Low-refractive-index compound and organic electroluminescent device thereof

Abstract

The invention belongs to the technical field of organic electroluminescent materials, and particularly relates to a low-refractive-index compound and an organic electroluminescent device.The core group of the series of low-refractive-index compounds provided by the invention is (perfluoropropane-2, 2-diyl) diphenyl, and the series of low-refractive-index compounds have certain flexibility, high C-F bond energy and excellent thermal stability; in the evaporation process, the film-forming property of the material is better; besides, the extension group of the series of compounds is meta-terphenyl, and the meta-substituted steric hindrance effect can inhibit close packing of molecules and reduce polarization density in unit volume, so that the refractive index of the compounds is reduced, and the performance of devices can be improved when the compounds are matched with high refractive index in the preparation process of the devices.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic electroluminescent materials, and particularly relates to a low-refractive-index compound and an organic electroluminescent device thereof. BACKGROUND

[0002] As a new generation of display and lighting technology, the top-emission structure (Top-Emission OLED) of an organic electroluminescent diode (OLED) realizes light extraction from the top of the device through a semi-transparent cathode, significantly improving the aperture ratio and light emission uniformity. However, due to the refractive index mismatch of the multi-layer film structure, more than 70% of the light generated by the light-emitting layer is limited in the device due to total reflection when the light is transmitted to the cathode interface, resulting in a significant reduction in light out-coupling efficiency (LOCE) and severely restricting the further improvement of the device performance.

[0003] To break through this optical bottleneck, the capping layer (Capping Layer) technology has become a key means to optimize the light transmission path. Studies have shown that although the use of high-refractive-index organic small molecule materials (refractive index 1.7-2.3) as the light out-coupling layer (CPL) can partially improve the microcavity effect, the single material system has approached the theoretical limit for the improvement of the light out-coupling efficiency. In recent years, the dual capping layer structure (Dual Capping Layer) combines a high-refractive-index CPL layer and a low-refractive-index CPL layer to form multiple reflections and interference effects between multiple interfaces, recovers the back loss light, and improves the light out-coupling efficiency by more than 30%, while effectively improving the viewing angle-dependent color shift problem. Therefore, in order to obtain high-efficiency and long-life OLED devices, the development of low-refractive-index CPL materials with excellent performance is the key direction of the current capping layer research and development. SUMMARY

[0004] To solve the problems in the background art, the application provides a low-refractive-index compound, which has the following general formula I structure: ; In the formula, Z is independently selected from N or CH, and n is independently selected from an integer from 2 to 5.

[0005] As a preferred embodiment of the application, n is independently selected from 2 or 3 or 5.

[0006] As a preferred embodiment of the application, n is independently selected from 2 or 3.

[0007] As a preferred embodiment of the application, n is 2.

[0008] As a preferred embodiment of the application, the low-refractive-index compound is selected from the following structures: ; ; ; ; ; ; ; ; ; ; ; ; ; .

[0009] Another object of the present application is to provide an organic electroluminescent device, comprising a cathode and an anode disposed opposite to each other, and an organic layer disposed between the cathode and the anode, further comprising a light extraction layer disposed on the cathode, the light extraction layer comprising the low-refractive compound described above.

[0010] As a preferred embodiment of the present application, the organic electroluminescent device is applied in a display device, which is a mobile phone display screen, a computer display screen, a television display screen, a smart watch display screen, a smart car display panel, a VR or AR helmet display screen, or a display screen of various smart devices.

[0011] The beneficial effects of the present application are as follows:

[0012] The series of compounds provided by the present application have the following advantages: firstly, the core group of the compounds is (perfluoropropane-2,2-diyl)diphenyl, which has a certain flexibility, high C-F bond energy, excellent thermal stability, and better film-forming property of the material in the evaporation process; secondly, the extension group of the series of compounds is meta-triphenyl, and the steric hindrance effect of the meta-substitution can inhibit the close packing of molecules, reduce the polarization density in a unit volume, and thus reduce the refractive index of the compound; meanwhile, there are at least two CF3substituents on the terminal benzene, and CF3is an electron-withdrawing group that can reduce the π-electron density of the benzene ring and reduce the polarization of the molecule, thereby further reducing the refractive index of the compound; in addition, the extension group and the core group are connected in a para-position relationship, and the compound has a linear structure, which is easy to form a close and ordered packing state in the evaporation process, reduces the film defects, and enhances the stability of the device. DETAILED DESCRIPTION

[0013] The technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0014] The specific conditions not specified in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market. Some reaction compounds are purchased from commodity suppliers (Zhengzhou Alpha Chemical Co., Ltd.), and some compounds that cannot be directly purchased are prepared by simple reactions of commercially available raw materials. The percentages are all mass percentages, and the temperatures are in degrees Celsius. The principles of such methods, operation processes, conventional post-treatment, silica gel column, recrystallization purification and other means are well known to synthesis personnel in the art, and the synthesis process can be completely realized to obtain the target product. The reactions in each preparation example are generally carried out under the positive pressure of nitrogen or argon. Synthetic examples

[0015] Example 1: Preparation of compound 1 ; Synthesis of 1-3: 1-1 (44.8 g, 97 mmol), 1-2 (12.5 g, 46.2 mmol), cesium carbonate (Cs2CO3) (75 g, 231 mmol), tetrahydrofuran (THF) (150 ml), H2O (50 ml) were added to a 500 ml three-necked flask, and bubbled with nitrogen for 10 nin. [1,1'-bis(diphenylphosphino)ferrocene]dichloropalladium (II) (Pd(dppf)Cl2) (1.0 g, 1.5 mmol) was added, and the nitrogen was replaced three times. The temperature was raised to 65°C, and the reaction was carried out for 22 h. After cooling to room temperature, the liquid was separated, and the organic phase was rotary evaporated at 45°C. It was dissolved in 300 ml of dichloromethane (DCM), filtered and concentrated. A small amount of ethanol (EtOH) was added, stirred for 2 h, and then filtered under suction. After washing with a mixed solvent (EtOH / PE), 1-3 (33.0 g, 75.6%) was obtained; Synthesis of 1-5: In a 250 ml flask, add 1-3 (13.7 g, 14.5 mmol), 1-4 (4 g, 16 mmol), potassium acetate (KOAc) (14.2 g, 43.6 mmol), 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (S-Phos) (0.25 g, 6 mmol), 1,4-dioxane (78 ml), bubble nitrogen for 10 nin, add palladium acetate (Pd(OAc)2) (0.065 g, 0.3 mmol), replace nitrogen for three times, warm up to 100 °C, react for 19 h, cool down to room temperature, suction filter, rinse with a little DCM, spin dry, dissolve with DCM again, filter, spin dry, precipitate with EtOH, suction filter, to get 1-5 (10.2 g, 68.1%); Synthesis of compound 1: In a 250 ml flask, add 1-5 (18.8 g, 18.1 mmol), 1-6 (5.0 g, 8.2 mmol), Cs2CO3(13.4 g, 41.2 mmol), THF (50 ml), H2O (15 ml), bubble nitrogen for 10 nin, add Pd(dppf)Cl2(0.5 g, 0.66 mmol), replace nitrogen for three times, warm up to 65 °C, react for 18 h, cool down to room temperature, separate liquid, wash with water for three times, spin dry, dissolve with DCM, filter, spin dry, precipitate with EtOH, suction filter, to get compound 1 (14.0 g, 80.4%), MS: 2120.87.

[0016] Example 2: Preparation of compound 9 ; 9-3 is synthesized in the same way as 1-3, except that 9-1 replaces 1-1 and 9-2 replaces 1-2; 9-4 is synthesized in the same way as 1-5, except that 9-3 replaces 1-3; 9-7 is synthesized in the same way as 1-3, except that 9-5 replaces 1-1 and 9-6 replaces 1-2; 9-8 is synthesized in the same way as 1-5, except that 9-7 replaces 1-3; 9-9 Synthesis: In a 250 ml flask, add 9-8 (6.3 g, 8.2 mmol), 1-6 (5.0 g, 8.2 mmol), Cs2CO3(13.4 g, 41.2 mmol), THF (50 ml), H2O (15 ml), bubble with nitrogen for 10 nin, add Pd(dppf)Cl2(0.5 g, 0.66 mmol), replace with nitrogen three times, warm to 65 °C, react for 18 h, cool to room temperature, separate liquid, wash with water three times, spin dry, dissolve with DCM, filter and spin dry, precipitate with EtOH, and filter to obtain 9-9 (5.4 g, 60.5%); Compound 9 is synthesized in the same way as 9-9, except that 9-9 is used instead of 1-6, and 9-4 is used instead of 9-8. MS: 1443.96.

[0017] Example 3: Preparation of compound 15 ; 15-2 Synthesis: In a 500 ml flask, add 15-1 (15.1 g, 46.2 mmol), 9-6 (12.6 g, 46.2 mmol), Cs2CO3(75 g, 231 mmol), THF (150 ml), H2O (50 ml), bubble with nitrogen for 10 nin, add Pd(dppf)Cl2(1.0 g, 1.5 mmol), replace with nitrogen three times, warm to 65 °C, react for 22 h, cool to room temperature, separate liquid, spin dry the organic phase at 45 °C, dissolve with 300 ml DCM, filter and concentrate, precipitate with a small amount of EtOH, stir for 2 h, filter, and rinse with a mixed solvent (EtOH / PE) to obtain 15-2 (11.9 g, 54.1%); 15-4 is synthesized in the same way as 15-2, except that 25-2 is used instead of 9-6, and 15-3 is used instead of 15-1; 15-5 is synthesized in the same way as 1-5, except that 15-4 is used instead of 1-3; Compound 15 is synthesized in the same way as compound 1, except that 15-5 is used instead of 1-5. MS: 1446.84.

[0018] Example 4: Preparation of compound 25 ; 25-3 is synthesized in the same way as 15-2, except that 25-1 is used instead of 15-1, and 25-2 is used instead of 9-6; 25-5 is synthesized in the same way as 15-4, except that 25-3 is used instead of 15-2, and 25-4 is used instead of 15-3; 25-6 was synthesized in the same manner as 15-5 except that 25-5 replaced 15-4; 25-7 was synthesized in the same manner as 15-2 except that 25-1 replaced 15-1 and 1-2 replaced 9-6; 25-8 was synthesized in the same manner as 15-4 except that 25-7 replaced 15-2 and 25-4 replaced 15-3; 25-9 was synthesized in the same manner as 15-5 except that 25-8 replaced 15-4; 25-10 was synthesized in the same manner as 9-9 except that 25-9 replaced 9-8; Compound 25 was synthesized in the same manner as compound 9 except that 25-10 replaced 9-9 and 25-6 replaced 9-4, MS: 1441.67.

[0019] Example 5: Preparation of compound 34 ; 34-2 was synthesized in the same manner as 1-3 except that 34-1 replaced 1-1 and 9-2 replaced 1-2; 34-3 was synthesized in the same manner as 1-5 except that 34-2 replaced 1-3; Compound 34 was synthesized in the same manner as compound 1 except that 34-3 replaced 1-5, MS: 1306.66.

[0020] Example 6: Preparation of compound 53 ; 53-2 was synthesized in the same manner as 1-3 except that 9-5 replaced 1-1 and 53-1 replaced 1-2; 53-3 was synthesized in the same manner as 1-5 except that 53-2 replaced 1-3; Compound 53 was synthesized in the same manner as compound 1 except that 53-3 replaced 1-5, MS: 1580.62.

[0021] Example 7: Preparation of compound 61 ; 61-1 was synthesized in the same manner as 1-3 except that 15-1 replaced 1-1 and 9-6 replaced 1-2; 61-2 was synthesized in the same manner as 1-5 except that 61-1 replaced 1-3; Compound 61 was synthesized in the same manner as compound 1 except that 61-2 replaced 1-5, MS: 1582.57.

[0022] Example 8: Preparation of compound 81 ; 81-2 was synthesized in the same manner as 9-3 except that 81-1 replaced 9-1; 81-3 was synthesized in the same manner as 9-4 except that 81-2 replaced 9-3; 81-4 was synthesized in the same manner as 9-3 except that 81-1 replaced 9-1, and 25-2 replaced 9-2; 81-5 was synthesized in the same manner as 9-4 except that 81-4 replaced 9-3; 81-6 was synthesized in the same manner as 9-9 except that 81-5 replaced 9-8; Compound 81 was synthesized in the same manner as compound 9 except that 81-6 replaced 9-9, and 81-3 replaced 9-4, MS: 1306.66.

[0023] Example 9: Preparation of compound 97 ; 97-2 was synthesized in the same manner as 15-2 except that 9-5 replaced 15-1, and 97-1 replaced 9-6; 97-3 was synthesized in the same manner as 15-4 except that 97-2 replaced 15-2, and 9-1 replaced 15-3; 97-4 was synthesized in the same manner as 15-5 except that 97-3 replaced 15-4; 97-5 was synthesized in the same manner as 15-2 except that 9-5 replaced 15-1, and 9-2 replaced 9-6; 97-6 was synthesized in the same manner as 15-4 except that 97-5 replaced 15-2, and 9-1 replaced 15-3; 97-7 was synthesized in the same manner as 15-5 except that 97-6 replaced 15-4; 97-8 was synthesized in the same manner as 9-9 except that 97-7 replaced 9-8; Compound 97 was synthesized in the same manner as compound 9 except that 97-8 replaced 9-9, and 97-4 replaced 9-4, MS: 1442.99.

[0024] Example 10: Preparation of compound 115 ; 115-1 was synthesized in the same manner as 15-2 except that 1-1 replaced 15-1; 115-2 was synthesized in the same manner as 15-2, except 115-1 replaced 15-2, and 34-1 replaced 15-3; 115-3 was synthesized in the same manner as 15-5, except 115-2 replaced 15-4; 115-4 was synthesized in the same manner as 15-2, except 1-1 replaced 15-1, and 1-2 replaced 9-6; 115-5 was synthesized in the same manner as 15-4, except 115-4 replaced 15-2, and 34-1 replaced 15-3; 115-6 was synthesized in the same manner as 15-5, except 115-5 replaced 15-4; 115-7 was synthesized in the same manner as 9-9, except 115-6 replaced 9-8; Compound 115 was synthesized in the same manner as Compound 9, except 115-7 replaced 9-9, and 115-3 replaced 9-4, MS: 1715.61.

[0025] Example 11: Preparation of Compound 124 ; 124-1 was synthesized in the same manner as 9-3, except 34-1 replaced 9-1, and 9-6 replaced 9-2; 124-2 was synthesized in the same manner as 9-4, except 124-1 replaced 9-3; 124-3 was synthesized in the same manner as 9-7, except 34-1 replaced 9-5, and 1-2 replaced 9-6; 124-4 was synthesized in the same manner as 9-8, except 124-3 replaced 9-7; 124-5 was synthesized in the same manner as 9-9, except 124-4 replaced 9-8; Compound 124 was synthesized in the same manner as Compound 9, except 124-5 replaced 9-9, and 124-2 replaced 9-4, MS: 1307.64.

[0026] Example 12: Preparation of Compound 131 ; 131-1 was synthesized in the same manner as 1-3, except 15-1 replaced 1-1, and 53-1 replaced 1-2; 131-2 was synthesized in the same manner as 1-5, except 131-1 replaced 1-3; The synthetic method of compound 131 is the same as that of compound 1 except that 131-2 replaces 1-5. MS: 1580.63.

[0027] Example 13: Preparation of compound 145 ; The synthetic method of 145-1 is the same as that of 15-2 except that 9-5 replaces 15-1 and 9-6 replaces 15-2; The synthetic method of 145-2 is the same as that of 15-4 except that 145-1 replaces 15-2 and 9-1 replaces 15-3; The synthetic method of 145-3 is the same as that of 15-5 except that 145-2 replaces 15-4; The synthetic method of 145-4 is the same as that of 15-2 except that 9-5 replaces 15-1 and 25-2 replaces 9-6; The synthetic method of 145-5 is the same as that of 15-4 except that 145-4 replaces 15-2 and 9-1 replaces 15-3; The synthetic method of 145-6 is the same as that of 15-5 except that 145-5 replaces 15-4; The synthetic method of 145-7 is the same as that of 9-9 except that 145-6 replaces 9-8; The synthetic method of compound 145 is the same as that of compound 9 except that 145-7 replaces 9-9 and 145-3 replaces 9-4. MS: 1444.64.

[0028] Example 14: Preparation of compound 157 ; The synthetic method of 157-1 is the same as that of 1-3 except that 15-3 replaces 1-1; The synthetic method of 157-2 is the same as that of 1-5 except that 157-1 replaces 1-3; The synthetic method of compound 157 is the same as that of compound 1 except that 157-2 replaces 1-5. MS: 1304.66.

[0029] Example 15: Preparation of compound 172 ; The synthetic method of 172-1 is the same as that of 9-3 except that 1-1 replaces 9-1; The synthetic method of 172-2 is the same as that of 9-4 except that 172-1 replaces 9-3; 172-3 was synthesized in the same manner as 9-7 except that 34-1 replaced 9-5 and 9-2 replaced 9-6; 172-4 was synthesized in the same manner as 9-8 except that 172-3 replaced 9-7; 172-5 was synthesized in the same manner as 9-9 except that 172-4 replaced 9-8; Compound 172 was synthesized in the same manner as Compound 9 except that 172-5 replaced 9-9 and 172-2 replaced 9-4, MS: 1714.63.

[0030] Example 16: Preparation of Compound 181 ; 181-1 was synthesized in the same manner as 1-3 except that 53-1 replaced 1-2; 181-2 was synthesized in the same manner as 1-5 except that 181-1 replaced 1-3; Compound 181 was synthesized in the same manner as Compound 1 except that 181-2 replaced 1-5, MS: 2124.59.

[0031] Example 17: Preparation of Compound 199 ; 199-1 was synthesized in the same manner as 9-3 except that 34-1 replaced 9-1 and 53-1 replaced 9-2; 199-2 was synthesized in the same manner as 9-4 except that 199-1 replaced 9-3; 199-3 was synthesized in the same manner as 9-7 except that 34-1 replaced 9-5 and 97-1 replaced 9-7; 199-4 was synthesized in the same manner as 9-8 except that 199-3 replaced 9-7; 199-5 was synthesized in the same manner as 9-9 except that 199-4 replaced 9-8; Compound 199 was synthesized in the same manner as Compound 9 except that 199-5 replaced 9-9 and 199-2 replaced 9-4, MS: 1308.62.

[0032] In addition, it should be noted that other compounds of the present application can be obtained by referring to the preparation methods of the above-listed examples, and therefore will not be listed one by one.

[0033] Optical property evaluation of compounds:

[0034] The single layer films for optical property evaluation were prepared by depositing 80 nm thick films of Compounds 1, 9, 15, 25, 34, 53, 61, 81, 97, 115, 124, 131, 145, 157, 172, 181, 199 and Compounds Ref-1, Ref-2 on silicon substrates, and the refractive index n and extinction coefficient k values were measured at wavelengths of 460 nm, 530 nm, and 620 nm. The data are shown in Table 1 below. The structures of Compounds Ref-1 and Ref-2 are shown below (Ref-1 and Ref-2 are known low refractive index materials).

[0035] ; . Performance evaluation of the device:

[0036] The following examples illustrate the use of the low refractive index compounds of the present application in OLED devices to further demonstrate the beneficial effects of the compounds of the present application. The materials used in the examples were either commercially purchased or synthesized in-house.

[0037] Preparation of the OLED device: The top-emitting substrate was cleaned with an ultrasonic cleaner using isopropanol, acetone, and distilled water for 15 minutes each, followed by 30 minutes of UV ozone washing in air. The cleaned substrate was then vacuum deposited with hole injection (HT:HI, 10 nm, 2%), hole transport layer (HT, 100 nm), light-emitting auxiliary layer (B-prime, 5 nm), blue light-emitting layer (host material:dopant = Compound BH:Compound BD) (weight ratio 97:3, 30 nm), hole blocking layer (HB, 5 nm), electron transport layer (Compound ET:Liq = 1:1, 30 nm), electron injection layer (Yb, 1 nm), and sequentially deposited with Mg and Ag (weight ratio 1:9, 20 nm) to form a semi-transparent cathode, followed by deposition of CPL-L (20 nm) as a low refractive index capping layer and CPL-H (50 nm) as a high refractive index capping layer to form a dual capping layer structure. The cleaned cover plate was then coated with UV adhesive using a glue coating device, and the coated cover plate was then moved to the pressing section. The substrate with the deposited layers was placed on the top end of the cover plate, and the substrate and cover plate were then pressed together using a lamination device to complete the UV adhesive photocuring.

[0038] Structure of OLED device: ITO:Ag:ITO / HT:HI (2%, 10nm) / HT (100nm) / B-prime (5nm) / BH:BD (97:3, 30nm) / HB (5nm) / ET:Liq (50:50) / Yb (1nm) / Mg:Ag (1:9, 20nm) / CPL-L (20nm) / CPL-H (50nm).

[0039] CPL-L in device examples respectively adopts the compounds in Table 2 below, and CPL-L in device comparative examples respectively adopts Ref-1 and Ref-2.

[0040] It should be noted that the high-refractive covering layer material used in the present embodiment is only exemplary and does not constitute a special limitation of the high-refractive covering layer material of the present application. The high-refractive covering layer material can be selected from known or unknown materials, and the high-refractive covering layer material CPL-H of the present application can be replaced conventionally. The molecular structure of the related material is shown below (particularly preferably selected from the following structures, but not limited to the following structures): ; The driving voltage, BI value, luminous efficiency and lifetime (lifetime at a current density of 50 mA / cm 2 The driving voltage, BI value, luminous efficiency and lifetime (lifetime at a current density of 50 mA / cm 2 The driving voltage, BI value, luminous efficiency and lifetime (lifetime at a current density of 50 mA / cm 2 The driving voltage, BI value, luminous efficiency and lifetime (lifetime at a current density of 50 mA / cm 2

[0041]

[0042] In a blue light top-emitting device, the luminous efficiency is greatly affected by the chromaticity, therefore, the luminous efficiency and CIEy ratio are defined as BI value, i.e. BI=(cd / A) / CIEy, considering the influence of chromaticity on efficiency.

[0043] As shown in Table 1, the refractive index of the compounds corresponding to Examples 1-17 is lower than that of comparative compounds Ref-1 and Ref-2; as shown in Table 2, the device performance of device examples 1-17 is better than that of device comparative examples 1-2, indicating that the combination of high-refractive CPL-H and CPL-L with lower refractive index is beneficial to improving the performance of the device.

[0044] The above examples only list the effect data of devices made from a part of structural formulae, which is a representative sampling test. According to the experimental data, the overall data is not much different, and can represent the effect of other unlisted structures.

[0045] It will be apparent to those skilled in the art that numerous modifications and variations can be made without departing from the spirit and scope of the application. It is therefore intended that the present application cover the modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.

Claims

1. A low refractive index compound, characterized in that, It has the structure shown in general formula I: ； Where Z are independent of each other, either the same or different, and are selected from N or CH; n are independent of each other, either the same or different, and are selected from integers from 2 to 5.

2. The low refractive index compound according to claim 1, characterized in that, n are independent of each other, the same or different, and are selected from 2, 3 or 5.

3. The low refractive index compound according to claim 2, characterized in that, n are independent of each other, the same or different, and can be selected from 2 or 3.

4. The low refractive index compound according to claim 3, characterized in that, n is 2.

5. The low refractive index compound according to claim 1, characterized in that, The low refractive index compound is selected from the following structures: ； ； ； ； ； ； ； ； ； ； ； ； ； 。 6. An organic electroluminescent device, comprising a cathode and an anode disposed opposite to each other, and an organic layer disposed between the cathode and the anode, characterized in that, It also includes a light extraction layer disposed on the cathode, the light extraction layer being prepared from the low refractive index compound according to any one of claims 1 to 5.

7. The organic electroluminescent device according to claim 6, characterized in that, This organic electroluminescent device is used in display devices, such as mobile phone displays, computer displays, television displays, smartwatch displays, smart car display panels, VR or AR headset displays, and displays for various smart devices.

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