Preparation method of pure solid-state novel aromatic heterocyclic spiropyran-based intelligent color-changing materials

Abstract

The present invention provides a method for preparing a pure solid-state novel aromatic heterocyclic spiropyran-based intelligent color-changing material. By constructing a D-A conjugated system and increasing the molecular free volume in a synergistic strategy, a spiropyran-based photochromic material with significantly improved light-changing ability in the solid state and an adjustable color change range is developed. The method for preparing the pure solid-state novel aromatic heterocyclic spiropyran-based intelligent color-changing material described in the present invention can significantly improve the photochromic performance, improve the reversibility of the photochromic material, form a novel spiropyran-based intelligent color-changing film with an adjustable color change range, and increase the color change rate of the spiropyran-based material, thereby ensuring better color change ability of the color-changing material in the pure solid state and achieving a larger color change range of the color-changing material in the pure solid state, thereby effectively broadening its application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent color-changing photoelectric materials, and in particular to a method for preparing a pure solid-state novel aromatic heterocyclic spiropyran intelligent color-changing material. Background Art

[0002] As an emerging type of intelligent color-changing materials, photochromic materials play an important role in many fields such as optical information storage, targeted drugs and military camouflage. Photochromic materials do not require additional energy. Only by changing the intensity of external light can the molecules open and close their rings, causing their color to change, thus achieving intelligent color change. Therefore, photochromic materials are a type of intelligent color-changing materials with strong practicality. Figure 1 It is a partial application of photochromic materials and has broad application prospects. Photochromic materials can be divided into inorganic and organic materials. Compared with inorganic materials, organic photochromic materials can precisely control the physical and chemical properties of the materials through chemical modification, thereby achieving the improvement of light-changing performance and the regulation of the spectral range. Therefore, the current research focus is mainly on the field of organic photochromic materials. Spiropyrans is one of the most widely studied materials in photochromic materials. Its photochromic process is as follows: Figure 2 Spiropyran has excellent photochromic properties, but some challenges remain. Its photochromic rate and solid-state photochromic performance still need to be improved. Its single color after photochromic change makes it difficult to meet the practical needs of various intelligent color-changing applications. Therefore, by constructing new molecular frameworks and regulating the material's photochromic properties at the molecular level, its photochromic performance can be truly improved, achieving the needs of instant, rapid, and intelligent color change, and promoting the development of the intelligent color-changing field.

[0003] (1) Foreign technology

[0004] Spiropyran compounds have long been a research hotspot in the field of photochromism abroad. Sara Santiago et al. prepared a multi-responsive spiropyran ion gel, demonstrating that spiropyran ion gels can be used to develop smart materials for multi-stimulus-responsive molecular switches. Dipak Samanta et al. used 1,3,5-triimidazolebenzene to prepare a water-soluble flexible coordination cage into which spiropyran can be loaded. This solves the water solubility issue of spiropyran without introducing hydrophilic functional groups, while maintaining excellent photochromic properties in water. Shubham Garg et al. constructed a smart-responsive optoelectronic device. They embedded a nitro-substituted spiropyran into a conductive metal-organic framework (MOF). When the material was exposed to 365nm ultraviolet light, the non-polar SP form converted to the zwitterionic MC form. This reaction increased the conductivity of the MOF material tenfold, enabling intelligent control of the conductivity of the optoelectronic material. Harikrishnan et al. copolymerized a spiropyran-grafted methacrylate with another polyethylene glycol-modified methacrylate to form a photoresist. Under ultraviolet light, this photoresist undergoes a cross-linking reaction with maleimide, enabling 3D etching at the nanoscale. Samuel Stupp et al. synthesized a water-soluble sulfonic acid-substituted spiropyran and added it to a polymer to prepare a photoresponsive hydrogel. They further studied the effect of light stimulation on the volume expansion of the spiropyran hydrogel. Iftime Gabriel et al. invented a photochromic printing paper (see patent US20060251988 for details), which can preserve information longer than traditional erasable printing paper. They first chelated the spiropyran molecules with cations to impart their photochromic properties in the solid state. The chelated spiropyran molecules were then embedded in the polymer, further enhancing the stability of the ring-opened isomers. Chester Lee Drum has invented a photoresponsive, reversibly isomerizable protein-binding matrix (JP2021006594). This spiropyran binds to peptides in one isomer and releases them upon excitation at another wavelength, resulting in isomerization. This allows for light-controlled peptide binding and release. This matrix can be used for the separation and purification of target peptides. Using light as an eluent is simple, efficient, and widely applicable, it allows for the elution of target molecules without altering the chemical properties of the solvent.

[0005] (2) Domestic technology

[0006] Spiropyran-based photochromic materials have been extensively studied in China. Professor Wang Chaoxia and others from Jiangnan University used spiropyran compounds as the core material and chitosan as the shell to prepare photochromic chitosan microcapsules. These microcapsules were attached to wool fabric, resulting in significant photochromic responsiveness and dye fastness. Spiropyran compounds can also be used as drug carriers to synthesize targeted drugs. Chen Shuo and others synthesized a near-infrared light- and pH-responsive nanocomposite material that can be assembled with upconversion nanoparticles (UCNPs) using amphiphilic polymers functionalized with spiropyran. Under near-infrared light irradiation, the upconversion nanoparticles emit ultraviolet light that induces the core spiropyran to transform from a closed-ring (SP) state to an open-ring (MC) state. This configurational change causes the outer polymer layer to be destroyed, thereby releasing the drug inside. To construct a new near-infrared microlaser, Yin Meizhen and others used spiropyran and tetraphenylethylene (TPE) to synthesize a TPE-SP microsphere cap using a solvent evaporation method. The distorted geometry of tetraphenylethylene provides spiropyran with sufficient free volume for photoisomerization. Consequently, upon UV irradiation, a conversion from SP to MC occurs. This allows a novel near-infrared laser emitter developed based on this structure to exhibit excellent near-infrared laser emission. Li Gongke et al. have developed a bispiropyran cyanide fluorescent probe (see patent CN110357906A for details). This probe exhibits excellent selectivity for cyanide ions. Upon binding to cyanide ions, isomerization occurs, causing strong optical and fluorescent changes in the probe. Simultaneously, cyanide ions combine with the C cations on the isomerized spiropyran to form a strong electron-withdrawing group, the cyanide group, which influences the electron cloud distribution on the probe and promotes its optical and fluorescent changes. This probe is used to detect residual hydrocyanic acid produced by raw material hydrolysis in liquor. Compared to traditional cyanide ion detection methods such as spectrophotometry, chromatography, and electrochemistry, it offers the advantages of simple sample pretreatment and rapid detection without the need for large instrumentation. Han Hui et al. invented a spiropyran derivative probe that can be used to detect chromium III ions through color change (see patent CN109369662A for details). This probe consists of spiropyran and a benzimidazole group connected by an amino group, wherein the benzimidazole group is a recognition group for chromium III ions and can coordinate with chromium III ions, while the spiropyran acts as a fluorescent emission group. After the benzimidazole coordinates with the chromium III ion, it induces the breakage of the CO bond in the spiropyran, and the isomerization ring-opening emits fluorescence to realize the probe's recognition and detection function for chromium III ions.Guo Yuan et al. invented a spiropyran derivative probe for detecting G-quadruplex DNA (see patent CN108047241A for details). Using confocal microscopy and ultra-high-resolution microscopy, this probe successfully achieved simultaneous detection of G4 DNA and lysosomes in living cells. In particular, it achieved in situ, real-time, and ultra-clear imaging of the cancer target molecule G4 DNA in living cells. This is crucial for early cancer screening. Targeting lysosomes with drugs is also an effective way to selectively destroy cancer cells. Successful detection of lysosomes also has positive implications for understanding the mechanisms of cellular metabolism, membrane circulation, apoptosis, and other vital activities. Spiropyran molecules can respond to ultraviolet light irradiation by undergoing isomerization and producing fluorescence changes. The fluorescence emission spectrum of NBD benzoxadiazole derivatives effectively overlaps with the UV-visible absorption spectrum of MC after spiropyran isomerization, demonstrating a FRET effect with MC. Liao Liqiong et al. have developed a method (CN 109294561A) for preparing light-controlled dual-color fluorescent nanoparticles (NBD-SP) under mild conditions, simple preparation, and straightforward post-processing. The method begins by preparing 4-amino-7-nitro-2,1,3-benzoxadiazole and spiropyran-modified cyclodextrin. The light-controlled dual-color fluorescent nanoparticles are then synthesized using 4-amino-7-nitro-2,1,3-benzoxadiazole and spiropyran-modified cyclodextrin. The nanoparticles prepared using this method have an average functionality of 2.985 and a fluorescence intensity of 990 a.u. They exhibit excellent responsiveness, reversibility, and stability. Furthermore, the mild reaction conditions, easy control, and simple post-processing make them highly practical.

[0007] While extensive research has been conducted on spiropyran-based photochromic materials, several pressing challenges remain. The photochromic rate, reversibility of the photochromic effect in the pure solid state, and photostability of spiropyran materials still require improvement. Their color after photochromic change is also relatively monotonous, making it difficult to meet the growing demand for intelligent color-changing camouflage. Both domestically and internationally, most research on spiropyrans focuses on developing photochromic properties through functional group modification or material composites, while maintaining the molecular backbone. However, efforts to enhance the photochromic properties of spiropyran-based materials by exploiting the intrinsic properties of the molecular backbone are rare. Consequently, the photochromic properties of these materials, such as the photochromic rate, reversibility, and color range of the ring-opened structure after photochromic change, have not been significantly improved or altered. Therefore, research on improving the photochromic rate, reversibility, and stability of photochromic materials in the pure solid state is of great significance.

[0008] Patent CN105670389B mentions a reversible solid-state photochromic fluorescent ink material and its application. The reversible solid-state photochromic fluorescent ink material uses aromatic or heteroaromatic substituents (Ar) and spiropyran as structural units, and a new type of fluorescent dye is synthesized through esterification reaction. The specific synthesis steps are: 1-carboxyethylindoline spiropyran molecule (2mmol, 0.76g) is dissolved in 5mL of anhydrous dichloromethane, and 4-dimethylaminopyridine (3mg) and 9,10-bis[4-hydroxyphenylvinyl]anthracene (1mmol, 0.414g) are added. The temperature was lowered to 0°C, and dicyclohexylcarbodiimide (3 mmol, 0.618 g) was slowly added dropwise to the reaction system. The mixture was kept at 0°C and stirred for 5 min, then returned to room temperature and stirred for 10 h. Post-treatment: The insoluble precipitate in the reaction mixture was first removed by filtration, and the filtrate was washed twice with 0.5 M hydrochloric acid and saturated sodium bicarbonate solution, respectively. The dichloromethane organic phase was separated and then dried over anhydrous magnesium sulfate. The anhydrous magnesium sulfate was removed by filtration, and the filtrate was evaporated to remove the solvent under reduced pressure. The product was separated and purified by silica gel chromatography (petroleum ether / ethyl acetate, 4:1 v / v). The final product DSA-2SP was a yellow powder (0.34 g, 30%), which was a photochromic dye. It can improve the stability and reversibility of the light-changing properties of the photochromic material to a certain extent, but its color change range is still relatively single. Summary of the Invention

[0009] In view of this, the present invention aims to propose a method for preparing a pure solid-state novel aromatic heterocyclic spiropyran-based intelligent color-changing material to solve the key problems currently existing in the prior art, such as the difficulty in improving the color-changing rate of spiropyran-based materials, poor color-changing ability in pure solid state, and a single color-changing range; thereby significantly improving the photochromic performance, making the reversibility of the photochromic material better, and forming a new spiropyran-based intelligent color-changing film with an adjustable color-changing range, and also improving the color-changing rate of the spiropyran-based material, ensuring better color-changing ability of the color-changing material in pure solid state, and realizing that the color-changing material in pure solid state can still have a larger color-changing range.

[0010] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0011] The present invention relates to a method for preparing a pure solid-state novel aromatic heterocyclic spiropyran intelligent color-changing material, comprising the following steps:

[0012] Step 1: constructing a basic skeleton and synthesizing aromatic heterocycles and the basic skeleton to form an initial photochromic material;

[0013] Step 2: characterizing the initial photochromic material to determine the structure of the initial photochromic material;

[0014] Step 3: By testing the color-changing properties of the initial photochromic material, determine whether the synthesized photochromic material meets the requirements. If yes, the development is successful.

[0015] Furthermore, the basic skeleton in step one is a spiropyran molecular skeleton, and the initial photochromic material is an aromatic heterocyclic spiropyran photochromic material.

[0016] Furthermore, step one includes:

[0017] Step S11: constructing a spiropyran molecular skeleton through an organic reaction;

[0018] Step S12: synthesizing the target aromatic heterocyclic group with the spiropyran molecular skeleton through Suzuki coupling to form an aromatic heterocyclic spiropyran photochromic material.

[0019] Furthermore, the target aromatic heterocyclic group includes any one of phenyl-B, thienyl-T, pyridyl-Py, 3-pyridyl-3-Py and pyrimidinyl-Md.

[0020] Further, step S11 includes:

[0021] Step S111: preparing iodine salt compound b by methylation reaction of compound a;

[0022] Step S112: the iodine salt compound b is subjected to an organic reaction with 5-bromosalicylic acid to construct a spiropyran molecular skeleton.

[0023] Further, step S12 includes:

[0024] Step S121: selecting any one of phenyl-B, thienyl-T, pyridyl-Py, 3-pyridyl-3-Py and pyrimidinyl-Md as the target aromatic heterocyclic group;

[0025] Step S122: The target aromatic heterocyclic group is coupled with the spiropyran molecular skeleton through Suzuki coupling to construct a shape, thereby obtaining an initial photochromic material.

[0026] Furthermore, step 2 includes:

[0027] Step S21: characterizing the molecular structure of the aromatic heterocyclic spiropyran photochromic material;

[0028] Step S22: characterizing the physical and chemical properties of the aromatic heterocyclic spiropyran photochromic material.

[0029] Furthermore, in step three, the method of testing the color change performance of the initial photochromic material includes any one or more testing methods of testing the color change characteristics of the photochromic material in 365nm light source irradiation, solution state, pure solid state and blended film state.

[0030] Furthermore, the color-changing property refers to any one or more properties of the color-changing rate, reversibility, and recovery rate of the photochromic material.

[0031] Furthermore, in step S22, the physical and chemical property characterization includes any one or more of UV-visible absorption spectroscopy test, thermogravimetric analysis test, electrochemical test, SEM morphology characterization test and density functional theory (DFT) calculation molecular test.

[0032] Compared with the prior art, the method for preparing a pure solid-state novel aromatic heterocyclic spiropyran intelligent color-changing material described in the present invention has the following beneficial effects:

[0033] This development method can significantly improve the photochromic performance, make the reversibility of photochromic materials better, and form a new type of spiropyran-based smart color-changing film with an adjustable color change range. It can also increase the color change rate of spiropyran-based materials, ensure better color change ability of color-changing materials in pure solid state, and achieve a larger color change range of color-changing materials in pure solid state; in addition, by introducing a molecular setting strategy of aromatic heterocycles into the spiropyran molecular skeleton, a series of new smart color-changing materials that can undergo significant photochromic processes in pure solid state are developed. The introduction of conjugated aromatic heterocycles not only significantly improves the photochromic ability and reversibility of this type of material in solid state, but also the expansion of the conjugated system significantly broadens the color change range of this type of color-changing material, making it have broad application prospects in multiple optoelectronic fields such as photoelectric storage, smart sensing, smart color-changing coatings, targeted drugs, and anti-counterfeiting identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 Schematic diagram of the application of photochromic materials;

[0036] Figure 2 Schematic diagram of the photochromic process of spiropyran;

[0037] Figure 3 Schematic diagram of the setup strategy for aromatic heterocyclic spiropyran derivatives;

[0038] Figure 4 This is a schematic diagram of the preparation process of spiropyran photochromic materials;

[0039] Figure 5 This is a schematic diagram of the structural formula of the prepared aromatic heterocyclic spiropyran photochromic materials;

[0040] Figure 6Schematic diagram of the UV-visible absorption spectrum (dilute dichloromethane solution) of heteroaromatic spiropyran photochromic materials;

[0041] Figure 7a-7f Schematic diagram of the UV-visible absorption spectra of the aromatic heterocyclic spiropyran photochromic materials MCH-Br, MCH-B, MCH-T, MCH-Py, MCH-3-Py, and MCH-Md under acidic conditions (dilute dichloromethane solution with gradual addition of trifluoroacetic acid);

[0042] Figure 8a-8e Schematic diagram of the molecular conformation and HOMO / LUMO energy level distribution of the aromatic heterocyclic spiropyran photochromic materials SP-B, SP-T, SP-Py, SP-3-Py, and SP-Md before ring opening (SP state);

[0043] Figure 9a-9e Schematic diagram of the molecular conformation and HOMO / LUMO energy level distribution of the aromatic heterocyclic spiropyran photochromic materials MC-B, MC-T, MC-Py, MC-3-Py, and MC-Md after ring opening (MC state);

[0044] Figure 10a-Figure 10e Schematic diagram of thermogravimetric analysis of aromatic heterocyclic spiropyran photochromic materials SP-B, SP-T, SP-Py, SP-3-Py and SP-Md;

[0045] Figure 11 For compound b 1 Schematic diagram of H NMR spectrum;

[0046] Figure 12 For SP-Br 1 Schematic diagram of H NMR spectrum;

[0047] Figure 13 For SP-B 1 Schematic diagram of H NMR spectrum;

[0048] Figure 14 For SP-T 1 Schematic diagram of H NMR spectrum;

[0049] Figure 15 For SP-Py 1 Schematic diagram of H NMR spectrum;

[0050] Figure 16 For SP-3-Py 1 Schematic diagram of H NMR spectrum;

[0051] Figure 17 For SP-Md 1 Schematic diagram of H NMR spectrum;

[0052] Figure 18 Schematic diagram of the comparison of the aromatic heterocyclic spiropyran material before and after irradiation (365nm) in solution;

[0053] Figure 19 Schematic diagram of the comparison of the aromatic heterocyclic spiropyran material before and after illumination (365nm) in pure solid state;

[0054] Figure 20a-20f Schematic diagram of scanning electron microscopy (SEM) of SP-Br, SP-B, SP-T, SP-Py, SP-3-Py and SP-Md in pure solid state (powder state);

[0055] Figure 21a-Figure 21h Schematic diagram of the color changes of SP-B, SP-T, SP-Py, SP-3-Py and Py-Md in pure solid state (thin film state) before and after irradiation with 365nm ultraviolet light for different lengths of time. DETAILED DESCRIPTION

[0056] The inventive concepts of the present disclosure will be described below using terms commonly used by those skilled in the art to convey the essence of their work to other persons skilled in the art. However, these inventive concepts can be embodied in many different forms and should not be considered limited to the embodiments described herein.

[0057] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0058] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0059] In the existing technology, the photochromic rate, reversibility of photosensitivity in pure solid state, and photostability of spiropyran materials still need to be improved; their colors after light change are also relatively single, which makes it difficult to meet further demands in the field of intelligent color-changing camouflage.

[0060] In order to solve the key problems of the existing spiropyran materials in the prior art, such as the difficulty in improving the color change rate, poor color change ability in pure solid state, and a single color change range, this embodiment proposes a method for preparing a pure solid-state novel aromatic heterocyclic spiropyran-based intelligent color-changing material, comprising the following steps:

[0061] Step 1: constructing a basic skeleton and synthesizing aromatic heterocycles and the basic skeleton to form an initial photochromic material;

[0062] Step 2: characterizing the initial photochromic material to determine the structure of the initial photochromic material;

[0063] Step 3: Determine whether the synthesized photochromic material meets the requirements by testing the color-changing properties of the initial photochromic material. If yes, the synthesized photochromic material is successfully developed. If not, further adjust the composition of the constructed photochromic material or the type of target aromatic heterocyclic group by characterizing the structure and physicochemical properties of the initial photochromic material in Step 2, and then adjust the overall structure of the photochromic material to meet the requirements;

[0064] In this embodiment, the basic skeleton in step 1 is a spiropyran molecular skeleton, and the initial photochromic material is an aromatic heterocyclic spiropyran photochromic material.

[0065] Through the above-mentioned development method, the photochromic performance can be significantly improved, the reversibility of the photochromic material can be improved, and a new type of spiropyran-based smart color-changing film with an adjustable color change range can be formed. The color change rate of the spiropyran-based material can also be increased, ensuring that the color change ability of the color-changing material in the pure solid state is better, and the color-changing material in the pure solid state can still have a large color change range. Through the reasonable and efficient setting of compound synthesis strategies, theoretical calculation assistance and synthesis route optimization, a series of new spiropyran materials with significantly enhanced color change rate and solid-state light change ability and adjustable color change range have been developed. material; further characterize the physical and chemical properties of a series of new spiropyran small molecule materials synthesized, deeply analyze the structure-activity relationship and color change mechanism of this type of materials, and explore the key factors affecting the photochromic performance of this type of materials; finally, by optimizing the film preparation process of this type of spiropyran small molecule materials, establish the characterization test standard of its photochromic properties, and develop a new type of spiropyran smart color-changing film with significantly improved photochromic performance, good reversibility, and adjustable color change range, which can greatly improve the reversibility, color change range and stability of photochromic materials in pure solid state.

[0066] Step one includes:

[0067] Step S11: constructing a spiropyran molecular skeleton through an organic reaction;

[0068] Step S12: synthesizing the target aromatic heterocyclic group with the spiropyran molecular skeleton through Suzuki coupling to form an aromatic heterocyclic spiropyran photochromic material; wherein the target aromatic heterocyclic group includes any one of phenyl-B, thienyl-T, pyridyl-Py, 3-pyridyl-3-Py and pyrimidinyl-Md.

[0069] By first constructing a molecular skeleton and then coupling the aromatic heterocyclic group with the spiropyran molecular skeleton, the synthesis efficiency of the photochromic material can be greatly simplified, the stability and reversibility of the photochromic material in the pure solid state can be simplified, and further, the color change range of the photochromic material in the pure solid state can be expanded, solving the current problem of the single color change range of the photochromic material in the solid state, greatly improving the quality of the photochromic material, saving the cost of material preparation, and simplifying the material preparation process.

[0070] Step S11 includes:

[0071] Step S111: preparing iodine salt compound b by methylation reaction of compound a. In this embodiment, compound a is 2,3,3-trimethylindole, and iodine salt compound b is 2,3,3-trimethyl-3-hydrogen-indole iodide.

[0072] Step S112: conducting an organic reaction between the iodine salt compound b and 5-bromosalicylic acid to construct a spiropyran molecular skeleton, which is a bromine-substituted spiropyran molecule SP-Br;

[0073] Specifically, step S111 includes reacting compound a with a methyl group to obtain an iodine salt compound b having the structural formula:

[0074]

[0075] The preparation steps are as follows: 5.0 g of compound a and 2.5 equivalents (ep) of iodomethane are added to a 250 mL two-necked flask and treated to be anhydrous and oxygen-free. Then, 100 mL of anhydrous chloroform is injected into the reaction system, and the temperature is raised to reflux with stirring; after reacting for 6 hours, the reaction is stopped, and after the temperature in the two-necked flask is cooled to room temperature, the product is extracted with dichloromethane (100 mL×3) three times, and the organic phase is collected; and the product is separated and purified by silica gel column chromatography using petroleum ether or ethyl acetate as the purification solvent to finally obtain a yellow product compound b, and the yield of compound b is measured and calculated to be 80%.

[0076] Next, in step S112, the iodine salt compound b is subjected to an organic reaction with 5-bromosalicylic acid to construct a spiropyran molecular skeleton SP-Br having the structural formula:

[0077]

[0078] The preparation steps are as follows: 1.6 g of compound b and an equal amount of 5-bromosalicylaldehyde are added to a 250 mL two-necked flask, and the mixture is anhydrous and oxygen-free. 80 mL of anhydrous ethanol is then injected into the reaction system, and the temperature is raised to 55 degrees Celsius. 0.8 mL of piperidine is dropwise added to the reaction system, and the temperature is continued to be raised and stirred until reflux. After reacting for 8 hours, the reaction is stopped, and after the temperature in the two-necked flask is cooled to room temperature, the mixture is extracted three times with dichloromethane (70 mL×3), and the organic phase is collected. The organic phase is separated and purified by silica gel column chromatography, using petroleum ether or ethyl acetate as the purification solvent, to finally obtain a yellow product SP-Br, and the yield of the yellow product SP-Br is measured and calculated to be 75%.

[0079] Through the preparation of the spiropyran molecular skeleton in the above-mentioned research on the pure solid-state new aromatic heterocyclic spiropyran intelligent color-changing material, the stability and reliability of the intermediate skeleton structure of the aromatic heterocyclic spiropyran photochromic material in the pure solid state can be effectively improved.

[0080] Step S12 includes:

[0081] Step S121: selecting any one of phenyl-B, thienyl-T, pyridyl-Py, 3-pyridyl-3-Py and pyrimidinyl-Md as the target aromatic heterocyclic group;

[0082] Step S122: The target aromatic heterocyclic group is coupled with the spiropyran molecular skeleton through Suzuki coupling to construct a shape, thereby obtaining an initial photochromic material.

[0083] Specifically, the preparation method of spiropyran photochromic small molecules through step S11 and step S12: first, 2,3,3-trimethylindole, namely compound a, is subjected to a methylation reaction to obtain an iodine salt compound b, which is then reacted with 5-bromosalicylic acid to obtain a bromine-substituted spiropyran molecule SP-Br; further attempts are made to introduce phenyl-B, thienyl-T, pyridyl-Py, 3-pyridyl-3-Py and pyrimidinyl-Md units into the spiropyran molecular skeleton through Suzuki coupling; then, by changing any one or more conditions among the feed ratio of the photochromic material components, the catalyst type, the type of the coupling reaction base, different solvents, the reaction temperature and the reaction time; finally, after multiple experimental condition optimization, various aromatic heterocyclic spiropyrans are successfully prepared. A photochromic small molecule material, wherein the feed ratio refers to the ratio of SP-Br: boric acid reagent in the range of 1:1.5 to 1:4, the catalyst type is any one or more types of Pd(PPh3)4, Pd(OAc)2, PdCl2(dppf) and PdCl2(PPh3)2, the type of coupling reaction base is any one or more types of K2CO3, Cs2CO3, different solvent types in the preparation process of photochromic materials include any one or more solvent types of a mixture of tetrahydrofuran and water, a mixture of dioxane and water, N,N-dimethylformamide, and toluene, the reaction temperature range is between 55°C and 145°C during the construction of the photochromic material, and the reaction time range of the photochromic material is 2h-48h.

[0084] By constructing a series of aromatic heterocyclic spiropyran molecules, the conjugation length of the molecule is effectively increased, the HOMO / LUMO energy level and band gap of the molecule and the opening and closing rate of the molecule are regulated, thereby effectively regulating the photochromic ability and color change range of the material. Among them, HOMO refers to the highest occupied molecular orbital, that is, the orbital with the highest energy level of occupied electrons, and LUMO refers to the lowest unoccupied molecular orbital, that is, the orbital with the lowest energy level of unoccupied electrons; in addition, the introduction of conjugated units can significantly increase the free volume of the material in the solid state, thereby enabling a series of DA-type conjugated materials to produce obvious photochromic processes in the pure solid state. Using brominated spiropyran SP-Br and different boronic acid reagents as coupling monomers, Suzuki palladium-catalyzed coupling , the molecular skeleton is coupled and constructed under the action of alkali, among which DA-type conjugation is a molecular form that already exists in the prior art; compared with the prior art, spiropyran is a type of organic photochromic material with excellent color-changing performance. However, due to the lack of in-depth understanding of its color-changing mechanism, its photochromic properties such as color-changing rate, reversibility and photochromic range are gradually unable to meet the needs of practical applications, and its application prospects are also greatly limited. The series of spiropyran photochromic materials synthesized in this application that introduce aromatic heterocycles have developed spiropyran photochromic materials with significantly improved solid-state photochromic ability and controllable color-changing range through the synergistic strategy of constructing a DA conjugated system and increasing the free volume of the molecule, effectively broadening its application prospects.

[0085] Step 2 includes:

[0086] Step S21: characterizing the molecular structure of the aromatic heterocyclic spiropyran photochromic material;

[0087] Step S22: Characterizing the physical and chemical properties of the aromatic heterocyclic spiropyran photochromic material, wherein in step S22, the physical and chemical property characterization includes any one or more of UV-visible absorption spectroscopy testing, thermogravimetric analysis testing, electrochemical testing, SEM morphology characterization testing, and density functional theory (DFT) calculation molecular testing.

[0088] In step three, the method of testing the color-changing performance of the initial photochromic material includes any one or more test methods of testing the color-changing characteristics of the photochromic material under 365nm light source irradiation, solution state, pure solid state and blended film state; wherein the color-changing characteristics refer to any one or more properties of the photochromic material including the color-changing rate, reversibility and recovery rate.

[0089] By characterizing the structure of the constructed aromatic heterocyclic spiropyran photochromic smart material and testing its color-changing properties, the characterization data can effectively visualize the photochromic material, providing an effective basis for subsequent optimization of the photochromic material feed ratio or feed type adjustment. Combined with the color-changing property test, it can also be effectively judged whether the color-changing performance of the prepared photochromic material meets the requirements, thereby further determining whether the developed material is successful, and thus effectively improving the stability and reliability of material development.

[0090] Through screening and experimenting with a series of synthetic conditions, a series of aromatic heterocyclic spiropyran molecular frameworks constructed with different conjugated segments were successfully developed. By varying any one or more of the following conditions: feed ratio, catalyst type, type of base in the coupling process, reaction solvent, reaction temperature, and reaction time, various aromatic heterocyclic spiropyran small molecule materials were successfully developed. The optimized preparation conditions for SP-Py, SP-3-Py, and SP-Md are shown below:

[0091] Example 1:

[0092] In step S121, the target aromatic heterocyclic group is phenyl, that is, -B, and the prepared aromatic heterocyclic spiropyran photochromic material is SP-B. The structural formula of the prepared SP-B is:

[0093]

[0094] The preparation method is as follows: 250 mg of compound SP-Br, 3 equivalents of phenylboronic acid, 10% equivalents of tetrakistriphenylphosphine palladium, and 6 equivalents of potassium carbonate are added to a 100 mL two-necked flask, and then nitrogen replacement and deoxygenation treatment are performed. 12 mL of a mixed solvent of tetrahydrofuran and water is injected into the reaction system, wherein the mixed solvent components include THF and H2O, and the component ratio of the mixed solvent is: THF:H2O=3:1. The mixture is further frozen and pumped with liquid nitrogen three times, and after strict deoxygenation operation, the two-necked flask is heated to 85°C until it refluxes. After the reaction for 10 hours, the reaction is stopped, and after the two-necked flask is cooled to room temperature, it is extracted with dichloromethane (50 mL×3), and the organic phase is collected and separated and purified by silica gel column chromatography. The purification solvent is petroleum ether or ethyl acetate, and finally a yellow-white product SP-B is obtained. The yield of the yellow-white product SP-B is measured and calculated to be 91%, as shown in Table 1 below.

[0095] Table 1

[0096]

[0097] Example 2:

[0098] In step S121, the target aromatic heterocyclic group is a thienyl group, i.e., -T, and the prepared aromatic heterocyclic spiropyran photochromic material is SP-T. The structural formula of the prepared SP-T is:

[0099]

[0100] The preparation method is as follows: 200 mg of compound SP-Br, 3 equivalents of thiopheneboronic acid, 10% equivalents of tetrakistriphenylphosphine palladium, and 8 equivalents of potassium carbonate are added to a 100 mL two-necked flask, and then the mixture is replaced with nitrogen to remove oxygen. 10 mL of N,N-dimethylformamide (DMF) is injected into the reaction system, and the mixture is further frozen and pumped with liquid nitrogen three times. After strict deoxygenation operation, the two-necked flask is heated to 120° C. After reacting for 6 hours, the reaction is stopped, and after the two-necked flask is cooled to room temperature, the organic phase is extracted with dichloromethane (50 mL×3) to collect the organic phase; the mixture is separated and purified by silica gel column chromatography, and the purification solvent is petroleum ether or ethyl acetate, and finally a light yellow product SP-T is obtained. The yield of the light yellow product SP-T is measured and calculated to be 85%, as shown in Table 2 below.

[0101] Table 2

[0102]

[0103] Example 3:

[0104] In step S121, the target aromatic heterocyclic group is pyridyl, i.e., -Py, and the prepared aromatic heterocyclic spiropyran photochromic material is SP-B. The structural formula of the prepared SP-B is:

[0105]

[0106] The preparation method is as follows: 200 mg of compound SP-Br, 4 equivalents of pyridine boronic acid, 10% equivalents of tetrakistriphenylphosphine palladium, and 8 equivalents of cesium carbonate are added to a 100 mL two-necked flask, and then nitrogen is replaced to remove oxygen. 10 mL of a mixed solvent of tetrahydrofuran and water is injected into the reaction system. The mixed solvent components include THF and H2O, and the component ratio of the mixed solvent is: THF:H2O=6:1. The mixture is further frozen and pumped with liquid nitrogen three times. After strict deoxygenation operation, the two-necked flask is heated to 85°C to reflux state. After reacting for 8 hours, the reaction is stopped, and after the two-necked flask is cooled to room temperature, it is extracted with dichloromethane (50 mL×3), and the organic phase is collected. It is separated and purified by silica gel column chromatography. The purification solvent is petroleum ether or ethyl acetate, and finally a light yellow product SP-Py is obtained. The yield of the light yellow product SP-Py is measured and calculated to be 80%, as shown in Table 3 below.

[0107] Table 3

[0108]

[0109] Example 4:

[0110] In step S121, the target aromatic heterocyclic group is 3-pyridyl, i.e., -3-Py, and the obtained aromatic heterocyclic spiropyran photochromic material is SP-B. The structural formula of the prepared SP-B is:

[0111]

[0112] The preparation method is as follows: 200 mg of compound SP-Br, 4 equivalents of 3-pyridineboronic acid, 10% equivalents of tetrakistriphenylphosphine palladium, and 8 equivalents of cesium carbonate are added to a 100 mL two-necked flask, and then the mixture is purged with nitrogen and oxygen-free. 10 mL of a mixed solvent of tetrahydrofuran and water is injected into the reaction system, wherein the mixed solvent comprises THF and H2O, and the ratio of the mixed solvent is THF:H2O=9:1. The mixture is further frozen and pumped with liquid nitrogen three times, and after strict deoxygenation, the two-necked flask is heated to 85°C and refluxed. After reacting for 10 hours, the reaction is stopped, and after the two-necked flask is cooled to room temperature, it is extracted with dichloromethane (50 mL×3), and the organic phase is collected and separated and purified by silica gel column chromatography. The purification solvent is petroleum ether or ethyl acetate, and finally a pale yellow product SP-3-Py is obtained. The yield of the pale yellow product SP-3-Py is measured and calculated to be 62%, as shown in Table 4 below.

[0113] Table 4

[0114]

[0115] Example 5

[0116] In step S121, the target aromatic heterocyclic group is a pyrimidine group, i.e., -Md, and the prepared aromatic heterocyclic spiropyran photochromic material is SP-B. The structural formula of the prepared SP-B is:

[0117]

[0118] The preparation method is as follows: 200 mg of compound SP-Br, 3 equivalents of pyrimidineboronic acid, 10% equivalents of tetrakistriphenylphosphine palladium, and 8 equivalents of cesium carbonate are added to a 100 mL two-necked flask, followed by nitrogen replacement and oxygen-freezing treatment, and 10 mL of anhydrous N,N-dimethylformamide DMF is injected into the reaction system, and further frozen and pumped with liquid nitrogen three times. After strict deoxygenation operation, the two-necked flask is heated to 140 ° C. After the reaction for 8.5 hours, the reaction is stopped, and after the two-necked flask is cooled to room temperature, it is extracted three times with dichloromethane (50 mL×3), and the organic phase is collected, separated and purified by silica gel column chromatography, and the purification solvent is petroleum ether or ethyl acetate, and finally a light yellow product SP-Md is obtained, and the yield of the light yellow product SP-Md is measured and calculated = 58%, as shown in Table 5 below.

[0119] Table 5

[0120]

[0121] By using the above-mentioned aromatic heterocyclic spiropyran molecular skeleton constructed with different conjugated segments, the construction of photochromic materials can be successfully optimized by changing any one or more of the feed ratio, catalyst type, type of base in the coupling process, reaction solvent, reaction temperature and reaction time. At the same time, its preparation process is simple, which can greatly improve the efficiency of material preparation. Through a series of optimizations, the quality of the material can also be improved.

[0122] In step S21 and step S22, the molecular structure and physicochemical properties of the aromatic heterocyclic spiropyran photochromic material are characterized, specifically:

[0123] The prepared aromatic heterocyclic spiropyran was separated and purified by silica gel column chromatography, concentrated to remove the solvent, and dried in a vacuum oven to obtain a solid powder. 1 H-NMR nuclear magnetic resonance hydrogen spectrum and HRMS high-resolution mass spectrometry tests were performed to verify the correctness of the obtained product structure.

[0124] Final product 1 The H NMR spectrum is shown in the figure, and the corresponding peak data are shown below:

[0125] SP-Br: 1 H NMR(400MHz,Chloroform-d)δ7.22(qd,3H),7.11(dd,1H),6.89(t,1H),6.82(d,1H), 6.65–6.61(m,1H),6.57(d,1H),5.77(d,1H),2.76(s,3H),1.34(s,3H),1.21(s,3H).

[0126] SP-B:1 H NMR(400MHz,Chloroform-d)δ7.57–7.54(m,2H),7.43(t,2H),7.37–7.30(m,3H),7.24–7.19(m,1H),7.12(dd,1H),6.94(d,1H),6.90–6.86(m,1H),6.81(d,1H),6.57(d,1H),5.76(d,1H),2.79(s,3H),1.37(s,3H),1.22(s,3H).

[0127] SP-T: 1 H NMR(400MHz,Chloroform-d)δ7.36(dd,1H),7.30(d,1H),7.23–7.17(m,3H),7.09(dd,1H),7.05(dd,1H),6.92–6.84(m,2H),6.74(d,1H),6.55(d,1H),5.75(d,1H),2.76(s,3H),1.34(s,3H),1.19(s,3H).

[0128] SP-Py: 1 H NMR(400MHz,Chloroform-d)δ8.68–8.56(m,2H),7.50–7.44(m,2H),7.42(dd,1H),7.37(d,1H),7.21(td,1H),7.11(dd,1H),6.95(d,1H),6.88(td,1H),6.84(d,1H),6.56(d,1H),5.79(d,1H),2.77(s,3H),1.35(s,3H),1.21(s,3H).

[0129] SP-3-Py: 1 H NMR(400MHz,Chloroform-d)δ8.84–8.78(m,1H),8.55(dd,1H),7.86–7.79(m,1H),7.34(ddd,2H),7.29(d,1H),7.21(td,1H),7.11(dd,1H),6.94(d,1H),6.88(td,1H),6.84(d,1H),6.56(d,1H),5.78(d,1H),2.78(s,3H),1.36(s,3H),1.21(s,3H).

[0130] SP-Md: 1H NMR(400MHz,Chloroform-d)δ9.16(s,1H),8.91(s,2H),7.33(dd,1H),7.28(d,1H),7.21(td,1H),7.11(d d,1H),6.95(d,1H),6.91–6.84(m,2H),6.57(d,1H),5.81(d,1H),2.78(s,3H),1.35(s,3H),1.21(s,3H).

[0131] The high resolution mass spectrometry (HRMS) test data of each final product are shown in Table 6 below:

[0132] Table 6

[0133] No. Name Formula <![CDATA[calcd[M+H] + ]]> <![CDATA[Found[M+H] + ]]> 1 SP-B <![CDATA[C 25 H 23 NO]]> 354.1780 354.1852 2 SP-T <![CDATA[C 23 H 21 WE]]> 360.1344 360.1417 3 SP-Py <![CDATA[C 24 H 22 N2O]]> 355.1732 355.1805 4 SP-3-Py <![CDATA[C 24 H 22 N2O]]> 355.1805 355.1804 5 SP-Md <h2 style=";text-align:left;direction:ltr"><![CDATA[C <h2 style=";text-align:left;direction:ltr"> 23 <h2 style=";text-align:left;direction:ltr"> H<h2 style=";text-align:left;direction:ltr"> 21 <h2 style=";text-align:left;direction:ltr"> N3O]]><h2 style=";text-align:left;direction:ltr"> 356.1757 356.1759

[0134] Through polyaromatic heterocyclic spiropyran 1 H NMR and HRMS tests can confirm the correctness of the final product structure.

[0135] In addition, in step S22, the characterization of the physical and chemical properties of the substance also includes any one or more of thermal stability analysis, UV-visible absorption spectrum test, and density functional theory (DFT) calculation of the HOMO / LUMO energy level and molecular conformation of the molecule.

[0136] Specifically, 1) thermal stability analysis: The obtained series of aromatic heterocyclic spiropyran small molecule materials were further subjected to thermogravimetric analysis. Under nitrogen conditions, the obtained series of aromatic heterocyclic spiropyran small molecule materials were heated from room temperature to 800°C, and their thermal decomposition temperatures were observed. As shown in the figure, the thermal decomposition temperatures of SP-B, SP-T, SP-Py, SP-3-Py and SP-Md were 257°C, 248°C, 260°C, 240°C and 270°C, respectively. The results show that the synthesized series of aromatic heterocyclic spiropyran molecules all exhibit good thermal stability, which can well ensure the subsequent characterization test and thin film processing process.

[0137] II) UV-visible absorption spectroscopy test: The obtained heterocyclic spiropyran-type photochromic small molecule material was prepared into a dilute dichloromethane solution and subjected to UV-visible absorption spectroscopy test with a scanning range of 250 nm to 650 nm. As shown in the figure, SP-Br and various heterocyclic spiropyran end products exhibited relatively similar absorption spectra. However, after the introduction of the heterocyclic ring, the conjugated system of the molecule was enhanced to a certain extent, and both the main peak and the shoulder peak showed a certain red shift. However, since the molecular conformation of this series of molecules before ring opening was relatively distorted and the delocalization ability of the π electron was general, the red shift of the absorption peak of the molecule after the introduction of the conjugated fragment was not obvious, and was basically within 10 nm. Among them, the DA structure of SP-T with the introduction of the thiophene unit was the most significant, and the intramolecular charge transfer (ICT) effect was the strongest, so the red shift of its absorption peak was also the most obvious. The main peak of SP-T red-shifted from 250 nm to 261 nm, and the shoulder peak red-shifted from 292 nm to 302 nm.

[0138] Since this type of material has good light reversibility, after irradiation in the solution state, the material will return to the ring-closed state within a few seconds. Therefore, it is difficult to monitor the absorption spectrum of this type of material in the solution state after light (365nm). The SP state spiropyran will open the ring and become the MCH state after adding acid (the structure of the open MC after protonation is MCH), which will cause its color to change significantly. Therefore, we tried to add different proportions of trifluoroacetic acid to characterize its absorption spectrum after ring opening; as shown in the figure, with the increase of trifluoroacetic acid concentration, all spiropyran molecules produce new absorption peaks at long wavelengths, and with the increase of acid concentration, the intensity of the newly generated absorption peak increases significantly. This result shows that the newly synthesized aromatic heterocyclic spiropyrans can undergo obvious ring-opening color change process.

[0139] 3) Density functional theory (DFT) calculation of the HOMO / LUMO energy level and molecular conformation of the molecule: In order to further explore the structure-activity relationship of the material, we performed density functional theory (DFT) calculation simulation on the molecular conformation and HOMO / LUMO energy level of this type of material using Gaussian (the team selected B3LYP / 6-31G,d,p); As shown in the figure, there is a dihedral angle of about 30 degrees between spiropyran and the introduced conjugated fragment, among which the dihedral angle of SP-B with the introduction of benzene ring is the largest, reaching 37.65 degrees; after the introduction of aromatic heterocycles, the dihedral angle between spiropyran and the conjugated fragment is reduced to a certain extent Among them, the dihedral angle of SP-T with the introduction of thiophene is the smallest, which is 29.65 degrees, followed by SP-Py with the introduction of pyridine, whose dihedral angle is 34.57 degrees. The corresponding dihedral angles of SP-3-Py and SP-Md also decrease to a certain extent; therefore, it can be determined that the introduction of aromatic heterocycles can effectively reduce the dihedral angles between conjugated fragments, thereby enhancing the π electron delocalization ability of the molecular skeleton; in addition, through the computational simulation of HOMO / LUMO energy levels and electron cloud distribution, it can be known that the electron cloud distribution of all molecules has significant changes between HOMO and LUMO, indicating that the molecules do have a significant DA structure, which is conducive to π electron delocalization.

[0140] In addition, the molecular conformations, HOMO / LUMO energy levels, and electron clouds of the MC state of each material after ring opening were simulated. As shown in the figure, all molecules have dihedral angles in the open state MC that are reduced to a certain extent compared with the closed state SP, indicating that the π electron delocalization ability of the molecules of this type of material is further enhanced after ring opening.

[0141] In addition, the color change performance of the initial photochromic material, i.e., the photochromic performance test of the aromatic heterocyclic spiropyran photochromic camouflage material, in step 3 includes any one or more of the photochromic properties of the material in solution, the photochromic properties of the material in pure solid state, and the photochromic properties of the PMMA blend film;

[0142] Specifically, (1) the photochromic properties of the material in solution:

[0143] The test method and results are as follows: the synthesized series of spiropyran molecules were prepared into 10 mg / mL acetone solution and irradiated with a 365 nm ultraviolet lamp for 10 seconds. The results are as follows Figure 17As shown in the figure, the color of the solution of the brominated and benzene-substituted spiropyran derivatives SP-Br and SP-B did not change significantly before and after illumination, and therefore did not exhibit obvious photochromic properties; while the aromatic heterocyclic spiropyran derivatives SP-T, SP-Py, SP-3-Py and SP-Md all exhibited significant photochromic properties, and the aromatic heterocyclic spiropyran derivatives SP-T, SP-Py, SP-3-Py and SP-Md all changed from the previous colorless and transparent to a blue (blue-green) solution, showing significant photochromic properties. At the same time, when the light source was removed, the material returned to the original colorless and transparent liquid within seconds, indicating that this type of material has good light-changing reversibility.

[0144] The above experimental results show that the introduction of aromatic heterocyclic conjugated units into the spiropyran molecular skeleton can significantly improve the photochromic properties of this type of material.

[0145] (2) Photochromic properties of materials in pure solid state:

[0146] The developed SP-B, SP-T, SP-Py, SP-3-Py, and SP-Md were tested for their photochromic properties. Irradiated with a 365nm UV lamp, all three examples exhibited significant photochromic properties, changing from yellow-white to blue within seconds. The specific implementation methods are shown in Table 7 below:

[0147] Table 7

[0148]

[0149] The test method and results are as follows: various aromatic heterocyclic spiropyran derivatives (derivatives include any one or more of SP-T, SP-Py, SP-3-Py and SP-Md) and bromospiropyran SP-Br, nitro-substituted spiropyran SP-NO2, and benzene-substituted spiropyran SP-B are ground into pure solid powders, and their photochromic properties in pure solid state are tested; Figure 18As shown in the test results in Table 7, the classic spiropyran molecule SP-NO2 does not show photochromic properties in pure solid powder, nor do SP-Br and SP-B. In addition, thiophene-substituted SP-T also does not show obvious photochromic properties in pure solid state. However, other aromatic heterocyclic-substituted spiropyrans SP-Py, SP-3-Py and SP-Md all show obvious photochromic properties in pure solid state. They all change from the previous light yellow to blue powder after irradiation with 365nm ultraviolet light for 10s. Among them, SP-Py The color change of SP-3-Py and SP-Md is the most obvious, turning into dark blue, while SP-3-Py and SP-Md turn into blue-green. Since the dihedral angles of all spiropyran derivatives connecting conjugated segments are around 30 degrees, it can be seen that almost the same free volume is obtained after the introduction of the conjugated unit. "Almost the same" means that the free volume of the compound before and after the introduction of the conjugated unit is extremely close. Therefore, the color change characteristics of several aromatic ring spiropyran derivatives in the solid state can be attributed to the difference in the intrinsic properties of the molecules and the different stacking modes in the solid state. Further scanning electron microscopy (SEM) tests were carried out on their solid powders, as shown in Figure 2. Figure 19 As shown, combined with the SEM results, a reasonable explanation is given for the color-changing behavior of aromatic heterocyclic spiropyran in the solid state: the photochromic properties of this type of material in the pure solid state are determined by a combination of factors, including any one or more of the free volume of the material itself in the solid state, the photo-ring-opening ability of the material itself, and the compactness of the material in the solid state; the experimental results in the solution state show that the introduction of aromatic heterocycles, whether electron-withdrawing groups or electron-donating groups, can significantly improve the photo-ring-opening ability of the material; combined with the electron microscopy data, it can be seen that in the pure solid state, the solid-state stacking of SP-T is tighter than that of SP-Py and SP-3-Py, showing a certain regular arrangement , while the stacking of pyridine-substituted spiropyran in the solid state is obviously more disordered. Therefore, it is believed that the inability of SP-T to photochromic in the pure solid state is due to its relatively dense stacking in the solid state, which in turn results in it being unable to generate sufficient free volume for an effective opening-closing ring process; in addition, the stacking of SP-Md is more ordered than that of SP-Py and SP-3-Py, almost equivalent to that of SP-T. However, it can also exhibit color-changing properties in the pure solid state, which may be due to the strong electron-withdrawing ability of the pyrimidine structure, resulting in a certain increase in its ring-opening rate compared to SP-T. Therefore, even if the stacking is orderly in the pure solid state, it can still exhibit certain pure solid-state photochromic properties.

[0150] The above results indicate that the pure solid-state photochromism of spiropyran materials is a relatively complex process, requiring the intrinsic molecular structure to provide sufficient free volume and good opening-closing ring ability, and also requiring the material to be relatively disordered in the pure solid state. If all the above factors are met, it is possible to obtain significant photochromic properties in the pure solid state.

[0151] (3) Photochromic properties of PMMA blend films:

[0152] The test method and results are as follows: various aromatic heterocyclic spiropyran materials and polymethyl methacrylate (PMMA) were blended and prepared into solid films on a glass substrate to obtain yellow-white solid films. The films were then irradiated with ultraviolet light (365nm). Figure 21a-Figure 21h As shown, after irradiation for 15 seconds, the photochromic effect of the material is as follows Figure 21c As shown in the figure, SP-B connected to the benzene ring also shows a certain color-changing effect, but it is not obvious; all aromatic heterocyclic spiropyrans show obvious photochromic properties, among which SP-Py connected to pyridine and SP-T connected to thiophene units show very obvious photochromic properties, SP-Py changes from light yellow-white before irradiation to dark blue-green, SP-T changes from a white film before irradiation to sky blue, among which SP-Py can maintain good photochromic reversibility while maintaining a certain period of photochromic stability, and the color has not completely faded after 5 minutes; although SP-3-Py and SP-Md can show obvious photochromic process in pure solid state, their color-changing effect is not ideal in PMMA blend film, and they only change to light blue-gray and fade quickly.

[0153] The above experimental results show that the introduction of aromatic heterocycles can indeed effectively improve the photochromic properties of the material. Through reasonable optimization and screening, SP-Py with excellent photochromic properties in the solid state was obtained, which exhibited ideal photochromic ability both in pure solid state and in blended films.

[0154] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A pure solid-state novel aromatic heterocyclic spiropyran intelligent color-changing material, characterized in that: The pure solid-state novel aromatic heterocyclic spiropyran intelligent color-changing material is SP-Md, and its structural formula is:

2. The method for preparing the pure solid-state novel aromatic heterocyclic spiropyran intelligent color-changing material according to claim 1, characterized in that: The following steps are involved: Step S1: preparing iodine salt compound b by methylation reaction of compound a; Step S2: conducting an organic reaction between the iodine salt compound b and 5-bromosalicylic acid to construct a spiropyran molecular skeleton; Step S3: preparing the SP-Md according to the following chemical reaction formula;

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