A method for preparing boron-nitrogen co-doped carbon dots with ultraviolet light-controlled dynamic multicolor phosphorescence transition, the resulting product, and its applications.

Abstract

This invention belongs to the field of carbon dot material preparation, specifically relating to a method for preparing boron-nitrogen co-doped carbon dots with ultraviolet light-controlled dynamic multicolor phosphorescence transition, the resulting product, and its applications. This invention employs a microwave-assisted one-step synthesis, grafting phenylboronic acid (PBA) onto carbon dots to obtain boron-nitrogen co-doped carbon dots (B,N-CDs) with dynamic multicolor phosphorescence conversion characteristics. Compared to traditional color-changing phosphorescent materials, the preparation method provided by this invention achieves multicolor phosphorescence modulation through a dynamic bonding mechanism, realizing the transition between different colors. This dynamically responsive multicolor phosphorescence characteristic provides new materials and design concepts for developing information encryption and optical display applications.

Description

Technical Field

[0001] This invention belongs to the field of carbon dot material preparation, specifically relating to a method for preparing boron-nitrogen co-doped carbon dots with ultraviolet light-controlled dynamic multicolor phosphorescence transition, the resulting products, and their applications. Background Technology

[0002] Organic room-temperature phosphorescence (RTP) materials have shown significant application potential in information encryption, bioimaging, and sensing due to their excellent photostability and tunable luminescence properties. However, developing multicolor phosphorescent materials with dynamic response to 365 nm ultraviolet light remains challenging. Current technologies are often limited by complex synthesis processes and limited dynamic response capabilities, making it difficult to achieve significant multicolor phosphorescence transitions. The current mainstream photoresponsive RTP mechanisms mainly fall into two categories: photoinduced structural changes that modulate phosphorescence properties through alterations in molecular conformation or cyclic structure, and radical-mediated photochromism that perturbs the excited-state process by generating radical intermediates with specific optical / paramagnetic properties. While these methods can regulate phosphorescence intensity and lifetime by adjusting the singlet-triplet bandgap (ΔEST), most systems can only achieve monochromatic switching or phosphorescence on / off states, making it difficult to achieve dynamic multicolor transitions of emission colors.

[0003] Carbon dots (CDs), as zero-dimensional carbon nanomaterials, exhibit excellent phosphorescence tunability due to their highly tunable structural design (such as the introduction of functional groups like hydroxyl, carboxyl, and amino groups, and the regulation of conjugated structures). For example, introducing multiple carbonyl groups (C=O) or doping with elements like boron (B) and nitrogen (N) can effectively regulate the energy level structure and enhance the phosphorescence emission wavelength range. However, existing carbon dot systems are mostly limited to a single phosphorescence color, and their photochromic phenomena are mainly concentrated on fluorescence modulation; research on dynamic multicolor phosphorescence responses is rarely reported.

[0004] Therefore, developing material systems that can produce significant dynamic changes in multicolor phosphorescence under external stimuli such as 365 nm ultraviolet light is crucial for advancing multidimensional optical information encryption and intelligent display technologies. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing boron-nitrogen co-doped carbon dots with ultraviolet light-controlled dynamic multicolor phosphorescence transition. The method introduces ultraviolet-responsive dynamic covalent units onto the carbon dot surface, constructing a photosensitive structure and multiple phosphorescent emission centers. Under light stimulation, the dynamic bond-induced structural reconstruction directly regulates the electron transfer process, altering the lifetime proportions of different phosphorescent centers, thereby achieving dynamic evolution of phosphorescence color. This mechanism provides a new approach for the preparation of multicolor phosphorescent materials.

[0006] The present invention also provides boron-nitrogen co-doped carbon dots with ultraviolet light-controlled dynamic multicolor phosphorescence transition prepared by the above preparation method.

[0007] Another objective of this invention is to provide the application of the aforementioned boron-nitrogen co-doped carbon dots in the fields of information encryption, bioimaging, and sensing.

[0008] The technical solution adopted by the present invention to achieve the above objectives is as follows: This invention provides a method for preparing boron-nitrogen co-doped carbon dots with ultraviolet light-controlled dynamic multicolor phosphorescence transition, comprising the following steps: (1) Grind the carbon source, nitrogen source and boron source thoroughly until they are mixed evenly. Then, add deionized water and continue grinding until a uniform mixture is formed. (2) The mixture is subjected to microwave heating reaction; (3) After the reaction is completed, the reaction product is ground into powder; the powder is added to a mixture of deionized water and petroleum ether; ultrasonic treatment is performed to form a suspension; vacuum filtration is performed and the product is dried to obtain boron-nitrogen co-doped carbon dots B,N-CDs.

[0009] Preferably, in step (1), the carbon source is citric acid; the nitrogen source is urea; the boron source is phenylboronic acid; the mass ratio of the carbon source, nitrogen source and boron source is 1:0.1:1; and the material-liquid ratio of the carbon source and deionized water is 6-8 mg:1 μL.

[0010] Preferably, in step (2), the specific process of the microwave heating reaction is as follows: first, heat at a power of 360-370W for 10-12 minutes, then adjust the power to 500-515W and continue heating for 5-8 minutes.

[0011] Preferably, in step (3), the volume ratio of deionized water to petroleum ether in the mixture is 1:6.

[0012] The present invention also provides a boron-nitrogen co-doped carbon dot with ultraviolet light-controlled dynamic multicolor phosphorescence transition prepared by the above preparation method. Under 365 nm ultraviolet light irradiation, the phosphorescence of the boron-nitrogen co-doped carbon dot gradually changes from blue-cyan to red.

[0013] Another objective of this invention is to provide the application of the aforementioned boron-nitrogen co-doped carbon dots in the fields of information encryption, bioimaging, and sensing.

[0014] This invention employs a microwave-assisted one-step synthesis to graft phenylboronic acid (PBA) onto carbon dots, yielding boron-nitrogen co-doped carbon dots (B, N-CDs) with dynamic multicolor phosphorescence conversion characteristics. Under 365 nm ultraviolet light irradiation, the phosphorescence of this material gradually changes from blue-cyan to red. Through molecular design, PBA forms dynamic borate ester bonds with the hydroxyl groups on the carbon dot surface via its borate groups. This reaction generates a rigid covalent network structure, stabilizing the initial phosphorescent centers. Citric acid serves as the carbon source, providing abundant surface hydroxyl and carboxyl groups; urea acts as both a nitrogen source and a crosslinking agent. Microwave irradiation simultaneously promotes carbon nucleus formation and surface functionality. The initial phosphorescence exhibits a broad peak at 481 nm. Under continuous ultraviolet light irradiation, photoinduced breakage of the borate bonds generates oxygen vacancies, disrupting the originally stable rigid microenvironment of the T1 exciton state. Simultaneously, structural reorganization leads to the formation of a new triplet energy state with a narrower bandgap, causing the phosphorescence to gradually shift towards longer wavelengths. Compared to traditional color-changing phosphorescent materials, the preparation method provided by this invention achieves multicolor phosphorescence modulation through a dynamic bonding mechanism, enabling the transition between different colors. This dynamically responsive multicolor phosphorescence characteristic provides new materials and design concepts for the development of information encryption and optical display applications.

[0015] The beneficial effects of this invention are as follows: (1) The boron-nitrogen co-doped carbon dots prepared by the present invention have photoresponse characteristics of dynamic multicolor phosphorescence transition controlled by ultraviolet light. Under 365nm ultraviolet light irradiation, they exhibit time-dependent phosphorescence red shift state changes and can achieve phosphorescence transition from blue-cyan to red with irradiation time. The color change process is rapid and highly complete. Moreover, in the afterglow state, they can exhibit rich phosphorescence color changes with multi-regional differences. In addition, based on the photoresponse phosphorescence color change characteristics, the B,N-CDs prepared by the present invention have significant advantages in the application of color-changing phosphorescent materials, and at the same time have good application potential in the fields of digital information encryption.

[0016] (2) The present invention uses microwave-assisted one-step synthesis, the preparation process is simple and controllable, and the mass production of materials can be realized. Attached Figure Description

[0017] Figure 1 TEM image of B, N-CDs prepared in Example 1; Figure 2 HR-TEM images of B, N-CDs prepared in Example 1; Figure 3 Figure 4 shows the Fourier transform infrared spectra of B, N-CDs prepared in Example 1 under the same UV irradiation time; Figure 5 shows the B 1s X-ray photoelectron spectra of B, N-CDs prepared in Example 1 before and after UV irradiation. Figure 5 shows the evolution of phosphorescence spectra of B, N-CDs prepared in Example 1 under different UV irradiation times; Figure 6 shows the time-resolved phosphorescence spectra of B, N-CDs prepared in Example 1 after 30s of UV irradiation; Figure 7 shows the photoresponsive dynamic phosphorescence color-changing behavior and application demonstration of B, N-CDs prepared in Example 1. Figure 8 Phosphor-free image of N-CDs prepared in Comparative Example 1; Figure 9 The phosphorescence color change image of the material prepared in Comparative Example 2; Figure 10 The phosphorescence color change image of the material prepared in Comparative Example 3. Detailed Implementation

[0018] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0019] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0020] Example 1 B, Preparation of N-CDs Citric acid was used as the carbon source, and urea and phenylboronic acid were used as the nitrogen and boron sources, respectively. The specific process was as follows: (1) Place citric acid (600 mg), urea (60 mg), and phenylboronic acid (600 mg) in a mortar and grind thoroughly until well mixed. Then, add deionized water (100 μL) and continue grinding until a uniform paste is formed; (2) Transfer this mixture to a 25 ml beaker and place it in a 700 W microwave reactor. First, heat it at a low power of 364 W for 10 minutes, then adjust it to a medium power of 511 W and heat it for another 5 minutes. (3) After the reaction is complete, allow the beaker to cool naturally to room temperature and grind the resulting solid into a white powder. Transfer this white powder to a 30 mL beaker and add a pre-prepared deionized / petroleum ether mixture (volume ratio 1:6, total volume 14 mL). Place the beaker in an ultrasonic cleaner and sonicate for 5 minutes to fully disperse and form a suspension. Then slowly pour the suspension into a Buchner funnel containing a 0.22 μm microporous membrane for vacuum filtration. Dry the filtered solid sample in a 60 °C oven overnight to obtain the final white solid B,N-CDs.

[0021] TEM images of the white solid B,N-CDs prepared in Example 1 are shown below. Figure 1 As shown, B, N-CDs are spherical and encapsulated within a crystalline matrix material. HR-TEM, as Figure 2As shown, the image displays clear lattice fringes with a spacing of 0.21 nm, corresponding to the (100) crystal plane of graphite, indicating that B, N-CDs have a graphitized core structure.

[0022] The structural changes of the carbon dot materials prepared in Example 1 after UV irradiation for different durations were analyzed by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Figure 3 shows the FT-IR spectra of B, N-CDs after irradiation with 365 nm UV light for 0 seconds and 130 seconds. The broad peak at 3443 cm⁻¹ represents the stretching vibration of the O–H or N–H bond. The characteristic peaks at 1730 cm⁻¹ and 1660 cm⁻¹ are attributed to the stretching vibration of C=O and the amide functional group (–CONH), respectively, confirming the condensation reaction between urea and carboxylic acid. The peaks at 1250 cm⁻¹, 960 cm⁻¹, and 759 cm⁻¹ are related to the stretching vibration of B–O, and the out-of-plane bending vibrations of C–B and B–N, respectively. The strength of the BO bond at 1250 cm⁻¹ gradually weakened with time and increased irradiation intensity, indicating that the borate ester bond broke during ultraviolet irradiation.

[0023] XPS full-spectrum analysis of B,N-CDs before and after 130 seconds of irradiation revealed that the B 1s spectrum of the unirradiated sample (Figure 4) contained three components: BCO2 (192.03 eV), B–O (193.20 eV), and B–C (190.58 eV). After irradiation, the fitted components were BCO2 (192.00 eV), B–O (193.60 eV), and B–C (190.29 eV), with a significant change in the binding energy of the BO bond, which is attributed to photoinduced boronic acid ester bond breakage.

[0024] In summary, both FT-IR and XPS results confirm that 365 nm UV irradiation induces structural changes in the borate ester bonds on the surface of B, N-CDs. With increasing irradiation time, the intensity of the characteristic FT-IR peak of the borate ester bonds gradually decreases. XPS analysis also reveals a shift in the BO binding energy, indicating a corresponding change in the chemical bonds, consistent with the FT-IR observations. These results collectively demonstrate that UV irradiation leads to the breaking of borate ester bonds in B, N-CDs, thereby altering the photoresponse properties of the material.

[0025] Comparative Example 1 Using citric acid as a carbon source and urea as a nitrogen source, the specific process is as follows: (1) Place citric acid (600 mg) and urea (60 mg) in a mortar and grind thoroughly until well mixed. Then, add deionized water (100 μL) and continue grinding until a uniform paste is formed; (2) Transfer this mixture to a 25 ml beaker and place it in a 700 W microwave reactor. First, heat it at a low power of 364 W for 10 minutes, then adjust it to a medium power of 511 W and heat it for another 5 minutes. (3) After the reaction is complete, allow the beaker to cool naturally to room temperature and grind the resulting solid into a white powder. Transfer this white powder to a 30 mL beaker and add a pre-prepared deionized / petroleum ether mixture (volume ratio 1:6, total volume 14 mL). Place the beaker in an ultrasonic cleaner and sonicate for 5 minutes to fully disperse and form a suspension. Then slowly pour the suspension into a Buchner funnel containing a 0.22 μm microporous membrane for vacuum filtration. Dry the filtered solid sample in a 60 °C oven overnight to obtain the final white solid N-CDs.

[0026] Under the same synthetic conditions, the carbon dots synthesized in Comparative Example 1 did not produce phosphorescence and showed no photoresponsive effect. Specifically, as follows... Figure 8 As shown.

[0027] Comparative Example 2 Step (1) is the same as in Example 1; (2) Transfer this mixture to a 25 mL beaker and place it in a 700 W microwave reactor. Heat at a low power of 364 W for 15 minutes. Step (3) is the same as in Example 1.

[0028] During microwave heating, when only low power is used for the microwave heating reaction, the prepared material does not change color, specifically as follows: Figure 9 As shown.

[0029] Comparative Example 3 Step (1) is the same as in Example 1; (2) Transfer this mixture to a 25 mL beaker and place it in a 700 W microwave reactor. Heat at a low power of 511 W for 15 minutes. Step (3) is the same as in Example 1.

[0030] During microwave heating, using only medium power will cause an initial phosphorescence red shift, turning it into green emission. Specifically, as shown below... Figure 10 As shown.

[0031] Example 1: Phosphorescence Performance Test To investigate the luminescence characteristics of B,N-CDs, this invention employed a PR-305 long afterglow spectrometer for phosphorescence spectroscopy testing. Specific testing conditions were as follows: all measurements were performed at room temperature; the excitation source was a 365nm ultraviolet LED; and the phosphorescence emission spectrum was collected in the range of 450–750nm. Figure 5 As shown, the instantaneous phosphorescence spectrum of the sample under unirradiated conditions and the instantaneous phosphorescence spectrum after continuous irradiation with 365nm ultraviolet light for 130s were collected. Figure 6 This shows the time-resolved phosphorescence spectra of the sample after 30s of UV pre-irradiation at different delay times.

[0032] As shown in Figure 5, the initial B, N-CDs exhibit a broad phosphorescent emission peak at 481 nm. After 130 seconds of continuous 365 nm UV irradiation, the intensity of this peak decays to almost complete disappearance. The initial phosphorescent signal in the long-wavelength region shows a structure with a main peak at 622 nm and a shoulder peak at 663 nm. After 130 seconds of irradiation, this region transforms into a broad peak dominated by 622 nm. The intensity of the 481 nm peak continuously decreases with prolonged UV irradiation time, while the intensity of the 622 nm peak increases accordingly. This observation confirms the existence of two distinct phosphorescent emission centers, whose intensity is negatively correlated with irradiation time. Time-resolved phosphorescence spectroscopy measurements of the B, N-CDs sample after 30 seconds of UV irradiation (Figure 6) show enhanced peak intensities at 622 nm and 663 nm. However, with increasing delay time, the broad peaks in the long-wavelength region exhibit a rapid overall decay trend, thereby triggering dynamic phosphorescent color shift. It is noteworthy that the peak intensity ratio at 622 nm and 663 nm (I622 / I663≈1.40±0.11) remained stable at different phosphorescence delay times, confirming that they belong to the same luminescent species.

[0033] Example 2 Based on the photostimulated variable afterglow properties of B,N-CDs, this invention demonstrates color-changing behavior and potential applications. The material prepared in Example 1 was prepared into the target shape by placing the powder in a perforated template.

[0034] B,N-CDs exhibit dynamic phosphorescence under 365 nm UV irradiation. Initially, after approximately 0.1 seconds of irradiation, the material emits a bright blue-cyan phosphorescence. As irradiation time increases, a competitive transition occurs between the two emission centers. The emission lifetime at 481 nm continuously decays, while the intensity and lifetime at 622 nm increase simultaneously, resulting in a significant redshift of the phosphorescence. This process occurs rapidly after UV irradiation and is accompanied by a time-dependent phosphorescence color phenomenon. After 130 seconds of irradiation, only red phosphorescence remains, confirming the completion of the photoresponsive color change. Benefiting from this photoresponsive phosphorescence color-changing characteristic, a flower pattern was formed using solid B,N-CDs powder. This flower pattern appears gray under sunlight and exhibits cyan fluorescence under 365 nm excitation. By partitioning the irradiation, the petal region designated as region a and the leaf region designated as region b were irradiated for different durations (Figure 7). After turning off the light source, spatially customized phosphorescence colors were achieved. The flower pattern exhibits a remarkably rich variation in phosphorescent color: initially displaying only a bluish-green afterglow, but after differential irradiation of areas a and b, the phosphorescent colors produced by a and b differ, exhibiting different colors of emission. After 130 seconds of irradiation, the phosphorescent color of one area turns red. This dynamic color-changing process not only demonstrates the material's excellent color-changing phosphorescent properties but also verifies the feasibility and potential of digital information encryption based on afterglow variations.

Claims

1. A method for preparing boron-nitrogen co-doped carbon dots with ultraviolet light-controlled dynamic multicolor phosphorescence transition, characterized in that, Includes the following steps: (1) Grind the carbon source, nitrogen source and boron source thoroughly until they are mixed evenly. Then, add deionized water and continue grinding until a uniform mixture is formed. (2) The mixture is subjected to microwave heating reaction; (3) After the reaction is completed, the reaction product is ground into powder; the powder is added to a mixture of deionized water and petroleum ether; ultrasonic treatment is performed to form a suspension; vacuum filtration is performed and the product is dried to obtain boron-nitrogen co-doped carbon dots B,N-CDs.

2. The preparation method according to claim 1, characterized in that, In step (1), the carbon source is citric acid; the nitrogen source is urea; the boron source is phenylboronic acid; the mass ratio of the carbon source, nitrogen source and boron source is 1:0.1:1; and the material-liquid ratio of the carbon source and deionized water is 6-8 mg:1 μL.

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), the specific process of the microwave heating reaction is as follows: first, heat at a power of 360-370W for 10-12 minutes, then adjust the power to 500-515W and continue heating for 5-8 minutes.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (3), the volume ratio of deionized water to petroleum ether in the mixture is 1:

6.

5. A boron-nitrogen co-doped carbon dot with ultraviolet light-controlled dynamic multicolor phosphorescence transition, prepared by the preparation method according to any one of claims 1-4, characterized in that, When the boron-nitrogen co-doped carbon dots are irradiated with 365 nm ultraviolet light, the phosphorescence of the carbon dots gradually changes from blue-cyan to red.

6. An application of the boron-nitrogen co-doped carbon dots as described in claim 5 in the fields of information encryption, bioimaging, and sensing.

Images