KR20140023589A - Phosphorescent host compound and organic electroluminescent device using the same - Google Patents

Abstract

The present invention provides a phosphorescent host compound which is represented by following chemical formula, wherein G is a hetero ring which includes at least one sulfur and at least one nitrogen or is selected from a hetero ring compound which includes at least one sulfur in which at least one oxygen is substituted.

Description

Phosphorescent host compound and Organic electroluminescent device using the same

The present invention relates to a phosphorescent host material and an organic electroluminescent device using the same. More specifically, the present invention relates to a phosphorescent host material having a high triplet energy and an organic electroluminescent device driven by low voltage by using the same.

In recent years, the demand for a flat display device having a small space occupancy has been increased due to the enlargement of the display device. The technology of the organic electroluminescent device, which is also called an organic light emitting diode (OLED) And several prototypes have already been announced.

An organic electroluminescent device is a device that injects electric charge into a light emitting material layer formed between an electron injecting electrode (cathode) and a hole injecting electrode (anode) to form an electron and a hole. The device can be formed on a flexible transparent substrate such as a plastic substrate and can be driven at a lower voltage (10 V or less) than a plasma display panel or an inorganic electroluminescence (EL) It also has the advantage of low power consumption and excellent color. In addition, organic electroluminescence (EL) devices can display three colors of green, blue, and red, making them a next-generation rich color display device and attracting a lot of interest from many people. Here, the process of fabricating the organic electroluminescent device will be briefly described.

(1) First, a material such as indium tin oxide (ITO) is deposited on a transparent substrate to form an anode.

(2) A hole injecting layer (HIL) is formed on the anode. The hole injection layer mainly comprises 4,4'-bis [N- (4- {N, N-bis (3-methylphenyl) amino} phenyl] -N- phenylamino] biphenyl 10 nm to 60 nm thick.

(3) Next, a hole transport layer (HTL) is formed on the hole injection layer. This hole transport layer is formed by depositing about 30nm to 60nm 4,4'-bis [N- (1-naphtyl) -N-phenylamino] -biphenyl (NPD) represented by the following formula (1-2).

(4) Next, an emitting material layer (EML) is formed on the hole transport layer. At this time, a dopant is added as needed. For example, Bis (N-carbazolyl) biphenyl (CBP) represented by the following Chemical Formula 1-3 is a red dopant represented by the following Chemical Formula 1-4, and Bis (2-phenylquinoline) (acetylacetonate) iridium (III) (Ir ( It can be formed by doping about 5-10% of phq) 2acac) or by doping tris ((3,5-difluoro-4-cyanophenyl) pyridine) irdium (III) (FCNIr) which is a blue dopant represented by the following Chemical Formula 1-5. Can be. Alternatively, N-Methylquinacridone (MQD) may be doped with 8-droxyquinolatealuminum (Alq3) with a dopant of 1 to 3 wt% to form a thickness of about 300 μs.

(5) Next, an electron transport layer (ETL) and an electron injecting layer (EIL) are successively formed on the light emitting material layer. On the other hand, in the case of using CBP having excellent hole characteristics, Bis (2-methyl-8-quinolinolato-N1, O8)-(1,1'-Biphenyl-4-olato) aluminum (Balq) is used to trap triplet excitons in the light emitting layer. A hole blocking layer may be formed to have a thickness of about 5 nm between the emission layer and the electron transport layer.

(6) Next, a cathode is formed on the electron injection layer, and finally, a protective film is formed on the cathode.

Formula 1 -One

Formula 1 -2

Formula 1 -3

Formula 1 -4

Formula 1 -5

In recent years, a phosphorescent material is used more frequently than a fluorescent material in a luminescent material layer. In the case of a fluorescent material, only about 25% of the single excitons formed in the emitter layer are used to make light, and 75% of the triplet is mostly lost to heat, while the phosphors convert both singlet and triplet to light It has a luminescent mechanism. Phosphorescent dopants generally contain heavy atoms such as Ir, Pt, and Eu in the center of organic matter, and have a high probability of electron transition from triplet to singlet.

However, since such a dopant is abruptly reduced in efficiency due to the concentration quenching phenomenon, the light emitting material layer can not be constituted by itself. Thus, a luminescent layer is formed together with the host material having higher thermal stability and higher triplet energy than the dopant.

In the light emitting process of an organic electroluminescent device including a phosphor, a hole injected from an anode and electrons injected from a cathode are encountered in a host material of the light emitting layer, and a single-excited exciton formed in the host is a single- Energy transition occurs, and the triplet exciton becomes energy transfer to the triplet of the dopant. Since the excitons transferred to a single term of the dopant are again transferred to the triplet of the dopant, all the excitons are terminated at the triplet level of the dopant. The excitons thus formed transition to the ground state and emit light.

In this case, the triplet energy of the host material must be greater than the triplet energy of the dopant for efficient energy transfer to the dopant. However, referring to FIG. 1, since CBP, which is widely used as a host material, is less than the triplet energy of the well-known Firpic phosphorescent dopant since the triplet energy is 2.6 eV, an energy reverse transition phenomenon occurs from the host material to the dopant. Inefficient Therefore, the development of a novel phosphor having a triplet energy of 2.6 eV or more is required.

The present invention is to provide a phosphorescent host material having a triplet energy of 2.6 eV or more, to prevent the problem of lowering the luminous efficiency of the organic light emitting device.

In addition, by using such a phosphorescent host material, it is an object to improve the efficiency of the organic light emitting device.

In order to solve the above problems, the present invention is represented by the following formula, G is a heterocyclic ring containing at least one sulfur and at least one nitrogen or a heterocyclic ring containing at least one sulfur substituted with at least one oxygen. It provides a phosphorescent host material characterized by being selected from compounds.

In the phosphorescent host material of the present invention, G is selected from C5 to C18 heterocyclic compounds including S1 to S4 and N1 to N5, or C5 to C18 heterocyclic compounds including S1 to S4 substituted with O1 to O4. It is characterized by.

In the phosphorescent host material of the present invention, G is one of a plurality of materials represented by the following formula.

In the phosphorescent host material of the present invention, each of A and B is independently an aromatic group consisting of C4 to C18, a heterocyclic compound containing N1 to N5, O1 to O4, and S1 to S4 in C4 to C16, respectively or together. It is characterized by being selected.

In the phosphorescent host material of the present invention, the heterocyclic compound of A or B is characterized by being substituted by alkyl group, alkoxy group, halogen group, silyl group, deuterium, tritium and hydrogen.

In another aspect, the present invention provides a liquid crystal display comprising: a first electrode; A second electrode facing the first electrode; Located between the first and second electrodes, comprising a light emitting material layer consisting of red, green and blue light emitting material pattern, at least one of the green and blue light emitting material pattern is represented by the following formula, G is Provided is an organic electroluminescent device comprising a phosphorescent host material, characterized in that it is selected from a heterocyclic ring containing at least one sulfur and at least one nitrogen or a heterocyclic compound comprising at least one sulfur substituted with at least one oxygen. do.

In the organic light emitting device of the present invention, G is a C5 ~ C18 heterocyclic compound containing S1 ~ S4 and N1 ~ N5 or C5 ~ C18 heterocyclic compound containing S1 ~ S4 substituted with O1 ~ O4 It is characterized by being selected.

In the organic electroluminescent device of the present invention, each of A and B independently has an aromatic group consisting of C4 to C18, and a heterocyclic compound containing N1 to N5, O1 to O4, and S1 to S4 in C4 to C16, respectively or together. It is characterized in that selected from.

Since the phosphorescent host material of the present invention has a triplet energy of greater than 2.6 eV, the efficiency of the organic light emitting device can be improved.

Since the phosphorescent host material of the present invention is used in the light emitting material layer and has a greater triplet energy than that of the dopant, it is possible to prevent the problem of lowering the luminous efficiency.

In addition, due to the bipolarity characteristics, the hole and the electronic characteristics are balanced in the organic light emitting device, thereby improving the device characteristics.

In addition, by using the phosphorescent host material of the present invention having a triplet energy of greater than 2.6 eV in the light emitting material layer, the luminous efficiency of the organic light emitting diode is improved and low voltage driving is possible, thereby reducing power consumption.

1 is a PL spectrum of CBP which is a host material for a conventional organic electroluminescent device.
2A and 2B are PL spectra at room temperature and low temperature, respectively, of a phosphor for an organic light emitting display device according to an exemplary embodiment of the present invention.
3 is a schematic cross-sectional view of an organic electroluminescent device according to an embodiment of the present invention.

Hereinafter, a structure of a phosphorescent host material according to the present invention, a synthesis example thereof, and an organic light emitting display device using the same will be described.

The phosphorescent host material of the present invention is used in a green or blue light emitting material layer, and includes sulfur (S) substituted with a heterocyclic ring containing oxygen (S) and nitrogen (N) or oxygen (O) in carbazole nitrogen. The heterocyclic ring is combined to have a high triplet energy and to balance the electrical and electronic properties in the device, it is represented by the following formula (2).

(2)

In Formula 2, G is a heterocyclic ring including at least one sulfur and at least one nitrogen, or a heterocyclic ring including at least one sulfur substituted with at least one oxygen. More specifically, G may be a C5 to C18 heterocyclic compound including S1 to S4 and N1 to N5, or a C5 to C18 heterocyclic compound including S1 to S4 substituted with O1 to O4.

In addition, in Formula 2, each of A and B is independently selected from an aromatic group consisting of C4 to C18, a heterocyclic compound containing N1 to N5, O1 to O4, and S1 to S4 in C4 to C16, respectively or together. A and B may be the same or different. At this time, the heterocyclic compound may be substituted with alkyl, alkoxy, halogen, silyl, deuterium, tritium and hydrogen.

For example, G may be any one of a plurality of materials represented by the following formula (3).

(3)

In addition, each of A and B may be any one of a plurality of substances represented by Formula 4 below.

Formula 4

Such phosphorescent host material has high triplet energy by combining a heterocyclic ring containing sulfur (S) and nitrogen (N) with a heterocyclic ring containing sulfur (S) substituted with oxygen (O) to the nitrogen of carbazole. Will have In addition, by displacing the release ring containing sulfur having a strong electronic properties in the carbazole core having a strong hole properties, the phosphorescent compound has a bipolarity properties, thereby balancing the hole and electronic properties in the organic electroluminescent device, The efficiency of the organic light emitting device can be further increased.

Hereinafter, the synthesis example of the phosphorescent host material shown in the following formula (5).

Formula 5

1st Synthetic example

9- (9- (benzo [d] thiazol-2-yl) -3- (9H-carbazol-9-yl) -9H-carbazol-6-yl) -9H-carbazole represented by "A" in Chemical Formula 5 is It is synthesized by the following scheme.

(1) Synthesis of 9- (benzo [d] thiazol-2-yl) -9H-carbazole

Carbazole (5g, 29.9 mmol), 2-iodobenzo [d] thiazole (8.58 g, 32.9 mmol), CuI (0.85 g, 4.50 mmol), 1,6-diaminocyclohexane (1.02 g, 8.97 mmol), K ₃ PO ₄ ( 38 g, 179.4 mmol) and 150 mL of 1,4-dioxane were placed in a 250 mL 2-neck flask and refluxed at 100 ° C. for 24 hours. At the end of the reaction, 1,4-dioxane is removed and the resulting solids are filtered off. Recrystallization with dichloromethane and methanol afforded 9- (benzo [d] thiazol-2-yl) -9H-carbazole (6.7 g, 75%).

(2) Synthesis of 9- (benzo [d] thiazol-2-yl) -3,6-dibromo-9H-carbazole

Dissolve 9- (benzo [d] thiazol-2-yl) -9H-carbazole (5.01 g, 16.7 mmole) in 300 mL CHCl3 in a 500 mL two-neck flask. To the dissolved solution is slowly added dropwise Br2 (33.7 mmole) dissolved in CHCl ₃ for 30 minutes. After 2 hours, an aqueous thiopansulfate solution is added dropwise to the reaction solution. Recrystallization using dichloromentane and methanol afforded 9- (benzo [d] thiazol-2-yl) -3,6-dibromo-9H-carbazole (6.6 g, 87%).

(3) Synthesis of 9- (9- (benzo [d] thiazol-2-yl) -3- (9H-carbazol-9-yl) -9H-carbazol-6-yl) -9H-carbazole

9- (benzo [d] thiazol-2-yl) -3,6-dibromo-9H-carbazole (2.99g, 6.56 mmol), carbazole (2.40 g, 14.4 mmol), CuI (15 mol%), 1, 6-diaminocyclohexane (30 mol%), K3PO4 (6.0 eq) and 150 mL of 1,4-dioxane were added to a 250 mL 2-neck flask and refluxed at 100 ° C. for 24 hours. At the end of the reaction, 1,4-dioxane is removed and the resulting solids are filtered off. Recrystallized from dichloromethane and methanol to give 9- (9- (benzo [d] thiazol-2-yl) -3- (9H-carbazol-9-yl) -9H-carbazol-6-yl) -9H-carbazole (73%) was obtained.

2nd to 5th Synthetic example

"B", "C", "D", "E" in the formula (5) using "b", "c", "d", "e" of the formula (6) instead of "a" of the scheme The phosphors indicated were synthesized.

6

Photoluminescence (PL) spectra at room temperature (rt) and low temperature (77K, lt) of the phosphorescent host material of the present invention shown in Chemical Formula 5 were measured and shown in FIGS. 2A and 2B, and the conventional phosphorescent host material CBP and Physical properties of the phosphorescent host material of the present invention are summarized in Table 1 below.

Band-gap (E _g ) [eV] Triplet state (E _T ) [eV] CBP 2.62 A 2.99 2.80 B 3.20 2.76 C 3.27 2.90 D 3.12 2.85 E 3.45 2.87

As shown in Figures 2A, 2B and Table 1, the phosphorescent host material of the present invention has a triplet energy of at least 2.75 eV. Therefore, since it has a triplet energy higher than CBP used as a host material of the conventional light emitting material layer and is larger than 2.7 eV, which is a triplet energy of a commonly used dopant, it prevents an energy reverse transition phenomenon from the host material to the dopant. can do. Therefore, the luminous efficiency is improved.

An embodiment of an organic light emitting display device including the phosphorescent host material is illustrated in FIG. 3.

As shown, the organic electroluminescent device includes first and second substrates (not shown) facing each other, and an organic light emitting diode (E) formed between the first and second substrates (not shown) .

The organic light emitting diode E includes a first electrode 110 serving as an anode, a second electrode 130 serving as a cathode, and an organic emission layer 120 formed between the first and second electrodes 110 and 130. [ ).

The first electrode 110 is made of a relatively high work function material such as indium-tin-oxide (ITO), and the second electrode 130 is made of a material having a relatively low work function value, For example, aluminum (Al) or an aluminum alloy (AlNd). In addition, the organic light emitting layer 120 has red, green, and blue organic light emission patterns.

The organic light emitting layer 120 has a multi-layer structure, that is, a hole injection layer (HTL) 121, a hole transporting layer (HIL) in order to maximize the luminous efficiency sequentially from the first electrode 110 ) 122, an emitting material layer (EML) 123, an electron transporting layer 124, and an electron injection layer 125.

Here, the light emitting material layer of at least one of the green and blue organic light emitting patterns includes a phosphorescent host material represented by Chemical Formula 2. In other words, it has a structure in which a heterocyclic ring containing sulfur (S) and nitrogen (N) or a heterocyclic ring containing sulfur (S) substituted with oxygen (O) is combined with nitrogen of carbazole, thus having high triplet energy. By using the phosphorescent host material, the luminous efficiency of the organic electroluminescent device is improved.

In addition, by displacing the release ring containing sulfur having a strong electronic properties in the carbazole core having a strong hole properties, the phosphorescent compound has a bipolarity properties, thereby balancing the hole and electronic properties in the organic electroluminescent device, The efficiency of the organic light emitting device can be further increased.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It can be understood that

110: first electrode 120: organic light emitting layer
121: Hole injection layer 122: Hole transport layer
123: light emitting material layer 124: electron transport layer
125: electron injection layer 130: second electrode

Claims (8)

A phosphorescent host material represented by the following formula, wherein G is a heterocyclic ring containing at least one sulfur and at least one nitrogen or a heterocyclic compound including at least one sulfur substituted with at least one oxygen.

The method of claim 1,
G is a phosphorescent host material, characterized in that selected from C5 ~ C18 heterocyclic compounds containing S1 ~ S4 and N1 ~ N5 or C5 ~ C18 heterocyclic compounds containing S1 ~ S4 substituted with O1 ~ O4.
The method of claim 1,
G is a phosphorescent host material, characterized in that one of a plurality of materials represented by the following formula.

The method of claim 1,
A and B are each independently selected from aromatic groups consisting of C4 to C18, heterocyclic compounds containing N1 to N5, O1 to O4, and S1 to S4 in C4 to C16, respectively or together. .
5. The method of claim 4,
A heterocyclic compound which is A or B is phosphorescent host material, characterized in that substituted by alkyl group, alkoxy group, halogen group, silyl group, deuterium, tritium and hydrogen.
A first electrode;
A second electrode facing the first electrode;
Located between the first and second electrodes, and comprises a light emitting material layer consisting of a red, green and blue light emitting material pattern,
At least one of the green and blue light emitting material patterns is represented by the following formula, and G is a release ring including at least one sulfur and at least one nitrogen or a release including at least one sulfur substituted with at least one oxygen. An organic electroluminescent device comprising a phosphorescent host material, characterized in that selected from cyclic compounds.

The method according to claim 6,
G is an organic electroluminescent device characterized in that it is selected from C5 ~ C18 heterocyclic compounds containing S1 ~ S4 and N1 ~ N5 or C5 ~ C18 heterocyclic compounds containing S1 ~ S4 substituted with O1 ~ O4 .
The method according to claim 6,
A and B are each independently selected from an aromatic group consisting of C4 to C18, heterocyclic compounds containing N1 to N5, O1 to O4, S1 to S4 in C4 to C16, or together. device.

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