TWI657081B - An organic electroluminescent device containing a bipolar host material of a 1,2,4-triazine group - Google Patents

Abstract

The invention relates to an organic electroluminescence device containing a bipolar host material containing 1,2,4-triazine groups. The organic electroluminescence device includes a cathode, an anode, and an organic layer. The organic layer is a hole transport layer. Or one or more of a hole blocking layer, an electron transporting layer, and a light-emitting layer, wherein the organic layer has a compound having the structure of formula (I), wherein R _{1 to} R ₄ are substituted or unsubstituted acridinyl groups , Phenothiazinyl, carbazolyl, diphenylamino, hydrogen, halogen, substituted or unsubstituted alkyl. At least one of R _{1 to} R _{4 is} a substituted or unsubstituted acridinyl group, a phenothiazinyl group, a carbazolyl group, or a diphenylamino group. Experiments show that the electroluminescent device prepared by using the bipolar host material of the present invention has lower lighting voltage, higher current efficiency under the same current density, is more conducive to carrier injection and transmission balance, and has better electrical properties. The photoluminescence performance meets the requirements of host materials for high-performance organic semiconductor devices.

Description

Organic electroluminescent device with bipolar host material containing 1,2,4-triazine group

The invention relates to an organic electroluminescence device, and belongs to the technical field of organic light-emitting materials, in particular to an organic electroluminescence device prepared by using a bipolar host material with 1, 2, 4-triazine as a core.

Organic light emitting diodes (OLEDs) have the characteristics of high speed, low energy consumption, high brightness, wide viewing angle, flexible, and active light emission, and have been highly valued by the scientific and industrial circles. Its application in display and lighting has great potential. Electrofluorescence and electrophosphorescence are referred to as first and second generation OLEDs, respectively. OLEDs based on fluorescent materials have the characteristics of high stability, but are limited by the laws of quantum statistics. The ratio of singlet excitons and triplet excitons generated by electrical activation is 1: 3, so fluorescent materials The maximum quantum efficiency in electroluminescence is only 25%. Phosphorescent materials have the spin-orbit coupling effect of heavy atoms, and can use singlet excitons and triplet excitons in combination. The theoretical internal quantum efficiency can reach 100%, but phosphorescent-based OLEDs have significant efficiency roll-off effects. There are certain obstacles in high brightness applications. In addition, phosphorescent materials need to use noble metals such as Pt, Ir, so the phosphorescent materials are expensive. At present, phosphorescent materials are mainly used as guest materials in OLED devices.

Phosphorescent materials can use singlet excitons and triplet excitons in combination to achieve 100% internal quantum efficiency. However, the excited state exciton lifetime of the transition metal complex is relatively long, which causes the triplet state to triplet state (T ₁ -T ₁ ) to be quenched in the actual operation of the device. To overcome this problem, researchers often dope phosphorescent materials into organic host materials. Therefore, for efficient organic light-emitting diodes, it is important to develop high-performance host materials and guest materials.

At present, the host material widely used in phosphorescent devices is CBP (4,4'-bis (9-carbazolyl) biphenyl), but it requires a higher driving voltage and a lower glass transition temperature (T _g ) (T _g = 62 ° C), easy to crystallize. In addition, CBP is a P-type material. The hole mobility is much higher than the electron mobility, which is not conducive to carrier injection and transport balance, and has low luminous efficiency.

Aiming at the problems of high driving voltage required by the existing host (CBP) material, easy glass transition temperature, carrier injection, and imbalanced transport, the present invention provides a bipolar containing 1,2,4-triazine group. A host material of an organic electroluminescence device uses a 1,2,4-triazine group bipolar host material as a light-emitting layer host material, and the 1,2,4-triazine group serves as a strong pull electron center core, and has a strong Derivatives such as diphenylamines, carbazoles, acridine, etc., which are electron-donating capabilities, are used as connecting groups to form DA-type and DAD-type bipolar materials. The organic electroluminescent device has good stability, low starting voltage, and high luminous efficiency. Has better application prospects.

An organic electroluminescent device includes a cathode, an anode, and an organic layer. The organic layer is one or more of a hole transport layer, a hole blocking layer, an electron transport layer, and a light emitting layer. The organic layer has the formula (I). A compound of the structure,

Wherein, R ₁ -R ₄ represent substituted or unsubstituted acridinyl, phenothiazinyl, carbazolyl, diphenylamino, hydrogen, halogen, C1-C4 alkyl, and at least one of R ₁ -R ₄ is Substituted or unsubstituted acridinyl, phenothiazinyl, carbazolyl, diphenylamino, R ₅ and R ₆ are hydrogen, halogen, C1-C4 alkyl, said substitution is C1-C4 alkyl substitution, Phenyl substituted or alkylphenyl substituted.

Among them, R ₅ and R ₆ are hydrogen; one of R ₁ and R ₂ is hydrogen, and the other is substituted or unsubstituted acridinyl, phenothiazinyl, carbazolyl, diphenylamino; R ₃ and R _{One of 4} is hydrogen and the other is alkyl-substituted or unsubstituted acridinyl, phenothiazinyl, carbazolyl, diphenylamino.

Wherein R ₁ is the same as R ₃ and R ₂ is the same as R ₄ .

R ₁ and R ₃ are hydrogen, and R ₂ and R ₄ are C1-C4 alkyl or phenyl substituted or unsubstituted acridinyl or carbazolyl.

The compound of formula (I) is a compound of the following structure

It should be particularly pointed out that the above-mentioned organic layers can be according to requirements, and these organic layers do not need to exist in each layer.

The compound of the formula (I) is a material of a light emitting layer.

The total thickness of the organic layer of the electronic device of the present invention is 1-1000 nm, preferably 1-500 nm, and more preferably 5-300 nm.

The organic layer may be formed into a thin film by evaporation or spin coating.

As mentioned above, the compounds of formula (I) of the present invention are as follows, but are not limited to the enumerated structures:

The method for preparing the above bipolar material includes the following preparation steps: firstly reacting a dihalogen-substituted arylethylenedione (a) with a substituted or unsubstituted arylenehydrazine (b) under the condition of sodium tert-butoxide to obtain an imine Intermediate solution, filtered solution with suction, the solvent was removed under reduced pressure, acetic acid was added, and ammonium acetate was added and heated under reflux. This gave 3,5,6- (substituted or unsubstituted phenyl) -1,2,4-triazine (c). Finally 3,5,6-tri (halogen-substituted benzene) -1,2,4-triazine (c) and substituted or unsubstituted acridinyl, phenothiazinyl, carbazolyl, diphenylamino (d) The palladium-catalyzed Buchwald reaction is used to obtain the bipolar host material.

Compound a is obtained by halogenated benzaldehyde through a benzoin condensation reaction and then oxidized; compound b is prepared by hydrazation of a substituted methyl benzoate; compound d is obtained on the market.

Experiments show that the compound of the present invention has a higher glass transition temperature than the commonly used host material CBP, and the present invention significantly improves the thermal stability of the host material. The electroluminescent device prepared by using the bipolar host material of the present invention has a lower lighting voltage than a device prepared by the widely used host material CBP, and at the same current density, the current efficiency is higher, which is more conducive to carrier injection. And the transmission balance, the device prepared using the organic material of the invention has better electroluminescence performance, and more in line with the requirements of host materials for high-performance organic semiconductor devices.

10‧‧‧ glass substrate

20‧‧‧Anode

30‧‧‧ hole injection layer

40‧‧‧ hole transport layer

50‧‧‧Light emitting layer

60‧‧‧ hole blocking layer

70‧‧‧ electron transmission layer

80‧‧‧ electron injection layer

90‧‧‧ cathode

Fig. 1 is a DSC curve of compound 4; Fig. 2 is a device structure diagram of the present invention, where 10 represents a glass substrate, 20 represents an anode, 30 represents a hole injection layer, 40 represents a hole transport layer, and 50 represents light emission Layers, 60 for the hole blocking layer, 70 for the electron transport layer, 80 for the electron injection layer, and 90 for the cathode; and FIG. 3 is a graph of current density-current efficiency of the device of the example and the device of the comparative example. (Where 4 is an example and 5 is a comparative example)

The present invention is described in further detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

Example 1

(1) Synthesis of 5,6-bis (4-bromophenyl) -3-phenyl-1,2,4-triazine (c1)

The synthetic route is as follows:

The specific synthetic steps are: weigh out sodium tert-butoxide (1.44g, 15mmol) and add it to dry tetrahydrofuran (50mL), add phenylhydrazine (1.36g, 10mmol) (b1), and then add 1,2-bis (4- Bromophenyl) ethyl-1,2-dione (3.68 g, 10 mmol) (a1) (prepared by benzoin condensation and reoxidation of 4-bromobenzaldehyde), stirred for 1 hour, suction filtered and washed with dichloromethane to obtain filtrate. After removing the solvent on a rotary evaporator, 20 mL of glacial acetic acid and ammonium acetate (7.7 g, 100 mmol) were added, and the mixture was heated to reflux and stirred for 4 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, and a yellow solid precipitated. The sand core funnel was filtered with suction and washed with water. Silica gel column chromatography gave 3 g of a yellow solid. Yield: 64%.

(2) 9,9 '-((3-phenyl-1,2,4-triazine-5,6-diyl) bis (4,1-phenylene)) bis (9H-carbazole) ( 1) Synthesis

The synthetic route is as follows:

The specific synthetic steps are as follows: 5,6-bis (4-bromophenyl) -3-phenyl-1,2,4-triazine (0.93g, 2mmol) ( c1 ), carbazole (0.67g, 4mmol) ), Pd ₂ (dba) ₃ (0.19 g, 0.2 mmol), NaOtBu (0.77 g, 8 mmol) in a 25 mL three-necked flask, and nitrogen was changed three times. Tri-tert-butylphosphine toluene solution (0.16 g, 0.4 mmol) was dissolved in 10 mL of dry toluene and poured into a reaction flask. The temperature was increased to reflux for 16 hours. After the reaction was completed, a 5% sodium bisulfite solution was added and the mixture was extracted with dichloromethane. The organic layers were combined and dried over anhydrous magnesium sulfate. Sand core funnel was filtered, the solvent was spin-dried, n-hexane: dichloromethane = 2: 1 was used as eluent, and the silica gel column was purified to obtain 1.27 g of a yellow powder solid. Yield: 93.5%. Product identification information is as follows: ¹ H NMR (400MHz, CDCl ₃ ) δ = 8.80-8.69 (m, 2 H), 8.16 (d, J = 7.7Hz, 4 H), 8.06 (d, J = 8.4Hz, 2 H ), 7.99 (d, J = 8.4Hz, 2 H), 7.73 (d, J = 8.4Hz, 4 H), 7.67-7.57 (m, 3 H), 7.56-7.48 (m, 4 H), 7.44 ( t, J = 7.6 Hz, 4 H), 7.32 (dt, J = 3.2, 7.2 Hz, 4 H) ppm. ¹³ C NMR (100 MHz, CDCl ₃ ) = 161.6, 154.8, 154.6, 140.4, 140.2, 139.3, 134.6 , 134.2,134.2,131.9,131.6,131.1,129.0,128.5,127.0,126.7,126.3,126.2,123.9,123.7,120.6,120.5,120.5,120.5,109.7ppm.Ms (ESI: Mz 640) (M + 1)

Example 2

(1) Synthesis of 5,6-bis (3-bromophenyl) -3-phenyl-1,2,4-triazine (c2)

The synthetic route is as follows:

The specific synthetic steps are: weigh out sodium tert-butoxide (1.44g, 15mmol) and add it to dry tetrahydrofuran (50mL), add phenylhydrazine (1.36g, 10mmol) (b1), and then add 1,2-bis (3- Bromophenyl) ethyl-1,2-dione (3.68 g, 10 mmol) (a2) (prepared by 3-bromobenzaldehyde's benzoin condensation and reoxidation), stirred for 1 hour, suction filtered and washed with dichloromethane to obtain filtrate. After removing the solvent on a rotary evaporator, 20 mL of glacial acetic acid and ammonium acetate (7.7 g, 100 mmol) were added, and the mixture was heated to reflux and stirred for 4 hours. After the reaction was completed, excess acetic acid was spin-dried under reduced pressure. Silica gel column chromatography gave 3.2 g of a pale yellow oil. Yield: 69%.

(2) 10,10 '-((3-phenyl-1,2,4-triazine-5,6-diyl) bis (3,1-phenylene)) bis (9,9-dimethyl Of acryl) (4)

The synthetic route is as follows:

Weigh 5,6-bis (3-bromophenyl) -3-phenyl-1,2,4-triazine (0.93g, 2mmol) ( c2 ), 9,9-dimethylacridine (0.84g , 4 mmol) ( d2 ), Pd ₂ (dba) ₃ (0.19 g, 0.2 mmol), NaOtBu (0.77 g, 8 mmol) in a 25 mL three-necked flask, and nitrogen was changed three times. Tri-tert-butylphosphine toluene solution (0.16 g, 0.4 mmol) was dissolved in 10 mL of dry toluene and poured into a reaction flask. The temperature was increased to reflux for 16 hours. After the reaction was completed, a 5% sodium bisulfite solution was added and the mixture was extracted with dichloromethane. The organic layers were combined and dried over anhydrous magnesium sulfate. Sand core funnel was filtered, the solvent was spin-dried, n-hexane: dichloromethane = 2: 1 was used as eluent, and the silica gel column was purified to obtain 1.3 g of a yellow powder solid. It was dissolved in 10 mL of dichloromethane, 20 mL of ethyl acetate was added, and the crystal was placed in a refrigerator at 5 ° C. to obtain 1.1 g of pale yellow crystals. Yield: 74%. Product identification information is as follows: ¹ H NMR (400 MHz, CDCl ₃ ) δ = 8.81-8.67 (m, 2 H), 8.03 (d, J = 8.4 Hz, 2 H), 7.97 (d, J = 8.3 Hz, 2 H ), 7.67-7.56 (m, 3 H), 7.52-7.38 (m, 8 H), 6.92 (dt, J = 3.4, 6.4Hz, 8 H), 6.34 (dd, J = 3.5, 5.9Hz, 4 H ), 1.68 (s, 12H) ppm. ¹³ C NMR (100 MHz, CDCl ₃ ) δ = 161.8, 155.1, 155.0, 144.0, 142.8, 140.6, 140.5, 135.3, 135.3, 134.6, 132.5, 132.1, 132.0, 131.8, 131.2 , 130.7, 130.4, 129.0, 128.6, 126.5, 125.3, 125.2, 121.2, 121.0, 114.3, 114.0, 36.1, 36.1, 31.6, 31.0, 30.9, 22.7, 14.2

Example 3

Glass transition temperature test:

The glass transition temperature of compound 4 was tested by differential scanning calorimetry (DSC) at a heating and cooling rate of 20 ° C / min under nitrogen protection. The glass transition temperature T _g of Compound 4 was measured to be 129 ° C. (FIG. 1). The glass transition temperature of CBP reported in the literature is only 62 ° C.

It can be seen that the compound in the present invention has a higher glass transition temperature than the commonly used host material CBP, and the present invention significantly improves the thermal stability of the host material.

Example 4

Preparation of organic electroluminescent device

Device structure is ITO / MoO ₃ (10nm) / NPB (40nm) / Compound 4 : Ir (ppy): (7wt%, 30nm) / BCP (10nm) / Alq ₃ (30nm) / LiF (1nm) / AL (100nm )

The device preparation method is described as follows: See Figure 2

First, the transparent conductive ITO glass substrate (including 10 and 20) was processed according to the following steps: washed with detergent solution, deionized water, ethanol, acetone, deionized water in advance, and then treated with oxygen plasma for 30 seconds.

Then, MoO _{3 having} a thickness of 10 nm was evaporated on ITO as the hole injection layer 30.

Then, a 40 nm-thick NPB was evaporated on the hole injection layer as the hole transport layer 40.

Then, 30 nm thick compound 4 : Ir (ppy): (7 wt%) was evaporated on the hole transport layer as the light emitting layer 50.

Then, a 10-nm-thick BCP was evaporated on the light-emitting layer as the hole blocking layer 60.

Then, Alq _{3 having} a thickness of 30 nm was evaporated on the hole blocking layer as the electron transporting layer 70.

Then, Alq _{3 having} a thickness of 1 nm was evaporated as an electron injection layer 80 on the electron transport layer.

Finally, 100 nm thick aluminum was evaporated on the electron injection layer as the device cathode 90.

The prepared device has a start-up voltage of 4.1V, a current density of 3.33mA / cm ² at a current of 1000nit, a current efficiency of 30.33cd / A, a luminous efficiency of 14.16lm / W, a green emission CIEx of 0.303, and a CIEy The current is 0.626; at a working current density of 20 mA / cm ² , the brightness is 4836 cd / m ² , the current efficiency is 24.18 cd / A, the green emission CIEx is 0.299, and the CIEy is 0.626.

Comparative example

Preparation of organic electroluminescent device

Device structure is ITO / MoO ₃ (10nm) / NPB (40nm) / CBP: Ir (ppy): (7wt%, 30nm) / BCP (10nm) / Alq ₃ (30nm) / LiF (1nm) / AL (100nm)

The method is the same as that in Example 4, except that a commercially available compound CBP is used as a host material to produce an electroluminescent organic semiconductor diode device for comparison.

The prepared device has a starting voltage of 6.2V, a current density of 3.89mA / cm ² at a current of 1000nit, a current efficiency of 25.52cd / A, a luminous efficiency of 6.85lm / W, a green emission CIEx of 0.312, and a CIEy of 0.612; Under the working current density of 20mA / cm ² , the brightness is 4579cd / m ² , the current efficiency is 22.9cd / A, the green emission CIEx is 0.311, and the CIEy is 0.612.

Experiments show that the electroluminescent device prepared by using the bipolar host material of the present invention has a lower lighting voltage than a device prepared by the widely used host material CBP, and at the same current density, the current efficiency is higher, which is more conducive to loading. The balance of the injection and transmission of the electrons, the device prepared by using the organic material of the invention has better electroluminescence performance, and is more in line with the requirements of the host material of the high-performance organic semiconductor device.

Claims (10)

An organic electroluminescent device includes a cathode, an anode, and an organic layer. The organic layer is one or more of a hole transport layer, a hole blocking layer, an electron transport layer, and a light emitting layer. The organic layer has the formula (I ) The compound of the structure, Wherein, R ₁ -R ₄ represent substituted or unsubstituted acridinyl, phenothiazinyl, carbazolyl, diphenylamino, hydrogen, halogen, C1-C4 alkyl, and at least one of R ₁ -R ₄ is Substituted or unsubstituted acridinyl, phenothiazinyl, carbazolyl, diphenylamino, R ₅ and R ₆ are hydrogen, and the substitution is C1-C4 alkyl substitution, phenyl substitution, or alkylphenyl To replace. The organic electroluminescent device according to item 1 of the scope of the patent application, wherein one of R ₁ and R ₂ is hydrogen, and the other is a substituted or unsubstituted acridinyl, phenothiazinyl, carbazolyl, Diphenylamino; one of R ₃ and R ₄ is hydrogen, and the other is alkyl-substituted or unsubstituted acridinyl, phenothiazinyl, carbazolyl, diphenylamino. According to the organic electroluminescence device described in item 2 of the patent application scope, wherein R ₁ is the same as R ₃ and R ₂ is the same as R ₄ . According to the organic electroluminescence device described in item 3 of the scope of patent application, R ₁ and R ₃ are hydrogen, and R ₂ and R ₄ are C1-C4 alkyl or phenyl substituted or unsubstituted acridinyl and carbazolyl . According to the organic electroluminescence device according to item 2 of the scope of patent application, the organic layer has a compound of the following structure: According to the organic electroluminescence device described in item 5 of the scope of patent application, the organic layer has a compound having the following structure: According to the organic electroluminescence device described in item 1 of the scope of patent application, the compound of formula (I) is a material of a light emitting layer. According to the organic electroluminescence device described in item 1 of the scope of patent application, the total thickness of the organic layer is 1-1000 nm. According to the organic electroluminescence device described in item 8 of the scope of patent application, the total thickness of the organic layer is 5-300 nm. According to the organic electroluminescence device according to claim 1, the organic layer is formed into a thin film by evaporation or spin coating.