A dynamic room-temperature phosphorescent material based on matrix-free carbon dots and a preparation method and application thereof

Abstract

The application discloses a kind of dynamic room temperature phosphorescent material based on matrix-free carbon dots and preparation method and application thereof, belong to luminescent material technical field, urea, aromatic anhydride / anhydride derivative and nitrogen-containing heterocyclic compound are dissolved in the mixed solvent of ethanol and water, carbonization reaction is carried out, cooling to room temperature, the obtained solid powder is added into water to obtain carbon dot dispersion solution, centrifugation, filtration, freeze drying are sequentially carried out, and the dynamic room temperature phosphorescent material based on matrix-free carbon dots is prepared.The application adopts one-step pyrolysis method, process is simple, condition is mild, reproducibility is good, and is suitable for large-scale preparation.The application realizes dynamic phosphorescence, and provides technical scheme that different aromatic anhydride / anhydride derivative is combined with urea and nitrogen-containing heterocyclic compound, which proves the universality of the preparation method.

Description

Technical Field

[0001] This invention belongs to the field of luminescent materials technology, and in particular relates to a dynamic room temperature phosphorescent material based on matrix-free carbon dots, its preparation method and application. Background Technology

[0002] Fluorescent anti-counterfeiting technology has attracted much attention due to its superior security performance and significant ease of identification, showing great promise for applications in anti-counterfeiting and information encryption. However, traditional fluorescent materials lose their emission immediately after the excitation source is turned off, making them easy to counterfeit and limiting their security. Room-temperature phosphorescent materials, as materials that continue to emit light for a period of time (milliseconds to seconds) after the excitation source is removed, possess unique advantages such as long lifetime, large Stokes shift, and high signal-to-noise ratio. This delayed emission characteristic allows room-temperature phosphorescent materials to be detected even after the background fluorescence has completely disappeared, greatly enhancing the concealment and identification capabilities of anti-counterfeiting measures and providing a new dimension for advanced information encryption. Room-temperature phosphorescent materials, due to their unique delayed emission characteristics, demonstrate great potential in the fields of anti-counterfeiting and information encryption. Carbon dots, as an emerging zero-dimensional carbon nanomaterial, have become an ideal platform for constructing room-temperature phosphorescent materials due to their advantages such as simple preparation, low cost, and good biocompatibility.

[0003] However, most high-performance carbon dot room-temperature phosphorescent materials currently rely on the confinement or coating of rigid matrices (such as polyvinyl alcohol, boric acid, zeolites, etc.) to achieve their properties, which limits the realization of their intrinsic characteristics and the convenience of practical applications. Furthermore, existing phosphorescent materials are mostly static monochromatic luminescent, making it difficult to meet the security requirements of dynamic, multi-level anti-counterfeiting measures. Therefore, developing a matrix-free carbon dot material that requires no external matrix and possesses dynamically tunable color or lifetime phosphorescence is a pressing technical problem to be solved in this field. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a dynamic room-temperature phosphorescent material based on matrix-free carbon dots, its preparation method, and its applications. This invention uses three precursor monomers (urea, aromatic anhydride / anhydride derivative, and nitrogen-containing heterocyclic compound) as raw materials, and forms a dynamic room-temperature phosphorescent material based on matrix-free carbon dots through a one-step pyrolysis self-crosslinking polymerization. This invention prepares pure carbon dot powder through a one-step pyrolysis method. The three components synergistically form a three-dimensional crosslinked network during pyrolysis, and multiple emission centers are constructed through multi-element doping, achieving dynamic room-temperature phosphorescence without an external matrix. The preparation method provided by this invention is simple, low-cost, and exhibits excellent performance. The dynamic phosphorescence properties demonstrated have broad application potential and prospects in fields such as advanced anti-counterfeiting and information encryption.

[0005] In a first aspect, the present invention provides a method for preparing a dynamic room temperature phosphorescent material based on matrix-free carbon dots, wherein the dynamic room temperature phosphorescent material based on matrix-free carbon dots is prepared by a one-step pyrolysis method using urea, aromatic anhydride / anhydride derivatives and nitrogen-containing heterocyclic compounds as raw materials.

[0006] Furthermore, the preparation method specifically includes the following steps: dissolving urea, aromatic anhydride / anhydride derivative and nitrogen-containing heterocyclic compound in a mixed solvent of ethanol and water, carrying out a pyrolysis reaction, cooling to room temperature, adding the obtained solid powder to water to obtain a carbon dot dispersion solution, and sequentially centrifuging, filtering and freeze-drying to prepare the dynamic room temperature phosphorescent material based on matrix-free carbon dots.

[0007] Furthermore, the mass ratio of the urea, aromatic anhydride / anhydride derivative and nitrogen-containing heterocyclic compound is (187-3745):57:2; the volume ratio of the nitrogen-containing heterocyclic compound and the mixed solvent is 2mg:50mL.

[0008] Furthermore, the pyrolysis reaction is carried out at a temperature of 200°C for 6 hours.

[0009] Furthermore, the aromatic anhydride / anhydride derivative is selected from 1,8-naphthalenedicarboxylic anhydride, 1,8-naphthalenedicarboxylimine, naphthalimide ethylamine, 4-bromo-1,8-naphthalenedicarboxylic anhydride, or 4-bromo-1,8-naphthalimide ethylamine.

[0010] The structural formula of the urea is: ; The structural formula of the 1,8-naphthalenedicarboxylic anhydride is: ; The structural formula of the 4-bromo-1,8-naphthalenedicarboxylic anhydride is: ; The structural formula of the 1,8-naphthalenediamine is: ; The structural formula of the naphthimide ethylamine is: ; The structural formula of the 4-bromo-1,8-naphthalimide ethylamine is: .

[0011] Furthermore, the nitrogen-containing heterocyclic compound is selected from levofloxacin; The structural formula of levofloxacin is: .

[0012] Furthermore, the volume ratio of ethanol to water in the mixed solvent of ethanol and water is 4:1.

[0013] The method for preparing dynamic room-temperature phosphorescent materials based on matrix-free carbon dots provided by this invention is simple and controllable.

[0014] Secondly, the present invention provides a dynamic room temperature phosphorescent material based on matrix-free carbon dots prepared by the preparation method described above.

[0015] This invention provides a highly efficient room-temperature phosphorescent material composed of pure carbon dot powder that does not depend on an external rigid matrix.

[0016] Thirdly, the present invention provides the application of the aforementioned matrix-free carbon dot-based dynamic room temperature phosphorescent material in the preparation of anti-counterfeiting products.

[0017] Fourthly, this invention provides the application of the aforementioned matrix-free carbon dot-based dynamic room-temperature phosphorescent material in information encryption.

[0018] The dynamic room-temperature phosphorescent material based on matrix-free carbon dots provided by this invention has time-dependent dynamic phosphorescent properties (such as color evolution over time), and can be applied in the fields of advanced dynamic anti-counterfeiting and information encryption.

[0019] This invention utilizes a one-step pyrolysis method to construct matrix-free carbon dot materials with dynamic room-temperature phosphorescence properties through the synergistic combination of three precursors: urea, aromatic anhydrides / anhydride derivatives, and levofloxacin. Urea, acting as both a nitrogen and carbon source, forms a cross-linked structure and enhances material rigidity through the reaction of amino and anhydride groups. Aromatic anhydrides / anhydride derivatives provide a rigid aromatic framework and reaction sites, constructing conjugated carbon cores to form a π-electron system for phosphorescence emission. Levofloxacin, as a nitrogen-containing heterocyclic compound, not only provides additional nitrogen doping and carboxyl reaction sites, but its fluorine atoms also enhance spin-orbit coupling, promoting singlet-to-triplet transitions and thus improving phosphorescence efficiency. During pyrolysis, the three precursors form a covalent cross-linked network through amidation, constructing a three-dimensional rigid structure that effectively suppresses nonradiative transitions and stabilizes triplet excitons. Simultaneously, multi-element co-doping with N, O, and F is achieved, introducing abundant surface states and defect energy levels, forming multiple emission centers, and realizing multicolor emission of fluorescence and phosphorescence. By controlling the precursor ratio and structure, the phosphorescence color can dynamically evolve over time due to differences in excited-state lifetime and relaxation rate at different emission centers, such as transitioning from yellow to green or from orange to yellow. When using bromine-containing derivatives, bromine atoms and fluorine atoms in levofloxacin synergistically enhance the spin-orbit coupling effect, further controlling the phosphorescence lifetime and color. Through the above synergistic effect, this invention achieves for the first time highly efficient room-temperature phosphorescence without an external matrix, and endows the material with time-dependent dynamic color evolution characteristics, which has significant application advantages in advanced dynamic anti-counterfeiting and information encryption.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects: (1) The dynamic room temperature phosphorescent material based on matrix-free carbon dots provided by the present invention is pure carbon dot powder, which completely eliminates the dependence on external matrices such as polymers and inorganic salts, simplifies the material system, and is more conducive to studying its intrinsic phosphorescence mechanism.

[0021] (2) This invention achieves dynamic evolution of phosphorescent color over time (from yellow to green, from orange to yellow) through a unique precursor combination, increasing the information dimension and the concealment and complexity of anti-counterfeiting. For example, the dynamic room temperature phosphorescent materials CDs-A (1, 2, 3), CDs-C (1, 2, 3), and CDs-D (1, 2, 3) provided by this invention exhibit white fluorescence under ultraviolet light irradiation at a wavelength of 365 nm. After the 365 nm ultraviolet light irradiation is turned off, CDs-A1 first shows a yellow afterglow, which gradually turns into a green afterglow within about 0.5 seconds and disappears after 5 seconds. CDs-A2 first shows a yellow afterglow, which gradually turns into a green afterglow within about 0.5 seconds and disappears after 7 seconds. CDs-A3 first shows a yellow afterglow, which gradually turns into a green afterglow within about 0.5 seconds and disappears after 8 seconds.

[0022] (3) This invention can effectively control the fluorescence and phosphorescence colors of materials by adjusting the type of precursor (such as introducing bromine atoms to achieve the heavy atom effect). The CDs-B (1, 2, 3) dynamic room temperature phosphorescent materials provided by this invention exhibit a yellow-green fluorescence color under ultraviolet light irradiation at a wavelength of 365 nm. After the 365 nm ultraviolet light irradiation is turned off, CDs-B1 first shows a yellow afterglow, which gradually turns into a green afterglow within about 0.5 seconds and disappears after 3.5 seconds. CDs-B2 first shows a yellow afterglow, which gradually turns into a green afterglow within about 0.5 seconds and disappears after 6 seconds. CDs-B3 first shows a yellow afterglow, which gradually turns into a green afterglow within about 0.5 seconds and disappears after 6 seconds. The CDs-E (1, 2, 3) dynamic room-temperature phosphorescent materials exhibit the following fluorescence colors under 365 nm ultraviolet light irradiation: CDs-E1 displays an orange fluorescence, while CDs-E2 and CDs-E3 display a yellow fluorescence. After the 365 nm ultraviolet light irradiation is turned off, CDs-E1 exhibits an orange afterglow that disappears after 0.2 s. CDs-E2 initially displays an orange afterglow, which gradually turns to a yellow afterglow within approximately 0.5 seconds and disappears after 4 s. CDs-E3 initially displays an orange afterglow, which gradually turns to a yellow afterglow within approximately 0.5 seconds and disappears after 4.5 s.

[0023] (4) The present invention employs a one-step pyrolysis method, which is simple, mild, and reproducible, making it suitable for large-scale preparation. While achieving dynamic phosphorescence, the present invention provides a technical solution for combining different aromatic anhydrides / anhydride derivatives with urea and nitrogen-containing heterocyclic compounds, demonstrating the universality of the preparation method of the present invention. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The fluorescence color diagram of CDs-A1 prepared in Example 1 after 365 nm ultraviolet light irradiation and the fluorescence emission spectrum under different wavelengths of excitation; Figure 2 The fluorescence color diagram and fluorescence emission spectrum of the CDs-A2 material prepared in Example 2 after irradiation with 365 nm ultraviolet light are shown. Figure 3 The fluorescence color diagram of the CDs-A3 material prepared in Example 3 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under excitation at different wavelengths are shown. Figure 4 The afterglow color of CDs-A1, CDs-A2, and CDs-A3 after the 365 nm UV light illumination was turned off is shown as a function of time, and the phosphorescence emission spectrum excited by 365 nm UV light (delay 0.001 s). Figure 5 The fluorescence color diagram and fluorescence emission spectrum of the CDs-B1 material prepared in Example 4 after 365 nm ultraviolet light irradiation are shown. Figure 6 The fluorescence color diagram of the CDs-B2 material prepared in Example 5 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under excitation at different wavelengths are shown. Figure 7 The fluorescence color diagram of the CDs-B3 material prepared in Example 6 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under excitation at different wavelengths are shown. Figure 8 The graphs show the afterglow color of CDs-B1, CDs-B2, and CDs-B3 materials after the 365 nm ultraviolet light illumination is turned off, and their phosphorescence emission spectra excited by 365 nm ultraviolet light (delay 0.001 s). Figure 9 The fluorescence color diagram of the CDs-C1 material prepared in Example 7 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under excitation at different wavelengths are shown. Figure 10 The fluorescence color diagram of the CDs-C2 material prepared in Example 8 after 365 nm ultraviolet light irradiation and the fluorescence emission spectrum under different wavelengths of excitation are shown. Figure 11 The fluorescence color diagram of the CDs-C3 material prepared in Example 9 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under excitation at different wavelengths are shown. Figure 12 The graphs show the afterglow color of CDs-C1, CDs-C2, and CDs-C3 materials after the 365 nm ultraviolet light illumination is turned off, and the phosphorescence emission spectra excited by 365 nm ultraviolet light (delay 0.001 s). Figure 13 The fluorescence color diagram and fluorescence emission spectrum of the CDs-D1 material prepared in Example 10 after 365 nm ultraviolet light irradiation; Figure 14 The fluorescence color diagram and fluorescence emission spectrum of the CDs-D2 material prepared in Example 11 after 365 nm ultraviolet light irradiation are shown. Figure 15 The fluorescence color diagram and fluorescence emission spectrum of the CDs-D3 material prepared in Example 12 after 365 nm ultraviolet light irradiation are shown. Figure 16 The afterglow color of CDs-D1, CDs-D2, and CDs-D3 materials after the 365 nm ultraviolet light illumination was turned off changed over time, and the phosphorescence emission spectrum excited by 365 nm ultraviolet light (delay 0.001 s). Figure 17 The fluorescence color diagram and fluorescence emission spectrum of the CDs-E1 material prepared in Example 13 after 365 nm ultraviolet light irradiation are shown. Figure 18 The fluorescence color diagram and fluorescence emission spectrum of the CDs-E2 material prepared in Example 14 after 365 nm ultraviolet light irradiation are shown. Figure 19 The fluorescence color diagram and fluorescence emission spectrum of the CDs-E3 material prepared in Example 15 after 365 nm ultraviolet light irradiation are shown. Figure 20 The graphs show the afterglow color of CDs-E1, CDs-E2, and CDs-E3 materials after the 365 nm ultraviolet light illumination is turned off, and their phosphorescence emission spectra excited by 365 nm ultraviolet light (delay 0.001 s).

[0026] Figure 21 The 1H NMR spectrum of the intermediate in the preparation of naphthalimide ethylamine (N). Figure 22 The image shows the 1H NMR spectrum of naphthalimide ethylamine (N). Figure 23 The 1H NMR spectrum of the intermediate in the preparation of 4-bromo-1,8-naphthalimide ethylamine (N1); Figure 24 The 1H NMR spectrum of 4-bromo-1,8-naphthalimide ethylamine (N1). Detailed Implementation

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0030] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0031] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0032] The room temperature in this invention refers to 25±2℃.

[0033] The preparation method of naphthalimide ethylamine (N) used in this embodiment of the invention is as follows: 1,8-naphthalenedicarboxylic anhydride (0.198 g, 1 mmol), N-tert-butyloxycarbonylethylenediamine (0.16 g, 1 mmol), and triethylamine (0.75 mL, 5 mmol) are added to ethanol and mixed to obtain a yellow solution. The solution is stirred overnight at 80 °C, and then the solvent is removed under vacuum. The residue is washed with water and filtered to obtain an intermediate, which is a yellow solid crude product. The intermediate is purified by recrystallization from chloroform and methanol, and then stirred with trifluoroacetic acid (TFA) in dichloromethane at room temperature for 4 hours. After the reaction is complete, the solvent is removed under reduced pressure, the residue is diluted with deionized water, and then the pH is adjusted to about 10 with saturated sodium carbonate aqueous solution. The mixture is extracted with dichloromethane (3 × 20 mL), the organic phases are combined, dried over anhydrous sodium sulfate, filtered, and concentrated under vacuum to obtain product N. The chemical synthesis route is as follows: Figure 21 The 1H NMR spectrum of the intermediate in the preparation of naphthalimide ethylamine (N). Figure 22 This is the 1H NMR spectrum of naphthalimide ethylamine (N).

[0034] The preparation method of 4-bromo-1,8-naphthalimide ethylamine (N1) used in this embodiment of the invention is as follows: 4-bromo-1,8-naphthalenedicarboxylic anhydride (5.54 g, 0.02 mmol), N-tert-butoxycarbonylethylenediamine (3.6 g, 0.02 mmol), and triethylamine (0.75 mL, 5 mmol) were dissolved in 150 mL of N,N-dimethylformamide (DMF). The solution was stirred at 75°C under vacuum for 15 hours. After cooling, 500 mL of cooled deionized water was added, resulting in a large amount of yellow solid. The intermediate was collected by centrifugation and was a brownish-yellow crude solid. It was dried under vacuum at 60°C for one week. The intermediate was placed in a three-necked flask, and 30 mL of dichloromethane and 7 mL of trifluoroacetic acid (TFA) were added. The mixture was stirred in a water bath at 0°C for 8 hours. After the reaction was completed, the solvent was removed under reduced pressure. The residue was diluted with deionized water, and the pH was adjusted to approximately 10 with a saturated sodium carbonate aqueous solution. The mixture was extracted three times with a mixed solution of methanol and dichloromethane (methanol:dichloromethane = 1:10), the organic phases were combined, dried over anhydrous sodium sulfate, filtered, and concentrated under vacuum to obtain product N1. Its chemical synthesis route is as follows: Figure 23 The 1H NMR spectrum of the intermediate in the preparation of 4-bromo-1,8-naphthalimide ethylamine (N1); Figure 24 The 1H NMR spectrum of 4-bromo-1,8-naphthalimide ethylamine (N1) is shown.

[0035] All other raw materials used in the embodiments of the present invention were obtained through commercial purchase.

[0036] Example 1 187 mg of urea, 57 mg of 1,8-naphthalenedicarboxylic anhydride, and 2 mg of levofloxacin (mass ratio 187:57:2) were weighed and dissolved in a mixture of 40 mL of ethanol and 10 mL of water. The mixture was sonicated until a homogeneous precursor solution was formed. The resulting precursor solution was transferred to a beaker and placed in an oven at 200 °C for 6 hours. After the reaction was completed, the mixture was cooled to room temperature. The resulting solid powder was added to 40 mL of water to form a carbon dot dispersion solution. Insoluble solids were removed by centrifugation. The centrifuged liquid was filtered through a 0.22 μm filter membrane to remove large particles. Finally, the reaction product was freeze-dried to obtain a white powder. A dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-A1, was thus prepared.

[0037] Figure 1 The fluorescence color diagram of CDs-A1 prepared in Example 1 after 365 nm ultraviolet light irradiation and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0038] Example 2 Same as Example 1, except that the amount of urea was adjusted to 1865 mg, and the mass ratio of urea, 1,8-naphthalenedicarboxylic anhydride and levofloxacin was 1865:57:2, to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-A2.

[0039] Figure 2 The fluorescence color diagram of the CDs-A2 material prepared in Example 2 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0040] Example 3 Same as Example 1, except that the amount of urea was adjusted to 3745 mg, and the mass ratio of urea, 1,8-naphthalenedicarboxylic anhydride and levofloxacin was 3745:57:2, to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-A3.

[0041] Figure 3 The fluorescence color diagram of the CDs-A3 material prepared in Example 3 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0042] Figure 4The graphs show the afterglow color changes of CDs-A1, CDs-A2, and CDs-A3 after the 365 nm UV light illumination was turned off over time, and their phosphorescence emission spectra excited by 365 nm UV light (delay 0.001 s). The time and color change measurements show that under 365 nm UV light illumination, the fluorescence color is white. After the 365 nm UV light illumination was turned off, CDs-A1 initially showed a yellow afterglow, which gradually turned green within approximately 0.5 seconds and disappeared after 5 seconds. CDs-A2 initially showed a yellow afterglow, which gradually turned green within approximately 0.5 seconds and disappeared after 7 seconds. CDs-A3 initially showed a yellow afterglow, which gradually turned green within approximately 0.5 seconds and disappeared after 8 seconds.

[0043] Example 4 Same as Example 1, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of 4-bromo-1,8-naphthalenedicarboxylic anhydride to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-B1.

[0044] Figure 5 The fluorescence color diagram of the CDs-B1 material prepared in Example 4 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0045] Example 5 Same as Example 2, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of 4-bromo-1,8-naphthalenedicarboxylic anhydride to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-B2.

[0046] Figure 6 The fluorescence color diagram of the CDs-B2 material prepared in Example 5 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0047] Example 6 Same as Example 3, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of 4-bromo-1,8-naphthalenedicarboxylic anhydride to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-B3.

[0048] Figure 7 The fluorescence color diagram of the CDs-B3 material prepared in Example 6 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0049] Figure 8The graphs showing the afterglow color change over time for CDs-B1, CDs-B2, and CDs-B3 materials after the 365 nm ultraviolet light illumination was turned off, and the phosphorescence emission spectra excited by 365 nm ultraviolet light (delay 0.001 s), obtained by measuring the time and color changes, show that the dynamic room-temperature phosphorescent materials provided by this invention exhibit a yellow-green fluorescence color under 365 nm ultraviolet light irradiation. After the 365 nm ultraviolet light illumination was turned off, CDs-B1 initially showed a yellow afterglow, which gradually turned into a green afterglow within approximately 0.5 seconds and disappeared after 3.5 seconds. CDs-B2 initially showed a yellow afterglow, which gradually turned into a green afterglow within approximately 0.5 seconds and disappeared after 6 seconds. CDs-B3 initially showed a yellow afterglow, which gradually turned into a green afterglow within approximately 0.5 seconds and disappeared after 6 seconds.

[0050] Example 7 Same as Example 1, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of 1,8-naphthalenedicarboxyliimide to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-C1.

[0051] Figure 9 The fluorescence color diagram of the CDs-C1 material prepared in Example 7 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0052] Example 8 Same as Example 2, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of 1,8-naphthalenedicarboxyliimide to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-C2.

[0053] Figure 10 The fluorescence color diagram of the CDs-C2 material prepared in Example 8 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0054] Example 9 Same as Example 3, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of 1,8-naphthalenedicarboxyliimide to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-C3.

[0055] Figure 11 The fluorescence color diagram of the CDs-C3 material prepared in Example 9 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0056] Figure 12The graphs show the afterglow color of CDs-C1, CDs-C2, and CDs-C3 materials after the 365 nm ultraviolet light illumination is turned off, and the phosphorescence emission spectra excited by 365 nm ultraviolet light (delay 0.001 s).

[0057] Measurements of time and color changes showed that under 365 nm ultraviolet light irradiation, the fluorescence color was white. After the 365 nm ultraviolet light irradiation was turned off, CDs-C1 initially showed a yellow afterglow, which gradually turned into a green afterglow within about 0.5 seconds and disappeared after 4 seconds. CDs-C2 initially showed a yellow afterglow, which gradually turned into a green afterglow within about 0.5 seconds and disappeared after 7 seconds. CDs-C3 showed a yellow afterglow, which gradually turned into a green afterglow within about 0.5 seconds and disappeared after 9 seconds.

[0058] Example 10 Same as Example 1, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of naphthalimide ethylamine to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-D1.

[0059] Figure 13 The fluorescence color diagram of the CDs-D1 material prepared in Example 10 after 365 nm ultraviolet light irradiation and the fluorescence emission spectrum under different wavelengths of excitation.

[0060] Example 11 Same as Example 2, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of naphthalimide ethylamine to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-D2.

[0061] Figure 14 The fluorescence color diagram of the CDs-D2 material prepared in Example 11 after 365 nm ultraviolet light irradiation and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0062] Example 12 Same as Example 3, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of naphthalimide ethylamine to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-D3.

[0063] Figure 15 The fluorescence color diagram of the CDs-D3 material prepared in Example 12 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0064] Figure 16The graphs show the afterglow color of CDs-D1, CDs-D2, and CDs-D3 materials after the 365 nm ultraviolet light illumination is turned off, and the phosphorescence emission spectra excited by 365 nm ultraviolet light (delay 0.001 s).

[0065] Measurements of time and color changes showed that under 365 nm ultraviolet light irradiation, the fluorescence color was white. After the 365 nm ultraviolet light irradiation was turned off, CDs-D1 initially showed a yellow afterglow, which gradually turned into a green afterglow within about 0.5 seconds and disappeared after 2.5 seconds. CDs-D2 initially showed a yellow afterglow, which gradually turned into a green afterglow within about 0.5 seconds and disappeared after 4 seconds. CDs-D3 initially showed a yellow afterglow, which gradually turned into a green afterglow within about 0.5 seconds and disappeared after 6 seconds.

[0066] Example 13 Same as Example 1, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of 4-bromo-1,8-naphthalimide ethylamine to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-E1.

[0067] Figure 17 The fluorescence color diagram of the CDs-E1 material prepared in Example 13 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0068] Example 14 Same as Example 2, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of 4-bromo-1,8-naphthalimide ethylamine to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-E2.

[0069] Figure 18 The fluorescence color diagram of the CDs-E2 material prepared in Example 14 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0070] Example 15 Same as Example 3, except that 1,8-naphthalenedicarboxylic anhydride was replaced with an equal mass of 4-bromo-1,8-naphthalimide ethylamine to prepare a dynamic room temperature phosphorescent material based on matrix-free carbon dots, denoted as CDs-E3.

[0071] Figure 19 The fluorescence color diagram of the CDs-E3 material prepared in Example 15 after irradiation with 365 nm ultraviolet light and the fluorescence emission spectrum under different wavelengths of excitation are shown.

[0072] Figure 20The graphs show the afterglow color of CDs-E1, CDs-E2, and CDs-E3 materials after the 365 nm ultraviolet light illumination is turned off, and their phosphorescence emission spectra excited by 365 nm ultraviolet light (delay 0.001 s).

[0073] Measurements of time and color changes revealed that, under 365 nm ultraviolet light irradiation, CDs-E1 exhibited an orange fluorescence, while CDs-E2 and CDs-E3 displayed a yellow fluorescence. After the 365 nm ultraviolet light irradiation was turned off, CDs-E1 displayed an orange afterglow that disappeared after 0.2 seconds. CDs-E2 initially displayed an orange afterglow, gradually transitioning to a yellow afterglow within approximately 0.2 seconds, which disappeared after 4 seconds. CDs-E3 initially displayed an orange afterglow, gradually transitioning to a yellow afterglow within approximately 0.5 seconds, which disappeared after 4.5 seconds.

[0074] Depend on Figure 1 , 2 As can be seen from 1, 2, 3, 9, 10, 11, 13, 14, and 15, the CDs-A1, CDs-A2, CDs-A3, CDs-C1, CDs-C2, CDs-C3, CDs-D1, CDs-D2, and CDs-D3 carbon dot materials prepared in this invention exhibit white fluorescence under ultraviolet light excitation.

[0075] Depend on Figure 5 , 6 As can be seen from 7, the introduction of bromine atoms into aromatic anhydrides / anhydride derivatives achieves the heavy atom effect. CDs-B1, CDs-B2 and CDs-B3 exhibit a yellow-green fluorescence color under ultraviolet light irradiation at a wavelength of 365 nm.

[0076] Depend on Figure 17 , 18 As can be seen from Figure 19, CDs-E1 exhibits orange fluorescence under ultraviolet light irradiation at a wavelength of 365 nm, while CDs-E2 and CDs-E3 exhibit yellow fluorescence.

[0077] Depend on Figure 4 , 8As can be seen from Figures 12 and 16, CDs-A1, CDs-A2, CDs-A3, CDs-B1, CDs-B2, CDs-B3, CDs-C1, CDs-C2, CDs-C3, CDs-D1, CDs-D2, and CDs-D3 exhibit a dynamic afterglow change from yellow to green after the 365 nm ultraviolet light illumination is turned off. CDs-E1 exhibits an orange afterglow change after the 365 nm ultraviolet light illumination is turned off. CDs-E2 and CDs-E3 exhibit a dynamic afterglow change from orange to yellow after the 365 nm ultraviolet light illumination is turned off.

[0078] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing dynamic room-temperature phosphorescent materials based on matrix-free carbon dots, characterized in that, The dynamic room-temperature phosphorescent material based on matrix-free carbon dots was prepared by a one-step pyrolysis method using urea, aromatic anhydrides / anhydride derivatives and nitrogen-containing heterocyclic compounds as raw materials.

2. The preparation method according to claim 1, characterized in that, Specifically, the following steps are included: Urea, aromatic anhydride / anhydride derivatives, and nitrogen-containing heterocyclic compounds were dissolved in a mixed solvent of ethanol and water and subjected to pyrolysis. After cooling to room temperature, the resulting solid powder was added to water to obtain a carbon dot dispersion solution. The solution was then centrifuged, filtered, and freeze-dried to prepare the dynamic room temperature phosphorescent material based on matrix-free carbon dots.

3. The preparation method according to claim 2, characterized in that, The mass ratio of urea, aromatic anhydride / anhydride derivative and nitrogen-containing heterocyclic compound is (187-3745):57:2; the volume ratio of nitrogen-containing heterocyclic compound and mixed solvent is 2mg:50mL.

4. The preparation method according to claim 2, characterized in that, The pyrolysis reaction was carried out at a temperature of 200°C for 6 hours.

5. The preparation method according to claim 2, characterized in that, The aromatic anhydride / anhydride derivative is selected from 1,8-naphthalenedicarboxylic anhydride, 1,8-naphthalenedicarbimide, naphthalimide ethylamine, 4-bromo-1,8-naphthalenedicarboxylic anhydride, or 4-bromo-1,8-naphthalimide ethylamine.

6. The preparation method according to claim 2, characterized in that, The nitrogen-containing heterocyclic compound is selected from levofloxacin.

7. The preparation method according to claim 2, characterized in that, The volume ratio of ethanol to water in the mixed solvent of ethanol and water is 4:

1.

8. A dynamic room-temperature phosphorescent material based on matrix-free carbon dots prepared by the preparation method according to any one of claims 1-7.

9. The application of the dynamic room temperature phosphorescent material based on matrix-free carbon dots as described in claim 8 in the preparation of anti-counterfeiting products.

10. The application of the dynamic room-temperature phosphorescent material based on matrix-free carbon dots as described in claim 8 in information encryption.

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