KR20050057769A - Red organic electroluminescent materials - Google Patents

Abstract

The present invention relates to a novel red fluorescent substance of the general formula (I), a method for preparing the same, and an organic electroluminescent device comprising the same as a light emitting material. The red fluorescent substance according to the present invention has excellent stability, The organic electroluminescent device comprising mainly red color and can be expressed up to the deep red region.

(I)

 N is 1 to 2,

R ¹ means that the methyl group or the whole molecule can be symmetric ,

R ² and R ³ represent the same or different alkyl groups or aryl groups.

Description

Red Organic Electroluminescent Materials

The present invention relates to a novel compound having a red light emission property, a method for preparing the same, and an organic electroluminescent device including the same. Until now, as a red fluorescent dye for organic electroluminescent devices, light emitting pigments of the following structural formulas, widely known as DCM, have been used.

However, the conventional DCM-based pigments are low in heat resistance and are mainly expressed in the orange region when used as the light emitting layer doping material of the organic electroluminescent device, and in order to obtain a deep red color, the doping concentration must be increased, and as a result, the luminous efficiency is lowered. This has been pointed out.

Accordingly, it is an object of the present invention to provide a red fluorescent substance capable of expressing red spirits to deep reds with excellent stability, a method for preparing the same, and an organic electroluminescent device including the same.

In order to achieve the above object, the present invention provides a novel red fluorescent substance of the general formula (I).

(I)

 N is 1 to 2,

R ¹ means that the methyl group or the whole molecule can be symmetric ,

R ² and R ³ represent the same or different alkyl groups or aryl groups.

In addition, the present invention provides a method for preparing the compound of Formula (I) and an organic electroluminescent device comprising the compound in a light emitting layer.

Hereinafter, the present invention will be described in more detail.

The synthesis process of the novel red fluorescent substance of the general formula (I) according to the present invention is represented as follows.

In the above formula, n, R ¹ , R ² , and R ³ are each as defined above.

Specifically, the compound of formula (I) is a pyran derivative compound and a general formula of the thiobarbitic acid group of the general formula (II) substituted in the presence of an amine compound such as piperidine in an alcohol solvent such as methanol, ethanol, propanol It can synthesize | combine by making the aldehyde derivative compound of (III) react, or it can synthesize | combine acetic anhydride by heat-reacting in presence of phosphoric acid with a solvent. The above reaction can be synthesized using about equimolar amounts of reactants at a low temperature of about 5 degrees Celsius to a temperature at which the solvent is boiling.

The pyran compounds of the general formula (II) used as starting materials can be synthesized from thiobarbitic acid derivatives of the general formula (IV) and pyran derivatives of the general formula (V).

By using the equimolar amount of the compound of formula (IV) and the compound of formula (V) to reflux in acetic anhydride, which can advance the dehydration reaction in the forward direction, the compound of formula (II) can be synthesized in high yield.

The organic electroluminescent device comprising the compound of formula (I) of the present invention comprises a hole transporting layer on an ITO glass substrate, a light emitting layer and an electron transport layer containing the compound of formula (I) of the present invention as a dopant in a conventional manner. After laminating | stacking in order, it can obtain by laminating | stacking the metal electrode for cathodes. The compound of general formula (I) of the present invention is used as a red or deep red light emitting doping material in the light emitting layer.

The hole transport layer, the light emitting layer and the electron transport layer of the organic electroluminescent device may be deposited by wet coating or vacuum deposition such as spin coating, doctor blading, roll printing or screen printing, and the metal electrode may be coated by vacuum deposition. .

The material used for the formation of the hole transport layer and the electron transport layer may be any known one, and examples of the metal electrode for the cathode may include magnesium, silver, calcium, aluminum, lithium, and alloys thereof.

The novel red fluorescent substance according to the present invention has excellent stability, and the organic electroluminescent device including the same in the light emitting layer has a light emission color expressed from red to deep red region.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the method presented in the Examples.

Preparation Example: Preparation of Pyran Derivative Compound of Formula (II)

0.40 g (3.2 mmole) of 2,6-dimethyl-r-pyrone and 0.64 g (3.2 mmmole) of 1,3-diethyl-2-thiobarbituric acid were added to 40 mL of acetic anhydride and the temperature was raised to reflux for 12 hours. After cooling to room temperature, excess water was added to give a solid, which was filtered, washed and dried to obtain a pale yellow solid compound (0.76 g, 77.5%).

Example 1 Compound 1 Synthesis

306.4 mg (1.0 mmole) of the pyran derivatives synthesized above and 273.3 mg (1.0 mmole) of N, N-diphenylbenzaldehyde were added to 40 mL of methanol and cooled to 5 ° C while stirring. 0.12 mL (1.2 mmole) of piperidine was added at 5 ° C and stirred at that temperature for 16 hours.

 The solvent was distilled off under reduced pressure and the column was purified by silica gel to obtain 253 mg of Compound 1 as a red fluorescent substance (yield 45.0%).

The fluorescence spectrum measured by dissolving the material in chloroform showed a maximum fluorescent wavelength of 615 nm (red) and is shown in FIG. 5.

1 H-NMR (400 MHz, CDCl ₃ ): δ = 8.9 (s, 1H), 8.7 (s, 1H), 6.7-7.5 (m, 16H), 4.6 (q, 4H), 2.5 (s, 3H), 1.3 (t, 6H).

FT-IR (KBr): 2977, 2927, 1639, 1589, 1529, 1465, 1382, 1282, 1106, 935, 754 cm ^-1 .

Example 2: Compound 2 Synthesis

0.20 g of Compound 2 was obtained as a red solid, except that 149.2 mg of N, N-dimethylbenzaldehyde was used instead of N, N-diphenylbenzaldehyde (yield 46.9%).

The fluorescence spectrum measured by dissolving the material in chloroform showed a maximum fluorescence wavelength of 620 nm (red) and is shown in FIG. 6.

1 H-NMR (400 MHz, CDCl ₃ ): δ = 8.9 (s, 1H), 8.7 (s, 1H), 7.4 (m, 3H), 6.6 (m, 3H), 4.6 (q, 4H), 3.1 ( s, 3H), 2.5 (s, 3H), 1.3 (t, 6H)

FT-IR (KBr): 3122, 2979, 2925, 1639, 1610, 1533, 1457, 1382, 1299, 1105, 937 cm ^-1

^{Example 3: Compound 3 Synthesis}

0.22 g of Compound 3 was obtained as a red solid, except that 175.2 mg of 4- (dimethylamino) cinnamaldehyde was used instead of N, N-diphenylbenzaldehyde (yield 47.5%).

The fluorescence spectrum measured by dissolving the material in chloroform showed a maximum fluorescent wavelength of 640 nm (deep red) and is shown in FIG. 7.

1 H-NMR (400 MHz, CDCl ₃ ): δ = 9.6 (d, 1H), 8.9 (s, 1H), 8.7 (s, 1H), 7.4 (m, 3H), 6.9 (d, 1H), 6.6 ( d, 2H), 6.3 (d, 1H), 4.6 (q, 4H), 3.1 (s, 3H), 2.5 (s, 3H), 1.4 (t, 6H)

FT-IR (KBr): 3120, 2979, 2929, 1673, 1591, 1513, 1465, 1382, 1106, 933 cm ^-1

^{Example 4: Compound 4 Synthesis}

The reaction was carried out in the same manner as in Example 1 except that the reaction was carried out at a boiling temperature of methanol instead of the reaction at 5 ° C to obtain 0.12 g of Compound 4 in a red solid form (yield 29.4%).

The fluorescence spectrum measured by dissolving the material in chloroform showed a maximum fluorescence wavelength of 640 nm (deep red) and is shown in FIG. 8.

1 H-NMR (400 MHz, CDCl ₃ ): δ = 8.9 (s, 2H), 6.8-7.6 (m, 13H), 6.6 (d, 2H), 4.6 (q, 4H), 1.3 (t, 6H)

FT-IR (KBr): 3038, 2980, 2922, 1631, 1579, 1451, 1374, 1272, 1106, 690 cm ^-1

^{Example 5 Fabrication of Organic Electroluminescent Device}

Compound 2 obtained in Example 2 was used as a doping material for a light emitting layer using tris (8-hydroquinolinato) aluminum (Alq3) as a host material, to produce an organic electroluminescent device according to a conventional method.

First, α-NPD was formed in a hole transport layer having a thickness of 50 nm on the ITO layer formed on a glass substrate under a vacuum of 10 ^-6 Torr. The light emitting layer was formed by evaporating to a thickness of 300 mW. On the light emitting layer, Alq3 was formed to a thickness of 200 mW using an electron transport layer, and aluminum was then deposited as a cathode metal at a thickness of 2000 mW at a rate of 10 mW / sec under a vacuum of 10 ^-6 Torr to fabricate an organic electroluminescent device.

The structure of the device is shown in FIG. 9, and the applied voltage and emission luminance characteristic curves are shown in FIG. The device of the present invention emits light stably in the red region and can implement a device of high brightness having a brightness of at least 12,000 cd / m ² or more.

The red fluorescent dye for organic electroluminescence of the present invention has excellent stability and can emit light from red to deep red, and thus may be applied to the development of organic photoconductors, solar cells, and the like.

1 to 4 show NMR spectra of the novel red phosphors obtained in Examples 1 to 4 according to the present invention, respectively.

5 to 8 are fluorescence spectra of chromoform solutions of the novel red phosphors obtained in Examples 1 to 4 according to the present invention, respectively.

9 is a view showing the structure of an organic electroluminescent device manufactured in Example 5 of the present invention;

10 is a voltage-luminance characteristic curve of an organic electroluminescent device including a compound according to the present invention.

Claims (4)

New red fluorescent substance of the following general formula (I). (I)  N is 1 to 2, R ¹ means that the methyl group or the whole molecule can be symmetric , R ² and R ³ represent the same or different alkyl groups or aryl groups. The red phosphor according to claim 1, which has a structure of any one of the following structural formulas. A process for producing a red fluorescent substance of the general formula (I) according to claim 1, comprising reacting a pyran derivative of the general formula (II) and an aldehyde derivative of the general formula (III) in the presence of a base in an alcohol solvent. In the above formula, n, R ¹ , R ² , R ³ are as defined in claim 1. An organic electroluminescent device having a light emitting layer comprising a red fluorescent substance according to claim 1.