 32 mg of spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color material are mixed and added to 5 ml of an aqueous solution containing isophthalic acid and benzimidazole ligands, wherein the weight ratio of isophthalic acid to benzimidazole ligands is 10:1. After stirring for 30 minutes, the mixture is allowed to stand at room temperature for 1 hour, centrifuged, washed with distilled water, and freeze-dried to obtain a thermoluminescent color material / Eu-MOF composite material.

[0022] As a preferred embodiment of the above technical solution, in the step five, 10 mg of the above-mentioned thermofluorescent color material / Eu-MOF composite material is taken, and added together with 0.46 g of ultraviolet polymerizable monomer 6301 and 0.01 g of photoinitiator UV-329 to 0.56 g of nematic liquid crystal 1717, and the mixture is placed in a magnetic stirring constant temperature oil bath, and continuously heated at 45°C and magnetically stirred for 2 hours to obtain a porous liquid crystal material with dual thermochromic and fluorescent responses.

[0023] The porous liquid crystal material with dual responses of thermochromism and fluorescence is prepared by adopting the preparation method.

[0024] Application of the porous liquid crystal material with dual response of thermochromic and fluorescence: Take out two pieces of dry ITO glass, separate them with a 20μm thick polyethylene terephthalate film on both sides of the two pieces of glass, and glue them with strong glue to complete the preparation of a blank liquid crystal box; fill the above-mentioned porous liquid crystal material with dual response of thermochromic and fluorescence into the blank liquid crystal box by the siphon effect of the capillary; finally, irradiate with a commercial 365nm UV curing lamp for 20 minutes, and the UV polymerization light intensity is constant at 10mW / cm during the irradiation process. 2 , a liquid crystal display with thermoluminescent color-changing properties is obtained.

[0025] The beneficial effects of the present invention are as follows: the porous liquid crystal material with dual thermochromic and fluorescent responses of the present invention, by introducing phase change material and fluorescent material into the liquid crystal, enables the liquid crystal to have different fluorescent display effects above and below the phase change temperature, and can realize dynamic control of color and shape, thereby being applied to fields such as information storage, camouflage and display. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the XRD pattern of the thermochromic fluorescent material / Eu-MOF composite material;

[0027] Figure 2 is the SEM image of the thermochromic fluorescent material / Eu-MOF composite material;

[0028] Figure 3 This is the TEM image of the thermochromic fluorescent material / Eu-MOF composite material. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] Add 7.6 g of 2-bromoethanol and 8.0 g of 2,3,3-trimethyl-2H-indole and 50 mL of dichloromethane to a flask equipped with a reflux condenser, stir, heat to 90°C, and reflux for 12 h; after stopping the reaction, remove dichloromethane by distillation, add 60 mL of n-hexane, filter, purify by recrystallization with 80 mL of ethyl acetate, and dry under vacuum for 6 h to obtain pink-purple granular crystals;

[0032] Under nitrogen protection, 200 mL of 10% sodium hydroxide solution was added dropwise to a flask containing 13.9 g of the above-mentioned purple granular crystals, and the mixture was stirred to obtain a yellow solution, which was extracted with ethyl acetate. The organic layer was dried over anhydrous MgSO4 for 24 h, filtered, and the ethyl acetate was removed by rotary evaporation to obtain a yellow oil.

[0033] Under light-proof conditions, 6.6 g of the above yellow oil and 5.5 g of 2-hydroxy-5-nitrobenzaldehyde were placed in a reaction container, 50 mL of anhydrous ethanol was added, nitrogen was introduced for protection, the reaction was heated to 80° C., refluxed for 6 h, cooled to room temperature, the solvent was removed by rotary evaporation, and recrystallized with acetone to obtain purple crystals, namely spiropyran.

[0034] 2.8 g of hexadecanoic acid solid, 5.6 mg of spiropyran and 5.6 mg of 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene were weighed separately, mixed and magnetically stirred for 3 h in a constant temperature oil bath environment at 80°C to allow spiropyran and 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene to be fully dissolved in the hexadecanoic acid liquid to obtain spiropyran / cyanostyryl derivative / hexadecanoic acid thermofluorescent color-changing material.

[0035] Take 21 mg of isophthalic acid, 56 mg of europium nitrate and 58 mg of hexadecyltrimethylammonium bromide, dissolve them in 50 mL of dimethylformamide solution, stir at room temperature for 30 min, let stand for 2 h, centrifuge, wash with ethanol and distilled water respectively, and finally freeze-dry to obtain a white solid powder, which is Eu-MOF.

[0036] 18 mg of Eu-MOF and 32 mg of spiropyran / cyanostyrene derivative / hexadecanoic acid thermofluorescent material were mixed and added to 5 ml of aqueous solution containing isophthalic acid and benzimidazole ligands, wherein the weight ratio of isophthalic acid to benzimidazole ligands was 10:1. After stirring for 30 minutes, the mixture was allowed to stand at room temperature for 1 hour, centrifuged, washed with distilled water, and freeze-dried to obtain a thermofluorescent material / Eu-MOF composite material. The XRD pattern of the thermofluorescent material / Eu-MOF composite material is shown in Figure 2. Figure 1 As shown in the SEM images Figure 2 As shown in the TEM image Figure 3 shown.

[0037] Take 10 mg of the above-mentioned thermofluorescent color material / Eu-MOF composite material, add it together with 0.46 g of UV polymerizable monomer 6301 and 0.01 g of photoinitiator UV-329 to 0.56 g of nematic liquid crystal 1717, place the mixture in a magnetic stirring constant temperature oil bath, continue heating at 45 ° C and continuously magnetically stir for 2 hours to obtain a porous liquid crystal material with dual thermochromic and fluorescent responses.

[0038] Take out two pieces of dried ITO glass, separate them with a 20μm thick polyethylene terephthalate film on both sides of the two pieces of glass, and glue them together with strong glue to complete the preparation of a blank liquid crystal box; use the siphon effect of the capillary to fill the above-mentioned thermochromic and fluorescent dual-responsive porous liquid crystal material into the blank liquid crystal box; finally, irradiate with a commercial 365nm UV curing lamp for 20 minutes, and the UV polymerization light intensity during the irradiation process is constant at 10mW / cm 2 , a liquid crystal display with thermoluminescent color-changing properties is obtained.

[0039] Example 2

[0040] The rest is the same as Example 1, except that the amount of spiropyran in the spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color-changing material is adjusted from 5.6 mg to 6.8 mg.

[0041] Example 3

[0042] The rest is the same as Example 1, except that the amount of spiropyran in the spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color-changing material is adjusted from 5.6 mg to 8.0 mg.

[0043] Example 4

[0044] The rest is the same as Example 1, except that the amount of 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene in the spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color-changing material is adjusted from 5.6 mg to 6.8 mg.

[0045] Example 5

[0046] The rest is the same as Example 1, except that the amount of 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene in the spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color-changing material is adjusted from 5.6 mg to 8.0 mg.

[0047] Comparative Example 1

[0048] The rest is the same as Example 1, except that the amount of Eu-MOF is adjusted, 22 mg Eu-MOF and 28 mg thermoluminescent color material are mixed. Others remain unchanged, 5 ml isophthalic acid and benzimidazole ligand are mixed in a ratio of 10:1

[0049] Comparative Example 2

[0050] The rest is the same as Example 1, except that the amount of Eu-MOF is adjusted, 26 mg Eu-MOF and 24 mg thermoluminescent color material are mixed. Other things remain unchanged, 5 ml of isophthalic acid and benzimidazole ligand are mixed in a ratio of 10:1

[0051] Comparative Example 3

[0052] The rest is the same as Example 1, except that the amount of Eu-MOF is adjusted, 30 mg Eu-MOF and 20 mg thermoluminescent color material are mixed. Others remain unchanged, 5 ml of isophthalic acid and benzimidazole ligand are mixed in a ratio of 10:1

[0053] Comparative Example 4

[0054] The rest is the same as Example 1, except that the amount of Eu-MOF is adjusted, 34 mg Eu-MOF and 16 mg thermoluminescent color material are mixed. Other things remain unchanged, 5 ml isophthalic acid and benzimidazole ligand are mixed in a ratio of 10:1.

[0055] Performance Testing

[0056] The liquid crystal displays prepared in Examples 1-5 and Comparative Examples 1-4 were tested for fluorescence intensity at different temperatures under ultraviolet light irradiation. The test results are shown in the table below.

[0057]

[0058] Fluorophores are introduced into phase change materials (PCMs) to prepare dual-response temperature fluorescent materials that can switch fluorescence from "off" to "on" according to temperature. Phase change materials with self-crystallization properties can significantly affect the molecular arrangement of fluorophores during heating, leading to a change in fluorescence behavior.

[0059] Since the fluorescence emission peak of spiropyran is 640nm, which belongs to red light, it realizes cis-trans isomerization under ultraviolet light, and its fluorescence intensity gradually weakens; while the fluorescence emission peak of cyanostyrene derivatives is 443nm, which belongs to blue light, and it transforms from trans structure to cis structure under ultraviolet irradiation, and its fluorescence intensity increases with the extension of irradiation time. Therefore, under ultraviolet light irradiation, the fluorescence color of liquid crystal materials can achieve red-orange-blue color changes.

[0060] 1. The results of the comparative examples and comparative examples show that, below the phase transition temperature (45°C), the fluorescence effect cannot be displayed by ultraviolet light irradiation; while within the phase transition temperature range (45-50°C), a weak fluorescence phenomenon can be displayed; when the temperature is raised to above the phase transition temperature (50°C), the clean fluorescence can be observed by ultraviolet light irradiation. It is mainly the self-crystallization ability of the phase change material that can adjust the dispersion or aggregation state of the fluorescent dye to achieve the adjustment of the color and fluorescence emission characteristics. This change is particularly obvious in fluorescent molecules such as spiropyran and cyanostyrene derivatives. When the ambient temperature is lower than the phase transition point of the fatty alcohol, the fatty alcohol molecules form a crystalline structure through hydrogen bonds, which reduces the hydrogen bond competition with the fluorescent molecules, promotes the aggregation of the fluorescent molecules, and triggers the change of color and fluorescence characteristics. On the contrary, when the temperature exceeds the phase transition point, the fatty alcohol releases the hydrogen bonds, the solvent molecules become more active, and the hydrogen bond interaction between them and the fluorescent molecules is enhanced, resulting in the dispersion of the fluorescent molecules, thereby changing their fluorescence characteristics.

[0061] 2. Comparative Example: Increasing the content of spiropyran will delay the existence time of red light; while increasing the content of 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene will shorten the time of red light and promote the appearance of blue light.

[0062] 3. The comparative results show that changing the MOF framework content will also affect the display time. Controlling the MOF content within a certain range has little effect on the display time; when the MOF content is large (Comparative Example 4), it will have a great impact on the display time, resulting in no color. It should be that when the MOF content is too high, the structure of the material will undergo unstable changes, thus affecting its optical properties.

[0063] In summary, this paper uses fatty acids as the matrix and spiropyran and cyanostyrene derivatives as fluorophores to prepare a thermochromic material with good reversibility and obvious fluorescence emission changes. Subsequently, based on liquid crystal as a thermal responsive emission source, combined with thermosensitive long-chain carboxylic acids with self-crystallization properties, a liquid crystal material with tunable fluorescence and temperature color-changing properties is obtained.

[0064] It is worth mentioning that the technical features such as the flask equipped with a reflux condenser involved in the patent application of this invention should be regarded as the prior art. The specific structure, working principle and possible control method and spatial layout method of these technical features can be selected by conventional methods in the field, and should not be regarded as the inventive point of the patent of this invention. The patent of this invention will not be further elaborated.

[0065] The preferred specific embodiments of the present invention are described in detail above. It should be understood that ordinary technicians in this field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in this technical field through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the existing technology should be within the scope of protection determined by the claims.

Claims

1. A method for preparing a porous liquid crystal material with dual responses of thermochromism and fluorescence, characterized in that: The following steps are included: Step 1, synthesis of spiropyran, under nitrogen protection, add a certain amount of 2-bromoethanol and a certain amount of 2,3,3-trimethyl-2H-indole, and a certain amount of dichloromethane into a flask equipped with a reflux condenser, stir, heat to a certain temperature, and reflux for a period of time; after stopping the reaction, remove dichloromethane by distillation, add a certain amount of n-hexane, filter, recrystallize and purify with a certain amount of ethyl acetate, and dry under vacuum to obtain pink purple granular crystals; Under nitrogen protection, a certain amount of sodium hydroxide solution was added dropwise to a flask containing a certain amount of the above-mentioned purple granular crystals, and the mixture was stirred to obtain a yellow solution, which was extracted with ethyl acetate. The organic layer was dried with anhydrous MgSO4 for a period of time, filtered, and the ethyl acetate was removed by rotary evaporation to obtain a yellow oily substance. Under light-proof conditions, a certain amount of the yellow oil and a certain amount of 2-hydroxy-5-nitrobenzaldehyde are placed in a reaction container, a certain amount of anhydrous ethanol is added, nitrogen is introduced for protection, the reaction is heated to a certain temperature, refluxed for a period of time, cooled to room temperature, the solvent is removed by rotary evaporation, and recrystallized with acetone to obtain purple crystals, namely spiropyran; Step 2, preparing a spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color-changing material, respectively weighing a certain amount of hexadecanoic acid solid, spiropyran and 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene, mixing and magnetically stirring for a period of time in a constant temperature oil bath environment, so that the spiropyran and 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene are fully dissolved in the hexadecanoic acid liquid, and the spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color-changing material is obtained; Step 3: Prepare Eu-MOF. Take a certain amount of isophthalic acid, europium nitrate and hexadecyltrimethylammonium bromide, dissolve them in a certain amount of dimethylformamide solution, stir at room temperature for a period of time, let stand, centrifuge, wash with ethanol and distilled water respectively, and finally freeze-dry to obtain a white solid powder, which is Eu-MOF. Step 4: preparing a thermoluminescent color-changing material / Eu-MOF composite material, mixing a certain amount of cadmium nitrate and a dye, adding the mixture to an aqueous solution containing isophthalic acid and a benzimidazole ligand, stirring the mixture for reaction, standing the mixture at room temperature, centrifuging the mixture, washing the mixture with distilled water, and freeze-drying the mixture to obtain a thermoluminescent color-changing material / Eu-MOF composite material; Step 5. Prepare a porous liquid crystal material with dual responses of thermochromism and fluorescence. Take a certain amount of the above-mentioned thermochromic fluorescent material / Eu-MOF composite material, add it into the nematic liquid crystal 1717 together with the ultraviolet polymerizable monomer 6301 and the photoinitiator UV-329, place the mixture in a magnetic stirring constant temperature oil bath, continue to heat and magnetically stir at a certain temperature, and obtain a porous liquid crystal material with dual responses of thermochromism and fluorescence.

2. The method for preparing a porous liquid crystal material with dual responses of thermochromism and fluorescence according to claim 1, characterized in that: In the step 1, 7.6 g of 2-bromoethanol and 8.0 g of 2,3,3-trimethyl-2H-indole and 50 mL of dichloromethane are added to a flask equipped with a reflux condenser, stirred, heated to 90° C., and refluxed for 12 h; after stopping the reaction, dichloromethane is removed by distillation, 60 mL of n-hexane is added, filtered, purified by recrystallization with 80 mL of ethyl acetate, and dried under vacuum for 6 h to obtain pink-purple granular crystals; Under nitrogen protection, 200 mL of 10% sodium hydroxide solution was added dropwise to a flask containing 13.9 g of the above-mentioned purple granular crystals, and the mixture was stirred to obtain a yellow solution, which was extracted with ethyl acetate. The organic layer was dried over anhydrous MgSO4 for 24 h, filtered, and the ethyl acetate was removed by rotary evaporation to obtain a yellow oil. Under light-proof conditions, 6.6 g of the above yellow oil and 5.5 g of 2-hydroxy-5-nitrobenzaldehyde were placed in a reaction container, 50 mL of anhydrous ethanol was added, nitrogen was introduced for protection, the reaction was heated to 80° C., refluxed for 6 h, cooled to room temperature, the solvent was removed by rotary evaporation, and recrystallized with acetone to obtain purple crystals, namely spiropyran.

3. The method for preparing a porous liquid crystal material with dual responses of thermochromism and fluorescence according to claim 1, characterized in that: In the step 2, 2.8 g of hexadecanoic acid solid, 5.6 mg of spiropyran and 5.6 mg of 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene are weighed respectively, mixed and magnetically stirred for 3 hours in a constant temperature oil bath environment at 80° C., so that the spiropyran and 1-(2-cyanostyryl)-4-(4-cyanostyryl)benzene are fully dissolved in the hexadecanoic acid liquid to obtain a spiropyran / cyanostyryl derivative / hexadecanoic acid thermoluminescent color-changing material.

4. The method for preparing a porous liquid crystal material with dual responses of thermochromism and fluorescence according to claim 1, characterized in that: In the step 3, 21 mg of isophthalic acid, 56 mg of europium nitrate and 58 mg of hexadecyltrimethylammonium bromide were taken and dissolved in 50 mL of dimethylformamide solution. The mixture was stirred at room temperature for 30 min and then allowed to stand for 2 h. The mixture was centrifuged and washed with ethanol and distilled water respectively. The mixture was freeze-dried to obtain a white solid powder, namely Eu-MOF.

5. The method for preparing a porous liquid crystal material with dual responses of thermochromism and fluorescence according to claim 1, characterized in that: In the step 4, 18 mg of Eu-MOF and 32 mg of spiropyran / cyanostyrene derivative / hexadecanoic acid thermoluminescent color material are mixed and added to 5 ml of an aqueous solution containing isophthalic acid and benzimidazole ligands, wherein the weight ratio of isophthalic acid to benzimidazole ligands is 10:

1. After stirring for 30 minutes, the mixture is allowed to stand at room temperature for 1 hour, centrifuged, washed with distilled water, and freeze-dried to obtain a thermoluminescent color material / Eu-MOF composite material.

6. The method for preparing a porous liquid crystal material with dual responses of thermochromism and fluorescence according to claim 1, characterized in that: In the step five, 10 mg of the above-mentioned thermofluorescent color material / Eu-MOF composite material is taken, and added together with 0.46 g of ultraviolet polymerizable monomer 6301 and 0.01 g of photoinitiator UV-329 to 0.56 g of nematic liquid crystal 1717, and the mixture is placed in a magnetic stirring constant temperature oil bath, and continuously heated at 45°C and magnetically stirred for 2 hours to obtain a porous liquid crystal material with dual thermochromic and fluorescent responses.

7. A porous liquid crystal material with dual thermochromic and fluorescent responses, characterized in that: The method is prepared according to any one of claims 1 to 6.

8. The use of the porous liquid crystal material with dual thermochromic and fluorescent responses as claimed in claim 7, characterized in that: Take out two pieces of dried ITO glass, separate them with a 20μm thick polyethylene terephthalate film on both sides of the two pieces of glass, and glue them together with strong glue to complete the preparation of a blank liquid crystal box; use the siphon effect of the capillary to fill the above-mentioned thermochromic and fluorescent dual-responsive porous liquid crystal material into the blank liquid crystal box; finally, irradiate with a commercial 365nm UV curing lamp for 20 minutes, and the UV polymerization light intensity during the irradiation process is constant at 10mW / cm 2 , a liquid crystal display with thermoluminescent color-changing properties is obtained.

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