A method for preparing high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor. 4-x Au x Se2 method

Abstract

This invention relates to the field of fluorescent materials technology, and more particularly to a method for preparing high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymers as precursors. 4‑ x Au x The method using Se2 involves Au(I)-Thiolate as a gold precursor. The structure and properties of the product can be controlled by adjusting the concentration of the active substance within a temperature range of 4–150 °C. Ag synthesized within this temperature range… 4‑x Au x The quantum yield of Se2 is 37.8%–99.3%. Among these, 150℃ can unify Ag2Se seeds and Ag... 4‑ x Au x The synthesis temperature of Se2 significantly simplifies the preparation process. The near-infrared fluorescent materials obtained by this method have a fluorescence quantum yield of up to 100%, and also have advantages such as long fluorescence lifetime, small and uniform size, and wide applicability.

Description

Technical Field

[0001] This invention relates to the field of fluorescent materials technology, and more particularly to the preparation of high quantum yield near-infrared II fluorescent nanocrystals Ag based on an Au(I)-Thiolate coordination polymer as a precursor. 4-x Au x The method of Se2. Background Technology

[0002] Near-infrared II (1000–1700 nm) fluorescent materials have significant applications in bioimaging, surgical navigation, and low-visibility environment sensing. However, their quantum yield is typically low due to the enhanced nonradiative transitions caused by the narrowing bandgap in this band. Currently, InAs-based quantum dots can achieve near-100% quantum yield around 1050 nm, but the presence of arsenic poses a potential biotoxicity risk. In contrast, silver chalcogenide quantum dots (such as Ag₂Se) are considered ideal alternatives because they do not contain highly toxic elements, but their quantum yield is still limited by high silver ion mobility and the ease with which cation vacancies can be formed, making it difficult to achieve significant improvements. Existing technologies mainly address this through doping or alloying (such as introducing Pb). 2+ Forming Pb:Ag2Se or introducing Au to form AgAuSe alloys can improve quantum yield, but the introduced foreign metal may cause lattice distortion or generate new defects, limiting further improvement in efficiency.

[0003] Current synthetic methods struggle to produce high-quality near-single-crystal Ag3AuSe2, often resulting in heterostructures or complex core-shell structures composed of Ag3AuSe2 and gold nanoparticles. This challenge stems primarily from the dual constraints of redox activity and thermal stability of the gold precursor: excessively low activity leads to incomplete reactions, while excessively high activity results in complex product structures that deviate from the target single-crystal phase. For instance, using highly reactive Au(III) compounds as the gold source often yields Au@Ag3AuSe2 heterostructures or AgAuSe alloys; while using less reactive gold nanoparticle precursors readily forms Au@Ag 4-x Au x Se2 (0≤x≤1) heterostructure, these byproducts significantly affect the final properties of the material.

[0004] Therefore, how to overcome the low quantum yield of near-infrared II fluorescent materials by synthesizing near-single-crystal Ag3AuSe2 while taking into account biosafety is a technical challenge that urgently needs to be solved. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the related art. Therefore, the first objective of the present invention is to provide a method for preparing Ag based on the precursor Au(I)-Thiolate for sustained release of gold-active substances.4-x Au x A method for producing Se2 (0≤x≤1) nanocrystals; a second objective of this invention is to provide a near-infrared Ag based on a gold precursor. 4-x Au x Se2 (0≤x≤1) nanocrystals (quantum yield 37.8~99.3%).

[0006] To achieve the first objective, the technical solution adopted by this invention is as follows: Near-infrared II fluorescent nanocrystals Ag were synthesized by adding gold precursor to Ag2Se seed solution and reacting at 4–170℃ for 1 min–7 days. 4-x Au x Se2; Among them, Ag can be prepared by adjusting the amount of gold precursor added to the Ag2Se seed dispersion. 4-x Au x The Se2 (0≤x≤1) product, based on the molar ratio of Ag to Au, ranges from 3.5 to 26.9. The synthesis process of the gold precursor is as follows: using an alcoholic solution of chloroauric acid and thiol I as raw materials, the mercapto group in thiol I reduces Au(ⅠII) in the alcoholic solution of chloroauric acid to Au(I) and coordinates with Au(I) to form Au(I)-Thiolate coordination polymer; The preparation of Ag2Se seed dispersion includes the following steps: S100. Using terminal olefin I and selenium powder as raw materials, prepare a selenium precursor solution; S200. After uniformly mixing terminal olefin II, thiol II and silver salt, heat to 100-180°C under argon protection. Inject the selenium precursor solution within 1-10 seconds, and maintain Ag2Se seed crystals at 100-180°C until the photoluminescence emission peak is 1100-1850 nm to obtain Ag2Se seed crystal dispersion.

[0007] Preferably, thiols I and thiols II are each independently selected from octahthiol (OTT), butanethiol, and dodecathiol.

[0008] Preferably, the solvent of the alcohol solution in the synthesis process of the gold precursor is selected from methanol and / or ethanol.

[0009] Preferably, the temperature for synthesizing near-single-crystal Ag3AuSe2 near-infrared fluorescent materials with a quantum yield close to 100% based on gold precursors is 140℃~150℃.

[0010] Preferably, during the synthesis of the gold precursor, the volume ratio of the added thiol I to the alcohol solvent is 1:3 to 3:1.

[0011] Preferably, the synthesis temperature of the gold precursor is 60℃~85℃, and the reaction time is 0.5h~8h.

[0012] Preferably, both the terminal olefin I and the terminal olefin II are selected from 1-octadecene.

[0013] Preferably, in step S200, the silver salt is selected from silver acetate.

[0014] Preferably, in step S200, the temperature for maintaining seed crystal growth is 140°C to 150°C.

[0015] To achieve the second objective, the technical solution adopted by this invention is as follows: Near-infrared II fluorescent nanocrystals Ag based on gold precursors 4-x Au x Se2, utilizing the gold precursor-based near-infrared II fluorescent nanocrystals Ag as described in any of the above-mentioned embodiments. 4-x Au x It is prepared by the method of preparing Se2.

[0016] The above-described one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: This invention provides a method for preparing high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymers as precursors. 4-x Au x The Se2 method uses Au(I)-OTT as the gold precursor. This precursor allows for temperature-controlled concentration of the active material within a range of 4–160 °C, avoiding excessive grain boundaries at low reaction temperatures or runaway reactions due to high temperatures. Therefore, the precursor phase transition initiation point (T0) is selected. m，onset Using temperature as the synthesis temperature of Ag3AuSe2 can minimize product grain boundaries while ensuring controllable reaction, and at the same time, it is consistent with the synthesis temperature of Ag2Se seeds, avoiding the increase in product complexity due to temperature variation.

[0017] The Ag3AuSe2 near-infrared fluorescent material based on the gold precursor prepared by the method provided in this invention has the following advantages: I. Quantum Yield: Near-single-crystal Ag3AuSe2 nanocrystals exhibit a quantum yield as high as 99.3% at approximately 1000 nm; II. High biosafety: It does not contain highly toxic heavy metals such as arsenic and lead, and has potential for biomedical applications; III. Good controllability of synthesis: The product structure and luminescence properties can be precisely controlled by temperature and feed ratio; IV. Long fluorescence lifetime: Fluorescence lifetime is approximately 4 μs; 5. Small and uniform size: average size is 3.3±0.6nm; VI. Wide range of applications: It is expected to be applicable to near-infrared II fluorescent probes, bioimaging, photoelectric sensing and other fields.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] Figure 1 The above are the characterization results of Au(I)-OTT provided in Example 1 of this invention; wherein, Figure a is the X-ray diffraction pattern of Au(I)-OTT powder, Figure b is the high-resolution XPS spectrum of the Au 4f region, and Figure c is the solid-state image of Au(I)-OTT at a sample rotation frequency of 10 kHz. 13 Figure C shows the cross-polarized magic angle rotating nuclear magnetic resonance spectrum, Figure d shows the Fourier transform infrared spectrum of Au(I)-OTT and the OTT reference, Figure e shows the differential scanning calorimetry curve of Au(I)-OTT, and Figure f shows the thermogravimetric analysis curve and the corresponding differential thermogravimetric curve of Au(I)-OTT.

[0020] Figure 2 This refers to the Ag based on gold precursors under different Ag / Au molar ratios provided in Example 1 of the present invention. 4-x Au x Optical properties, characterization, morphology, and elemental distribution of Se2 (0≤x≤1) near-infrared fluorescent materials; Figure a shows the steady-state photoluminescence spectrum, Figure b shows the UV-Vis-NIR absorption spectrum, Figure c shows the quantum yield (QY) as a function of composition, Figure d shows the test results of the absolute quantum yield of photoluminescence, Figure e shows the X-ray diffraction pattern with β-Ag3AuSe2 phase (PDF NO.01-075-4098) as the reference standard, and Figure f shows the distribution of Au4f and Ag4f. High-resolution X-ray photoelectron spectroscopy (XPS) of 3d; g is a transmission electron microscope (TEM) image of the fluorescent material synthesized with an Ag / Au molar ratio of 26.9; h is a TEM image of the fluorescent material synthesized with an Ag / Au molar ratio of 13.3; i is a TEM image of the fluorescent material synthesized with an Ag / Au molar ratio of 4.3; j is an elemental distribution surface scan of the fluorescent material synthesized with an Ag / Au molar ratio of 26.9; k is an elemental distribution surface scan of the fluorescent material synthesized with an Ag / Au molar ratio of 4.3.

[0021] Figure 3 This refers to the near-infrared II fluorescent nanocrystals Ag with different Ag / Au molar ratios provided in Example 1 of the present invention. 4- x Au x TEM image of Se2 and its corresponding Fourier transform image and atomic structure model diagram.

[0022] Figure 4 This refers to the near-infrared II fluorescent nanocrystals Ag with different Ag / Au molar ratios provided in Example 1 of the present invention. 4- x Au x Se2 band structure evolution and carrier dynamics analysis results; Figure a shows the UPS spectra of samples with different Ag / Au molar ratios (Fermi level set at 0 eV, the left region shows the relationship between the valence band position and EF, and the right region shows the secondary electron cutoff edge, with the cutoff energy shifted by the incident photon energy of 21.22 eV to establish a reference for the vacuum level relative to EF); Figure b shows a schematic diagram of the energy levels (E... C and E V Figure c represents the energy of the conduction band edge and the valence band edge, respectively. Figure d shows the transient absorption spectrum at 760 nm, Figure d shows the kinetic curve at the probe wavelength of 760 nm, and Figure e shows the differential absorption spectrum.

[0023] Figure 5 This document describes the optical properties and structural characterization of near-single-crystal Ag3AuSe2 near-infrared fluorescent materials under different temperature conditions provided in Example 2 of this invention. Figure a shows the absorption spectra of the material at different temperatures; Figure b shows the photoluminescence spectra of the material at different temperatures; Figure c shows the X-ray diffraction pattern of the material [with reference spectra of β-Ag3AuSe2 (PDF NO.01-075-4098) and Ag2Se (PDF NO.00-27-0619) for comparison]; Figure d shows the X-ray photoelectron spectrum of the material; Figure e shows the spherical aberration transmission electron microscope images and corresponding fast Fourier transform spectra of the material at 150℃ (no grain boundaries) and 120℃ (rich grain boundaries); and Figure f shows the photoluminescence quantum yield of the material prepared at different temperatures.

[0024] Figure 6 The excitation-emission spectra are provided in Example 3 of this invention after replacing octylthiol in the preparation process with butylthiol and dodecathiol, respectively.

[0025] Figure 7 The results of the feasibility study of the reaction between Au(I)-OTT and Ag2Se at 4°C provided in Example 4 of this invention are shown; where Figure a is the PL spectrum and Figure b is the absolute fluorescence quantum yield. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The following embodiments are used to illustrate this invention, but cannot be used to limit the scope of this invention.

[0027] In the following embodiments, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available, unless otherwise specified, and are carried out in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions.

[0028] Example 1 A method for preparing high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor. 4-x Au x The Se2 method, the process is as follows: I. Preparation of gold precursor Au(Ⅰ)-Thiolate.

[0029] Chloroauric acid (1 g) was dissolved in ethanol (10 mL), followed by the addition of octylthiol (30 mL). The mixture was reacted at 80 °C for 3 h under an argon atmosphere. The product was then centrifuged at 8000 rpm, the precipitate was collected, and ultrasonically washed in ethanol. This was followed by centrifugation under the same conditions. The washing process was repeated three times with ultrapure water. The Au(I)-Thiolate precursor powder was purified and dried. When octylthiol was used, it was designated Au(I)-OTT. The characterization results are as follows: Figure 1 As shown.

[0030] II. Preparation of ODE-Se selenium precursor.

[0031] 1-Octadecene (ODE) (60 mL) was mixed with selenium powder (356 mg) and sonicated until the selenium powder was completely impregnated with ODE. The mixture was then subjected to three cycles of vacuuming and argon purging. Under argon protection, the mixture was continuously stirred at 500 rpm, and the temperature was raised to 80 °C within 10 min, then to 200 °C within 45 min, and maintained at this temperature for 100 min to obtain the ODE-Se selenium precursor solution.

[0032] III. Preparation of Ag2Se seed dispersion.

[0033] A mixed solution of ODE (10 mL), OTT (0.5 mL), and silver acetate (AgOAc) (16.7 mg) was placed in a 25 mL three-necked flask. The flask was evacuated and purged with argon three times. Then, the mixed solution was heated to 170 °C with stirring at 1000 rpm. Subsequently, 1.5 mL of ODE-Se precursor solution was rapidly injected. After the injection was completed, the temperature was lowered to 150 °C and maintained at this temperature to allow seed crystal growth until the photoluminescence (PL) emission peak reached 1600 nm, thus obtaining the Ag2Se seed crystal solution.

[0034] IV. Synthesis of Ag 4-x Au x Se2 (0≤x≤1) near-infrared fluorescent nanocrystals.

[0035] Different masses (7 mg, 10 mg, 15 mg, 20 mg, 25 mg, 30 mg, 35 mg, 40 mg, 45 mg, and 50 mg) of Au(I)-OTT powder (corresponding Ag / Au molar ratios of 3.5, 3.9, 4.0, 4.3, 5.7, 6.5, 13.3, 20.3, 24.3, and 26.9, respectively) were added to the Ag2Se seed solution prepared according to the aforementioned method. The reaction system was maintained at 150 °C for 1-10 min, preferably 2 min. Subsequently, the mixture was transferred to acetone to quench the reaction. The product was precipitated with acetone (60 mL), and the precipitate was collected by centrifugation and washed three times. The purified nanocrystals were redispersed in tetrachloroethylene (20 mL). The resulting dispersion was centrifuged at 10000 rpm for 10 min, and the supernatant was filtered through a 0.22 μm filter membrane to obtain Ag2Se. 4-x Au x For Se2 (0≤x≤1) near-infrared fluorescent materials, the quantum yields at Ag / Au molar ratios of 3.5, 3.9, 4.0, 4.3, 5.7, 6.5, 13.3, 20.3, 24.3, and 26.9 are 99.8±2.5%, 101.0±2.5%, 99.9±2.5%, 98.9±2.5%, 94.8±2.4%, 77.4±1.9%, 64.8±1.6%, 25.9±0.6%, 12.5±0.3%, and 5.1±0.01%, respectively (error bars represent standard deviation; values ​​exceeding 100% are due to measurement system errors).

[0036] The fluorescent material was sealed in a sample vial and stored at –20°C. Near-infrared II fluorescent nanocrystals based on the gold precursor were observed at different Ag / Au molar ratios. 4-x Au x The optical properties, characterization, morphology, and elemental distribution of Se2, such as Figure 2As shown, TEM images of Ag3AuSe2 fluorescent material, along with their corresponding Fourier transform images and atomic structure model diagrams, are displayed when the Ag / Au molar ratios are 26.9, 13.3, and 4.3, respectively. Figure 3 As shown; Near-infrared II fluorescent nanocrystals of Ag under different Ag / Au molar ratios 4- x Au x The band structure evolution and carrier dynamics analysis results of Se2 are as follows: Figure 4 As shown.

[0037] Example 2 The preparation process was the same as in Example 1. The quantum yields of near-single-crystal Ag3AuSe2 near-infrared fluorescent materials synthesized at temperatures of 80℃, 100℃, 120℃, 130℃, 140℃, 150℃, and 160℃ with an Ag / Au molar ratio of 4.0 were investigated. These yields were 46.5±1.2%, 65.8±1.6%, 67.8±1.7%, 75.9±1.9%, 82.0±2.1%, 99.3±2.5%, and 69.0±1.7%, respectively. The optical properties and structural characterization of the synthesized products at different temperatures were also examined. Figure 5 As shown.

[0038] Example 3 The Ag / Au molar ratio was 4.3, and the temperature was 150℃. Octylthiol in the preparation process of Example 1 was replaced with butylthiol and dodecathiol, respectively. The remaining preparation process was the same as that of the near-single-crystal Ag3AuSe2 near-infrared fluorescent material based on the gold precursor in Example 1. The excitation-emission spectrum of the prepared infrared fluorescent material is shown below. Figure 6 As shown.

[0039] Example 4 The feasibility of reacting Au(I)-OTT with Ag₂Se at 4℃ was investigated. The preparation process was the same as in Example 1. The near-single-crystal Ag₃AuSe₂ near-infrared fluorescent materials obtained after 3 and 7 days of reaction at 4℃ with an Ag / Au molar ratio of 4.0 were analyzed, including their PL spectra and absolute fluorescence quantum yield (PLQY). Figure 7 As shown; Figure a shows the PL spectrum, and figure b shows the absolute fluorescence quantum yield.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor. 4-x Au x The method of Se2 is characterized by, The process is as follows: Near-infrared II fluorescent nanocrystals Ag were synthesized by adding gold precursors to Ag2Se seed solutions and reacting at temperatures ranging from 4 to 170 °C for 1 min to 7 days. 4-x Au x Se2; Among them, Ag can be prepared by adjusting the amount of gold precursor added to the Ag2Se seed dispersion. 4-x Au x The Se2 (0≤x≤1) product, based on the molar ratio of Ag to Au, ranges from 3.5 to 26.

9. The synthesis process of the gold precursor is as follows: using an alcoholic solution of chloroauric acid and thiol I as raw materials, the mercapto group in thiol I reduces Au(ⅠII) in the alcoholic solution of chloroauric acid to Au(I) and coordinates with Au(I) to form Au(I)-Thiolate coordination polymer; The preparation of Ag2Se seed dispersion includes the following steps: S100. Using terminal olefin I and selenium powder as raw materials, prepare a selenium precursor solution; S200. After uniformly mixing terminal olefin II, thiol II and silver salt, heat to 100-180°C under argon protection. Inject the selenium precursor solution within 1-10 seconds, and maintain Ag2Se seed crystals at 100-180°C until the photoluminescence emission peak is 1100-1850 nm to obtain Ag2Se seed crystal dispersion.

2. The method for preparing high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor as described in claim 1. 4-x Au x The method of Se2 is characterized by, The thiol I and the thiol II are each independently selected from octylthiol, butylthiol, and dodecanethiol.

3. The method for preparing high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor as described in claim 1. 4-x Au x The method of Se2 is characterized by, The solvent for the alcohol solution in the synthesis of the gold precursor is selected from methanol and / or ethanol.

4. The preparation of high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor as described in claim 1. 4-x Au x The method of Se2 is characterized by, Synthesis of near-infrared II fluorescent nanocrystals Ag 4- x Au x The required temperature for Se2 is 4–160℃.

5. The preparation of high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor as described in claim 1. 4-x Au x The method of Se2 is characterized by, In the synthesis of the gold precursor, the volume ratio of thiol I to alcohol solvent is 1:3 to 3:

1.

6. The preparation of high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor as described in claim 1. 4-x Au x The method of Se2 is characterized by, The synthesis temperature of the gold precursor is 60℃~85℃, and the reaction time is 0.5h~8h.

7. The preparation of high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor as described in claim 1. 4-x Au x The method of Se2 is characterized by, Both terminal olefin I and terminal olefin II are selected from 1-octadecene.

8. The preparation of high quantum yield near-infrared II fluorescent nanocrystals Ag using Au(I)-Thiolate coordination polymer as a precursor as described in claim 1. 4-x Au x The method of Se2 is characterized by, In step S200, the silver salt is selected from silver acetate.

9. A near-infrared II fluorescent nanocrystalline Ag 4-x Au x Se2, characterized in that, High quantum yield near-infrared II fluorescent nanocrystals Ag were prepared using the Au(I)-Thiolate coordination polymer as a precursor as described in any one of claims 1 to 9. 4-x Au x It was prepared by the Se2 method.

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