A carborane derivative with space charge transfer properties and its application in preparing optoelectronic materials

Abstract

The present invention discloses a carborane derivative with spatial charge transfer properties, having the following structure: #imgabs0# wherein R represents a group selected from carbazole, 9,9-dimethylacridine, triphenylamine, phenothiazine, and phenoxazine. The present invention utilizes the unique three-dimensional aromaticity and cage structure of carborane to construct a novel "V"-shaped D-A-D'-A' molecule, where D and D' represent electron-donating groups, and A and A' represent electron-withdrawing groups. This type of molecule exhibits spatial charge transfer (TSCT) from the R group to the triazine group and exhibits thermally activated delayed fluorescence (TADF) properties. The molecule has a maximum emission wavelength of 591 nm in the thin film state, and a quantum yield of up to 89%. The carborane derivative described in the present invention has excellent thermal stability as a thermally activated delayed fluorescence material and has been successfully applied to organic light-emitting diodes (OLEDs), with the device having a maximum emission wavelength of 592 nm and a maximum external quantum efficiency of 12.7%.

Description

Technical Field

[0001] The present invention belongs to the field of luminescent materials, and in particular relates to a carborane derivative with spatial charge transfer properties and an application thereof in preparing photoelectric materials. Background Art

[0002] Compared with traditional display technologies, OLEDs have advantages such as wide viewing angle, low energy consumption, and high contrast. In recent years, OLED devices have made great progress in process flow, manufacturing cost, and service life, and have gradually become the mainstream display technology. They have been widely used in televisions, smartphones, and wearable devices, and have shown great application potential in many fields such as lighting, automobiles, and medical care. The first generation of OLEDs is based on fluorescent small molecules and can only utilize 25% of singlet excitons. Its external quantum efficiency (EQE) is a maximum of 5%; the second generation of OLEDs is based on phosphorescent complexes. Although it can utilize triplet excitons, it requires the use of heavy metals such as Ir; the third generation of OLEDs is based on TADF molecules. It can utilize all excitons and does not contain metal atoms. It has the advantages of low cost and environmental friendliness. Carborane is the product of some boron atoms in borane being replaced by carbon atoms. It has many B–H–B three-center two-electron bonds and therefore has unique electronic properties. Among them, 1,2-dicarbon-closed-dodecaborane (1,2-C2B 10 H 12 Ortho-carborane (o-carborane) exhibits a closed icosahedral cage structure with unique three-dimensional aromaticity and excellent chemical and thermal stability. Furthermore, o-carborane exhibits significant steric hindrance (approximately 1 nm), excellent solubility, and inherent sublimation properties, laying the foundation for the development of carborane-based optoelectronic materials and OLED devices. Among carborane-based molecules, molecules exhibiting TADF properties are also extremely rare.

[0003] In recent years, there have been many applications of ortho-carborane in regulating molecular luminescence, but there are few studies on its application in OLEDs. In 2016, Japanese scholars Takuma Yasuda et al. first introduced carborane derivative luminescent materials into OLED devices (Angew. Chem. Int. Ed. 2016, 55 (25), 7171-7175.); in 2021, Wang Zhaojin et al. from Yancheng Institute of Technology in Jiangsu Province reported the second carborane-based OLED device (Inorg. Chem. 2021, 60 (7), 4705-4716.); in 2023, Jun Yeob Lee et al. from South Korea reported the third OLED device based on carborane luminescent materials (Dyes and Pigments 2023, 215, 111278); in 2024, Min Hyung Lee et al. from South Korea reported the fourth OLED device based on carborane derivatives (Adv. Sci. 2024, 11, 2309016). Among them, only the molecules reported by Takuma Yasuda et al. are TADF molecules based on the TSCT process. However, these molecules have a D–A–A' structure, and the distance between the electron-donating and electron-withdrawing fragments is large, which to some extent hinders the charge transfer process. This application creatively proposes a "V"-shaped D–A–D'–A' structure. Compared with the D–A–A' type carborane luminescent molecules, the D–A–D'–A' structural skeleton has more regulatory sites, making the molecule more modifiable. It can also better control the relative arrangement and spatial distance between the electron-donating and electron-withdrawing fragments, making the TSCT process more smooth. Summary of the Invention

[0004] The present invention addresses the deficiencies of the prior art and provides a carborane derivative with space charge transfer properties. The compound emits orange-red light, has a high quantum yield, and has the advantages of simple synthesis, high thermal stability, and excellent luminescence properties.

[0005] The specific technical solutions of the present invention are as follows:

[0006] A carborane derivative with space charge transfer properties has the following structure: Wherein, the R group represents a group substituted by one or more H, C1-10 alkyl, halogen or a combination thereof at any position. One of the groups.

[0007] The compound of the present invention can be prepared by adopting the method of synthesizing carborane by alkyne insertion method.

[0008] Taking the molecule with a carbazole group at the R position as an example, the synthesis process is as follows:

[0009]

[0010] In the above preparation method, all solvents were dried over Na, refluxed, and redistilled before use, and all reactions were carried out under anhydrous and oxygen-free conditions. The resulting product was extracted, dried, and concentrated, then purified by column chromatography using 200–300 mesh silica gel and vacuum-dried for 12 hours to obtain the final product.

[0011] Another object of the present invention is to provide the use of the carborane derivatives having space charge transfer properties described herein in the preparation of optoelectronic materials. These optoelectronic materials are luminescent materials that emit orange-red light and exhibit both space charge transfer properties and thermally activated delayed fluorescence. The carborane derivatives having space charge transfer properties described herein can be used to prepare organic light-emitting diode (OLED) devices. Specifically, they can be used to prepare the light-emitting layer of OLED devices.

[0012] The carborane in the compound structure described in this invention possesses unique three-dimensional aromaticity. Unlike structures with conjugated bonds, such as phenyl groups, the electron cloud cannot be transferred from the terminal R group through the carborane structure to the triazine group. Because the molecules involved in this application have a novel "V"-shaped D-A-D'-A' structure, the spatial distance between the R group and the triazine group is small, and the charge transfer from the R group to the triazine group occurs through space. At the same time, the unique aromaticity and electron-withdrawing effect of the carborane can effectively control the luminescent color and luminous efficiency of the molecule.

[0013] Advantages of the present invention:

[0014] 1. This invention utilizes the unique electronic effects and steric structure of carborane to construct a novel "V"-shaped D–A–D'–A' structure. Due to the regulatory effect of carborane, a thermally activated delayed fluorescence material with space charge transfer-induced emission is obtained. The material emits orange-red light with a maximum wavelength of 591 nm and a quantum yield of up to 89% for the luminescent molecules.

[0015] 2. The carborane derivatives with space charge transfer properties invented by the present invention have good thermal stability and have been successfully applied to organic light-emitting diodes (OLEDs), opening up a new path for the design of high-performance OLED light-emitting materials.

[0016] 3. The carborane derivatives designed in the present invention have the advantages of novel structure and efficient synthesis, and are suitable for industrial production and commercial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The crystal structure of the carborane derivative of the present invention.

[0018] Figure 2is the HOMO and LUMO electron cloud distribution of the carborane derivatives of the present invention.

[0019] Figure 3 These are the emission spectra of the carborane derivatives of the present invention in toluene solution at room temperature and 77K, as well as the phosphorescence emission spectra.

[0020] Figure 4 This is the room temperature transient decay curve of the carborane derivative of the present invention in toluene solution.

[0021] Figure 5 The present invention shows a temperature-dependent emission spectrum of a doped film of a host material 1,3-bis(carbazolyl)benzene (mCP) doped with the carborane derivative at a concentration of 20%.

[0022] Figure 6 This is the temperature-dependent transient decay curve of the doped film of the main material mCP doped with the carborane derivative of the present invention at a concentration of 20%.

[0023] Figure 7 This is a schematic structural diagram of device AD ​​in which the carborane derivative is used as the luminescent material and DBFPO is used as the main material.

[0024] Figure 8 It is the molecular structure involved in the AD structure of the device.

[0025] Figure 9 This is a schematic diagram of the structure of device E in which the carborane derivative of the present invention is used as the luminescent material and mCP is used as the main material.

[0026] Figure 10 It is the molecular structure involved in the structure of device E.

[0027] Figure 11 is the CIE (Commission Internationale de L'Eclairage) coordinate of an OLED device in which the carborane derivative of the present invention is used as a light-emitting layer.

[0028] Figure 12 This is a relationship diagram between brightness and external quantum efficiency of OLED devices AD prepared using the carborane derivatives described in the present invention as light-emitting layers.

[0029] Figure 13 This is a relationship diagram between brightness and external quantum efficiency of an OLED device E prepared using the carborane derivatives of the present invention as a light-emitting layer. DETAILED DESCRIPTION

[0030] The specific steps of the present invention are described below by way of examples, but are not limited to the examples.

[0031] Unless otherwise specified, the terms used in the present invention generally have the meanings commonly understood by those skilled in the art.

[0032] The present invention will be described in further detail below in conjunction with specific examples and with reference to data. It should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention in any way.

[0033] In the following examples, various processes and methods not described in detail are conventional methods known to those of ordinary skill in the art.

[0034] Example 1

[0035]

[0036] Step 1: Synthesis of Cz-PhA-CzSi. To a 250 mL three-necked flask, add 4.10 g (10 mmol) of Cz-Si, 4.00 g (15 mmol) of Cz-PhA, 57.7 mg (0.5 mmol) of Pd(PPh3)4, and 19.5 mg (1 mmol) of CuI. After replacing the gas three times, add 85 mL of redistilled tetrahydrofuran and 85 mL of triethylamine. Heat and reflux at 80°C for 24 h. After the reaction is complete, cool to room temperature and extract three times with DCM / H2O. Separate the mixture by column chromatography using PE:DCM = 5:1 as the eluent to obtain 3.83 g of a white solid powder. The yield is 70.1%. 1 H NMR (400MHz, Chloroform-d) δ = 8.19 (d, J = 2.2Hz, 1H), 7.78 (m, 3H), 7.70–7.59 (m, 2H), 7.55 (m, 1H) ,7.46(m,1H),7.35–7.25(m,2H),7.20–6.91(m,7H),6.87–6.65(m,2H),0.81(s,9H),0.63(s,6H).

[0037] Step 2: Synthesis of Cz-PhCb-CzSi. To a 100 mL three-necked flask, add 1.64 g (3 mmol) of Cz-PhA-CzSi and 1.22 g (6 mmol) of decaborane acetonitrile complex, 51 mg (0.3 mmol) of AgNO₃ as catalyst, and 40 mL of redistilled toluene as solvent. Heat and reflux at 120°C for 24 h. After the reaction, cool to room temperature and extract three times with DCM / H₂O. Separate the mixture by column chromatography using PE:DCM = 3:1 as eluent to obtain 1.22 g of a pale yellow solid powder. The yield is 61.2%. 1HNMR (400MHz, Chloroform-d) δ = 8.09 (d, J = 2.2Hz, 1H), 7.95 (m, 3H), 7.66–7.57 (m, 2H), 7.49 (d, J = 8.4Hz, 1H), 7.39 (dd, J = 8. 9,2.2Hz,1H),7.35–7.25(m,2H),7.24–7.04(m,7H),6.97–6.88(m,2H),1.73–3.94(br,B–H,10H),0.85(s,9H),0.60(s,6H). 13 C NMR(101MHz,Chloroform-d)δ=141.45,140.61,133.59,131.09,128.69,127.64,127.51,127.25,12 4.76,123.90,123.08,121.63,121.54,121.14,115.65,114.58,110.67,88.44,86.09,27.71,21.78. 11 B NMR (128MHz, Chloroform-d) δ = -1.89, -10.14.

[0038] Step 3: Synthesis of Cz-PhCb-Cz: 2.0 g (3 mmol) of Cz-PhCb-CzSi was added to a 100 mL round-bottom flask and dissolved in 30 mL of anhydrous THF. 15 mL of 1 mol / L tetrabutylammonium fluoride was added and stirred at room temperature for 2 h. After stopping the reaction, the mixture was separated by column chromatography using PE:DCM (3:1) as the eluent to obtain 0.97 g of a pale yellow solid powder. The yield was 58.6%. 1 H NMR(400MHz,Chloroform-d)δ=8.09(d,J=2.0Hz,1H),8.03–7.91(m,4H),7.64–7.55(m,2H),7.48(dd,J=8.7,2.1Hz, 1H),7.43–7.26(m,2H),7.24–7.16(m,3H),7.16–7.02(m,5H),6.89(dt,J=7.9,0.9Hz,2H),1.61–3.76(br,B–H,10H). 11 B NMR (128MHz, Chloroform-d) δ = -1.90, -8.90, -10.31.

[0039] Step 4: Synthesis of Trz-mCzCbCz: In a 100 mL three-necked flask, add 0.88 g (1.6 mmol) of Cz-PhCb-Cz, 0.70 g (1.8 mmol) of 2-(3-bromophenyl)-4,6-diphenyltriazine, 90 mg (0.09 mmol) of Pd2(dba)3, 115 mg (0.27 mmol) of t-BuXPhos, and 250 mg (0.29 mmol) of sodium tert-butoxide. After replacing the gas three times, add 50 mL of anhydrous 1,4-dioxane and heat under reflux at 120°C for 24 hours. After stopping the reaction, extract three times with DCM / H2O. Separate the mixture by column chromatography using PE:DCM = 2:1 as the eluent to obtain 0.95 g of a pale yellow-green solid powder. The yield is 69.6%. 1 H NMR (400MHz, Chloroform-d) δ=8.93–8.82(m,2H),8.75–8.66(m,3H),8.30(d,J=2.1Hz,1H),8.21–8.12(m,1H),8.00(dt,J=4.6,3.2Hz,2H) ,7.78(t,J=7.8Hz,1H),7.74–7.64(m,3H),7.63–7.53(m,3H),7.53–7.44(m,5H),7.40–7.23(m,6H),7.18–7.10(m,4H),7.07–6.99(m,2H). 13 C NMR(101MHz,Chloroform-d)δ=171.90,140.12,139.44,137.43,135.82,132.75,132.33,130.84,130.41,129.74,128.97,128.68 ,128.55,127.40,127.14,126.40,125.93,123.50,123.26,120.98,120.42,120.28,110.27,109.37,109.29,87.18,84.93,77.22. 11 BNMR (128MHz, Chloroform-d) δ = -2.42, -10.66.

[0040] The crystal diffraction data of the carborane derivative Trz-mCzCbCz were collected using CCD-Bruker Smart APEX 11, the structure was solved using the OLEX 2 program integrated with Shelx, and the ball-and-stick model was drawn using Diamond software. The crystal structure of the compound is shown in FIG. Figure 1 The single crystal structure confirmed the V-shaped D–A–D'–A' structure of the molecule.

[0041] Density functional theory (DFT) was used to optimize the ground state of the Trz-mCzCbCz molecule at the PBE0 / 6-31G(d) level. Based on the optimized structure, the electron cloud distribution and related energy levels of the molecule in the excited state were calculated using time-dependent density functional theory (TD-DFT) at the PBE0 / 6-31G(d) level. All calculations were performed using Gaussian 16 software. The HOMO and LUMO electron cloud distributions of the compound are shown in Figure 2. Figure 2 The calculation results confirm that the Trz-mCzCbCz molecule has TSCT properties.

[0042] The emission and phosphorescence spectra of the compounds in toluene solutions at room temperature and 77 K were measured using a HORIBA FL-3 transient steady-state fluorescence spectrometer equipped with an integrating sphere. Figure 3 ), excited state transient decay curve ( Figure 4 ), the absolute quantum yield at room temperature under different states, and the above photophysical properties are shown in Table 1. The above experimental results show that the molecule has orange-red emission and TADF properties.

[0043] Figure 5 Temperature-dependent emission spectra of a 20%-doped thin film of the carborane derivative Trz-mCzCbCz in the host material 1,3-bis(carbazolyl)benzene (mCP). Figure 6 The temperature-dependent transient decay curve of the doped film of the carborane derivative Trz-mCzCbCz at a concentration of 20% in the host material mCP. The above test results fully confirm the TADF properties of the molecule.

[0044] Table 1 Photophysical properties of Trz-mCzCbCz molecules

[0045]

[0046] OLED Examples

[0047] OLED devices were prepared by vacuum evaporation, wherein the light-emitting layer used the carborane derivative Trz-mCzCbCz as the guest material and DBFPO as the host material. Five OLED devices were prepared, namely device AE. The structure of device AD ​​is shown in FIG. Figure 7 As shown, the molecular structures involved in the device structure are as follows Figure 8 As shown. In the light-emitting layer of device A, the concentration of Trz-mCzCbCz is 100wt%; in devices B, C and D, the concentration of Trz-mCzCbCz is 10wt%, 20wt% and 30wt% respectively, and the rest of the light-emitting layer is composed of the main material DBFPO. The structure of device E is shown as follows Figure 9 As shown, the molecular structures involved in the device structure are as follows Figure 10The light-emitting layer uses the carborane derivative as the guest material, mCP as the host material, and the concentration of Trz-mCzCbCz is 20wt%. The CIE (Commission Internationale de L'Eclairage) coordinates of the device AE are shown as follows: Figure 11 The relationship between the brightness and external quantum efficiency of device AD ​​is shown in the figure below. Figure 12 As shown in Figure 2, device C has the highest external quantum efficiency, which is 6.29%. The brightness-external quantum efficiency relationship diagram of device E is shown in Figure 2. Figure 13 As shown, the external quantum efficiency is 12.7%, which is currently the highest value reported for carborane-based TSCT-type OLED devices. The results show that the example carborane derivatives are suitable for OLED light-emitting materials. The electroluminescence data of device AE are summarized in Table 2. on Represents the lighting voltage, J max Represents the maximum current density, CE max Represents the maximum current efficiency, PE max Represents the maximum energy efficiency, EQE max represents the maximum external quantum efficiency, λ max Represents the maximum emission wavelength of the device at 10V voltage, L max Represents maximum brightness.

[0048] Table 2 Summary of electroluminescent parameters of device AE

[0049]

Claims

1. A carborane derivative having space charge transfer properties, characterized in that Has the following structure: , wherein R represents a group substituted by one or more H, C1-10 alkyl, or halogen at any position .

2. Use of the carborane derivative having space charge transfer properties according to claim 1 in the preparation of optoelectronic materials.

3. The use according to claim 2, characterized in that The photoelectric material is a luminescent material that emits orange-red light and has space charge transfer properties and thermally activated delayed fluorescence.

4. The use according to claim 3, characterized in that The carborane derivative with space charge transfer property is used for preparing OLED devices.

5. The use according to claim 4, characterized in that The carborane derivative with space charge transfer property is used to prepare the light-emitting layer of an OLED device.

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