1, 3, 4-oxadiazole derivative with strong solvatochromism and acid-induced fluorescence enhancement as well as preparation method and application of 1, 3, 4-oxadiazole derivative

Abstract

The invention belongs to the technical field of stimuli-responsive fluorescent materials, and discloses a 1, 3, 4-oxadiazole derivative with strong solvatochromism and acid-induced fluorescence enhancement as well as a preparation method and application of the 1, 3, 4-oxadiazole derivative. The preparation method comprises the following steps: mixing 3-dimethylaminobenzoyl hydrazine, acyl chloride and a solvent, and reacting to obtain an intermediate product; and mixing the intermediate product and phosphorus oxychloride, and reacting to obtain the 1, 3, 4-oxadiazole derivative. The prepared molecules can distinguish different polar solvents, and also have sensitive response to protons. With the addition of TFA, the fluorescence emission peak is blue-shifted and enhanced, and the fluorescence quantum efficiency after acidification reaches 69.8%. The solid film can also show good pH response, and after acid fumigation, the film shifts from yellow-green light emission to blue light emission, and fluorescence is enhanced. The protonated molecule is stable in property, shows an acid-induced fluorescence enhancement property, is beneficial to improving the sensitivity of pH detection, and plays an important role in the fields of medical care, environmental monitoring, industrial process and the like.

Description

Technical Field

[0001] The invention relates to the technical field of stimulus-responsive fluorescent materials, and in particular to a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement, and a preparation method and application thereof. Background Art

[0002] Polarity is an important parameter in chemistry and biology and plays a pivotal role. Compared with many traditional tools, fluorescent probes are still the most commonly used polarity detection methods in vitro and biological systems because of their advantages such as simple operation, high selectivity and sensitivity, real-time monitoring, non-invasiveness and high spatiotemporal resolution. Among them, DA-type organic conjugated small molecules are also widely used in polarity detection due to their solvent-induced color change characteristics. Lin et al. (YIN J, PENGM, 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 DA-type molecule CTPA to detect cancer by detecting polarity in 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 a highly polar medium. Nagano et al. (NAGANO HS, YU, HK 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 that is sensitive to polarity based on the photoinduced electron transfer mechanism using fluoroboron dipyrrole as a fluorescent group. The probe can distinguish low polarity from high polarity by the level of fluorescence intensity 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 inliving cells with the detection of heterogeneity and polarity [J]. Analytica Chimica Acta, 2020, 1096: 166-173.) designed and synthesized a series of biological probe families LDP1-LDP4 with push-pull structures and excellent solvent color change effects. These probes all showed specificity and selectivity for environmental polarity.However, existing research on the determination of polarity size is still limited, and a wider range of polarity detection probes need to be studied, so the development of organic conjugated small molecules with strong ICT properties is needed.

[0003] In addition, many acidic wastes are produced 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. If it is not inhaled, it will strongly irritate the respiratory tract and cause harm to the body. If it drips on the skin surface, it will be absorbed by the skin and will also have adverse effects on the body. Hydrochloric acid is usually an irritating and volatile chemical agent with strong corrosiveness and volatility, and can be accumulated chronically. Contact with hydrochloric acid will cause certain harm and chronic disease effects to the human body. Most of the existing methods for acid detection using different fluorescent probes have defects such as complicated operation methods, long reaction time, and low sensitivity. Therefore, a detection method that is simple to operate, rapid in detection, and can have high sensitivity recognition of 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 industry attention. Materials with deep blue light emission can not only achieve a wider color gamut, but also effectively reduce the power consumption of displays and lighting equipment. The development of stable deep blue organic fluorescent materials can not only achieve efficient blue light emission as a light-emitting layer, but also achieve stable red and green phosphorescence emission as a doping host material, so the prospects are broad. At present, many mature red and green light-emitting materials have appeared 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, blue light, especially in the wavelength range of 405 to 470 nm, has an inherent antibacterial effect and does not require the addition of exogenous photosensitizers. In addition, blue light is much less harmful to mammalian cells than ultraviolet irradiation. Blue light can regulate multicellular behaviors involving intercellular communication through blue light receptors in bacteria and inhibit the formation of biofilms, thereby enhancing photoinactivation.

[0005] Therefore, developing an organic small molecule material with strong ICT properties that can enhance acid-induced fluorescence and produce deep blue emission has become an urgent problem to be solved by those skilled in the art. Summary of the invention

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

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

[0008] The present invention provides a method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement, comprising the following steps:

[0009] (1) mixing 3-dimethylaminobenzoic acid hydrazide, acyl chloride and a solvent to react to obtain an intermediate product;

[0010] (2) mixing the intermediate product and phosphorus oxychloride to react, thereby obtaining the 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement;

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

[0012] Preferably, in the above method for preparing a strongly solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative, the molar ratio of 3-dimethylaminobenzoic acid hydrazide to acid chloride in step (1) is 2 to 2.5:1.

[0013] Preferably, in the above-mentioned method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement, the reaction temperature in step (1) is 20 to 30° C.; and the reaction time is 5 to 16 hours.

[0014] Preferably, in the above-mentioned method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement, the amount ratio of the 3-dimethylaminobenzoic acid hydrazide to the solvent in step (1) is 1-4 g: 100-300 mL.

[0015] Preferably, in the above-mentioned method for preparing a strongly solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative, the usage ratio of the intermediate product and phosphorus oxychloride in step (2) is 0.5-5 g: 40-80 mL.

[0016] Preferably, in the above-mentioned method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement, the reaction temperature in step (2) is 150-200° C.; and the reaction time is 36-72 h.

[0017] The invention also provides a method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromism and acid-induced fluorescence enhancement, and obtains a 1,3,4-oxadiazole derivative with strong solvatochromism and acid-induced fluorescence enhancement.

[0018] The present invention also provides a strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative for use in polarity detection, acid detection or information encryption transmission.

[0019] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The 1,3,4-oxadiazole derivative prepared by the present invention can distinguish solvents of different polarities. The fluorescence emission peak undergoes a red shift of 120 nm from cyclohexane to tetrahydrofuran, achieving a change from blue-purple to amber. The color changes clearly in different polarities, has a wide detection range, and is sensitive, which is of great significance for the detection of polarity.

[0021] (2) The 1,3,4-oxadiazole derivative film after acid fumigation has a blue shift from yellow-green light emission to blue light emission and fluorescence enhancement, which is a blue light material with excellent performance. 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 emission material PlmPI with an asymmetric structure connected by two identical groups, and HOMO and LUMO were distributed on two conjugated groups respectively through asymmetric connection. The molecule exhibited a strong emission ability and was used to make an efficient deep blue device. The molecule of the present invention achieves deep blue light emission and enhancement by combining protons, has a more excellent efficiency, proposes a new idea of ​​blue light emission, and realizes efficient blue light emission.

[0022] (3) In terms of proton detection, the molecular properties of the present invention are stable after protonation. With the addition of trifluoroacetic acid, the fluorescence emission peak blue-shifts and enhances, and emits ultraviolet light invisible to the human eye under ultraviolet light, thereby improving the confidentiality of information encryption transmission. However, existing molecules will undergo fluorescence quenching after protonation. For example, Xu et al. (ZHANG Q, YANG L, HANY, et al. A pH-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 responsiveness. Since the N atom on the imine structure in the benzothiazole group is protonated under acidic conditions, its emission wavelength and intensity can be switched in multiple ways by different pH stimuli to achieve multicolor emission, which has been successfully used for anti-counterfeiting and food freshness detection; for 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 type of pH-responsive donor-acceptor quinoline compound BN, which contains two basic nitrogen atoms, an aniline group and a pyridine-type quinoline nitrogen. It exhibits yellow-green fluorescence in CH2Cl2 solution. Under the action of low-concentration acid, the quinoline nitrogen atom is protonated and the fluorescence is completely quenched, turning into a dark purple compound BN-H + Compared with the existing acid-induced fluorescence quenching molecules, the molecules of the present invention have 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 THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments or the prior art are briefly introduced below.

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

[0025] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of B-mDMAOXDBEN prepared in Example 2 in deuterated chloroform solution;

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

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

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

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

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

[0031] Figure 8 The fluorescence emission spectrum of L-mDMAOXDBEN prepared in Example 1 in chloroform solution;

[0032] Fig. 9 The fluorescence emission spectra of L-mDMAOXDBEN prepared in Example 1 with different volumes of TFA added to chloroform solution;

[0033] Fig.10 The fluorescence emission spectra of L-mDMAOXDBEN prepared in Example 1 when different volumes of hydrochloric acid were added to tetrahydrofuran solution;

[0034] Fig.11 UV-visible absorption spectra of B-mDMAOXDBEN prepared in Example 2 with different volumes of TFA added to chloroform solution;

[0035] Fig.12 The fluorescence emission spectrum of B-mDMAOXDBEN prepared in Example 2 in chloroform solution;

[0036] Fig.13 The fluorescence emission spectra of B-mDMAOXDBEN prepared in Example 2 with different volumes of TFA added to chloroform solution;

[0037] Fig.14 These are pictures of L-mDMAOXDBEN films irradiated with 365nm UV light after being acid-fumigated for different times;

[0038] Fig.15 is the fluorescence emission spectrum of L-mDMAOXDBEN film before and after protonation;

[0039] Fig.16 These are pictures of L-mDMAOXDBEN prepared in Example 1 under 365nm ultraviolet light irradiation in solvents of different polarities; wherein CHEX is cyclohexane, BEN is benzene, TOL is toluene, CHL is chloroform, DCM is dichloromethane, EA is ethyl acetate, and THF is tetrahydrofuran;

[0040] Fig.17 The excitation spectra of L-mDMAOXDBEN prepared in Example 1 with different volumes of TFA added;

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

[0042] Fig.19 This is a schematic diagram of the application of the chloroform solution of L-mDMAOXDBEN prepared in Example 1 in information encryption transmission;

[0043] Fig. 20 Schematic diagram of the frontier molecular orbital distribution, 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. DETAILED DESCRIPTION

[0044] The present invention provides a method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement, comprising the following steps:

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

[0046] (2) The intermediate product and phosphorus oxychloride are mixed and reacted to obtain the 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement.

[0047] In the present invention, the acyl chloride in step (1) is preferably terephthaloyl chloride or isophthaloyl chloride, and more preferably terephthaloyl chloride.

[0048] In the present invention, the molar ratio of 3-dimethylaminobenzoic acid hydrazide to acyl chloride in step (1) is preferably 2-2.5:1, more preferably 2:1.

[0049] In the present invention, the usage ratio of the 3-dimethylaminobenzoic acid hydrazide and the solvent in step (1) is preferably 1-4 g:100-300 mL, more preferably 1-3 g:120-200 mL, and more preferably 2 g:150 mL.

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

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

[0052] In the present invention, the reaction process in step (1) also includes stirring.

[0053] In the present invention, after the reaction in step (1) is completed, the steps further include filtering, recrystallizing using methanol, and drying.

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

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

[0056] In the present invention, after the reaction in step (2) is completed, the process further comprises recrystallization and drying using ethanol.

[0057] The invention also provides a method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromism and acid-induced fluorescence enhancement, and obtains a 1,3,4-oxadiazole derivative with strong solvatochromism and acid-induced fluorescence enhancement.

[0058] The present invention also provides a strong solvatochromic and acid-induced fluorescence-enhanced 1,3,4-oxadiazole derivative for use in polarity detection, acid detection or information encryption transmission.

[0059] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] Example 1

[0061] This embodiment provides a 1,3,4-oxadiazole derivative, and the preparation method thereof comprises the following steps:

[0062] (1) Dissolve 1 g of 3-dimethylaminobenzoic acid hydrazide in 150 mL of tetrahydrofuran, add terephthaloyl chloride (the molar ratio of terephthaloyl chloride to 3-dimethylaminobenzoic acid hydrazide is 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 a conical flask, 50 mL of phosphorus oxychloride was added, and the mixture was condensed and refluxed at 150° C. for 40 h; the obtained mixed solution was poured into ice water to obtain a light green solid, which was recrystallized from 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 example is as follows:

[0065]

[0066] The H NMR spectrum of L-mDMAOXDBEN prepared in this example in deuterated chloroform solution is shown in FIG. Figure 1 As shown. Figure 1 It can be obtained that the hydrogen on the central benzene ring is at 8.30 ppm, the hydrogen atoms on the outside close to the oxadiazole unit are around 7.56 ppm and 7.42 ppm, the hydrogen on the benzene ring close to the dimethylamino group is around 6.98 ppm, and the hydrogen atoms on the dimethylamino group are around 3.08 ppm.

[0067] Example 2

[0068] This embodiment provides a 1,3,4-oxadiazole derivative, and the preparation method thereof comprises the following steps:

[0069] (1) Dissolve 1 g of 3-dimethylaminobenzoic acid hydrazide in 150 mL of tetrahydrofuran, add isophthaloyl chloride (the molar ratio of isophthaloyl chloride to 3-dimethylaminobenzoic acid hydrazide is 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 a conical flask, 50 mL of phosphorus oxychloride was added, and the mixture was condensed and refluxed at 150° C. for 40 h; the obtained mixed solution was poured into ice water to obtain a light green solid, which was recrystallized from 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 example is as follows:

[0072]

[0073]

[0074] The H NMR spectrum of B-mDMAOXDBEN prepared in this example in deuterated chloroform solution is shown in FIG. Figure 2 As shown. Figure 2 It can be obtained that the hydrogen atoms on the central benzene ring are around 8.89ppm, 8.34ppm, and 7.74ppm respectively, the hydrogen atoms on the outside close to the oxadiazole unit are around 7.54ppm, the hydrogen atoms on the benzene ring close to the dimethylamino group are around 7.43ppm and 7.02ppm, and the hydrogen atoms on the dimethylamino group are around 3.09ppm.

[0075] Example 3

[0076] This embodiment provides a 1,3,4-oxadiazole derivative, and the preparation method thereof comprises the following steps:

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

[0078] (2) 2 g of white solid was placed in a conical flask, 60 mL of phosphorus oxychloride was added, and the mixture was condensed and refluxed at 200° C. for 72 h; the obtained mixed solution was poured into ice water to obtain a light green solid, which 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, and the preparation method thereof comprises the following steps:

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

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

[0083] The normalized UV-visible absorption spectra of L-mDMAOXDBEN prepared in Example 1 in different solvents are as follows: Figure 3 The normalized fluorescence emission spectra in different solvents are shown in Figure 4 As shown. Figure 3 and Figure 4 It can be seen that L-mDMAOXDBEN molecules in different solvents (1×10 -5 mol / L) in the ultraviolet absorption spectrum does not change significantly, with only a slight shift of a few nanometers, indicating 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 ultraviolet absorption spectrum of the L-mDMAOXDBEN molecule has roughly two ultraviolet absorption peaks, 314nm and 370nm respectively. Compared with the ultraviolet absorption spectrum, the fluorescence emission spectrum of L-mDMAOXDBEN changes more significantly. The position of the fluorescence emission peak of the L-mDMAOXDBEN molecule in cyclohexane is 402nm, and the position of the fluorescence emission peak in the relatively polar tetrahydrofuran solution is 522nm. The maximum fluorescence emission peak red-shifts 120nm from non-polar cyclohexane to polar tetrahydrofuran. This means that there is an intramolecular charge transfer state in the molecule, and the molecular charge transfer excited state dipole moment is much larger than the dipole moment of the ground state.

[0084] The normalized UV-visible absorption spectra of B-mDMAOXDBEN prepared in Example 2 in different solvents are as follows: Figure 5 The normalized fluorescence emission spectra in different solvents are shown in Figure 6 As shown. Figure 5 and Figure 6 It can be seen that B-mDMAOXDBEN molecules in different solvents (1×10 -5mol / L) in the ultraviolet absorption spectrum does not change significantly, with only a slight movement of a few nanometers, indicating that the electronic structure of the molecular ground state and the electronic structure of the Frank Condon excited state do not change much. The ultraviolet absorption spectrum of the B-mDMAOXDBEN molecule has roughly two ultraviolet absorption peaks, 270nm and 353nm respectively. Compared with the ultraviolet absorption spectrum, the fluorescence emission spectrum of B-mDMAOXDBEN changes more significantly. The position of the fluorescence emission peak of the B-mDMAOXDBEN molecule in cyclohexane is 394nm, and the position of the fluorescence emission peak in the relatively polar tetrahydrofuran solution is 460nm. The maximum fluorescence emission peak red-shifts 66nm from non-polar cyclohexane to polar tetrahydrofuran. This means that there is an intramolecular charge transfer state in the molecule, and the molecular charge transfer excited state dipole moment is much larger than the dipole moment of the ground state.

[0085] The UV-visible absorption spectra of the L-mDMAOXDBEN molecules prepared in Example 1 when different volumes of trifluoroacetic acid (TFA) were added to chloroform solution are shown in FIG. Figure 7 The fluorescence emission spectrum in chloroform solution is shown in Figure 8 As shown in Figure 2, the fluorescence emission spectra of different volumes of TFA added to chloroform solution are shown in Figure 2. Fig. 9 As shown in the figure, the fluorescence emission spectra of adding different volumes of hydrochloric acid into tetrahydrofuran solution are as follows Fig.10 As shown. Figure 7 to Figure 10 It can be obtained that for the L-mDMAOXDBEN molecule, it is dissolved in chloroform solution with a concentration of 1×10 -5 mol / L, and then different volumes (volume unit is μL) of TFA were added thereto. The results showed that the L-mDMAOXDBEN molecule had two absorption peaks in the UV absorption spectrum of the chloroform solution, which were 324nm and 382nm. With the continuous addition of TFA, the absorption peak at 324nm showed a trend of first decreasing, then increasing, and then decreasing. The absorption peak intensity at 382nm gradually decreased without obvious movement. At the same time, an isosbestic point appeared at 350nm, which showed that with the addition of TFA, the L-mDMAOXDBEN molecule was gradually protonated. Compared with the UV absorption spectrum, the fluorescence emission spectrum has undergone more obvious changes. In the chloroform solution that does not contain TFA, the position of the fluorescence maximum emission peak is at 477nm, along with the continuous adding of TFA, the fluorescence intensity at 477nm place reduces gradually until quenching, meanwhile, at 371nm place, near ultraviolet region, a new fluorescence emission peak is produced again, and fluorescence intensity strengthens along with the continuous adding of TFA, when adding the TFA of 50 μ L, fluorescence intensity reaches the strongest, and when adding TFA again, fluorescence intensity begins to decline until quenching. The situation of adding hydrochloric acid is basically the same. The fluorescence quantum efficiency of the TFA adding 50 μ L that L-mDMAOXDBEN molecule direct method of the present invention records is 69.8%.

[0086] The UV-visible absorption spectra of the B-mDMAOXDBEN molecules prepared in Example 2 after adding different volumes of TFA to chloroform solution are as follows: Fig.11 The fluorescence emission spectrum in chloroform solution is shown in Fig.12 As shown in Figure 2, the fluorescence emission spectra of different volumes of TFA added to chloroform solution are shown in Figure 2. Fig.13 As shown. Figure 11 to Figure 13 It can be obtained that for the B-mDMAOXDBEN molecule, it is dissolved in chloroform solution with a concentration of 1×10 -5 mol / L, and then different volumes (volume unit is μL) of TFA were added thereto. The results showed that the absorption peaks of the ultraviolet absorption spectrum of B-mDMAOXDBEN molecules in chloroform solution were 281nm and 353nm. With the continuous addition of TFA, the absorption peak at 281nm showed a trend of first decreasing, then increasing, and then decreasing, and the absorption peak at 353nm gradually disappeared, and there was no obvious movement. This shows that with the addition of TFA, B-mDMAOXDBEN molecules were gradually protonated. Compared with the ultraviolet absorption spectrum, the fluorescence emission spectrum has undergone more obvious changes. In the chloroform solution without TFA, the position of the maximum fluorescence emission peak is 434nm. With the continuous addition of TFA, the fluorescence intensity at 434nm gradually decreases until it is quenched. At the same time, at 350nm, in the near-ultraviolet region, a new fluorescence emission peak is generated, and the fluorescence intensity increases with the continuous addition of TFA. When 14μL of TFA is added, the fluorescence intensity reaches the highest level. When TFA is added again, the fluorescence intensity begins to decrease until it is quenched.

[0087] The L-mDMAOXDBEN prepared in Example 1 was prepared into an L-mDMAOXDBEN film. The specific method was as follows: L-mDMAOXDBEN was dissolved in chloroform solvent at a concentration of 5×10 -2 M, and then evenly spin-coated on quartz glass, dried to remove the solvent, to obtain L-mDMAOXDBEN film. The pictures of L-mDMAOXDBEN film after acid fumigation for different times under 365nm ultraviolet light are as follows Fig.14 As shown in Figure 2, the fluorescence emission spectra of L-mDMAOXDBEN films before and after protonation are as follows: Fig.15 As shown. Fig.14 It can be seen that the L-mDMAOXDBEN film emits a light yellow light under a 365nm ultraviolet lamp before fumigation. After being fumigated with TFA for 5s, the film turns into a blue-violet light under the ultraviolet lamp, and the blue-violet light gradually increases as the fumigation continues. Fig.15The luminescence of the film before and after protonation can be obtained more intuitively. Before protonation, the peak intensity of the fluorescence emission spectrum of the film was relatively low. After being fumigated with TFA for 5 s, the fluorescence emission spectrum of the film showed a blue shift and the intensity increased significantly. After being fumigated for 10 s, the fluorescence intensity of the film continued to increase to the strongest. This indicates that after protonation, the luminescence performance of the device is more excellent and can emit bright blue-violet light. However, the fumigation time needs to be controlled to avoid affecting the efficiency of the device.

[0088] Pictures of the L-mDMAOXDBEN prepared in Example 1 under 365 nm ultraviolet light irradiation in different polar solvents are as Fig.16 shown. From Fig.16 it can be seen that in cyclohexane with relatively low polarity, the solution shows blue-violet light invisible in the ultraviolet region, sky blue in benzene and toluene, lake blue in chloroform, light yellow in dichloromethane, dark yellow in ethyl acetate, and amber in tetrahydrofuran. The red shift of the fluorescence emission spectrum caused by intramolecular charge transfer can clearly distinguish solvents with different polarities.

[0089] The excitation spectra of the L-mDMAOXDBEN molecule prepared in Example 1 with different volumes (volume unit: μL) of TFA added are as Fig.17 shown, and the excitation spectra of the B-mDMAOXDBEN molecule prepared in Example 2 with different volumes (volume unit: μL) of TFA added are as Fig.18 shown. From Fig.17 and Fig.18 it can be seen that after adding TFA to the two molecules, only the intensity of the excitation spectrum changes, and the position does not change, indicating that no new substances are generated during the protonation process.

[0090] A schematic diagram of the chloroform solution of the L-mDMAOXDBEN prepared in Example 1 in the application of information encryption transmission is as Fig.19 shown. From Fig.19 it can be seen that using the chloroform solution (1×10 -4 mol / L) of L-mDMAOXDBEN to write "中" on filter paper, it shows yellow-green fluorescence under 365 nm ultraviolet light. After being fumigated with TFA for 10 s, near-ultraviolet light (371 nm) with higher intensity is generated. Since the emission after protonation is in the invisible light region and cannot be seen by the naked eye, it can be detected by instruments, and the encryption effect is better.

[0091] The frontier molecular orbital distribution diagrams, energy changes, and HOMO-LUMO energy band gap schematic diagrams of the L-mDMAOXDBEN prepared in Example 1 and the B-mDMAOXDBEN prepared in Example 2 in chloroform solution are as Fig. 20As shown. Gaussian 16 quantum chemistry program was used as the software for theoretical calculations. CAM-B3LYP functional and 6-31G (d, p) basis set were selected in the calculation process. Chloroform solvent was selected as the PCM solvent model. After calculation, the excitation energy (E, eV), oscillator strength (f) and main orbital composition of the main contribution energy levels of L-mDMAOXDBEN and B-mDMAOXDBEN molecules before and after protonation are shown in Table 1.

[0092] Table 1 Excitation energy (E, eV), oscillator strength (f) and main orbital composition of the main contribution energy levels of L-mDMAOXDBEN and B-mDMAOXDBEN molecules before and after protonation

[0093]

[0094]

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

[0096] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement, characterized in that: The following steps are involved: (1) mixing 3-dimethylaminobenzoic acid hydrazide, acyl chloride and a solvent to react to obtain an intermediate product; (2) mixing the intermediate product and phosphorus oxychloride to react, thereby obtaining the 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement; Wherein, the acyl chloride in step (1) is terephthaloyl chloride or isophthaloyl chloride.

2. The method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement according to claim 1, characterized in that: The molar ratio of 3-dimethylaminobenzoic acid hydrazide to acyl chloride in step (1) is 2-2.5:

1.

3. The method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement according to claim 2, characterized in that: The reaction temperature in step (1) is 20 to 30° C. and the reaction time is 5 to 16 hours.

4. The method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement according to claim 1 or 2, characterized in that: The usage ratio of the 3-dimethylaminobenzoic acid hydrazide and the solvent in step (1) is 1-4 g: 100-300 mL.

5. The method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement according to claim 4, characterized in that: The usage ratio of the intermediate product and phosphorus oxychloride in step (2) is 0.5-5 g: 40-80 mL.

6. The method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement according to claim 5, characterized in that: The reaction temperature in step (2) is 150-200° C. and the reaction time is 36-72 hours.

7. A 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement obtained by the method for preparing a 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement as described in any one of claims 1 to 6.

8. Use of the 1,3,4-oxadiazole derivative with strong solvatochromic and acid-induced fluorescence enhancement as claimed in claim 7 in polarity detection, acid detection or information encryption transmission.

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