A fluorescent molecule, host-guest complex, and preparation method and application thereof

Abstract

The present invention belongs to the technical field of mechanochromic materials and relates to a fluorescent molecule, a host-guest complex, and its preparation method and application. The host-guest complex comprises a fluorescent molecule of formula (I) and a cucurbituril. The complex is an intelligent color-changing material that exhibits a more pronounced spectral change trend than the guest molecule under mechanical stimulation.

Description

Technical Field

[0001] The present invention belongs to the field of mechanical color-changing materials, and more specifically, relates to a fluorescent molecule, a host-guest complex, and a preparation method and application thereof. Background Art

[0002] Mechanochromism refers to the fluorescent color change that occurs in solid samples after being subjected to grinding, squeezing, or friction. This change can usually be restored to its original state through annealing or solvent treatment. This unique stimulus-responsive behavior has broad application prospects in fields such as mechanical sensors, anti-counterfeiting, and information storage. To date, many mechanochromic materials have been reported. However, the construction of the mechanochromic materials reported so far is almost all based on a single organic molecular component. For example, CN113896677A reported a fluorescent molecule in which the donor and the acceptor are connected by cyanoethylene. The donor material (Donor) includes triphenylamine, indoline, and carbazole, and the acceptor material (Acceptor) includes pyridyl, nitrophenyl, or cyanophenyl with different substitution positions. The fluorescence wavelength red-shift caused by the fluorescent molecule after being subjected to force does not exceed 42nm, and the fluorescence quantum yield is 0.49 to 0.81; CN113896677A reported the fluorescent molecule: 1,1,2,2-(tetrakis(4-9hydro-carbazole)phenyl)ethylene (TCPE). Although the fluorescence wavelength red-shift caused by the fluorescent molecule after being subjected to force is 62nm, the yield of the overall synthetic route of the fluorescent molecule is only 56.69%. At present, it is still a challenge to simultaneously prepare mechanochromic materials with high quantum yield and large color difference, and the use of multi-component materials to regulate molecular mechanochromic properties is still rare.

[0003] Cucurbituril, as a well-known macrocyclic supramolecular entity, has a wide range of uses in the fields of regulating molecular assembly and changing the photophysical properties of compounds. At present, a variety of stimulus-responsive materials have been constructed based on the combination of cucurbituril and other molecules, such as photochromic and vapor-chromic materials. However, great challenges are faced in the construction of mechanochromic materials. Cucurbituril itself does not have luminescent properties. If it can be combined with other fluorescent components to develop mechanochromic materials based on cucurbituril and fluorescent molecules, it will not only further broaden the application of such macrocyclic materials, but also make it possible to regulate the mechanical force response behavior of fluorescent molecules, such as changing the direction and range of wavelength changes, thereby achieving multiple changes in molecular fluorescence under a single stimulus behavior. This is of great significance for the construction and practical application of functional fluorescent materials. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a complex constructed from two components, a host and a guest. The compound is a mechanical color-changing material. Under mechanical stimulation, the host-guest complex exhibits a more obvious spectral change trend than the guest molecule.

[0005] To achieve the above objectives, the first aspect of the present invention provides a fluorescent molecule having mechanochromic properties, the general formula of which is shown in formula (I):

[0006] wherein R1 and R2 represent methyl groups, and X is a chloride ion.

[0007] The fluorescent molecule is: 3-(1-methyl-4-yl-pyridinium)-9-methyl-carbazole chloride.

[0008] The second aspect of the present invention provides a method for preparing the fluorescent molecule, which comprises the following steps:

[0009] 1) Under inert gas protection, 3-bromocarbazole and 4-pyridinylboronic acid are subjected to a coupling reaction to introduce a 4-pyridyl group at the 3-position of carbazole. After the reaction, the solid is extracted by filtration, and the organic layer is collected, washed, dried, the solvent is removed, and purified to obtain 3-(4-pyridinyl)carbazole;

[0010] 2) 3-(4-pyridyl)carbazole is methylated with methyl halide under inert gas protection to introduce a methyl group at the 9-position of carbazole to obtain compound 2;

[0011] 3) Compound 2 is subjected to an alkylation reaction with a methyl halide to introduce a methyl group at the 1-position of pyridine, and then the fluorescent molecule is obtained by an anion exchange method.

[0012]

[0013] Specifically, the preparation method of the fluorescent molecule is:

[0014] 1) adding 3-bromocarbazole, 4-pyridinylboronic acid, and potassium carbonate as a base to a mixed solution of DMF and water from which dissolved oxygen has been removed, then adding tetrakis(triphenylphosphine)palladium, and conducting a coupling reaction under inert gas conditions. After the reaction, filtering, extracting a solid, collecting an organic layer, washing, drying, removing the solvent, and purifying to obtain 3-(4-pyridyl)carbazole;

[0015] 2) adding 3-(4-pyridyl)carbazole, potassium tert-butoxide, and a halogenated hydrocarbon to THF to undergo a methylation reaction under inert gas conditions, removing the solvent by rotary evaporation after the reaction, and purifying the extract to obtain 9-methyl-9H-carbazole-3-(4-pyridyl);

[0016] 3) 9-Methyl-9H-carbazole-3-(4-pyridyl) and halogenated hydrocarbon are added to acetonitrile, heated at 80° C., and after the reaction, the solid is separated, and the fluorescent molecule is obtained by an anion exchange method.

[0017] Furthermore, in the method for preparing the fluorescent molecule:

[0018] In step 1), the reaction molar ratio of 3-bromocarbazole to 4-pyridineboronic acid is 1:1.1 to 1:1.3;

[0019] In step 2), the reaction molar ratio of 3-(4-pyridyl)carbazole to halogenated hydrocarbon is 1:1.1 to 1:1.3;

[0020] In step 3), the reaction molar ratio of 9-methyl-9H-carbazole-3-(4-pyridyl) to halogenated hydrocarbon is 1:2 to 1:3.

[0021] Furthermore, in the method for preparing fluorescent molecules, the inert gas is nitrogen.

[0022] In the preparation method of the fluorescent molecule:

[0023] The reaction conditions in step 1) include: temperature of 80-100° C. and time of 20-25 h.

[0024] The reaction conditions in step 2) include: temperature of 60° C. and time of 5-6 h.

[0025] The reaction conditions in step 3) include: temperature of 80° C. and time of 1-2 h.

[0026] According to the method of the present invention, preferably, the method further comprises a post-treatment step: removing the solvent from the reaction solution obtained by the reflux reaction, extracting and drying, and separating by column chromatography. The above steps can all be carried out using conventional operating conditions in the field of organic synthesis.

[0027] A third aspect of the present invention provides a host-guest complex, wherein the host-guest complex comprises a fluorescent molecule of formula (I) and a cucurbituril, and the host-guest complex has a reversible mechanochromic property.

[0028] Furthermore, the cucurbituril is cucurbit[8]uril.

[0029] The host-guest complex thus contains the host molecule cucurbit[8]uril (a) and the fluorescent molecule:

[0030]

[0031] The third aspect of the present invention provides a method for preparing the above-mentioned host-guest complex, characterized in that the method comprises: configuring the fluorescent molecule according to claim 1 into an aqueous solution with water to obtain solution I, adding the cucurbituril to part of solution I to configure it into a cucurbituril-luminescent molecule solution to obtain solution II, and freeze-drying to obtain the host-guest complex.

[0032] Furthermore, the method for preparing the host-guest complex includes: ultrasound and centrifugation before freeze-drying.

[0033] According to the present invention, preferably, the concentration of the guest molecule aqueous solution is 10-16 mM and the volume is 1-2 mL.

[0034] According to the present invention, preferably, the content of the added cucurbit[8]uril solid is 25 to 45 mg.

[0035] According to the present invention, preferably, the ultrasonication time is 3 to 5 minutes.

[0036] In the present invention, the water is conventional deionized water in the field of analytical testing.

[0037] The fluorescent molecules or host-guest complexes are used in the fields of mechanical sensing, anti-counterfeiting materials, information storage, etc.

[0038] The mechanical color change characteristics of the guest molecule (b) solid were studied and it was found that it has the following characteristics.

[0039] 1. Irreversible mechanical stimulus responsiveness (mechanical color change characteristics):

[0040] 1) When the solid compound is ground by mechanical force, its fluorescence emission wavelength shifts from 511 nm to 534 nm.

[0041] 2) After mechanical grinding of the solid compound, it was dissolved in methanol and the solvent evaporated, and its fluorescence emission wavelength shifted from 534 nm to 519 nm.

[0042] In the above-mentioned mechanical stimulus responsiveness, the fluorescence color of the guest molecule can be changed by mechanical grinding, but it does not return to the initial state after methanol recrystallization.

[0043] The mechanochromic properties of the host-guest complex (I) were studied and it was found that it has the following characteristics.

[0044] 1. Reversible mechanical stimulus responsiveness (mechanical color change characteristics):

[0045] 1) When the solid composite is ground by mechanical force, its fluorescence emission wavelength shifts from 493 nm to 565 nm.

[0046] 2) After mechanical grinding, treatment with aqueous solution and drying of the solid composite, the fluorescence emission wavelength is restored from 565 nm to 493 nm.

[0047] In the above-mentioned mechanical stimulus responsiveness, the fluorescence color of the complex can be changed by mechanical grinding and then restored by aqueous solution treatment.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. The fluorescent molecule (b) and host-guest complex described in the present invention exhibit excellent responsiveness to mechanical stimulation. Mechanical grinding of the fluorescent molecule (b) can red-shift the emission wavelength, but the range of change is small. Mechanical grinding of the host-guest complex can also red-shift the emission wavelength, with a more pronounced range. The carbazole unit in the fluorescent molecule (b) acts as an electron-donating group, while the pyridine unit acts as an electron-withdrawing group, forming a DA-type molecule. Therefore, the charge transfer effect can be exploited to modulate the luminescence properties of the molecule. Furthermore, the fluorescent molecule (b), whose anion is chloride, exhibits excellent water solubility, enabling specific host-guest recognition with cucurbituril in aqueous solution.

[0050] 2. The compound of the present invention has a simple and easy synthesis process, and the raw materials are cheap and readily available, resulting in low preparation costs. Compared with common mechanochromic compounds, the construction of the host-guest complex achieves the regulation of the mechanochromic properties of the fluorescent molecule (b).

[0051] 3. The overall yield of the synthetic route of the fluorescent molecule (b) of the present invention is: 65.06%. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings.

[0053] Figure 1 The NMR spectrum of the fluorescent molecule (b) represented by formula (I) and the carbazole derivative having mechanochromic properties;

[0054] Figure 2 The fluorescence emission spectra of the solid of the fluorescent molecule (b) represented by formula (I) before and after grinding and after treatment with MeOH; wherein the excitation wavelength is 360 nm; Unground represents before grinding, Ground represents after grinding, and MeOH represents methanol treatment;

[0055] Figure 3 The powder X-ray diffraction (XRD) patterns of the solid fluorescent molecule (b) represented by formula (I) before and after grinding; wherein unground represents before grinding and ground represents after grinding;

[0056] Figure 4 The fluorescence emission spectra of the solid host-guest complex represented by formula (I) before and after grinding and after water treatment after grinding; the excitation wavelength is 360 nm; Unground represents before grinding, Ground represents after grinding, and Water represents water treatment.

[0057] Figure 5The powder X-ray diffraction (XRD) patterns of the solid host-guest complex represented by formula (I) before and after grinding; wherein unground represents before grinding, and ground represents after grinding;

[0058] Figure 6 Fluorescence photographs of the fluorescent molecule (b) represented by formula (I) before and after solid grinding under 365 nm ultraviolet light irradiation;

[0059] Figure 7 These are fluorescence photographs of the host-guest complex represented by formula (I) before and after solid grinding under 365 nm ultraviolet light irradiation. DETAILED DESCRIPTION

[0060] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0061] Example 1

[0062] Synthesize the fluorescent molecule (b) represented by formula (I),

[0063] The synthetic route is as follows:

[0064]

[0065] In the reaction formula, K2CO3 is potassium carbonate, Pd(pph3)4 is tetrakis(triphenylphosphine)palladium, DMF is N,N-dimethylformamide, CH3I is iodomethane, t-BuOK is potassium tert-butoxide, THF is tetrahydrofuran, MeCN is acetonitrile, and anion exchange means anion exchange.

[0066] The specific synthesis steps are as follows:

[0067] 1. Add 3-bromocarbazole (2 g, 8.13 mmol), 4-pyridineboronic acid (1.2 g, 9.75 mmol), potassium carbonate (1.69 g, 12.2 mmol), and tetrakis(triphenylphosphine)palladium (0.474 g, 0.41 mmol) to a two-necked flask under nitrogen protection using standard Schlenk double-row vacuum line technology. Add the deaerated solvent (40 mL of N,N-dimethylformamide and 12 mL of water) to the flask and heat under reflux for 24 h. After the reaction, the mixture was cooled to room temperature, and water was added to the reaction system. Solids precipitated and were filtered off. The solids were collected and the filtrate was extracted four times with dichloromethane. The lower organic phases were combined and washed with brine several times. After drying over anhydrous sodium sulfate, the solvent was removed by distillation under reduced pressure. The crude product was separated by column chromatography to obtain a light yellow pure product, namely compound 1,3-(4-pyridyl)carbazole (eluent: petroleum ether: ethyl acetate = 2:1), with a yield of 89%.

[0068] 2. Under nitrogen, 3-(4-pyridyl)carbazole (1300 mg, 5.32 mmol), potassium tert-butoxide (896 mg, 7.98 mmol), tetrahydrofuran (20 mL), and iodomethane (0.4 mL, 6.39 mmol) were added to a two-necked flask and refluxed at 60°C for 6 h. After the reaction was completed, the solution was cooled to room temperature and the solvent was removed by rotary evaporation to obtain a yellow solid. The solid was extracted and dried, and then separated by column chromatography to obtain a light yellow solid, compound 2, 9-methyl-9H-carbazole-3-(4-pyridyl) (eluent: petroleum ether:ethyl acetate = 6:1), with a yield of 86%.

[0069] 3. Under nitrogen protection, 9-methyl-9H-carbazole-3-(4-pyridyl) (800 mg, 3.1 mmol), iodomethane (0.58 mL, 9.3 mmol), and acetonitrile (35 mL) were added to a two-necked flask and refluxed at 80°C for 2 h. After the reaction was completed and cooled to room temperature, the reaction solution was centrifuged, and the solid was washed several times with a small amount of acetonitrile and then vacuum-dried to obtain a yellow solid 3-(1-methyl-4-yl-pyridine)-9-methyl-carbazole iodide. The yellow solid was then obtained by anion exchange, which is the fluorescent molecule (b) represented by formula (I) of the present invention, 3-(1-methyl-4-yl-pyridine)-9-methyl-carbazole chloride, with a yield of 85%. 1 H NMR(600MHz,D2O)δ(ppm):8.02(d,J=6.4Hz,2H),7.99(s,1H),7.92(d,J=7.7Hz,1H),7.59–7.53(m, 4H), 7.39 (d, J = 8.1Hz, 1H), 7.36 (d, J = 8.6Hz, 1H), 7.28 (t, J = 7.4Hz, 1H), 3.96 (s, 3H), 3.73 (s, 3H).

[0070] Example 2

[0071] Preparation of host-guest complex represented by formula (I)

[0072] At room temperature, cucurbit[8]uril (43 mg) was added to a 16 mM, 2 mL aqueous solution of the guest molecule, compound (b). The resulting mixture was sonicated for 3 minutes and then centrifuged to separate the resulting liquid. The resulting liquid was freeze-dried to obtain the host-guest complex represented by formula (I).

[0073] Example 3

[0074] (b) Irreversible mechanochromic properties of fluorescent molecules.

[0075] The fluorescent molecule (b) of Example 1 was processed and tested in the following different ways.

[0076] 1) A solid state fluorescent molecule (b) prepared in Example 1 was prepared and its fluorescence emission spectrum was measured using 360 nm excitation light. The UV-visible absorption peak of fluorescent molecule (b) was 450 nm, and the maximum emission peak was 511 nm. The solid-state fluorescence quantum yield of the material was 37.83%, indicating good luminous efficiency in the solid state.

[0077] 2) The solid of the fluorescent molecule (b) prepared in Example 1 was placed in a mortar and ground thoroughly. Its fluorescence emission spectrum was measured using 360 nm as the excitation light.

[0078] 3) The solid of the fluorescent molecule (b) prepared in Example 1 was ground thoroughly in a mortar, and the ground solid powder was dissolved in methanol. After the solvent evaporated, the fluorescence emission spectrum was measured using 360 nm as the excitation light.

[0079] like Figure 2 As shown in the figure, by comparing the fluorescence emission spectra of fluorescent molecule (b) after different treatments, it can be seen that the fluorescence emission wavelength of fluorescent molecule (b) undergoes a red shift (from 511nm to 534nm) after mechanical grinding. When the ground solid powder is dissolved in methanol, the solid fluorescence does not return to its initial state (from 534nm to 519nm) after the solvent evaporates. This shows that fluorescent molecule (b) exhibits irreversible mechanochromic behavior.

[0080] like Figure 3 As shown, the XRD data of the fluorescent molecule (b) show that the fluorescent molecule (b) has a strong and sharp diffraction peak before grinding, indicating that it has a crystalline structure; after grinding, the intensity of the diffraction peak is slightly weakened, indicating that the crystalline structure of the sample is destroyed to a certain extent.

[0081] Example 4

[0082] Reversible mechanochromic properties of host-guest complexes.

[0083] The host-guest complex of Example 2 was processed and tested in the following different ways.

[0084] 1) Take the host-guest complex prepared in Example 2 and measure its fluorescence emission spectrum using 360 nm as the excitation light.

[0085] 2) The solid of the host-guest complex prepared in Example 2 was placed in a mortar and ground thoroughly, and its fluorescence emission spectrum was measured using 360 nm as the excitation light.

[0086] 3) The solid of the host-guest complex prepared in Example 2 was placed in a mortar and ground thoroughly. A certain amount of deionized water was added and ultrasonicated to evaporate the solvent. The fluorescence emission spectrum was then measured using 360 nm as the excitation light.

[0087] like Figure 4 As shown in the figure, by comparing the fluorescence emission spectra of the compounds after different treatments, it can be seen that the fluorescence emission wavelength of the host-guest complex undergoes a significant red shift (from 493nm to 565nm) after mechanical grinding. After the ground solid powder is added with water and ultrasonicated, the solid fluorescence can be restored to its initial state after the solvent evaporates. It can be seen that the host-guest complex exhibits reversible mechanochromic behavior and shows a more obvious spectral change trend under mechanical stimulation compared to the fluorescent molecule (b).

[0088] like Figure 5 As shown in the figure, the XRD data of the host-guest complex show that: the sample of the host-guest complex before grinding has a strong and sharp diffraction peak, indicating that it is a crystalline structure; after grinding, the intensity of the diffraction peak is significantly weakened, indicating that its crystalline structure is significantly destroyed. Compared with the fluorescent molecule (b), the crystalline structure of the host-guest complex formed after adding cucurbit[8]uril is more easily destroyed, which may be the reason for its better mechanochromic properties. Mechanochromic properties are related to molecular structure. Small changes in molecular structure will have a greater impact on mechanochromic properties. If the pyridine group and carbazole group of the fluorescent molecule (b) are modified into other forms, the molecular structure will change and it may not have mechanochromic properties.

[0089] Cucurbituril host-guest recognition is specific. Cucurbiturils of different cavity sizes have different recognition sites and binding ratios for the fluorescent molecule (b), thus forming different host-guest complexes with different mechanochromic properties. The cucurbituril [8] uril host-guest complex has excellent mechanochromic properties (Δλ = 75nm). However, when cucurbituril [8] uril is replaced by cucurbituril [7] uril or cucurbituril

[10] uril, the cucurbituril [7] uril host-guest complex has weaker mechanochromic properties before and after grinding (Δλ = 6nm). Similarly, the cucurbituril

[10] uril host-guest complex also has weaker mechanochromic properties before and after grinding (Δλ = 15nm).

[0090] Example 5

[0091] (b) Changes in the fluorescence color of the solid before and after grinding.

[0092] The fluorescent molecule (b) of Example 1 was processed and tested in the following different ways.

[0093] 1) Take the solid of the fluorescent molecule (b) prepared in Example 1, irradiate it with 365 nm ultraviolet light, and take a fluorescence photograph thereof.

[0094] 2) The solid of the fluorescent molecule (b) prepared in Example 1 was placed in a mortar and ground thoroughly, and then irradiated with 365 nm ultraviolet light to take a fluorescence photograph.

[0095] like Figure 4 As shown, the unground solid emits yellow-green fluorescence under 365 nm ultraviolet light; the ground solid emits yellow fluorescence under 365 nm ultraviolet light.

[0096] Example 6

[0097] Changes in the fluorescence color of the host-guest complex solid before and after grinding.

[0098] 1) Take the solid of the host-guest complex prepared in Example 2, irradiate it with 365 nm ultraviolet light, and take a fluorescence photograph thereof.

[0099] 2) The solid of the host-guest complex prepared in Example 2 was placed in a mortar and ground thoroughly, and then irradiated with 365 nm ultraviolet light to take a fluorescence photograph.

[0100] like Figure 5 As shown, the unground host-guest complex solid emits green fluorescence under 365 nm ultraviolet light; the ground solid emits orange fluorescence under 365 nm ultraviolet light.

[0101] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A fluorescent molecule having mechanochromic properties, the general formula of which is shown in formula (I): (I), wherein R1 and R2 represent methyl groups, and X is a chloride ion.

2. A host-guest complex, characterized in that The host-guest complex comprises the fluorescent molecule according to claim 1 and cucurbituril, and the host-guest complex has a reversible mechanochromic property.

3. The host-guest complex according to claim 2, characterized in that The cucurbituril is cucurbituril[8].

4. The method for preparing the host-guest complex according to claim 2, characterized in that: The method comprises: preparing the fluorescent molecule of claim 1 into an aqueous solution with water to obtain solution I; adding the cucurbituril into part of solution I to prepare a cucurbituril-luminescent molecule solution to obtain solution II; and freeze-drying to obtain a host-guest complex.

5. The method for preparing a host-guest complex according to claim 4, wherein: The method comprises: ultrasonication and centrifugation before freeze drying.

6. The method for preparing a host-guest complex according to claim 4 or 5, wherein: The concentration of the fluorescent molecule aqueous solution is 10~16 mM, the volume is 1~2 mL, and the content of cucurbituril is 25~45 mg.

7. Use of the fluorescent molecule according to claim 1 or the host-guest complex according to any one of claims 2 to 3 in the fields of mechanical sensing, anti-counterfeiting materials, and information storage.

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