Squarylium dye molecule doped liquid crystal host material, preparation method and application thereof

Abstract

The application belongs to the technical field of intelligent responsive materials, and discloses a squarylium dye molecule doped liquid crystal host material, a preparation method and application, wherein the squarylium dye molecule doped liquid crystal host material is formed by mixing squarylium dye molecules and a liquid crystal host, the structural formula of the squarylium dye molecule includes R, R is a flexible functional group, and is selected from an alkyl chain, an alkyl chain with a double bond / triple bond, an oligomeric ethylene glycol chain or a siloxane chain, and the liquid crystal host is in a nematic phase or a smectic phase at room temperature; the application can realize fast color change response performance by adjusting the molecular aggregate structure, the material has multiple stimulus response characteristics, including photochromism, thermochromism and solvent annealing, is suitable for functional requirements under complex environmental changes, and also exhibits excellent system compatibility, and can be combined with various polymer matrices to construct sandwich type composite films, polymer dispersed liquid crystal films and other functional materials.

Description

Technical Field

[0001] This invention relates to the field of smart responsive materials technology, specifically to a squaric acid cyanine dye-doped liquid crystal host material, its preparation method, and its application. Background Technology

[0002] As an important branch of stimulus-responsive smart materials, mesophilic materials use unique optical signal output to identify and respond to external stimuli, and have important application prospects in fields such as sensing, information storage, display and anti-counterfeiting.

[0003] In recent years, researchers have developed a variety of mechanochromic materials, including inorganic quantum dots, transition-state metal compounds, metal-organic frameworks, organic dye molecules, and photonic crystals. The color-changing principles of these materials can be divided into two main categories: one is based on molecular-level response, where the introduction of mechanoresponsive groups allows the molecules to change their optical properties through isomerization or bond-breaking reactions under mechanical stimulation. For example, spiropyran molecules transform from a closed-ring structure to an open-ring anthocyanin structure under stress. Nature , 2009, 459(7243): 68-729). This method often relies on complex chemical design and synthesis steps. The second is based on the supramolecular level, which achieves optical response by adjusting the phase structure and molecular aggregation mode, and has received much research attention in recent years. One method is inspired by the natural biological stretching of pigment cells to change their own color to achieve camouflage effect. With the help of the self-assembly structure of chiral nematic phases, the dynamic change of structural color can be achieved by changing the pitch under the action of external force. However, uneven pitch change often leads to the problem of uneven color distribution. ACS Macro Lett 2013, 2, 818-821. The optical properties of materials are closely related to the packing pattern of aggregates, and therefore color response can also be achieved by changing intermolecular interactions (such as π-π interactions, hydrogen bonds, host-guest interactions, etc.). However, most existing aggregate modulation techniques are limited to crystal-crystal or crystal-amorphous transitions, such as the mechanochromic material based on anthracene derivatives reported by Tian's group (…). Angew. Chem. Int. Ed. (2012, 51, 10782-10785), mechanical grinding gradually enhances the π-π interactions between anthracene molecules, resulting in three single crystals of different colors. However, this crystal form transformation is insensitive to external stimuli, often exhibiting problems such as high energy thresholds and slow response speeds. Furthermore, achieving multi-field responses is difficult, significantly limiting its application in various scenarios.

[0004] In summary, responses at the supramolecular scale avoid complex chemical synthesis and are relatively simple to operate. However, the types and quantities of materials that achieve color-changing properties by adjusting the molecular aggregate structure are still limited. More importantly, the color changes in these materials mainly originate from the crystal form transformation after prolonged grinding or scratching, which not only significantly limits their response speed but also restricts the development of their response performance under multi-field coupling. This situation highlights the urgent need to develop novel supramolecular color-changing material systems. Summary of the Invention

[0005] The purpose of this invention is to provide a squaric acid cyanine dye-doped liquid crystal host material, its preparation method, and its application, so as to overcome the problems of insensitivity to external stimuli at the supramolecular scale, high energy threshold, and slow response speed in the prior art. This invention can achieve rapid color change response performance by adjusting the molecular aggregation state structure.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a squaricine dye molecule-doped liquid crystal host material, formed by mixing squaricine dye molecules with a liquid crystal host, wherein the squaricine dye molecules have the structural formula shown in formula (I): , Wherein, R is a flexible functional group, selected from alkyl chains, alkyl chains with double / triple bonds, oligoethylene glycol chains, or siloxane chains; The liquid crystal substrate is a nematic or smectic phase at room temperature.

[0007] In some embodiments, the liquid crystal host is one or a combination of 4-cyano-4'-butylbiphenyl, 4-cyano-4'-pentylbiphenyl, and 4-cyano-4'-hexylbiphenyl.

[0008] In some embodiments, the content of the squaricine dye molecules is 10-40 wt%, and the content of the liquid crystal substrate is 60-90 wt%.

[0009] Secondly, the present invention provides a method for preparing a squaricine dye-doped liquid crystal host material, which, based on the above-mentioned squaricine dye-doped liquid crystal host material, includes the following steps: After a catalytic reaction, m-aminophenol and methyl acrylate were subjected to neutralization, first extraction, first concentration, and first column chromatography purification to obtain the first compound. The first compound was subjected to an acetal-protected reaction with 3,4-dihydro-pyran in dichloromethane solvent, followed by a second extraction, a second concentration, and a second column chromatography purification to obtain the second compound. A tetrahydrofuran solution of lithium aluminum hydride was added dropwise to a tetrahydrofuran solution of the second compound and reacted at room temperature. The mixture was then purified by water quenching, first filtration, first concentration, and third column chromatography to obtain the third compound. The third compound was subjected to an amidation condensation reaction with the 3,4,5-substituted benzoic acid derivative F in dichloromethane solvent. Following washing with water, drying, second concentration, and fourth column chromatography purification, the fourth compound was obtained. The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R is a flexible functional group, selected from alkyl chains, alkyl chains with double / triple bonds, oligoethylene glycol chains, or siloxane chains; The fourth compound was refluxed with an acidic ion exchange resin in a tetrahydrofuran / methanol mixed solvent, and then successively filtered and concentrated to obtain the fifth compound. After the fifth compound was condensed with squaric acid in a toluene / n-butanol mixed solvent, the mixture was successively subjected to precipitation, third filtration, column chromatography separation and recrystallization to obtain squaric acid cyanine dye molecules. Squaricine dye molecules are mixed with liquid crystal substrates to obtain squaricine dye-doped liquid crystal substrate materials.

[0010] In some embodiments, the temperature of the catalytic reaction is 90~100 °C, the time of the catalytic reaction is 10~14 h, and the catalyst for the catalytic reaction is glacial acetic acid and sodium bromide; The temperature of the acetal protection reaction is -5~5℃, the reaction time is 20~28 h, and the catalyst for the acetal protection reaction is pyridinium salt of p-benzenesulfonate. The room temperature reaction is at a temperature of 20~25℃, and the room temperature reaction time is 1.5~3h; The amidation condensation reaction is carried out at a temperature of 20-30°C for 10-14 h, and the catalysts for the amidation condensation reaction are 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine. The reflux temperature is 75~80℃, and the reflux time is 10~14 h; The condensation reaction is carried out at a temperature of 135~145℃ for 10~14 h. The recrystallization was performed using dichloromethane and methanol; The mass ratio of the squaric acid cyanine dye molecules to the liquid crystal substrate is (1.11-6.67):10.

[0011] Thirdly, the present invention provides the application of a squaric acid cyanine dye-doped liquid crystal host material according to the above in the field of smart response materials.

[0012] Fourthly, the present invention provides a polymer / liquid crystal sandwich type composite film, which is constructed based on the above-mentioned squaric acid cyanine dye molecule-doped liquid crystal host material, including a first polymer layer and a second polymer layer, wherein the squaric acid cyanine dye molecule-doped liquid crystal host material is distributed between the first polymer layer and the second polymer layer.

[0013] In some embodiments, the first polymer layer and the second polymer layer are each independently selected from polyvinyl alcohol or polydimethylsiloxane. The thickness of the first polymer layer is 50-100µm; The thickness of the second polymer layer is 50-100µm; The thickness of the squaricine dye-doped liquid crystal host material between the first polymer layer and the second polymer layer is 10-30µm.

[0014] Fifthly, the present invention provides a polymer-dispersed liquid crystal film based on the above-mentioned squaricine dye molecule-doped liquid crystal host material, comprising the following steps: The squaric acid cyanine dye-doped liquid crystal host material is mixed with an organic solvent to form a homogeneous solution. The homogeneous solution is then cast into a film and volatilized to obtain a polymer-dispersed liquid crystal film.

[0015] In some embodiments, the organic solvent includes one or a combination of chloroform and dichloromethane; The thickness of the polymer-dispersed liquid crystal film is 30-100µm.

[0016] The above technical solution has the following advantages or beneficial effects: Firstly, this invention provides a squaricine dye-doped liquid crystal host material. By combining a specially structured squaricine dye with room-temperature liquid crystal, the isotropic fluid achieves stable existence at room temperature and exhibits excellent stimulus response performance. This material can produce rapid color changes with high contrast under weak external force fields, significantly reducing the energy threshold and improving response sensitivity. It possesses multiple response characteristics, including photochromism, thermochromism, and solvent dehumidification, enabling it to flexibly adapt to complex and changing environmental conditions. This system ingeniously utilizes the interaction between dye and liquid crystal molecules to effectively amplify external stimulus signals at the supramolecular scale, fundamentally overcoming the bottlenecks of slow response and insufficient sensitivity in existing technologies, and providing innovative ideas for developing next-generation intelligent sensing, display, and anti-counterfeiting materials.

[0017] In some embodiments, the liquid crystal host is preferably one or a mixture of 4-cyano-4'-butylbiphenyl (CB4), 4-cyano-4'-pentylbiphenyl (CB5), or 4-cyano-4'-hexylbiphenyl (CB6). These classical liquid crystal materials with well-defined nematic phases can form a uniform and stable doping system with squaricocyanine dye molecules, which is a key host component for achieving room temperature isotropic fluid properties, high contrast, and rapid stimulus response.

[0018] In some embodiments, the content of the cyanine dye molecules and the liquid crystal host is provided, and this composition range is key to achieving stable doping, maintaining fluid properties, and producing a fast, high-contrast color response.

[0019] Secondly, this invention provides a method for preparing a squaric acid cyanine dye-doped liquid crystal host material. Through stepwise functional group modification, protection and deprotection, and the key squaric acid condensation reaction, multiple flexible functional side chains (R) can be controllably introduced, thereby precisely controlling the solubility of the dye molecules and the host-guest compatibility of the liquid crystal. Each step is accompanied by purification operations such as extraction and column chromatography, ensuring the high purity of the intermediates and the final dye product, which is a prerequisite for achieving stable and uniform doping of the material. The final physical blending step with the preferred liquid crystal host is simple and easy to scale up. The entire process provides a reliable and reproducible synthetic basis for obtaining functional materials with excellent room temperature fluid stability and rapid, high-contrast multi-stimulus response performance.

[0020] In some embodiments, this method ensures the efficiency and controllability of the synthetic route by optimizing key parameters (temperature, time, catalyst, and purification conditions) of each reaction step. For example, acetal protection is carried out at low temperatures to improve selectivity, squaric acid condensation completes ring closure at specific high temperatures, and the final recrystallization step precisely purifies the product. These conditions together ensure the high yield, high purity, and excellent compatibility of squaric acid cyanine dye molecules with the liquid crystal host, which is key to obtaining a stable and responsive final material.

[0021] Thirdly, this invention provides an application of a squaric acid cyanine dye-doped liquid crystal host material in the field of smart response materials. This material can be used to prepare smart response devices, such as sensor tags, anti-counterfeiting labels, and dynamic display units. By utilizing its rapid and high-contrast color changes in multiple stimuli (light / heat / solvent), information encryption and visual environmental monitoring can be achieved.

[0022] Fourthly, the present invention provides a polymer / liquid crystal sandwich composite film, which consists of upper and lower polymer layers and a squaric acid cyanine dye / liquid crystal composite material sandwiched between them. It can effectively encapsulate and stabilize the liquid crystal fluid, so as to maintain its macroscopic fluidity. The film can achieve the coordinated and rapid orientation of liquid crystal molecules and dye molecules under weak external force, thereby exhibiting high-contrast color changes, which is suitable for the development of flexible smart response devices.

[0023] In some embodiments, the composite film uses flexible polyvinyl alcohol or polydimethylsiloxane as an encapsulation layer, with a thickness of 50-100µm providing good mechanical support and isolation protection; the intermediate 10-30µm functional layer thickness optimizes the optical path and response sensitivity, enabling the encapsulated liquid crystal / dye fluid to still produce significant and rapid macroscopic color changes under weak stress. This structural design balances stability, flexibility, and excellent stimulus response performance.

[0024] Fifthly, this invention provides a polymer-dispersed liquid crystal film. This method achieves in-situ dispersion and curing of squaric acid cyanine dye / liquid crystal composite material in a polymer matrix through solution casting process. The resulting film has a uniform structure and combines the mechanical stability of the polymer matrix with the multi-stimulus response characteristics of functional materials. It can produce rapid and significant macroscopic color changes through light, heat or solvent stimulation, providing a simple and effective way to prepare flexible, large-area smart responsive films.

[0025] In some embodiments, the use of specific organic solvents ensures the full dissolution and uniform film formation of the squaric acid cyanine dye / liquid crystal composite material, ultimately obtaining a film with a thickness of 30-100µm, which has good flexibility, transparency and significant multi-stimulus response performance. Attached Figure Description

[0026] Figure 1 The differential scanning calorimetry curve of the mixture shown in Example 1 of this invention; Figure 2 This is a schematic diagram of the response of the squartz cyanine dye-doped liquid crystal host material on a quartz substrate, corresponding to Embodiment 1 of the present invention. Figure 3 This is a schematic diagram of the response of the squartz cyanine dye-doped liquid crystal host material on a quartz substrate, corresponding to Embodiment 3 of the present invention. Figure 4 This is a schematic diagram of the response of the squartz cyanine dye-doped liquid crystal host material on a quartz substrate, corresponding to Embodiment 5 of the present invention. Figure 5 This is a schematic diagram of the response of the squartz cyanine dye-doped liquid crystal host material on a quartz substrate, corresponding to Embodiment 8 of the present invention. Figure 6This is a schematic diagram of the response of the squartz cyanine dye-doped liquid crystal host material on a quartz substrate, corresponding to Embodiment 9 of the present invention. Figure 7 This is a schematic diagram of the structure of Embodiment 1 of the present invention, wherein (a) is the unsheared state of the liquid crystal host material doped with squaric acid cyanine dye molecules; (b) is the optical texture under a polarizing microscope after shearing, and the inset is the optical texture after inserting the λ-plate; Figure 8 The UV-Vis absorption curves of the squartz cyanine dye-doped liquid crystal host material on a quartz substrate before and after shearing are shown in the embodiments of the present invention. Among them, (a) is the UV-Vis absorption curve of Example 1, (b) is the UV-Vis absorption curve of Example 5, (c) is the UV-Vis absorption curve of Example 8, and (d) is the UV-Vis absorption curve of Example 9. Figure 9 The following is a graph showing the fluorescence emission curves of the material obtained in Application Example 1 of this invention before and after shearing. Figure 10 This is a schematic diagram of the response of the sandwich-type composite film obtained in Application Example 2 of the present invention under force stimulation and heating. Figure 11 The images are morphological images of the polymer-dispersed liquid crystal film doped with squaricine dye molecules obtained in Example 3 of the present invention under a conventional optical microscope, wherein (a) is the morphological image in the unstretched state and (b) is the morphological image after uniaxial stretching. Figure 12 This is a schematic diagram of the mechanochromic effect of the polymer-dispersed liquid crystal film doped with squaric acid cyanine dye molecules obtained in Example 3 of the present invention under different stretching ratios. Figure 13 The diagram shows the response of the liquid crystal host material doped with cyanine dye molecules according to the present invention. (a) is a schematic diagram of the response of the material obtained in Application Example 1 under a dichloromethane solvent atmosphere; (b) is a schematic diagram of the response of the film obtained in Application Example 3 after uniaxial stretching and color change and then placed under a red laser. Figure 14 This is a schematic diagram of the preparation process of the acid cyanine dye-doped liquid crystal host material of the present invention. Detailed Implementation

[0027] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a squaricine dye-doped liquid crystal host material, formed by mixing squaricine dye molecules with a liquid crystal host, wherein the squaricine dye molecules have the structural formula shown in formula (I): , Wherein, R is a flexible functional group, selected from alkyl chains, alkyl chains with double / triple bonds, oligoethylene glycol chains, or siloxane chains; The liquid crystal substrate is a nematic or smectic phase at room temperature.

[0031] Specifically, squaricine dye molecules can have different functional groups R. When R is an alkyl chain, compound II is designated as SQD. n, n The number of carbon atoms in the flexible functional group R is shown in structural formula (II): ; When R is an alkyl chain with a triple bond, compound III is designated as SQT. n, n The number of carbon atoms in the flexible functional group R is shown in compound (III): ; When R is an oligoethylene glycol chain, compound IV is designated as SQP. n, n The number of carbon atoms in the flexible functional group R is shown in compound (IV): .

[0032] This invention also provides a method for preparing a squaricine dye-doped liquid crystal host material, comprising the following steps: Step 1: After catalytic reaction of m-aminophenol and methyl acrylate, the mixture is subjected to neutralization, first extraction, first concentration and first column chromatography purification to obtain the first compound; Step 2: The first compound is reacted with 3,4-dihydro-pyran in dichloromethane solvent under acetal protection, followed by a second extraction, a second concentration, and a second column chromatography purification to obtain the second compound. Step 3: The tetrahydrofuran solution of lithium aluminum hydride is added dropwise to the tetrahydrofuran solution of the second compound to carry out the reaction at room temperature. Then, the mixture is quenched with water, filtered first, concentrated first, and purified by column chromatography to obtain the third compound. Step 4: The third compound and the 3,4,5-substituted benzoic acid derivative F are subjected to an amidation condensation reaction in dichloromethane solvent. The mixture is then washed with water, dried, concentrated twice, and purified by column chromatography to obtain the fourth compound. The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R is a flexible functional group, selected from alkyl chains, alkyl chains with double / triple bonds, oligoethylene glycol chains, or siloxane chains; Step 5: The fourth compound is refluxed with an acidic ion exchange resin in a tetrahydrofuran / methanol mixed solvent, and then sequentially filtered and concentrated to obtain the fifth compound. Step 6: After the fifth compound and squaric acid are condensed in a toluene / n-butanol mixed solvent, the mixture is then subjected to precipitation, third filtration, column chromatography separation, and recrystallization to obtain squaric acid cyanine dye molecules. Step 7: Mix the squaric acid cyanine dye molecules with the liquid crystal substrate, and then heat the mixture to a temperature above the melting point. After the two components are uniformly mixed, a squaric acid cyanine dye molecule-doped liquid crystal substrate material is obtained.

[0033] The core principle of the above steps lies in constructing dye molecules with strong light absorption and ordered arrangement through multi-step organic synthesis, and then utilizing their compatibility with liquid crystal molecules to achieve functional doping. Starting from m-aminophenol, through Michael addition, THP protection, reduction, amidation, and deprotection steps, an asymmetric precursor with electron-donating amino groups, a rigid benzene ring, and a flexible terminal chain is constructed. Finally, it condenses with squaric acid to form a highly conjugated squaric acid cyanine chromophore. This structure exhibits strong absorption in the near-infrared region, and the flexible chain (R) enhances its compatibility with liquid crystals. The dye molecules are then dissolved in the liquid crystal matrix by heating, and the self-assembly capability of the liquid crystal drives the dye molecules to arrange themselves in an ordered manner within the liquid crystal phase, thereby obtaining anisotropic optical functional materials. Such doped materials can be applied in liquid crystal displays, optical modulation, or sensing fields.

[0034] This invention also provides two thin films prepared based on squaric acid cyanine dye-doped liquid crystal host materials, as follows: (1) A polymer / liquid crystal sandwich type composite film A mixture of squaric acid cyanine dye molecules doped with liquid crystal was drop-coated between two polymer substrates, and then spin-coated / sheared at 50°C to ensure that the mixture of squaric acid cyanine dye molecules doped with liquid crystal was uniformly distributed on the polymer substrate, thus obtaining a polymer / liquid crystal sandwich composite film.

[0035] Specifically, it includes a first polymer layer and a second polymer layer, with the squaricocyanine dye-doped liquid crystal host material distributed between the first and second polymer layers. The thickness of the first polymer layer is 50-100µm; the thickness of the second polymer layer is 50-100µm; and the thickness of the squaricocyanine dye-doped liquid crystal host material between the first and second polymer layers is 10-30µm.

[0036] (2) A polymer-dispersed liquid crystal film Polymer-dispersed liquid crystal films were prepared using the solvent-induced phase separation (SIPS) method. A mixture of squaricine dye-doped liquid crystals was dissolved in an organic solvent and mixed with the polymer to form a homogeneous solution. The solution was then uniformly spread in a petri dish, and after the solvent evaporated, a polymer-dispersed liquid crystal film doped with squaricine dye was obtained.

[0037] Specifically, the organic solvent includes one or a combination of chloroform and dichloromethane; the thickness of the polymer-dispersed liquid crystal film is 30-100µm.

[0038] As can be seen, the squaricocyanine dye-doped liquid crystal host material provided by this invention is a stable isotropic fluid at room temperature and exhibits a fast color response with high contrast under an applied force field. This material possesses multiple stimulus-response characteristics, including photochromism, thermochromism, and solvent annealing, adapting to functional requirements under complex environmental changes. Simultaneously, the squaricocyanine dye-doped liquid crystal host material also demonstrates excellent system compatibility, and can be combined with various polymer matrices to construct functional materials such as sandwich-type composite films and polymer-dispersed liquid crystal films. Finally, this material is simple to prepare, low in cost, and widely applicable. Its design concept has significant scalability and versatility, making it a highly sensitive, multi-response intelligent response material with significant application potential in fields such as intelligent sensing and information encryption.

[0039] Example 1: This embodiment provides a method for preparing a squaric acid cyanine dye-doped liquid crystal host material. (See [link to previous document]) Figure 14 This includes the following steps: Step 1: Under anhydrous and oxygen-free conditions at 95 °C, m-aminophenol and methyl acrylate were combined and added to glacial acetic acid and sodium bromide for 12 h for catalysis. After the reaction was completed, sodium bicarbonate was added sequentially for neutralization, extraction and separation, and concentration. The product was separated by column chromatography to obtain the first compound (colorless oily liquid product).

[0040] Step 2: Under anhydrous and oxygen-free conditions at 0 °C, 3,4-dihydro-pyran (DHP) was gradually added dropwise to a dichloromethane solution of the first compound and pyridinium p-benzenesulfonate (PPTS) and reacted for 24 h. After extraction and separation by sodium bicarbonate solution, the mixture was concentrated and separated by column chromatography to obtain the second compound (colorless liquid product).

[0041] Step 3: Under anhydrous and oxygen-free conditions at 0 °C, the tetrahydrofuran solution of lithium aluminum hydride was added dropwise to the tetrahydrofuran solution of the second compound. After the addition was completed, the mixture was transferred to room temperature (25 °C) and reacted for 2 h. Then, the mixture was quenched with water, filtered to remove water, and concentrated. The crude product was subjected to rapid column chromatography to obtain the third compound (yellow oily product). Step 4: Under anhydrous and oxygen-free conditions at room temperature (25°C), the third compound and the 3,4,5-substituted benzoic acid derivative F were reacted in dichloromethane solvent with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine as catalysts for 12 h. After the reaction, the mixture was washed with water, dried, and concentrated to obtain the crude product. The crude product was then purified by a fourth column chromatography to obtain the fourth compound (white powder solid). The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R represents an alkyl chain.

[0042] Step 5: Under anhydrous and oxygen-free conditions at 78 °C, the fourth compound was mixed with Dowex (50WX8-100-200(H)) resin in a mixed solvent of tetrahydrofuran and methanol and refluxed for 12 h. After the reaction was completed, the mixture was filtered and concentrated to obtain the fifth compound.

[0043] Step 6: Under anhydrous and oxygen-free conditions at 140 °C, the fifth compound was reacted with squaric acid in a toluene / n-butanol mixed solvent in a Dean-Stark reaction apparatus for 12 h. After the reaction was completed, methanol was added to precipitate the solid, which was then filtered to obtain a solid. The solid was dissolved, separated by column chromatography, and then recrystallized in a solution of dichloromethane and methanol to obtain a dark purple or blue solid, which is a squaric acid cyanine dye molecule, denoted as SQD8, with the structural formula shown in formula (II): ; In the formula, n Indicates the number of carbon atoms in the flexible functional group R. n= 8.

[0044] Step 7: Mix 2.5 mg of squaric acid cyanine dye molecule SQD8 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 20 wt% SQD8 dye molecule-doped 5CB liquid crystal substrate mixture, wherein the structural formula of the SQD8 dye molecule is shown in formula (II). n=8; The structural formula of the 5CB molecule is shown in formula (V), and it exhibits a nematic phase at room temperature: .

[0045] Example 2: The only difference compared to Example 1 is: Step 7: Mix 1.11 mg of squaric acid cyanine dye molecule SQD8 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 10 wt% SQD8 dye molecule-doped 5CB liquid crystal substrate mixture. The structural formula of the SQD8 dye molecule is shown in formula (II). n =8; The structural formula of the 5CB molecule is shown in formula (V), and it exhibits a nematic phase at room temperature: .

[0046] Example 3: The only difference compared to Example 1 is: Step 7: Mix 4.29 mg of squaric acid cyanine dye molecule SQD8 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 30 wt% SQD8 dye molecule-doped 5CB liquid crystal substrate mixture. The structural formula of the SQD8 dye molecule is shown in formula (II). n =8; The structural formula of the 5CB molecule is shown in formula (V), and it exhibits a nematic phase at room temperature: .

[0047] Example 4: The only difference compared to Example 1 is: Step 7: Mix 6.67 mg of squaric acid cyanine dye molecules SQD8 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 40 wt% SQD8 dye molecule-doped 5CB liquid crystal substrate mixture. The structural formula of the SQD8 dye molecule is shown in formula (II). n =8; The structural formula of the 5CB molecule is shown in formula (V), and it exhibits a nematic phase at room temperature: .

[0048] Example 5: This embodiment provides a method for preparing a squaric acid cyanine dye-doped liquid crystal host material. (See [link to previous document]) Figure 14 This includes the following steps: Step 1: Under anhydrous and oxygen-free conditions at 95℃, m-aminophenol and methyl acrylate were combined and added to glacial acetic acid and sodium bromide for 12 h for catalysis. After the reaction was completed, sodium bicarbonate was added sequentially for neutralization, extraction and separation, and concentration. The product was separated by column chromatography to obtain the first compound (colorless oily liquid product).

[0049] Step 2: Under anhydrous and oxygen-free conditions at 0 °C, 3,4-dihydro-pyran (DHP) was gradually added dropwise to a dichloromethane solution of the first compound and pyridinium p-benzenesulfonate (PPTS) and reacted for 24 h. After extraction and separation by sodium bicarbonate solution, the mixture was concentrated and separated by column chromatography to obtain the second compound (colorless liquid product).

[0050] Step 3: Under anhydrous and oxygen-free conditions at 0 °C, the tetrahydrofuran solution of lithium aluminum hydride was added dropwise to the tetrahydrofuran solution of the second compound. After the addition was completed, the mixture was transferred to room temperature (25 °C) and reacted for 2 h. Then, the mixture was quenched with water, filtered to remove water, and concentrated. The crude product was subjected to rapid column chromatography to obtain the third compound (yellow oily product). Step 4: Under anhydrous and oxygen-free conditions at room temperature (25°C), the third compound and the 3,4,5-substituted benzoic acid derivative F were reacted in dichloromethane solvent with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine as catalysts for 12 h. After the reaction, the mixture was washed with water, dried, and concentrated to obtain the crude product. The crude product was then purified by a fourth column chromatography to obtain the fourth compound (white powder solid). The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R represents an alkyl chain.

[0051] Step 5: Under anhydrous and oxygen-free conditions at 78 °C, the fourth compound was mixed with Dowex (50WX8-100-200(H)) resin in a mixed solvent of tetrahydrofuran and methanol and refluxed for 12 h. After the reaction was completed, the mixture was filtered and concentrated to obtain the fifth compound.

[0052] Step 6: Under anhydrous and oxygen-free conditions at 140 °C, the fifth compound was reacted with squaric acid in a toluene / n-butanol mixed solvent in a Dean-Stark reaction apparatus for 12 h. After the reaction was completed, methanol was added to precipitate the solid, which was then filtered to obtain a solid. The solid was dissolved, separated by column chromatography, and then recrystallized in a solution of dichloromethane and methanol to obtain a dark purple or blue solid, which is a squaric acid cyanine dye molecule, denoted as SQD12, with the structural formula shown in formula (II): ; In the formula, n Indicates the number of carbon atoms in the flexible functional group R. n= 12.

[0053] Step 7: Mix 2.5 mg of squaric acid cyanine dye molecule SQD12 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 20 wt% SQD12 dye molecule-doped 5CB liquid crystal substrate mixture, wherein the structural formula of the SQD12 dye molecule is shown in formula (II). n =12; The structural formula of the 5CB molecule is shown in formula (V), and it exhibits a nematic phase at room temperature: .

[0054] Example 6: This embodiment provides a method for preparing a squaric acid cyanine dye-doped liquid crystal host material. (See [link to previous document]) Figure 14 This includes the following steps: Step 1: Under anhydrous and oxygen-free conditions at 95℃, m-aminophenol and methyl acrylate were combined and added to glacial acetic acid and sodium bromide for 12 h for catalysis. After the reaction was completed, sodium bicarbonate was added sequentially for neutralization, extraction and separation, and concentration. The product was separated by column chromatography to obtain the first compound (colorless oily liquid product).

[0055] Step 2: Under anhydrous and oxygen-free conditions at 0 °C, 3,4-dihydro-pyran (DHP) was gradually added dropwise to a dichloromethane solution of the first compound and pyridinium p-benzenesulfonate (PPTS) and reacted for 24 h. After extraction and separation by sodium bicarbonate solution, the mixture was concentrated and separated by column chromatography to obtain the second compound (colorless liquid product).

[0056] Step 3: Under anhydrous and oxygen-free conditions at 0 °C, the tetrahydrofuran solution of lithium aluminum hydride was added dropwise to the tetrahydrofuran solution of the second compound. After the addition was completed, the mixture was transferred to room temperature (25 °C) and reacted for 2 h. Then, the mixture was quenched with water, filtered to remove water, and concentrated. The crude product was subjected to rapid column chromatography to obtain the third compound (yellow oily product). Step 4: Under anhydrous and oxygen-free conditions at room temperature (25°C), the third compound and the 3,4,5-substituted benzoic acid derivative F were reacted in dichloromethane solvent with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine as catalysts for 12 h. After the reaction, the mixture was washed with water, dried, and concentrated to obtain the crude product. The crude product was then purified by a fourth column chromatography to obtain the fourth compound (white powder solid). The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R represents an oligoethylene glycol chain.

[0057] Step 5: Under anhydrous and oxygen-free conditions at 78 °C, the fourth compound was mixed with Dowex (50WX8-100-200(H)) resin in a mixed solvent of tetrahydrofuran and methanol and refluxed for 12 h. After the reaction was completed, the mixture was filtered and concentrated to obtain the fifth compound.

[0058] Step 6: Under anhydrous and oxygen-free conditions at 140 °C, the fifth compound was reacted with squaric acid in a toluene / n-butanol mixed solvent in a Dean-Stark reactor for 12 h. After the reaction was completed, methanol was added to precipitate the solid, which was then filtered to obtain a solid. The solid was dissolved, separated by column chromatography, and then recrystallized in a solution of dichloromethane and methanol to obtain a dark purple or blue solid, which is a squaric acid cyanine dye molecule, denoted as SQP8, with the structural formula shown in formula (IV): ; In the formula, n Indicates the number of carbon atoms in the flexible functional group R. n= 8.

[0059] Step 7: Mix 2.5 mg of squaric acid cyanine dye molecule SQP8 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 20 wt% SQP8 dye molecule-doped 5CB liquid crystal substrate mixture. The structural formula of the SQP8 dye molecule is shown in formula (IV). n =8; The structural formula of the 5CB molecule is shown in formula (V), and it exhibits a nematic phase at room temperature: .

[0060] Example 7: This embodiment provides a method for preparing a squaric acid cyanine dye-doped liquid crystal host material. (See [link to previous document]) Figure 14 This includes the following steps: Step 1: Under anhydrous and oxygen-free conditions at 95℃, m-aminophenol and methyl acrylate were combined and added to glacial acetic acid and sodium bromide for 12 h for catalysis. After the reaction was completed, sodium bicarbonate was added sequentially for neutralization, extraction and separation, and concentration. The product was separated by column chromatography to obtain the first compound (colorless oily liquid product).

[0061] Step 2: Under anhydrous and oxygen-free conditions at 0 °C, 3,4-dihydro-pyran (DHP) was gradually added dropwise to a dichloromethane solution of the first compound and pyridinium p-benzenesulfonate (PPTS) and reacted for 24 h. After extraction and separation by sodium bicarbonate solution, the mixture was concentrated and separated by column chromatography to obtain the second compound (colorless liquid product).

[0062] Step 3: Under anhydrous and oxygen-free conditions at 0 °C, the tetrahydrofuran solution of lithium aluminum hydride was added dropwise to the tetrahydrofuran solution of the second compound. After the addition was completed, the mixture was transferred to room temperature (25 °C) and reacted for 2 h. Then, the mixture was quenched with water, filtered to remove water, and concentrated. The crude product was subjected to rapid column chromatography to obtain the third compound (yellow oily product). Step 4: Under anhydrous and oxygen-free conditions at room temperature (25°C), the third compound and the 3,4,5-substituted benzoic acid derivative F were reacted in dichloromethane solvent with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine as catalysts for 12 h. After the reaction, the mixture was washed with water, dried, and concentrated to obtain the crude product. The crude product was then purified by a fourth column chromatography to obtain the fourth compound (white powder solid). The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R represents an oligoethylene glycol chain.

[0063] Step 5: Under anhydrous and oxygen-free conditions at 78 °C, the fourth compound was mixed with Dowex (50WX8-100-200(H)) resin in a mixed solvent of tetrahydrofuran and methanol and refluxed for 12 h. After the reaction was completed, the mixture was filtered and concentrated to obtain the fifth compound.

[0064] Step 6: Under anhydrous and oxygen-free conditions at 140 °C, the fifth compound was reacted with squaric acid in a toluene / n-butanol mixed solvent in a Dean-Stark reaction apparatus for 12 h. After the reaction was completed, methanol was added to precipitate the solid, which was then filtered to obtain a solid. The solid was dissolved, separated by column chromatography, and then recrystallized in a solution of dichloromethane and methanol to obtain a dark purple or blue solid, which is a squaric acid cyanine dye molecule, denoted as SQP12, with the structural formula shown in formula (IV): ; In the formula, n Indicates the number of carbon atoms in the flexible functional group R. n= 12.

[0065] Step 7: Mix 2.5 mg of squaric acid cyanine dye molecule SQP12 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 20 wt% SQP12 dye molecule-doped 5CB liquid crystal substrate mixture. The structural formula of the SQP12 dye molecule is shown in formula (IV). n =12; The structural formula of the 5CB molecule is shown in formula (V), and it exhibits a nematic phase at room temperature: .

[0066] Example 8: This embodiment provides a method for preparing a squaric acid cyanine dye-doped liquid crystal host material. (See [link to previous document]) Figure 14 This includes the following steps: Step 1: Under anhydrous and oxygen-free conditions at 95 °C, m-aminophenol and methyl acrylate were combined and added to glacial acetic acid and sodium bromide for 12 h for catalysis. After the reaction was completed, sodium bicarbonate was added sequentially for neutralization, extraction and separation, and concentration. The product was separated by column chromatography to obtain the first compound (colorless oily liquid product).

[0067] Step 2: Under anhydrous and oxygen-free conditions at 0 °C, 3,4-dihydro-pyran (DHP) was gradually added dropwise to a dichloromethane solution of the first compound and pyridinium p-benzenesulfonate (PPTS) and reacted for 24 h. After extraction and separation by sodium bicarbonate solution, the mixture was concentrated and separated by column chromatography to obtain the second compound (colorless liquid product).

[0068] Step 3: Under anhydrous and oxygen-free conditions at 0 °C, the tetrahydrofuran solution of lithium aluminum hydride was added dropwise to the tetrahydrofuran solution of the second compound. After the addition was completed, the mixture was transferred to room temperature (25 °C) and reacted for 2 h. Then, the mixture was quenched with water, filtered to remove water, and concentrated. The crude product was subjected to rapid column chromatography to obtain the third compound (yellow oily product). Step 4: Under anhydrous and oxygen-free conditions at room temperature (25°C), the third compound and the 3,4,5-substituted benzoic acid derivative F were reacted in dichloromethane solvent with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine as catalysts for 12 h. After the reaction, the mixture was washed with water, dried, and concentrated to obtain the crude product. The crude product was then purified by a fourth column chromatography to obtain the fourth compound (white powder solid). The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R represents an alkyl chain.

[0069] Step 5: Under anhydrous and oxygen-free conditions at 78 °C, the fourth compound was mixed with Dowex (50WX8-100-200(H)) resin in a mixed solvent of tetrahydrofuran and methanol and refluxed for 12 h. After the reaction was completed, the mixture was filtered and concentrated to obtain the fifth compound.

[0070] Step 6: Under anhydrous and oxygen-free conditions at 140 °C, the fifth compound was reacted with squaric acid in a toluene / n-butanol mixed solvent in a Dean-Stark reaction apparatus for 12 h. After the reaction was completed, methanol was added to precipitate the solid, which was then filtered to obtain a solid. The solid was dissolved, separated by column chromatography, and then recrystallized in a solution of dichloromethane and methanol to obtain a dark purple or blue solid, which is a squaric acid cyanine dye molecule, denoted as SQD8, with the structural formula shown in formula (II): ; In the formula, n Indicates the number of carbon atoms in the flexible functional group R. n= 8.

[0071] Step 7: Mix 2.5 mg of squaric acid cyanine dye molecules SQD8 with 10 mg of E7 liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 20 wt% SQD8 dye molecule-doped E7 liquid crystal substrate mixture. The structural formula of the SQD8 dye molecule is shown in formula (II). n=8; E7 molecules are mixed liquid crystals, exhibiting a nematic phase at room temperature. Their composition and chemical structural formula are shown in Table 1: Table 1. Composition and Chemical Structural Formula of E7 Molecule

[0072] Example 9: The only difference from Example 8 is that: Step 7: Mix 2.5 mg of squaric acid cyanine dye molecule SQD8 with 10 mg of 8CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 20 wt% SQD8 dye molecule-doped 8CB liquid crystal substrate mixture, wherein the structural formula of the SQD8 dye molecule is shown in formula (II). n =8;8CB has the structural formula shown in formula (VI), and exhibits a smectic phase at room temperature: .

[0073] Example 10: This embodiment provides a method for preparing a squaric acid cyanine dye-doped liquid crystal host material. (See [link to previous document]) Figure 14 This includes the following steps: Step 1: Under anhydrous and oxygen-free conditions at 95 °C, m-aminophenol and methyl acrylate were combined and added to glacial acetic acid and sodium bromide for 12 h for catalysis. After the reaction was completed, sodium bicarbonate was added sequentially for neutralization, extraction and separation, and concentration. The product was separated by column chromatography to obtain the first compound (colorless oily liquid product).

[0074] Step 2: Under anhydrous and oxygen-free conditions at 0 °C, 3,4-dihydro-pyran (DHP) was gradually added dropwise to a dichloromethane solution of the first compound and pyridinium p-benzenesulfonate (PPTS) and reacted for 24 h. After extraction and separation by sodium bicarbonate solution, the mixture was concentrated and separated by column chromatography to obtain the second compound (colorless liquid product).

[0075] Step 3: Under anhydrous and oxygen-free conditions at 0 °C, the tetrahydrofuran solution of lithium aluminum hydride was added dropwise to the tetrahydrofuran solution of the second compound. After the addition was completed, the mixture was transferred to room temperature (25 °C) and reacted for 2 h. Then, the mixture was quenched with water, filtered to remove water, and concentrated. The crude product was subjected to rapid column chromatography to obtain the third compound (yellow oily product). Step 4: Under anhydrous and oxygen-free conditions at room temperature (25°C), the third compound and the 3,4,5-substituted benzoic acid derivative F were reacted in dichloromethane solvent with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine as catalysts for 12 h. After the reaction, the mixture was washed with water, dried, and concentrated to obtain the crude product. The crude product was then purified by a fourth column chromatography to obtain the fourth compound (white powder solid). The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R is an alkyl chain with a triple bond.

[0076] Step 5: Under anhydrous and oxygen-free conditions at 78 °C, the fourth compound was mixed with Dowex (50WX8-100-200(H)) resin in a mixed solvent of tetrahydrofuran and methanol and refluxed for 12 h. After the reaction was completed, the mixture was filtered and concentrated to obtain the fifth compound.

[0077] Step 6: Under anhydrous and oxygen-free conditions at 140 °C, the fifth compound and squaric acid were reacted in a toluene / n-butanol mixed solvent in a Dean-Stark reaction apparatus for 12 h. After the reaction was completed, methanol was added to precipitate the solid, which was then filtered to obtain a solid. The solid was dissolved, separated by column chromatography, and then recrystallized in a solution of dichloromethane and methanol to obtain a dark purple or blue solid, which is a squaric acid cyanine dye molecule, denoted as SQT8, with the structural formula shown in formula (III): ; In the formula, n Indicates the number of carbon atoms in the flexible functional group R. n= 8.

[0078] Step 7: Mix 2.5 mg of squaric acid cyanine dye molecule SQT8 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 20 wt% SQT8 dye molecule-doped 5CB liquid crystal substrate mixture. The structural formula of the SQT8 dye molecule is shown in formula (III). n =8;5CB's structural formula is shown in equation (V):

[0079] Example 11: This embodiment provides a method for preparing a squaric acid cyanine dye-doped liquid crystal host material. (See [link to previous document]) Figure 14 This includes the following steps: Step 1: Under anhydrous and oxygen-free conditions at 90 °C, m-aminophenol and methyl acrylate were combined and added to glacial acetic acid and sodium bromide for 14 h for catalysis. After the reaction was completed, sodium bicarbonate was added sequentially for neutralization, extraction and separation, and concentration. The product was separated by column chromatography to obtain the first compound (colorless oily liquid product).

[0080] Step 2: Under anhydrous and oxygen-free conditions at -5 ℃, 3,4-dihydro-pyran (DHP) was gradually added dropwise to a dichloromethane solution of the first compound and pyridinium p-benzenesulfonate (PPTS) and reacted for 20 h. After extraction and separation by sodium bicarbonate solution, the mixture was concentrated and separated by column chromatography to obtain the second compound (colorless liquid product).

[0081] Step 3: Under anhydrous and oxygen-free conditions at 0 °C, the tetrahydrofuran solution of lithium aluminum hydride was added dropwise to the tetrahydrofuran solution of the second compound. After the addition was completed, the mixture was transferred to room temperature (20 °C) and reacted for 3 h. Then, the mixture was quenched with water, filtered to remove water, and concentrated. The crude product was subjected to rapid column chromatography to obtain the third compound (yellow oily product). Step 4: Under anhydrous and oxygen-free conditions at room temperature (20°C), the third compound and the 3,4,5-substituted benzoic acid derivative F were reacted in dichloromethane solvent with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine as catalysts for 14 h. After the reaction, the mixture was washed with water, dried, and concentrated to obtain the crude product. The crude product was then purified by a fourth column chromatography to obtain the fourth compound (white powder solid). The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R represents an alkyl chain.

[0082] Step 5: Under anhydrous and oxygen-free conditions at 75 °C, the fourth compound was mixed with Dowex (50WX8-100-200(H)) resin in a mixed solvent of tetrahydrofuran and methanol and refluxed for 14 h. After the reaction was completed, the mixture was filtered and concentrated to obtain the fifth compound.

[0083] Step 6: Under anhydrous and oxygen-free conditions at 135 °C, the fifth compound and squaric acid were reacted in a toluene / n-butanol mixed solvent in a Dean-Stark reaction apparatus for 14 h. After the reaction was completed, methanol was added to precipitate the solid, which was then filtered to obtain a solid. The solid was dissolved, separated by column chromatography, and then recrystallized in a solution of dichloromethane and methanol to obtain a dark purple or blue solid, which is a squaric acid cyanine dye molecule, denoted as SQD8, with the structural formula shown in formula (II): ; In the formula, n Indicates the number of carbon atoms in the flexible functional group R. n= 8.

[0084] Step 7: Mix 2.5 mg of squaric acid cyanine dye molecule SQD8 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 20 wt% SQD8 dye molecule-doped 5CB liquid crystal substrate mixture, wherein the structural formula of the SQD8 dye molecule is shown in formula (II). n =8; The structural formula of the 5CB molecule is shown in formula (V), and it exhibits a nematic phase at room temperature: .

[0085] Example 12: This embodiment provides a method for preparing a squaric acid cyanine dye-doped liquid crystal host material. (See [link to previous document]) Figure 14 This includes the following steps: Step 1: Under anhydrous and oxygen-free conditions at 100 °C, m-aminophenol and methyl acrylate were combined and added to glacial acetic acid and sodium bromide for 10 h for catalysis. After the reaction was completed, sodium bicarbonate was added sequentially for neutralization, extraction and separation, and concentration. The product was separated by column chromatography to obtain the first compound (colorless oily liquid product).

[0086] Step 2: Under anhydrous and oxygen-free conditions at 5 °C, 3,4-dihydro-pyran (DHP) was gradually added dropwise to a dichloromethane solution of the first compound and pyridinium p-benzenesulfonate (PPTS) and reacted for 28 h. After extraction and separation by sodium bicarbonate solution, the mixture was concentrated and separated by column chromatography to obtain the second compound (colorless liquid product).

[0087] Step 3: Under anhydrous and oxygen-free conditions at 0 °C, the tetrahydrofuran solution of lithium aluminum hydride was added dropwise to the tetrahydrofuran solution of the second compound. After the addition was completed, the mixture was transferred to room temperature (23 °C) and reacted for 1.5 h. Then, the mixture was quenched with water, filtered to remove water, and concentrated. The crude product was subjected to rapid column chromatography to obtain the third compound (yellow oily product). Step 4: Under anhydrous and oxygen-free conditions at room temperature (30°C), the third compound and the 3,4,5-substituted benzoic acid derivative F were reacted in dichloromethane solvent with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine as catalysts for 10 h. After the reaction, the mixture was washed with water, dried, and concentrated to obtain the crude product. The crude product was then purified by a fourth column chromatography to obtain the fourth compound (white powder solid). The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R represents an alkyl chain.

[0088] Step 5: Under anhydrous and oxygen-free conditions at 80 °C, the fourth compound was mixed with Dowex (50WX8-100-200(H)) resin in a mixed solvent of tetrahydrofuran and methanol and refluxed for 10 h. After the reaction was completed, the mixture was filtered and concentrated to obtain the fifth compound.

[0089] Step 6: Under anhydrous and oxygen-free conditions at 145 °C, the fifth compound was reacted with squaric acid in a toluene / n-butanol mixed solvent in a Dean-Stark reaction apparatus for 10 h. After the reaction was completed, methanol was added to precipitate the solid, which was then filtered to obtain a solid. The solid was dissolved, separated by column chromatography, and then recrystallized in a solution of dichloromethane and methanol to obtain a dark purple or blue solid, which is a squaric acid cyanine dye molecule, denoted as SQD8, with the structural formula shown in formula (II): ; In the formula, n Indicates the number of carbon atoms in the flexible functional group R. n= 8.

[0090] Step 7: Mix 2.5 mg of squaric acid cyanine dye molecule SQD8 with 10 mg of 5CB liquid crystal substrate, and place on an 80°C hot plate until the two components are uniformly mixed to obtain a 20 wt% SQD8 dye molecule-doped 5CB liquid crystal substrate mixture, wherein the structural formula of the SQD8 dye molecule is shown in formula (II). n =8; The structural formula of the 5CB molecule is shown in formula (V), and it exhibits a nematic phase at room temperature: .

[0091] Application Example 1: Quartz Sheet Substrate Thin Film Take a circular quartz plate with a diameter of 16 mm and a thickness of 0.4 mm, place it on a 50°C hot stage, and drop-coat the squartz cyanine dye-doped liquid crystal host mixture (20 wt% SQD8 dye-doped 5CB liquid crystal host mixture) prepared in Example 1 onto the quartz plate. Then take another quartz plate to cover the sample and press it firmly. The sample is evenly distributed on the quartz plate through capillary action, or the quartz plate is slightly cut with a wooden stick at 50°C to make the sample evenly distributed. Thus, a squartz cyanine dye-doped liquid crystal host mixture film with a quartz plate as the substrate is prepared.

[0092] Application Example 2: Polymer / Liquid Crystal Sandwich Composite Film The squaric acid cyanine dye-doped liquid crystal host mixture (20 wt% SQD8 dye-doped 5CB liquid crystal host mixture) prepared in Example 1 of the present invention was drop-coated between two layers of polyvinyl alcohol (PVA) substrate, and spin-coated / sheared at 50°C to make the sample uniformly distributed on the polymer substrate, thus obtaining a sandwich-type composite film based on polymer / liquid crystal material.

[0093] The sandwich-type composite film of the polymer / liquid crystal material includes a first polymer layer and a second polymer layer, with the squaricocyanine dye-doped liquid crystal host material distributed between the first polymer layer and the second polymer layer. The thickness of the first polymer layer is 90µm, the thickness of the second polymer layer is 90µm, and the thickness of the squaricocyanine dye-doped liquid crystal host material between the first polymer layer and the second polymer layer is 20µm.

[0094] Application Example 3: Polymer / Liquid Crystal Sandwich Composite Film The squaric acid cyanine dye-doped liquid crystal host mixture (20 wt% SQD8 dye-doped 5CB liquid crystal host mixture) prepared in Example 1 of the present invention was drop-coated between two layers of polyvinyl alcohol (PVA) substrate, and spin-coated / sheared at 50°C to make the sample uniformly distributed on the polymer substrate, thus obtaining a sandwich-type composite film based on polymer / liquid crystal material.

[0095] The sandwich-type composite film of the polymer / liquid crystal material includes a first polymer layer and a second polymer layer, with the squaricocyanine dye-doped liquid crystal host material distributed between the first and second polymer layers. The thickness of the first polymer layer is 50 µm. The thickness of the second polymer layer is 50 µm, and the thickness of the squaricocyanine dye-doped liquid crystal host material between the first and second polymer layers is 10 µm.

[0096] Application Example 4: Polymer-dispersed liquid crystal thin films doped with squaricine dye molecules First, an aqueous solution containing 7g of PVA solid particles was heated to 100℃ in an oil bath and maintained for 3 hours until the polyvinyl alcohol solid particles were completely dissolved in the water, yielding a PVA aqueous solution with a solid content of 7%. 2.5mg of SQD8 dye molecules and 10mg of 5CB liquid crystal matrix were weighed and completely dissolved in chloroform. Then, 5ml of the above PVA aqueous solution was added to the SQD8 / 5CB chloroform solution, and the mixture was stirred at 600r / min for 4 hours using a magnetic stirrer until the liquid crystal microdroplets were fully emulsified, resulting in a uniform blue emulsion. Next, the polyvinyl alcohol solution of the liquid crystal microdroplets dissolved in chloroform was placed in the air and allowed to evaporate completely, yielding a dye / liquid crystal dispersion with a polyvinyl alcohol aqueous solution as the matrix. A certain amount of the dispersion was evenly spread in a petri dish, and the petri dish was then placed in a fume hood to dry until a film was formed, yielding a polymer-dispersed liquid crystal film doped with squaricine dye molecules.

[0097] The thickness of the polymer-dispersed liquid crystal film doped with squaricine dye molecules is 50µm.

[0098] Test example: (1) Differential scanning calorimeter: Instrument: Differential scanning calorimeter (DSC250) from TA Company; Test sample: Samples of 1 mg or more are placed in a special aluminum crucible; Test method: The temperature range and heating / cooling rate are set by program.

[0099] (2) Polarizing microscope: Instrument: Olympus polarizing microscope (BX51) equipped with in-situ heating device; Test sample: Thin film sample placed in glass interlayer; Test method: The sample is placed between a polarizer and an analyzer that are perpendicular to each other.

[0100] (3) Ultraviolet-visible absorption spectrum: Instrument: Shimadzu UV-Vis spectrophotometer (UV-3600plus), test sample: thin film uniformly dispersed in quartz, test wavelength: 250~800nm.

[0101] (4) Fluorescence spectroscopy test: Instrument: Fluorescence spectrometer (FLS1000) of Edinburgh Company, UK; Test sample: Liquid crystal film sandwiched between quartz plates; Excitation wavelength: 280nm, 320nm; Test wavelength: 290~800nm, 330~800nm.

[0102] The multimodal stimulus-responsive materials provided in the embodiments of this specification have mechanochromic, photochromic, thermochromic, and solvent-annealed properties.

[0103] The mechanochromatic effect is as follows: at room temperature, by applying a weak shear force to the multimodal stimulus-responsive material, the color of the multimodal stimulus-responsive material changes from cyan to purple, such as... Figures 2-6 as well as Figure 10 As shown.

[0104] The photochromic effect is as follows: after irradiation with a 635nm red laser, the material's color changes from purple to cyan, such as... Figure 13 As shown in (b).

[0105] The thermochromic effect refers to the process where, after heating the material to a certain temperature, its color changes from purple to cyan, such as... Figures 2-6 as well as Figure 10 .

[0106] The solvent annealing process involves placing the material in an atmosphere of one or more organic solvents, such as dichloromethane, chloroform, toluene, acetonitrile, tetrahydrofuran, etc., causing the material's color to change from purple to cyan. Figure 13 As shown in (a).

[0107] Figure 1 The differential scanning spectroscopy (DSS) thermodynamic curves of the mixture obtained in Example 1, measured at heating and cooling rates of 10 K / min during a single cooling and a second heating cycle, are shown. The phase transition peaks represent the transition from molten liquid to liquid crystal. The material in Example 1 is an isotropic liquid at room temperature (25°C).

[0108] Figures 2-6 This is a schematic diagram illustrating the response of the corresponding embodiment of the squartz cyanine dye-doped liquid crystal host material on a quartz substrate. Under slight shear force: Figure 2 A 5CB liquid crystal host mixture doped with 20 wt% SQD8 dye molecules changed from cyan to purple within 50-55 seconds; Figure 3 A 5CB liquid crystal host mixture doped with 30 wt% SQD8 dye molecules changed from cyan to purple within 20-25 seconds; Figure 4 A 5CB liquid crystal host mixture doped with 20 wt% SQD12 dye molecules changed from cyan to purple within 10-15 seconds; Figure 5 A mixture of E7 liquid crystal substrates doped with 20 wt% SQD8 dye molecules changed from cyan to purple within 20-25 seconds; Figure 6 A mixture of 20 wt% SQD8 dye molecules doped with 8CB liquid crystal substrates changes from cyan to purple within 30–35 seconds. Purple samples subjected to force stimulation revert to cyan within 3 seconds when placed at 40°C. This material requires less input, responds faster, and exhibits significantly higher contrast than traditional crystalline mechanochromic materials.

[0109] Figure 7 The material obtained in Example 1 is shown in (a) before shearing and (b) after shearing under a polarizing microscope, with the inset showing the optical texture after inserting a full-wave plate. Before shearing, the sample was isotropic and showed no birefringence under crossed polarized light. After shearing, a significant birefringent texture was observed under crossed polarized light, exhibiting a broken fan-shaped structure with prominent liquid crystal schlieren texture. Under full-wave plate insertion, needle-like or fibrous elongated crystals were observed, indicating that the texture is a mixture of crystalline and nematic phases.

[0110] Figure 8 The images show the UV-Vis absorption curves of the squartz substrate and the doped liquid crystal host material with squartz cyanine dye molecules before and after shearing, according to embodiments of the present invention. In Examples 1 and 5, the absorption peak of the squartz cyanine dye molecules before shearing is broadened at 654 nm, indicating that the squartz cyanine molecules formed irregular aggregates at this concentration, i.e., the chromophores did not form regular aggregates. In Examples 8 and 9, the absorption peak of the squartz cyanine dye molecules before shearing is sharp at 654 nm, indicating that the squartz cyanine molecules are dispersed in the liquid crystal host as single molecules. After shearing, the absorption spectra of all embodiments show a significant H-aggregate absorption signal at 530 nm. The large contrast color change of the material is attributed to an absorption color shift of approximately 120 nm before and after shearing.

[0111] Figure 9 These are the fluorescence emission curves of the material obtained in Example 1 before and after shearing (excited at 280 nm and 320 nm, respectively). Before shearing, the 5CB emission peak in the liquid crystal film is located at 336 nm, which can be attributed to the emission of the 5CB monomer; while after shearing, its emission redshifts to 380 nm, which can be attributed to the emission of the 5CB nematic excimer. This indicates that after shearing, the isotropic 5CB liquid transforms into a nematic phase structure.

[0112] Figure 10 This is a schematic diagram illustrating the response of the sandwich-type composite film obtained in Example 2 under force stimulation and heating. The film sample rapidly changes color under a small shear force at room temperature and recovers its color after being held at 35°C for 5 seconds.

[0113] Figure 11These are morphological images of the polymer-dispersed liquid crystal film doped with squaricine dye molecules obtained in Example 3 under a conventional optical microscope. (a) shows the film in its unstretched state; (b) shows it after uniaxial stretching. Before stretching, the dispersed droplets in the film appear as uniformly distributed cyan spheres. After uniaxial stretching, the droplet shape changes to ellipsoids, and the droplets appear purple due to the aggregation of H atoms from the dye molecules.

[0114] Figure 12 These are force-induced color-changing photographs of the polymer-dispersed liquid crystal film doped with squaricine dye molecules obtained in Application Example 3 at different stretching ratios. The film sample obtained in Application Example 3 was cut into strips of 2 cm × 1.5 cm and fixed on a stretching device. Three strips were taken and stretched uniaxially along the horizontal direction to elongation of 200%, 300%, and 400%, respectively. The macroscopic color of the polymer-dispersed liquid crystal film changed from cyan to purple.

[0115] Figure 13 This is a schematic diagram of the response of the material obtained in Application Example 1 under a dichloromethane solvent atmosphere; after being subjected to a force stimulus, the material obtained in Application Example 1 was placed in a dichloromethane solvent atmosphere for 5 seconds and quickly returned to its cyan color. Furthermore, using 0.8 W / cm²... 2 When a purple sample is irradiated with a 635nm red laser for 6-7 minutes, the sample turns cyan. This material exhibits excellent solvochromatic and photochromic properties, and its optical properties can be modulated under multi-field coupling.

[0116] The squaricine dye-doped liquid crystal host material proposed in this invention has extremely fast response characteristics and extremely high contrast.

[0117] It exhibits sensitive mechanical response characteristics: this material is a stable isotropic fluid at room temperature, and its color can be rapidly changed through slight shearing. This color change originates from the blue shift in the absorption spectrum caused by the aggregation of H atoms between squaric acid cyanine dye molecules in the squaric acid cyanine dye host material, with a spectral color shift exceeding 100 nm. The squaric acid cyanine dye-doped squaric acid cyanine dye host material proposed in this invention solves the problems of small color difference, slow response speed, and high energy consumption in traditional mechanochromic materials.

[0118] Exhibiting significant photochromic properties: This scacyanine dye-doped liquid crystal host material overcomes the limitations of traditional mechanochromic materials that rely on a single mechanical stimulus, achieving dynamic control of the material's optical properties through the synergistic effect of multiple stimuli. Based on the unique dynamic responsiveness of liquid crystals, the scacyanine dye-doped liquid crystal host material proposed in this invention can quickly return to its initial isotropic state through low-temperature heating and solvent annealing, exhibiting good cycle stability and demonstrating excellent reversible stimulus-responsive mechanochromic properties. Simultaneously, the H-aggregates formed by scacyanine dye molecules in the scacyanine dye-doped liquid crystal host material system of this invention have high photothermal conversion efficiency, endowing the material with a significant photochromic effect. This multimode responsive material can adapt to functional requirements under complex environmental changes, and the synergistic effect of multiple stimulus responses broadens the material's application potential.

[0119] Exhibiting Outstanding System Compatibility: The scacyanine dye-doped liquid crystal host material proposed in this invention exhibits excellent system compatibility. This scacyanine dye-doped liquid crystal host material exists in a liquid crystal fluid state at room temperature, thus limiting its application to planar structures and allowing it to adapt to various complex surface morphologies, including but not limited to curved and irregular surfaces. It is also suitable for diverse force application methods, including shearing, extrusion, and stretching. Furthermore, this scacyanine dye-doped liquid crystal host material can be combined with various polymer matrices to construct functional materials such as sandwich-type composite films and PDLC films, while maintaining stable mechanochromic properties.

[0120] The squaricine dye-doped liquid crystal host material proposed in this invention exhibits significant scalability and versatility in material system design, providing an important reference for the development of next-generation smart responsive materials. The mechanochromic material provided by this invention is constructed by doping a functional dye with molecular aggregation-induced color-changing properties into a liquid crystal host. This method is applicable to various dyes and liquid crystal systems. By simply adjusting the structural parameters of the dye molecules, such as changing the alkyl chain length or replacing the chromophore core, its color rendering range can be adjusted. This allows for flexible control of the material's optical properties according to actual application requirements, overcoming the limitations of traditional mechanochromic material systems and providing a technical foundation for the development of a series of smart responsive materials. It has broad application prospects in fields such as smart sensing, flexible displays, and anti-counterfeiting packaging.

[0121] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or basic characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects.

[0122] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention fall within the scope of protection of this invention.

Claims

1. A squaricine dye-doped liquid crystal host material, characterized in that, It is formed by mixing squaricine dye molecules with a liquid crystal substrate, wherein the squaricine dye molecules have the structural formula shown in formula (I): ， Wherein, R is a flexible functional group, selected from alkyl chains, alkyl chains with double / triple bonds, oligoethylene glycol chains, or siloxane chains; The liquid crystal substrate is a nematic or smectic phase at room temperature.

2. The squaric acid cyanine dye-doped liquid crystal host material according to claim 1, characterized in that, The liquid crystal host is one or a combination of 4-cyano-4'-butylbiphenyl, 4-cyano-4'-pentylbiphenyl, and 4-cyano-4'-hexylbiphenyl.

3. The squaric acid cyanine dye-doped liquid crystal host material according to claim 1, characterized in that, The content of the squaric acid cyanine dye molecules is 10-40 wt% by mass percentage, and the content of the liquid crystal substrate is 60-90 wt%.

4. A method for preparing a liquid crystal host material doped with squaricine dye molecules, characterized in that, The squaric acid cyanine dye-doped liquid crystal host material according to any one of claims 1-3 includes the following steps: After a catalytic reaction, m-aminophenol and methyl acrylate were subjected to neutralization, first extraction, first concentration, and first column chromatography purification to obtain the first compound. The first compound was subjected to an acetal-protected reaction with 3,4-dihydro-pyran in dichloromethane solvent, followed by a second extraction, a second concentration, and a second column chromatography purification to obtain the second compound. A tetrahydrofuran solution of lithium aluminum hydride was added dropwise to a tetrahydrofuran solution of the second compound and reacted at room temperature. The mixture was then purified by water quenching, first filtration, first concentration, and third column chromatography to obtain the third compound. The third compound was subjected to an amidation condensation reaction with the 3,4,5-substituted benzoic acid derivative F in dichloromethane solvent. Following washing with water, drying, second concentration, and fourth column chromatography purification, the fourth compound was obtained. The structural formula of the 3,4,5-substituted benzoic acid derivative F is as follows: R is a flexible functional group, selected from alkyl chains, alkyl chains with double / triple bonds, oligoethylene glycol chains, or siloxane chains; The fourth compound was refluxed with an acidic ion exchange resin in a tetrahydrofuran / methanol mixed solvent, and then successively filtered and concentrated to obtain the fifth compound. After the fifth compound was condensed with squaric acid in a toluene / n-butanol mixed solvent, the mixture was successively subjected to precipitation, third filtration, column chromatography separation and recrystallization to obtain squaric acid cyanine dye molecules. Squaricine dye molecules are mixed with liquid crystal substrates to obtain squaricine dye-doped liquid crystal substrate materials.

5. The method for preparing a squaricine dye-doped liquid crystal host material according to claim 4, characterized in that, The catalytic reaction is carried out at a temperature of 90-100 °C for 10-14 h, and the catalysts are glacial acetic acid and sodium bromide. The temperature of the acetal protection reaction is -5~5℃, the reaction time is 20~28 h, and the catalyst for the acetal protection reaction is pyridinium salt of p-benzenesulfonate. The room temperature reaction is at a temperature of 20~25℃, and the room temperature reaction time is 1.5~3h; The amidation condensation reaction is carried out at a temperature of 20-30°C for 10-14 h, and the catalysts for the amidation condensation reaction are 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine. The reflux temperature is 75~80℃, and the reflux time is 10~14 h; The condensation reaction is carried out at a temperature of 135~145℃ for 10~14 h. The recrystallization was performed using dichloromethane and methanol; The mass ratio of the squaric acid cyanine dye molecules to the liquid crystal substrate is (1.11-6.67):

10.

6. The application of the squaric acid cyanine dye-doped liquid crystal host material according to any one of claims 1-3 in the field of smart response materials.

7. A polymer / liquid crystal sandwich type composite film, characterized in that, The squaricocyanine dye-doped liquid crystal host material according to any one of claims 1-3 is constructed, comprising a first polymer layer and a second polymer layer, wherein the squaricocyanine dye-doped liquid crystal host material is distributed between the first polymer layer and the second polymer layer.

8. The polymer / liquid crystal sandwich composite film according to claim 7, characterized in that, The first polymer layer and the second polymer layer are each independently selected from polyvinyl alcohol or polydimethylsiloxane; The thickness of the first polymer layer is 50-100µm; The thickness of the second polymer layer is 50-100µm; The thickness of the squaricine dye-doped liquid crystal host material between the first polymer layer and the second polymer layer is 10-30µm.

9. A polymer-dispersed liquid crystal film, characterized in that, The squaric acid cyanine dye-doped liquid crystal host material according to any one of claims 1-3 includes the following steps: The squaric acid cyanine dye-doped liquid crystal host material is mixed with an organic solvent to form a homogeneous solution. The homogeneous solution is then cast into a film and volatilized to obtain a polymer-dispersed liquid crystal film.

10. A polymer-dispersed liquid crystal film according to claim 9, characterized in that, The organic solvent includes one or a combination of chloroform and dichloromethane; The thickness of the polymer-dispersed liquid crystal film is 30-100µm.

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