A solid-state phosphorescent carbon dot that becomes brighter upon contact with water and has an extended naked-eye recognition time, and a preparation method and application thereof

Abstract

The present invention belongs to the fields of phosphorescent materials, anti-counterfeiting, and biological imaging applications, and provides a solid-state phosphorescent carbon dot that becomes brighter upon contact with water and has an extended naked-eye recognition time, as well as a preparation method and application thereof. The purpose of the present invention is to develop a class of humidity-stimulus-induced ultra-long-lifetime room-temperature phosphorescent carbon dot materials. Based on this technical purpose, the present invention provides a solid-state phosphorescent carbon dot. The solid-state phosphorescent carbon dot emits a phosphorescent emission peak with a wavelength of 512 nm under ultraviolet light excitation. The quantum yield and phosphorescence lifetime of these solid phosphorescent carbon dots are significantly improved after adding water compared to the dry solid carbon dots, achieving a several-fold change in the lifetime (from 174.51 ms) and quantum yield (from 6.7%) to the lifetime (900.17 ms) and quantum yield (26.9%) of the solid-state phosphorescent-emitting carbon dots. The preparation process of this solid-state phosphorescent carbon dot material is simple and easy to produce, and has the advantages of simplicity, rapidity, metal-free, long lifetime, cost-effectiveness, low toxicity, etc.

Description

Technical Field

[0001] The present invention belongs to the fields of phosphorescent materials, anti-counterfeiting, and bioimaging applications, and particularly relates to a carbon dot with solid-state phosphorescence (RTP) emission, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention and is not necessarily to be regarded as an admission or any form of implication that this information constitutes prior art already known to those of ordinary skill in the art.

[0003] Stimulus-responsive luminescent materials are a class of materials whose luminescence properties change correspondingly under the stimulation of external environmental factors (including temperature, pressure, light, humidity, acid-base, etc.) and can return to the initial state under specific conditions. So far, most stimulus-responsive luminescent materials have been designed and developed based on the change of fluorescence emission color or intensity, and have been applied in fields such as data storage, anti-counterfeiting encryption, sensors, and bioimaging. In recent years, stimulus-responsive luminescent materials based on room-temperature phosphorescence have attracted extensive attention from researchers and have become one of the current research hotspots. Room-temperature phosphorescent materials refer to materials that can still generate emission light after the excitation light is stopped at room temperature, and the luminescence time can generally be delayed by milliseconds or even several seconds or more. Compared with traditional fluorescent materials, room-temperature phosphorescent materials not only have the stimulation factors of luminescence color and intensity but also have the attribute of long lifetime, so they can exhibit richer stimulus-responsive characteristics, which endows them with higher security in the fields of information anti-counterfeiting and encryption and decryption. In addition, because the triplet excitons of room-temperature phosphorescent materials are easily affected by the surrounding environment, they are more sensitive to external stimuli. Therefore, the development of stimulus-responsive room-temperature phosphorescent materials is of great significance for the next-generation information anti-counterfeiting and encryption and decryption technologies.

[0004] Research shows that carbon dots are a kind of room-temperature phosphorescent material that can meet the above conditions and has great application potential. It is a carbon nanoparticle with a size less than 10 nm, composed of an sp 2 / sp 3 hybridized carbon core and abundant surface functional groups or polymer chains. As an important member of the family of carbon-based nanomaterials, carbon dots have been favored by many researchers in recent years due to their advantages such as high quantum yield, tunable emission wavelength, low cost, environmental friendliness, and easy functionalization. However, most of the reported stimulus-responsive phosphorescent carbon dots are developed based on an anhydrous and dry environment, which is not conducive to long-term use in a humidity environment. Therefore, the development of directly humidity-stimulus-responsive room-temperature phosphorescent carbon dots is of great research significance for both the development of new stimulus-responsive phosphorescent materials and the expansion of practical applications. However, the triplet state of phosphorescent carbon dots is extremely easy to combine with triplet oxygen in water ( 3 O2 ) Electron transfer occurs, generating singlet oxygen ( 1 O 2 ), resulting in phosphorescence quenching. It is generally difficult for carbon dot materials to simultaneously possess both humidity-stimuli responsiveness and room-temperature phosphorescence. Therefore, how to rationally design and successfully prepare a humidity-stimuli responsive room-temperature phosphorescent carbon dot still poses a great challenge. Summary of the Invention

[0005] To solve the above problems, the present invention provides a humidity-stimuli responsive room-temperature phosphorescent carbon dot, namely: a solid-state phosphorescent carbon dot that becomes brighter when exposed to water and has an extended naked-eye recognition time, and is applied to anti-counterfeiting and bioimaging. Before and after humidity stimulation, the carbon dots change several times in terms of lifetime (from 174.51 ms) and quantum yield (6.7%) to lifetime (900.17 ms) and quantum yield (26.9%). Compared with traditional metal complex materials, the carbon dot material provided by the present invention has the advantages of simplicity, rapidity, metal-free, cost-effectiveness, low toxicity, etc.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In the first aspect of the present invention, a preparation method of a solid-state phosphorescent carbon dot that becomes brighter when exposed to water and has an extended naked-eye recognition time is provided, including:

[0008] Using cyanuric acid as a carbon source precursor and N,N-dimethylformamide as a solvent, reacting at 210 - 240 °C to obtain the solid-state phosphorescent carbon dot. If the reaction time and reaction temperature are changed, it will affect the generation of the structure of the solid-state phosphorescent carbon dot, and further affect the phosphorescence intensity and quantum yield.

[0009] The solid-state phosphorescent carbon dot provided by the present invention uses cyanuric acid as a carbon source precursor and N,N-dimethylformamide (DMF) as a solvent. Under high-temperature conditions, the carbon source precursor will form a cross-linked network polymer to obtain the solid-state phosphorescent carbon dot. Under ultraviolet light, it can emit green phosphorescence stronger than the precursor cyanuric acid.

[0010] In some embodiments, the purity of the cyanuric acid is 98% or more.

[0011] In some embodiments, the mass concentration of cyanuric acid in N,N-dimethylformamide is 10% - 15%.

[0012] In some embodiments, cyanuric acid is added to N,N-dimethylformamide and dissolved by ultrasonic treatment. Ultrasonic treatment makes the reactant solution more uniform and achieves better results.

[0013] If the temperature is too high, carbonization is severe and phosphorescence becomes weak; if the temperature is too low, it is difficult for the raw materials to carbonize, and the yield of solid fluorescent carbon dots is relatively low. Therefore, in this application, the reaction temperature is 210-240°C.

[0014] In some embodiments, the reaction time is 10-25h.

[0015] In the second aspect of the present invention, the method for heating the solid-state phosphorescence prepared above is as follows: First, ultrasonic treatment is performed on the mixed reaction solution, and then a solid-state phosphorescent carbon dot is obtained through a high-temperature reaction in an oven.

[0016] The carbon dots, the solid-state phosphorescent carbon dots have N-H bonds, O-H bonds, C-N bonds, C=O bonds, etc. The obtained solid-state phosphorescent carbon dots have a particle size of 2.57 nm. When excited by ultraviolet light, the sample produces a fluorescence emission peak with a wavelength of 479 nm and a phosphorescence emission peak with a wavelength of 512 nm.

[0017] The solid-state phosphorescent carbon dots provided by the present invention emit a fluorescence emission peak with a wavelength of 479 nm and a phosphorescence emission peak with a wavelength of 512 nm under ultraviolet light excitation. The quantum yield and lifetime of this carbon dot have changed significantly compared with other solid carbon dots in an aqueous environment. In an aqueous environment, the quantum yield and phosphorescence lifetime can be increased and enhanced by several times.

[0018] In the third aspect of the present invention, a cryptographic code is provided, including: the above-mentioned solid-state phosphorescent carbon dots.

[0019] In the fourth aspect of the present invention, an application of the above-mentioned solid-state phosphorescent carbon dots in the field of anti-counterfeiting and encryption is provided.

[0020] In the fifth aspect of the present invention, an application of the above-mentioned solid-state phosphorescent carbon dots in biological imaging is provided.

[0021] Advantages of the present invention

[0022] (1) The solid-state phosphorescent carbon dots provided by the present invention have a fluorescence emission peak with a wavelength of 479 nm for the sample under ultraviolet light excitation, and a phosphorescence emission peak with a wavelength of 512 nm is displayed after turning off the ultraviolet lamp. The quantum yield and lifetime of this carbon dot have changed significantly compared with other solid carbon dots in an aqueous environment. In an aqueous environment, the quantum yield and phosphorescence lifetime can be increased and enhanced by several times.

[0023] (2) The preparation method of the solid-state fluorescent carbon dots of the present invention uses cyanuric acid as a carbon source precursor and N,N-dimethylformamide (DMF) as a solvent. Under high-temperature conditions, the carbon source precursor will form a cross-linked network polymer to obtain solid-state phosphorescent carbon dots. Its preparation process is simple, rapid, easy to operate, and has a high yield; complex and expensive equipment is not required in the preparation process, the cost is low, and no other harmful substances are generated during the preparation process, which is easy to realize industrial production.

[0024] (3) The preparation method of the present invention is simple, highly practical, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0026] Figure 1 It is the fluorescence and phosphorescence emission spectrogram of the raw material cyanuric acid in Example 1;

[0027] Figure 2 It is the ultraviolet-visible absorption spectrogram of the raw material cyanuric acid in Example 1;

[0028] Figure 3 It is the X-ray photoelectron energy spectrum spectrogram of the raw material cyanuric acid in Example 1;

[0029] Figure 4 It is the phosphorescence emission spectra of the solid-state phosphorescent carbon dots prepared in Example 1 at different temperatures;

[0030] Figure 5 It is the phosphorescence lifetime decay spectra of the solid-state phosphorescent carbon dots prepared in Example 1 at different temperatures;

[0031] Figure 6 It is the phosphorescence emission spectra of the solid-state phosphorescent carbon dots prepared in Example 1 at different times;

[0032] Figure 7 It is the phosphorescence lifetime decay spectra of the solid-state phosphorescent carbon dots prepared in Example 1 at different times;

[0033] Figure 8 It is the fluorescence emission spectrum and phosphorescence emission spectrum of the solid-state phosphorescent carbon dots prepared in Example 1 under 365 nm excitation;

[0034] Figure 9 It is the excitation spectrum of the raw material cyanuric acid prepared in Example 1 and the excitation spectrum of the solid-state phosphorescent carbon dots;

[0035] Figure 10 It is the ultraviolet-visible absorption spectrogram of the solid-state phosphorescent carbon dots prepared in Example 1;

[0036] Figure 11 It is the scanning electron microscope image of the solid-state phosphorescent carbon dots prepared in Example 1;

[0037] Figure 12 It is the transmission electron microscope image of the solid-state phosphorescent carbon dots prepared in Example 1;

[0038] Figure 13Size distribution of the solid-state phosphorescent carbon dots prepared in Example 1;

[0039] Figure 14 X-ray photoelectron spectroscopy spectrum of the solid-state phosphorescent carbon dots prepared in Example 1;

[0040] Figure 15 Phosphorescence lifetime decay curve of the solid-state phosphorescent carbon dots prepared in Example 1 with the change of storage time;

[0041] Figure 16 Phosphorescence emission spectra of the solid-state phosphorescent carbon dots prepared in Example 1 in vacuum and air;

[0042] Figure 17 Phosphorescence lifetime decay spectra of the solid-state phosphorescent carbon dots prepared in Example 1 in vacuum and air;

[0043] Figure 18 Phosphorescence emission spectra of the solid-state phosphorescent carbon dots prepared in Example 1 under different high-temperature conditions;

[0044] Figure 19 Phosphorescence lifetime decay spectra of the solid-state phosphorescent carbon dots prepared in Example 1 under different high-temperature conditions;

[0045] Figure 20 Thermogravimetric curves of cyanuric acid, the raw material of Example 1, and the prepared solid-state phosphorescent carbon dots.

[0046] Figure 21 Phosphorescence lifetime decay spectra of the solid-state phosphorescent carbon dots prepared in Example 1 under different pressures;

[0047] Figure 22 Phosphorescence emission spectra of the solid-state phosphorescent carbon dots prepared in Example 1 under different water addition amounts;

[0048] Figure 23 Phosphorescence lifetime decay spectra of the solid-state phosphorescent carbon dots prepared in Example 1 under different water addition amounts;

[0049] Figure 24 Changes in quantum yield and lifetime of the solid-state phosphorescent carbon dots prepared in Example 1 under 50% water addition amount;

[0050] Figure 25 Differential scanning calorimetry spectra of the solid-state phosphorescent carbon dots prepared in Example 1 under different water addition amounts;

[0051] Figure 26 Laser Raman spectra of the solid-state phosphorescent carbon dots prepared in Example 1 under different water addition amounts;

[0052] Figure 27Infrared spectra of the solid-state phosphorescent carbon dots prepared in Example 1 in the solid state, with water added, and under heavy water;

[0053] Figure 28 Application 1 of the solid-state phosphorescent carbon dots prepared in Example 1 in digital encryption;

[0054] Figure 29 Application 2 of the solid-state phosphorescent carbon dots prepared in Example 1 in digital encryption;

[0055] Figure 30 Injection and imaging mechanism of the solid-state phosphorescent carbon dots prepared in Example 1 in the back of mice;

[0056] Figure 31 Fluorescence imaging and phosphorescence imaging pictures of phosphorescent carbon dots with different concentrations prepared in Example 1 in the back imaging of mice;

[0057] Figure 32 Fluorescence imaging and phosphorescence imaging pictures of the phosphorescent carbon dot solution prepared in Example 1 in the axilla imaging of mice;

[0058] Figure 33 Quantification of the afterglow intensity of the phosphorescent carbon dot solutions with different concentrations prepared in Example 1;

[0059] Figure 34 Quantification of the fluorescence intensity and phosphorescence intensity of the phosphorescent carbon dot solutions with different concentrations prepared in Example 1 in the back imaging of mice;

[0060] Figure 35 Fluorescence signal-to-noise ratio and phosphorescence signal-to-noise ratio of the phosphorescent carbon dot solution prepared in Example 1 in the back imaging of mice. Detailed implementation manners

[0061] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0062] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are explanations rather than limitations of the present invention.

[0063] Example 1. Preparation of solid-state phosphorescent carbon dots (composite materials)

[0064] Take 2 g of cyanuric acid in N,N-dimethylformamide (DMF) (20 mL), then transfer the solution to an ultrasonic machine and sonicate for 15 minutes. Heat at 210 - 240 °C for 5 - 25 h (heating at 230 °C for 10 h is the optimal solution). After the reaction is completed, the crucible is naturally cooled to room temperature, and a brown solid is obtained to obtain a solid phosphorescent carbon dot composite material (hereinafter referred to as: composite material, i.e., CNDs@CA).

[0065] The solid yellow fluorescent carbon dots prepared in this example emit weak green phosphorescence under an ultraviolet lamp (365 nm), as Figure 2 shown. The ultraviolet-visible spectrum of the raw material cyanuric acid shows a strong exciton absorption peak at 215 nm. As Figure 1 shown. The fluorescence emission of the raw material cyanuric acid is at 435 nm, and the phosphorescence emission spectrum is at 477 nm. As Figure 3 shown. The X-ray photoelectron spectroscopy spectrum of the raw material cyanuric acid clearly shows the relevant bond types of C=O, O-H, N-H…O, C=O…H, C-H…O, and C-O-H…O. As Figure 2 shown. The fluorescence spectrum of the composite material has an excitation peak at 479 nm, and the phosphorescence spectrum has an excitation peak at 512 nm. As Figure 4 shown. The phosphorescence intensity of the composite material reaches the highest value at 230 °C at different reaction temperatures, as Figure 5 shown. The phosphorescence decay lifetime also reaches the highest at 230 °C. As Figure 6 shown. The reaction time of the composite material reaches the maximum value at 10 hours, as Figure 7 shown. The phosphorescence decay lifetime also reaches the highest at 10 hours. In summary, the optimal reaction time selected is 230 °C, 10 hours.

[0066] As Figure 8 shown, the fluorescence emission peak of the composite material at a sample wavelength of 479 nm under ultraviolet light excitation under long-term irradiation of the ultraviolet lamp, and a green phosphorescence emission peak at 512 nm is shown in the dark environment after turning off the ultraviolet lamp. As Figure 9 shown. The optimal position of the excitation peak of cyanuric acid is 360 nm, while a new excitation peak position appears at 380 nm in the excitation map of the solid-state phosphorescent carbon dots. As Figure 10 shown, the absorption spectrum of the solid-state phosphorescent carbon dots, compared with cyanuric acid, the resulting composite material can absorb a wider range of light. As Figure 11 shown. According to the scanning electron microscope results of the solid-state phosphorescent carbon dots, it can be seen that the crystal structure of the composite material presents a flaky three-dimensional structure, as Figure 12 shown. According to the transmission electron microscope results of the solid-state phosphorescent carbon dots, carbon dots can be observed therein, as Figure 13 shown, with an average particle size of 2.57 nm, as Figure 14As shown, the X-ray photoelectron spectroscopy spectrum of the composite material also clearly shows the relevant bond types of C=O, O-H, N-H···O, C=O···H, C-H···O, and C-O-H···O. As Figure 15 shown. During the 0 - 12 months of placement of the composite material, its lifespan did not change significantly, as Figure 16 , Figure 17 shown. The phosphorescence intensity and lifespan of the composite material did not change in vacuum and air. As Figure 18 , Figure 19 shown. The phosphorescence intensity and lifespan of the composite material also did not change in a high-temperature environment. As Figure 20 shown. The composite material showed better stability in thermal stability than the raw material cyanuric acid. As Figure 21 shown. The phosphorescence lifespan of the composite material only decreased by about 10% under different pressure conditions. In summary, the composite material has excellent stability under different conditions.

[0067] As Figure 22 , Figure 23 shown. When water was dropped onto the surface of the composite material and waited until the water was completely absorbed by the composite material, it was found that the phosphorescence intensity was greatly enhanced, and at the same time, the phosphorescence lifespan was also greatly extended. This is a great new discovery. As Figure 24 shown. When the water content was 50%, the quantum yield of the composite material increased from 6.7% to 26.9%, and the phosphorescence lifespan increased from 174.51 ms to 900.17 ms, achieving a several-fold increase. As Figure 25 shown. As the water content gradually increased from 10 wt% to 70 wt%, an endothermic melting peak appeared in the differential scanning calorimetry curve in the temperature range of 67 - 75 °C, which can be attributed to the presence of non-freezing bound water in the hydrogen bond network. In addition, a broad endothermic peak appeared and shifted from 73 °C to 118 °C, indicating the gradual evaporation of free water and peripheral bound water at elevated temperatures. As Figure 26 shown. The laser Raman spectrum shows that after adding water, the Raman spectrum in the 700 and 1726 cm -1 bands changed significantly. As Figure 27 shown. After adding water and heavy water to the composite material respectively, characteristic peaks corresponding to obvious hydrogen bonds were observed in the spectral range of 3094 - 3698 cm -1 , further proving the formation of hydrogen bonds between water and the composite material.

[0068] Example 2, Application 1 of Anti-counterfeiting and Encryption

[0069] Using non-fluorescent filter papers, elaborate patterns were created using blue fluorescent CDs (F-CDs), green phosphorescent CDs (P-CDs), and CNDs@CA, marked as "8888". CNDs@CA specifically marked the green segment, while interfering F-CDs and P-CDs were coated on the blue and white segments respectively. The fluorescence properties of the two interfering materials were similar to those of CNDs@CA, and P-CDs showed green RTP characteristics but were quenched in water. Under ultraviolet irradiation (365 nm), the pattern showed a blue "8888", serving as the first layer of security code authentication. Subsequently, after the ultraviolet light source was deactivated, the pattern emitted recognizable green afterglow, thus revealing the secondary security code "2829". It is worth noting that only after spraying water was the correct code "2023" visible. The time-resolved and water-responsive afterglow properties of CNDs@CA also showed great potential for more complex data encryption schemes. As Figure 28 shown.

[0070] Example 3. Application 2 of anti-counterfeiting encryption

[0071] The proof-of-concept experiment involved using a dot matrix (4×8) groove to load a series of powders of F-CD, P-CD, and composite materials. In this design, the present invention defined "1" as the emission process point and "0" as the emission disappearance point. Figure 29 Sunlight irradiation in showed all points as white, indicating an invalid binary code. However, after stopping ultraviolet excitation for 0.5 s, a spatially resolved binary code appeared, which was misencoded as "QLGD" according to the ASCII (American Standard Code for Information Interchange) system. Subsequently, after adding water, a valid binary code could be decoded as "1814" based on ASCII. The above results indicate that CNDs@CA with stimulus-responsive RTP properties has enhanced flexibility and complexity, making it suitable for advanced information security applications. As Figure 29 shown.

[0072] Example 4. Application of bioimaging

[0073] Healthy Kunming mice were anesthetized with 1 g chloral hydrate solution dissolved in 10 ml physiological saline and then placed in an instrument box. Subsequently, 100 μL of the composite material solution (10 mg / mL) was injected into the front paw / subcutaneous of the Kunming live mice, irradiated with a handheld ultraviolet lamp (365 nm, 5 mW) for 60 s, and imaged using the instrument. During the entire imaging process, the mice were kept warm using a heating pad. The mechanism is as Figure 30 shown. Phosphorescence images were obtained in the bioluminescence mode using an open filter setting (exposure time: automatic), while fluorescence images were obtained in the fluorescence mode using a DsRed filter setting (exposure time: automatic). As Figures 31 - 35 shown.

[0074] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of solid-state phosphorescent carbon dots that become brighter when exposed to water and have an extended naked-eye recognition time, characterized in that, it includes: Using cyanuric acid as a carbon source precursor and N,N-dimethylformamide as a solvent, reacting at 210 - 240 °C for 10 - 25 h to obtain the solid-state phosphorescent carbon dots; The mass concentration of cyanuric acid in N,N-dimethylformamide is 10% - 15%.

2. The preparation method of solid-state phosphorescent carbon dots that become brighter when exposed to water and have an extended naked-eye recognition time according to claim 1, characterized in that, the purity of the cyanuric acid is 98% or above.

3. The preparation method of solid-state phosphorescent carbon dots that become brighter when exposed to water and have an extended naked-eye recognition time according to claim 1, characterized in that, Adding cyanuric acid to N,N-dimethylformamide and dissolving it by ultrasonic wave.

4. Solid-state phosphorescent carbon dots prepared by the method according to any one of claims 1 - 3.

5. The solid-state phosphorescent carbon dots according to claim 4, characterized in that, when excited by ultraviolet light, a fluorescence emission peak with a wavelength of 479 nm is generated, and when there is no ultraviolet light irradiation, a phosphorescence emission peak of 512 nm is shown.

6. A password, characterized in that, it includes: the solid-state phosphorescent carbon dots according to claim 4 or 5.

7. The application of the solid-state phosphorescent carbon dots according to claim 4 or 5 in the field of anti-counterfeiting and encryption.

8. The application of the solid-state phosphorescent carbon dots according to claim 4 or 5 in biological imaging.

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