Electron donor-receptor type benzothiadiazole liquid luminescent material as well as preparation method and piezo-chromic application thereof

Abstract

The invention discloses an electron donor-acceptor type benzothiadiazole liquid luminescent material and a preparation method and piezo-chromic application thereof, the liquid luminescent material is a single-component compound with the following structural formula, an N, N-diphenylnaphthalene-1-amine group is used as an electron donor, a benzothiadiazole group is used as an electron acceptor, and the structural formula of the liquid luminescent material is shown in the specification. An electron donor-acceptor endows a benzothiadiazole group with a narrower excited state-ground state energy gap, Stokes displacement is greatly expanded, and the self-absorption problem is avoided; and meanwhile, the tetraethylene glycol chain space isolates the benzothiadiazole unit, so that pi-pi accumulation among conjugated molecules is hindered, and the problems of aggregation-induced quenching and photobleaching of condensed-phase fluorophores are inhibited. The luminescent material is oily, emits bright red light and is extremely sensitive to hydrostatic pressure; the piezochromic material has the characteristics of reversible piezochromic property, printable property, integratable property and the like due to the liquid property, is simple in preparation method and mild in reaction condition, and is a piezochromic material with great application potential.

Description

Technical Field

[0001] This invention belongs to the field of liquid luminescent materials technology, specifically relating to a benzothiadiazole liquid luminescent material with intramolecular charge transfer characteristics, and the application of this liquid luminescent material as a novel pressure-sensitive material. Background Technology

[0002] Under external mechanical stress, luminescent materials often exhibit significant changes in their luminescent properties. Pressure, as one such stressor, is widely present in nature and industrial applications. Changes in pressure can disrupt the original energy balance of a material, triggering a series of significant physicochemical transformations. For example, during compression, the interatomic spacing within the material decreases, and the crystal structure is reconstructed, further altering the material's luminescent properties. Pyrochromic materials have attracted considerable attention due to their unique advantages. These materials can produce significant color changes under external pressure or mechanical abrasion stimulation. Based on this characteristic, pyrochromic materials have been widely used in pressure-sensitive sensing and optical recording systems.

[0003] However, traditional varistor fluorescent materials also face numerous challenges, limiting their performance improvement and application expansion. Traditional varistor fluorescent materials mostly exist in crystalline or powder form. These solid-state materials often suffer from problems such as self-absorption, aggregation-induced quenching, and photodegradation. Furthermore, these solid-state materials typically have rigid structures, making them difficult to process and shape, and exhibiting poor varistor reversibility, thus failing to meet the diverse material processing performance requirements of emerging fields such as flexible electronics and wearable devices. Therefore, we have turned our attention to liquid-based luminescent materials, hoping to replace traditional solid-state luminescent materials.

[0004] Solvent-free organic liquids (SOLs) have attracted considerable attention as a novel class of functional oily compounds. The relatively free movement of oily dye molecules avoids key limitations such as aggregation quenching and photodegradation that restrict their applications. Furthermore, the solvent-free nature endows oily luminescent molecules with excellent photostability, demonstrating significant potential in the field of optoelectronic materials and devices. In addition, the excellent processing adaptability of liquid materials allows for the fabrication of flexible and foldable devices through simple coating, printing, or blending, showing broad application prospects in sensing, display, and lighting fields.

[0005] Currently, there are few reports on liquid pressure-sensitive materials that combine high luminous efficiency, strong processability, and excellent performance. Therefore, there is an urgent need to develop new pressure-sensitive liquid luminescent materials. Summary of the Invention

[0006] To address the problems of easy quenching of luminescence, photodegradation, and irreversible pressure response in existing crystalline or powdered pressure-sensitive luminescent materials, this invention provides an electron donor-acceptor type benzothiadiazole liquid luminescent material and its preparation method.

[0007] The molecular structure of the electron donor-acceptor type benzothiadiazole liquid luminescent material provided by this invention is shown below:

[0008]

[0009] The preparation method of the above-mentioned electron donor-acceptor type benzothiadiazole liquid luminescent material includes the following steps:

[0010] Step 1: Under N2 protection, compound I is added to an organic solvent and undergoes a Suzuki coupling reaction with 4-(N-(naphthyl-1-yl)-N-aniline-1-phenylboronic acid under alkaline conditions provided by potassium carbonate and catalysis by triphenylphosphine palladium to generate compound II.

[0011] The structural formula of compound I is as follows:

[0012]

[0013] The structural formula of 4-(N-(naphth-1-yl)-N-anilino)phenylboronic acid is as follows:

[0014]

[0015] The structural formula of compound II is as follows:

[0016]

[0017] Step 2: Add the compounds of formula II and formula III to an organic solvent, and under the catalysis of 1-hydroxybenzotriazole, add a dehydrating agent and triethylamine in sequence to generate an electron donor-acceptor type benzothiadiazole fluorescent compound.

[0018] The structural formula of compound III is as follows:

[0019]

[0020] The dehydrating agent is dicyclohexylcarbodiimide or 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride.

[0021] In step 1 above, the preferred molar ratio of compound I to 4-(N-(naphthyl-1-yl)-N-anilino)phenylboronic acid, potassium carbonate, and triphenylphosphine palladium is 1:1~2:5~10:0.05~0.1.

[0022] In step 1 above, the Suzuki coupling reaction is preferably carried out at the reflux temperature of the reaction solvent for 18-24 hours; the reaction solvent is a mixed solvent of 1,4-dioxane and water or a mixed solvent of tetrahydrofuran and water. Preferably, the volume ratio of 1,4-dioxane or tetrahydrofuran to water in the mixed solvent is 1:0.1-0.2.

[0023] In step 2 above, the preferred molar ratio of the compound of formula II to the compound of formula III, the dehydrating agent, triethylamine, and 1-hydroxybenzotriazole is 1:1.5-2.5:1-2:2-3:0.5-1.

[0024] Furthermore, in step 2 above, the reaction is first carried out in an ice bath for 0.5 to 1 hour, and then at 20 to 40 °C for 16 to 24 hours.

[0025] In step 2 above, the organic solvent is preferably either dichloromethane or tetrahydrofuran.

[0026] On the other hand, this invention also provides the application of the aforementioned electron donor-acceptor type benzothiadiazole liquid luminescent material as a pressure-sensitive material. This liquid luminescent material appears as a bright red, oily, viscous liquid under sunlight. It exhibits almost no spontaneous flow when stationary, only showing slow flow characteristics when poured or subjected to external force. Under hydrostatic pressure, the fluorescence wavelength shows a clear linear relationship with the pressure; and under hydrostatic pressure, it exhibits a dual reversible response characteristic in both luminescence intensity and emission wavelength, with excellent reversible cycle count, making it a highly promising pressure-sensitive material. Therefore, it has significant application value in pressure sensing and information data storage and processing.

[0027] Compared with existing technologies, the present invention has the following advantages:

[0028] 1. This invention synthesizes an electron donor-acceptor type benzothiadiazole liquid luminescent material by using an N,N-diphenylnaphthyl-1-amine group as an electron donor, a benzothiadiazole group as a strong electron acceptor, and introducing a hydrophilic tetraethylene glycol chain as a flexible unit. In the excited state, this material undergoes intramolecular charge transfer, significantly broadening its Stokes shift and thus further enhancing its sensitivity to the microenvironment. Furthermore, the propeller-like structure of the N,N-diphenylnaphthyl-1-amine group suppresses fluorescence quenching caused by tight molecular aggregation, while the introduction of the tetraethylene glycol chain improves molecular fluidity, ultimately resulting in a viscous, oily morphology for the obtained electron donor-acceptor type benzothiadiazole material.

[0029] 2. The electron donor-acceptor type benzothiadiazole liquid luminescent material of the present invention is red transparent oil and has a photoluminescence quantum yield (PLQY) of up to 39.7%. This material retains the good fluidity and processability unique to liquid materials, and also has the luminescence sensitivity given by the DA system, effectively solving the pain points of poor reversibility and inconvenient processability of traditional pressure-sensitive materials.

[0030] 3. The electron donor-acceptor type benzothiadiazole liquid luminescent material prepared in this invention exhibits a good linear response between its fluorescence emission wavelength and the applied pressure value under hydrostatic pressure regulation, with a correlation coefficient of 0.999. After five pressure-relief cycles, the macroscopic morphology of the sample remained intact, and the fluorescence performance was basically consistent with the initial state without significant fluctuations. Compared with most molecular materials that are prone to irreversible conformational distortion or aggregation changes under hydrostatic pressure, this material exhibits complete reversibility and recovery ability in both wavelength and intensity, demonstrating excellent cycling stability. Attached Figure Description

[0031] Figure 1 These are the ultraviolet absorption and fluorescence emission spectra of the electron donor-acceptor type benzothiadiazole liquid luminescent material in different polar solvents in Example 1.

[0032] Figure 2 The image shows the differential scanning calorimetry (DSC) curve of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1.

[0033] Figure 3 The thermogravimetric analysis (TGA) curves of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1 are shown.

[0034] Figure 4 This is the X-ray diffraction (XRD) pattern of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1.

[0035] Figure 5 This is the ultraviolet absorption spectrum of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1 under hydrostatic pressure.

[0036] Figure 6 This is the fluorescence emission spectrum of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1 under hydrostatic pressure.

[0037] Figure 7 This is the fluorescence emission spectrum of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1 under hydrostatic pressure relief.

[0038] Figure 8 These are visible light and fluorescence images of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1 under different hydrostatic pressures.

[0039] Figure 9 This is the photostability spectrum of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1.

[0040] Figure 10 It is a linear fitting curve between the fluorescence wavelength and hydrostatic pressure of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1.

[0041] Figure 11 The results are from the pressure-decompression cycle test of the electron donor-acceptor type benzothiadiazole liquid luminescent material in Example 1. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below with reference to the accompanying drawings and embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the invention and should not be construed as specific limitations thereof.

[0043] Example 1

[0044] Step 1: After deoxygenating 50 mL of tetrahydrofuran with N2 for 30 min, 194.31 mg (0.75 mmol) of compound I, 379.904 mg (1.12 mmol) of 4-(N-(naphthyl-1-yl)-N-aniline)phenylboronic acid, 69 mg (0.06 mmol) of triphenylphosphine palladium, 829.24 mg (6 mmol) of potassium carbonate, and 8 mL of ultrapure water were added sequentially. The mixture was heated to 60 °C and refluxed for 24 h with stirring. After the reaction was complete, the mixture was cooled to room temperature, the solvent was evaporated, and the mixture was washed with dichloromethane. The precipitate was dissolved in methanol, and 0.1 mol / L hydrochloric acid aqueous solution was added dropwise until the pH reached 3-4. The precipitate was filtered, dried, and then an orange-red powder, namely compound II, was obtained, with a yield of 70%.

[0045]

[0046]

[0047] The characterization results of the obtained compound II are as follows: 1H NMR (600 MHz, CDCl3, TMS): δ (ppm) 8.64-8.63 (d, 2H, Ar-H), 7.98-7.88 (m, 4H, Ar-H), 7.88-7.83 (m, 2H, Ar-H), 7.54-7.48 (m, 2H, Ar-H), 7.43-7.39 (m, 2H, Ar-H), 7.29-7.27 (m, 2H, Ar-H), 7.23-7.22 (m, 2H, Ar-H), 7.11-7.04 (m, 2H, Ar-H); Mass Spectrometry ESI-MS m / z: Molecular formula C 29 H 19 N3O2S, theoretical value 472.1198 ([MH]) - ); Experimental value 472.1127 ([MH]) - ).

[0048] Step 2: 170 mg (0.36 mmol) of compound II, 69 mg (0.36 mmol) of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl), and 48.63 mg (0.36 mmol) of 1-hydroxybenzotriazole (HOBt) were dissolved in 10 mL of dichloromethane until fully dissolved. After 30 min on ice, 285 mg (0.54 mmol) of compound III and 0.1 mL (0.72 mmol) of triethylamine were slowly added. The mixture was then kept on ice for another 30 min before the ice bath was removed, and the reaction was continued at room temperature for 24 h. After the reaction was complete, most of the solvent was removed by vacuum distillation. The crude product was obtained using a mixed solvent of ethyl acetate and methanol as the mobile phase (V). 乙酸乙酯 :V 甲醇 = 10:1), silica gel was used as the stationary phase for column chromatography separation and purification, followed by a mobile phase of a mixed solvent of chloroform and methanol (V 三氯甲烷 :V 甲醇 = 10:1), silica gel was used as the stationary phase for column chromatography separation and purification again, the solvent was removed by vacuum distillation, and after drying, a bright red oily liquid was obtained, namely the electron donor-acceptor type benzothiadiazole liquid luminescent material, with a yield of 55%.

[0049]

[0050] The characterization results of the obtained electron donor-acceptor type benzothiadiazole liquid luminescent material are as follows: 1H NMR (600MHz, CDCl3, TMS): δ (ppm) 9.72-9.70(d, 1H, CONH), 8.63-8.61(d, 1H, ArH), 7.99-7.77(m, 6H, ArH), 7.54-7.46(m, 2H, ArH), 7.43-7.38(m,2H, ArH), 7.28-7.24(m, 2H, ArH), 7.21-7.19(d, 2H, ArH), 7.12-7.01(t, 3H, ArH), 5.06-5.01(m, 1H,CHNH), 4.38-4.36(m, 2H, CH2CH2OCO), 4.20-4.18(m, 2H, CH2CH2OCO), 3.78-3.45 (m, 28H, OCH2CH2O), 3.37-3.36 (d, 6H, OCH3), 2.64-2.53 (m, 2H, COOCH2CH2), 2.51-2.40 (m, 1H, COOCH2CH2), 2.29-2.20 (m, 1H, COOCH2CH2); APCI-MS mass spectrometry m / z: molecular formula C 52 H 62 N4O 13 S, theoretical value 983.4034 ([M+H]) + ); Experimental value 983.4112 ([M+H] + ).

[0051] The aforementioned electron donor-acceptor type benzothiadiazole liquid luminescent material was dissolved in organic solvents of different polarities to prepare dilute solutions with a concentration of 50 μM. Subsequently, at room temperature, UV-Vis absorption spectra in different organic solvents were collected using a JASCO UV spectrophotometer. The UV light sources were xenon and tungsten lamps. The tests were conducted using a four-way quartz cuvette with a diameter of 1 cm. The results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the maximum absorption peak of the luminescent material is between 447 and 469 nm in organic solvents of different polarities. The ultraviolet absorption spectrum is less affected by the properties of the solvent, that is, the ground state properties of the luminescent material are basically unaffected by the polarity of the solvent.

[0052] The fluorescence emission spectra of the above-mentioned electron donor-acceptor type benzothiadiazole liquid luminescent material in different solvents were measured using an Edinburgh FLS 980 single-photon counting time-resolved fluorescence spectrometer. The results are as follows: Figure 1 As shown. By Figure 1It can be seen that as the solvent polarity increases, the emission of the luminescent material exhibits a significant solvent effect, and the Stokes shift is continuously broadened, indicating that the solvent polarity can tune the excited state of the liquid luminescent material to the intramolecular charge transfer state.

[0053] The thermal properties, stability, and crystal structure of the aforementioned electron donor-acceptor type benzothiadiazole liquid luminescent material were characterized. Differential scanning calorimetry (DSC) curves were measured using a Discovery DSC250. The test conditions were 10℃ / min, and the temperature range was -80℃ to 80℃. The test results are as follows: Figure 2 As shown. Thermal stability was tested using a Themys One thermogravimetric analyzer under the following conditions: 20℃ / min; temperature range 30–1000℃; carrier gas N2. The test results are as follows. Figure 3 As shown. Phase analysis was performed using a Bruker D8 Advance X-ray diffractometer, and the results are shown in the figure. Figure 4 .

[0054] Depend on Figure 2 As can be seen, the glass transition temperature (Tg) of this luminescent material is -29.84℃, and the hydrophilic tetraethylene glycol chains hinder crystallization, making this luminescent material a liquid material that can be directly processed. Figure 3 It is evident that the initial decomposition temperature of this luminescent material is 335.90℃, indicating that the material maintains structural integrity and thermal stability below this temperature. Figure 4 It is evident that the luminescent material exhibits only one broadened and diffuse diffraction peak, and no sharp, elongated characteristic diffraction peaks were observed, proving that the luminescent material is a processable liquid material.

[0055] The properties of the aforementioned electron donor-acceptor type benzothiadiazole liquid luminescent material were studied using a diamond anvil cell as a controllable means of hydrostatic pressure. The experimental setup employed a pair of diamond anvil cells, each with a diameter of 400 μm, sealed with T301 stainless steel gaskets. The gaskets were pre-compressed to a thickness of 40 μm, and then laser-drilled to create 180 μm diameter holes, forming a working chamber for sample placement. During sample encapsulation, the sample was encapsulated together with a ruby ​​sphere used for pressure calibration, providing hydrostatic pressure to the target system. Daphne 7474 was used as the pressure transfer medium (PTM). This PTM did not affect the testing process. After sample loading, the sealing of the sample chamber and the position of the ruby ​​sphere were verified to ensure no misalignment or leakage.

[0056] The absorption properties of this liquid material were tested using a deuterium halide light source that emits stable white light. The white light was focused onto the sample area within a diamond anvil cell (DAC), and the transmitted beam signal was collected. Figure 5 As shown, during the hydrostatic pressurization process, as the pressure gradually increases, the characteristic absorption peak of the sample exhibits a significant red shift, and the corresponding optical band gap gradually widens with increasing pressure.

[0057] Subsequently, steady-state fluorescence of the liquid luminescent material was tested. A 378 nm optical fiber connected to a diode-pumped solid-state (DPSS) laser was used as the excitation source for photoluminescence (PL) testing, and data were collected using an OceanOptics QE65000 spectrometer. The test results are as follows: Figure 6 As shown, during hydrostatic pressurization, the fluorescence emission peak exhibits a significant redshift: the emission wavelength shift is significant, indicating a sensitive response to pressure. Figure 7 As shown, under hydrostatic pressure reduction, the emitted wavelength and intensity also recover to the initial atmospheric pressure, exhibiting good resilience.

[0058] PL microscopy images of this liquid luminescent material were captured using a Canon EOS 5D Mark II camera mounted on a Nikon Eclipse Ti-U microscope. All images were recorded under the same exposure time and light intensity conditions. Figure 8 As shown, during hydrostatic pressurization, the color of the sample gradually changes from orange-yellow to deep red under sunlight, a change that is clearly visible to the naked eye; when the sample is excited by laser, its color shows a gradual change from orange-red to deep red, reflecting the material's potential for visualization applications.

[0059] The photostability of this liquid luminescent material was tested using an Edinburgh FLS 980 single-photon counting time-resolved fluorescence spectrometer, such as... Figure 9 As shown, the fluorescence signal remained stable during 3000 s of continuous testing, with no significant attenuation or photobleaching. This demonstrates that the liquid luminescent material exhibits excellent resistance to photobleaching and stability.

[0060] Subsequently, a quantitative linear fitting was performed on the dependence of the fluorescence emission wavelength of the liquid luminescent material on hydrostatic pressure. The fitting results are as follows: Figure 10 As shown in the figure. The fitting results show that the fluorescence wavelength of this material exhibits an ideal linear relationship with the hydrostatic pressure, and the fitting coefficient Rf is [value missing]. 2 The linearity is as high as 0.999. For pressure-sensitive materials, a good linear relationship is the core prerequisite for achieving accurate pressure detection. This liquid luminescent material is of great significance for the development of fluorescent sensing materials that can accurately quantify hydrostatic pressure.

[0061] Finally, the liquid luminescent material was subjected to a pressure-decompression cycle test. Figure 11As shown, in five hydrostatic pressure pressurization-depressurization cycles, the liquid luminescent material exhibits excellent cyclic stability: each time the pressure is depressurized to 0 GPa, both its fluorescence emission wavelength and luminescence intensity recover to their initial states. After five cycles, the material retains its initial morphology, without irreversible morphological damage caused by repeated pressurization, demonstrating highly reversible pressure response behavior and stable cycle repeatability. Compared to most molecules that are prone to irreversible conformational distortion or aggregation state changes under hydrostatic pressure, the liquid luminescent material of this invention can simultaneously achieve complete recovery of both wavelength and intensity, exhibiting stable performance advantages.

Claims

1. An electron donor-acceptor type benzothiadiazole liquid luminescent material, characterized in that... The molecular structure of the liquid luminescent material is shown below: 。 2. A method for preparing the electron donor-acceptor type benzothiadiazole liquid luminescent material according to claim 1, characterized in that... Includes the following steps: Step 1: Under N2 protection, compound I is added to the reaction solvent and undergoes a Suzuki coupling reaction with 4-(N-(naphth-1-yl)-N-aniline)phenylboronic acid under alkaline conditions provided by potassium carbonate and catalysis of triphenylphosphine palladium to generate compound II. The structural formula of compound I is as follows: The structural formula of 4-(N-(naphth-1-yl)-N-anilino)phenylboronic acid is as follows: The structural formula of compound II is as follows: Step 2: Add the compounds of formula II and formula III to an organic solvent, and under the catalysis of 1-hydroxybenzotriazole, add a dehydrating agent and triethylamine in sequence to react and generate an electron donor-acceptor type benzothiadiazole liquid luminescent material. The structural formula of compound III is as follows: The dehydrating agent is dicyclohexylcarbodiimide or 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride.

3. The method for preparing the electron donor-acceptor type benzothiadiazole liquid luminescent material according to claim 2, characterized in that: In step 1, the molar ratio of the compound of formula I to 4-(N-(naphthyl-1-yl)-N-anilino)phenylboronic acid, potassium carbonate, and triphenylphosphine palladium is 1:1~2:5~10:0.05~0.

1.

4. The method for preparing the electron donor-acceptor type benzothiadiazole liquid luminescent material according to claim 2, characterized in that: In step 1, the Suzuki coupling reaction is carried out at the reflux temperature of the reaction solvent for 18 to 24 hours; the reaction solvent is a mixed solvent of 1,4-dioxane and water or a mixed solvent of tetrahydrofuran and water.

5. The method for preparing the electron donor-acceptor type benzothiadiazole liquid luminescent material according to claim 4, characterized in that: The volume ratio of 1,4-dioxane or tetrahydrofuran to water in the mixed solvent is 1:0.1 to 0.

2.

6. The method for preparing the electron donor-acceptor type benzothiadiazole liquid luminescent material according to claim 2, characterized in that: In step 2, the molar ratio of the compound of formula II to the compound of formula III, the dehydrating agent, triethylamine, and 1-hydroxybenzotriazole is 1:1.5-2.5:1-2:2-3:0.5-1.

7. The method for preparing the electron donor-acceptor type benzothiadiazole liquid luminescent material according to claim 2, characterized in that: In step 2, the reaction is first carried out in an ice bath for 0.5 to 1 hour, and then at 20 to 40 °C for 16 to 24 hours.

8. The method for preparing the electron donor-acceptor type benzothiadiazole liquid luminescent material according to claim 2, characterized in that: In step 2, the organic solvent is either dichloromethane or tetrahydrofuran.

9. Use of the electron donor-acceptor type benzothiadiazole liquid luminescent material according to claim 1 as a piezochromic material.

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