JPH028287A - Organic fluorescent substance for el element of organic thin film - Google Patents

Abstract

PURPOSE:To obtain the title fluorescent substance usable for inexpensive full color indication of large area, useful for a light source of plane, display, etc., consisting of a metallic complex containing a compound of 8-hydroxyquinoline with formed condensed ring as a ligand. CONSTITUTION:The title fluorescent substance consists of a metallic complex comprising one or more of Al, Be, Mg, Ca, Zn, Cd, Cr, Ni, Bi, In, Tl, Ti, Sn, V, Rh, lead, iron, silver, copper, Sr, Ba, Sc, Ca, Y and Co, containing a compound of 8-hydroxyquinoline with one or more formed condensed rings as a ligand.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an organic phosphor for organic thin-film EL devices, and more specifically, an organic phosphor for organic thin-film EL devices used in planar light sources, displays, etc. It's about the body.

[Prior Art] EL (electroluminescent) devices using organic materials as raw materials are attracting attention as they can realize inexpensive large-area full-color display devices. Although this 11 EL element was actively researched for a period of time, it was not put into practical use because its brightness was lower than that of ZnS:Hn-based inorganic thin film EL elements and its characteristics were severely degraded. Furthermore, the fact that the driving voltage was as high as about 100 V DC was also an obstacle to practical application.

However, recently, a new type of organic thin film EL device with a two-layered organic thin film structure has been reported and is attracting strong interest (Applied Physics Letters, Vol. 51, 91).
3 pages, 1987). According to reports, this organic thin film EL device has a two-layer structure using a fluorescent metal chelate complex for the organic phosphor thin film layer 4 and an amine material for the charge injection layer 3, as shown in FIG. It is disclosed that by sandwiching this between a transparent electrode 2 and a back electrode 5, bright green light emission was obtained, and several hundred c
A brightness of d/m2 is obtained. Also, the maximum luminous efficiency is 1.
5 Im/W, which has performance close to the practical level.

[Problems to be Solved by the Invention] As mentioned above, an organic thin film EL device having a multilayer structure of an organic phosphor thin film and a charge injection layer emits very bright green light, and this device is characterized by: The organic phosphor thin film material is tris(8-oxyquinolinato)aluminum. As described above, there are organic phosphors for organic thin-film El elements that can provide a practical brightness level for green light emission. In order to display full color, it is necessary to emit light in red and blue, but it has been difficult to emit light in various colors at a practical brightness level with the organic phosphors developed to date.

For example, anthracene has been reported as a material that exhibits other luminescent colors, but the luminescence of organic thin film EL devices using this as an organic phosphor was very weak (for example, Thin Solid Films, Vol. 94, 171 pages, 1
982, and Japanese Applied Physics, vol. 27.

(269 pages, 1988). Therefore, although a new organic phosphor is absolutely necessary for the practical application of full-color organic thin film EL devices, there has been no suitable material among conventional organic phosphors.

The present invention has been made in response to the conventional circumstances as described above, and an object of the present invention is to provide an organic phosphor for an organic thin film El element that is capable of full-color display at a practical level.

[Means for Solving the Problems] The present invention provides an organic film comprising a metal mirror having as a ligand a compound in which at least one condensed ring is formed on 8-hydroxyquinoline. This is an organic phosphor for EL devices.

Here, the central metal constituting the metal complex is aluminum, beryllium, magnesium, calcium, zinc,
Cadmium, chromium, nickel, bismuth, indium, thallium, titanium, tin, vanadium, rhodium,
It is preferably at least one of lead, iron, silver, copper, scandium, barium, scandium, gallium, yttrium, and cobalt.

The reason why a metal complex with 8-hydroxyquinoline as a ligand exhibits particularly strong light emission is because the lone pair of electrons on the nitrogen of 8-hydroxyquinoline flows into the metal, and the lowest excited singlet state and lowest excited triplet state of the complex. very pure π−π−
This is because it is close to an excited state. Therefore, if the complex structure portion of 8-hydroxyquinoline and metal is maintained, the luminescence intensity in EL emission can be maintained. Based on the above research results, the present inventors searched for a new organic phosphor for organic thin-film EL devices, and found that an organic phosphor characterized by the above structure can change the emission wavelength without changing the emission intensity. It has been discovered that the emission wavelength of a metal complex containing 8-hydroxyquinoline as a ligand can be changed to a longer wavelength side.

As the organic light-emitting substance for the organic thin film EL device of the present invention, a metal complex having aluminum as the central metal is desirable. This is because aluminum complexes have a particularly strong luminescence intensity. However, by changing the central metal, it is also possible to roughly or subtly change the basic emission wavelength.

Next, some general formulas are listed as examples of organic phosphors according to the present invention.

(In the formula, M represents an n-valent metal ion, and X represents an n/m-valent anion.) In the present invention, the substances used as the charge injection layer are:
For example, examples of organic compounds include aromatic amines and aromatic polyamine compounds for the hole transfer layer, and compounds having a quinone structure, tetracyanoquinodimethane, tetracyanoethylene, and the like for the electron transfer layer.

Further, examples of the charge injection layer of an inorganic compound include P-type or N-type IV group, ■-V group, II-Vl group compound semiconductors, and the like. The organic substance or inorganic substance used as the charge injection layer can be selected from among these compounds as necessary.

[Example 1 The present invention will be explained below using Examples.

Example 1 Three times the equivalent amount of 1-aza-10-hydroxy-anthracene dissolved in ethanol was dropped into an aqueous solution of aluminum nitrate nonahydrate. After stirring this solution for 3 hours,
Dilute sodium hydroxide was added dropwise until f) H was 8. The precipitate that had precipitated in this case was filtered and then thoroughly washed with dilute aqueous sodium hydroxide solution. The obtained compound was thoroughly dried at 70°C under reduced pressure. The solution of the metal complex thus obtained exhibited fluorescence centered at 510°.

Then, 800 g of 1,1-bis(4-N,N-ditolylaminophenyl)cyclohexane was evaporated as a charge injection layer on the transparent electrode formed on the glass substrate, and then the cyclohexane obtained by the above procedure was deposited. 500 people deposited the metal complex as an organic phosphor layer. A magnesium/aluminum alloy was deposited thereon as a negative electrode. Obtained organic thin film E
When we investigated the light emitting characteristics of the L element, we found that it was 0.05 mW/Cm.
Emission of 2 was obtained at 3 mA/cm2. The emitted light color was slightly yellow-green, and could be shifted to the longer wavelength side compared to the case where an organic fluorescent material of tris(8-oxyquinolinato)aluminum was used.

Reference Example A 3-fold equal amount of 8-quinolitool dissolved in ethanol was dropped into an aqueous solution of aluminum nitrate nonahydrate. After stirring this solution for 3 hours, dilute sodium hydroxide was added to p
The mixture was added dropwise until H reached 8.

The precipitate that had precipitated in this case was filtered and then thoroughly washed with dilute aqueous sodium hydroxide solution. The obtained compound was thoroughly dried at 70°C under reduced pressure. The solution of the metal complex obtained in this way shows fluorescence centered at 475nllll, and the physical property values are the literature values (R, Ba1lardir
i et al., Inorganic Chemistry, Volume 25, 3
p. 858, 1986).

After depositing 800 1,1-bis(4-N,N-ditolylaminophenyl)cyclohexane as a charge injection layer on a transparent electrode formed on a glass substrate, the metal complex obtained by the above procedure. was deposited by 500 people as an organic phosphor layer. A magnesium/aluminum alloy was deposited thereon as a negative electrode. When the emission characteristics of the obtained organic thin film EL device were investigated, it was found that the emission of 0.05 mW/Cm2 was 3
mA/cm2 was obtained. The emitted light color was green.

Example 2 Three times the equivalent amount of 12-aza-11-hydroxynaphthacene dissolved in ethanol was dropped into an aqueous solution of aluminum nitrate nonahydrate. After stirring this solution for 3 hours, dilute sodium hydroxide was added dropwise until the pH reached 8. The precipitate that had precipitated in this case was filtered and then thoroughly washed with dilute aqueous sodium hydroxide solution. The obtained compound was thoroughly dried at 70°C under reduced pressure.

Then, 800 1,1-bis(4-N,N-ditolylaminophenyl)cyclohexane was deposited as a charge injection layer on the transparent electrode formed on the glass substrate, and then the cyclohexane obtained by the above procedure was 50 using a metal mirror as an organic phosphor layer
0 people were deposited. On top of that, magnesium/
An aluminum alloy was deposited. When the light emitting characteristics of the obtained organic thin film EL device were investigated, 1 of 0.05 mW/cm2 was obtained at 3 mA/cm2. The luminescent color was orange.

Example 3 Three times the equivalent amount of 13-aza-14-hydroxypentacene dissolved in ethanol was dropped into an aqueous solution of aluminum nitrate nonahydrate. After stirring this solution for 3 hours, dilute sodium hydroxide was added dropwise until the pH reached 8. The precipitate that had precipitated in this case was filtered and then thoroughly washed with dilute aqueous sodium hydroxide solution. The obtained compound was thoroughly dried at 70°C under reduced pressure.

Next, 800% of N,N"-metamethylphenylbenzidine was vapor-deposited as a charge injection layer on the transparent electrode formed on the glass substrate, and then 500% of the metal complex obtained by the above procedure was deposited as an organic phosphor layer. On top of that, a magnesium/aluminum alloy was deposited as a negative electrode.When the luminescent properties of the obtained organic thin film EL device were investigated, light emission of 0.04 mW/cm2 was obtained at 3 mA/cm2. .The luminescent color was red.

Example 4 Three times the equivalent amount of 1-aza-10-hydroxyanthracene dissolved in ethanol was dropped into an aqueous solution of bismuth nitrate pentahydrate. After stirring this solution for 3 hours, diluted sodium hydroxide was added dropwise until l)H was 8. The precipitate that had precipitated in this case was filtered and then thoroughly washed with dilute aqueous sodium hydroxide solution. The obtained compound was thoroughly dried at 70°C under reduced pressure.

800 nm of N,N-metamethylphenylbenzidine was deposited as a charge injection layer on a transparent electrode formed on a glass substrate, and then the metal complex obtained by the above procedure was deposited as an organic phosphor layer for 500 nm. Deposited. On top of that, a magnesium/silver alloy was deposited as a negative electrode. When the luminescent properties of the obtained organic thin film EL device were investigated, it was found that 0.04 m
Emission of W/cm2 was obtained at 3 mA/cm2. The emitted light color was a slightly yellowish green.

[Effects of the Invention] As explained above, if the organic phosphor for organic thin film EL devices according to the present invention is used, the emission wavelength can be changed without changing the good luminous efficiency. It is extremely useful for producing full color images. As described above, the present invention makes it possible to raise the organic thin film EL device to a practical level, making it possible to provide an inexpensive, large-area, full-color display device, and its industrial value is high.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a typical organic thin film EL device. 1... Glass substrate 2... Transparent electrode 3... Charge injection layer 4... Organic phosphor thin film layer 5... Back electrode

Claims (2)

[Claims] (1) An organic phosphor for an organic thin film EL device, which is composed of a metal complex having as a ligand a compound in which at least one condensed ring is formed on 8-hydroxyquinoline. (2) The central metals constituting the metal complex are aluminum, beryllium, magnesium, calcium, zinc, cadmium, chromium, nickel, bismuth, indium,
thallium, titanium, tin, vanadium, rhodium, lead,
The organic phosphor for an organic thin film EL device according to claim 1, which is at least one of iron, silver, copper, strontium, barium, scandium, gallium, yttrium, and cobalt.