Multifunctional Benzothiadiazole Schiff Base Luminescent Liquid Crystal and Its Preparation and Application

Abstract

The compounds of the present invention have benzothiadiazole as the central core. By introducing six alkyl chains at the ends of benzaldehyde / salicylaldehyde Schiff base compounds, multifunctional luminescent liquid crystal compounds BTDim1 / n and BTDim2 / n are prepared, as shown in the figure below. BTDim1 / n and BTDim2 / n exhibit a tetragonal columnar liquid crystal phase and a hexagonal columnar liquid crystal phase, respectively. Compound BTDim2 / n can be applied to a light-emitting liquid crystal display (LE-LCD). In addition, BTDim2 / n can form a gel in a specific solvent. Using the suspension adsorption technique, compound BTDim2 / n can be used for latent fingerprint imaging. In addition, the salicylaldehyde Schiff base unit in the molecule of compound BTDim2 / n has the function of chelating metal ions, and it can coordinate and bind with aluminum ions in a 1:2 form, with high specificity. The multifunctional characteristics of such materials make them promising for wide applications in real life.

Description

Technical Field

[0001] The present invention relates to the field of multifunctional light-emitting liquid crystal materials, in particular to benzothiadiazole Schiff base light-emitting liquid crystals and their preparation methods and applications in light-emitting liquid crystal displays (LE-LCDs), organic gels, fingerprint recognition, and aluminum ion (Al 3+ ) chemical sensors. Background Art

[0002] Light-emitting liquid crystals (LE-LCs) combine inherent light-emitting properties with the unique assembly order and self-healing properties of liquid crystals, and have important application values in the fields of anisotropic light-emitting diodes, polarization lasers, information storage, sensors, and one-dimensional semiconductors. In particular, after shearing, their property of emitting linearly polarized light or circularly polarized light can be used for the efficient and simple preparation of bright light-emitting liquid crystal displays (LE-LCDs).

[0003] Organic gels are semi-solid gels presented after organic gelators spontaneously aggregate and self-assemble into an ordered network structure in a solvent, preventing the flow of solvent molecules. They can swell and retain a large amount of liquid phase, absorb and release substances, and respond to various physical and chemical stimuli such as temperature, light, pH, and mechanical deformation. Nevertheless, compared with hydrogels, there are fewer research reports on organic gels. The research on organic gels is crucial.

[0004] Fingerprints are an important type of physical evidence, unique and lifelong for each person, and play an important role in personal identification. Latent fingerprints are ubiquitous at crime scenes. In daily forensic practice, appropriate methods are needed to visualize them to determine the source of the fingerprints. Fluorescent imaging of latent fingerprints has the advantages of high contrast, high sensitivity, good selectivity, and less dependence on instruments. Therefore, it is of great significance to develop fingerprint imaging materials with good light-emitting properties.

[0005] Aluminum, as the third most abundant metal element on Earth, has a wide range of applications in many fields. Al 3+ also exists in natural waters and can enter the human body through food and drinking water. Excessive Al 3+ will affect the pulmonary system and may cause other serious health hazards. Finding a basic, rapid, sensitive, and selective method for detecting excessive Al 3+ in the environment and biological systems is of great significance.

[0006] Schiff base compounds have multifunctionality and structural diversity. Schiff base derivatives based on salicylaldehyde are a class of multi-stimulus-responsive fluorescent materials and have large Stokes shifts, aggregation-induced emission (AIE) characteristics, liquid crystallinity, and photochromic properties, etc. Schiff base compounds have been widely studied and applied in many fields of materials science.

[0007] 2,1,3-Benzothiadiazole (BTD) dyes exhibit strong fluorescence in both solution and solid states. As a typical electron acceptor, the BTD structural unit has been used to construct a large number of π-conjugated organic fluorescent functional materials. The construction of emissive liquid crystals still poses a great challenge due to the existence of aggregation-caused quenching phenomenon. Currently, there is no reported research on the preparation of emissive liquid crystals by combining Schiff base and BTD and their related applications. Summary of the Invention

[0008] The present invention provides a preparation method of BTD benzaldehyde / salicylaldehyde Schiff base emissive liquid crystals, and their applications in LE-LCD, gels, latent fingerprint imaging, and Al 3+ fluorescence recognition.

[0009] The present invention is achieved through the following technical solutions.

[0010] Benzaldehyde / salicylaldehyde Schiff base liquid crystal compounds, called BTDim1 / n and BTDim2 / n, are characterized in that the compounds have the following structural formula:

[0011] wherein, when X is H and n is 12, 14, or 16, the compound is BTDim1 / n; or when X is OH and n is 12, 14, or 16, the compound is BTDim2 / n.

[0012] The benzaldehyde / salicylaldehyde Schiff base liquid crystal compounds are characterized in that the preparation steps of the compounds are as follows:

[0013] 1. Step 1, methyl gallate reacts with bromoalkane (bromododecane to bromohexadecane) under the conditions of N,N-dimethylformamide (DMF) and potassium carbonate (K2CO3) at 90 °C for 12 hours to obtain compound 1 / n;

[0014] 2. Step 2, dissolve the compound 1 / n obtained in Step 1 in methanol, add potassium hydroxide (KOH), react at 70 °C for 6 hours, and adjust the pH to 2 with dilute hydrochloric acid to obtain compound 2 / n;

[0015] 3. Step 3, dissolve the compound 2 / n obtained in Step 2 and 4-hydroxybenzaldehyde or 2,4-dihydroxybenzaldehyde in anhydrous dichloromethane, add 1.5 equivalents of dicyclohexylcarbodiimide and a catalytic amount of 4-dimethylaminopyridine under ice bath, warm up to 35 °C, stir and react for 12 hours. After the reaction is completed, extract with dichloromethane, and the crude product is separated and purified by column chromatography to obtain compounds 3 / n and 4 / n;

[0016] 4. Step 4: Dissolve 4,7-dibromo-2,1,3-benzothiadiazole and 4-aminophenylboronic acid in tetrahydrofuran (THF). Subsequently, add the potassium carbonate solution dissolved in water to the THF solution. Under nitrogen protection, deoxygenate by ultrasound for 15 minutes. Add a catalytic amount of tetrakis(triphenylphosphine)palladium ((Pd(PPh3)4)), and stir and reflux at 78 °C for 12 hours. Remove the organic solvent under reduced pressure. The crude product is separated and purified by column chromatography to obtain pure 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dianiline;

[0017] 5. Step 5: Dissolve the compound 3 / n or 4 / n obtained in Step 3 and the compound 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dianiline obtained in Step 4 in ethanol, add two drops of glacial acetic acid, react at 80 °C for 12 hours, then cool to room temperature, precipitate the product, filter, wash with ethanol, and recrystallize with petroleum ether to obtain pure BTDim1 / n and BTDim2 / n.

[0018] Among them, the compound 1 / n is 1 / 12, 1 / 14, 1 / 16 in sequence, which are methyl 3,4,5-tridodecyloxybenzoate, methyl 3,4,5-tritetradecyloxybenzoate, and methyl 3,4,5-trihexadecyloxybenzoate respectively;

[0019] The compound 2 / n is 2 / 12, 2 / 14, 2 / 16 in sequence, which are 3,4,5-tridodecyloxybenzoic acid, 3,4,5-tritetradecyloxybenzoic acid, and 3,4,5-trihexadecyloxybenzoic acid respectively;

[0020] The compound 3 / n is 3 / 12, 3 / 14, 3 / 16 in sequence, which are 4-formylphenyl-3,4,5-tridodecyloxybenzoate, 4-formylphenyl-3,4,5-tritetradecyloxybenzoate, and 4-formylphenyl-3,4,5-trihexadecyloxybenzoate respectively;

[0021] The compound 4 / n is 4 / 12, 4 / 14, 4 / 16 in sequence, which are 4-formyl-3-hydroxyphenyl-3,4,5-tridodecyloxybenzoate, 4-formyl-3-hydroxyphenyl-3,4,5-tritetradecyloxybenzoate, and 4-formyl-3-hydroxyphenyl-3,4,5-trihexadecyloxybenzoate respectively;

[0022] The compound BTDim1 / n exhibits an obvious tetragonal columnar liquid crystal phase under a polarized light microscope (POM) and an X-ray diffractometer (XRD), while the compound BTDim2 / n is a hexagonal columnar liquid crystal phase. In addition, BTDim2 / n can also be used as a bright-emitting liquid crystal material to prepare LE-LCD devices, gel materials, potential fingerprint imaging, and a fluorescence probe for identifying Al 3+ and

[0023] Attached drawings of the specification

[0024] Figure 1 is the preparation route of the present invention;

[0025] Figure 2 is the columnar liquid crystal texture diagram of the compound BTDim1 / 14 observed under POM;

[0026] Figure 3 is the columnar liquid crystal texture diagram of the compound BTDim2 / 14 observed under POM;

[0027] Figure 4 is the XRD diagram of the compound BTDim1 / 14 at 120 °C;

[0028] Figure 5 is the XRD diagram of the compound BTDim2 / 14 at 160 °C;

[0029] Figure 6 is the SEM diagram of the gel formed by the compound BTDim2 / 14 in dichloromethane;

[0030] Figure 7 is the polarized fluorescence spectrum of the light-emitting liquid crystal cell of the compound BTDim2 / 14 and the mixed liquid crystal in the state of the electric field being turned off;

[0031] Figure 8 is the patterned LE-LCD device of the liquid crystal mixture of the compound BTDim2 / 14 in the state of the electric field being turned off and the electric field being turned on;

[0032] Figure 9 is the potential fingerprint fluorescence imaging of the compound BTDim2 / 14 on a glass substrate;

[0033] Figure 10 is the ultraviolet absorption spectrum and fluorescence emission spectrum diagram of the solution and film of the compound BTDim2 / 14;

[0034] Figure 11 is the change in the fluorescence spectrum after the compound BTDim2 / 14 responds to each metal ion;

[0035] Figure 12Effect of non-specific metal ions on the fluorescence response between BTDim2 / 14 and aluminum ions;

[0036] Figure 13 Job's curve of the coordination of compound BTDim2 / 14 with aluminum ions;

[0037] Figure 14 Linear relationship between the fluorescence intensity and the aluminum ion concentration after the response of compound BTDim2 / 14 to aluminum ions;

[0038] Figure 15 1H NMR characterization of compound BTDim1 / 14;

[0039] Figure 16 13C NMR characterization of compound BTDim1 / 14;

[0040] Figure 17 1H NMR characterization of compound BTDim2 / 14;

[0041] Figure 18 13C NMR characterization of compound BTDim2 / 14. Specific embodiments

[0042] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0043] Example 1: Preparation and characterization of benzaldehyde / salicylaldehyde Schiff base luminescent liquid crystal compounds BTDim1 / n and BTDim2 / n

[0044] According to Figure 1 the preparation route, the detailed implementation steps are as follows:

[0045] 1. Step 1: Take an appropriate amount of methyl gallate (10 mmol) and dissolve it in DMF. Add K2CO3 (40 mmol), heat to 90 °C, stir for 30 min, then add alkyl bromide (35 mmol). After reacting for 12 hours, quench the reaction with water, extract three times with ethyl acetate, and use petroleum ether as the eluent to purify by crude silica gel column chromatography. Obtain white solid 1 / n, yield: 92%;

[0046] The reaction formula is:

[0047]

[0048] 2. Step 2: Dissolve 1 / n (5 mmol) in anhydrous methanol, add potassium hydroxide (10 mmol), react at 70 °C for 6 hours, cool to room temperature, adjust the pH of the reaction solution to 2 by dropping dilute hydrochloric acid, filter, and wash with methanol to obtain white solid 2 / n, yield: 95%;

[0049] The reaction formula is as follows:

[0050]

[0051] 3. Step 3: Weigh 2 / n (1 mmol) and 4-hydroxybenzaldehyde (1.1 mmol) or 2,4-dihydroxybenzaldehyde (1.1 mmol) and dissolve them in dry dichloromethane (30 mL). Cool the reaction mixture to 0 °C in an ice bath, and slowly add dicyclohexylcarbodiimide (1.2 mmol). Then add a catalytic amount of 4-dimethylaminopyridine, remove the cooling bath, and stir at 35 °C for 12 h. Filter to remove the solid, and remove the organic solvent in vacuo. The residue is separated and purified by chromatography, and the eluents are petroleum ether:dichloromethane 5:8 and petroleum ether:dichloromethane 1:1 respectively.

[0052] Obtain 3 / n or 4 / n, yield: 90% and 85%;

[0053] The reaction formula is as follows:

[0054]

[0055] The NMR data of compound 3 / 14 (4-formylphenyl 3,4,5-tris(tetradecyloxy)benzoate) are as follows: 1 HNMR(CDCl3, 400 MHz), δ (ppm): 9.96 (s, 1H, Ar-CHO), 7.92 - 7.90 (d, 2H, J = 7.60 Hz, 2Ar-H), 7.33 - 7.31 (d, 4H, J = 7.6 Hz, 4Ar-H), 4.01 - 3.96 (m, 6H, 3ArOCH2), 1.80 (m, 6H, 3ArOCH2CH2), 1.41 (m, 6H, 3ArOCH2CH2CH2), 1.19 (m, 60H, 30CH2), 0.82 (t, 9H, 3CH3);

[0056] The NMR data of compound 4 / 14 (4-formyl-3-hydroxyphenyl 3,4,5-tris(tetradecyloxy)benzoate) are as follows: 11H NMR (CDCl3, 400 MHz), δ (ppm): 11.29 (s, 1H, Ar-OH), 9.92 (s, 1H, Ar-CHO), 7.66 - 7.64 (d, 1H, J = 8.40 Hz, Ar-H), 7.40 (s, 1H, Ar-H), 6.93 - 6.91 (m, 1H, Ar-H), 6.91 - 6.89 (d, 1H, J = 8.40 Hz, Ar-H), 4.10 - 4.05 (m, 6H, 3ArOCH2), 1.87 (m, 6H, 3ArOCH2CH2), 1.52 (m, 6H, 3ArOCH2CH2CH2), 1.28 (m, 60H, 30CH2), 0.91 (t, 9H, 3CH3);

[0057] 4. Step 4: Dissolve 4,7-dibromo-2,1,3-benzothiadiazole (1 mmol) and 4-aminophenylboronic acid (2.1 mmol) in 15 mL of THF. Then add 5 mL of an aqueous solution of K2CO3 (5 mmol) thereto. Under N2 protection, degas by ultrasound for 15 minutes. Quickly add a catalytic amount of (Pd(PPh3)4). Then reflux the reaction at 78 °C for 12 hours. Monitor the reaction by thin-layer chromatography. After the reaction is completed, add 20 mL of water to the reaction system, and extract three times with dichloromethane. Combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, distill off the organic solvents under reduced pressure. The crude product is purified by column chromatography, and the eluent is petroleum ether:ethyl acetate = 5:2 to obtain a yellow solid 4,4'-(benzo[c][1,2,5]

[0058] thiadiazole-4,7-diyl)dianiline, yield: 80%;

[0059] The reaction formula is as follows:

[0060]

[0061] The NMR data of 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dianiline are as follows: 1 1H NMR (CDCl3, 400 MHz), δ (ppm): 6.80 (d, J = 8.0, 6H, 6ArH), 6.65 (d, J = 8.0, 4H, 4ArH), 3.50 (s, 4H, 2Ar-NH2);

[0062] 5. Step 5: Add 3 / n (0.3 mmol) or 4 / n (0.3 mmol) to 20 mL of anhydrous ethanol (EtOH), heat until dissolved, then add 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)diphenylamine (0.15 mmol), add 2 drops of glacial acetic acid (ACOH), stir at 80 °C and reflux for 12 h. Perform hot filtration, wash the precipitate with ethanol several times, and recrystallize with petroleum ether. Obtain the target compounds, dark green solid BTDim1 / n and orange solid BTDim2 / n, with yields: 75% and 86%;

[0063] The reaction formula is as follows:

[0064]

[0065] The NMR data of BTDim1 / 14 is as Figure 15 、 Figure 16 shown below: 1 H NMR(CDCl3, 400 MHz), δ(ppm): 8.51 (s, 2H, 2Ar-CH=N), 8.01 - 7.99 (d, 4H, J = 8.40 Hz, 4Ar-H), 7.98 - 7.96 (d, 4H, J = 8.40 Hz, 4Ar-H), 7.79 (s, 2H, 2Ar-H), 7.36 - 7.34 (d, 8H, J = 6.80 Hz, 8Ar-H), 7.29 - 7.27 (d, 4H, J = 8.40 Hz, 4Ar-H), 4.02 - 3.98 (m, 12H, 6ArOCH2), 1.79 (m, 12H, 6ArOCH2CH2), 1.43 (m, 12H, 6ArOCH2CH2CH2), 1.29 (m, 120H, 60CH2), 0.83 (t, 18H, 6CH3). 13 C NMR(CDCl3; 100 MHz): 164.8, 159.5, 154.2, 153.6, 153.0, 152.0, 143.2, 135.2, 133.9, 132.7, 130.2, 130.1, 127.9, 123.6, 122.4, 121.2, 108.6, 73.6, 69.3, 32.0, 30.4, 29.8, 29.7, 29.7, 29.6, 29.4, 29.4, 29.3, 26.1, 22.7, 14.1;

[0066] The NMR data of BTDim2 / 14 is as Figure 17 、 Figure 18 shown below: 11H NMR (CDCl3, 400 MHz), δ (ppm): 13.66 (s, 2H, 2Ar-OH), 8.78 (s, 2H, 2Ar-CH=N), 8.12 - 8.10 (d, 4H, J = 8.40 Hz, 4Ar-H), 7.89 (s, 2H, 2Ar-H), 7.53 - 7.51 (d, 6H, J = 8.40 Hz, 6Ar-H), 7.43 (s, 4H, 4Ar-H), 6.95 - 6.94 (d, 2H, J = 4.0 Hz, 2Ar-H), 6.88 - 6.86 (d, 2H, J = 8.40 Hz, 2Ar-H), 4.11 - 4.07 (m, 12H, 6ArOCH2), 1.90 (m, 12H, 6ArOCH2CH2), 1.54 (m, 12H, 6ArOCH2CH2CH2), 1.39 (m, 120H, 60CH2), 0.92 (t, 18H, 6CH3). 13 13C NMR (CDCl3; 100 MHz): 164.5, 162.7, 162.0, 155.0, 154.1, 153.0, 148.2, 143.2, 136.1, 133.4, 132.6, 130.4, 128.0, 123.5, 121.5, 117.3, 113.2, 110.8, 108.7, 73.6, 69.3, 32.0, 30.4, 29.8, 29.7, 29.7, 29.7, 29.6, 29.4, 29.4, 29.3, 26.1, 26.1, 22.7, 14.1。

[0067] Among them, the compounds 1 / n are 1 / 12, 1 / 14, 1 / 16 in sequence, which are methyl 3,4,5-tridodecyloxybenzoate, methyl 3,4,5-tritetradecyloxybenzoate, and methyl 3,4,5-trihexadecyloxybenzoate respectively;

[0068] The compounds 2 / n are 2 / 12, 2 / 14, 2 / 16 in sequence, which are 3,4,5-tridodecyloxybenzoic acid, 3,4,5-tritetradecyloxybenzoic acid, and 3,4,5-trihexadecyloxybenzoic acid respectively;

[0069] The compounds 3 / n are 3 / 12, 3 / 14, 3 / 16 in sequence, which are 4-formylphenyl 3,4,5-tridodecyloxybenzoate, 4-formylphenyl 3,4,5-tritetradecyloxybenzoate, and 4-formylphenyl 3,4,5-trihexadecyloxybenzoate respectively;

[0070] Compounds 4 / n are 4 / 12, 4 / 14, and 4 / 16 in sequence, which are 4-formyl-3-hydroxyphenyl-3,4,5-tridodecyloxybenzoate, 4-formyl-3-hydroxyphenyl-3,4,5-tritetradecyloxybenzoate, and 4-formyl-3-hydroxyphenyl-3,4,5-trihexadecyloxybenzoate respectively.

[0071] Example 2: Study on the optical properties of compound BTDim2 / 14

[0072] For the compound BTDim2 / 14 prepared by the above steps, the ultraviolet absorption spectrum and fluorescence emission spectrum of its THF solution (10 -5 M) and thin film state were studied. As Figure 10 shown, the maximum ultraviolet absorption wavelengths of compound BTDim2 / 14 in THF solution are 351 and 408 nm, the maximum ultraviolet absorption wavelengths in thin film state are 365 and 425 nm, the maximum fluorescence emission wavelengths in THF solution are 528 and 624 nm, and the maximum fluorescence emission wavelength in thin film state is 617 nm. The spectral energy gap of BTDim2 / 14 in THF solution is 3.12 eV, and the spectral energy gap in solid thin film state is 2.93 eV.

[0073] Example 3: Study on the liquid crystal properties of compounds BTDim1 / n and BTDim2 / n

[0074] Typical columnar liquid crystal textures ( Figure 2 , Figure 3 ) were observed for compounds BTDim1 / n and BTDim2 / n under a polarized light microscope (POM). XRD tests of the low-temperature columnar phases of compounds BTDim1 / 14 and BTDim2 / 14 showed that BTDim1 / n and BTDim2 / n form tetragonal and hexagonal lattice columnar phases with p4mm and p6mm symmetries respectively ( Figure 4 , Figure 5 ).

[0075] Table 1: Phase transition temperatures and lattice constants of compounds BTDim1 / n and BTDim2 / n

[0076]

[0077] Note: Cr: Crystal; Col squ / p4mm: Tetragonal columnar phase; Col hex / p6mm: Hexagonal columnar phase; Iso: Isotropic liquid.

[0078] Example 4: Study on the organogel properties of compounds BTDim1 / n and BTDim2 / n

[0079] The gelation test was carried out on the compounds of the present invention. For compounds BTDim1 / 14 and BTDim2 / 14, the ability to form gels in their different solvents (2.0 mg mL -1 ) was systematically tested, and the results are shown in Table 2. BTDim1 / 14 could not form gels in the listed solvents, while BTDim2 / 14 could obtain yellow fluorescent organic gels in dichloromethane, ethyl acetate and dioxane. This may be due to the combined action of π-π stacking and hydrogen bonds. Through SEM photographs Figure 6 It is shown that the formed gel is composed of a 3D network structure of partially helically wound fibers, with a diameter of about 20 - 600 nm and a length exceeding 5 μm.

[0080] Table 2: Gelation ability of compounds BTDim1 / 14 and BTDim2 / 14 in different solvents

[0081]

[0082] Note: S: solution; G: gel; P: precipitate

[0083] Example 5: Preparation of a light-emitting liquid crystal display device of compound BTDim2 / 14

[0084] Compound BTDim2 / 14 was mixed with a commercially available nematic liquid crystal (5CB) at a concentration of 0.5% (w / w) to study the dichroic ratio of its polarized emission spectrum. The results are as Figure 7 shown that the dichroic ratio of the mixture is 6.1. This indicates that the mixture can be used for the preparation of LE-LCDs. Letters TM were etched on the ITO glass layer of the liquid crystal cell, and the etched area is non-conductive. Then the prepared liquid crystal mixture was added to the liquid crystal cell with a capillary, and a UV lamp (365 nm) was used as a light source to irradiate the mixed material, and the change of fluorescence was detected with a polarizer whose transmission direction is parallel to the liquid crystal alignment direction. When the liquid crystal cell is in the off state of the external electric field, a bright orange image will appear under UV light irradiation. When an external electric field (1 KHz, 8 V) is applied to the liquid crystal cell, as Figure 8 shown, only the central area where the word "TM" is etched emits light, and the unetched area does not emit light. This proves that BTDim2 / n can be used for the preparation of light-emitting liquid crystal displays.

[0085] Example 6: Potential fingerprint imaging study of compound BTDim2 / 14

[0086] Based on the excellent solid-state fluorescence properties of compound BTDim2 / n, the suspension adsorption technique was used to apply compound BTDim2 / n to latent fingerprint imaging. Rub a clean finger on the greasy area of the face, and then gently press the finger on a glass substrate to obtain a fingerprint. Subsequently, 2 mg of compound BTDim2 / 14 was dissolved in 5 ml of THF, and 2 ml of water was added to form a suspension. The glass substrate was placed in the suspension. After 15 minutes, the substrate was taken out and the surface of the substrate was gently rinsed with pure water. Under irradiation with 365 nm ultraviolet light, as Figure 9 shown, a latent fingerprint image with bright yellow fluorescence can be obtained. Thus, the information at three levels (global level, local level, and fine level) of the latent fingerprint treated with the compound BTDim2 / 14 suspension can be well imaged under ultraviolet light.

[0087] Example 6: Spectral behavior and specificity study of the response of compound BTDim2 / 14 to aluminum ions

[0088] It has been reported that salicylaldehyde Schiff base compounds can coordinate with metal ions through N and OH units to enhance or weaken fluorescence, thereby achieving the function of detecting harmful metal ions. The recognition ability of BTDim2 / 14 in THF (1×10 -5 M) towards metal ions (Li + , K + , Ba 2+ , Cd 2+ , Pb 2+ , Hg 2+ , Mg 2+ , Cu 2+ , Ni 2+ , Cr 3+ , Fe 3+ , As 3+ , Al 3+ , 2.0-fold equivalents) was studied. As Figure 11 shown, only after adding Al 3+ did the emission spectrum change significantly. In the presence of Al 3+ , the emission color was red, and the fluorescence enhancement ability observed at 670 nm was 11 times that of BTDim2 / 14, indicating that BTDim2 / 14 has high fluorescence selectivity towards Al 3+ . Using fluorescence (Job's) curve analysis, as Figure 13 shown, the stoichiometric ratio of BTDim2 / 14 to Al 3+ was 1:2. The anti-interference test was carried out in a buffer solution, and the results were as Figure 12 shown, indicating that other metal ions had no obvious effect on the fluorescence intensity of the BTDim2 / 14 - Al 3+ system. The fluorescence titration method was used to determine the binding constant of BTDim2 / 14 to Al3+ Detection limit (LOD). In the THF solution of BTDim2 / 14, add Al 3+ The amount of ionic substance ranges from 0 to 2.5 equivalents until the fluorescence intensity no longer changes ( Figure 14 ), according to the change in the fluorescence intensity of Al 3+ , the LOD in THF is calculated to be 5.9×10 -6 M. Compound BTDim2 / n can be used as a fluorescence sensor for detecting Al 3+ ions in water.

[0089] Above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A multifunctional luminescent liquid crystal compound based on benzothiadiazole and salicylaldehyde Schiff base, characterized in that Has the following structural general formula: Wherein, X is OH, n is 12, 14, 16 respectively, and the compound is BTDim2 / n.

2. Use of the luminescent liquid crystal compound based on benzothiadiazole and salicylaldehyde Schiff base according to claim 1 as an organic liquid crystal material.

3. Use of the luminescent liquid crystal compound based on benzothiadiazole and salicylaldehyde Schiff base according to claim 1 in the preparation of a light-emitting liquid crystal display (LE-LCD).

4. Use of the luminescent liquid crystal compound based on benzothiadiazole and salicylaldehyde Schiff base according to claim 1 as an organic gel.

5. Use of the luminescent liquid crystal compound based on benzothiadiazole and salicylaldehyde Schiff base according to claim 1 for fluorescence imaging of latent fingerprints on a glass substrate.

6. Use of the luminescent liquid crystal compound based on benzothiadiazole and salicylaldehyde Schiff base according to claim 1 as a highly sensitive Al 3+ fluorescent probe.

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