Luminescent metal nanocluster as well as preparation method and application thereof

Abstract

The invention discloses a luminescent metal nanocluster and a preparation method and application thereof, and belongs to the technical field of nano luminescent materials, the luminescent metal nanocluster is composed of a core metal and a peripheral ligand in a specific coordination mode, and the chemical formula is AumCu22-m (tBuPhC is equivalent to C) 18; wherein m is larger than or equal to 19 and smaller than or equal to 21. The preparation method comprises the following steps: adding an alkyne compound into a mixed solution of a gold complex and organic amine, reacting for a period of time, doping a copper complex, adding a reductive borane complexing agent, carrying out a reduction reaction, removing a solvent after the reaction is finished, and crystallizing and purifying to obtain the luminous metal nanocluster. According to the method, under different copper source doping proportions, precise and controllable synthesis of the gold-copper alloy nanocluster of a brand new structure is achieved for the first time, a new breakthrough is provided for structural regulation and performance optimization of the metal nanocluster, and a new high-performance material system is provided for photoelectric sensing and imaging application.

Description

Technical Field

[0001] The present invention belongs to the technical field of nano luminescent materials, and particularly relates to a luminescent metal nanocluster, a preparation method thereof and an application thereof. Background Art

[0002] Electrochemiluminescence (ECL), also known as electrochemically generated chemiluminescence, refers to the phenomenon of luminescence generated by the transition of an excited state back to the ground state after a high-energy electron transfer reaction occurs between oxidized and reduced active species generated on the surface of an electrode by applying a voltage to generate an excited state. Electrochemiluminescence is a technology that combines electrochemistry and chemiluminescence, can be regulated through electrochemical reactions and does not require external light source excitation, and has the advantages of strong reaction spatiotemporal controllability, low background signal, high sensitivity, etc., and is one of the most advanced signal transduction methods at present. Therefore, electrochemiluminescence is widely used in research fields such as immunoassay, biosensing, environmental monitoring, nucleic acid detection, cell imaging, etc., especially in the detection and analysis at the picomolar to femtomolar or even single molecule / single cell level in recent years. The research on electrochemiluminescence can be traced back to 1927 at the earliest. With the development of modern high-sensitivity optoelectronic sensing instruments and technologies, scientists have a deeper understanding of the mechanism and reaction process of electrochemiluminescence, and continuously expand the application scope of electrochemiluminescence.

[0003] Electrochemiluminescence can be mainly generated through the annihilation pathway and the coreactant pathway. In the annihilation pathway, the generation of electrochemiluminescence usually requires applying positive and negative potentials on the electrode surface. The luminophore undergoes electrochemical reduction and oxidation on the electrode surface to generate anionic radicals and cationic radicals, and an annihilation reaction occurs between the two active intermediates to generate excited state molecules, and luminescence is generated during the transition of the excited state molecules back to the ground state. The electrochemiluminescence generated by the annihilation pathway requires strict control of experimental conditions such as supporting electrolyte and potential. Most reactions occur only in organic solvents because the energy required to generate the excited state by the annihilation pathway is relatively high, and the potential window of the aqueous solution is relatively narrow, which is not conducive to the generation of electroactive intermediates on the electrode surface; in addition, dissolved oxygen in water will quench the radicals generated on the electrode surface, which is not conducive to the generation of excited state molecules. Therefore, such reactions need to select appropriate organic solvents, electrode materials, supporting electrolytes, etc., and the dissolved oxygen needs to be removed before the reaction.

[0004] At present, the application of electrochemiluminescence (ECL) technology is mainly based on co-reactant type ECL. When both a luminophore and a co-reactant are present in the system, a unidirectional scanning potential or step potential applied to the electrode surface can generate a stronger luminescence signal in a short time. Depending on the positive and negative voltages applied, the luminophore and co-reactant can undergo oxidation or reduction reactions on the electrode surface to generate free radicals. The intermediate generated by the co-reactant decomposes to produce substances with strong reducibility or strong oxidizability, which further react with the free radicals generated by the luminophore to form an excited state, and light radiation is generated during the process of its return to the ground state. So far, researchers have explored various types of ECL luminescent materials, including silicon nanocrystals, organic molecular materials, inorganic complexes, and metal nanoclusters (MNCs), and they have broad application prospects in the fields of bioimaging, immunoassay, food analysis, environmental monitoring, photoelectric sensing, etc. With the rapid development of nanotechnology, compared with traditional inorganic metal complexes and organic molecular dye electrochemiluminescent materials, metal nanoclusters with precise atoms and tunable luminescence have become a relatively ideal type of ECL luminescent material. Seeking ECL luminescent materials with higher luminescence efficiency and exploring the luminescence mechanisms and new applications of different ECL luminescent materials are still the focus of attention.

[0005] Since the Brust-Schiffrin method achieved the controllable synthesis of metal nanoparticles in the 1990s, metal nanoclusters have gradually become a research hotspot in the field of nanomaterials. These tiny structures with a size of 1-3 nm have a core composed of dozens to hundreds of metal atoms and are stabilized by peripheral ligands, showing unique quantum confinement effects. Their optical properties, such as size-dependent fluorescence emission and tunable quantum yields, have attracted extensive attention. In addition, due to their size being close to the Fermi wavelength of electrons, their electronic transitions exhibit discrete energy level characteristics, showing the potential as electrochemiluminescent materials. Typical metal nanoclusters include gold (Au), silver (Ag), copper (Cu), and their alloy nanoclusters (such as Au-Ag doping). At present, through alloying (regulating the electronic structure), ligand engineering (reducing surface defects), and host-guest interactions (reducing non-radiative transitions), their luminescence properties can be improved to a certain extent. However, existing studies have shown that in the process of improving the luminescence efficiency, metal nanoclusters often aggregate, dissociate, or change in morphology due to unstable structures, resulting in a decrease in their reliability and persistence, and it is difficult to meet the actual application requirements. The contradiction between improving luminescence efficiency and structural stability is still the key bottleneck, severely restricting their practical application process in the fields of in vivo imaging, photoelectric sensing, etc.

[0006] Therefore, how to provide an electrochemiluminescent material with high luminescence efficiency and stable structure is a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0007] To solve the contradiction between the efficiency improvement and structural stability of metal nanoclusters, the present invention proposes a luminescent metal nanocluster and its preparation method and application.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A luminescent metal nanocluster, wherein the luminescent metal nanocluster is composed of a core metal and a peripheral ligand through a specific coordination mode, and the chemical formula is Au m Cu 22-m ( t BuPhC≡C) 18 ;

[0010] wherein, 21≥m≥19.

[0011] Preferably, the m is 19.11 or 20.08.

[0012] Preferably, the chemical formula is Au 20.08 Cu 1.92 ( t BuPhC≡C) 18 or Au 19.11 Cu 2.89 ( t BuPhC≡C) 18 .

[0013] Beneficial effects: As shown in the structural formulas in Figure 2 and 3 , the metal nanoclusters obtained by the present invention have a highly ordered core-shell structure. The core is composed of gold and doped copper atoms and is stabilized by gold-gold and gold-copper interactions. This alloy structure not only optimizes the electronic structure, improves the photoluminescence (PL) and ECL properties of the nanoclusters, but also endows them with excellent structural rigidity and stability. In addition, the alkynyl ligands on the surface of the nanoclusters are uniformly distributed to form a stable organic coordination layer, which improves the solubility and dispersibility, and regulates the electron coupling characteristics through the π-π conjugation effect, further optimizing the energy level distribution, so that the obtained luminescent metal nanoclusters have broad application potential in the field of optoelectronic materials.

[0014] A preparation method of a luminescent metal nanocluster, comprising the following steps:

[0015] Adding an alkyne compound to a mixed solution of a gold complex and an organic amine, reacting for a period of time, then incorporating a copper complex, and subsequently adding a reducing borane complexing agent for a reduction reaction. After the reaction is completed, the solvent is removed, and then crystallization and purification are carried out to obtain the luminescent metal nanocluster.

[0016] Beneficial effects: The gold complex in the present invention first undergoes a coordination reaction with the alkyne compound to form a stable complex structure, providing a good coordination environment for the subsequent doping of copper elements. On this basis, the present invention synthesizes by a one-pot method, directly introducing a copper complex, enabling the in-situ generation of gold-copper alloy nanoclusters under mild conditions, ensuring the stability of the alloy structure, and effectively regulating their luminescence properties. In addition, the addition of an organic amine (such as Et3N) can adjust the pH of the reaction system, provide an alkaline environment, optimize the formation conditions of the gold-alkyne complex, effectively promote the deprotonation of the alkyne compound, thereby enhancing its coordination ability with the gold complex, avoiding side reactions, and improving the stability and uniformity of the metal nanoclusters.

[0017] Preferably, the addition ratio of the gold complex, organic amine, alkyne compound, copper complex, and borane complexing agent is 0.1 mmol : (0.25 - 0.3) mmol : 0.1 mmol : (0.03 - 0.04) mmol : (0.015 - 0.02) mmol.

[0018] Beneficial effects: The doping of the copper complex in the present invention can effectively regulate the electronic structure of the nanoclusters, affect their PL and ECL properties. By reasonably controlling the doping ratio of Cu, the emission wavelength and quantum yield can be adjusted, improving the sensitivity and stability of photoelectric sensing.

[0019] Preferably, the gold complex is Me2SAuCl; and / or,

[0020] the organic amine is Et3N; and / or,

[0021] the alkyne compound is 4- t BuPhC≡CH; and / or,

[0022] the copper complex is Cu(MeCN)4PF6; and / or,

[0023] the borane complexing agent is BH3· t BuNH2.

[0024] More preferably, the solvent of the mixed solution of the gold complex and the organic amine is chloroform or toluene; and / or,

[0025] the borane complexing agent is BH3· t an ethanol solution of BuNH2 with a concentration of 0.02 mmol / mL.

[0026] Beneficial effects: The borane complexing agent in the present invention can achieve a mild and somewhat selective reduction reaction, avoiding the uneven cluster size or structural disintegration caused by strong reducing agents (such as NaBH4). At the same time, BH3· tThe ethanol solution of BuNH2 can further optimize the polarity of the reaction system and improve the yield and quality of the target product.

[0027] Preferably, the temperature of the coordination reaction is room temperature and the time is 4 h.

[0028] More preferably, the coordination reaction is carried out under light-shielded conditions.

[0029] Beneficial effects: The coordination reaction in the present invention is carried out at room temperature, avoiding the decomposition or uneven growth of metal nanoclusters that may be caused by high temperature conditions, and at the same time ensuring the structural integrity of the metal nanoclusters. The setting of light-shielded conditions can prevent photolysis or oxidation side reactions caused by light and improve the stability of the product.

[0030] Preferably, the purification includes the following steps:

[0031] The solid obtained after removing the solvent is dissolved in an organic solvent, and then after centrifuging to collect the supernatant, a polar solvent is added for diffusion crystallization.

[0032] Preferably, the organic solvent is a mixture of toluene and dichloromethane in a volume ratio of 1:1; and / or,

[0033] The polar solvent is acetonitrile or n-hexane.

[0034] Beneficial effects: The use of a mixed organic solvent (toluene and dichloromethane) in the purification process of the present invention can improve the solubility of the target product, and then diffusion crystallization through a polar solvent (such as acetonitrile or n-hexane) helps to improve the crystallinity and purity of the product, while reducing the aggregation effect of the clusters, thereby optimizing its optoelectronic properties.

[0035] An application of a luminescent metal nanocluster in the field of optoelectronic material design or electrochemiluminescence.

[0036] Beneficial effects: The metal nanoclusters prepared in the present invention have wide applications in the fields of optoelectronic materials and electrochemiluminescence, and can be used in fields such as highly sensitive sensing detection, light-emitting devices, bioimaging, and catalysis. Especially in ECL sensing, the nanoclusters doped with copper can exhibit more excellent electrochemical stability and higher luminescence intensity, providing the possibility for the development of new sensors.

[0037] Compared with the prior art, the present invention has the following advantages and technical effects:

[0038] By gradually increasing the amount of copper doping, the present invention successfully prepared atomically precise and structurally clear gold-copper alloy nanoclusters, breaking through the technical bottlenecks of traditional metal nanoclusters, such as poor stability, low photoluminescence quantum yield, and low electrochemiluminescence efficiency. The obtained gold-copper alloy nanoclusters have dual characteristics of high-efficiency photoluminescence (quantum yield > 99%) and high-stability electrochemiluminescence, where the annihilation-path ECL efficiency is increased to 13.2 times that of the standard sample (Ru(bpy)3 2+ ), and the co-reactant-path ECL efficiency is increased to 6.3 times. For the first time, the present invention realizes the precise and controllable synthesis of gold-copper alloy nanoclusters with a new structure under different copper-source doping ratios, providing a new breakthrough for the structural regulation and performance optimization of metal nanoclusters, and also providing a new high-performance material system for optoelectronic sensing and imaging applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings constituting a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof of this application are used to explain this application and do not constitute an improper limitation of this application. In the drawings:

[0040] Figure 1 For the molecular structure (a), core metal (b), coordination mode (c), and structural evolution (d) of Au 22 NCs obtained in Comparative Example 1;

[0041] Figure 2 For the molecular structure (a), core metal (b), coordination mode (c), and structural evolution (d) of Au 20 Cu2 NCs obtained in Example 1;

[0042] Figure 3 For the molecular structure (a), core metal (b), coordination mode (c), and structural evolution (d) of Au 19 Cu3 NCs obtained in Example 2;

[0043] Figure 4 For the ultraviolet-visible absorption spectra (a), photoluminescence spectra (b), and decay curves (c) of the metal nanoclusters obtained in Examples 1-2 and Comparative Example 1;

[0044] Figure 5 For (a) the cyclic voltammograms of annihilation (i) and co-reactant (TPrA) (ii) of Au 22 NCs obtained in Comparative Example 1, the corresponding ECL-potential curves, and electrochemiluminescence spectra (iii); (b) the cyclic voltammograms of annihilation (i) and co-reactant (TPrA) (ii) of Au 20 Cu2 NCs obtained in Example 1, the corresponding ECL-potential curves, and electrochemiluminescence spectra (iii); (c) the cyclic voltammograms of annihilation (i) and co-reactant (TPrA) (ii) of Au 19Annihilation of Cu3 NCs (i) and co-reactant (TPrA) (ii) cyclic voltammograms, corresponding ECL-potential curves, and electrochemiluminescence spectra (iii);

[0045] Figure 6 For Au obtained in Comparative Example 1 22 In-situ electrochemiluminescence spectra of the co-reactant (TPrA) of NCs (a); Au obtained in Example 1 20 In-situ electrochemiluminescence spectra of the co-reactant (TPrA) of Cu2 NCs (b); Au obtained in Example 2 19 In-situ electrochemiluminescence spectra of the co-reactant (TPrA) of Cu3 NCs (c). Detailed implementation manners

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0047] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0048] Unless otherwise specified, the raw materials in the embodiments of the present invention are obtained through commercial channels.

[0049] Unless otherwise specified, the room temperature or normal temperature in the embodiments of the present invention is 25 ± 3 °C.

[0050] Example 1

[0051] A preparation method of luminescent metal nanoclusters, with the chemical formula Au 20.08 Cu 1.92 ( t BuPhC≡C) 18 Specifically includes the following steps:

[0052] Take 29.5 mg (0.1 mmol) of Me2SAuCl and 40 μL of Et3N, dissolve them in 5 mL of toluene solution, add 4- t BuPhC≡CH (18 μL, 0.1 mmol), and stir for 5 minutes. Subsequently, add Cu(MeCN)4PF6 (11.18 mg, 0.03 mmol), and then quickly add BH3· t BuNH2 solution (1.7 mg of BH3· tDissolve BuNH2 in 1 mL of ethanol), and stir the reaction mixture in the dark at room temperature for 4 hours. After the reaction is completed, remove the solvent using a rotary evaporator to obtain a black-red solid. Then dissolve this black-red solid in a mixed solution of 2 mL of toluene and dichloromethane (v:v = 1:1), and centrifuge at 10,000 rpm for 3 minutes. Collect the black-red solution, add acetonitrile for diffusion crystallization, and store it in a 4 °C refrigerator. After two weeks of crystallization, red crystals, namely the product Au 20.08 Cu 1.92 ( t BuPhC≡C) 18 , denoted as Au 20 Cu2NCs.

[0053] Example 2

[0054] A method for preparing luminescent metal nanoclusters with the chemical formula Au 19.11 Cu 2.89 ( t BuPhC≡C) 18 , specifically including the following steps:

[0055] Take 29.5 mg (0.1 mmol) of Me2SAuCl and 40 μL of Et3N, dissolve them in 5 mL of toluene solution, add 4- t BuPhC≡CH (18 μL, 0.1 mmol), and stir for 5 minutes. Subsequently, add Cu(MeCN)4PF6 (14.91 mg, 0.04 mmol), and then quickly add BH3· t BuNH2 solution (1.7 mg of BH3· t BuNH2 dissolved in 1 mL of ethanol), and stir the reaction mixture in the dark at room temperature for 4 hours. After the reaction is completed, remove the solvent using a rotary evaporator to obtain a black-red solid. Then dissolve this black-red solid in a mixed solution of 2 mL of toluene and dichloromethane (v:v = 1:1), and centrifuge at 10,000 rpm for 3 minutes. Collect the black-red solution, add acetonitrile for diffusion crystallization, and store it in a 4 °C refrigerator. After two weeks of crystallization, red crystals, namely the product Au 19.11 Cu 2.89 ( t BuPhC≡C) 18 , denoted as Au 19 Cu3NCs.

[0056] Comparative Example 1

[0057] A method for preparing luminescent metal nanoclusters with the chemical formula Au 22 ( t BuPhC≡C) 18, specifically including the following steps:

[0058] Take 29.5 mg (0.1 mmol) of Me2SAuCl and 28.7 mg (0.1 mmol) of 1,2,3-Ph3(CN3H2) and dissolve them in 5 mL of chloroform solution. Add 4- t BuPhC≡CH (18 μL, 0.1 mmol), and stir for 5 minutes. Subsequently, add a methanol solution of sodium hydroxide (8.0 mg (0.2 mmol) of sodium hydroxide dispersed in 1 mL of methanol), and stir the reaction mixture in the dark at room temperature for 12 hours. During the reaction, the color of the solution gradually deepens. After the reaction is completed, remove the solvent using a rotary evaporator to obtain an orange solid. Dissolve the orange solid in a 2 mL mixed solution of toluene and dichloromethane (v:v = 1:1), and centrifuge at 10,000 rpm for 3 minutes. Collect the orange solution, add methanol for diffusion crystallization, and let it stand in a 4 °C refrigerator for storage. After two weeks of crystallization, an orange-red crystal is obtained, which is the product Au 22 ( t BuPhC≡C) 18 , denoted as Au 22 NCs.

[0059] Technical effects:

[0060] 1. Through an X-ray diffractometer, a detailed analysis is carried out on the molecular structure, core metal, coordination mode, and structural evolution of three metal nanocluster crystals, Au 22 NCs, Au 20 Cu2NCs, Au 19 Cu3NCs.

[0061] Figure 1-3 Respectively show the accurate molecular formulas and molecular structures of the three nanoclusters obtained in Examples 1-2 and Comparative Example 1. Taking Au 19 Cu3NCs as an example, the present invention first clarifies that the core metal of the cluster is 22 metal atoms, with a total of 18 positive charges, and the peripheral ligand is 18 negatively charged p-tert-butylphenylacetylene anions. Among the 22 metal atoms, the ratio of Au to Cu is 19.11∶2.89. As shown in part a of Figure 3 , the orange balls are gold atoms, the orange / blue balls are gold-copper co-occupancy atoms, the purple framework is carbon atoms, and hydrogen atoms have been omitted; secondly, the present invention determines the types and bonding modes of the metals in the cluster. As shown in part b of Figure 3 , the metal core is first formed by sharing the vertices of two regular tetrahedrons to form an hourglass-shaped (Au-Cu)7 core, and its periphery is surrounded by 3 Au atoms and 3 Au-Cu co-occupancy atoms to construct a stable nanocluster structure; then from Figure 3The bonding mode between the alkynyl ligand and the core metal can be observed in part c of the Chinese text, where both σ-bond coordination and π-bond coordination exist; finally, from Figure 3 In part d of the Chinese text, it can be clearly seen that ligands with two connection modes are added to the periphery of the hourglass-shaped metal core. The above technical effects are unprecedented for other inorganic nanomaterials. Understanding the composition and structure of the cluster at the molecular level is neither the same as that of complexes with single metal centers nor that of organic small molecules, which greatly facilitates the precise control of the structure and the optimization and improvement of performance. By revealing the mechanism of action of the core metal ratio, the present invention pioneered the simultaneous breakthrough of the photoluminescence quantum yield and the electrochemiluminescence efficiency in Au 19 Cu3 NCs, and successfully solved the contradiction between the high luminescence performance and the unstable structure of traditional metal nanomaterials.

[0062] 2. Optical property detection: Weigh the products obtained in Examples 1-3, select dichloromethane as the solvent, prepare a metal nanocluster solution with a concentration of 0.01 mM, transfer it to a quartz cuvette with four-way light to test its optical properties, and the results are as Figure 4 shown.

[0063] Figure 4 Part a in the Chinese text is the ultraviolet-visible absorption spectrum. It can be seen that the characteristic absorption peaks of Au 22 NCs are located at 479 nm and 527 nm; with the doping of copper, the absorption peaks of Au 20 Cu2 NCs show a red shift and are located at 481 nm and 540 nm respectively; when the copper doping amount further increases, the characteristic absorption peaks of Au 19 Cu3 NCs further red shift to 520 nm and 580 nm. The gradual red shift of the absorption peaks with the increase of the copper doping amount indicates that the introduction of copper effectively reduces the optical band gap of the cluster molecules.

[0064] Furthermore, the photoluminescence spectrum, quantum yield and luminescence lifetime of the cluster solution were measured using a fluorescence spectrometer and an integrating sphere, and the results are as Figure 4 shown in part b (photoluminescence spectrum) and part c (decay curve diagram) of the Chinese text. It can be seen that with the increase of the copper doping amount, the emission peak of the photoluminescence red shifts from 685 nm (Au 22 NCs) to 689 nm (Au 20 Cu2 NCs) and 710 nm (Au 19 Cu3 NCs), and the quantum yield increases significantly from 10.71% (Au 22 NCs) to 71.82% (Au 20 Cu2 NCs), and then to nearly 100% (Au 19For Cu3 NCs, the luminescence lifetime increased correspondingly from 522.51 ns to 1468 ns and then to 1524 ns. This is because copper doping not only effectively reduces the optical band gap, but also the shorter bond length leads to structural contraction, greatly inhibiting the non-radiative transition of cluster molecules and accelerating the intersystem crossing rate of electrons, thus achieving a significant improvement in optical properties.

[0065] 2. Electrochemiluminescence test: Weigh the metal nanoclusters obtained in Examples 1-2 and Comparative Example 1, and prepare dichloromethane solutions with metal nanocluster concentrations of 0.05 mM (for annihilation ECL test) and 0.1 mM (for co-reactant ECL test) as electrolytes respectively. Add 0.1 M tetrabutylammonium hexafluorophosphate as the supporting electrolyte, select a platinum disk electrode as the working electrode, a platinum wire electrode as the reference electrode and the counter electrode, construct a three-electrode system, and conduct electrochemiluminescence tests. The results are as Figure 5 shown.

[0066] Comparing Figure 5 Figure i) of parts a, b, and c in it, it can be seen that under the same test conditions, Au 19 Cu3 NCs exhibit more excellent annihilation ECL signals. During the negative and positive scans, Au 19 Cu3 NCs undergo electron gain and loss reactions to generate cationic and anionic radicals with higher stability and longer lifetimes. These radicals have high reactivity and react to generate a large number of excited states of Au 19 Cu3 NCs. After returning to the ground state, stronger ECL signals are generated. Taking Ru(bpy)3 2+ as the standard sample, the relative annihilation ECL efficiency of Au 19 Cu3 NCs is 13.2 times that of the standard sample.

[0067] To further enhance the ECL signal, the present invention selects tripropylamine (TPrA) as the co-reactant and finds that a significantly enhanced ECL signal can be obtained in a short time through single-direction scanning. The co-reactant ECL test is carried out using a metal nanocluster solution with a concentration of 0.1 mM. As shown in Figure ii) of parts a, b, and c in 5, under their respective optimal test conditions, the cationic radicals of Au 19 Cu3 NCs react with TPrA radicals to generate a large number of excited states of Au 19 Cu3 NCs. After returning to the ground state, strong co-reactant ECL signals are generated. The relative co-reactant ECL efficiency of Au 19 Cu3 NCs is 6.3 times that of the standard sample, which is an unprecedented performance for metal nanoclusters.

[0068] To further clarify the ECL luminescence mechanism, the present invention used an ECL spectrometer to accurately measure the ECL emission wavelength of the nanoclusters. The results are as Figure 5 shown in Figure iii) of parts a, b, and c. It can be seen that the ECL emission wavelengths of the three nanoclusters also show a consistent red-shift phenomenon, from 685 nm of Au 22 NCs to 689 nm of Au 20 Cu2 NCs. With the further increase of the copper doping amount, the ECL emission wavelength of Au 19 Cu3 NCs redshifts to 710 nm. This phenomenon is highly consistent with the emission wavelength of photoluminescence, proving that the electrochemiluminescence bandgap is completely consistent with the photoluminescence bandgap, and further verifying that the precise regulation of ECL properties can be achieved by adjusting the copper doping amount.

[0069] The present invention further verified the electrochemiluminescence performance and mechanism of the nanoclusters through time-resolved ECL spectroscopy. The results are as Figure 6 shown. It can be seen that the ECL signal fluctuates significantly with the change of the scanning potential, and the ECL intensity shows a dynamic response with the change of the potential, clearly demonstrating the luminescence mechanism of the nanoclusters during the electrochemiluminescence process. Taking Au 19 Cu3NCs as an example, during the coreaction ECL process, when the voltage is scanned to 1.07 V, Au 19 Cu3 NCs lose one electron to generate Au 19 Cu3 monovalent cation, which reacts with the TPrA cation radical to generate Au 19 Cu3 zero-valent excited state, and the ECL signal starts to appear when returning to the ground state; when the voltage is scanned to a more positive range, Au 19 Cu3 NCs further lose the second, third, and fourth electrons to generate Au 19 Cu3 divalent, trivalent, and tetravalent cations, and the ECL signal is significantly enhanced, proving the contribution of the high-valent oxidation state to the ECL signal. It reacts with the TPrA cation radical to generate a large number of Au 19 Cu3 high-valent excited states, and returns to the ground state to emit a stronger ECL signal.

[0070] In summary, based on the analysis of electrochemical and ECL results, the present invention puts forward the following speculation on the ECL reaction and signal enhancement mechanism: First, copper doping changes the electron distribution of the cluster, making it easier to gain or lose electrons, forming ionic radicals with high stability and longer lifetime in the reduced state and high oxidation state, thereby generating a stronger annihilation ECL efficiency. At the same time, the reaction activity of the high-valent oxidation state ions with the TPrA radical is enhanced, resulting in a stronger coreaction type ECL signal. Second, the relative ECL efficiency of Au 19 Cu3 NCs is much higher than that of Ru(bpy)32+ , the possible reason is that after the high-valence excited state transitions back to the ground state, the generated low-valence cations can still further lose electrons, regenerate high-valence ions and react with TPrA radicals. This process forms a positive feedback loop, continuously enhancing the ECL signal. In addition, when the concentration of TPrA is high enough, a cascade reaction may occur, that is, the TPrA radical can directly oxidize the ground-state cation generated in the previous step to form an excited state with a lower oxidation state, superimposing the luminescence intensity, thereby further enhancing the ECL signal.

[0071] The above are only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A luminescent metal nanocluster, characterized in that: The luminescent metal nanocluster is composed of a core metal and a peripheral ligand in a specific coordination manner, and the chemical formula is Au m Cu 22-m ( t BuPhC≡C) 18 ; Among them, 21≥m≥19.

2. The luminescent metal nanocluster according to claim 1, characterized in that: The m is 19.11 or 20.

08.

3. The luminescent metal nanocluster according to claim 1, characterized in that: The chemical formula is Au 20.08 Cu 1.92 ( t BuPhC≡C) 18 or Au 19.11 Cu 2.89 ( t BuPhC≡C) 18 .

4. A method for preparing a luminescent metal nanocluster according to any one of claims 1 to 3, characterized in that: The following steps are involved: An alkyne compound is added to a mixed solution of a gold complex and an organic amine, and after a period of reaction, a copper complex is added, and then a reducing borane complexing agent is added to carry out a reduction reaction. After the reaction is completed, the solvent is removed, and then the luminescent metal nanoclusters are obtained by purification through crystallization.

5. The method for preparing a luminescent metal nanocluster according to claim 4, characterized in that: The ratio of the added amounts of the gold complex, the organic amine, the alkyne compound, the copper complex and the borane complexing agent is 0.1 mmol: (0.25-0.3) mmol: 0.1 mmol: (0.03-0.04) mmol: (0.015-0.02) mmol.

6. The method for preparing a luminescent metal nanocluster according to claim 5, characterized in that: The gold complex is Me2SAuCl; and / or, The organic amine is Et3N; and / or, The alkyne compound is 4- t BuPhC≡CH; and / or, The copper complex is Cu(MeCN)4PF6; and / or, The borane complexing agent is BH3· t BuNH2.

7. The method for preparing a luminescent metal nanoclusters according to claim 4, characterized in that: The reaction conditions are room temperature in the dark and the reaction time is 4 hours.

8. The method for preparing a luminescent metal nanocluster according to claim 4, characterized in that: The purification comprises the following steps: The solid obtained after removing the solvent is dissolved in an organic solvent, and then the supernatant is collected by centrifugation, and then a polar solvent is added to perform diffusion crystallization.

9. The method for preparing a luminescent metal nanocluster according to claim 8, characterized in that: The organic solvent is a mixture of toluene and dichloromethane in a volume ratio of 1:1; and / or, The polar solvent is acetonitrile or n-hexane.

10. Use of a luminescent metal nanocluster as claimed in any one of claims 1 to 3 in the field of optoelectronic material design or electrochemical luminescence.

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