Synthesis method of N-heterocyclic carbene precursor and metal complex based on nano graphene fragment

Abstract

The invention discloses a synthesis method of an N-heterocyclic carbene precursor and a metal complex based on a nano graphene fragment, and belongs to the technical field of chemical synthesis. The synthesis method of the precursor comprises the following steps: taking 1, 3, 5-tri (3, 4-dimethoxybenzyl) benzene as an initial raw material to react with a benzaldehyde derivative, carrying out a Suzuki coupling reaction catalyzed by Pd on a preliminary reaction product, and then carrying out an N-terminal alkyl substitution reaction and an anion exchange reaction to obtain the precursor. Or carrying out a Suzuki coupling reaction catalyzed by Pd, and then carrying out a Schiff base reaction, a ring closing reaction and an anion exchange reaction, or carrying out alkyl imidazole substitution reaction and anion exchange reaction on the primary reaction product. According to the invention, the N-heterocyclic carbene precursor and the metal complex taking the nano graphene fragment as the central aromatic nucleus skeleton are synthesized by a short path, the N-heterocyclic carbene precursor and the metal complex have high yield and excellent luminescence property, the functionality of a supramolecular structure is enriched, and a new idea is provided for the expansion of a topological structure library and the development of efficient functional materials.

Description

Technical Field

[0001] The invention relates to the technical field of chemical synthesis, and in particular to a method for synthesizing a nitrogen heterocyclic carbene precursor and a metal complex based on a nanographene fragment. Background Art

[0002] As part of the structural composition of common carbon materials, nanographene can be regarded as a two-dimensional graphene fragment with nanoscale. This π-conjugated molecule not only has beautiful symmetry and superior mechanical, thermal and electrical properties, but also usually has a unique edge structure and functional modification sites, showing great research value in the field of materials. Nanographene fills the size gap between macroscopic graphene and polycyclic aromatic hydrocarbon molecules, and can be used as a template for studying the structure and properties of complex carbon materials. At present, although several relatively mature "bottom-up" synthesis strategies for nanographene have been developed, there are still problems such as long synthesis routes, low yields, and few modification sites. In addition, π-π stacking is prone to occur between molecules, which limits its development in some fields. Therefore, its precise and controllable synthesis at the molecular level and the subsequent development of its functionality have always been a major challenge in related fields.

[0003] In the field of supramolecular chemistry, various metal carbene assembly structures formed by coordination-driven self-assembly are common, but their performance depends largely on the introduction of central skeleton building modules, which leads to the slow development of the application of related materials. Therefore, the rational selection of molecular primitives with in-depth research value is a necessary prerequisite for the subsequent development of application performance. In view of the potential performance of nanographene fragments in many fields, it can be used as an ideal skeleton molecule to design supramolecular systems with unique properties, which can inject vitality into the design and development of functional materials. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a method for synthesizing a nitrogen heterocyclic carbene precursor and a metal complex based on nanographene fragments, so as to solve the problem that it is difficult to realize the application of supramolecular systems to nanographene and it is difficult to realize the synthesis of functional materials in the field of supramolecular chemistry based on nanographene fragments.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] In the first aspect of the present invention, a plurality of nitrogen heterocyclic carbene precursors based on nanographene fragments are provided, and the chemical structural formula is shown in any one of Formula I to Formula III:

[0007]

[0008] In the formula, X is CH or N; R is any one of the straight-chain alkanes with 1 to 8 carbon atoms; R' is any one of n-butyl, mesitylene and 2,6-dimethylphenyl; Y is BF 4 PF 6 , OTf and SbF 6 Any one of .

[0009] The second aspect of the present invention provides a method for synthesizing the above-mentioned nitrogen heterocyclic carbene precursor based on nanographene fragments, and the nitrogen heterocyclic carbene precursors shown in Formula I to Formula III are synthesized by the following methods respectively:

[0010] (1) Synthesis of the nitrogen heterocyclic carbene precursor shown in Formula I:

[0011] First, 1,3,5-tris(3,4-dimethoxybenzyl)benzene and benzaldehyde derivatives are subjected to Friedel-Crafts reaction and Shore reaction, and then the obtained product is subjected to Pd-catalyzed Suzuki coupling reaction with a Br-substituted aromatic compound, and finally the product of the Suzuki coupling reaction is sequentially subjected to N-terminal alkyl substitution reaction with a brominated straight-chain alkane, and an anion exchange reaction with a target anion salt is carried out to obtain;

[0012] (2) Synthesis of the nitrogen heterocyclic carbene precursor shown in formula II:

[0013] First, 1,3,5-tris(3,4-dimethoxybenzyl)benzene and benzaldehyde derivatives are subjected to Friedel-Crafts reaction and Shore reaction, and then the obtained product is subjected to Pd-catalyzed Suzuki coupling reaction with 5-bromo-2-pyridinecarboxaldehyde, and then the product of the Suzuki coupling reaction is subjected to Schiff base reaction with an amine compound, and finally a ring-closing reaction is carried out, and then an anion exchange reaction is carried out with a target anion salt to obtain;

[0014] (3) Synthesis of the nitrogen heterocyclic carbene precursor shown in formula III:

[0015] Firstly, 1,3,5-tris(3,4-dimethoxybenzyl)benzene and 4-bromomethylbenzaldehyde are subjected to Friedel-Crafts reaction and Shore reaction, then the obtained product is subjected to substitution reaction with linear alkyl imidazole, and finally the substitution reaction product is subjected to anion exchange reaction with target anion salt to obtain the compound.

[0016] Furthermore, in method (1):

[0017] The benzaldehyde derivative in the Friedel-Crafts reaction and the Shore reaction is 4-formylphenylboronic acid pinacol ester; the molar ratio of 1,3,5-tri(3,4-dimethoxybenzyl)benzene to 4-formylphenylboronic acid pinacol ester is 1:(3-4); the reaction temperature is 20-30°C and the reaction time is 8-10h;

[0018] The Br-substituted aromatic compound in the Pd-catalyzed Suzuki coupling reaction is 1-(4-bromophenyl)-1H-imidazole or 1-(4-bromophenyl)-1H-triazole; the molar ratio of the product after the Friedel-Crafts reaction and the Shore reaction to the Br-substituted aromatic compound is 1:(3-4); the reaction temperature is 90-120°C and the reaction time is 20-30h;

[0019] The molar ratio of the Suzuki coupling reaction product to the brominated straight-chain alkane in the N-terminal alkyl substitution reaction is 1:(5-10); the reaction temperature is 90-120°C and the reaction time is 20-30h;

[0020] The molar ratio of the Suzuki coupling reaction product to the target anion salt in the anion exchange reaction is 1:(5-10); the reaction temperature is 20-30°C, and the reaction time is 10-24h.

[0021] Preferably, in method (1):

[0022] The benzaldehyde derivative in the Friedel-Crafts reaction and the Shore reaction is 4-formylphenylboronic acid pinacol ester; the molar ratio of 1,3,5-tri(3,4-dimethoxybenzyl)benzene to 4-formylphenylboronic acid pinacol ester is 1:3.3; the reaction temperature is 25°C and the reaction time is 8h;

[0023] The Br-substituted aromatic compound in the Pd-catalyzed Suzuki coupling reaction is 1-(4-bromophenyl)-1H-imidazole or 1-(4-bromophenyl)-1H-triazole; the molar ratio of the product after Friedel-Crafts reaction and Shore reaction to the Br-substituted aromatic compound is 1:3.3; the reaction temperature is 100°C and the reaction time is 24h;

[0024] The molar ratio of the Suzuki coupling reaction product to the brominated straight-chain alkane in the N-terminal alkyl substitution reaction was 1:6; the reaction temperature was 120°C and the reaction time was 24h;

[0025] The molar ratio of the Suzuki coupling reaction product and the target anion salt in the anion exchange reaction was 1:5; the reaction temperature was 25°C and the reaction time was 12 h.

[0026] Furthermore, the Friedel-Crafts reaction and Shore reaction system also includes boron trifluoride etherate and acetic anhydride, and the molar ratio of 1,3,5-tris(3,4-dimethoxybenzyl), boron trifluoride etherate and acetic anhydride is 1:(4-8):(4-8).

[0027] Furthermore, the Pd-catalyzed Suzuki coupling reaction system also includes potassium carbonate and tetrakis(triphenylphosphine)palladium, and the molar ratio of the product after Friedel-Crafts reaction and Shore reaction, potassium carbonate and tetrakis(triphenylphosphine)palladium is 1:(3-6):(0.1-0.3).

[0028] Furthermore, in method (2):

[0029] The benzaldehyde derivative in the Friedel-Crafts reaction and the Shore reaction is 4-formylphenylboronic acid pinacol ester; the molar ratio of 1,3,5-tri(3,4-dimethoxybenzyl)benzene to 4-formylphenylboronic acid pinacol ester is 1:(3-4); the reaction temperature is 20-30°C and the reaction time is 8-10h;

[0030] The molar ratio of the reaction product after Friedel-Crafts reaction and Shore reaction to 5-bromo-2-pyridinecarboxaldehyde in the Pd-catalyzed Suzuki coupling reaction is 1:(3-5); the reaction temperature is 90-120°C and the reaction time is 20-30h;

[0031] The molar ratio of the Suzuki coupling reaction product and the amine compound in the Schiff base reaction is 1:(3-6); the reaction temperature is 70-80°C and the reaction time is 10-20h;

[0032] The temperature of the ring-closing reaction is 50-70°C and the time is 8-10h;

[0033] The molar ratio of the Suzuki coupling reaction product and the target anion salt in the anion substitution reaction is 1:(5-10); the reaction temperature is 20-30°C, and the reaction time is 10-24h.

[0034] Preferably, in method (2):

[0035] The benzaldehyde derivative in the Friedel-Crafts reaction and the Shore reaction is 4-formylphenylboronic acid pinacol ester; the molar ratio of 1,3,5-tri(3,4-dimethoxybenzyl)benzene to 4-formylphenylboronic acid pinacol ester is 1:3.3; the reaction temperature is 25°C and the reaction time is 8h;

[0036] The molar ratio of the reaction product after Friedel-Crafts reaction and Shore reaction to 5-bromo-2-pyridinecarboxaldehyde in the Pd-catalyzed Suzuki coupling reaction was 1:3.3; the reaction temperature was 100°C and the reaction time was 24h;

[0037] The molar ratio of the Suzuki coupling reaction product to the amine compound in the Schiff base reaction was 1:4.5; the reaction temperature was 75°C and the reaction time was 16 h;

[0038] The temperature of the ring-closure reaction was 60°C and the time was 8 h;

[0039] The molar ratio of the Suzuki coupling reaction product and the target anion salt in the anion substitution reaction is 1:5; the reaction temperature is 25°C and the reaction time is 12h.

[0040] Furthermore, the Friedel-Crafts reaction and Shore reaction system also includes boron trifluoride etherate and acetic anhydride, and the molar ratio of 1,3,5-tris(3,4-dimethoxybenzyl), boron trifluoride etherate and acetic anhydride is 1:(4-8):(4-8).

[0041] Further, the Pd-catalyzed Suzuki coupling reaction system further includes potassium carbonate and tetrakis(triphenylphosphine)palladium, and the molar ratio of the product after the Friedel-Crafts reaction and the Scholl reaction, potassium carbonate, and tetrakis(triphenylphosphine)palladium is 1:(3-6):(0.1-0.3).

[0042] Further, in method (3):

[0043] In the Friedel-Crafts reaction and the Scholl reaction, the molar ratio of 1,3,5-tris(3,4-dimethoxybenzyl)benzene to 4-bromomethylbenzaldehyde is 1:(3-4); the reaction temperature is 20-30 °C, and the time is 8-10 h;

[0044] In the substitution reaction, the molar ratio of the product after the Friedel-Crafts reaction and the Scholl reaction to the linear alkyl imidazole is 1:(5-10); the reaction temperature is 90-120 °C, and the time is 20-30 h;

[0045] In the anion exchange reaction, the molar ratio of the substitution reaction product to the target anion salt is 1:(5-10); the reaction temperature is 20-30 °C, and the time is 10-24 h.

[0046] Preferably, in method (3):

[0047] In the Friedel-Crafts reaction and the Scholl reaction, the molar ratio of 1,3,5-tris(3,4-dimethoxybenzyl)benzene to 4-bromomethylbenzaldehyde is 1:3.6; the reaction temperature is 25 °C, and the time is 8 h;

[0048] In the substitution reaction, the molar ratio of the product after the Friedel-Crafts reaction and the Scholl reaction to the linear alkyl imidazole is 1:4; the reaction temperature is 110 °C, and the time is 24 h;

[0049] In the anion exchange reaction, the molar ratio of the substitution reaction product to the target anion salt is 1:5; the reaction temperature is 25 °C, and the time is 12 h.

[0050] Further, the Friedel-Crafts reaction and the Scholl reaction system further includes boron trifluoride diethyl ether and acetic anhydride, and the molar ratio of 1,3,5-tris(3,4-dimethoxybenzyl), boron trifluoride diethyl ether, and acetic anhydride is 1:(4-8):(4-8).

[0051] Further, the target anion salt in any one of methods (1)-(3) includes NH 4 BF 4 、NH 4 PF 6 、NaOTf and NaSbF 6 Any one of them.

[0052] In the third aspect of the present invention, a metal complex based on the above-mentioned N-heterocyclic carbene precursor is provided, and the chemical structural formula is shown in any one of Formulas IV-VI:

[0053]

[0054]

[0055] In the formula, X is CH or N; M is Cu I 、Ag I and Au I any one of; R is any one of the straight-chain alkanes having 1 to 8 carbon atoms; R' is any one of n-butyl, mesitylene and 2,6-dimethylphenyl; Y is BF 4 PF 6 , OTf and SbF 6 Any one of .

[0056] A fourth aspect of the present invention provides a method for synthesizing the above-mentioned metal complex, comprising the following steps:

[0057] (A) Synthesis of silver carbene assemblies:

[0058] The nitrogen heterocyclic carbene precursor of claim 1 is reacted with silver oxide in a solvent in the dark to obtain;

[0059] (B) Synthesis of gold carbene assembly:

[0060] The silver carbene assembly obtained in step (A) is reacted with tetrahydrothiophene gold chloride in a solvent in the dark to obtain the product.

[0061] Furthermore, in step (A), the molar ratio of the nitrogen heterocyclic carbene precursor to silver oxide is 1:(2-5); the reaction temperature is 60-70° C., and the reaction time is 12-30 h.

[0062] Preferably, in step (A), the molar ratio of the nitrogen heterocyclic carbene precursor to silver oxide is 1:3; the reaction temperature is 60° C., and the reaction time is 24 h.

[0063] Furthermore, in step (B), the molar ratio of the silver carbene assembly to tetrahydrothiophene gold chloride is 1:(3-4); the reaction temperature is 20-30°C, and the reaction time is 20-30h.

[0064] Preferably, in step (B), the molar ratio of the silver carbene assembly to tetrahydrothiophene gold chloride is 1:3; the reaction temperature is 25° C., and the reaction time is 24 h.

[0065] A fifth aspect of the present invention provides the above-mentioned metal complex Applications in energy transfer systems.

[0066] The present invention has the following beneficial effects:

[0067] The present invention synthesizes a series of nitrogen heterocyclic carbene salt precursors with nanographene fragments (hexabenzocorone) as the central skeleton, and obtains the corresponding Ag and Au carbene assemblies through coordination-driven self-assembly and metal exchange reaction. The introduction of nanographene fragments gives the assembly unique optical properties, which can be used to develop efficient Energy transfer system.

[0068] The present invention uses a short path and high yield to design and synthesize nanographene fragments (hexabenzocoronene) as the coordination precursor of the central aromatic core skeleton, assembling to form metal carbene assemblies with different topological structures, with high yield and excellent luminescence performance. The introduction of nanographene enriches the functionality of supramolecular structures and provides new ideas for the expansion of novel topological structure libraries and the development of efficient functional materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 The synthetic route of the nitrogen heterocyclic carbene precursor in Examples 1 to 3;

[0070] Figure 2 The synthetic route of the nitrogen heterocyclic carbene precursor in Example 4;

[0071] Figure 3 The Ag carbene assembly obtained in Example 7 [Ag 3 (3) 2 ] 2 (PF 6 ) 6 High-resolution mass spectrum and ion mobility mass spectrum of, wherein (a) is a high-resolution mass spectrum, and (b) is an ion mobility mass spectrum;

[0072] Figure 4 The nanographene-based Au carbene assembly obtained in Example 9 [Au 3 (1) 2 ](PF 6 ) 3 High-resolution mass spectra of

[0073] Figure 5 The nanographene-based Au carbene assembly obtained in Example 10 [Au 3 (2) 2 ](PF 6 ) 3 High-resolution mass spectra of

[0074] Figure 6 The nanographene-based Au carbene assembly obtained in Example 11 [Au 3 (4) 2 ](SbF 6 ) 3 High-resolution mass spectra of

[0075] Figure 7 The nanographene-based Au carbene assembly obtained in Example 11 [Au 3 (4) 2 ](SbF 6 ) 3 The crystal structure diagram of , where C is gray, N is blue, O is red, and Au is orange;

[0076] Figure 8 is the Au carbene assembly [Au 3 (4) 2 ](SbF 6 ) 3 Normalized processing diagram of fluorescence emission spectrum and absorption spectrum of rhodamine 6G;

[0077] Figure 9 In the experimental example, Au carbene assembly [Au 3 (4) 2 ](SbF 6 ) 3 Fluorescence emission spectrum of titrated Rhodamine 6G;

[0078] Figure 10 is the Au carbene assembly [Au 3 (4) 2 ](SbF 6 ) 3 Nonlinear fitting diagram of energy transfer efficiency measured with rhodamine 6G in different solvents. DETAILED DESCRIPTION

[0079] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0080] Embodiment 1:

[0081] A nitrogen heterocyclic carbene precursor based on nanographene fragments, the chemical structure of which is shown below:

[0082]

[0083] Its synthesis method comprises the following steps (synthesis route diagram as shown in Figure 1 shown):

[0084] (1) Synthesis of Compound 1

[0085] Under nitrogen atmosphere, 1,3,5-tris(3,4-dimethoxybenzyl)benzene (0.502 g, 0.950 mmol) and 4-formylphenylboronic acid pinacol ester (0.728 g, 3.135 mmol) were added to a 100 mL Schlenk tube, and 20 mL of anhydrous dichloromethane was added and stirred to dissolve, resulting in a colorless clear solution; then boron trifluoride etherate (0.703 mL, 5.700 mmol) and acetic anhydride (0.535 mL, 5.700 mmol) were added dropwise, and the reaction solution turned light brown and then dark, and stirred at room temperature for 8 h. After completion, acetic anhydride (3.212 mL, 34.200 mmol) was added under ice bath, and 2,3-dichloro-5,6-dicyanobenzoquinone (1.510 g, 6.650 mmol) was added, and the reaction was stirred under ice bath for 2 h, and then saturated NaHCO was added. 3 The aqueous solution was neutralized until no bubbles were generated, stirred for 2 h after neutralization, extracted three times with dichloromethane / water, and the organic phases were combined, concentrated by rotary evaporation, and then column chromatography (ethyl acetate / petroleum ether volume ratio 1:1) was performed. The product was collected, concentrated, and vacuum dried to obtain a yellow solid. Yield: 77% (0.732 mmol, 0.848 g). 1 H NMR (400 MHz, CDCl 3 )::δ=9.96(s,3H),9.33(d,3H,J=8.2Hz),8.84(s,3H),8.77(s,3H),8.22(d,J=8.2Hz,3H),4.28(s,9H),4.22(s,9H),1.44(s,36H)ppm.

[0086] (2) Synthesis of Compound 2

[0087] Under nitrogen atmosphere, compound 1 (0.579 g, 0.500 mmol), 1-(4-bromophenyl)-1H-imidazole (0.368 g, 1.650 mmol), potassium carbonate (0.346 g, 2.500 mmol) were placed in a 50 mL Schlenk tube, 20 mL of anhydrous DMF was added and stirred evenly, and tetrakis(triphenylphosphine)palladium (0.087 g, 0.075 mmol) was added, and the mixture was stirred at 100°C for 24 h. After the reaction was completed and cooled to room temperature, the solid was removed by vacuum filtration, the organic phase was collected and concentrated to DMF, and a large amount of water was added to precipitate a yellow solid, which was filtered and washed with water to obtain a crude product, which was extracted with chloroform and concentrated to about 1-2 mL, and 20 mL of ether was added to precipitate a pure product, which was filtered to obtain a yellow solid and dried in vacuo. Yield: 65% (0.325 mmol, 0.392 g). 1 H NMR (400 MHz, CDCl 3): δ=9.43(s,3H),9.30(d,J=8.2Hz,3H),8.63(d,J=6.9Hz,6H),8.06-8.02(d,J=9.7Hz,6H),7.96 (d,J=8.2Hz,6H),7.59(d,J=8.3Hz,6H),7.42(s,3H),7.31(s,3H),4.18(s,9H),4.13(s,9H)ppm.

[0088] (3) Precursor H 3 -1(PF 6 ) 3 Synthesis

[0089] Compound 2 (0.724 g, 0.600 mmol) was placed in a 25 mL Schlenk tube, 8 mL DMF was added and stirred to dissolve, and then bromobutane (0.493 g, 3.600 mmol) was added and stirred at 120°C for 24 h. After the reaction was completed and cooled to room temperature, it was transferred to a bottle containing 100 mL ethyl acetate. A large amount of yellow solid was precipitated immediately, which was collected by filtration and washed three times with ethyl acetate; the obtained bromine salt product was dissolved in 12 mL methanol and NH 4 PF 6 (0.489 g, 3.000 mmol) in aqueous solution (1.5 mL), a large amount of yellow solid precipitated immediately, and the mixture was stirred at room temperature for 12 h, then filtered to collect the yellow solid, washed with a large amount of water, and dried in vacuo. Yield: 90% (0..540 mmol, 0.979 g, two-step reaction). 1 H NMR (400MHz, CD 3 CN): δ=9.21(s,3H),9.09-8.74(m,3H),8.40-7.85(m,24H),7.79(s,6H),4.42(t,J=6.8Hz,6H),4.22- 3.65(m,18H),2.07(t,J=7.2Hz,6H),1.63-1.49(m,6H),1.09(d,J=7.3Hz,9H)ppm.HRMS(ESI,positive ions):m / z=761.7844(calcd for[H 3 -1(PF 6 )] 2+ 761.7940,m / z=459.5386(calcd for[H 3 -1] 3+ 459.5411).

[0090] Embodiment 2:

[0091] A nitrogen heterocyclic carbene precursor based on nanographene fragments, the chemical structure of which is shown below:

[0092]

[0093] Its synthesis method comprises the following steps (synthesis route diagram as shown in Figure 1 shown):

[0094] (1) Synthesis of Compound 1

[0095] The synthesis method is the same as that in Example 1.

[0096] (2) Synthesis of Compound 3

[0097] Under nitrogen atmosphere, compound 1 (0.579 g, 0.500 mmol), 1-(4-bromophenyl)-1H-triazole (0.370 g, 1.650 mmol), potassium carbonate (0.346 g, 2.500 mmol) were placed in a 50 mL Schlenk tube, 20 mL of anhydrous DMF was added and stirred evenly, tetrakis(triphenylphosphine)palladium (0.087 g, 0.075 mmol) was added, and the mixture was stirred at 100°C for 24 h. After the reaction was completed and cooled to room temperature, the solid was removed by vacuum filtration, the organic phase was collected and concentrated to DMF, and a large amount of water was added to precipitate a yellow solid, which was filtered and washed with water to obtain a crude product, which was extracted with chloroform and concentrated to about 1-2 mL, 20 mL of ether was added to precipitate a pure product, and the yellow solid was filtered and dried in vacuo. Yield: 63% (0.315 mmol, 0.381 g). 1 H NMR (400 MHz, CDCl 3 ): δ=9.29(d,J=8.5Hz,3H),8.83(s,3H),8.72-8.37(m,6H),8.26(s,3H), 8.01(d,J=8.5Hz,3H),7.98-7.43(m,15H),4.15(s,9H),4.02(s,9H)ppm.

[0098] (3) Precursor H 3 -2(PF 6 ) 3 Synthesis

[0099] Compound 3 (0.726 g, 0.600 mmol) was placed in a 25 mL Schlenk tube, 8 mL of DMF was added and stirred until dissolved, then bromobutane (0.493 g, 3.600 mmol) was added, and the mixture was stirred at 120 °C for 24 h. After the reaction was completed and cooled to room temperature, it was transferred to a bottle containing 100 mL of ethyl acetate, and a large amount of yellow solid precipitated immediately. It was filtered and collected and washed three times with ethyl acetate; the obtained bromide salt product was dissolved in 12 mL of methanol, and an aqueous solution (1.5 mL) of NH 4 PF 6 (0.489 g, 3.000 mmol) was added, and a large amount of yellow solid precipitated immediately. Stirring was continued at room temperature for 12 h, and then the yellow solid was filtered and collected and washed with a large amount of water, and dried in vacuo. Yield: 85% (0.512 mmol, 0.930 g, two-step reaction). 1 H NMR (400 MHz, CD 3 CN): δ = 10.41 - 10.06 (m, 3H), 9.24 (s, 3H), 9.01 (s, 3H), 8.83 (s, 3H), 8.33 - 7.80 (m, 18H), 7.69 (s, 3H), 4.54 (t, J = 7.3 Hz, 6H), 4.09 (s, 9H), 3.78 (s, 9H), 2.16 (s, 6H), 1.67 - 1.54 (m, 6H), 1.12 (d, J = 7.1 Hz, 9H) ppm. HRMS (ESI, positive ions): m / z = 460.5350 (calcd for [H 3 -2] 3+ 460.5364).

[0100] Example 3:

[0101] A nitrogen heterocyclic carbene precursor based on nano-graphene fragments, and its chemical structural formula is as follows:

[0102]

[0103] In the formula, Mes is 2,4,6-trimethylphenyl.

[0104] Its synthesis method includes the following steps (the synthesis route diagram is as Figure 1 shown):

[0105] (1) Synthesis of Compound 1

[0106] The synthesis method is the same as that in Example 1.

[0107] (2) Synthesis of Compound 4

[0108] Under nitrogen atmosphere, compound 1 (0.579 g, 0.500 mmol), 5-bromo-2-pyridinecarboxaldehyde (0.372 g, 2.000 mmol), potassium carbonate (0.346 g, 2.500 mmol) were placed in a 50 mL Schlenk tube, 20 mL of anhydrous DMF was added and stirred evenly, tetrakis(triphenylphosphine)palladium (0.087 g, 0.075 mmol) was added, and the reaction was stirred at 100 ° C for 24 h. After the reaction was completed and cooled to room temperature, the solid was removed by vacuum filtration, the organic phase was collected and concentrated to DMF, and a large amount of water was added to precipitate a yellow solid, which was filtered and washed with water to obtain a crude product, which was extracted with chloroform and concentrated to about 1-2 mL, and 20 mL of ether was added to precipitate a pure product, which was filtered to obtain an orange-yellow solid and dried in vacuo. Yield: 58% (0.290 mmol, 0.317 g). 1 H NMR (400 MHz, CDCl 3 ): δ=10.02(s,3H),9.49(s,3H),9.34(d,J=8.7Hz,3H),9.30(s,3H),8.58(s,6H),8.30(d, J=8..7Hz,3H),8.19(d,J=8.2Hz,3H),8.07(d,J=8.2Hz,3H),4.17(s,9H),4.12(s,9H)ppm.

[0109] (3) Precursor H 3 -3(PF 6 ) 3 Synthesis

[0110] Under nitrogen atmosphere, compound 4 (0.274 g, 0.250 mmol) was dissolved in 30 mL of chloroform and 10 mL of ethanol, and then 2,4,6-trimethylaniline (0.152 g, 1.125 mmol) and 5 drops of glacial acetic acid were added, and the reaction was stirred at 75 ° C for 16 h. After the reaction was completed, the reaction solution was concentrated to 2-3 mL by rotary evaporation, and about 30 mL of ice methanol was added. The precipitated brown solid was collected by filtration and washed with a small amount of ice methanol. The obtained product was initially dried and transferred to a 50 mL reaction bottle, 20 mL of toluene and polyformaldehyde (0.068 g, 0.750 mmol) were added, and 4 mol / L hydrochloric acid dioxane solution (0.3 mL) was added after stirring. The brown solid was immediately precipitated, and the reaction was stirred at 60 ° C for 8 h. After the reaction was completed, it was cooled to room temperature, the solid was collected by filtration, the chloride product was extracted with a large amount of methanol, and concentrated to about 10 mL, and NH 4 PF 6(0.204 g, 1.250 mmol) in an aqueous solution (1.0 mL), a large amount of brown-yellow solid precipitated immediately, and the mixture was stirred at room temperature for 12 h, then the solid was collected by filtration and washed with a large amount of water, and dried in vacuo. Yield: 69% (0.173 mmol, 0.332 g, three-step reaction). 1 H NMR (400MHz, CD 3 CN): δ=9.60(s,3H),9.36(d,J=8.5Hz,3H),9.08(s,3H),9.01(s,3H),8. 67(d,J=9.6Hz,3H),8.55(d,J=8.5Hz,3H),8.33(s,3H),8.13(s,3H),8. 05(d,J=9.6Hz,3H),7.99(s,3H),7.38-7.23(m,,6H),4.08(s,9H),3.55(s,9H),2.48(s,9H),2.39(s,9H),2.28(s,9H)ppm.HRMS(ESI,positive ions):m / z=495.5293(calcd for[H 3 -3] 3+ 495.5411).

[0111] Embodiment 4:

[0112] A nitrogen heterocyclic carbene precursor based on nanographene fragments, the chemical structure of which is shown below:

[0113]

[0114] Its synthesis method comprises the following steps (synthesis route diagram as shown in Figure 2 shown):

[0115] (1) Synthesis of Compound 5

[0116] Under nitrogen atmosphere, 1,3,5-tris(3,4-dimethoxybenzyl)benzene (0.502 g, 0.950 mmol) and 4-bromomethylbenzaldehyde (0.681 g, 3.420 mmol) were added to a 100 mL Schlenk tube, and 20 mL of anhydrous dichloromethane was added and stirred to dissolve, resulting in a colorless clear solution; then boron trifluoride etherate (0.703 mL, 5.700 mmol) and acetic anhydride (0.535 mL, 5.700 mmol) were added dropwise, and the reaction solution turned from light brown to dark green, and the reaction was stirred at room temperature for 8 h. After completion, acetic anhydride (3.212 mL, 34.200 mmol) was added under ice bath, and 2,3-dichloro-5,6-dicyanobenzoquinone (1.510 g, 6.650 mmol) was added, and the reaction was stirred under ice bath for 2 h, and then saturated NaHCO was added. 3The aqueous solution was neutralized until no bubbles were generated, and then stirred for 2 hours. During the process, a large amount of yellow solid was precipitated and dispersed. Finally, the yellow crude solid was filtered and separated, and recrystallized and collected using chloroform / ether for multiple times, and then dried in vacuum. Yield: 72% (0.683mmol, 0.724g). 1 H NMR (400 MHz, CDCl 3 ): δ=9.31(s,3H),9.17(d,J=8.5Hz,3H),8.61(d,J=3.9Hz,6H),7.71-7.66(m,3H ),4.85(d,J=10.6Hz,3H),4.73(d,J=10.6Hz,3H),4.19(s,9H),4.11(s,9H)ppm.

[0117] (2) Precursor H 3 -4(SbF 6 ) 3 Synthesis

[0118] Compound 5 (0.700 g, 0.660 mmol) and N-butylimidazole (0..328 g, 2.640 mmol) were dissolved in 5 mL of DMF solution, and the reaction was stirred at 110 ° C for 24 h. After the reaction was completed and cooled to room temperature, it was transferred to a bottle containing 50 mL of ethyl acetate. A large amount of yellow solid was precipitated immediately, which was collected by filtration and washed three times with ethyl acetate; the obtained bromide product was dissolved in 12 mL of methanol, and NaSbF was added. 6 (0.854 g, 3.300 mmol) in aqueous solution (1.5 mL), a large amount of yellow solid precipitated immediately, and the mixture was stirred at room temperature for 12 h, then filtered to collect the yellow solid, washed with a large amount of water, and dried in vacuo. Yield: 89% (0.590 mmol, 1.121 g, two-step reaction). 1 H NMR (400MHz, CD 3CN): δ=9.42(d,J=8.6Hz,3H),9.38-9.36(m,3H),8.65(d,J=3.0Hz,6H),8.61(s,3H) ),7.86(dd,J=8.6,1.6Hz,3H),7.54(t,J=1.8Hz,3H),7.45(t,J=1.8Hz,3H),5.71( d,J=3.8Hz,6H),4.14(s,9H),4.12(d,J=7.3Hz,6H),4..09(s,9H),1.80(p,J=7.5H z,6H),1.30(dq,J=14.8,7.4Hz,6H),0.91(t,J=7.4Hz,9H)ppm.HRMS(ESI,positive ions):m / z=397.1884(calcd for[H 3 -4] 3+ 397.1911).

[0119] Embodiment 5:

[0120] A Ag carbene assembly based on the above-mentioned nitrogen heterocyclic carbene precursor [Ag 3 (1) 2 ](PF 6 ) 3 , its chemical structure is shown below:

[0121]

[0122] In the formula, X is CH, M is Ag I .

[0123] The synthesis method thereof comprises the following steps:

[0124] Under the operating conditions of anhydrous and oxygen-free, the precursor H obtained in Example 1 was 3 -1(PF 6 ) 3 (0..054g, 0.030mmol) was dissolved in 15mL acetonitrile, and then silver oxide powder (0.021g, 0.090mmol) was added to the solution, and the reaction was stirred at 60°C for 24h under light-proof conditions. After the reaction was completed, it was cooled to room temperature, allowed to stand and settle, and the supernatant was aspirated. The supernatant was concentrated to 2mL under light-proof conditions, and a large amount of ether was added to precipitate a brown solid. The solid was collected by filtration, washed with ether, and vacuum dried to obtain a brown solid powder. Yield: 87% (0.013mmol, 0.046g). 1 H NMR (400MHz, CD 3CN): δ=9.41(d,J=8.4Hz,6H),9.11(s,6H),8.20(s,6H),8.18(d,J=8.1Hz,12 H),8.08(d,J=8.4Hz,6H),8.04(s,6H),7.92(s,6H),7.86(d,J=8.1Hz,12H),7 .63(s,6H),4.49(t,J=7.41Hz,12H),4.10(s,18H),3.65(s,18H),2.10-2.04( m,12H),1.62-1.49(m,12H),1.09(t,J=7.35Hz,18H)ppm.HRMS(ESI,positive ions):m / z=1024.9733(calcd for[Ag 3 (1) 2 ] 3+ 1024.9711).

[0125] Embodiment 6:

[0126] A Ag carbene assembly based on the above-mentioned nitrogen heterocyclic carbene precursor [Ag 3 (2) 2 ](PF 6 ) 3 , its chemical structure is shown below:

[0127]

[0128] In the formula, X is N, M is Ag I .

[0129] The synthesis method thereof comprises the following steps:

[0130] Under the operating conditions of anhydrous and oxygen-free, the precursor H obtained in Example 2 was 3 -2(PF 6 ) 3 (0..055g, 0.030mmol) was dissolved in 15mL acetonitrile, and then silver oxide powder (0.021g, 0.090mmol) was added to the solution, and the mixture was stirred at 60°C for 24h under light-proof conditions. After the reaction was completed, the mixture was cooled to room temperature, allowed to stand for sedimentation, and the supernatant was aspirated. The supernatant was concentrated to 2mL under light-proof conditions, and a large amount of ether was added to precipitate a brown solid. The solid was collected by filtration, washed with ether, and dried in vacuo to obtain a brown solid powder. Yield: 93% (0.014mmol, 0.049g). 1 H NMR (400MHz, CD 3CN): δ=9.53-9.43(m,6H),9.17(s,6H),8.80(s,6H),8.48(d,J=8.2Hz,12H),8.20(s,6H),8.03(s,6H),7.89(d,J=8.2Hz,12H),7.68(s,6H),4 .54(t,J=7.77Hz,12H),4.12(s,18H),3.61(s,18H),2.12-2.07(m,12H),1.64-1.52(m,12H),1.10(t,J=7.16Hz,18H)ppm.HRMS(ESI,positive ions):m / z=1612.9203(calcd for[Ag 3 (2) 2 (PF 6 )] 2+ 1612.9248),m / z=1026.9609(calcd for[Ag 3 (2) 2 ] 3+ 1026.9616).

[0131] Embodiment 7:

[0132] A Ag carbene assembly based on the above-mentioned nitrogen heterocyclic carbene precursor [Ag 3 (3) 2 ] 2 (PF 6 ) 6 Its chemical structure is shown below (high resolution mass spectrometry and ion mobility mass spectrometry are shown in Figure 3 shown):

[0133]

[0134] In the formula, Mes is 2,4,6-trimethylphenyl.

[0135] The synthesis method thereof comprises the following steps:

[0136] Under the operating conditions of anhydrous and oxygen-free, the precursor H obtained in Example 3 was 3 -3(PF 6 ) 3(0.058g, 0.030mmol) was dissolved in 15mL of acetonitrile, and then silver oxide powder (0.021g, 0.090mmol) was added to the solution, and the reaction was stirred at 60°C for 24h under light-proof conditions. After the reaction was completed, it was cooled to room temperature, allowed to stand and settle, and the supernatant was aspirated. The supernatant was concentrated to 2mL under light-proof conditions, and a large amount of ether was added to precipitate a brown solid. The solid was collected by filtration, washed with ether, and vacuum dried to obtain a brown solid powder. Yield: 93% (0.007mmol, 0.052g). HRMS (ESI, positive ions): m / z=2338.9148 (calcd for [Ag 6 (3) 4 (PF 6 ) 3 ] 3+ 2338.9124),m / z=1717.9584(calcd for[Ag 6 (3) 4 (PF 6 ) 2 ] 4+ 1717.9397),m / z=1345.3688(calcd for[Ag 6 (3) 4 (PF 6 )] 5+ 1345.3621),m / z=1096.9683(calcd for[Ag 6 (3) 4 ] 6+ 1096.9741).

[0137] Embodiment 8:

[0138] A Ag carbene assembly based on the above-mentioned nitrogen heterocyclic carbene precursor [Ag 3 (4) 2 ](SbF 6 ) 3 , its chemical structure is shown below:

[0139]

[0140] Where M is Ag I .

[0141] The synthesis method thereof comprises the following steps:

[0142] Under the operating conditions of anhydrous and oxygen-free, the precursor H obtained in Example 4 was 3 -4(SbF 6 ) 3(0.095g, 0.050mmol) was dissolved in 15mL acetonitrile, and then silver oxide powder (0.035g, 0.150mmol) was added to the solution, and the reaction was stirred at 60°C for 24h under light-proof conditions. After the reaction was completed, it was cooled to room temperature, allowed to stand and settle, and the supernatant was aspirated. The supernatant was concentrated to 2mL under light-proof conditions, and a large amount of ether was added to precipitate a brown solid. The solid was collected by filtration, washed with ether, and vacuum dried to obtain a brown solid powder. Yield: 88% (0.022mmol, 0.075g). 1 H NMR (600MHz, CD 3 CN): δ=9.11(d,J=7.9Hz,6H),8.90(s,6H),8.09(d,J=7.7Hz,6H),7.96(s,6H),7. 63(s,6H),7.53(s,6H),7.22(s,6H),5.52(d,J=15.5Hz,6H),5.26(d,J=15.5Hz,6 H),4.29(dt,J=13.3,7.1Hz,6H),4.00(s,6H),3.97(s,18H),3.50(s,18H),1.89- 1.81(m,12H),1.43-1.35(m,12H),0.98(t,J=7.2Hz,18H)ppm.HRMS(ESI,positive ions):m / z=900.9495(calcd for[Ag 3 (4) 2 ] 3+ 900.9398).

[0143] Embodiment 9:

[0144] An Au carbene assembly based on the above nitrogen heterocyclic carbene precursor [Au 3 (1) 2 ](PF 6 ) 3 Its chemical structure is shown below (high resolution mass spectrum is shown in Figure 4 shown):

[0145]

[0146] In the formula, X is CH, M is Au I .

[0147] The synthesis method thereof comprises the following steps:

[0148] Under anhydrous and oxygen-free operating conditions, the Ag carbene assembly [Ag 3 (1) 2 ](PF 6 ) 3(0.070g, 0.020mmol) was dissolved in 15mL acetonitrile, and then [AuCl(THT)] (0.019g, 0.06mmol) was added to the solution, and the reaction was stirred for 24h at room temperature in the dark. After the reaction was completed, it was allowed to settle, and the supernatant was concentrated to 2mL. A large amount of ether was added to precipitate a brown solid, which was collected by filtration, washed with ether, and dried in vacuo to obtain a brown solid powder. The yield was 90% (0.018mmol, 0.068g). 1 H NMR (400MHz, CD 3 CN): δ=9.44(d,,J=8.7Hz,6H),9.13(s,6H),8.24(s,J=8.8Hz,18H),8.06(s,6H),8.01(d,J=8.2Hz,6H),,7.87(s,6H),7.81(s,6H),7.79(s, 6H),7.63(s,6H),4.56(t,12H),4.10(s,18H),3..70(s,18H),2.12-2.09(m,12H),1.58-1.53(m,12H),1.12(t,18H)ppm.HRMS(ESI,positive ions):m / z=1114.0253(calcd for[Au 3 (1) 2 ] 3+ 1114.0337).

[0149] Embodiment 10:

[0150] An Au carbene assembly based on the above nitrogen heterocyclic carbene precursor [Au 3 (2) 2 ](PF 6 ) 3 Its chemical structure is shown below (high resolution mass spectrum is shown in Figure 5 shown):

[0151]

[0152] In the formula, X is N, M is Au I .

[0153] The synthesis method thereof comprises the following steps:

[0154] Under anhydrous and oxygen-free operating conditions, the Ag carbene assembly [Ag 3 (2) 2 ](PF 6 ) 3(0.091g, 0.026mmol) was dissolved in 15mL acetonitrile, and then [AuCl(THT)] (0.025g, 0.078mmol) was added to the solution, and the reaction was stirred for 24h at room temperature in the dark. After the reaction was completed, it was allowed to settle, and the supernatant was concentrated to 2mL. A large amount of ether was added to precipitate a brown solid, which was collected by filtration, washed with ether, and dried in vacuo to obtain a brown solid powder. The yield was 92% (0.024mmol, 0.091g). 1 H NMR (400MHz, CD 3 CN): δ=9.51(d,,J=8.8Hz,6H),9.17(s,6H),8.84(s,6H),8.56(d,J=8.2Hz,12H),8.22(s,6H),8.14(d,J=8.8Hz,6H),8.05(s,6H),7.85(d,J= 8.2Hz,12H),4.61-4.55(t,12H),4.13(s,18H),3.65(s,18H),2.19(m,12H),1.63-1.57(m,12H),1.13-1.08(t,18H)ppm.HRMS(ESI,positive ions):m / z=1746.5139(calcd for[Au 3 (2) 2 (PF 6 )] 2+ 1746.5187),m / z=1115.6861(calcd for[Au 3 (2) 2 ] 3+ 1115.6897).

[0155] Embodiment 11:

[0156] An Au carbene assembly based on the above nitrogen heterocyclic carbene precursor [Au 3 (4) 2 ](SbF 6 ) 3 Its chemical structure is shown below (high resolution mass spectrum is shown in Figure 6 The crystal structure is shown in Figure 7 shown):

[0157]

[0158] Where M is Au I .

[0159] The synthesis method thereof comprises the following steps:

[0160] Under anhydrous and oxygen-free operating conditions, the Ag carbene assembly [Ag 3 (4) 2 ](SbF 6 ) 3 (0.068g, 0.020mmol) was dissolved in 15mL acetonitrile, and then [AuCl(THT)] (0.019g, 0.060mmol) was added to the solution, and the reaction was stirred for 24h at room temperature in the dark. After the reaction was completed, it was allowed to settle, and the supernatant was concentrated to 2mL. A large amount of ether was added to precipitate a brown solid, which was collected by filtration, washed with ether, and dried in vacuo to obtain a brown solid powder. The yield was 95% (0.019mmol, 0.070g). 1 H NMR (600MHz, CD 3 CN): δ=9.18(d,,J=8.0Hz,6H),9.11(s,6H),8.15(d,J=8.0Hz,6H),8.01(s,6H),7.77(s,6 H),7.66(s,6H),7.41(s,6H),5.88(d,J=15.1Hz,6H),5.30(d,J=15.2Hz,6H),4.54(dt,J= 14.1,7.4Hz,6H),4.19(dt,J=13.4,7.0Hz,6H),4.04(s,18H),3.73(s,18H),2.01(td,J=7 .2,3..7Hz,12H),1.52(h,J=7.4Hz,12H),1.07(t,J=7.4Hz,18H)ppm.HRMS(ESI,positive ions):m / z=989.6654(calcd for[Au 3 (4) 2 ] 3+ 989.6680).

[0161] Embodiment 12:

[0162] Preparation of metal complexes using different nitrogen heterocyclic carbene precursors

[0163]

[0164]

[0165]

[0166]

[0167]

[0168] Test example: Development of energy transfer systems

[0169] Since the aromatic core skeleton is a nanographene fragment with extended π conjugation, all the nitrogen heterocyclic carbene salt precursors and metal carbene assemblies described in the present invention have good fluorescence properties and show the strongest fluorescence double emission peak in the range of 505-520nm. Therefore, it is considered to be an energy donor, and rhodamine 6G with maximum absorption near 500-550nm can be used as an ideal energy acceptor, thereby developing an efficient Energy transfer system.

[0170] Weigh a certain amount of the Au carbene complex [Au 3 (4) 2 ](SbF 6 ) 3 and rhodamine 6G were dissolved in acetonitrile solution to prepare concentrations of 1×10 -4 mol / L and 1×10 -3 mol / L mother solution, UV-visible spectrum and fluorescence spectrum were tested on Agilent Cary 100 and HORIBAQM 8000 respectively.

[0171] The test steps are as follows:

[0172] 1. Take 0.03mL of Rhodamine 6G stock solution and dilute to 3mL to prepare 1×10 -5 mol / L solution to test the absorption spectrum of Rhodamine 6G;

[0173] 2. Take 0.3mL [Au 3 (4) 2 ](SbF 6 ) 3 The mother solution was diluted to 3 mL to prepare 1×10 -5 mol / L solution, and the emission spectrum of Au carbene complex was tested at the maximum excitation wavelength of 420nm;

[0174] 3. To 1×10 -5 mol / L[Au 3 (4) 2 ](SbF 6 ) 3 In the cuvette solution, 3.0 μL of Rhodamine 6G mother solution (0.1 eq.) was added in situ each time. After mixing evenly, the emission spectrum of the current system at the maximum excitation wavelength of 420 nm was tested, and 25 groups were titrated in sequence.

[0175] After normalizing the absorption spectrum obtained in step 1 and the emission spectrum obtained in step 2, it can be observed that there is a large overlap between the two ( Figure 8) that meet the prerequisites for energy transfer. The titration test results ( Figure 9 ) show that as the titration process progresses, the emission peak intensity attributed to the energy donor [Au 3 (4) 2 (SbF 6 ) 3 gradually decreases, while the emission peak intensity attributed to the energy acceptor rhodamine 6G gradually increases. The calculation of the system energy transfer efficiency is based on the formula: Φ ET =(I D -I DA ) / I D ; where I D and I DA are the initial emission intensity of the donor and the emission intensity in the coexisting state. Nonlinear fitting is performed on the energy transfer efficiency during the titration process, and the correlation coefficient R 2 =0.9995. When the acceptor is titrated to 2.5 eq, the energy transfer efficiency can reach approximately 90%.

[0176] To explore the influence of different solvents (DMF, acetone, and DMSO) on the energy transfer efficiency, the method for monitoring energy transfer is the same as above, except that different solvents are used when preparing the stock solution.

[0177] The experimental results are as Figure 10 shown. After comparison, the above-mentioned energy donor and acceptor have better energy transfer efficiency in acetonitrile solution.

[0178] In addition to the above-mentioned developable high-efficiency energy transfer system, the nano-graphene-based metal carbene assembly prepared by the present invention is also expected to be developed in the field of high-efficiency optoelectronic materials, broadening the functional applications of metal carbene assemblies.

[0179] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A nitrogen heterocyclic carbene precursor based on nanographene fragments, characterized in that: The chemical structure of the nitrogen heterocyclic carbene precursor is shown in any one of Formula I to Formula III: Formula I: Formula II: Formula III: In the formula, X is CH or N; R is any one of straight-chain alkanes having 1 to 8 carbon atoms; R' is any one of n-butyl, mesitylene and 2,6-dimethylphenyl; and Y is any one of BF4, PF6, OTf and SbF6.

2. The method for synthesizing a nitrogen heterocyclic carbene precursor based on nanographene fragments according to claim 1, characterized in that: The nitrogen heterocyclic carbene precursors shown in Formula I to Formula III are synthesized by the following methods: (1) Synthesis of the nitrogen heterocyclic carbene precursor shown in Formula I: First, 1,3,5-tris(3,4-dimethoxybenzyl)benzene and benzaldehyde derivatives are subjected to Friedel-Crafts reaction and Shore reaction, and then the obtained product is subjected to Pd-catalyzed Suzuki coupling reaction with a Br-substituted aromatic compound, and finally the product of the Suzuki coupling reaction is sequentially subjected to N-terminal alkyl substitution reaction with a brominated straight-chain alkane, and an anion exchange reaction with a target anion salt is carried out to obtain; (2) Synthesis of the nitrogen heterocyclic carbene precursor shown in formula II: First, 1,3,5-tris(3,4-dimethoxybenzyl)benzene and benzaldehyde derivatives are subjected to Friedel-Crafts reaction and Shore reaction, and then the obtained product is subjected to Pd-catalyzed Suzuki coupling reaction with 5-bromo-2-pyridinecarboxaldehyde, and then the product of the Suzuki coupling reaction is subjected to Schiff base reaction with an amine compound, and finally a ring-closing reaction is carried out, and then an anion exchange reaction is carried out with a target anion salt to obtain; (3) Synthesis of the nitrogen heterocyclic carbene precursor shown in formula III: Firstly, 1,3,5-tris(3,4-dimethoxybenzyl)benzene and 4-bromomethylbenzaldehyde are subjected to Friedel-Crafts reaction and Shore reaction, then the obtained product is subjected to substitution reaction with linear alkyl imidazole, and finally the substitution reaction product is subjected to anion exchange reaction with target anion salt to obtain the compound.

3. The method for synthesizing a nitrogen heterocyclic carbene precursor based on nanographene fragments according to claim 2, characterized in that: In the method (1): The benzaldehyde derivative in the Friedel-Crafts reaction and the Shore reaction is 4-formylphenylboronic acid pinacol ester; the molar ratio of 1,3,5-tri(3,4-dimethoxybenzyl)benzene to 4-formylphenylboronic acid pinacol ester is 1:(3-4); the reaction temperature is 20-30°C and the reaction time is 8-10h; The Br-substituted aromatic compound in the Pd-catalyzed Suzuki coupling reaction is 1-(4-bromophenyl)-1H-imidazole or 1-(4-bromophenyl)-1H-triazole; the molar ratio of the product after the Friedel-Crafts reaction and the Shore reaction to the Br-substituted aromatic compound is 1:(3-4); the reaction temperature is 90-120°C and the reaction time is 20-30h; The molar ratio of the Suzuki coupling reaction product to the brominated straight-chain alkane in the N-terminal alkyl substitution reaction is 1:(5-10); the reaction temperature is 90-120°C and the reaction time is 20-30h; The molar ratio of the Suzuki coupling reaction product to the target anion salt in the anion exchange reaction is 1:(5-10); the reaction temperature is 20-30°C, and the reaction time is 10-24h.

4. The method for synthesizing a nitrogen heterocyclic carbene precursor based on nanographene fragments according to claim 2, characterized in that: In the method (2): The benzaldehyde derivative in the Friedel-Crafts reaction and the Shore reaction is 4-formylphenylboronic acid pinacol ester; the molar ratio of 1,3,5-tri(3,4-dimethoxybenzyl)benzene to 4-formylphenylboronic acid pinacol ester is 1:(3-4); the reaction temperature is 20-30°C and the reaction time is 8-10h; The molar ratio of the reaction product after Friedel-Crafts reaction and Shore reaction to 5-bromo-2-pyridinecarboxaldehyde in the Pd-catalyzed Suzuki coupling reaction is 1:(3-5); the reaction temperature is 90-120°C and the reaction time is 20-30h; The molar ratio of the Suzuki coupling reaction product and the amine compound in the Schiff base reaction is 1:(3-6); the reaction temperature is 70-80°C and the reaction time is 10-20h; The temperature of the ring-closing reaction is 50-70°C and the time is 8-10h; The molar ratio of the Suzuki coupling reaction product and the target anion salt in the anion substitution reaction is 1:(5-10); the reaction temperature is 20-30°C, and the reaction time is 10-24h.

5. The method for synthesizing a nitrogen heterocyclic carbene precursor based on nanographene fragments according to claim 2, characterized in that: In the method (3): The molar ratio of 1,3,5-tris(3,4-dimethoxybenzyl)benzene to 4-bromomethylbenzaldehyde in the Friedel-Crafts reaction and the Shore reaction is 1:(3-4); the reaction temperature is 20-30°C and the reaction time is 8-10h; In the substitution reaction, the molar ratio of the product after Friedel-Crafts reaction and Shore reaction to the linear alkyl imidazole is 1:(5-10); the reaction temperature is 90-120°C and the reaction time is 20-30h; The molar ratio of the substitution reaction product to the target anion salt in the anion exchange reaction is 1:(5-10); the reaction temperature is 20-30° C., and the reaction time is 10-24 hours.

6. A metal complex based on the nitrogen heterocyclic carbene precursor according to claim 1, characterized in that: The chemical structural formula of the metal complex is shown in any one of Formulas IV-VI: Formula IV: Formula V: Formula VI: In the formula, X is CH or N; M is Cu I 、Ag I and Au I any one of; R is any one of straight-chain alkanes having 1 to 8 carbon atoms; R' is any one of n-butyl, mesitylene and 2,6-dimethylphenyl; Y is any one of BF4, PF6, OTf and SbF6.

7. The method for synthesizing the metal complex according to claim 6, characterized in that: The following steps are involved: (A) Synthesis of silver carbene assemblies: The nitrogen heterocyclic carbene precursor of claim 1 is reacted with silver oxide in a solvent in the dark to obtain; (B) Synthesis of gold carbene assembly: The silver carbene assembly obtained in step (A) is reacted with tetrahydrothiophene gold chloride in a solvent in the dark to obtain the product.

8. The method for synthesizing a metal complex according to claim 7, characterized in that: In the step (A), the molar ratio of the nitrogen heterocyclic carbene precursor to silver oxide is 1:(2-5); the reaction temperature is 60-70° C., and the reaction time is 12-30 hours.

9. The method for synthesizing a metal complex according to claim 7, characterized in that: In the step (B), the molar ratio of the silver carbene assembly to tetrahydrothiophene gold chloride is 1:(3-4); the reaction temperature is 20-30° C., and the reaction time is 20-30 hours.

10. The metal complex according to claim 6 Applications in energy transfer systems.

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