An ultra-stable strong luminescent n-heterocyclic carbene-protected chiral heterometallic cluster and a preparation method thereof

Abstract

This invention belongs to the interdisciplinary field of coordination chemistry and nanomaterials, and discloses an ultrastable, strongly luminescent N-heterocyclic carbene-protected chiral heterometallic cluster and its preparation method. This invention utilizes multidentate chiral... R / S -NHC ql A well-designed and modular construction strategy using the -PF6 ligand resulted in a highly stable chiral heterometallic cluster, which remains stable in air up to 200°C. The chemical formula of this enantiomeric cluster is: C 74 H 66 AuCu4F6I4N8OP (abbreviated as: R / S -NHC ql -AuCu4 ‑ I), belongs to the orthorhombic crystal system, and its space group is chiral space group. P 21212. This cluster exhibits strong orange luminescence at room temperature with a luminescence quantum yield as high as 93%. It possesses advantages such as ultra-high photoluminescence quantum yield with thermally activated delayed luminescence characteristics, microsecond lifetime at room temperature, circularly polarized luminescence, and good solubility, radiation resistance, and high-temperature resistance. The external quantum efficiency of the CP-OLED prepared by solution processing reaches as high as 20.8%, opening up new avenues for developing novel solution-processable cluster-based CP-OLEDs.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of coordination chemistry and nanomaterials, and relates to an ultra-stable, strongly luminescent chiral heterometallic cluster protected by an N-heterocyclic carbene prepared by a modular strategy and its application in CP-OLED. Background Technology

[0002] Atomic-precise coin metal (gold, silver, copper) clusters are a class of clusters with precise atomic structures, formed by three or more coin metal atoms through metalophilic interactions, with an outer layer protected by organic ligands. Nanoclusters represent a state of matter between atoms, molecules, and bulk materials, serving as a bridge connecting atoms, molecules, and macroscopic matter. Their size is typically on the nanometer scale, and they often exhibit quantum confinement effects, leading to many novel phenomena and properties. Their excellent photophysical properties and potential applications in catalysis, bioimaging, and other fields have become a research hotspot in materials science and inorganic chemistry in recent years.

[0003] Current research on coin metal nanoclusters mainly focuses on the synthesis and application of novel nanoclusters. The excellent optical properties, superior lightfastness, and good biocompatibility of nanoclusters give them broad application prospects. However, the reported stability of coin metal nanoclusters at room temperature is relatively poor, and these shortcomings greatly hinder the application and development of nanoclusters. Therefore, designing and synthesizing atomically precise and structurally stable nanoclusters is one of the key research areas in the field of nanoclusters.

[0004] Chirality is a ubiquitous phenomenon in nature, and the chirality of nanoclusters can usually be endowed by chiral ligands. Selecting suitable chiral ligands can synthesize chiral nanocluster structures. Therefore, based on the different coordination abilities of coin metal atoms to coordinating atoms, the rational design of chiral N-heterocyclic carbene ligands for constructing chiral heterometallic nanoclusters is beneficial for their development and application in fields such as organic optoelectronics, information storage, biological cell imaging, and diagnostics. Summary of the Invention

[0005] The present invention aims to provide an ultra-stable, strongly luminescent N-heterocyclic carbene-protected chiral heterometallic cluster. Another objective is to provide a method for its preparation.

[0006] To achieve the objectives of this invention, a modular strategy for preparing ultrastable N-heterocyclic carbene-protected chiral heterometallic clusters has been developed, with the chemical formula: C 74 H 66 AuCu4F6I4N8OP (abbreviated as: R / S-NHC) ql -AuCu4-I), belongs to the orthorhombic crystal system, space group is chiral space group P21212, R-NHC ql -AuCu4-I: α=90°, β=90°, γ=90°; S-NHC ql -AuCu4-I: α=90°, β=90°, γ=90°.

[0007] Among them, R / S-NHC ql -PF6 is a chiral N-heterocyclic carbene ligand, and its molecular structure is as follows:

[0008]

[0009] The method for preparing the chiral carbene ligand of the present invention is achieved through the following steps:

[0010] A methanol solution of (1R,2R)-(+)-1,2-diphenyl-1,2-ethylenediamine or (1S,2S)-(-)-1,2-diphenyl-1,2-ethylenediamine and glyoxylic acid monohydrate was stirred at room temperature. N-bromosuccinimide (NBS) was added to the mixture and stirred overnight at room temperature. The reaction was quenched with saturated sodium metabisulfite, and the solvent was removed under vacuum to obtain a solid. NaOH solution was added, and the solid was extracted with ethyl acetate. The organic layer was dried with anhydrous magnesium sulfate, and the solvent was removed under vacuum to obtain a chiral imidazole. The synthesized chiral imidazole was dissolved in ethanol, and 2-(chloromethyl)quinoline hydrochloride and sodium bicarbonate were added and refluxed for two days. After filtration, the solvent was removed under vacuum, and the resulting solid was dissolved in dichloromethane. The solid was dried with anhydrous magnesium sulfate, and the solution was filtered. The solvent was removed under vacuum to obtain an oily substance, which was mixed with tetrahydrofuran to obtain a powder. Further washing with tetrahydrofuran and drying under vacuum yielded a white powder. In a flask, the above powder was dissolved in methanol, and an excess of ammonium hexafluorophosphate aqueous solution was added dropwise to form a precipitate. The precipitate was filtered, thoroughly washed with water / methanol, and dried under vacuum to obtain the above R / S-NHC. ql -PF6 chiral carbene ligand ( Figure 1 (As shown).

[0011] The method for preparing chiral heterometallic clusters of the present invention is achieved through the following steps:

[0012] The chiral ligand, silver oxide, and tetrabutylammonium hexafluorophosphate were dispersed in a dichloromethane solution and reacted under light-protected conditions with stirring at room temperature. NaOH solution was then added, and the reaction was continued with stirring. The mixture was filtered, and the filtrate was concentrated under vacuum. Ether was added to obtain a powder. The powder was dissolved in dichloromethane, and a dichloromethane solution of thiophene gold was added. The mixture was stirred in a light-protected environment to form a precipitate. The solution was filtered to remove the precipitate, and the filtrate was concentrated. Ether was added to obtain a powder. The powder was dissolved in dichloromethane, and CuI was added. The mixture was stirred to form a solution. The mixture was filtered, and the filtrate was concentrated. The powder was precipitated with ether. The powder was dissolved in dichloromethane, and gas-phase diffusion with ether was used to obtain yellow crystals. The crystals were filtered, washed with ether, and air-dried at room temperature.

[0013] The chiral heterometallic cluster consists of a metallic framework composed of four copper atoms and one gold atom, surrounded by two organic ligands and four iodide ions. Figure 2 (As shown). Five metal atoms form two triangular frameworks sharing a single gold atom through metalophilic interactions. These two triangles are almost orthogonal, with a dihedral angle of 88.873°. Figure 3 (As shown). Each central gold atom forms a strong coordination bond with a carbene carbon atom. Each copper atom is coordinated by two iodine atoms and one pyridine nitrogen atom (as shown). Figure 4 (As shown).

[0014] The properties of the ultra-stable, strongly luminescent N-heterocyclic carbene-protected chiral heterometallic clusters of this invention are described in detail below:

[0015] The material has an ultra-stable crystal structure, and can maintain its crystalline structure even at a high temperature of 200℃. Figure 5 (As shown). Cluster materials with ultra-high stability are a prerequisite for their further application and a goal pursued by cluster researchers. Chiral ligands endow the entire cluster molecule with chiral properties (as shown). Figure 6 As shown in the figure, the material has excellent application prospects. It exhibits strong orange luminescence in air at room temperature, with an optimal emission wavelength of 613 nm (excitation wavelength 400 nm). Figure 7 (As shown); the fluorescence lifetime at room temperature is 2 μs; the fluorescence quantum yield at room temperature is 93%. This ultra-high quantum yield is the highest reported value for N-heterocyclic carbene ligand-protected clusters to date. High quantum yield is an essential condition for excellent luminescent materials, and high quantum yield cluster materials are a goal pursued by cluster researchers. The chiral ligand endows the entire cluster molecule with chiral properties; the chiral structure and strong luminescence give it strong chiral luminescence characteristics. Figure 8(As shown). Combining the advantages of ultra-high photoluminescence quantum yield, microsecond lifetime at room temperature, circularly polarized emission, and good solubility, radiation resistance, and high-temperature performance, CP-OLEDs (as shown) were prepared through solution processing. Figure 9 The external quantum efficiency (as shown) is as high as 20.8% ( Figure 10 As shown in the figure, this is the highest external quantum efficiency reported to date for coin metal cluster-based organic light-emitting diodes. Furthermore, the electro-polarized emission spectrum of the device fabricated from this material exhibits perfectly mirror-symmetric spectra. Figure 11 (As shown).

[0016] The beneficial effects of this invention are as follows: Based on the different coordination abilities of coordinating atoms and metals, heterometallic clusters are constructed. Increasing the rigidity of the ligands in this invention helps reduce nonradiative transitions of the metal clusters in the excited state. Simultaneously, the introduction of Au atoms can overcome the small spin-orbit coupling in pure Cu clusters, achieving high luminescence quantum efficiency. This is further demonstrated by the development of multidentate chiral R / S-NHC... ql The rational design and modular construction strategy of the -PF6 ligand led to the formation of highly stable chiral heterometallic clusters. The heterometallic cluster material of this invention exhibits high stability, maintaining its crystalline structure even at 200℃, and possesses ultra-high luminescence quantum yield and chiral luminescence properties. Further fabrication of these clusters into devices with very high external quantum efficiency demonstrates potential application value. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the chiral carbene ligand of the present invention.

[0018] Figure 2 This is a schematic diagram of a pair of enantiomeric structures of the heterometallic cluster material of the present invention.

[0019] Figure 3 This is a schematic diagram of the metal core structure of the heterometallic cluster material of the present invention.

[0020] Figure 4 This is a schematic diagram illustrating the ligand coordination mode and function of the heterometallic cluster material of the present invention.

[0021] Figure 5 The PXRD diagram of the heterometallic cluster material of the present invention is shown at varying temperatures (293 to 473 K).

[0022] Figure 6 This is a chiral circular dichroism chromatogram of the heterometallic cluster material of the present invention.

[0023] Figure 7 This is an excitation-emission curve of the heterometallic cluster material of the present invention.

[0024] Figure 8 This is a circularly polarized emission curve of the heterometallic cluster material of the present invention.

[0025] Figure 9 This is a diagram of the fabrication device for the heterometallic cluster material of this invention.

[0026] Figure 10 This is the external quantum efficiency diagram of the heterometallic cluster material of the present invention.

[0027] Figure 11 This is an electro-circularly polarized emission pattern of the heterometallic cluster material of the present invention. Detailed Implementation

[0028] The invention will be further illustrated by the following examples:

[0029] Example 1: Synthesis of the chiral carbene ligand of the present invention

[0030] A methanol (100 mL) solution of (1R,2R)-(+)-1,2-diphenyl-1,2-ethylenediamine or (1S,2S)-(-)-1,2-diphenyl-1,2-ethylenediamine (3.00 g, 14.11 mmol) and glyoxylic acid monohydrate (1.50 g, 16.50 mmol) was stirred at room temperature for 4 hours. N-bromosuccinimide (NBS) (3.30 g, 18.00 mmol) was added to the mixture and stirred overnight at room temperature. The reaction was quenched with saturated sodium metabisulfite, and the solvent was removed under vacuum to obtain a solid. The solid was extracted with ethyl acetate after adding 5% NaOH solution. The organic layer was dried over anhydrous magnesium sulfate, and the solvent was removed under vacuum to obtain a chiral imidazole. The synthesized chiral imidazole (2.22 g, 10 mmol) was dissolved in ethanol (100 mL), and 2-(chloromethyl)quinoline hydrochloride (4.38 g, 20.40 mmol) and sodium bicarbonate (2.52 g, 31.12 mmol) were added and refluxed for two days. After filtration, the solvent was removed under vacuum, and the resulting solid was dissolved in dichloromethane, dried with anhydrous magnesium sulfate, and then the solution was filtered. The solvent was removed under vacuum to obtain an oily substance, which was mixed with 15 mL of tetrahydrofuran to obtain a powder. Further washing with tetrahydrofuran and drying under vacuum yielded a white powder. In a flask, the powder was dissolved in methanol, and the addition of excess aqueous solution of ammonium hexafluorophosphate immediately formed a precipitate. The precipitate was filtered, thoroughly washed with water / methanol, and dried under vacuum to obtain the above R / S-NHC. ql -PF6 chiral carbene ligand.

[0031] Example 2: Synthesis of heterometallic clusters of the present invention

[0032] The chiral ligand (0.65 g, 1 mmol), silver oxide (66 mg, 0.28 mmol), and tetrabutylammonium hexafluorophosphate (40 mg) were dispersed in 40 mL of dichloromethane solution and stirred at room temperature for 10 minutes in the dark. Then, 1 M NaOH solution was added, and stirring continued for 4 hours. The mixture was filtered, and the clear filtrate was concentrated to 2 mL under vacuum. Ether was added to obtain a large amount of white powder. The white powder (0.38 mg, 0.3 mmol) was dissolved in 30 mL of dichloromethane, and 10 mL of a dichloromethane solution of thiophene gold (0.096 g, 0.3 mmol) was added. The mixture was stirred in the dark for 30 minutes to form a precipitate. The solution was filtered to remove the precipitate, and the clear filtrate was concentrated to 2 mL. A large amount of ether was added to obtain a white powder. The powder (0.05 mmol, 68 mg) was dissolved in 6 mL of dichloromethane, and CuI (0.2 mmol, 38 mg) was added. Stirring continued for 3 hours to form a yellow solution. The mixture was filtered, and the clear filtrate was concentrated to 2 mL. A yellow powder was precipitated with diethyl ether. The yellow powder was dissolved in 1 mL of dichloromethane, and the solution was diffused in the gas phase with diethyl ether to obtain yellow crystals. The crystals were filtered, washed with diethyl ether, and dried at room temperature for use in the test of its properties.

[0033] The gold and silver cluster material of the present invention prepared in Example 2 was further characterized as follows:

[0034] (1) Crystal structure determination

[0035] X-ray single-crystal diffraction data of the complexes were determined using appropriately sized single-crystal samples on a Rigaku XtaLAB Pro single-crystal diffractometer. All data were obtained using graphite-monochromated CuKα rays. The diffraction source was collected at 300 K using ω-scan mode, and corrected for Lp factor and semi-empirical absorption. Structural analysis was performed by first obtaining the initial structure using the direct method with the SHELXL-97 program, and then refining it using the full-matrix least squares method with the SHELXL-97 program. All non-hydrogen atoms were refined using anisotropic thermal parameter methods. All hydrogen atoms were refined using isotropic thermal parameter methods. Detailed crystallographic data are shown in Table 1; important bond length data are shown in Table 2.

[0036] Table 1. Main crystallographic data of the heterometallic cluster material of the present invention.

[0037] Table 1. Main crystallographic data

[0038]

[0039] R1=∑||F o |-|F c || / Σ|F o |.wR2=[∑w(F o2 -F c 2 ) 2 / ∑w(F o 2 ) 2 ] 1 / 2

[0040] Table 2 R-NHC ql -AuCu4-I important bond length

[0041]

[0042]

[0043] The above embodiments are only used to illustrate the content of this invention. Other embodiments of this invention are also possible. However, all technical solutions formed by equivalent substitution or equivalent modification fall within the protection scope of this invention.

Claims

1. A chiral heterometallic cluster protected by N-heterocyclic carbene, characterized in that: Its chemical formula is: C 74 H 66 AuCu4F6I4N8OP, abbreviated as: R / S -NHC ql -AuCu4 - I belongs to the orthorhombic crystal system and its space group is chiral space group. P 21212, R -NHC ql -AuCu4 - I: a = 26.7253(11) Å, b = 19.5313(7) Å, c = 14.9188(7) Å, V = 7787.3(6) Å 3 , α = 90°, β = 90° γ = 90°; S -NHC ql -AuCu4 - I: a = 26.701(2) Å, b =19.506(2)Å, c =14.9367(14)Å, V = 7779.6(13)Å 3 , α = 90°, β = 90° γ = 90°; in R / S -NHC ql - For chiral N-heterocyclic carbene ligands R / S -NHC ql -PF6 lost PF 6 The formed groups, R / S -NHC ql The simplified molecular structure of PF6 is as follows: 。 2. The heterometallic cluster protected by N-heterocyclic carbene as described in claim 1, characterized in that: It consists of a metallic framework composed of four copper atoms and one gold atom, with two organic ligands and four iodine atoms coordinated on the periphery; the five metal atoms form two triangular frameworks sharing one gold atom through metalophilic interactions, and the two triangles are orthogonal; each central gold atom forms a strong coordination bond with the carbon atom of the carbene ligand, and each copper atom is coordinated by two iodine atoms and one pyridine nitrogen atom.

3. The method for preparing N-heterocyclic carbene-protected heterometallic clusters as described in claim 1, characterized in that: This can be achieved through the following steps: (1) Chiral N-heterocyclic carbene, silver oxide and tetrabutylammonium hexafluorophosphate were dispersed in dichloromethane solution in the dark and stirred at room temperature; then NaOH solution was added and the reaction was continued by stirring. The mixture was filtered, the filtrate was concentrated under vacuum, and ether was added to obtain powder. (2) Dissolve the above powder in dichloromethane, add a dichloromethane solution of tetrahydrothiophene gold chloride, place the mixture in a light-protected environment and stir to form a precipitate; filter the solution to remove the precipitate, concentrate the filtrate, and add diethyl ether to obtain the powder; (3) Dissolve the above powder in dichloromethane, add CuI to it, and continue stirring to form a solution; filter the mixture, concentrate the filtrate, and precipitate the powder with diethyl ether; dissolve the powder in dichloromethane and diffuse it with diethyl ether in the gas phase to obtain the target crystal; The simplified structural formula of the chiral N-heterocyclic carbene molecule is as follows: 。

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