JP2015153768A - Fluorine-substituted phenyl pyridine derivative, electron transport material comprising the same, and organic electroluminescent element using the fluorine-substituted phenyl pyridine derivative - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a novel fluorine-substituted phenyl pyridine derivative that maintains high triplet energy while exhibiting electron transport characteristics, is also excellent in solubility to an organic solvent and electron injection properties and is useful for a highly efficient phosphorescent organic EL element; an electron transport material comprising the fluorine-substituted phenyl pyridine derivative; and an organic EL element using the fluorine-substituted phenyl pyridine derivative.SOLUTION: A fluorine-substituted phenyl pyridine derivative represented by the following general formula (1) is used for an organic EL element. (In the formula (1), R-Reach independently represent hydrogen or fluorine.)

Description

  The present invention relates to a novel fluorine-substituted phenylpyridine derivative, an electron transport material comprising the same, and an organic electroluminescence device (hereinafter abbreviated as an organic EL device) using the same.

The organic EL has been put into practical use for some products, but further enhancement of the efficiency of the element is one of the important issues for application to the large display and lighting fields. In particular, in order to realize white light emission with high color purity and high efficiency, there is a problem of improving the efficiency and extending the life of the blue organic EL element.
In order to solve such problems, attention has been focused on phosphorescent organic EL elements that can achieve a four-fold higher efficiency than conventional fluorescent elements.

In the phosphorescent organic EL device, development of a material having a high triplet level is essential. On the other hand, there are very few electron transport materials having a high triplet level.
As electron transport materials having a high triplet level, dipyridylphenyl derivatives such as B3PyPB shown below are known (for example, see Patent Document 1).

Japanese Patent No. 5063992

  However, the dipyridylphenyl derivative as described above is not suitable for application to an organic EL device because the solubility in an organic solvent is remarkably lowered due to the substitution position of nitrogen and crystallizes.

  Therefore, in order to further increase the efficiency of the organic EL device, it has a high triplet level, a high electron transporting property and a high electron injecting property, and it can be applied to a coating type organic EL device. There is a demand for an electron transport material having excellent properties.

  The present invention has been made to solve the above-described problems, and maintains high triplet energy while exhibiting electron transport properties, and is excellent in solubility in an organic solvent and electron injectability. It is an object of the present invention to provide a novel fluorine-substituted phenylpyridine derivative useful for a phosphorescent organic EL device, an electron transport material comprising the same, and an organic EL device using the same.

  The fluorine-substituted phenylpyridine derivative according to the present invention is represented by the following general formula (1).

In the formula (1), R ^{1 to} R ¹⁵ are each independently hydrogen or fluorine.
The fluorine-substituted phenylpyridine derivative having the above structure has a high triplet level, a high electron transporting property and a high electron injecting property, and is excellent in solubility in an organic solvent.

  The present invention also provides an electron transport material comprising the fluorine-substituted phenylpyridine derivative.

Moreover, according to the present invention, there is provided an organic EL device characterized in that the fluorine-substituted phenylpyridine derivative is used.
By using the fluorine-substituted phenylpyridine derivative according to the present invention, it is possible to produce an organic EL device by low voltage driving and a coating process.

The novel fluorine-substituted phenylpyridine derivative according to the present invention has a high electron transport property, a high triplet energy, and is excellent in solubility in an organic solvent and an electron injection property, and a phosphorescent organic EL device, It is particularly suitable as an electron transport material for blue phosphorescent organic EL devices.
Therefore, by using the fluorine-substituted phenylpyridine derivative according to the present invention, the organic EL element can be driven at a low voltage, and the organic EL element can be produced by a coating process.

It is the schematic sectional drawing which showed typically an example of the layer structure of the organic EL element which concerns on this invention.

Hereinafter, the present invention will be described in more detail.
The fluorine-substituted phenylpyridine derivative according to the present invention is a compound represented by the general formula (1).
In the formula (1), R ^{1 to} R ¹⁵ are each independently hydrogen or fluorine.
Such a fluorine-substituted phenylpyridine derivative is a novel compound and is characterized by having a fluorine-substituted aromatic hydrocarbon that imparts improved solubility in an organic solvent and electron injection properties. That is, the solubility in an organic solvent is improved by fluorine substitution, and the high electron injection property is improved by introducing an electron withdrawing group, so that it can be suitably used as an electron transporting material.

  Among the compounds represented by the general formula (1), typical examples include fluorine-substituted phenylpyridine derivatives as shown below.

  The method for synthesizing the fluorine-substituted phenylpyridine derivative according to the present invention as described above is not particularly limited, and for example, it can be synthesized by a method as shown in the following examples.

In addition, the organic EL device according to the present invention using the above-described fluorine-substituted phenylpyridine has a structure in which at least one organic layer is laminated between a pair of electrodes. As a specific layer structure, for example, anode / light emitting layer / cathode, anode / hole transport layer / light emitting layer / electron transport layer / cathode, or substrate 1 / anode 2 / hole as shown in FIG. Examples thereof include a transport layer 3 / light emitting layer 4 / electron transport layer 5 / electron injection layer 6 / cathode 7 structure.
Furthermore, a known laminated structure including a hole injection layer, a hole transport light emitting layer, an electron transport light emitting layer, and the like may be used.
The organic EL element according to the present invention may be an element having a multi-photon emission structure in which a plurality of light emitting units including one light emitting layer are stacked in series via a charge generation layer.

  In the organic EL element, the fluorine-substituted phenylpyridine derivative according to the present invention may be used as an organic EL material in any of the organic layers, and may be used as a hole transport material or dispersed with a light emitting material. However, it can be suitably used as an electron transport material, and enables the phosphorescent organic EL device to be driven at a low voltage.

In the organic EL element, the constituent material of each layer other than the fluorine-substituted phenylpyridine derivative according to the present invention is not particularly limited, and can be appropriately selected from known ones. Or any of a high molecular type may be sufficient.
The film thickness of each of the layers is appropriately determined depending on the situation in consideration of adaptability between the layers and the required total layer thickness, but is usually preferably in the range of 5 nm to 5 μm.

  The formation method of each of the above layers may be a dry process such as a vapor deposition method, a sputtering method, etc., but the present invention has an advantage in that it can be formed by a coating process, in particular, a spin coating method, an inkjet method, Wet processes such as casting methods, dip coating methods, bar coating methods, blade coating methods, roll coating methods, gravure coating methods, flexographic printing methods, spray coating methods, and methods using nanoparticle dispersions can be suitably applied. .

  Also, the electrode may be a known material and configuration, and is not particularly limited. For example, a so-called ITO substrate is generally used in which a transparent conductive thin film is formed on a transparent substrate made of glass or polymer, and an indium tin oxide (ITO) electrode is formed as an anode on the glass substrate. On the other hand, the cathode is composed of a metal, alloy, or conductive compound having a small work function (4 eV or less) such as Al.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not restrict | limited by the following Example.
(Synthesis of fluorine-substituted phenylpyridine derivatives)
Synthesis examples of B3PyMFB and B4PyMFB are shown below as representative examples of the fluorine-substituted phenylpyridine derivatives (BPyMFBs) according to the present invention. After synthesizing the following precursors, B3PyMFB and B4PyMFB were synthesized by reaction with pyridine boronic acid ester. Furthermore, the synthesized BPyMFBs were purified by sublimation using a sublimation purification apparatus. In addition, the target object in each process was identified by ¹ H-NMR and EI-MS.

(Synthesis Example 1) Synthesis of B3PyMFB (1-1) Synthesis of Precursor BDCPMFB

In a four-necked flask, 1.83 g (7.2 mmol) of 1,3-dibromo-5-fluorobenzene, 2.78 g (14.6 mmol) of DCPB, 8.3 g (60.1 mmol) of K ₂ CO ₃ , 2M aqueous solution, 40 ml of toluene and 20 ml of ethanol were added, and after nitrogen bubbling for 1 hour, 0.50 g (0.43 mmol) of Pd (PPh ₃ ) ₄ was added, and the mixture was refluxed for 22 hours with stirring under a nitrogen stream.
After confirming the consumption of the raw material by thin layer chromatography (TLC), the reaction mixture was returned to room temperature, a small amount of ion-exchanged water was added and stirred for 20 minutes to dissolve the precipitated salt. The reaction mixture was filtered and washed with water and methanol. The filtrate was extracted with toluene, washed with saturated brine, and dried over anhydrous magnesium sulfate. After magnesium sulfate was filtered off, the filtrate was concentrated to obtain a brown viscous body. The obtained filtrate and concentrated filtrate were each dissolved in 100 ml of toluene, suction filtered through silica gel, and washed with 100 ml of toluene. Each of the obtained solutions was concentrated and washed with methanol to obtain 2.09 g (yield 75%) of a pale yellow solid.

(1-2) Synthesis of B3PyMFB

To a four-necked flask was added 1.33 g (3.44 mmol) of BDCPMFB, 3.54 g (17.2 mmol) of 3PyDOB, 4.87 g (22.9 mmol) of K ₃ PO ₄ , 43 ml of 1,4-dioxane. After nitrogen bubbling for 1 hour, 0.064 g (0.07 mmol) of Pd ₂ (dba) _{3 and} 0.059 g (0.143 mmol) of S-Phos were added, and the mixture was refluxed for 23 hours with stirring in a nitrogen stream.
After confirming consumption of the raw material by TLC, the reaction mixture was returned to room temperature, a small amount of ion-exchanged water was added and stirred for 20 minutes to dissolve the deposited salt. Thereafter, the precipitated solid was separated by filtration and washed with water and methanol to obtain a gray solid. The filtrate was extracted with chloroform, washed with saturated brine, dried over anhydrous magnesium sulfate, filtered and concentrated to give a brown viscous body. The gray solid obtained previously by filtration was dissolved in 150 ml of chloroform under reflux, and then silica gel column chromatography (silica gel: 500 cc, developing solvent: chloroform / methanol = 200/1 (1.0 L) → 100/1. (3.0 L) → 100/5 (2.0 L)) to obtain 1.64 g (yield 86%) of a white solid.

(Synthesis Example 2) Synthesis of B4PyMFB

In a four-necked flask, 1.0 g (2.59 mmol) of BDCPMFB, 2.66 g (13.0 mmol) of 4PyDOB, 3.73 g (17.6 mmol) of K ₃ PO ₄ , 32 ml of 1,4-dioxane were added. After nitrogen bubbling for 1 hour, 0.049 g (0.053 mmol) of Pd ₂ (dba) _{3 and} 0.044 g (0.108 mmol) of S-Phos were added, and the mixture was refluxed for 61 hours with stirring under a nitrogen stream.
After confirming consumption of the raw material by TLC, the reaction mixture was returned to room temperature, a small amount of ion-exchanged water was added and stirred for 20 minutes to dissolve the deposited salt. Thereafter, the precipitated solid was separated by filtration and washed with water and methanol to obtain a gray solid. The filtrate was extracted with chloroform, washed with saturated brine, dried over anhydrous magnesium sulfate, filtered and concentrated to give a brown viscous body. The gray solid obtained by filtration in advance was dissolved in 1.0 L of a mixed solvent of chloroform / methanol (100/5) under reflux, and then the undissolved residue was filtered off. The undissolved residue was again dissolved in 1.0 L of a chloroform / methanol (100/5) mixed solvent under reflux, and the undissolved residue was filtered off. This operation was performed twice. The solution was purified by silica gel column chromatography (silica gel: 600 cc, developing solvent: chloroform / methanol = 100/5 (2.0 L) → 10/1 (2.0 L)) to obtain 0.385 g (yield 27) of a white solid. %).

  The B3PyMFBs synthesized as described above were evaluated for various properties as shown below. For comparison, the same evaluation was performed for B3PyPB.

(Thermal characteristics evaluation)
The thermal decomposition temperature (5% weight loss) T _d5 was measured by TGA. Moreover, melting | fusing point _Tm was measured by DSC.

(Optical property evaluation)
The ionization potential I _p (HOMO) was measured using a PYS (photoelectron yield spectroscopy) measurement apparatus. Further, the optical energy gap E _g was estimated from the absorption edge of the ultraviolet-visible light absorption spectrum, and the electron affinity E _a (LUMO) was calculated from the difference from the ionization potential I _p .

  The evaluation results of these thermal characteristics and optical characteristics are summarized in Table 1.

As can be seen from the results shown in Table 1, BPyMFB has a melting point higher by about 50 to 100 ° C. than B3PyPB, and is found to have excellent heat resistance.
Moreover, B3PyMFB was almost equivalent to B3PyPB in HOMO and LUMO. In contrast, B4PyMFB is deeper in both HOMO and LUMO than B3PyMFB and B3PyPB.

(Production and characteristic evaluation of organic EL elements)
An organic EL device having a structure as shown in FIG. 1 was prepared using B3PyPB, B3PyMFB, or B3PyPB: B4PyMFB at 50 wt% for the electron transport layer (ETL). The specific layer structure of the element is ITO / TAPC (40 nm) / TCTA: FIrpic 11 wt% (10 nm) / ETL (50 nm) / LiF (0.5 nm) / Al.
Note that B4PyMFB was used by being dispersed in B3PyPB because it has strong crystallinity and is crystallized by the heat of vapor deposition of metal.
The chemical formulas of TAPC, TCTA and FIrpic used in the device are shown below.

Each of the devices produced above was found to emit good blue phosphorescence.
For each element, the driving voltage, power efficiency, and external quantum efficiency were measured at emission luminances of 1 cd / m ² , 100 cd / m ² , and 1000 cd / m ² .
These measurement results are summarized in Table 2.

As can be seen from the results shown in Table 2, when B3PyMFB was used for the electron transport layer, the driving voltage at 100 cd / m ² was equivalent to that of B3PyPB.
When B4PyMFB: B3PyPB was used, the drive voltage (starting voltage) at 1 cd / m ² was lower than when B3PyPB or B3PyMFB was used. This is presumably because the electron injection property was improved by doping B4PyMFB with deep LUMO. However, since there is a difference in LUMO between B4PyMFB and B3PyPB, B4PyMFB functions as a carrier trap and transportability is lowered. Therefore, it is considered that the driving voltage is increased under a high current density (100 cd / m ² ).

  From the above evaluation results, the BPyMFBs synthesized in this example are excellent in heat resistance, and can be used as an electron transport material, whereby a blue phosphorescent material can be efficiently emitted, and an organic EL element that can be driven at a low voltage. It can be said that it can be provided.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole transport layer 4 Light emitting layer 5 Electron transport layer 6 Electron injection layer 7 Cathode

Claims (3)

A fluorine-substituted phenylpyridine derivative represented by the following general formula (1).

(In formula (1), R ^{1 to} R ¹⁵ are each independently hydrogen or fluorine.)   An electron transport material comprising the fluorine-substituted phenylpyridine derivative according to claim 1.   An organic electroluminescence device, wherein the fluorine-substituted phenylpyridine derivative according to claim 1 is used.

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