JP2006137956A - Luminescent material and organic thin film el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blue luminescent material suppressed in crystallization by introducing various substituent in an anthracene ring, capable of using as a luminescent layer of a separate thin film, usable as a host substance of other blue luminescent materials and having excellent heat resistance and temporal stability. <P>SOLUTION: The luminescent material comprises a derivative having as a base structure an anthracene ring substituted with a substituent such as H, an alkyl and an alkoxy, and a substituent such as naphthyl, anthryl, phenanthryl, biphenyl and terphenyl which may have a substituent selected from an alkyl and an alkoxy, and the like. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light emitting material, and relates to an organic light emitting material applicable to a light emitting material of a display element typified by an organic thin film EL element or the like, or a fluorescent material by ultraviolet excitation.

  The organic thin film EL element is a light emitting element in which an organic material utilizing an electroluminescence (hereinafter referred to as EL) phenomenon is a light emitting source, and is expected as a next generation self-luminous flat display element or a flat light source. This organic EL device research originated from an element using a single crystal of anthracene in the 1960s. After research using various organic thin films, C.E. W. Tang et al. Reported a revolutionary stacked element (Japanese Patent Laid-Open Nos. 59-194393, 63-264692, 63-295695, Applied Physics Letter Vol. 51, No. 12). No. 913 (1987) and Journal of Applied Physics Vol. 65, No. 9, No. 3610 (1989), etc.), active research and development activities have been developed. ing.

  C. described above. W. The organic thin film EL element produced by Tang et al. Has an element configuration in which an anode, an organic hole injection transport layer, an organic light emitting layer, and a cathode are laminated on a transparent substrate. As a method for producing the element, a transparent conductive film made of a composite oxide of indium and tin (hereinafter referred to as ITO) is used as an anode on a transparent insulating substrate such as glass or a resin film by an evaporation method or a sputtering method. A single layer film or a multilayer film of an organic hole injecting and transporting material typified by copper phthalocyanine or a tetraaryldiamine compound is formed thereon by a vapor deposition method with a thickness of about 100 nm or less as an organic hole injecting and transporting layer. Form. Next, an organic phosphor material such as tris (8-quinolinol) aluminum (hereinafter referred to as Alq) is formed by vapor deposition as an organic light emitting layer with a thickness of about 100 nm or less. On this organic light emitting layer, an alloy such as aluminum: lithium (Al: Li), magnesium: silver (Mg: Ag) is formed as a cathode having a thickness of about 200 nm by a co-evaporation method to produce an organic thin film EL device. Is done.

In the organic thin film EL device fabricated as described above, by applying a DC low voltage between the electrodes, positive charges (holes) are emitted from the anode, and negative charges (electrons) are emitted from the cathode. Injected into the layer. The injected holes and electrons move in the organic thin film by the applied electric field and recombine in the thin film with a certain probability. The energy released at this time excites the organic phosphor. The formed excitons emit light to the outside by the proportion of the emission quantum yield of the organic phosphor and return to the ground state. An element utilizing fluorescence emitted from excitons of the organic phosphor is an organic thin film EL element. Note that the DC low voltage applied to this element is usually about 10 to 30 V, and an EL element using a Mg: Ag alloy for the cathode has a luminance of 10000 cd / m ² or more.

  However, most of the light emitting materials used in the organic thin film EL elements described above have a green or yellow emission color, and there are limited reports of EL elements using blue and red light emitting materials necessary for full color display. Yes.

Blue light emitting EL elements using organic materials are disclosed in W.W. Starting from an element using an anthracene crystal of Helfrich et al. (Physical Review Letter, Vol. 14, p. 229 (1965)), in recent years, an element having a luminance of 100 cd / m ² or more using tetraphenylbutadiene as a light emitting material is used. A report (Japanese Patent Laid-Open No. 59-194393) and a device that emits blue-green light with a luminance of 800 cd / m ² or more using a distyrylbenzene derivative as a light-emitting material have been reported (Japanese Patent Publication No. 7-119407). ). In addition, blue light emission of 2500 cd / m ² or more has been reported from an element using an acridone-based compound as a light emitting material (Japanese Patent Laid-Open No. 8-67873).

  Such blue light-emitting materials have few reports compared to green and yellow light-emitting materials, and it can be said that the research and development of materials are delayed.

  As described above, few materials have been reported as blue light-emitting materials in organic thin-film EL elements, and the required characteristics are not always satisfied. Currently, development of a highly durable light-emitting material having excellent blue light emission efficiency is expected.

  Anthracene itself can be expected as a blue light emitting material because it emits blue fluorescence. However, anthracene is easily crystallized and is difficult to use as a thin film for a display element. For this reason, it is necessary to introduce a substituent into the anthracene ring to suppress crystallization. By selecting a substituent to be introduced, an anthracene derivative emitting blue fluorescence with improved thermal stability and stability over time when formed into a thin film can be expected. Furthermore, by introducing a substituent having a charge transporting property, it can be expected as a light emitting material or a charge transporting material which also has a charge transporting property. By introducing a substituent, it becomes possible to use a film of an anthracene derivative alone as a light emitting layer, and it can also be expected as a host material for other blue light emitting materials.

  The object of the present invention is to suppress the crystallization by introducing various substituents into the anthracene ring, and it can be used as a single thin film for a light emitting layer, or as a host material for other blue light emitting materials. An object is to provide an amorphous blue light-emitting material that has excellent heat resistance and stability over time.

The present invention provides a light emitting material which is a derivative having an anthracene ring as a basic skeleton and represented by the following general formula (1).

(In the formula, R _{1 to} R ₈ represent a hydrogen atom, an alkyl group, or an alkoxy group. R ₉ and R ₁₀ represent a naphthyl group or anthryl group that may have a substituent selected from an alkyl group and an alkoxy group. Represents a group, a phenanthryl group, a biphenyl group, or a terphenyl group.)

  The present invention provides a light emitting material having an anthracene ring as a basic skeleton and represented by the following general formula (2).

(Wherein R _{1 to} R ₈ represent a hydrogen atom, an alkyl group, or an alkoxy group. R _{9 to} R ₁₂ represent a phenyl group or naphthyl which may have a substituent selected from an alkyl group and an alkoxy group. Group, anthryl group, phenanthryl group, biphenyl group, and terphenyl group.)

  The present invention provides a luminescent material represented by the following general formula (3) in a luminescent material having an anthracene ring as a basic skeleton.

(Wherein R _{1 to} R ₈ represent a hydrogen atom, an alkyl group, or an alkoxy group. R ₉ represents a heterocyclic compound typified by an oxazole ring, an oxadiazole ring, or a thiophene ring. R ₁₀ represents (It represents a phenyl group, a naphthyl group, or a biphenyl group which may have a substituent selected from an alkyl group and an alkoxy group.)

  The present invention provides a luminescent material represented by the following general formula (4) in the luminescent material having an anthracene ring as a basic skeleton described in the general formula (3).

(In the formula, R _{1 to} R ₈ represent a hydrogen atom, an alkyl group, or an alkoxy group. R ₉ and R ₁₀ represent a phenyl group or naphthyl which may have a substituent selected from an alkyl group and an alkoxy group. Represents a biphenyl group.

  As described above, according to the present invention, it is difficult to crystallize with high heat resistance and high temporal stability by forming a light emitting site using a material having an anthracene ring with various substituents as a basic skeleton. An amorphous thin film can be obtained. Thereby, a light emitting element with high thermal stability and durability can be expected.

  The blue light-emitting material of the present invention is obtained by reacting an anthraquinone derivative with a halogenated aryl compound and subjecting it to dehydration cyclization. For example, an anthraquinone derivative and a halogenated aryl compound are reacted with butyllithium in a diethyl ether solvent, and the resulting compound is synthesized by dehydration cyclization using potassium iodide or sodium phosphinate under acidic conditions. be able to.

  The blue light-emitting material having an anthracene ring as the basic skeleton of the present invention can be expected to emit blue fluorescence because the anthracene ring itself emits blue fluorescence, and the emission efficiency can be increased by the introduced substituent. Further, by introducing a substituent, it is possible to improve thermal stability and stability over time when used as a thin film. Furthermore, it is also possible to obtain a material that simultaneously functions as a charge transport material by introducing a substituent having charge transport properties.

In the blue light-emitting material of the present invention represented by the general formulas (1) to (4), R _{1 to} R ₈ include a hydrogen atom, a methyl group, an ethyl group, an isopropyl group, a tertiary butyl group, a cyclohexyl group, a trimethyl group, Specific examples of alkyl groups typified by fluoromethyl groups (here, saturated cyclic hydrocarbon groups are also included in alkyl groups), methoxy groups, ethoxy groups, isopropoxy groups, alkoxy groups typified by tertiary butoxy groups, etc. Can be mentioned. R _{1 to} R ₈ may be the same as or different from each other.

In the blue light-emitting material of the present invention represented by the general formula (1), R _{9 to} R ₁₀ are naphthyl groups, anthryl groups, phenanthryl groups, which may have a substituent selected from an alkyl group and an alkoxy group, Biphenyl group and terphenyl group can be mentioned.

In the blue light-emitting material of the present invention represented by the general formula (2), R _{9 to} R ₁₂ may have a phenyl group, a naphthyl group, an anthryl group, which may have a substituent selected from an alkyl group and an alkoxy group, Examples include a phenanthryl group, a biphenyl group, and a terphenyl group.

In the blue light emitting material of the present invention represented by the general formula (3), R ₉ represents a heterocyclic compound containing at least one hetero atom. Representative examples of the heterocyclic compound include a thiophene ring, an oxazole ring, and an oxadiazole ring. R ₁₀ includes a phenyl group, a naphthyl group, a biphenyl group and the like which may have a substituent selected from an alkyl group and an alkoxy group.

In the blue light-emitting material of the present invention represented by the general formula (4), R _{9 to} R ₁₀ represent a phenyl group, a naphthyl group, or a biphenyl group that may have a substituent selected from an alkyl group and an alkoxy group. Show. Specific examples of the luminescent material represented by the general formulas (1), (2), (3), and (4) include the following.

  The blue light-emitting material of the present invention described above can be used by mixing with other charge transport materials, light-emitting materials, and the like.

Examples of the present invention will be described below.
(Example 1) In a nitrogen atmosphere, 8.16 g of 2-bromobiphenyl was added to diethyl ether, and 25 ml (1.60 mol / l) of n-butyllithium was added dropwise while cooling with ice. After stirring for 1 hour after the dropping, a diethyl ether solution added with 3.20 g of 2-tertiarybutylanthraquinone was added dropwise and stirred for 2 hours. After completion of the reaction, pure water was added to the reaction solution, and the product obtained by extracting the organic layer was purified by recrystallization using toluene as a good solvent and hexane as a poor solvent. Next, acetic acid was added to the purified compound, and potassium iodide and sodium phosphinate were sequentially added thereto, followed by stirring and refluxing for 1 hour. The obtained product was purified by recrystallization using toluene / hexane to obtain a white powdery anthracene derivative represented by the following chemical formula.

  From the mass spectrometric measurement (using JMN SX102 manufactured by JEOL Ltd.) of the anthracene derivative obtained as described above, an ion peak at m / z 538 corresponding to the molecular ion of the target compound was detected. , Formation of an anthracene derivative (Chemical Formula 7) was confirmed. FIG. 1 shows an IR spectrum of an anthracene derivative (using FTIR-8100M manufactured by Shimadzu Corporation, KBr tablet method).

  As a result of measuring the glass transition point (Tg) of this anthracene derivative using a DSC220C manufactured by Seiko Denshi Kogyo Co., Ltd. under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min, it was found to be 74 ° C. Since this anthracene derivative (Chemical Formula 7) did not show a crystallization peak, an amorphous thin film exhibiting high temporal stability can be expected. A deposited film made of this anthracene derivative was formed on quartz glass, and the ionization potential was measured using a surface analyzer (AC-1 manufactured by Riken Keiki Co., Ltd.). As a result, it was found to be 5.97 eV. It was.

  As a result of measuring fluorescence (PL) spectrum of anthracene derivative (using RF5000 manufactured by Shimadzu Corporation) using a thin film similar to the above, this anthracene derivative emits blue fluorescence having peaks at 423 and 444 nm. The material was confirmed.

(Example 2) In a nitrogen atmosphere, 10.3 g of 9-bromophenanthrene was added to diethyl ether, and 28 ml of n-butyllithium was added dropwise while cooling with ice. After stirring for 1 hour after the dropping, a diethyl ether solution added with 4.00 g of 2-tertiary butylanthraquinone was added dropwise and stirred for 2 hours. After completion of the reaction, pure water was added to the reaction solution, and the product obtained by extracting the organic layer was purified by recrystallization using toluene and hexane as a poor solvent.

  Acetic acid was added to the purified compound, then potassium iodide and sodium phosphinate were added, and the mixture was stirred and refluxed for 1 hour. The obtained product was purified by recrystallization using toluene to obtain a white powdery anthracene derivative represented by the following chemical formula.

  The anthracene derivative obtained as described above was subjected to mass spectrometry measurement, and an ion peak at m / z 586 corresponding to the molecular ion of the target compound was detected. Thus, the production of the anthracene derivative was confirmed. FIG. 2 shows an IR spectrum (KBr tablet method) of an anthracene derivative.

  As a result of measuring the glass transition point (Tg) of this anthracene derivative under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min, it was found to be 190 ° C. As a result of comparison with the anthracene derivative of Example 1, it was confirmed that Tg greatly changed depending on the substituent to be introduced.

  A vapor deposition film made of this anthracene derivative was formed on quartz glass, and the ionization potential was measured using a surface analyzer, and it was found to be 5.90 eV.

  As a result of measuring the fluorescence (PL) spectrum of the anthracene derivative using the same thin film as described above, it was found that this anthracene derivative is a material that emits blue fluorescence having a peak at 443 nm.

Example 3 In a nitrogen atmosphere, 7.53 g of 5′-bromo-1,1 ′: 3 ′, 1 ″ -terphenyl was added to diethyl ether, and 18 ml of n-butyllithium was added dropwise while cooling with ice. After the dropwise addition, the mixture was stirred for 1 hour, and then a diethyl ether solution added with 2.11 g of 2-tertiarybutylanthraquinone was added dropwise and stirred for 2 hours.After completion of the reaction, pure water was added to the reaction solution, and the organic layer was extracted. The product thus obtained was recrystallized and purified using toluene as a good solvent and hexane as a poor solvent.

  Acetic acid was added to the purified compound, then potassium iodide and sodium phosphinate were added, and the mixture was stirred and refluxed for 1 hour. The obtained product was purified by recrystallization using toluene / hexane to obtain a white powdery anthracene derivative represented by the following chemical formula.

  Mass spectrometry analysis of the anthracene derivative obtained as described above was performed, and an ion peak at m / z 690 corresponding to the molecular ion of the target compound was detected, so the production of the anthracene derivative was confirmed. FIG. 3 shows the NMR spectrum of the anthracene derivative (Chemical Formula 9).

  As a result of measuring the glass transition point (Tg) of the anthracene derivative under a nitrogen atmosphere under a temperature increase rate of 10 ° C./min, it was found to be 130 ° C. Since this anthracene derivative did not show a crystallization peak, an amorphous thin film exhibiting high temporal stability can be expected.

  A vapor deposition film made of this anthracene derivative was formed on quartz glass, and the ionization potential was measured using a surface analyzer, and it was found to be 5.83 eV.

  As a result of measuring the fluorescence (PL) spectrum of the anthracene derivative using the same thin film as described above, it was found that this anthracene derivative is a material emitting blue fluorescence having a peak at 453 nm.

Example 4 In a nitrogen atmosphere, 9.83 g of 2- (3-bromophenyl) -5- (2-naphthyl) -1,3,4-oxadiazole was added to THF, and n-butyllithium was added thereto. 22 ml was added dropwise. After stirring for 1 hour after dropping, 2.65 g of 2-tertiary butylanthraquinone was added dropwise and stirred for 2 hours. The obtained product was purified by recrystallization using toluene as a good solvent and hexane as a poor solvent.

  Acetic acid was added to the purified compound, then potassium iodide and sodium phosphinate were added, and the mixture was stirred and refluxed for 1 hour. The obtained product was purified by recrystallization using toluene / hexane to obtain a white powdery anthracene derivative represented by the following chemical formula.

  The anthracene derivative obtained as described above was subjected to mass spectrometric measurement, and an ion peak at m / z 774 corresponding to the molecular ion of the target compound was detected. Thus, production of the anthracene derivative was confirmed. FIG. 4 shows the NMR spectrum of the anthracene derivative.

  As a result of measuring the glass transition point (Tg) of this anthracene derivative under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min, it was found to be 147 ° C. Since this anthracene derivative did not show a crystallization peak, an amorphous thin film exhibiting high temporal stability can be expected.

  A vapor deposition film made of this anthracene derivative was formed on quartz glass, and the ionization potential was measured using a surface analyzer, and it was found to be 5.88 eV.

  As a result of measuring the fluorescence (PL) spectrum of the anthracene derivative using the same thin film as described above, it was found that the anthracene derivative is a material emitting blue fluorescence having a peak at 445 nm.

  The blue light-emitting material having the anthracene ring as a basic skeleton in the above examples can change the glass transition point and crystallinity by introducing a substituent, has excellent thermal stability, and is stable over time. A good thin film can be obtained.

Explanatory drawing which shows IR spectrum of the luminescent material concerning Example 1 of this invention. Explanatory drawing which shows IR spectrum of the luminescent material concerning Example 2 of this invention. Explanatory drawing which shows the NMR spectrum of the luminescent material concerning Example 3 of this invention. Explanatory drawing which shows the NMR spectrum of the luminescent material concerning Example 4 of this invention.

Claims (4)

A light-emitting material having the anthracene ring as a basic skeleton and represented by the following general formula (1):

(In the formula, R _{1 to} R ₈ represent a hydrogen atom, an alkyl group, or an alkoxy group. R ₉ and R ₁₀ represent a naphthyl group or anthryl group that may have a substituent selected from an alkyl group and an alkoxy group. Represents a group, a phenanthryl group, a biphenyl group, or a terphenyl group.) A light emitting material having an anthracene ring as a basic skeleton and represented by the following general formula (2):

(Wherein R _{1 to} R ₈ represent a hydrogen atom, an alkyl group, or an alkoxy group. R _{9 to} R ₁₂ represent a phenyl group or naphthyl which may have a substituent selected from an alkyl group and an alkoxy group. Group, anthryl group, phenanthryl group, biphenyl group, and terphenyl group.) A light emitting material having an anthracene ring as a basic skeleton and represented by the following general formula (3):

(Wherein R _{1 to} R ₈ represent a hydrogen atom, an alkyl group, or an alkoxy group. R ₉ represents a heterocyclic compound typified by an oxazole ring, an oxadiazole ring, or a thiophene ring. R ₁₀ represents (It represents a phenyl group, a naphthyl group, or a biphenyl group which may have a substituent selected from an alkyl group and an alkoxy group.) A light emitting material having an anthracene ring as a basic skeleton according to claim 3, wherein the light emitting material is represented by the following general formula (4).

(In the formula, R _{1 to} R ₈ represent a hydrogen atom, an alkyl group, or an alkoxy group. R ₉ and R ₁₀ represent a phenyl group or naphthyl which may have a substituent selected from an alkyl group and an alkoxy group. Represents a biphenyl group.)

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