A method for preparing a reversible, fast-light-responsive, multicolor fluorescent CDs material and the resulting products and applications

Abstract

This invention belongs to the field of functional material preparation, specifically relating to a method for preparing a reversible, fast-response, multicolor fluorescent CDs material, as well as the resulting products and applications. The method comprises the following steps: first, preparing N-CDs using naphthalene-1,4,5,8-tetracarboxylic acid, urea, diethylamine, and deionized water; then, dissolving the N-CDs in tetraethylenepentamine (TEPA) solutions of varying concentrations to produce N-CDs / tetraethylenepentamine (N-CDs / TEPA) solutions of varying concentrations. This invention achieves for the first time a wide range of tunable photoresponsive fluorescence color changes from deep red to light green, filling a gap in this technology. It also enables the application of repeatable dynamic information encoding, demonstrating significant potential for advanced dynamic information encryption. This work offers the distinct advantage of rapidly achieving photoresponsive, reversible, multicolor fluorescence emission from the CDs material, with a response time as fast as 0.5 seconds. The present invention utilizes a simple and rapid method to prepare a fast-response, multicolor fluorescent CDs material, with a simple and low-cost preparation process.

Description

Technical Field

[0001] The present invention belongs to the field of functional material preparation, and in particular relates to a preparation method of a reversible fast-response multicolor fluorescent CDs material and the obtained product and application. Background Art

[0002] Photoresponsive dynamic luminescent materials exhibit specific responses to light, typically undergoing changes in sunlight and fluorescence under UV irradiation. These are the two most studied phenomena under UV irradiation: photochromism and photoinduced fluorescence color change. Photoresponsive dynamic luminescent materials possess a wide range of luminescence color-changing properties and rapid response to UV light stimulation. They demonstrate great potential for application in sensors, advanced anti-counterfeiting, optoelectronics, and other fields, and have been extensively studied in recent years. Although currently reported photoresponsive luminescent materials exhibit good luminescence properties, they primarily focus on organic small molecule materials, which are relatively complex to synthesize and require relatively long preparation times. Therefore, further exploration of optical materials with simple preparation processes and excellent photoresponsive luminescence properties is imperative.

[0003] Carbon dots (CDs), a novel fluorescent carbon nanomaterial that combines simple preparation, tunable optical properties, and wide applications, have attracted significant attention in a variety of cutting-edge fields, including smart materials development and information security. In recent years, photoresponsive CDs have become a hot topic in the field of photostimuli-responsive materials. Gao's group encapsulated a spiropyran compound in CD-functionalized silica to create a fluorescent material with UV-stimuli-responsive emission. The material exhibited dynamic photochromic and photoluminescent behavior under UV light stimulation, successfully demonstrating its application in dynamic anti-counterfeiting. Chen's group combined photochromic and photoluminescent properties by encapsulating a naphthalimide structure in CDs and then embedding it in polyvinylpyrrolidone. The material achieved a color transition from colorless to brown within 100 seconds and a luminescent color transition from blue to yellow within 60 seconds. While significant progress has been made in the development of photoresponsive carbon dots, their relatively long photoresponse times, coupled with the difficulty of recovering to their initial state or requiring additional stimulation (such as heating), have limited their application. Furthermore, most reports on photoresponsive dynamic luminescence are limited to monochromatic emission from one color to another. Studies on widely tunable photoresponsive multicolor CDs are relatively rare, limiting their potential for security in the field of information protection. Therefore, the search for a fast photoresponsive multicolor fluorescent CD material that is simple, fast, and reversible remains a significant challenge. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for preparing a reversible, fast-response, multi-color fluorescent CDs material.

[0005] The present invention also provides a reversible, fast-response, multi-color fluorescent CDs material prepared by the above-mentioned preparation method.

[0006] Another object of the present invention is to provide an application of the above-mentioned reversible, fast-response, multi-color fluorescent CDs material.

[0007] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows:

[0008] The present invention provides a method for preparing a reversible, fast-response, multi-color fluorescent CDs material, comprising the following steps:

[0009] (1) Synthesis of N-CDs

[0010] Naphthalene-1,4,5,8-tetracarboxylic acid, urea, diethylamine and deionized water were ultrasonically mixed and then subjected to microwave heating reaction. After the reaction was completed, the mixture was cooled to room temperature to obtain CDs powder, which was then washed and purified with deionized water to obtain N-CDs.

[0011] (2) Preparation of N-CDs / tetraethylenepentamine (N-CDs / TEPA) solutions of different concentrations

[0012] N-CDs were dissolved in tetraethylenepentamine (TEPA) solutions of different concentrations to obtain N-CDs / tetraethylenepentamine (N-CDs / TEPA) solutions of different concentrations.

[0013] Preferably, in step (1), the mass volume ratio of the naphthalene-1,4,5,8-tetracarboxylic acid, urea, diethylamine and deionized water is 0.3 g:3 g:1 mL:10 mL.

[0014] Preferably, in step (1), the microwave heating is carried out at a power of 275-285 W for 10 minutes.

[0015] Preferably, in step (2), the volume ratio of tetraethylenepentamine (TEPA) to deionized water in the tetraethylenepentamine (TEPA) solution is 1:0-1500.

[0016] Preferably, in step (2), the mass volume ratio of the N-CDs to tetraethylenepentamine (TEPA) solution is 40 mg:1-16 mL.

[0017] The present invention also provides a multi-color fluorescent CDs material prepared by the above preparation method.

[0018] The present invention further provides the application of the multi-color fluorescent CDs material in the field of repeatable dynamic information encryption.

[0019] This study rapidly prepared functional group-rich CDs (N-CDs) using a microwave method. The N-CDs were then surface-modified with a tetraethylenepentamine solution (N-CDs / TEPA), achieving rapid and reversible UV-responsive behavior. The N-CDs / TEPA transitioned between daylight and fluorescent color in as little as 0.5 seconds, and could be directly restored to its original state by shaking. Importantly, the method provided by this study achieved a wide range of tunable photoresponsive fluorescence color changes, from deep red to light green, simply by adjusting the concentration of the tetraethylenepentamine solution. This has not been reported in previous studies. A series of characterizations demonstrated that the introduction of different concentrations of tetraethylenepentamine solution resulted in varying numbers of naphthaleneimide structures on the N-CDs surface, generating varying amounts of radical anions upon UV irradiation, thereby achieving photoresponsive multicolor fluorescence. The dependence of the UV-responsive time of N-CDs / TEPA at varying concentrations enabled the application of repeatable dynamic information encoding, demonstrating significant potential for advanced dynamic information encryption. The advantage of this work is that it can quickly realize the photoresponsive reversible multicolor fluorescence emission of CDs materials, with the fastest response time reaching 0.5s, which has obvious advantages.

[0020] The beneficial effects of the present invention are:

[0021] (1) The present invention rapidly prepares a composite material with a fast and reversible ultraviolet light response through a microwave solid-phase reaction method. The color transition between sunlight and fluorescence can be achieved within 0.5 seconds, and the original state can be directly restored by shaking.

[0022] (2) This invention, for the first time, achieves a wide range of tunable photoresponsive fluorescence color changes from deep red to light green, filling a gap in this technology. It also enables the application of repeatable dynamic information encoding, showing great potential for advanced dynamic information encryption. The advantage of this work is the rapid realization of photoresponsive, reversible, multicolor fluorescence emission from CDs materials, with a response time as fast as 0.5 s, which is a significant advantage.

[0023] (3) The present invention adopts a simple and quick method to prepare a fast-response multicolor fluorescent CDs material, and the preparation process is simple and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 XRD pattern of N-CDs prepared in Example 1;

[0025] Figure 2 This is the Fourier transform infrared spectrum of N-CDs prepared in Example 1;

[0026] Figure 3 (a) Fluorescence spectra of N-CDs / TEPA solutions at different concentrations before UV irradiation; (b) Fluorescence spectra of N-CDs / TEPA solutions at different concentrations after UV irradiation.

[0027] Figure 4 Reversible fluorescence spectra of N-CDs / TEPA solutions with different concentrations;

[0028] Figure 5 (a) UV-visible absorption spectra of N-CDs / TEPA solutions with different concentrations before UV irradiation; (b) UV-visible absorption spectra of N-CDs / TEPA solutions with different concentrations after UV irradiation.

[0029] Figure 6 . Application of reproducible dynamic information encoding based on time-dependent fluorescence of photoresponse. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further explained and illustrated by means of specific embodiments below.

[0031] Unless otherwise specified, the raw materials used in the present invention are commercially available.

[0032] Example 1

[0033] 1. Synthesis of N-CDs

[0034] Combine 0.3 g of naphthalene-1,4,5,8-tetracarboxylic acid, 3 g of urea, 1 ml of diethylamine, and 10 ml of deionized water in a beaker and mix thoroughly by ultrasonication. Then, thaw the mixture in a household microwave oven and heat for 10 minutes until the reaction is complete. Then, cool to room temperature to obtain CDs powder, designated N-CDs. Finally, wash with deionized water for purification.

[0035] 2. Preparation of N-CDs / tetraethylenepentamine (N-CDs / TEPA) solutions of different concentrations

[0036] Equal amounts of N-CDs were dissolved in tetraethylenepentamine (TEPA) solutions of varying concentrations to obtain eight N-CDs / tetraethylenepentamine (N-CDs / TEPA) solutions with different concentrations: 0:1, 1:1, 10:1, 100:1, 300:1, 500:1, 1000:1, and 1500:1. Specifically, 40 mg of N-CDs powder was placed in eight centrifuge tubes. Then, N-CDs / TEPA solutions with different concentrations were prepared by adding the following amounts of TEPA and deionized water: 1 mL TEPA (0:1), 1 mL deionized water and 1 mL TEPA (1:1), 1 mL deionized water and 100 μL TEPA (10:1), 1 mL deionized water and 10 μL TEPA (100:1), 3 mL deionized water and 10 μL TEPA (300:1), 5 mL deionized water and 10 μL TEPA (500:1), 10 mL deionized water and 10 μL TEPA (1000:1), and 15 mL deionized water and 10 μL TEPA (1500:1).

[0037] Figure 1 The XRD patterns of N-CDs are shown. Three distinct, sharp peaks are observed at 2θ = 19.88°, 2θ = 22.48°, and 2θ = 26.41°, corresponding to the (002) crystal plane of graphitic carbon. Additionally, two sharp peaks are observed at 2θ = 28.09° and 2θ = 29.79°, likely due to the formation of cyanuric acid structures within the CDs during microwave heating. The XRD patterns reveal sharp diffraction peaks in the N-CDs, indicating good crystallinity.

[0038] Figure 2 The Fourier transform infrared spectrum of N-CDs is shown to characterize the functional group structure of N-CDs. -1 and 3410 cm -1 There are two main absorption peaks at , which are attributed to the stretching vibrations of C=C / C=O and NH / OH, respectively. Infrared spectroscopy analysis shows that the surface of N-CDs may contain abundant amino and carboxyl functional groups.

[0039] Effect embodiment

[0040] The performance of the N-CDs prepared in Example 1 and N-CDs / tetraethylenepentamine (N-CDs / TEPA) solutions of different concentrations was characterized, specifically:

[0041] Figure 3Fluorescence spectra of N-CDs / TEPA solutions at different concentrations before and after UV irradiation are shown. All N-CDs / TEPA solutions exhibited photoinduced fluorescence color change. The different concentrations resulted in different photoresponse fluorescence colors after UV irradiation. As the TEPA concentration decreased, the photoresponse fluorescence color gradually shifted to the blue, achieving photoinduced multicolor fluorescence emission. The 0:1 solution exhibited a fluorescence emission wavelength of 663 nm before UV irradiation. After UV irradiation, the emission wavelengths exhibited two primary emission wavelengths at 660 nm and 858 nm, with the fluorescence color rapidly shifting to red and brighter within 0.5 s. Solutions with concentrations of 1:1 and 10:1 exhibited green fluorescence before irradiation, at wavelengths of 552 nm and 541 nm, respectively. After irradiation, these fluorescence colors shifted to bright red and orange, at wavelengths of 721 nm and 596 nm, respectively. Solutions with concentrations of 100:1, 300:1, and 500:1 all exhibited green fluorescence before irradiation, which shifted to a yellowish fluorescence after irradiation, with emission wavelengths of 564 nm / 613 nm, 562 nm, and 557 nm, respectively. Solutions with concentrations of 1000:1 and 1500:1 exhibited blue fluorescence before irradiation, with wavelengths of 452 nm and 474 nm, respectively, but shifted to a greenish fluorescence after irradiation, with wavelengths of 531 nm and 521 nm, respectively.

[0042] In addition, the light-responsive fluorescence of N-CDs / TEPA at different concentrations showed excellent reversibility and could be restored to its original state by vibration shaking. It could be repeatedly cycled between continuous UV irradiation and vibration shaking. The higher the TEPA concentration, the more cycles it could cycle. Figure 4 As shown, the fluorescence wavelength of eight N-CDs / TEPA solutions with different concentrations did not change before and after the first UV irradiation and before and after the second UV irradiation, and the fluorescence intensity remained almost unchanged, showing excellent reversibility.

[0043] Figure 5The UV-visible absorption spectra of N-CDs / TEPA solutions of varying concentrations before and after UV irradiation are shown. A 1:1 N-CDs / TEPA solution was used as an example to analyze the changes in the UV-visible absorption spectrum before and after irradiation. Before UV irradiation, N-CDs / TEPA exhibited three absorption peaks at 229 nm, 368 nm, and 390 nm. After continuous UV irradiation, the absorption peak near 229 nm slightly intensified, while the peaks at 368 nm and 390 nm weakened. New absorption peaks emerged in the 400-500 nm range. After UV irradiation, UV absorption weakened and visible light absorption increased, indicating the generation of radical anions. The new absorption peak in the 400-500 nm range is similar to the absorption peak of naphthaleneimide radical anions generated by photoinduced electron transfer, further demonstrating that the addition of TEPA to the surface of N-CDs generates a naphthaleneimide structure capable of photoresponsive behavior upon UV irradiation. The UV-visible absorption spectra of N-CDs / TEPA at various concentrations were also characterized, demonstrating similar changes to those observed for the 1:1 ratio. The UV-visible absorption spectra before and after UV irradiation demonstrated the formation of naphthaleneimide structures on the carbon dot surface, creating the conditions for photoresponsive behavior.

[0044] N-CDs / TEPA materials with different concentrations exhibit reversible multicolor fluorescence with different colors after UV irradiation. Based on the time dependence of the photoresponsive fluorescence, a dynamic information encoding model with repeatable function was designed, which has potential application prospects in the field of repeatable dynamic information encryption. Figure 6 As shown in the figure, a repeatable dynamic information encoding strip was designed using N-CDs / TEPA materials with four different concentrations: 1:1, 10:1, 300:1, and 1500:1. Red and yellow fluorescence were defined as the "-" signal in Morse code, orange and blue fluorescence as the "." signal, and greenish fluorescence as the pause signal. When UV light was first turned on, the four materials exhibited green and blue fluorescence, indicating the stored information "E." After 60 seconds of continuous UV light irradiation, all four concentrations of N-CDs / TEPA underwent a photoresponsive fluorescence color change, displaying red, orange, yellow, and green fluorescence, encoding the information "K." This system can be used for repeatable dynamic information encoding applications through vibration and continuous UV light irradiation.

Claims

1. A method for preparing a reversible, fast-response, multi-color fluorescent CDs material, characterized in that: The following steps are involved: (1) Synthesis of N-CDs Naphthalene-1,4,5,8-tetracarboxylic acid, urea, diethylamine and deionized water were ultrasonically mixed and then subjected to microwave heating reaction. After the reaction was completed, the mixture was cooled to room temperature to obtain CDs powder, which was then washed and purified with deionized water to obtain N-CDs. The mass volume ratio of the naphthalene-1,4,5,8-tetracarboxylic acid, urea, diethylamine and deionized water is 0.3 g:3 g:1 mL:10 mL; The microwave heating was carried out at a power of 275-285 W for 10 min; (2) Preparation of N-CDs / tetraethylenepentamine (N-CDs / TEPA) solutions of different concentrations N-CDs are dissolved in tetraethylenepentamine solutions of different concentrations to obtain N-CDs / tetraethylenepentamine solutions of different concentrations, which are reversible, fast-response, multi-color fluorescent CDs materials.

2. The preparation method according to claim 1, characterized in that In step (2), the volume ratio of tetraethylenepentamine to deionized water in the tetraethylenepentamine solution is 1:0-1500.

3. The preparation method according to claim 1, characterized in that In step (2), the mass volume ratio of the N-CDs and tetraethylenepentamine solution is 40 mg:1-16 mL.

4. A multicolor fluorescent CDs material prepared by the preparation method according to any one of claims 1 to 3.

5. An application of the multi-color fluorescent CDs material as claimed in claim 4 in the field of repeatable dynamic information encryption.

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