Tunable room-temperature phosphorescent carbon dot composites based on minoxidil, preparation methods, and their application in dynamic information encryption.

Abstract

This invention discloses a color-tunable room-temperature phosphorescent carbon dot composite material based on minoxidil, its preparation method, and its applications. The composite material is synthesized in situ through a one-step thermal treatment of the clinical drug minoxidil (MND) and boric acid (BA) in an aqueous phase. Minoxidil, as a carboxyl-free aminopyrimidine molecule, partially forms nitrogen-doped carbon dots during pyrolysis, while some exist in an incompletely carbonized molecular state. Both are firmly anchored in a BA-derived rigid borosilicate glass matrix via B–N covalent bonds, effectively suppressing nonradiative transitions of triplet excitons. By controlling the doping amount of minoxidil (preferably an MND:BA mass ratio of 1:60 to 1:3), the phosphorescent emission color of the material can be continuously tunable from blue to green, achieving a maximum photoluminescence quantum yield of 20.9% and a room-temperature phosphorescent lifetime of up to 1.43 seconds. This composite material has significant application value in fields such as multi-level dynamic information encryption, time-resolved anti-counterfeiting, and intelligent optical devices.

Description

Technical Field

[0001] This invention belongs to the field of optical functional materials technology, specifically relating to a tunable room temperature phosphorescent carbon dot composite material based on minoxidil, its preparation method, and the application of this material in the fields of anti-counterfeiting and information encryption. Background Technology

[0002] Room-temperature phosphorescent (RTP) materials possess unique photophysical properties such as long emission lifetime, large Stokes shift, and high signal-to-noise ratio, making them valuable for applications in anti-counterfeiting encryption, environmental monitoring, bioimaging, and optoelectronic devices. However, traditional phosphorescent materials are mainly based on heavy metal complex systems, which suffer from high costs and potential biotoxicity, severely hindering their commercial application.

[0003] Carbon dots (CDs), as emerging carbon-based luminescent nanomaterials, possess advantages such as tunable optical properties and good biocompatibility, providing a new approach for constructing efficient phosphorescence response (RTP) systems. Current synthesis methods for carbon dot-based RTP materials mainly fall into two categories: self-protection methods and matrix-assisted methods. Self-protection methods have stringent requirements on the precursor structure, making suitable precursors difficult to find. Matrix-assisted methods, on the other hand, achieve phosphorescence enhancement by embedding carbon dots into a host matrix (such as boric acid, polyvinyl alcohol, and silica), offering broader applicability. In boric acid matrix systems, existing technologies often use carboxyl-containing organic molecules as carbon sources (such as salicylic acid and levofloxacin), anchoring the carbon dots through the formation of CB covalent bonds and hydrogen bonds. However, this approach imposes significant limitations on precursor selection and makes it difficult to achieve a wide range of phosphorescence color modulation.

[0004] Therefore, developing a carbon dot RTP composite material with a wide range of precursor selection, simple preparation process, excellent phosphorescence performance and continuously tunable color / lifetime, as well as its preparation method, while having a good biosafety basis, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a boric acid-confined carbon dot room temperature phosphorescent composite material based on minoxidil as a carbon source, so as to solve the problems of limited precursor selection, narrow phosphorescence color control range and poor biocompatibility in the prior art.

[0006] Another objective of this invention is to provide a simple one-step hydrothermal preparation process that enables simultaneous carbon doping, nitrogen doping, surface functionalization, and matrix confinement.

[0007] Another object of the present invention is to provide the application of the composite material in the fields of multi-level dynamic information encryption, advanced anti-counterfeiting and potential bioimaging.

[0008] Technical solution of the present invention: 1. Material composition design. A boric acid-confined carbon dot room temperature phosphorescent composite material, characterized in that: Precursor: Minoxidil (MND), a drug molecule Matrix: Boric acid (BA) Chemical bonding: Carbon dots and residual precursor molecules are anchored to the boron oxide rigid network via BN covalent bonds. Dual luminescent centers: consisting of fully carbonized nitrogen-doped carbon dot centers and incompletely carbonized residual molecular centers.

[0009] 2. Preparation Method: A one-step hydrothermal synthesis method, comprising the following steps: Dissolve 3.0 g of boric acid and X mg of MND (X = 5–200) in 30 mL of deionized water, stirring until completely dissolved. Seal the container with aluminum foil to prevent excessive evaporation of moisture. Place in an oven and react at 180–220 °C (preferably 200 °C) for 4–6 hours (preferably 5 hours). Cool to room temperature to obtain a glassy solid product, which is then ground into a uniform powder.

[0010] 3. Performance Parameters Phosphorescence lifetime: 0.8–1.43 seconds (optimal up to 1.43 seconds) Photoluminescence quantum yield: 10–20.9% (optimal up to 20.9%) Phosphorescence color: continuously adjustable from blue (λem ≈ 450 nm) to green (λem ≈ 520 nm) as the precursor doping concentration increases. Afterglow duration: 5–10 seconds 4. The luminescent material contains two independent phosphorescent emission centers: Center A: Triplete radiation originating from nitrogen-doped carbon dots Center B: Originating from incompletely carbonized minoxidil molecules Regulation mechanism: High-concentration precursors increase the nitrogen doping level of carbon dots, enhance surface BN functional groups, and promote residual intermolecular π-π stacking. The dual effects synergistically reduce the triplet excitation energy level and drive the redshift of emission.

[0011] Compared with the prior art, the present invention has the following significant advantages: Precursor innovation: For the first time, the clinical drug minoxidil was used as a precursor, which broadened the range of precursors for RTP carbon dots and laid a good safety foundation for subsequent biological applications.

[0012] Excellent performance: phosphorescence lifetime up to 1.43 seconds and quantum yield up to 20.9%, far exceeding most metal-free RTP materials, achieving high efficiency triplet exciton utilization.

[0013] Dual adjustability: Color adjustable: By controlling the doping amount of a single precursor, continuous emission wavelength tuning from blue to green can be achieved.

[0014] Adjustable lifetime: Products with different doping levels exhibit differentiated phosphorescence decay kinetics Simple preparation: The one-step hydrothermal method simultaneously completes carbon dot generation, nitrogen doping, BN bonding and matrix confinement, without the need for post-processing modification, with good process reproducibility, and is suitable for large-scale production.

[0015] Application Innovation: By utilizing the dual adjustability of color and lifespan, time-dependent multi-level dynamic information encryption is achieved, significantly improving the anti-counterfeiting level and making it difficult to copy and crack. Attached Figure Description

[0016] Figure 1 BA / MND synthesis diagram and afterglow display Figure 2 Materials characterization (TEM, XRD, UV-Vis, XPS) Figure 3 Photophysical properties (phosphorescence spectrum, temperature variation, excitation variation, excitation-emission contour lines) Figure 4 Theoretical calculations (HOMO-LUMO, energy transfer, luminescence mechanism model) Figure 5 Dynamic information encryption application demonstration (flower pattern, Morse code, HELP distress signal) Detailed Implementation

[0017] Example 1: Preparation of BA / MND composite material Weigh 3.0 g of BA and 20 mg of MND into a beaker, add 30 mL of deionized water, and stir to dissolve. Seal the beaker with aluminum foil and place it in a 200°C oven for 5 hours. After the reaction is complete, a glassy solid is obtained, which is ground into powder and labeled as BA / MND. 20 .

[0018] Example 2: Preparation of samples with different doping levels Except for replacing the MND dosage with 5, 10, 15, 40, 60, 80, 100, and 200 mg respectively, the remaining steps are the same as in Example 1, yielding BA / MND5, BA / MND... 10 , ..., BA / MND 200 .

[0019] Example 3: Sample preparation at different temperatures Except for the reaction temperature being changed to 160℃, 180℃, and 220℃, the remaining steps are the same as in Example 1, and materials generated at different temperatures are obtained respectively.

[0020] Structural characterization: Transmission electron microscopy (TEM) confirmed the formation of the material. The CDs were monodisperse, nearly spherical particles with no obvious agglomeration, and the particle size distribution was concentrated in 3.0–4.0 nm, with an average diameter of about 3.4 nm. Under high-resolution TEM, the CDs could be clearly observed to have obvious lattice fringes with a lattice spacing of 0.21 nm, which is consistent with the (100) plane spacing of graphitic carbon, indicating that the synthesized carbon dots have graphite-like crystallization nuclei.

[0021] Performance testing: Phosphorescence spectroscopy was performed on the above samples. The results showed that BA / MND 20 It exhibits a blue afterglow after the 365 nm excitation source is turned off, while BA / MND 200 It then exhibits a green afterglow. Furthermore, the material with the best phosphorescence performance is BA / MND obtained at 200℃. 20 Its phosphorescence lifetime is 1.43 seconds and its photoluminescence quantum yield is 20.9%.

[0022] Application Example: Dynamic Information Encryption Example 3: Take BA / MND 20 Fill in the flower parts, BA / MND 200 The stems and leaves are filled in. Under sunlight, the pattern shows yellow branches and leaves and pale yellow flowers; when excited by 365 nm ultraviolet light, the pattern shows bright fluorescence; after 5 seconds when the light source is turned off, the afterglow of blue flowers and green branches and leaves is shown; after 7 seconds, the afterglow of branches and leaves disappears, leaving only faint blue flowers.

[0023] Example 4 Using BA / MND respectively 20 and BA / MND 200 Fill the square grid. Furthermore, we demonstrate the specific application of materials in information encryption. Utilizing BA / MND 20 and BA / MND 200 The system fills a square grid and encodes the data using Morse code: grids displaying a "blue + green" afterglow are defined as "—", and grids displaying only "blue" or "blue + blue" are defined as "·". No information is discernible under ultraviolet light; after the light source is turned off, the letters "Z" and "H" can be identified after 3 seconds and 7 seconds respectively.

[0024] Example 5 MND and BA / MND were used respectively. 20 The BA / MND5 is filled with four "8"s. Under ultraviolet light, it displays "8888"; after the ultraviolet light is turned off, the number changes to "8608"; over time, the phosphorescence of the BA / MND5 extinguishes first, eventually revealing the blue word "HELP". In summary, the sample performance test data demonstrates that the carbon dot composite material prepared in this invention possesses significant advantages: firstly, its preparation process is simple and environmentally friendly, with novel raw material sources and biocompatibility potential; secondly, by precisely controlling the drug molecule doping ratio, the phosphorescence color can be continuously tunable from blue to green, while simultaneously exhibiting a photoluminescence quantum yield as high as 20.9% and an ultra-long afterglow lifetime of 1.43 seconds. This "dual-luminescent center + rigid network fixation" design strategy not only elucidates the generation mechanism of efficient room-temperature phosphorescence but also endows the material with excellent temporal resolution characteristics. Therefore, this material shows great application potential and industrialization prospects in cutting-edge fields such as high-security dynamic information encryption, multi-level anti-counterfeiting labels, intelligent response displays, and bioimaging.

[0025] The content of this invention is not limited to the embodiments listed. Any equivalent modifications made by those skilled in the art to the technical solutions of this invention by reading this specification are covered by the claims of this invention.

Claims

1. A carbon dot composite material with tunable room-temperature phosphorescence, characterized in that, The composite material is prepared by a one-step heat treatment reaction of boric acid (BA) and minoxidil (MND), and contains dual luminescent centers.

2. The tunable room-temperature phosphorescent carbon dot composite material according to claim 1, characterized in that, The mass ratio of MND to BA is 1:60 to 1:

3.

3. A method for preparing a tunable room-temperature phosphorescent carbon dot composite material as described in claim 1 or 2, characterized in that, The process includes the following steps: Dissolve BA and MND in 10-100ml of deionized water, seal the solution, heat treat it at 180-220℃ for 3-8 hours, and grind the solid product after cooling.

4. A carrier for anti-counterfeiting or information encryption, characterized in that, The carrier comprises the tunable room temperature phosphorescent carbon dot composite material as described in claim 1 or 2, and the carrier has at least two composite material regions formed by different doping amounts of precursors, so that different afterglow colors and / or afterglow timing displays are presented after the excitation light is turned off to achieve information identification.

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