CN115746869B - A photochromic luminescent liquid crystal and its preparation method and application - Google Patents

Abstract

The invention belongs to the technical field of functional materials, and particularly relates to a photochromic luminescent liquid crystal and a preparation method and application thereof. The luminescent liquid crystal is obtained by coupling a platinum complex main body and a photochromic element through a connecting group. The photochromic luminescent liquid crystal belongs to a thermochromic liquid crystal, the apparent color, the luminescent behavior and the liquid crystal phase behavior of the photochromic luminescent liquid crystal can be reversibly regulated and controlled through the isomerization reaction of a photochromic element, and the excellent reversible color changing performance of the photochromic luminescent liquid crystal can provide an additional optical information display mode. In addition, the light-emitting process of the photochromic light-emitting liquid crystal does not need ultraviolet light excitation, can show excellent light-emitting performance under the excitation of visible light, and can effectively separate the light-emitting and isomerization light excitation processes, so that the light-emitting characteristics under various configurations can be accurately shown. The photochromic luminescent liquid crystal can be used as an intelligent material and applied to high-end anti-counterfeiting, optical sensing, data storage, high-resolution imaging and other high and new technical fields.

Description

A photochromic luminescent liquid crystal and its preparation method and application

Technical Field

The present invention belongs to the technical field of functional materials, and more specifically, relates to a photochromic luminescent liquid crystal and a preparation method and application thereof.

Background technique

Luminescent liquid crystals are prepared by combining luminescent units with mesogenic units. They have unique photoluminescent properties and mesogenic phase behaviors, and have broad application prospects in the fields of displays, chemical sensors, optical memories, polarized organic lasers, etc. Giving luminescent liquid crystals multifunctionality is conducive to expanding their application range. Among them, photoresponsive luminescent liquid crystals have attracted widespread interest because they can respond to both electric fields and light.

Currently, there are only a small number of photoresponsive luminescent liquid crystals with cyanostilbene as photoluminescent unit and photoisomerization unit (Adv. Funct. Mater. 2021, 31, 2007957), but its photoisomerization reaction is usually accompanied by side reactions such as cyclization and dimerization. Complex and uncontrollable photoisomerization reactions cause irreversible changes in the phase behavior and luminescence behavior of liquid crystals. Compared with cyanostilbene, photoisomerization units such as spiropyran and diarylethenes are less likely to undergo side reactions under light, which is conducive to reversible regulation of luminescence behavior and liquid crystal phase behavior, and giving luminescent liquid crystals reversible color-changing properties.

Usually, the excitation light for the luminescent element to produce luminescence is ultraviolet light, and the induction light for the photoisomerization reaction of photoisomerization elements such as spiropyran and diarylethene is also ultraviolet light. Therefore, for luminescent liquid crystals based on photoresponsive elements such as spiropyran and diarylethene, the photoisomerization reaction will interfere with the photoluminescence process, making it difficult to accurately obtain the luminescence characteristics of each configuration. In addition, the photoisomerization reaction of spiropyran and the like generally manifests as luminescence from nothing to something, while diarylethene and the like do not even emit light. It is still difficult to obtain luminescent liquid crystals that can emit light under visible light excitation and can isomerize under ultraviolet light excitation.

Summary of the invention

In view of the defects of the prior art, the purpose of the present invention is to provide a photochromic luminescent liquid crystal and a preparation method and application thereof, so as to realize the reversible transformation of the apparent color, liquid crystal texture and luminescence under the action of ultraviolet light or heating, so as to solve the technical problem of mutual crosstalk in the light excitation process of the luminescence and photoisomerization reaction of the luminescent liquid crystal in the prior art.

To achieve the above object, the present invention provides a photochromic luminescent liquid crystal, wherein the luminescent liquid crystal is a molecule obtained by coupling a platinum complex main body with a photochromic element through a connecting group, wherein the photochromic element is a spiropyran, a diarylethene or a fulgide molecule; and the connecting group is an alkyl chain containing an ester group or an amide group;

The luminescent liquid crystal has luminescent behavior under the excitation of visible light, and the structure of the luminescent liquid crystal can be isomerized under the action of ultraviolet light, and there is no crosstalk between the light excitation process of the luminescence and the photoisomerization reaction of the luminescent liquid crystal;

The luminescent liquid crystal presents an apparent color under natural light and has luminescent behavior after being excited by visible light; under the action of ultraviolet light or heating, the structure of the luminescent liquid crystal can undergo reversible isomerization, and the apparent color and the luminescent behavior after being excited by visible light can both undergo reversible changes.

Preferably, the wavelength of the visible light is any wavelength in the range of 420 to 500 nanometers; the wavelength of the ultraviolet light is any wavelength in the range of 250 to 400 nanometers; and the heating temperature is any temperature in the range of 50 to 120°C.

Preferably, the platinum complex body has one of the following structures:

Among them, the part marked with * is the linking site, _R1 and _R2 are each independently selected from hydrogen, methyl, ethyl, trifluoromethyl, tert-butyl, nitro, amino and phenyl, and _R1 and _R2 may be the same or different.

Preferably, the photochromic element has one of the following structures:

Among them, the part marked with * is the linking site, and R ₃ is hydrogen, methyl, nitro or phenyl.

Preferably, the linking element is one of the following structures:

Among them, the part marked with * is the linking site, and n is any integer from 1 to 10, preferably an integer from 1, 2 or 8 to 10.

According to another aspect of the present invention, a method for preparing the photochromic luminescent liquid crystal is provided, wherein the preparation method comprises a tridentate primary ligand, Pt(DMSO) ₂ Cl ₂ and a pyridine derivative containing the photochromic element through a coordination reaction; wherein the tridentate primary ligand has one of the following structures:

Wherein, _R4 and _R5 are each independently selected from hydrogen, methyl, ethyl, trifluoromethyl, tert-butyl, nitro, amino and phenyl, and _R4 and _R5 may be the same or different.

Preferably, the pyridine derivative containing a photochromic element is represented by In which L is the connecting group and Pr is the photochromic element.

Preferably, the catalyst used in the coordination reaction is at least one of ethylenediamine, triethylamine, N,N-diisopropylethylamine, and N,N-dimethylaniline;

The solvent used in the coordination reaction is at least one of methanol, ethanol, acetonitrile, 2-methoxyethanol, acetone, toluene and xylene.

According to another aspect of the present invention, there is provided an application of the photochromic luminescent liquid crystal as a smart material in the fields of high-end anti-counterfeiting, optical sensing, data storage or high-resolution imaging technology.

Preferably, the photochromic luminescent liquid crystal is dissolved in a solvent to make ink, which is written on a glass substrate. Its apparent color, luminescent behavior and liquid crystal texture are changed by ultraviolet light irradiation. The triple encryption mode is applied to high-end anti-counterfeiting.

In general, the above technical solution conceived by the present invention has the following advantages compared with the prior art:

Beneficial effects:

(1) The photochromic luminescent liquid crystal provided by the present invention is obtained by coupling a platinum complex body with a photochromic element through a connecting group. The present invention utilizes the rich photophysical and chemical properties of the platinum complex, which can emit light not only under ultraviolet light excitation, but also under visible light excitation, and couples it with a specific photochromic element. By designing the twisted structure between the platinum complex body and the photochromic element, the π-π stacking of the platinum complex and the Pt...Pt metal-metal interaction produce good self-assembly, which is beneficial to the formation of a liquid crystal state on the one hand, and forms a new molecular orbital on the other hand, which helps to improve the luminescence performance. Experiments have found that the excitation light of the luminescence behavior of the obtained liquid crystal molecules is visible light, and the induction light of isomerization is ultraviolet light, which can effectively separate the isomerization reaction and the light excitation process of luminescence, avoid the interference of the isomerization reaction on the luminescence process, and accurately display the luminescence characteristics under each configuration.

(2) The photochromic luminescent liquid crystal of the present invention can undergo an isomerization reaction under the action of ultraviolet light or heat, thereby reversibly regulating the apparent color, liquid crystal texture and luminescent behavior. The isomerization process changes rapidly, requires low ultraviolet light power, and requires low heating temperature.

(3) The apparent color, luminescence and liquid crystal texture of the photochromic luminescent liquid crystal of the present invention are related to the platinum complex main body and the light-responsive unit (photochromic unit). By changing the structure of the photochromic unit, the photochromic luminescent liquid crystal can have different apparent colors, luminescence and liquid crystal textures.

(4) The method for preparing the photochromic luminescent liquid crystal provided by the present invention is a one-pot coordination reaction to directly precipitate the final product, and the reaction is simple and the post-processing process is simple.

(5) The photochromic luminescent liquid crystal of the present invention has triple display functions of apparent color, luminescence and liquid crystal texture, and can realize triple encryption for application in high-end anti-counterfeiting; rapid photoisomerization can be applied to high-tech fields such as optical sensing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a color photograph of the photochromic luminescent liquid crystal prepared in Example 1 of the present invention before and after isomerization under indoor lighting;

FIG2 is a photo of the luminescence of the photochromic luminescent liquid crystal prepared in Example 1 of the present invention before and after photoisomerization under 480 nanometer light;

FIG. 3 is a polarizing microscope photograph of the photochromic luminescent liquid crystal prepared in Example 1 of the present invention before and after photoisomerization occurs.

FIG. 4 is a polarizing microscope photograph of the photochromic luminescent liquid crystal prepared in Example 2 of the present invention before and after photoisomerization occurs at room temperature.

FIG5 is a polarizing microscope photograph of the photochromic luminescent liquid crystal prepared in Example 15 of the present invention at room temperature.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

The present invention provides a photochromic luminescent liquid crystal, wherein the luminescent liquid crystal is a molecule obtained by coupling a platinum complex body with a photochromic element through a connecting group, wherein the photochromic element is a spiropyran, diarylethene or fulgide molecule; the connecting group is an alkyl chain containing an ester group or an amide group; the luminescent liquid crystal has luminescent behavior under visible light excitation, and under the action of ultraviolet light, the structure of the luminescent liquid crystal can be isomerized, and the light excitation process of the luminescence and photoisomerization reaction of the luminescent liquid crystal does not have mutual crosstalk. The luminescent liquid crystal presents an apparent color under natural light, and has luminescent behavior after being excited by visible light; under the action of ultraviolet light or heating, the structure of the luminescent liquid crystal can undergo reversible isomerization, and the apparent color and the luminescent behavior after being excited by visible light can both undergo reversible changes.

In some embodiments, the wavelength of the visible light is any wavelength in the range of 420 to 500 nanometers, the wavelength of the ultraviolet light is any wavelength in the range of 250 to 400 nanometers, and the heating temperature is any temperature in the range of 50 to 120°C.

In some embodiments, the platinum complex liquid crystal host has one of the following structures:

Among them, the part marked with * is the linking site, _R1 and _R2 are each independently hydrogen, methyl, ethyl, trifluoromethyl, tert-butyl, nitro, amino or phenyl, and _R1 and _R2 may be the same or different.

In some embodiments, the photochromic element has one of the following structures: Among them, the part marked with * is the linking site, and _R3 is one of hydrogen, methyl, nitro, and phenyl.

In some embodiments, the connection primitive is one of the following structures:

Among them, the part marked with * is the linking site, and n is any integer from 1 to 10, preferably an integer from 1, 2 or 8 to 10.

The present invention also provides a method for preparing the photochromic luminescent liquid crystal, which is prepared by a coordination reaction between a tridentate primary ligand (abbreviated as LG), Pt(DMSO) ₂ Cl ₂ and a pyridine derivative containing a photochromic element; the chemical reaction formula can be expressed as:

Wherein, the tridentate primary ligand LG has one of the following structures:

Wherein, R ₄ and R ₅ are independently selected from one of hydrogen, methyl, ethyl, trifluoromethyl, tert-butyl, nitro, amino and phenyl, and R ₄ and R ₅ may be the same or different. The pyridine derivative containing the photochromic element is represented by In which L is the connecting group and Pr is the photochromic element.

In some embodiments, the catalyst used in the coordination reaction is at least one of ethylenediamine, triethylamine, N,N-diisopropylethylamine, and N,N-dimethylaniline; the solvent used in the coordination reaction is at least one of methanol, ethanol, acetonitrile, 2-methoxyethanol, acetone, toluene, and xylene. The temperature of the coordination reaction is the boiling point of the solvent.

The photochromic luminescent liquid crystal of the present invention belongs to thermotropic liquid crystal, and its apparent color, luminescent behavior and liquid crystal phase behavior can be reversibly regulated by the isomerization reaction of the photochromic unit, and its excellent reversible color change performance can provide additional optical information display mode. The light excitation process of the luminescent liquid crystal of the present invention does not have mutual crosstalk between the luminescence and photoisomerization reaction, and the light excitation process of the luminescence and isomerization reaction can be effectively separated, so as to accurately present the luminescent characteristics under each configuration. At the same time, the luminescent liquid crystal presents an apparent color under natural light, and has a luminescent behavior after being excited by visible light; under the action of ultraviolet light or heating, the structure of the luminescent liquid crystal can undergo reversible isomerization, and the apparent color and the luminescent behavior after being excited by visible light can undergo reversible changes. In a preferred embodiment, for example, it is found in experiments that when the alkyl chain length in the connecting unit is controlled within a suitable range, the luminescent liquid crystal can also self-assemble under a polarizing microscope to present a liquid crystal texture, and under the action of ultraviolet light or heating, the liquid crystal texture presented under the polarizing microscope can also undergo reversible changes. Thus, the photochromic luminescent liquid crystal proposed in the present invention can be used as an intelligent material and applied to high-tech fields such as high-end anti-counterfeiting, optical sensing, data storage, and high-resolution imaging. In some embodiments, the photochromic luminescent liquid crystal is dissolved in a solvent to make ink, which is written on a glass substrate, and its apparent color, luminescent behavior, and liquid crystal texture are changed by ultraviolet irradiation, and the triple encryption mode is applied to high-end anti-counterfeiting. The solvent can be one or more of dichloromethane, chloroform, tetrahydrofuran, acetone, and N,N-dimethylformamide.

The following are examples:

Example 1

A photochromic luminescent liquid crystal and its preparation and application. The molecular structure of the photochromic luminescent liquid crystal involved is as follows:

The preparation process is:

4.89 g of a pyridine derivative containing a photochromic moiety in a molar ratio of 1:1:1 2.41 g tridentate primary ligand and 4.21 g of PtCl ₂ (DMSO) ₂ were added to a three-necked flask, ventilated three times, and 100 ml of anhydrous acetonitrile and 1.29 g of N,N-diisopropylethylamine as a catalyst were added under N ₂ atmosphere, and refluxed and stirred overnight for coordination reaction. After the system was cooled to room temperature, it was filtered and the filter cake was washed with acetonitrile three times to obtain a yellow solid precipitate (yield 68%), which was the photochromic luminescent liquid crystal C1.

When the yellow photochromic luminescent liquid crystal C1 is placed under 365-nanometer ultraviolet light, it emits orange light, but the light quickly changes. When placed under 480-nanometer visible light, it emits stable orange light. After continuous irradiation with 0.5 milliwatts per square centimeter of 250-405-nanometer ultraviolet light for 1 minute, it turns to red light and appears dark brown. After heat treatment at 50-120 degrees Celsius for 5 minutes, it can be restored to its original state.

Figure 1 is a color photograph of C1 before and after isomerization under visible light. It can be seen that C1 changes from yellow to dark brown under 365 nm violet light irradiation, and from dark brown to yellow under 80 °C heat action.

Figure 2 shows the luminescence photos of C1 before and after isomerization under 480-nanometer light. C1 changes from orange luminescence to red luminescence under 365-nanometer purple light irradiation, and changes from red luminescence to orange luminescence under 80°C heat treatment. Photoisomerization and luminescence do not interfere with each other.

The photochromic luminescent liquid crystal C1 was placed between two thin glass slides and the liquid crystal texture was observed under a polarizing microscope. When heated to 160°C, C1 was in an isotropic liquid state with no texture. After cooling to room temperature, as shown in Figure 3, a bright yellow-green liquid crystal texture was presented. After irradiation with 365 nm ultraviolet light at 0.5 mW/cm2 for 1 minute, the liquid crystal texture was observed to turn dark blue. Then, the liquid crystal texture turned yellow-green under the action of heat at 80°C.

The photochromic luminescent liquid crystal C1 of the present embodiment 1 is used as a smart material. Due to its triple display effects of apparent color, photoluminescence and liquid crystal texture and rapid photoisomerization, it can also be used as a smart material in high-tech fields such as high-end anti-counterfeiting, optical sensing, data storage, and high-resolution imaging.

Example 2

A photochromic luminescent liquid crystal and its preparation and application. The molecular structure of the photochromic luminescent liquid crystal involved is as follows:

The preparation process is:

6 g of a pyridine derivative containing a photochromic moiety in a molar ratio of 1:1:1 2.41 g tridentate primary ligand and 4.21 g of PtCl ₂ (DMSO) ₂ were added to a three-necked flask, ventilated three times, and 100 ml of anhydrous acetonitrile and 1.29 g of N,N-diisopropylethylamine as a catalyst were added under N ₂ atmosphere, and refluxed and stirred overnight for coordination reaction. After the system was cooled to room temperature, it was filtered and the filter cake was washed with acetonitrile three times to obtain a yellow solid precipitate (yield 68%), which was the photochromic luminescent liquid crystal C2.

The photochromic luminescent liquid crystal C4 was placed between two thin glass slides and the liquid crystal texture was observed under a polarizing microscope. When heated to 190°C, C1 was in an isotropic liquid state with no texture. After cooling to room temperature, as shown in Figure 4, a bright blue-yellow liquid crystal texture was presented. After irradiation with 365-nm ultraviolet light at 0.5 mW/cm2 for 1 minute, the liquid crystal texture was observed to turn blue. Then, the liquid crystal texture turned blue-yellow under the action of heat at 80°C.

This embodiment 2 also uses the photochromic luminescent liquid crystal C2 as a smart material. Due to its apparent color, triple display effects of photoluminescence and liquid crystal texture and rapid photoisomerization, it is used as a smart material in high-end anti-counterfeiting, optical sensing, data storage, high-resolution imaging and other high-tech fields.

Embodiments 3 to 8

They are respectively a photochromic luminescent liquid crystal and preparation and application. Their steps are basically the same as those in Example 1, except that the process parameters involved in the preparation and application are different, as shown in Table 1:

Table 1 List of process parameters in Examples 2 to 7

The other contents of Examples 3 to 8 are the same as those of Example 1.

The photochromic light-emitting liquid crystal structure involved in Example 3 is:

The photochromic light-emitting liquid crystal structure involved in Example 4 is:

The photochromic light-emitting liquid crystal structure involved in Example 5 is:

The photochromic light-emitting liquid crystal structure involved in Example 6 is:

The photochromic light-emitting liquid crystal structure involved in Example 7 is:

The photochromic light-emitting liquid crystal structure involved in Example 8 is:

Embodiments 9 to 14

They are respectively a photochromic luminescent liquid crystal and preparation and application. Their steps are basically the same as those in Example 1, except that the process parameters involved in the preparation and application are different, as shown in Table 2:

Table 2 List of process parameters in Examples 8 to 13

The contents of other parts of Examples 9 to 14 are the same as those of Example 1.

The photochromic light-emitting liquid crystal structure involved in Example 9 is:

The photochromic light-emitting liquid crystal structure involved in Example 10 is:

The photochromic light-emitting liquid crystal structure involved in Example 11 is:

The photochromic light-emitting liquid crystal structure involved in Example 12 is:

The photochromic light-emitting liquid crystal structure involved in Example 13 is:

The photochromic light-emitting liquid crystal structure involved in Example 14 is:

Embodiment 15

The difference between Example 15 and Example 1 and Example 2 is that the chain length of the linking primitive is different.

Where n=5.

The preparation process is:

5.45 g of a pyridine derivative containing a photochromic moiety in a molar ratio of 1:1:1 2.41 g tridentate primary ligand and 4.21 g of PtCl ₂ (DMSO) ₂ were added to a three-necked flask, ventilated three times, and 100 ml of anhydrous acetonitrile and 1.29 g of N,N-diisopropylethylamine as a catalyst were added under N ₂ atmosphere, and refluxed and stirred overnight for coordination reaction. After the system was cooled to room temperature, it was filtered and the filter cake was washed with acetonitrile three times to obtain a yellow solid precipitate (yield 68%), which was the photochromic luminescent liquid crystal C15.

The photochromic luminescent liquid crystal C15 was placed between two thin glass slides and the liquid crystal texture was observed under a polarizing microscope. When heated to 120°C, C15 was in an isotropic liquid state with no texture. When cooled to room temperature, as shown in Figure 5, it was difficult for C15 to produce liquid crystal texture by self-assembly, and only partial liquid crystal texture could be produced by friction.

The liquid crystal texture of the photochromic light-emitting liquid crystal C15 in Example 15 is difficult to appear, and it is difficult to present an excellent triple display function.

The photochromic luminescent liquid crystals C3, C6, C7, C8, C12, and C13 prepared in Examples 3, 6, 7, 8, 12, and 13 of the present invention present an apparent color under natural light, self-assemble to present a liquid crystal texture under a polarizing microscope, and have luminescent behavior after being excited by visible light; under the action of ultraviolet light or heating, the structures of these luminescent liquid crystal molecules can undergo reversible isomerization, and under the action of ultraviolet light or heating, the apparent color of these liquid crystal molecules, the liquid crystal texture presented under a polarizing microscope, and the luminescent behavior after being excited by visible light can all undergo reversible changes. Due to its triple display effects of apparent color, photoluminescence, and liquid crystal texture, and rapid photoisomerization, it is used as an intelligent material in high-tech fields such as high-end anti-counterfeiting, optical sensing, data storage, and high-resolution imaging.

The liquid crystal molecules of Examples 4, 5, 9, 10, 11, 14, and 15, due to the alkyl chain length of the connecting group in the liquid crystal molecules, are not only difficult to self-assemble to produce liquid crystal textures, but also have the luminescent properties of apparent color, photoluminescence dual display effect, and rapid photoisomerization, and can also be used as smart materials in high-tech fields such as high-end anti-counterfeiting, optical sensing, data storage, and high-resolution imaging. Analyzing the reasons, the short chain length may be due to the fact that the molecules are twisted to a suitable degree to self-assemble to form liquid crystals, while the long chain may be conducive to the formation of liquid crystals, so the value of n in the preferred connecting group of the present invention is an integer between 1, 2, or 8 to 10.

It will be easily understood by those skilled in the art that 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A photochromic luminescent liquid crystal is characterized in that the luminescent liquid crystal is a molecule obtained by coupling a platinum complex main body and a photochromic element through a connecting group, wherein,

The platinum complex body has one of the following structures:

Wherein the site marked is a linking site, R ₁ and R ₂ are each independently selected from hydrogen, methyl, ethyl, trifluoromethyl, t-butyl, nitro, amino and phenyl, R ₁ and R ₂ may be the same or different;

The photochromic primitive has one of the following structures:

wherein the site marked with x is a linking site, and R ₃ is hydrogen, methyl, nitro or phenyl;

the connecting group is one of the following structures:

Wherein the marked part is a linking site, and n is any integer from 1 to 10;

The luminescent liquid crystal has a luminescent behavior under the excitation of visible light, under the action of ultraviolet light, the structure of the luminescent liquid crystal can be isomerized, and the luminescent liquid crystal has no mutual crosstalk in the light excitation process of luminescence and photoisomerization reaction;

The luminescent liquid crystal presents apparent color under natural light, and has luminescent behavior after being excited by visible light; under the action of ultraviolet light or heating, the structure of the luminescent liquid crystal can be reversibly isomerized, and the apparent color and the luminescent behavior after being excited by visible light can be reversibly changed.

2. The luminescent liquid crystal according to claim 1, wherein the wavelength of the visible light is any wavelength of 420 to 500 nm; the wavelength of the ultraviolet light is any wavelength of 250-400 nanometers; the heating temperature is any temperature in 50-120 ℃.

3. A luminescent liquid crystal as claimed in claim 1, wherein n is 1,2 or an integer from 8 to 10.

4. A method of preparing a photochromic luminescent liquid crystal according to any one of claims 1 to 3, which is prepared by a coordination reaction of a tridentate primary ligand, pt (DMSO) ₂Cl₂ and a pyridine derivative containing the photochromic moiety; wherein the tridentate primary ligand has one of the following structures:

Wherein R ₄ and R ₅ are each independently selected from hydrogen, methyl, ethyl, trifluoromethyl, t-butyl, nitro, amino, and phenyl, and R ₄ and R ₅ may be the same or different;

The pyridine derivative containing the photochromic element is expressed as Wherein L is selected from L1 and L2 as described in claim 1; pr is selected from Pr-1, pr-2 and Pr-3 as defined in claim 1.

5. Use of a photochromic luminescent liquid crystal according to any one of claims 1 to 3 as a smart material in the field of high-end security, optical sensing, data storage or high resolution imaging technologies.

6. The use according to claim 5, wherein the photochromic luminescent liquid crystal is dissolved in a solvent to form an ink, written on a glass substrate, the apparent color, luminescent behavior and texture of the liquid crystal are changed by ultraviolet irradiation, and the triple encryption mode is applied to high-end security.