A method for preparing aggregation-induced emission carbon dots with adjustable emission wavelength

Abstract

The present invention discloses a method for preparing aggregation-induced luminescence carbon dots with adjustable luminescence wavelength. The present invention uses a solvothermal method to prepare carbon dots with aggregation-induced luminescence characteristics by using 2,2-dithiodibenzoic acid and urea as precursors. Under the condition that the reaction conditions such as the reaction precursor, the reaction ratio, and the reaction temperature remain unchanged, the controllable adjustment of the luminescence wavelength is achieved by simply changing the filling degree of the reactor. Aggregation-induced luminescence of the carbon dots is achieved by adding a poor solvent to the good solvent of the carbon dots.

Description

Technical Field

[0001] The invention relates to a method for preparing aggregation-induced luminescence carbon dots with adjustable luminescence wavelength, and belongs to the field of new materials. Background Art

[0002] Carbon dots are a new type of carbon-based fluorescent nanomaterials with a size of less than 10nm. They have the advantages of high photostability, low cost, good biocompatibility, easy surface modification, and adjustable luminescence wavelength. However, most carbon dots will undergo π-π stacking interactions in the aggregated state, resulting in severe aggregation-induced quenching. In order to overcome the aggregation-induced quenching effect of carbon dots, the commonly used method is to disperse the carbon dots in a solid matrix, such as starch, sodium chloride, polyvinyl alcohol, polymethyl methacrylate, etc. However, this method does not fundamentally solve the aggregation-induced quenching effect of carbon dots. When the amount of carbon dots added increases to a certain extent, aggregation-induced quenching will still occur. Therefore, constructing carbon dots that have aggregation-induced luminescence characteristics is of great research significance for expanding the application field of carbon dots. In 2001, Academician Tang Benzhong discovered a class of compounds that exhibit the opposite phenomenon of aggregation-induced quenching. They do not emit light or emit light weakly in dilute solutions, and their fluorescence is significantly enhanced in the aggregated state, which is called aggregation-induced luminescence (Chem. Commun., 2001, 1740-1741). Introducing the idea of ​​aggregation-induced emission into the preparation of carbon dots is expected to fundamentally solve the dilemma of aggregation-induced quenching of carbon dots.

[0003] Tunable emission wavelength is another research hotspot in the field of carbon dots. The choice of precursors, the ratio of precursors and the reaction conditions have an important influence on the emission wavelength of carbon dots. Among them, the reaction conditions reported in the literature include reaction temperature, reaction time, solvent and medium environment (acidic or alkaline environment). Reactor, as a closed container for high-temperature and high-pressure chemical reactions, is a common method for preparing carbon dots. Filling degree is an important parameter of the reactor, and research on the luminescence properties of carbon dots is relatively lacking. Studying the effect of reactor filling degree on the luminescence properties of carbon dots can provide a new way to regulate the emission wavelength of carbon dots. Summary of the invention

[0004] In order to solve the problem that carbon dots are prone to aggregation-induced quenching in the aggregated state, the present invention provides a method for preparing aggregation-induced luminescent carbon dots with adjustable luminescent wavelength. The method is simple to operate, and multi-color luminescent carbon dots with aggregation-induced luminescence are prepared using the same reaction precursors and reaction conditions, simply by changing the filling degree of the reactor.

[0005] A method for preparing aggregation-induced emission carbon dots with adjustable emission wavelength, characterized by the following specific steps:

[0006] ① Dissolve 2,2-dithiodibenzoic acid and urea in acetic acid, stir and dissolve, and disperse them evenly by ultrasonication to obtain a milky white liquid;

[0007] ② Transfer the milky white liquid to the reactor and fill the reactor to 20%, 30%, 40%, 50%, 60%, 70%, and 80% in sequence. React at a certain temperature for several hours, cool to room temperature, and take out the reaction product.

[0008] ③ The reaction product is mixed with boiling water and precipitated, and solid powder is obtained by filtration, and then freeze-dried to remove residual water, thereby obtaining multi-color luminescent carbon dots with aggregation-induced luminescence.

[0009] The mass ratio of the 2,2-dithiodibenzoic acid to urea is 1:4 to 1:8.

[0010] The reaction temperature is 160-200°C.

[0011] The reaction time is 8 to 12 hours.

[0012] The volume ratio of the reaction product to boiling water is 1:100-200.

[0013] The technical points of the present invention are as follows: (1) preparation of aggregation-induced luminescence carbon dots with adjustable luminescence wavelength; (2) studying the aggregation-induced luminescence properties of carbon dots by adding a poor solvent to a good solvent.

[0014] The outstanding features of the present invention are: 1) the preparation method is simple and feasible, highly designable and easy to scale up; 2) a preparation method of aggregation-induced luminescence carbon dots with adjustable luminescence wavelength is provided; 3) by adding a poor solvent to a good solvent for the carbon dots, the aggregation-induced luminescence enhancement of the carbon dots can be achieved.

[0015] The advantages of the present invention are: 1) no dispersion medium is required to construct carbon dots with aggregation-induced emission characteristics; 2) by using a solvothermal method, under the condition that the reaction conditions such as reaction precursors, reaction ratio, reaction temperature remain unchanged, aggregation-induced emission carbon dots with different emission colors are prepared by simply changing the filling degree of the reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Synthesis routes for aggregation-induced luminescent carbon dots with different luminescent colors.

[0017] Figure 2 This is the solid fluorescence spectrum of the carbon dots prepared in Example 1, with an excitation wavelength of 365 nm.

[0018] Figure 3 This is the solid fluorescence spectrum of the carbon dots prepared in Example 2, with an excitation wavelength of 365 nm.

[0019] Figure 4 This is the solid fluorescence spectrum of the carbon dots prepared in Example 3, with an excitation wavelength of 365 nm.

[0020] Figure 5 This is the solid fluorescence spectrum of the carbon dots prepared in Example 4, with an excitation wavelength of 365 nm.

[0021] Figure 6 This is the solid fluorescence spectrum of the carbon dots prepared in Example 5, with an excitation wavelength of 365 nm.

[0022] Figure 7 This is the solid fluorescence spectrum of the carbon dots prepared in Example 6, with an excitation wavelength of 365 nm.

[0023] Figure 8 This is the solid fluorescence spectrum of the carbon dots prepared in Example 7, with an excitation wavelength of 365 nm. DETAILED DESCRIPTION

[0024] 1. Preparation method of aggregation-induced emission carbon dots with tunable emission wavelength

[0025] Example 1

[0026] 2,2-Dithiodibenzoic acid and urea were ultrasonically dispersed in 180 mL of acetic acid at a mass ratio of 1:5.8 (i.e., 2.5 g 2,2-dithiodibenzoic acid + 14.4 g urea). 10 mL of the above dispersion was placed in a 50 mL reactor to a filling degree of 20%. The reactor was placed in a forced air drying oven at 180°C and reacted for 10 hours. After the reactor was cooled to room temperature naturally, the reaction solution was added to 1 L of boiling water for static precipitation, and the carbon dot solid was obtained by filtration. The residual water in it was removed by freeze-drying. The fluorescence spectrum of the obtained carbon dot powder is as follows: Figure 2 shown.

[0027] Example 2

[0028] As described in Example 1, the difference is that the volume of the dispersion added is 15 mL, so that the filling degree reaches 30%, and the reaction solution is purified by 1.5 L of boiling water. Other conditions remain unchanged. The fluorescence spectrum of the obtained carbon dot powder is as follows Figure 3 shown.

[0029] Example 3

[0030] As described in Example 1, the difference is that the volume of the dispersion added is 20 mL, so that the filling degree reaches 40%, the reaction solution is purified by 2.0 L of boiling water, and other conditions remain unchanged. The fluorescence spectrum of the obtained carbon dot powder is as follows Figure 4 shown.

[0031] Example 4

[0032] As described in Example 1, the difference is that the volume of the dispersion added is 25 mL, so that the filling degree reaches 50%, and the reaction solution is purified by 2.5 L of boiling water. Other conditions remain unchanged. The fluorescence spectrum of the obtained carbon dot powder is as follows Figure 5 shown.

[0033] Example 5

[0034] As described in Example 1, the difference is that the volume of the dispersion added is 30 mL, so that the filling degree reaches 60%, the reaction solution is purified by 3.0 L of boiling water, and other conditions remain unchanged. The fluorescence spectrum of the obtained carbon dot powder is as follows Figure 6 shown.

[0035] Example 6

[0036] As described in Example 1, the difference is that the volume of the dispersion added is 35 mL, so that the filling degree reaches 70%, and the reaction solution is purified by 3.5 L of boiling water. Other conditions remain unchanged. The fluorescence spectrum of the obtained carbon dot powder is as follows: Figure 7 shown.

[0037] Example 7

[0038] As described in Example 1, the difference is that the volume of the dispersion added is 40 mL, so that the filling degree reaches 80%, the reaction solution is purified by 4.0 L of boiling water, and other conditions remain unchanged. The fluorescence spectrum of the obtained carbon dot powder is as follows Figure 8 shown.

[0039] Examples 1-7 can be summarized in Table 1 below.

[0040] Table 1 Changes in emission peaks of carbon dot powders at different reactor filling levels in Examples 1-7

[0041]

[0042] 2. Aggregation-induced luminescence properties of carbon dots

[0043] Example 8

[0044] Weigh 15 mg of the solid powder obtained in Example 1, add 3 mL of acetic acid to fully dissolve, and configure to a mother solution with a concentration of 5 mg / mL. Add 0.3 mL of mother solution to ten glass bottles with a capacity of 5 mL, add acetic acid 2.7 mL, 2.4 mL, 2.1 mL, 1.8 mL, 1.5 mL, 1.2 mL, 0.9 mL, 0.6 mL, 0.3 mL, 0 mL to the glass bottles in sequence, and then add water 0 mL, 0.3 mL, 0.6 mL, 0.9 mL, 1.2 mL, 1.5 mL, 1.8 mL, 2.1 mL, 2.4 mL, 2.7 mL to the glass bottles in sequence, so that its water content is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% in sequence. As the water content increases, the solution gradually becomes turbid, and the fluorescence changes of the sample under a 365 nm ultraviolet lamp are observed. When the water content exceeds 60%, the fluorescence changes from blue to red, and aggregation-induced emission occurs. When the water content is 0%, the transmittance T = 99.8%, and the quantum yield Φ of the carbon dot solution = 0.5%; when the water content is 90%, the transmittance T = 49.6%, and the quantum yield Φ of the carbon dot solution = 6.0%.

[0045] Example 9

[0046] Weigh 15 mg of the solid powder obtained in Example 3, add 3 mL of acetic acid to fully dissolve, and configure to a mother solution with a concentration of 5 mg / mL. Add 0.3 mL of mother solution to ten glass bottles with a capacity of 5 mL, add acetic acid 2.7 mL, 2.4 mL, 2.1 mL, 1.8 mL, 1.5 mL, 1.2 mL, 0.9 mL, 0.6 mL, 0.3 mL, 0 mL to the glass bottles in sequence, and then add water 0 mL, 0.3 mL, 0.6 mL, 0.9 mL, 1.2 mL, 1.5 mL, 1.8 mL, 2.1 mL, 2.4 mL, 2.7 mL to the glass bottles in sequence, so that its water content is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% in sequence. As the water content increases, the solution gradually becomes turbid, and the fluorescence changes of the sample under a 365 nm ultraviolet lamp are observed. When the water content exceeds 60%, the fluorescence changes from blue to orange, and aggregation-induced emission occurs. When the water content is 0%, the transmittance T = 99.8%, and the quantum yield Φ of the carbon dot solution = 0.5%; when the water content is 90%, the transmittance T = 34.8%, and the quantum yield Φ of the carbon dot solution = 10.3%.

[0047] Example 10

[0048] Weigh 15 mg of the solid powder obtained in Example 5, add 3 mL of acetic acid to fully dissolve, and configure to a mother solution with a concentration of 5 mg / mL. Add 0.3 mL of mother solution to ten glass bottles with a capacity of 5 mL, add acetic acid 2.7 mL, 2.4 mL, 2.1 mL, 1.8 mL, 1.5 mL, 1.2 mL, 0.9 mL, 0.6 mL, 0.3 mL, 0 mL to the glass bottles in sequence, and then add water 0 mL, 0.3 mL, 0.6 mL, 0.9 mL, 1.2 mL, 1.5 mL, 1.8 mL, 2.1 mL, 2.4 mL, 2.7 mL to the glass bottles in sequence, so that its water content is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% in sequence. As the water content increases, the solution gradually becomes turbid, and the fluorescence changes of the sample under a 365 nm ultraviolet lamp are observed. When the water content exceeds 50%, the fluorescence changes from blue to yellow, and aggregation-induced emission occurs. When the water content is 0%, the transmittance T = 98.3%, and the quantum yield Φ of the carbon dot solution = 0.4%; when the water content is 90%, the transmittance T = 27.7%, and the quantum yield Φ of the carbon dot solution = 12.3%.

[0049] Embodiment 11

[0050] Weigh 15 mg of the solid powder obtained in Example 7, add 3 mL of acetic acid to fully dissolve, and configure to a mother solution with a concentration of 5 mg / mL. Add 0.3 mL of mother solution to ten glass bottles with a capacity of 5 mL, add acetic acid 2.7 mL, 2.4 mL, 2.1 mL, 1.8 mL, 1.5 mL, 1.2 mL, 0.9 mL, 0.6 mL, 0.3 mL, 0 mL to the glass bottles in sequence, and then add water 0 mL, 0.3 mL, 0.6 mL, 0.9 mL, 1.2 mL, 1.5 mL, 1.8 mL, 2.1 mL, 2.4 mL, 2.7 mL to the glass bottles in sequence, so that its water content is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% in sequence. As the water content increases, the solution gradually becomes turbid, and the fluorescence changes of the sample under a 365 nm ultraviolet lamp are observed. When the water content exceeds 50%, the fluorescence changes from blue to green, and aggregation-induced emission occurs. When the water content is 0%, the transmittance T = 99.2%, and the quantum yield Φ of the carbon dot solution = 0.4%; when the water content is 90%, the transmittance T = 30.7%, and the quantum yield Φ of the carbon dot solution = 12.8%.

Claims

1. A method for preparing aggregation-induced emission carbon dots with tunable emission wavelength, Features The specific steps are as follows: (1) dissolving 2,2-dithiodibenzoic acid and urea in acetic acid, stirring and dissolving, and uniformly dispersing by ultrasonication to obtain a milky white liquid, wherein the mass ratio of 2,2-dithiodibenzoic acid to urea is 1:4 to 1:8; (2) transferring the milky white liquid into a reaction kettle, making the filling degree of the reaction kettle 20%, 30%, 40%, 50%, 60%, 70%, and 80% in sequence, reacting at a certain temperature for several hours, cooling to room temperature, and taking out the reaction product, wherein the reaction temperature is 160-200 °C, and the reaction time is 8-12 h; (3) The reaction product is mixed with boiling water to precipitate, filtered to obtain a solid powder, and then freeze-dried to remove residual water to obtain multi-color luminescent carbon dots with aggregation-induced luminescence. The volume ratio of the reaction product to boiling water is 1:100-200.

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