A multi-color fluorescent molecular switch and its preparation method

Abstract

The present invention discloses a multicolor fluorescent molecular switch, which has a merocyanine structure and a pyrene group, and its structural formula is as shown in I. The molecular switch provided by the present invention can adjust its fluorescence switching performance by changing the merocyanine structure and the aggregation state of the molecule, and can realize the switching of multiple fluorescent colors. It can have the advantages of visible light stimulus response, high isomerization efficiency, spontaneous recovery, etc. It can be converted by more than 95% within 120 seconds under white light stimulation, can be switched cyclically for more than 5 times, and has good fatigue resistance. Moreover, the preparation method is simple. The present invention provides a synthetic idea of a fluorescent molecular switch with high conversion rate and simple adjustment of fluorescence performance, which greatly enriches the spiropyran-based molecular switch system.

Description

Technical Field

[0001] The present invention belongs to the field of molecular switches, and in particular relates to a multicolor fluorescent molecular switch and a preparation method thereof. Background Art

[0002] In recent years, smart materials, which refer to materials that are responsive to changes in external stimuli (such as light, heat, force, electricity, magnetism, etc.), have made great progress and have been widely used in the fields of smart display, sensing, information anti-counterfeiting, super-resolution imaging, etc. Among them, compared with other stimulus-responsive materials, light stimulus-responsive materials have the advantages of being non-toxic, simple to operate, environmentally friendly, precisely controlled, drivable closed systems, non-invasive, and wavelength-specific due to the particularity of light. The core of light stimulus-responsive materials is the light-controlled molecular switch, which mainly includes azobenzene derivatives, diarylethylene derivatives, cyanodiphenylethylene derivatives, spiropyran derivatives, etc. However, due to the particularity of these light-controlled molecular switches, there is currently little research on the application of light-controlled molecular switches in the field of multi-color fluorescence. The development of a molecular switch with high light stimulus response efficiency and a large range of fluorescence color change is a breakthrough direction for light-controlled multi-color fluorescent molecular switches.

[0003] Spiropyran-based photoswitchable molecular switches, characterized by their ability to respond to visible light, spontaneous recovery, and high photoresponse efficiency, have been used to develop light-controlled multicolor fluorescent molecular switches. Linlin Yang et al. synthesized a novel spiropyran derivative with a 2,4-dinitrobenzene structure that can switch to red fluorescence upon photostimulation. Yasuhiro Shiraishi et al. modified the spiropyran structure with coumarins, achieving bright blue fluorescence switching. Lingyun Wang et al. covalently bonded an AIE group to the spiropyran structure, achieving cyan / pink fluorescence switching upon photothermal stimulation. However, most of these molecular switches can only achieve fluorescence intensity changes, while a few multicolor fluorescent molecular switches have drawbacks such as a narrow color change range. Furthermore, most of these molecular switches require ultraviolet light for control. Therefore, the development of a multicolor fluorescent molecular switch capable of visible light (>405 nm) control and a wide fluorescence color change range is particularly urgent and important. Summary of the Invention

[0004] Objectives of the invention: The first objective of the present invention is to provide a fluorescent molecular switch capable of multi-color switching; the second objective of the present invention is to provide applications of the above-mentioned fluorescent molecular switch; the third objective of the present invention is to provide a method for preparing the above-mentioned fluorescent molecular switch.

[0005] Technical solution: The multicolor fluorescent molecular switch described in the present invention has a merocyanine structure and a pyrene group, and its structural formula is shown below:

[0006]

[0007] The molecular switch provided by the present invention is a light-controlled molecular switch based on the merocyanine structure, with white light responsiveness and multiple fluorescence color switching. Its purpose is to introduce the 'pyrene group', which has the special property of forming excimers, into the merocyanine structure. The specific molecular structure takes the merocyanine structure substituted by sulfonate as the basic structural unit, and covalently couples the large conjugated group - pyrene at the phenol end. The mutual transformation between the merocyanine structure and the spiropyran structure is achieved through light stimulation, and the transformation process is as follows:

[0008]

[0009] Meanwhile, by switching the solvent or solution concentration, the formation of excimers is controlled, and the fluorescence color of the molecular switch is jointly regulated to achieve the switching of fluorescence colors such as red, green, yellow, and blue. The emission wavelength range is 400 - 650 nm, and the fluorescence color can achieve time-dependent spontaneous changes. This solves the disadvantages of the existing fluorescence molecular switches, such as single color change and narrow color change range.

[0010] Furthermore, the multicolor fluorescence molecular switch controls its switching behavior through visible light with a wavelength of 400 nm - 650 nm.

[0011] The application of the multicolor fluorescence molecular switch described in the present invention in information encryption and anti-counterfeiting.

[0012] Furthermore, the application is carried out in a liquid state, and the solvents of the liquid state include one or more combinations of dimethyl sulfoxide (DMSO), ethanol (EtOH), chloroform, o-dichlorobenzene (o-DCB), 1,4-dioxane (Diox).

[0013] The preparation method of the multicolor fluorescence molecular switch described in the present invention includes the following steps:

[0014] (1) Covalently couple the pyrene group with active sites and salicylaldehyde through the Suzuki coupling reaction to obtain a pyrene-salicylaldehyde core;

[0015] (2) Modify the indole group with sultone to form a sulfonium inner salt core;

[0016] (3) Obtain the multicolor fluorescence molecular switch by subjecting the pyrene-salicylaldehyde core obtained in step (1) and the sulfonium inner salt core obtained in step (2) to a Michael addition reaction.

[0017] Furthermore, the specific steps include:

[0018] (1) Under the protection of inert gas, 2-hydroxybenzaldehyde, 1-pyrenylboronic acid, tetrakis(triphenylphosphine)palladium, and potassium carbonate are added to a mixed solvent of 1,4-dioxane and water from which oxygen has been removed. After complete dissolution, heating is carried out to obtain a yellow solid, which is the product;

[0019] (2) Under the protection of inert gas, 2,3,3-trimethylindole is added to acetonitrile, and then propane sultone is added dropwise. After heating, the reaction solution is dropped into ethyl acetate, and the purple solid obtained by filtration is the product;

[0020] (3) Under the protection of inert gas, the products generated in steps (1) and (2) are added to ethanol, and after heating and reaction, the reaction solution is dropped into ethyl acetate, and the solid is collected by filtration to obtain the above-mentioned multicolor fluorescent molecular switch.

[0021] Furthermore, the concentration of 2-hydroxybenzaldehyde added in step (1) is 7.2 - 7.6 mmol; the molar ratio of 2-hydroxybenzaldehyde, 1-pyrenylboronic acid, tetrakis(triphenylphosphine)palladium, and potassium carbonate is 1:1.2 - 1.5:0.012 - 0.015:3 - 4; the volume ratio of 1,4-dioxane to water is 4 - 4.2:1; the heating temperature is 70 - 90 °C, and the heating time is 18 - 36 hours.

[0022] Furthermore, the concentration of 2,3,3-trimethylindole added in step (2) is 60 - 65 mmol; the molar ratio of 2,3,3-trimethylindole to propane sultone is 1:0.8 - 1.2; the addition amount of acetonitrile is 40 - 60 mL; the heating temperature is 70 - 90 °C, and the heating time is 8 - 12 hours.

[0023] Furthermore, the addition amount of the product generated in step (2) in step (3) is 0.32 - 0.39 mmol, and its molar ratio to the product generated in step (1) is 1.1:1; the addition amount of acetonitrile is 10 - 20 mL; the heating temperature is 70 - 90 °C, and the heating time is 24 - 72 hours; the volume of ethyl acetate is 800 - 1100 mL.

[0024] Furthermore, step (1) also includes the steps of extracting with ethyl acetate, concentrating, and purifying the product; steps (2) and (3) also include the steps of washing with ethyl acetate and n-hexane.

[0025] Furthermore, the inert gas is N2.

[0026] Advantages: Compared with the prior art, the present invention has the following outstanding and remarkable advantages: The fluorescent molecular switch provided by the present invention can adjust its fluorescent switch performance by changing the merocyanine structure and the aggregation state of the molecule, and can realize the switching of multiple fluorescent colors. It can have advantages such as visible light stimulus response, high isomerization efficiency, spontaneous recovery, etc. It can be converted by more than 95% within 120 seconds under white light stimulation, can be switched cyclically for more than 5 times, and has good fatigue resistance. And the preparation method is simple. The present invention provides a synthetic idea of a fluorescent molecular switch with high conversion rate and simple adjustment of fluorescent performance, which greatly enriches the spiropyran molecular switch system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the synthesis route of the multicolor fluorescent molecular switch of the present invention;

[0028] Figure 2 Ultraviolet absorption spectra of the open-ring state MEH-Py and the closed-ring state SP-Py of the multicolor fluorescent molecular switch of the present invention in chloroform;

[0029] Figure 3 Fluorescence spectra of the open-ring state MEH-Py and the closed-ring state SP-Py of the multicolor fluorescent molecular switch of the present invention in chloroform;

[0030] Figure 4 Ultraviolet absorption spectra of the open-ring state MEH-Py and the closed-ring state SP-Py of the multicolor fluorescent molecular switch of the present invention in (A) o-dichlorobenzene, (B) dimethyl sulfoxide, (C) ethanol, and (D) 1,4-dioxane;

[0031] Figure 5 Fluorescence spectra of the open-ring state MEH-Py and the closed-ring state SP-Py of the multicolor fluorescent molecular switch of the present invention in (A) o-dichlorobenzene, (B) dimethyl sulfoxide, (C) ethanol, and (D) 1,4-dioxane;

[0032] Figure 6 CIE locus diagrams (A) and fluorescence photographs (B) of the open-ring state MEH-Py and the closed-ring state SP-Py of the multicolor fluorescent molecular switch of the present invention in chloroform, o-dichlorobenzene, dimethyl sulfoxide, ethanol, and 1,4-dioxane solutions;

[0033] Figure 7 CIE locus diagrams (A) and fluorescence photographs (B) and information anti-counterfeiting (C) of the multicolor fluorescent molecular switch of the present invention when standing still for one minute under dark conditions in chloroform and o-dichlorobenzene;

[0034] Figure 8 Ultraviolet absorption reversible switch cycle diagram of the multicolor fluorescent molecular switch of the present invention in chloroform for five light stimulations. DETAILED DESCRIPTION OF THE INVENTION

[0035] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

[0036] Example 1

[0037] (1) Under N2 protection, 2-hydroxybenzaldehyde (1.5 g, 7.46 mmol) was added to a mixed solvent of 60 mL of 1,4-dioxane and water (volume ratio 4:1) according to the molar ratio of 2-hydroxybenzaldehyde:1-pyrenylboronic acid:tetrakis(triphenylphosphine)palladium (catalyst):potassium carbonate of 1:1.5:0.015:3. The reaction mixture was heated to 85 °C for 24 hours. After the reaction, the mixture was extracted three times with 500 mL of ethyl acetate, and the organic layer was concentrated under vacuum. Then the obtained crude product was purified by flash chromatography to obtain 1.5 g of a pale yellow solid product, 4-pyrenylsalicylaldehyde (yield 62.5%). 1 1H-NMR (600 MHz, DMSO-d6) δ 11.00 (s, 1H), 10.41 (s, 1H), 8.43–8.31 (m, 3H), 8.23 (d, J = 28.1 Hz, 3H), 8.16–8.10 (m, 2H), 8.04 (d, J = 7.8 Hz, 1H), 7.88 (d, J = 7.9 Hz, 1H), 7.30–7.19 (m, 2H).

[0038] (2) Under N2 protection, 2,3,3-trimethylindole (10 g, 62.8 mmol) was added to 50 mL of acetonitrile, and then propane sultone was added dropwise (the molar ratio of added alkane sultone to 2,3,3-trimethylindole was 1.1:1). The reaction temperature was 80 °C for 12 hours. After the reaction, the reaction solution was dropped into 1 L of ethyl acetate, and the purple solid was collected by filtration and washed three times with 100 mL of ethyl acetate and n-hexane respectively to obtain 15.2 g of the product 2,3,3-trimethyl-1-(3-sulfopropyl)-3H-indole (yield 91.18%). 1 1H-NMR (600 MHz, DMSO-d6): δ 8.13–7.99 (m, 1H), 7.82 (dd, J = 7.1, 1.6 Hz, 1H), 7.62 (d, J = 1.9 Hz, 1H), 4.76–4.53 (m, 2H), 2.83 (s, 3H), 2.62 (t, J = 6.5 Hz, 2H), 2.15 (td, J = 7.1, 6.6, 3.5 Hz, 2H), 1.53 (s, 6H).

[0039] (3) Under N2 protection, 2,3,3-trimethyl-1-(3-sulfopropyl)-3H-indole (100 mg, 9.36 mmol) generated in step (2) and 4-pyrenylsalicylaldehyde generated in step (1) (the molar ratio of added 4-pyrenylsalicylaldehyde to 2,3,3-trimethyl-1-(3-sulfopropyl)-3H-indole is 1.1:1) were added to 50 mL of ethanol. The reaction temperature was 80 °C and the reaction time was 72 hours. After the reaction, the reaction solution was dropped into 1 L of ethyl acetate, and the solid was collected by filtration and washed three times with 100 mL of ethyl acetate and n-hexane respectively to obtain 0.1 g of the final product (E)-3-(2-(2-hydroxy-4-(pyridin-1-yl)styryl)-3,3-dimethyl-3H-indol-1-yl)propane-1-sulfonate (MEH-Py). 1 1H-NMR (600 MHz, DMSO-d6) δ 11.34 (s, 1H), 8.72 (d, J = 16.3 Hz, 1H), 8.52 (d, J = 8.1 Hz, 1H), 8.41 (dd, J = 8.0, 2.6 Hz, 1H), 8.38–8.32 (m, 2H), 8.29–8.20 (m, 4H), 8.13 (td, J = 7.6, 2.2 Hz, 1H), 8.09 (dd, J = 7.8, 2.5 Hz, 1H), 8.07–8.03 (m, 1H), 8.01 (s, 0H), 7.93–7.87 (m, 1H), 7.68–7.61 (m, 2H), 7.32 (d, J = 1.7 Hz, 1H), 7.29 (dd, J = 7.9, 1.9 Hz, 1H), 4.86 (t, J = 7.9 Hz, 2H), 2.69 (t, J = 6.5 Hz, 2H), 2.24 (p, J = 7.0 Hz, 2H), 1.84 (d, J = 2.7 Hz, 6H). 13 13C NMR (151 MHz, DMSO-d6): δ 182.10, 159.48, 148.76, 148.20, 143.98, 141.46, 136.21, 131.42, 131.19, 130.83, 130.60, 129.66, 129.60, 128.65, 128.39, 127.97, 127.84, 127.64, 127.08, 126.19, 125.81, 125.54, 124.80, 124.61, 124.43, 123.48, 122.88, 121.16, 118.75, 115.57, 112.06, 52.40, 47.89, 46.05, 26.96, 25.13. ESI-MS: C37H31NO4S, calculated value is 584.18901, measured value is 584.1914.

[0040] Figure 2 and Figure 3 are the UV absorption spectra and fluorescence spectra of MEH-Py in the open-loop state and SP-Py in the closed-loop state in chloroform. Since MEH-Py has a merocyanine structure, the excimer formed in solvents such as chloroform has poor solubility. Therefore, red fluorescence is obtained under the induction of ICT-excimer. After irradiating the chloroform solution of MEH-Py with white light (25 mW / cm 2 ) for two minutes, the merocyanine structure of MEH-Py is transformed into the spiropyran structure SP-Py. At this time, the conjugated system changes, and SP-Py has high solubility, thus obtaining blue fluorescence.

[0041] As Figure 2 shown, the changes in the UV absorption spectra of MEH-Py and SP-Py are obvious (the inset is a photo of the solution color before and after irradiation). As Figure 3 shown, the maximum emission wavelength of MEH-Py in chloroform is 650 nm, showing red fluorescence; the maximum emission wavelength of SP-Py in chloroform is 400 nm, showing blue fluorescence (the inset is a photo of the fluorescence color of the solution before and after irradiation).

[0042] Example 2

[0043] Dissolve 3.51 mg of MEH-Py prepared in Example 1 in 0.6 mL of dimethyl sulfoxide, and take 2970 μL of chloroform, o-dichlorobenzene, dimethyl sulfoxide, ethanol, and 1,4-dioxane respectively to prepare a solution with a MEH-Py concentration of 1×10 -4 M for spectroscopic tests and fluorescence observations, as Figure 4 shown in Figures 5 and 6.

[0044] Figure 4 are the UV absorption spectra of MEH-Py in o-dichlorobenzene (A), dimethyl sulfoxide (B), ethanol (C), and 1,4-dioxane (D) solutions respectively. The maximum absorption wavelength of MEH-Py is around 500 nm. After irradiating the MEH-Py solution with white light (25 mW / cm 2 ) for two minutes, the merocyanine structure of MEH-Py is transformed into the spiropyran structure SP-Py, and at this time, the absorption peak at 500 nm decreases significantly.

[0045] Figure 5 are the fluorescence emission spectra of MEH-Py in o-dichlorobenzene (A), dimethyl sulfoxide (B), ethanol (C), and 1,4-dioxane (D) solutions respectively. The maximum emission wavelength of the o-dichlorobenzene solution of MEH-Py is 650 nm, showing red fluorescence. After irradiating with white light (25 mW / cm 2) After two minutes of irradiation, the maximum emission wavelength of the o-dichlorobenzene solution of SP-Py is 420 nm, showing blue fluorescence. The fluorescence emission spectra of the ethanol solution, 1,4-dioxane solution and o-dichlorobenzene solution of MEH-Py change similarly. While the maximum emission wavelength of the dimethyl sulfoxide solution of MEH-Py is 550 nm, showing yellow-green fluorescence, after white light (25 mW / cm 2 ) After two minutes of irradiation, the maximum emission wavelength of the dimethyl sulfoxide solution of SP-Py is 450 nm, showing cyan fluorescence.

[0046] Figure 6 are the CIE chromaticity diagrams ( Figure 6 A) and fluorescence physical diagrams ( Figure 6 B, left MEH-Py, right SP-Py) of the chloroform solution, o-dichlorobenzene solution, dimethyl sulfoxide solution, 1,4-dioxane solution and ethanol solution of MEH-Py. The chloroform solution of MEH-Py shows red fluorescence, and the chloroform solution of SP-Py shows blue fluorescence. The o-dichlorobenzene solution of MEH-Py shows red fluorescence, and the chloroform solution of SP-Py shows blue fluorescence. The dimethyl sulfoxide solution of MEH-Py shows yellow-green fluorescence, and the dimethyl sulfoxide solution of SP-Py shows cyan fluorescence. The 1,4-dioxane solution of MEH-Py shows red fluorescence, and the 1,4-dioxane solution of SP-Py shows blue fluorescence. The ethanol solution of MEH-Py shows red fluorescence, and the ethanol solution of SP-Py shows purple fluorescence. The color changes of several solutions are consistent with the coordinate changes of the CIE chromaticity diagram, realizing the switching of multiple fluorescence colors.

[0047] Example 3

[0048] Chloroform and o-dichlorobenzene were selected to prepare an anti-counterfeiting solution; 3.51 mg of MEH-Py prepared in Example 1 was dissolved in 0.6 ml of DMSO, and 2970 μl of chloroform and o-dichlorobenzene were respectively taken for dilution to prepare a solution with a MEH-Py concentration of 1×10 -4 M. Prepare a mold, which is a 248 mm×248 mm×5 mm cuboid PVE plastic plate. 31×31 cuboid small grooves of 5 mm×5 mm×3 mm are processed on the plastic plate, and the interval between each small groove is 3 mm. According to the design pattern "SEU", the chloroform solution was dropped into the plate, and o-dichlorobenzene was used as the background solution. After two minutes of white light irradiation, observe again after one minute. As Figure 7 shown.

[0049] First, the solutions in the cuboid small grooves all show red fluorescence, which is invalid information. After white light (25 mW / cm 2)After irradiation for two minutes, the solutions in the cuboid troughs all showed blue fluorescence, which was still invalid information. Finally, the plastic plate was placed in the dark for one minute. Since the recovery efficiency of the chloroform solution and o-dichlorobenzene solution of SP-Py was different in the dark, different shades of blue would appear, thereby revealing the encrypted information "SEU".

[0050] Example 4

[0051] Dissolve 3.51 mg of MEH-Py prepared in Example 1 in 0.6 mL of DMSO, take 2970 μL of chloroform for dilution, and prepare a solution with a MEH-Py concentration of 1×10 -4 M. First, irradiate the MEH-Py chloroform solution with light (25 mW / cm 2 ) for 2 minutes, then quickly measure its ultraviolet absorption value. After the measurement is completed, control the temperature at 25 °C and place it in the dark for 300 min, and measure its ultraviolet absorption value. Repeat this process 5 times to obtain a time-dependent ultraviolet absorption spectrum, as Figure 8 shown.

[0052] As Figure 8 shown, the ultraviolet absorption value of MEH-Py was about 0.1. After irradiation with white light (25 mW / cm 2 ) for two minutes, MEH-Py isomerized to SP-Py. At this time, the ultraviolet absorption value was about 4.0, and the change rate of ultraviolet absorption exceeded 95%. That is, under white light stimulation, more than 95% of MEH-Py could be converted to SP-Py within 120 seconds. During the cycling process, the ultraviolet absorption curves of MEH-Py and SP-Py were basically consistent, and the attenuation degree was negligible. This shows that this fluorescent molecular switch has good anti-fatigue performance. After multiple cycles, the molecule can maintain its structure without being damaged and maintain the characteristics of tautomerism.

Claims

1. A multicolor fluorescent molecular switch, characterized in that, The multi-color fluorescent molecular switch has a phthalocyanine structure and a pyrene group, and its structural formula is as shown in I:

2. The multicolor fluorescence molecular switch according to claim 1, characterized in that, The multi-color fluorescent molecular switch controls its switching behavior by visible light with a wavelength of 400 nm to 650 nm.

3. Application of the multi-color fluorescent molecular switch according to claim 1 in information encryption and anti-counterfeiting.

4. The application according to claim 3, wherein The application is carried out in a liquid state, and the liquid solvent includes one or a combination of dimethyl sulfoxide, ethanol, chloroform, o-dichlorobenzene, 1,4-dioxane.

5. A method for preparing the multi-color fluorescence molecular switch according to claim 1, characterized in that, It includes the following steps: (1) Under the protection of an inert gas, 2-hydroxybenzaldehyde, 1-pyreneboronic acid, tetrakis(triphenylphosphine)palladium, and potassium carbonate are added to a mixed solvent of deoxygenated 1,4-dioxane and water. After complete dissolution, heating is carried out to obtain a yellow solid, which is the product. (2) Under the protection of an inert gas, 2,3,3-trimethylindole is added to acetonitrile, and then propane sultone is added dropwise. After heating, the reaction solution is dropped into ethyl acetate, and the purple solid obtained by filtration is the product. (3) Under the protection of an inert gas, the products generated in steps (1) and (2) are added to ethanol, heated, and after the reaction, the reaction solution is dropped into ethyl acetate, and the solid is collected by filtration to obtain the multi-color fluorescent molecular switch according to claim 1.

6. The preparation method according to claim 5, wherein In step (1), the added concentration of 2-hydroxybenzaldehyde is 7.2 to 7.6 mmol; the molar ratio of 2-hydroxybenzaldehyde, 1-pyreneboronic acid, tetrakis(triphenylphosphine)palladium, and potassium carbonate is 1:1.2 to 1.5:0.012 to 0.015:3 to 4; the volume ratio of 1,4-dioxane to water is 4 to 4.2:1; the heating temperature is 70 to 90 °C, and the heating time is 18 to 36 hours.

7. The preparation method according to claim 5, characterized in that, In step (2), the added concentration of 2,3,3-trimethylindole is 60 to 65 mmol; the molar ratio of 2,3,3-trimethylindole and propane sultone is 1:0.8 to 1.2; the added amount of acetonitrile is 40 to 60 mL; the heating temperature is 70 to 90 °C, and the heating time is 8 to 12 hours.

8. The preparation method according to claim 5, wherein In step (3), the added amount of the product generated in step (2) is 0.32 to 0.39 mmol, and its molar ratio to the product generated in step (1) is 1.1:1; the added amount of acetonitrile is 10 to 20 mL; the heating temperature is 70 to 90 °C, and the heating time is 24 to 72 hours; the volume of ethyl acetate is 800 to 1100 mL.

9. The preparation method according to claim 5, characterized in that, Step (1) also includes the steps of extracting with ethyl acetate, concentrating, and purifying the product; steps (2) and (3) also include the steps of washing with ethyl acetate and n-hexane.

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