CN107936038A - A kind of OLED electron transport layer materials and its preparation method and application - Google Patents

Abstract

Parent nucleus of the present invention using BTBT as electron transport material, the parent nucleus have excellent flatness, crystallinity and carrier transmission performance.By at least one middle electrophilic end-capping group for introducing nitrogenous aromatic heterocycle at both ends, the lumo energy of system is reduced, so as to improve the electronic transmission performance of material.Meanwhile BTBT brings material higher triplet as parent nucleus, be conducive to improve the stability of device.The OLED electron transport materials of the present invention have higher electronic transmission performance, and good film-forming property, at room temperature with preferable stability, therefore can reduce driving voltage, and preferable stability causes device work more to stablize at room temperature, and physical life is longer.

Description

A kind of OLED electron transport layer material and its preparation method and application

technical field

The invention relates to the field of organic luminescent materials, in particular to an OLED electron transport layer material and a preparation method and application thereof.

Background technique

OLED refers to an organic electroluminescent device. OLEDs are considered as cathode ray tubes (CRTs) due to their bright colors, wide viewing angles, compatibility with full-motion video, wide temperature range, thin and fit form factor, low power requirements, and potential for use in low-cost manufacturing processes. ) and future replacement technologies for liquid crystal displays (LCDs). Due to their high luminous efficiency, OLEDs are seen as having the potential to replace incandescent and perhaps even fluorescent lamps. At present, OLED displays have been applied to smart phones by companies such as Samsung, LG, and Apple. At the same time, people have also widely used OLED display screen-based MP3/TV and white lighting products to experience the perfect experience brought by OLED.

Organic electroluminescent devices have an all-solid-state structure. Organic electroluminescent materials are the core of the device. The development of new materials is the driving force for the development of electroluminescent technology. The preparation of raw materials and device optimization have also become the focus of the current organic electroluminescent industry. Research hotspots. In order to meet people's increasingly higher requirements for display products, scientists are committed to synthesizing more efficient electron transport materials, luminescent host-guest materials, and hole transport materials.

The hole mobility of the hole transport material in OLED devices is generally much greater than the electron mobility of the electron transport material, and this carrier transport rate imbalance will lead to a significant decline in device performance. Therefore, it is very important to design electron transport materials with excellent properties. Generally speaking, electron transport materials are planar aromatic compounds with large conjugated structures, most of them have good electron acceptance ability, and can effectively transfer electrons under a certain forward bias voltage. Currently available electron transport materials mainly include 8-hydroxyquinoline aluminum compounds, oxadiazole compounds, imidazole compounds, oxazole compounds, triazole compounds, nitrogen-containing six-membered heterocycles, and perfluorinated electron transport materials. Transport materials, organosilicon-based electron transport materials, etc. To design an electron transport material that can significantly improve the efficiency of organic electroluminescent devices, it needs to have the following properties: reversible electrochemical reduction stability and high reduction potential; there are suitable HOMO and LUMO to make electrons have a minimum The injection energy gap is lowered to reduce the initial and operating voltage; it needs to have a higher electron mobility; it has a good glass transition temperature and thermal stability; it can effectively form an amorphous film.

However, the current electron mobility of traditional electron transport materials including Alq ₃ , TAZ, TPBi, Bphen, BCP, etc. is not very high. Compared with the higher hole mobility of hole transport materials, the imbalance will cause Seriously affect the stability of the device. At the same time, with the development of blue phosphorescent devices and white light devices, the low triplet state of these materials cannot effectively confine the excitons in the light-emitting layer, and the diffusion and recombination quenching of excitons will greatly affect the luminous efficiency and luminescence of the device. purity. In addition, the glass transition temperature of these materials is relatively low, which leads to the crystallization of the material itself due to the heat generated during the operation of the device, and the stability of the device will be reduced.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a novel electron transport material and its preparation method and application, aiming at solving the problem of low electron mobility, low glass transition temperature and triplet energy of existing electron transport materials. low-level disadvantages. The present invention introduces [1]benzothieno[3,2-b][1]benzothiophene (BTBT) as the mother core in the electron transport material structure for the first time, providing a smooth and electron-rich conjugated plane, which is beneficial to The flow of electrons increases the electron mobility of the material. The electron-withdrawing groups of nitrogen-containing aromatic heterocyclic rings are introduced at both ends of the mother nucleus, which effectively reduces the LUMO energy level and facilitates electron transport; at the same time, due to the interaction between the lone electron pair of the nitrogen atom and the lithium ion, the electron injection ability is enhanced. In addition, the symmetrical structure of molecules can increase the regularity of molecular stacking, thereby improving the material carrier mobility. Therefore, the material has high electron transport performance, good film-forming properties, high stability at room temperature, and high glass transition temperature, and is a promising electron transport material.

The technical scheme that the present invention solves the problems of the technologies described above is as follows:

On the one hand, the present invention relates to an OLED electron transport material, and its molecular structural formula can be but not limited to the following:

Among them, the Ar group is represented as an aromatic heterocycle with electron-donating or electron-withdrawing properties, which can be but not limited to phenyl, naphthyl, anthracenyl, thienyl, thienyl, pyridyl, pyrimidyl, quinoline base, isoquinolyl, indolyl, isoindolyl, thiazolyl, oxazolyl, benzothiazolyl, benzothiadiazolyl, naphthyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, etc. . Meanwhile, at least one of the Ar groups is a nitrogen-containing aromatic heterocycle.

At the same time, the Ar group may be a derivative in which the above-mentioned groups are substituted by electron-withdrawing groups such as fluorine, trifluoromethyl, cyano and the like.

In another aspect, the present invention provides a method for preparing an OLED electron transport layer, using compound A (2,7-dibromo[1]benzothieno[3,2-b][1]benzothiophene) and electron-withdrawing heterocyclic boronic acid The ester (B) undergoes Suzuki coupling to obtain the corresponding electron transport material. The reaction formula is as follows:

Wherein, the solvent is a mixed system of toluene, water and ethanol, the catalyst is tetrakistriphenylphosphine palladium, the reaction temperature is 100 degrees Celsius, and the reaction time is 24 hours.

The invention also provides the application of a novel OLED electron transport material. In an organic electroluminescence device, at least one functional layer contains the above novel OLED electron transport material.

The present invention also provides an organic electroluminescent device, comprising an anode layer and a cathode layer constituting a pair of electrodes, and a light-emitting layer and an electron transport layer between the anode layer and the cathode layer, the electron transport layer containing the above-mentioned novel OLED Electron transport materials.

The novel OLED electron transport material provided by the present invention has high electron transport performance, good film-forming properties, and good stability at room temperature, so the driving voltage can be reduced, and the good stability at room temperature makes the device work more efficiently. Stable, long practical life.

Description of drawings

Fig. 1 is the molecular structural formula of the OLED electron transport material of the present invention, Fig. 1A represents formula I, Fig. 1B represents formula II;;

Fig. 2 is the synthesis roadmap of OLED electron transport material of the present invention;

Figure 3 is a synthetic route diagram of Compound A in the prior art.

Detailed ways

The present invention provides an organic electron transport material and its preparation method and application. In order to make the purpose, technical solution and effect of the present invention more clear and definite, the present invention will be further described in detail below. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

BTBT ([1]benzothieno[3,2-b][1]benzothiophene) is a molecular core widely used in the field of organic optoelectronics, especially in the field of p-type organic semiconductors. The hole mobility of semiconductor materials can reach 10cm ² /V ^-1 m ^-1 , which is much higher than that of anthracene, because BTBT has a very flat molecular structure and extremely tight intermolecular stack. Meanwhile, the triplet energy level of BTBT is much higher than that of anthracene.

Nitrogen-containing aromatic heterocyclic rings, such as pyridine (Py) groups, have been proved to effectively enhance the electron injection ability of ETM and thus obtain a lower start-up voltage, because the nitrogen atoms with lone electron pairs in pyridine can interact with metal take effect. At the same time, the electron-withdrawing effect of pyridine itself can lower the LUMO energy level of the material, making electron injection easier.

A kind of organic electron transport material provided by the present invention, its molecular structural formula (Fig. 1) is as follows:

Among them, the Ar group is represented as an aromatic heterocycle with electron-donating or electron-withdrawing properties, which can be but not limited to phenyl, naphthyl, anthracenyl, thienyl, thienyl, pyridyl, pyrimidyl, quinoline base, isoquinolyl, indolyl, isoindolyl, thiazolyl, oxazolyl, benzothiazolyl, benzothiadiazolyl, naphthyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, etc. . Meanwhile, at least one of the Ar groups is a nitrogen-containing aromatic heterocycle.

At the same time, the Ar group may be a derivative in which the above-mentioned groups are substituted by electron-withdrawing groups such as fluorine, trifluoromethyl, cyano and the like.

The present invention innovatively introduces [1]benzothieno[3,2-b][1]benzothiophene as the core of the electron transport material for the first time, and the core has excellent planarity, crystallinity and carrier transport performance. By introducing electron-withdrawing capping groups of nitrogen-containing aromatic heterocyclic rings at both ends, the LUMO energy level of the system is reduced, thereby improving the electron transport performance of the material. At the same time, BTBT as the mother nucleus brings a higher triplet energy level to the material, which is beneficial to improve the stability of the device.

As mentioned above, the structures of the compounds in Formula I are as follows, but not limited to the exemplified structures:

As mentioned above, the structure of the compound in formula II is as follows, but not limited to the exemplified structure:

The synthetic roadmap (Fig. 2) of the organic electron transport material of the present invention is as follows:

First, compound A (Figure 3) was prepared according to the method reported in the literature, and the specific steps were as follows:

Embodiment 1 prepares compound 1

Specific steps are as follows:

In a 100mL pressure bottle, sequentially add 2g (5mmol) of compound A, 2.69g (20mmol) of 2-pyridineboronic acid, 2.8g (20mmol) of potassium carbonate, 0.25g of palladium tetraphenylphosphine, 5mL of ethanol, 15mL of toluene, water After bubbling 5 mL of nitrogen gas for 15 min, cover the lid, react at 100°C for 24 h, cool to room temperature, filter and wash with water, methanol, and acetone in sequence to obtain 1.69 g of a gray-green crude product.

Put the crude product in a vacuum sublimation apparatus (Shenyang Kecheng, ZDF-5227), the sublimation parameters are sublimation vacuum degree 2×10-5Pa, sublimation zone three temperature 280°C, sublimation zone two temperature 240°C, sublimation zone one temperature The temperature is 160°C, and the set temperature is a gradient temperature rise, which increases by 50°C every 15 minutes. After reaching the target temperature, it is kept for sublimation for 12 hours, and a total of 1.5g of fine product is obtained by sublimation, and the sublimation yield is 90%. Elemental analysis shows that the compound contains 73.18 carbon, 3.49 hydrogen and 7.08 nitrogen, which is compound 1.

Embodiment 2 prepares compound 2

Specific steps are as follows:

In a 100mL pressure bottle, sequentially add 2g (5mmol) of compound A, 2.69g (20mmol) of 3-pyridineboronic acid, 2.8g (20mmol) of potassium carbonate, 0.25g of tetraphenylphosphine palladium, 5mL of ethanol, 15mL of toluene, water After bubbling 5 mL with nitrogen for 15 min, cover the lid, react at 100°C for 24 h, cool to room temperature, filter and wash with water, methanol, and acetone in sequence to obtain 1.72 g of a gray-green crude product.

Put the crude product in a vacuum sublimation apparatus (Shenyang Kecheng, ZDF-5227), the sublimation parameters are as follows: the sublimation vacuum degree is 2×10-5Pa, the temperature of the sublimation zone 3 is 270°C, the temperature of the sublimation zone 2 is 230°C, and the temperature of the sublimation zone 1 The temperature is 160°C, and the set temperature is a gradient temperature increase, which increases by 50°C every 15 minutes. After reaching the target temperature, it is kept for sublimation for 12 hours, and a total of fine product 1.39 is obtained by sublimation, and the sublimation yield is 88%. Elemental analysis shows that the compound contains 73.18 carbon, 3.49 hydrogen and 7.08 nitrogen, which is compound 2.

Embodiment 3 prepares compound 15

Specific steps are as follows:

In a 100mL pressure bottle, sequentially add 2g (5mmol) of compound A, 2.69g (20mmol) of 3-quinoline boronic acid, 2.8g (20mmol) of potassium carbonate, 0.25g of tetrakistriphenylphosphine palladium, 5mL of ethanol, 15mL of toluene, Water 5mL, nitrogen gas bubbling for 15min, cover the lid, react at 100°C for 24h, cool to room temperature, filter and wash with water, methanol, and acetone in sequence to obtain the gray-green crude product 1.79.

Put the crude product in a vacuum sublimation apparatus (Shenyang Kecheng, ZDF-5227), the sublimation parameters are the sublimation vacuum degree is 2×10-5Pa, the temperature of the sublimation zone 3 is 290°C, the temperature of the sublimation zone 2 is 250°C, and the temperature of the sublimation zone 1 The temperature is 180°C, and the set temperature is a gradient temperature rise, which increases by 50°C every 15 minutes. After reaching the target temperature, it is kept for sublimation for 12 hours, and a total of 1.59 fine products are obtained by sublimation, and the sublimation yield is 91%. Elemental analysis shows that the compound contains 77.70 carbon, 3.67 hydrogen and 5.66 nitrogen, which is compound 15.

Embodiment 4 device manufacture

The present invention also provides an application of the above-mentioned electron transport material, specifically applying the electron transport material to an organic electroluminescent device. In order to effectively characterize the electron transport capability of the material of the present invention, TAPC was selected as the hole transport material in the light-emitting device, CBP/Ir(ppy) ₃ was used as the light-emitting material, and TmPyPB was used as the hole blocking material. LG-201 was used as the reference electron transport material, and LiF was used as the electron injection material. The device structure is: ITO/MoO ₃ (1nm)/TAPC(40nm)/CBP:Ir(ppy) ₃ (20nm)/TmPyPB(20nm)/ETM(40nm)/LiF(1nm)/Al.

The device manufacturing process is as follows:

The glass substrate coated with the ITO transparent conductive layer is ultrasonically treated in acetone, rinsed in deionized water, ultrasonically degreased in acetone:ethanol mixed solvent (volume ratio 1:1), and baked in a clean environment until completely removed Moisture, cleaned with ultraviolet light and ozone, and bombarded the surface with low-energy positron beams; put the above-mentioned glass substrate with anodic layer in a vacuum chamber, and evacuate to 9*10 ^-5 Pa.

MoO3 was vacuum _- deposited on the above anode layer as a hole injection layer, the evaporation rate was 0.05nm/s, and the thickness of the evaporation film was 1nm; on the hole injection layer, TAPC was evaporated as a hole transport layer, and the evaporation rate was The evaporation rate is 0.05nm/s, and the evaporation film thickness is 40nm; vacuum evaporation is used as the CBP: Ir(ppy) ₃ device light-emitting layer on the hole transport layer, the evaporation rate is 0.05nm/s, and the total evaporation film thickness is 20nm ; Vacuum-deposit a layer of TmPyPB on the light-emitting layer as a hole blocking layer, the evaporation rate is 0.05nm/s, and the total film thickness is 20nm; on the hole blocking layer, a layer of compound 1 or LG is evaporated -201 is used as the electron transport layer of the device, and its evaporation rate is 0.05nm/s, and the total film thickness of the evaporation is 40nm; on the electron transport layer (ETL), LiF is vacuum-deposited as the electron injection layer of the device, and its evaporation rate is is 0.05nm/s, and the film thickness is 1nm; finally, metal aluminum is evaporated on the LiF as the cathode of the device, and the film thickness is 150nm.

The device performance is as follows:

It should be understood that the application of the present invention is not limited to the above examples, and those skilled in the art can make improvements or transformations according to the above descriptions, and all these improvements and transformations should belong to the protection scope of the appended claims of the present invention.

Claims (8)

1. An OLED electron transport material is characterized in that its molecular structural formula is as follows: Among them, Ar ₁ , Ar ₂ , Ar ₁ ′, Ar ₂ ′ are Ar groups, and the Ar groups are aromatic heterocyclic rings with electron-donating or electron-withdrawing properties, and each Ar group in the molecular structural formula At least one of them is a nitrogen-containing aromatic heterocycle. 2. The OLED electron transport material according to claim 1, wherein the Ar group comprises phenyl, naphthyl, anthracenyl, thienyl, thienyl, pyridyl, pyrimidyl, quinolinyl, Isoquinolyl, indolyl, isoindolyl, thiazolyl, oxazolyl, benzothiazolyl, benzothiadiazolyl, naphthyridyl, pyridazinyl, pyrimidinyl, pyrazinyl. 3. OLED electron transport material according to claim 1, is characterized in that, any of the. 4 . The OLED electron transport material according to claim 3 , wherein Ar ₁ , Ar ₂ , Ar ₁ ′, and Ar ₂ ′ are derivatives in which the aforementioned groups are replaced by electron-withdrawing groups. 5 . The OLED electron transport material according to claim 4 , wherein the electron-withdrawing group is any one of fluorine, trifluoromethyl, and cyano. 6. A preparation method for an OLED electron transport material, characterized in that the Suzuki coupling occurs between the compound A and the electron-withdrawing heterocyclic boronic acid ester B or C to obtain the corresponding electron transport material, and the reaction formula is one of the following: Among them, Ar ₁ , Ar ₂ , Ar ₁ ′, Ar ₂ ′ are Ar groups, and the Ar groups are aromatic heterocyclic rings with electron-donating or electron-withdrawing properties, and each Ar group in the molecular structural formula At least one of them is a nitrogen-containing aromatic heterocycle. 7. An application of an OLED electron transport material, characterized in that, in an organic electroluminescent device, at least one functional layer contains the OLED electron transport material described in claims 1-6. 8. An organic electroluminescent device, characterized in that, comprises an anode layer and a cathode layer constituting a pair of electrodes, and a light-emitting layer and an electron transport layer between the anode layer and the cathode layer, and the electron transport layer contains the above-mentioned OLED electron transport material as described in claims 1-6.