A strong lyotropic color change and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative, its preparation method and application

Abstract

The application belongs to the technical field of stimuli-responsive fluorescent materials, and discloses a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement, and a preparation method and application thereof. The intermediate product is obtained by mixing 3-dimethylaminobenzhydrazide, acyl chloride and a solvent for reaction; and the 1,3,4-oxadiazole derivative is obtained by mixing the intermediate product and phosphorus oxychloride for reaction. The molecule prepared by the application can distinguish different polar solvents and is also sensitive to protons. With the addition of TFA, the fluorescence emission peak is blue-shifted and enhanced, and the fluorescence quantum efficiency reaches 69.8% after acidification. The solid thin film can also exhibit good pH response, and the thin film is blue-shifted from yellow-green light emission to blue light emission and the fluorescence is enhanced after acid fumigation. The molecule of the application is stable after protonation, exhibits acid-induced fluorescence enhancement property, is beneficial to improve the sensitivity of pH detection, and has important roles in the fields of medical care, environmental monitoring and industrial processes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stimuli-responsive fluorescent materials, and particularly relates to a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement and a preparation method and application thereof. BACKGROUND

[0002] Polarity is an important parameter in chemistry and biology, and plays a crucial role. Compared with many traditional tools, fluorescent probes are still the most commonly used means of polarity detection in vitro and biological systems, because they have the advantages of simple operation, high selectivity and sensitivity, real-time monitoring, non-invasive and high spatial and temporal resolution. Among them, D-A type organic conjugated small molecules are also widely used in polarity detection due to their solventochromic characteristics. Lin et al. (YIN J, PENG M, MAY, et al. Rational design of a lipid-droplet-polarity based fluorescent probe for potential cancer diagnosis[J]. Chemical Communications, 2018, 54(85): 12093-12096.) synthesized a D-A type molecule CTPA, which detects cancer by detecting the polarity of lipid droplets. The probe includes an electron donor triphenylamine group and an electron acceptor coumarin. Due to the ICT process, CTPA produces a significant red-shifted emission peak and weak fluorescence in high-polarity media. Nagano et al. (NAGANO H. S., Y. U., H. K. et al. Design and Synthesis of a Library of BODIPY-Based Environmental Polarity Sensors Utilizing Photoinduced Electron-Transfer-Controlled Fluorescence ON / OFF Switching[J]. Journal of the American Chemical Society, 2007, 129: 5597-5604.) studied a probe based on photoinduced electron transfer mechanism sensitive to polarity, with fluoroboron dipyrryl as the fluorescent group. The probe can distinguish low polarity and high polarity by the intensity of fluorescence, and is widely used in polarity detection. Chen et al. (L. Li, Y. Xu, Y. Chen, et al. A family of push-pull bio-probes for tracking lipid droplets in living cells with the detection of heterogeneity and polarity[J]. Analytica Chimica Acta, 2020, 1096: 166-173.) designed and synthesized a family of bio-probes LDP1-LDP4 with push-pull structure and excellent solventochromic effect. These probes all show specificity and selectivity to environmental polarity.However, the existing research on the determination of polarity size is limited, and a wider range of polarity detection probes is needed, so the development of organic conjugated small molecules with strong ICT properties is needed.

[0003] In addition, many acidic waste materials are generated in life and production, which not only harm the environment, but also have certain effects on the human body. For example, trifluoroacetic acid is a volatile acid, which can cause strong irritation to the respiratory tract if inhaled, and can also cause harm to the body. If it drops on the surface of the skin, it will be absorbed by the skin and also have adverse effects on the body. Hydrochloric acid is usually a chemical agent with strong irritation and volatility, and has strong corrosive and volatile properties, and can accumulate chronically. Contact with hydrochloric acid can cause certain harm and chronic disease to the human body. The existing methods for detecting acid using different fluorescent probes mostly have defects such as complex operation method, long reaction time, and low sensitivity. Therefore, a detection method that is simple to operate, rapid to detect, and has high sensitivity to acid is needed.

[0004] In organic light-emitting diodes (OLEDs), blue, as one of the three primary colors in full-color display, has always been the focus of the industry. Materials with deep blue light emission not only can achieve a wider color gamut, but also can effectively reduce the power consumption of displays and lighting devices. Developing stable deep blue organic fluorescent materials not only can achieve efficient blue light emission as a light-emitting layer, but also can achieve stable red and green phosphorescent emission as a doped host material, so it has a broad prospect. At present, there are many mature red and green light-emitting materials on the market, but stable and inexpensive deep blue light-emitting materials are still lacking, and there are still many difficulties in developing efficient deep blue light-emitting materials. At the same time, especially in the wavelength range of 405-470 nm, blue light has inherent antibacterial effects without the need for external photosensitizers. In addition, the harm of blue light to mammalian cells is much smaller than that of ultraviolet radiation, and blue light can regulate multi-cell behaviors involving cell-to-cell communication through blue light receptors in bacteria, and inhibit the formation of biofilms, thereby enhancing photoinactivation.

[0005] Therefore, it is an urgent problem for those skilled in the art to develop an organic small molecule material with strong ICT properties that has acid-induced fluorescence enhancement and produces deep blue emission. SUMMARY

[0006] The purpose of the present application is to provide a 1,3,4-oxadiazole derivative with strong solvatochromism and acid-induced fluorescence enhancement, as well as a preparation method and application thereof, to solve the problem of low intramolecular charge transfer strength of existing D-A conjugated organic small molecules and the problem of acid-induced fluorescence quenching in information encryption materials.

[0007] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0008] The application provides a preparation method of a strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative, which comprises the following steps:

[0009] (1) mixing 3-dimethylaminobenzhydrazide, acyl chloride and a solvent to perform a reaction to obtain an intermediate product;

[0010] (2) mixing the intermediate product and phosphorus oxychloride to perform a reaction to obtain the strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative;

[0011] In step (1), the acyl chloride is terephthaloyl chloride or isophthaloyl chloride.

[0012] Preferably, in the preparation method of the strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative, the molar ratio of 3-dimethylaminobenzhydrazide to acyl chloride in step (1) is 2-2.5:1.

[0013] Preferably, in the preparation method of the strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative, the reaction temperature in step (1) is 20-30 DEG C, and the reaction time is 5-16 h.

[0014] Preferably, in the preparation method of the strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative, the amount ratio of 3-dimethylaminobenzhydrazide to the solvent in step (1) is 1-4 g:100-300 mL.

[0015] Preferably, in the preparation method of the strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative, the amount ratio of the intermediate product to phosphorus oxychloride in step (2) is 0.5-5 g:40-80 mL.

[0016] Preferably, in the preparation method of the strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative, the reaction temperature in step (2) is 150-200 DEG C, and the reaction time is 36-72 h.

[0017] The application further provides a strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative prepared by the preparation method.

[0018] The application further provides application of the strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative in polarity detection, acid detection or information encryption transmission.

[0019] According to the technical scheme, compared with the prior art, the application has the following beneficial effects:

[0020] (1)The 1,3,4-oxadiazole derivatives prepared by the present application can distinguish different polar solvents, and the fluorescence emission peak has a red shift of 120nm from cyclohexane to tetrahydrofuran, realizing the change from blue-violet to amber, the color change in different polarity is clear, the detection range is wide, the detection is sensitive, and it has important significance for the detection of polarity.

[0021] (2)The 1,3,4-oxadiazole derivative film after acid fumigation emits blue light from yellow-green light emission, and the fluorescence is enhanced, which is a kind of excellent blue light material. The prior art such as Li et al. (LI Z, LI C, XU Y, et al. Nonsymmetrical Connection of Two Identical Building Blocks: Constructing Donor-Acceptor Molecules as Deep Blue Emitting Materials for Efficient Organic Emitting Diodes [J]. The Journal of Physical Chemistry Letters, 2019, 10(4): 842-847.) reported a blue-emitting material PlmPI with a non-symmetrical structure of two identical groups. By non-symmetrical connection, the HOMO and LUMO are distributed on two conjugated groups, respectively, and the molecule shows strong emission ability and is used to make high-efficiency deep blue devices. The molecule of the present application combines protons to achieve deep blue light emission and enhancement, has more excellent efficiency, and proposes a new idea of blue light emission, realizing high-efficiency blue light emission.

[0022] (3) In terms of proton detection, the molecule of the present application is stable in substance after protonation, and with the addition of trifluoroacetic acid, the fluorescence emission peak is blue-shifted and enhanced, emitting ultraviolet light invisible to the human eye under ultraviolet light, improving the confidentiality in the information encryption transmission process. While existing molecules will undergo fluorescence quenching after protonation, for example, Xu et al. (ZHANG Q, YANG L, HAN Y, et al. ApH-sensitive ESIPT molecule with aggregation-induced emission and tunable solid-state fluorescence multicolor for anti-counterfeiting and food freshness detection[J]. Chemical Engineering Journal, 2022, 428: 130986.) reported an AIE fluorescent molecule (BTSA) with multiple pH responses. The emission wavelength and intensity can be switched by different pH stimuli to achieve multi-color emission, which is successfully used for anti-counterfeiting and food freshness detection; for another example, Müller's group (CINAR R, NORDMANN J, DIRKSENE, et al. Domino synthesis of protochromic“ON-OFF-ON”luminescent 2-styrylquinolines[J]. Organic & Biomolecular Chemistry, 2013, 11(16): 2597.) reported a new pH-responsive compound BN of donor-acceptor quinoline, which contains two basic nitrogen atoms, aniline groups and pyridine-type quinoline nitrogen. In CH2Cl2solution, it emits yellow-green fluorescence, and under the action of low-concentration acid, the quinoline nitrogen atom is protonated, and the fluorescence is completely quenched, becoming a deep purple compound BN-H + Compared with existing acid-induced fluorescence quenching molecules, the molecule of the present application has the property of acid-induced fluorescence enhancement, which makes up for the inconvenience of signal detection caused by fluorescence quenching in information encryption materials, and is more conducive to signal detection. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description.

[0024] Figure 1 Nuclear magnetic resonance hydrogen spectrum of L-mDMAOXDBEN prepared in Example 1 in deuterated chloroform solution;

[0025] Figure 2 NMR spectrum of B-mDMAOXDBEN prepared in Example 2 in deuterated chloroform solution;

[0026] Figure 3 Normalized UV-Vis absorption spectra of L-mDMAOXDBEN prepared in Example 1 in different solvents; where BEN is benzene, TOL is toluene, DCM is dichloromethane, CHL is chloroform, EA is ethyl acetate, THF is tetrahydrofuran;

[0027] Figure 4 Normalized fluorescence emission spectra of L-mDMAOXDBEN prepared in Example 1 in different solvents; where CHEX is cyclohexane, BEN is benzene, CHL is chloroform, DCM is dichloromethane, TOL is toluene, EA is ethyl acetate, THF is tetrahydrofuran;

[0028] Figure 5 Normalized UV-Vis absorption spectra of B-mDMAOXDBEN prepared in Example 2 in different solvents; where BEN is benzene, CHL is chloroform, DCM is dichloromethane, EA is ethyl acetate, TOL is toluene, THF is tetrahydrofuran;

[0029] Figure 6 Normalized fluorescence emission spectra of B-mDMAOXDBEN prepared in Example 2 in different solvents; where CHEX is cyclohexane, BEN is benzene, TOL is toluene, CHL is chloroform, DCM is dichloromethane, THF is tetrahydrofuran, EA is ethyl acetate;

[0030] Figure 7 UV-Vis absorption spectra of L-mDMAOXDBEN prepared in Example 1 in chloroform solution with different volumes of TFA added;

[0031] Figure 8 Fluorescence emission spectra of L-mDMAOXDBEN prepared in Example 1 in chloroform solution;

[0032] Figure 9 Fluorescence emission spectra of L-mDMAOXDBEN prepared in Example 1 in chloroform solution with different volumes of TFA added;

[0033] Figure 10 Fluorescence emission spectra of L-mDMAOXDBEN prepared in Example 1 in tetrahydrofuran solution with different volumes of hydrochloric acid added;

[0034] Figure 11 UV-Vis absorption spectra of B-mDMAOXDBEN prepared in Example 2 in chloroform solution with different volumes of TFA added;

[0035] Figure 12 Fluorescence emission spectra of B-mDMAOXDBEN prepared in Example 2 in chloroform solution;

[0036] Figure 13 Fluorescence emission spectra of B-mDMAOXDBEN prepared in Example 2 in chloroform solution with different volumes of TFA added;

[0037] Figure 14 Pictures of L-mDMAOXDBEN film under 365 nm ultraviolet light irradiation after being acid fumigated for different times;

[0038] Figure 15 Fluorescence emission spectra of L-mDMAOXDBEN film before and after protonation;

[0039] Figure 16 Pictures of L-mDMAOXDBEN prepared in Example 1 under 365 nm ultraviolet light irradiation in different polar solvents; CHEX is cyclohexane, BEN is benzene, TOL is toluene, CHL is chloroform, DCM is dichloromethane, EA is ethyl acetate, and THF is tetrahydrofuran;

[0040] Figure 17 Excitation spectra of L-mDMAOXDBEN prepared in Example 1 with different volumes of TFA added;

[0041] Figure 18 Excitation spectra of B-mDMAOXDBEN prepared in Example 2 with different volumes of TFA added;

[0042] Figure 19 Schematic diagram of a chloroform solution of L-mDMAOXDBEN prepared in Example 1 in information encryption transmission application;

[0043] Figure 20 Frontier molecular orbital distribution diagram, energy change, and HOMO-LUMO energy band gap schematic diagram of L-mDMAOXDBEN prepared in Example 1 and B-mDMAOXDBEN prepared in Example 2 in chloroform solution. DETAILED DESCRIPTION

[0044] The present application provides a preparation method of a 1,3,4-oxadiazole derivative with strong solvatochromism and acid-induced fluorescence enhancement, comprising the following steps:

[0045] (1) mixing 3-dimethylaminobenzhydrazide, acyl chloride, and a solvent to react to obtain an intermediate product;

[0046] (2) mixing the intermediate product and phosphorus oxychloride to react, to obtain the strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative.

[0047] In the present application, the acid chloride in step (1) is preferably terephthaloyl chloride or isophthaloyl chloride, and is further preferably terephthaloyl chloride.

[0048] In the present application, the molar ratio of 3-dimethylaminobenzhydrazide to acid chloride in step (1) is preferably 2-2.5:1, and is further preferably 2:1.

[0049] In the present application, the amount ratio of 3-dimethylaminobenzhydrazide to solvent in step (1) is preferably 1-4 g:100-300 mL, and is further preferably 1-3 g:120-200 mL, and is more preferably 2 g:150 mL.

[0050] In the present application, the solvent in step (1) is preferably tetrahydrofuran.

[0051] In the present application, the temperature of the reaction in step (1) is preferably 20-30℃, and is further preferably 22-27℃, and is more preferably 25℃; and the time of the reaction is preferably 5-16 h, and is further preferably 8-12 h, and is more preferably 8 h.

[0052] In the present application, the reaction in step (1) further comprises stirring.

[0053] In the present application, after the reaction in step (1) is completed, the process further comprises filtering, recrystallizing with methanol, and drying.

[0054] In the present application, the amount ratio of the intermediate product to phosphorus oxychloride in step (2) is preferably 0.5-5 g:40-80 mL, and is further preferably 0.8-3 g:50-70 mL, and is more preferably 0.93 g:50 mL.

[0055] In the present application, the temperature of the reaction in step (2) is preferably 150-200℃, and is further preferably 150-180℃, and is more preferably 150℃; and the time of the reaction is preferably 36-72 h, and is further preferably 40-72 h, and is more preferably 40 h.

[0056] In the present application, after the reaction in step (2) is completed, the process further comprises recrystallizing with ethanol, and drying.

[0057] The present application also provides a strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative prepared by the preparation method of the strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative.

[0058] This invention also provides an application of a strongly lyochromic and acid-fluorescent 1,3,4-oxadiazole derivative in polarity detection, acid detection, or encrypted information transmission.

[0059] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] Example 1

[0061] This embodiment provides a 1,3,4-oxadiazole derivative, the preparation method of which includes the following steps:

[0062] (1) Dissolve 1 g of 3-dimethylaminobenzoyl hydrazine in 150 mL of tetrahydrofuran, add terephthaloyl chloride (molar ratio of terephthaloyl chloride to 3-dimethylaminobenzoyl hydrazine 1:2), stir at room temperature for 8 h, filter, recrystallize with methanol, and dry to obtain a white solid;

[0063] (2) 0.93 g of white solid was placed in an Erlenmeyer flask, 50 mL of phosphorus oxychloride was added, and the mixture was refluxed at 150 °C for 40 h. The resulting mixed solution was poured into ice water to obtain a light green solid. The solid was recrystallized with ethanol and dried to obtain a 1,3,4-oxadiazole derivative with a yield of 58%, which was named L-mDMAOXDBEN.

[0064] The molecular synthesis process of L-mDMAOXDBEN prepared in this embodiment is as follows:

[0065]

[0066] The 1H NMR spectrum of L-mDMAOXDBEN prepared in deuterated chloroform solution in this embodiment is shown below. Figure 1 As shown. By Figure 1 It can be seen that the hydrogen atoms near the central benzene ring are around 8.30 ppm, the hydrogen atoms near the outer oxadiazole unit are around 7.56 ppm and 7.42 ppm, the hydrogen atoms near the dimethylamino benzene ring are around 6.98 ppm, and the hydrogen atoms on the dimethylamino are around 3.08 ppm.

[0067] Example 2

[0068] This embodiment provides a 1,3,4-oxadiazole derivative, the preparation method of which includes the following steps:

[0069] (1) Dissolve 1 g of 3-dimethylaminobenzoyl hydrazine in 150 mL of tetrahydrofuran, add isophthaloyl chloride (molar ratio of isophthaloyl chloride to 3-dimethylaminobenzoyl hydrazine 1:2), stir at room temperature for 8 h, filter, recrystallize with methanol, and dry to obtain a white solid;

[0070] (2) 0.93 g of white solid was placed in an Erlenmeyer flask, 50 mL of phosphorus oxychloride was added, and the mixture was refluxed at 150 °C for 40 h. The resulting mixed solution was poured into ice water to obtain a light green solid. The solid was recrystallized with ethanol and dried to obtain a 1,3,4-oxadiazole derivative with a yield of 71.8%, which was named B-mDMAOXDBEN.

[0071] The molecular synthesis process of B-mDMAOXDBEN prepared in this embodiment is as follows:

[0072]

[0073]

[0074] The 1H NMR spectrum of B-mDMAOXDBEN prepared in deuterated chloroform solution in this embodiment is shown below. Figure 2 As shown. By Figure 2 It can be seen that the hydrogen atoms on the central benzene ring are around 8.89 ppm, 8.34 ppm, and 7.74 ppm, respectively; the hydrogen atoms on the outer side near the oxadiazole unit are around 7.54 ppm; the hydrogen atoms on the benzene ring near the dimethylamino group are around 7.43 ppm and 7.02 ppm; and the hydrogen atoms on the dimethylamino group are around 3.09 ppm.

[0075] Example 3

[0076] This embodiment provides a 1,3,4-oxadiazole derivative, the preparation method of which includes the following steps:

[0077] (1) Dissolve 2g of 3-dimethylaminobenzoylhydrazine in 300mL of tetrahydrofuran, add terephthaloyl chloride (molar ratio of terephthaloyl chloride to 3-dimethylaminobenzoylhydrazine 1:2.5), stir at room temperature for 12h, filter, recrystallize with methanol, and dry to obtain a white solid;

[0078] (2) 2g of white solid was placed in an Erlenmeyer flask, 60mL of phosphorus oxychloride was added, and the mixture was refluxed at 200℃ for 72h. The resulting mixed solution was poured into ice water to obtain a light green solid. The solid was recrystallized with ethanol and dried to obtain a 1,3,4-oxadiazole derivative with a yield of 57%.

[0079] Example 4

[0080] This embodiment provides a 1,3,4-oxadiazole derivative, the preparation method of which includes the following steps:

[0081] (1) Dissolve 2g of 3-dimethylaminobenzoylhydrazine in 300mL of tetrahydrofuran, add isophthaloyl chloride (molar ratio of isophthaloyl chloride and 3-dimethylaminobenzoylhydrazine 1:2.5), stir at room temperature for 12h, filter, recrystallize with methanol, and dry to obtain a white solid;

[0082] (2) 2g of white solid was placed in an Erlenmeyer flask, 60mL of phosphorus oxychloride was added, and the mixture was refluxed at 200℃ for 72h. The resulting mixed solution was poured into ice water to obtain a light green solid. The solid was recrystallized with ethanol and dried to obtain a 1,3,4-oxadiazole derivative with a yield of 70%.

[0083] The normalized UV-Vis absorption spectra of L-mDMAOXDBEN prepared in Example 1 in different solvents are as follows: Figure 3 As shown, the normalized fluorescence emission spectra in different solvents are as follows: Figure 4 As shown. By Figure 3 and Figure 4 It can be seen that L-mDMAOXDBEN molecules in different solvents (1×10⁻⁶) -5 The position of the UV absorption spectrum in the L-mDMAOXDBEN (mol / L) solution shows only a slight shift of a few nanometers, indicating that the electronic structure of the ground state and the Frank-Condon excited state are not significantly different. The UV absorption spectrum of the L-mDMAOXDBEN molecule has approximately two absorption peaks, at 314 nm and 370 nm. Compared to the UV absorption spectrum, the fluorescence emission spectrum of L-mDMAOXDBEN shows more significant changes. The fluorescence emission peak of the L-mDMAOXDBEN molecule is located at 402 nm in cyclohexane, and at 522 nm in the relatively polar tetrahydrofuran solution. The maximum fluorescence emission peak red-shifts by 120 nm from the nonpolar cyclohexane to the polar tetrahydrofuran. This implies the existence of an intramolecular charge-transfer state, and that the dipole moment of the charge-transfer excited state is much larger than that of the ground state.

[0084] The normalized UV-Vis absorption spectra of B-mDMAOXDBEN prepared in different solvents in Example 2 are as follows: Figure 5 As shown, the normalized fluorescence emission spectra in different solvents are as follows: Figure 6 As shown. By Figure 5 and Figure 6 It can be seen that the B-mDMAOXDBEN molecule in different solvents (1×10⁻⁶) exhibits different properties. -5The position of the UV absorption spectrum of the B-mDMAOXDBEN molecule in chloroform solution does not change obviously, only a slight shift of a few nanometers, which indicates that the electronic structure of the ground state of the molecule does not change much from the electronic structure of the Franck-Condon excited state. The UV absorption spectrum of the B-mDMAOXDBEN molecule has two UV absorption peaks, at 270 nm and 353 nm. Compared with the UV absorption spectrum, the fluorescence emission spectrum of the B-mDMAOXDBEN molecule changes more obviously. The position of the fluorescence emission peak of the B-mDMAOXDBEN molecule in cyclohexane is at 394 nm, and the position of the fluorescence emission peak in the relatively polar tetrahydrofuran solution is at 460 nm. The fluorescence maximum emission peak red shifts by 66 nm from the non-polar cyclohexane to the polar tetrahydrofuran. This means that there is an intramolecular charge transfer state in the molecule, and the dipole moment of the charge transfer excited state of the molecule is much larger than that of the ground state.

[0085] The UV-Vis absorption spectrum of the L-mDMAOXDBEN molecule prepared in Example 1 in chloroform solution with different volumes of trifluoroacetic acid (TFA) added is shown in FIG. 1, the fluorescence emission spectrum in chloroform solution is shown in FIG. 2, the fluorescence emission spectrum in chloroform solution with different volumes of TFA added is shown in FIG. 3, and the fluorescence emission spectrum in tetrahydrofuran solution with different volumes of hydrochloric acid added is shown in FIG. 4. Figure 7 Figure 8 Figure 9 Figure 10 Figures 7-10 As can be seen from FIGS. 1 to 4, for the L-mDMAOXDBEN molecule dissolved in chloroform solution with a concentration of 1×10 -5 mol / L, and then different volumes (μL) of TFA added, the results show that the L-mDMAOXDBEN molecule has two absorption peaks in the UV absorption spectrum of the chloroform solution, at 324 nm and 382 nm. With the continuous addition of TFA, the absorption peak at 324 nm shows a trend of first decreasing, then increasing, and then decreasing again, and the absorption peak intensity at 382 nm gradually decreases without obvious movement, and an isosbestic point appears at 350 nm, which indicates that the L-mDMAOXDBEN molecule is gradually protonated with the addition of TFA. Compared with the UV absorption spectrum, the fluorescence emission spectrum changes more obviously. In the chloroform solution without TFA, the position of the fluorescence maximum emission peak is at 477 nm, and with the continuous addition of TFA, the fluorescence intensity at 477 nm gradually decreases until quenching, while in the near-ultraviolet region at 371 nm, a new fluorescence emission peak is produced, and the fluorescence intensity gradually increases with the continuous addition of TFA. When 50 μL of TFA is added, the fluorescence intensity reaches the strongest, and when more TFA is added, the fluorescence intensity begins to decrease until quenching. The same is true for the addition of hydrochloric acid. The fluorescence quantum efficiency of the L-mDMAOXDBEN molecule prepared by the direct method in the present application is 69.8% when 50 μL of TFA is added.​​​​

[0086] The UV-Vis absorption spectra of B-mDMAOXDBEN molecules prepared in Example 2 in chloroform solution with different volumes of TFA are shown in Figure 2, the fluorescence emission spectra of B-mDMAOXDBEN molecules in chloroform solution are shown in Figure 3, the fluorescence emission spectra of B-mDMAOXDBEN molecules in chloroform solution with different volumes of TFA are shown in Figure 4. Figure 11 Figure 12 Figure 13 Figures 11-13 -5 It can be seen from Figures 2-4 that, for B-mDMAOXDBEN molecules dissolved in chloroform solution with a concentration of 1 x 10 -2 mol / L, and then different volumes (μL) of TFA are added, the results show that the absorption peaks of the UV absorption spectra of B-mDMAOXDBEN molecules in chloroform solution are 281 nm and 353 nm. With the continuous addition of TFA, the absorption peak at 281 nm shows a trend of first decreasing, then increasing, and then decreasing again, and the absorption peak at 353 nm gradually disappears, without obvious movement, which indicates that B-mDMAOXDBEN molecules are gradually protonated with the addition of TFA. Compared with the UV absorption spectra, the fluorescence emission spectra have more obvious changes. In the chloroform solution without TFA, the position of the maximum fluorescence emission peak is at 434 nm, and with the continuous addition of TFA, the fluorescence intensity at 434 nm gradually decreases until quenching, while at 350 nm in the near-ultraviolet region, a new fluorescence emission peak is produced, and the fluorescence intensity increases with the continuous addition of TFA. When 14 μL of TFA is added, the fluorescence intensity reaches the strongest, and when more TFA is added, the fluorescence intensity begins to decrease until quenching.

[0087] L-mDMAOXDBEN prepared in Example 1 was prepared into L-mDMAOXDBEN film by the following method: L-mDMAOXDBEN was dissolved in chloroform solvent with a concentration of 5 x 10 -2 M, and then uniformly spin-coated on a quartz glass to remove the solvent to obtain L-mDMAOXDBEN film. The pictures of L-mDMAOXDBEN film after acid fumigation for different times under 365 nm ultraviolet lamp irradiation are shown in Figure 6, and the fluorescence emission spectra of L-mDMAOXDBEN film before and after protonation are shown in Figure 7. Figure 14 Figure 15 Figure 14 Figure 15 It can be seen from Figures 6-7 that, before fumigation, the L-mDMAOXDBEN film emits a light yellow light under 365 nm ultraviolet lamp, and after fumigation with TFA for 5 s, the film under the ultraviolet lamp becomes blue-violet light, and the blue-violet light gradually increases with the continuous fumigation.​​​​​​​​​​​​​​​​​​​The luminescence of the film before and after protonation can be more intuitive. Before protonation, the fluorescence emission spectrum of the film has a low peak intensity. After TFA fumigation for 5s, the fluorescence emission spectrum of the film has a blue shift and the intensity is obviously improved. After fumigation for 10s, the fluorescence intensity of the film continues to increase to the strongest. This shows that after protonation, the luminescence performance of the device is more excellent, and bright blue-violet light can be emitted. However, the fumigation time should be controlled to avoid affecting the efficiency of the device.

[0088] The pictures of L-mDMAOXDBEN prepared in Example 1 under 365nm ultraviolet light irradiation in different polar solvents are shown in Figure 16 As can be seen from Figure 16 , in cyclohexane with lower polarity, the solution presents blue-violet light invisible in the ultraviolet region, in benzene and toluene, the solution presents sky blue, in chloroform, the solution presents lake blue, in dichloromethane, the solution presents light yellow, in ethyl acetate, the solution presents dark yellow, and in tetrahydrofuran, the solution presents amber. The red shift of fluorescence emission spectrum caused by intramolecular charge transfer can be clearly distinguished in different polar solvents.

[0089] The excitation spectra of L-mDMAOXDBEN molecules prepared in Example 1 added with different volumes (volume unit: μL) of TFA are shown in Figure 17 The excitation spectra of B-mDMAOXDBEN molecules prepared in Example 2 added with different volumes (volume unit: μL) of TFA are shown in Figure 18 As can be seen from Figure 17 and Figure 18 , after adding TFA, the excitation spectra of the two molecules only change in intensity, not in position, indicating that no new substance is generated in the protonation process.

[0090] The schematic diagram of the chloroform solution of L-mDMAOXDBEN prepared in Example 1 in information encryption transmission application is shown in Figure 19 As can be seen from Figure 19 , using the chloroform solution (1×10 -4 mol / L) of L-mDMAOXDBEN, the word “zhong” is written on the filter paper, and under 365nm ultraviolet light, it presents yellow-green fluorescence. After fumigation with TFA for 10s, it produces near-ultraviolet light (371nm) with higher intensity. Since the emission after protonation is in the invisible light region, the naked eye cannot see it, and instruments can be used for detection, which is better for encryption.

[0091] The frontier molecular orbital distribution diagram, energy change and HOMO-LUMO energy band gap of L-mDMAOXDBEN prepared in Example 1 and B-mDMAOXDBEN prepared in Example 2 in chloroform solution are shown in Figure 20As shown in the figure. Gaussian 16 quantum chemistry program was used for the theoretical calculations, with CAM-B3LYP functionals and 6-31G(d,p) basis sets selected. Chloroform solvent was used as the PCM solvent model. The excitation energies (E, eV), oscillator strengths (f), and main orbital compositions of the main contributing energy levels of L-mDMAOXDBEN and B-mDMAOXDBEN molecules before and after protonation are shown in Table 1.

[0092] Table 1. Excitation energies (E, eV), oscillator strengths (f), and main orbital compositions of the major contributing energy levels of L-mDMAOXDBEN and B-mDMAOXDBEN molecules before and after protonation.

[0093]

[0094]

[0095] Depend on Figure 20 As shown in Table 1, after protonation, the fluorescence emission peak blue shifts due to the increased gap between HOMO and LUMO; after protonation, the probability of S0-S1 transition increases, resulting in enhanced fluorescence emission.

[0096] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a strongly lyochromic and acid-fluorescently enhanced 1,3,4-oxadiazole derivative, characterized in that, Includes the following steps: (1) 3-Dimethylaminobenzoylhydrazine, acyl chloride and solvent are mixed and reacted to obtain an intermediate product; (2) The intermediate product and phosphorus oxychloride are mixed and reacted to obtain the 1,3,4-oxadiazole derivative with strong solubility-induced color change and acid-induced fluorescence enhancement. Wherein, the acyl chloride in step (1) is terephthaloyl chloride or isophthaloyl chloride; The structural formula of the 1,3,4-oxadiazole derivative is shown below: or .

2. The method for preparing a strongly lyochromic and acid-enhanced 1,3,4-oxadiazole derivative according to claim 1, characterized in that, In step (1), the molar ratio of 3-dimethylaminobenzoyl hydrazine and acyl chloride is 2~2.5:

1.

3. The method for preparing a strongly lyochromic and acid-fluorescently enhanced 1,3,4-oxadiazole derivative according to claim 2, characterized in that, The reaction temperature in step (1) is 20~30℃; the reaction time is 5~16h.

4. The method for preparing a strongly lyochromic and acid-fluorescently enhanced 1,3,4-oxadiazole derivative according to claim 1 or 2, characterized in that, In step (1), the ratio of 3-dimethylaminobenzoyl hydrazine to solvent is 1~4g:100~300mL.

5. The method for preparing a strongly lyochromic and acid-fluorescently enhanced 1,3,4-oxadiazole derivative according to claim 4, characterized in that, The ratio of intermediate product to phosphorus oxychloride in step (2) is 0.5~5g:40~80mL.

6. The method for preparing a strongly lyochromic and acid-fluorescently enhanced 1,3,4-oxadiazole derivative according to claim 5, characterized in that, The reaction temperature in step (2) is 150~200℃; the reaction time is 36~72h.

7. A 1,3,4-oxadiazole derivative with strong lyochromic and acid-induced fluorescence enhancement prepared by the method of any one of claims 1 to 6.

8. The application of the 1,3,4-oxadiazole derivative of claim 7, which exhibits strong lyochromic and acid-induced fluorescence enhancement, in polarity or acid detection for non-disease diagnostic and therapeutic purposes.

9. The application of the 1,3,4-oxadiazole derivative with strong lyochromic and acid-induced fluorescence enhancement as described in claim 7 in encrypted information transmission.

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