JP7477950B2 - Fused ring compound, organic electroluminescence element, display device, and lighting device - Google Patents

Description

The present invention relates to fused ring compounds, organic electroluminescence (hereinafter, electroluminescence (field emission) may be abbreviated as "EL") elements, display devices, and lighting devices.

Due to their electronic properties, fused ring compounds such as heteroacene compounds have attracted attention as functional electronic device materials. For example, these fused ring compounds are expected to be used as channel layers in transistors, and in recent years, materials that exhibit high field-effect mobility have been reported (see, for example, Non-Patent Document 1).

The above-mentioned fused ring compounds are materials that can be applied to form films, and are widely used in the channel portion of transistors, but are rarely used in organic electroluminescence (EL) devices.

The above-mentioned organic EL element has a structure in which multiple layers including a light-emitting layer are laminated between a cathode and an anode (see, for example, Patent Document 1 and Non-Patent Documents 2 to 12). The organic EL element has a structure in which multiple layers such as an electron transport layer, a light-emitting layer, and a hole transport layer are laminated between a cathode and an anode, and is divided into so-called normal structure organic EL elements in which such a laminated structure is formed on an anode placed on a substrate, and so-called inverted structure organic EL elements in which such a laminated structure is formed on a cathode placed on a substrate. As for some of the organic EL elements with an inverted structure, an organic-inorganic hybrid type (Hybrid Organic Inorganic LED: HOILED) in which some of the layers constituting the organic EL element are made of inorganic substances has been reported. The characteristic of this hybrid type element is that it uses an inorganic oxide as an electron injection layer, which allows electron injection without using an alkali metal, and has the advantage of being highly resistant to oxygen and moisture compared to ordinary organic EL elements.

In the organic EL element with the inverted structure, the electron injection layer can be formed before the light-emitting layer is formed on the substrate. Therefore, for example, even if an electron injection layer of an inorganic oxide or the like is formed using a sputtering method, the light-emitting layer is not damaged, and the organic EL element with the inverted structure is preferable for producing the hybrid type element.

The inorganic oxide layer of this inverted organic EL element is used as an electron injection layer (see, for example, Non-Patent Document 3), but the inorganic oxide layer does not inject electrons into the organic layer sufficiently. Therefore, a technique is known for improving the electron injection properties of an organic EL element by forming an electron injection layer on top of the inorganic oxide layer. For example, Non-Patent Document 12 below reports that good electron injection properties can be obtained by forming a film by coating a specific electron transport compound.

Patent No. 5124785

Hiroaki Iino and two others, Nature Communications, 6:6828, DOI:10.1038/ncomms7828 Tae Jin Park and 7 others, "Applied Physics Letters", Vol. 92, 2008, p. 113308 Woo Sik Jeon and six others, "Applied Physics Letters", Vol. 92, 2008, p. 113311 Henk J. Bolink and 3 others, "Advanced Materials", 2010, Vol. 22, pp. 2198-2201 Henk J. Bolink and two others, Chemistry of Materials, 2009, Vol. 21, pp. 439-441 Hyosung Choi and 8 others, Advanced Materials, Vol. 23, 2011, p. 2759 Yinhua Zho and 21 others, Science, Vol. 336, 2012, p. 327 Young-Hoon Kim and 5 others, "Advanced Functional Materials", 2014, DOI: 10.1002/adfm.201304163 Stephen Forfl and 4 others, Advanced Materials, 2014, DOI: 10.1002/adma.201304666 Stephen Förfl and 5 others, Advanced Materials, Vol. 26, 2014, DOI: 10.1002/adma.201400332 Peng Wei and 3 others, Journal of American Chemical Society, Vol. 132, 2010, p. 8852 Hirohiko Fukagawa and 8 others, "Advanced Materials", DOI: 10.1002/adma.201706768

The above-mentioned non-patent document 12 reports that good electron injection properties can be obtained by forming a film by coating a specific electron transport compound, but the materials that can be formed into a film by coating are limited. In addition, although it has been reported that fused ring compounds such as the above-mentioned heteroacene compounds are already suitable for film formation by coating, many fused ring compounds do not have electron transporting substituents, making it difficult to apply them to the electron injection layer of an inverted structure organic EL element. Therefore, in order to enable electron injection from fused ring compounds, it is necessary to reconsider the basic design of fused ring compounds.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fused ring compound which can be formed into a film by coating and has excellent electron injection properties.
Another object of the present invention is to provide an organic EL device using such a fused ring compound, which has a low driving voltage and excellent luminous efficiency.

The present inventors conducted extensive research into fused ring compounds that can be coated to form a film and have excellent electron injection properties, and discovered that the above-mentioned problems can be solved by connecting a fused ring compound to a compound in which a phenyl group is bonded to a triazine ring via the ortho position of the phenyl group, thereby completing the present invention.
The gist of the present invention to solve the above problems is as follows.

［式（１）中のＲの少なくとも１つは、下記式（２）：

中のＸと結合しており、
式（１）中の環Ａ及び環Ａ’は、隣接環と任意の位置で縮合する、下記式（１ａ－１）、式（１ａ－２）、式（１ａ－３）：

のいずれかで表される環構造を表し、
式（１）中のＲであって、式（２）中のＸと結合していないＲ、並びに、式（１ａ－１）及び式（２）中のＲは、独立に水素、又は炭素数１～１０のアルキル基、炭素数１～１０のアルコキシ基、炭素数１～１０のアルキルチオ基、炭素数１～１０のアルキルアミノ基、炭素数２～１０のアシル基、炭素数７～２０のアラルキル基、置換若しくは未置換の炭素数６～３０の芳香族炭化水素基、及び置換若しくは未置換の炭素数３～３０の芳香族６員複素環基からなる群から選択される１価の置換基であり、隣接する置換基が一体となって環を形成してもよく、
式（１）中のｎは、１以上４以下の整数を示す。］で表されることを特徴とする。
かかる本発明の縮合環化合物は、塗布成膜可能であり、電子注入性に優れる。 The fused ring compound of the present invention is represented by the following formula (1):

[At least one of R in formula (1) is represented by the following formula (2):

It is bonded to X in the
The ring A and the ring A′ in the formula (1) are fused to the adjacent ring at any position, and are represented by the following formulae (1a-1), (1a-2), and (1a-3):

[0036]
R in formula (1) that is not bonded to X in formula (2), and R in formulas (1a-1) and (2) are independently hydrogen or a monovalent substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, and a substituted or unsubstituted aromatic 6-membered heterocyclic group having 3 to 30 carbon atoms, and adjacent substituents may be joined together to form a ring,
In the formula (1), n represents an integer of 1 or more and 4 or less.
Such a fused ring compound of the present invention can be formed into a film by coating, and has excellent electron injection properties.

The organic electroluminescent element of the present invention is an organic electroluminescent element including a cathode, a light-emitting layer, and an anode provided in this order on a substrate,
The present invention is characterized in that a layer made of the above-mentioned fused ring compound is provided between the cathode and the light-emitting layer.
In the organic electroluminescence device of the present invention, a layer made of the fused ring compound can be formed by coating, and the driving voltage is low and the luminous efficiency is excellent.

In a preferred embodiment of the organic electroluminescent element of the present invention, the layer made of the fused ring compound contains a reducing agent. In this case, electrons are sufficiently supplied from the cathode to the light-emitting layer, so that the driving voltage of the organic electroluminescent element is further reduced and the light-emitting efficiency is further improved.

In another preferred embodiment of the organic electroluminescent element of the present invention, the layer made of the fused ring compound contains a basic compound having an acid dissociation constant pKa of 1 or more. In this case, the electron injection property of the layer made of the fused ring compound is improved, so that the driving voltage of the organic electroluminescent element is further reduced and the light-emitting efficiency is further improved.

The organic electroluminescent element of the present invention preferably has an electron injection layer made of a metal oxide between the cathode and the light-emitting layer. In this case, the storage stability and driving stability of the organic electroluminescent element are improved.

The display device of the present invention is characterized by comprising the organic electroluminescence element described above. Such a display device of the present invention has excellent driving stability.

The lighting device of the present invention is characterized by comprising the organic electroluminescence element described above. Such a lighting device of the present invention has excellent driving stability.

According to the present invention, it is possible to provide a fused ring compound which can be formed into a film by coating and has excellent electron injection properties.
Furthermore, according to the present invention, it is possible to provide an organic EL element having a so-called inverted structure, which has a cathode on a substrate, and which has a low driving voltage and excellent luminous efficiency.

1 is a schematic diagram showing an example of the structure of an organic EL element of the present invention. 1 is an NMR spectrum of a fused ring compound represented by formula (15). 1 is a graph showing the results of measuring (a) the luminance-voltage characteristics and (b) the external quantum efficiency-current density characteristics of various organic EL elements produced in Example 1 and Comparative Example 1.

The fused ring compound, organic electroluminescence device, display device, and lighting device of the present invention will be illustrated in detail below with reference to their embodiments.
In addition, a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

<Fused Ring Compound>
The fused ring compound of the present invention is characterized by being represented by the above formula (1).
The fused ring compound represented by the formula (1) has a fused ring moiety bonded to the ortho-position (X) of a phenyl group bonded to a triazine structure, and the fused ring moiety improves solubility in a solvent, so that the compound can be formed into a film by coating.
In addition, the fused ring compound represented by the formula (1) has excellent electron injection properties since the triazine structure in the formula (2) has electron transport properties.
Therefore, the fused ring compound of the present invention can be formed into a film by coating, and has excellent electron injection properties.

で表されることを特徴とする。
上記式（１）中のｎは、１以上４以下の整数を示す。ここで、ｎは１であることが好ましい。 The fused ring compound of the present invention is represented by the following formula (1):

The present invention is characterized in that it is represented by the following formula:
In the above formula (1), n represents an integer of 1 to 4. Here, n is preferably 1.

中のＸと結合しており、式（１）中のＲの１つが式（２）中のＸと結合していることが好ましい。式（２）中のＸと結合するＲは、式（１）中のいずれのＲでもよく、換言すれば、式（１）中のＲで示される任意の位置に、式（２）で表される部位がＸで結合している。
なお、上記式（１）中のＲであって、式（２）中のＸと結合していないＲは、独立に水素、又は炭素数１～１０のアルキル基、炭素数１～１０のアルコキシ基、炭素数１～１０のアルキルチオ基、炭素数１～１０のアルキルアミノ基、炭素数２～１０のアシル基、炭素数７～２０のアラルキル基、置換若しくは未置換の炭素数６～３０の芳香族炭化水素基、及び置換若しくは未置換の炭素数３～３０の芳香族６員複素環基からなる群から選択される１価の置換基であり、隣接する置換基が一体となって環を形成してもよい。 At least one of R in the above formula (1) is represented by the following formula (2):

and it is preferable that one of R in formula (1) is bonded to X in formula (2). R bonded to X in formula (2) may be any R in formula (1), in other words, the moiety represented by formula (2) is bonded via X to any position represented by R in formula (1).
In addition, R in the above formula (1) that is not bonded to X in formula (2) is independently hydrogen or a monovalent substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, and a substituted or unsubstituted aromatic 6-membered heterocyclic group having 3 to 30 carbon atoms, and adjacent substituents may be joined together to form a ring.

X in the above formula (2) is located at the ortho position of the phenyl group bonded to the triazine structure, and is bonded to R in the above formula (1) at any position.
In addition, in formula (2), the two Rs bonded to the triazine ring are independently hydrogen or a monovalent substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, and a substituted or unsubstituted aromatic 6-membered heterocyclic group having 3 to 30 carbon atoms, and adjacent substituents may be joined together to form a ring.

のいずれかで表される環構造を表す。
上記式（１ａ－１）中のＲは、独立に水素、又は炭素数１～１０のアルキル基、炭素数１～１０のアルコキシ基、炭素数１～１０のアルキルチオ基、炭素数１～１０のアルキルアミノ基、炭素数２～１０のアシル基、炭素数７～２０のアラルキル基、置換若しくは未置換の炭素数６～３０の芳香族炭化水素基、及び置換若しくは未置換の炭素数３～３０の芳香族６員複素環基からなる群から選択される１価の置換基であり、隣接する置換基が一体となって環を形成してもよい。
ここで、式（１）中の環Ａ及び環Ａ’は、式（１ａ－３）で表される環構造を表すことが好ましい。この場合、縮合環化合物からなる層の電子輸送性が向上し、駆動電圧が更に低くなり、発光効率が更に向上する。 In addition, the ring A and the ring A′ in the above formula (1) are fused to the adjacent ring at any position, and are represented by the following formulae (1a-1), (1a-2), and (1a-3):

The ring structure represented by any one of the following formulas:
R in the above formula (1a-1) is independently hydrogen or a monovalent substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, and a substituted or unsubstituted aromatic 6-membered heterocyclic group having 3 to 30 carbon atoms, and adjacent substituents may be joined together to form a ring.
Here, ring A and ring A' in formula (1) preferably represent a ring structure represented by formula (1a-3). In this case, the electron transport property of the layer made of the fused ring compound is improved, the driving voltage is further lowered, and the luminous efficiency is further improved.

R in the above formula (1) that is not bonded to X in formula (2), and R in the above formulas (1a-1) and (2) are independently hydrogen or a monovalent substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, and a substituted or unsubstituted aromatic 6-membered heterocyclic group having 3 to 30 carbon atoms, and adjacent substituents may be joined together to form a ring.
Here, examples of the alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, and a nonyl group. Examples of the alkoxy group having 1 to 10 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, and an octyloxy group. Examples of the alkylthio group having 1 to 10 carbon atoms include a methylthio group, an ethylthio group, a propylthio group, a butylthio group, a pentylthio group, a hexylthio group, a heptylthio group, an octylthio group, and a nonylthio group. Examples of the alkylamino group having 1 to 10 carbon atoms include a methylamino group, an ethylamino group, a propylamino group, a butylamino group, a pentylamino group, a hexylamino group, a heptylamino group, and an octylamino group. Examples of the acyl group having 2 to 10 carbon atoms include an acetyl group, a propionyl group, a butyryl group, etc.; examples of the aralkyl group having 7 to 20 carbon atoms include a benzyl group, a phenethyl group, a phenylpropyl group, a naphthylmethyl group, etc.; examples of the substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms include a phenyl group, a 2,6-xylyl group, a mesityl group, a duryl group, a biphenyl group, a terphenyl group, a naphthyl group, an anthryl group, a pyrenyl group, a toluyl group, an anisyl group, a fluorophenyl group, a diphenylaminophenyl group, a dimethylaminophenyl group, a diethylaminophenyl group, a pyridylphenyl group, a phenanthrenyl group, etc.; and examples of the substituted or unsubstituted aromatic 6-membered heterocyclic group having 3 to 30 carbon atoms include a pyridyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, etc.

Specific examples of the fused ring compound represented by the above formula (1) include the compounds of the following formulas (3-1) to (3-9).

The fused ring compound represented by the formula (1) can be obtained by synthesis using a known method. The synthesis method for the fused ring compound represented by the formula (1) is not particularly limited, but an example is shown below.

First, a compound represented by formula (1) in which none of the Rs are bonded to X in formula (2) (hereinafter, sometimes referred to as "a compound represented by formula (1)") is prepared, and a boryl group such as a pinacolatoboryl group is introduced into the desired position (R) of the compound to obtain an organoboron compound. Here, the reaction to introduce the boryl group can be carried out by reacting the compound represented by formula (1) with a pinacol ester such as 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (iPrOBpin) in the presence of an organolithium compound such as n-butyllithium (n-BuLi).

On the other hand, a compound represented by formula (2) in which X is a halogen element (hereinafter, sometimes referred to as "a compound represented by formula (2)") is prepared. Here, the halogen element is preferably bromine, and an example of a compound represented by formula (2) is 2-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine.

Next, the organoboron compound obtained as described above is subjected to Suzuki coupling with a compound represented by formula (2) to produce a fused ring compound represented by formula (1). Here, the Suzuki coupling of an organoboron compound having a boryl group with a compound represented by formula (2) can be carried out, for example, by reacting an organoboron compound having a boryl group with a compound represented by formula (2) in the presence of a ligand such as S-Phos {dicyclohexyl(2',6'-dimethoxy-[1,1'-biphenyl]-2-yl)phosphine}, a palladium catalyst such as palladium acetate [Pd(OAc) ₂ ], and a base such as sodium carbonate.

<Organic electroluminescence element>
The organic electroluminescent device of the present invention is an organic electroluminescent device having a cathode, an emitting layer, and an anode provided in this order on a substrate, and is characterized in having a layer made of a fused ring compound represented by the above formula (1) between the cathode and the emitting layer.

In the organic electroluminescence device of the present invention, the triazine structure of the fused ring compound represented by the formula (1) has an electron transporting property, and therefore the layer made of the fused ring compound has an excellent electron injection property. Therefore, the organic electroluminescence device of the present invention has a low driving voltage and excellent luminous efficiency.
In addition, the fused ring compound represented by the formula (1) has excellent solubility, and therefore has the advantage that when a layer made of the fused ring compound represented by the formula (1) is formed, it can be formed into a film by coating.

Next, one embodiment of the organic electroluminescence element of the present invention will be described in detail with reference to the drawings. Figure 1 is a schematic diagram showing an example of the structure of the organic EL element of the present invention.

The organic EL element 1 shown in FIG. 1 includes a cathode 3, a light-emitting layer 6, and an anode 9 provided in this order on a substrate 2, and an electron injection/transport layer 5 between the cathode 3 and the light-emitting layer 6.
1, the electron injection/transport layer 5 contains the above-mentioned fused ring compound, i.e., is a layer made of the above-mentioned fused ring compound. As described above, by providing the electron injection/transport layer 5 made of the above-mentioned fused ring compound between the cathode 3 and the light-emitting layer 6, the driving voltage of the organic EL element having an inverted structure can be reduced and the luminous efficiency can be improved.

The layers constituting the organic EL element 1 include an anode 9, a cathode 3, a light-emitting layer 6, an electron injection/transport layer 5, a hole transport layer 7, a hole injection layer 8, and the like, and these layers are appropriately selected and laminated to form the organic EL element 1.
In addition, the organic electroluminescence element of the present invention is not particularly limited in terms of the configuration of the laminated layers, so long as it has a structure in which a plurality of layers are laminated between the anode 9 and the cathode 3 formed on the substrate 2. However, it is preferable for the element to have the cathode 3, the electron injection/transport layer 5, the light-emitting layer 6, and, if necessary, the hole transport layer 7, the hole injection layer 8, and the anode 9 laminated adjacent to each other in this order.

Materials for the substrate 2 include resin materials, glass materials, etc. Resin materials for the substrate 2 include polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, polyarylate, etc. It is preferable to use a resin material for the substrate 2 because it is possible to obtain an organic EL element 1 with excellent flexibility. On the other hand, glass materials for the substrate 2 include quartz glass, soda glass, etc.

When the organic EL element 1 is a bottom-emission type, a transparent substrate is used as the material for the substrate 2. On the other hand, when the organic EL element 1 is a top-emission type, not only a transparent substrate but also an opaque substrate may be used as the material for the substrate 2. Examples of opaque substrates include a substrate made of a ceramic material such as alumina, a substrate in which an oxide film (insulating film) is formed on the surface of a metal plate such as stainless steel, and a substrate made of a resin material.

The average thickness of the substrate 2 can be determined depending on the material of the substrate 2, and is preferably 0.1 to 30 mm, and more preferably 0.1 to 10 mm. The average thickness of the substrate 2 can be measured using a digital multimeter and a vernier caliper.

In the organic electroluminescence element of the present invention, the cathode 3 and the anode 9 may be made of known conductive materials, but it is preferable that at least one of them is transparent in order to extract light. Examples of known transparent conductive materials include ITO (tin-doped indium oxide), ATO (antimony-doped indium oxide), IZO (indium-doped zinc oxide), AZO (aluminum-doped zinc oxide), and FTO (fluorine-doped indium oxide). On the other hand, examples of opaque conductive materials include calcium, magnesium, aluminum, tin, indium, copper, silver, gold, platinum, and alloys thereof.
Of these, ITO, IZO, and FTO are preferable for the cathode 3 .
Of these, Au, Ag and Al are preferable for the anode 9 .

As mentioned above, since the metals generally used for the anode 9 can be used for the cathode 3 and anode 9, it is easy to realize the case where light is extracted from the upper electrode (top emission structure), and various electrodes can be selected and used for each electrode. For example, Al can be used for the lower electrode and ITO for the upper electrode.

The average thickness of the cathode 3 is not particularly limited, but is preferably 10 to 500 nm, and more preferably 100 to 200 nm. The average thickness of the cathode 3 can be measured by a stylus step gauge or spectroscopic ellipsometry.

The average thickness of the anode 9 is not particularly limited, but is preferably 10 to 1000 nm, and more preferably 30 to 150 nm. Even when an opaque material is used, the anode 9 can be used as a top emission type or transparent type anode 9 by setting the average thickness to, for example, about 10 to 30 nm. The average thickness of the anode 9 can be measured during deposition using a quartz crystal film thickness gauge.

The organic electroluminescent element of the present invention preferably has a metal oxide layer 4 between the anode 9 and the cathode 3. When a metal oxide is used as the material for the laminated structure between the anode 9 and the cathode 3, the organic EL element has a superior continuous operating life and storage stability compared to an organic EL element that does not have a layer made of a metal oxide.

The metal oxide layer 4 is a layer that functions as a part of the cathode 3 or as an electron injection layer.
The metal oxide layer 4 is a layer consisting of a single metal oxide film, or a semiconductor or insulator laminated thin film layer which is a layer in which a single metal oxide film or two or more kinds of metal oxides are laminated and/or mixed. The metal elements constituting the metal oxide are selected from the group consisting of magnesium, calcium, strontium, barium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, indium, gallium, iron, cobalt, nickel, copper, zinc, cadmium, aluminum, and silicon. Among these, it is preferable that at least one of the metal elements constituting the laminated or mixed metal oxide layer is a layer consisting of magnesium, aluminum, calcium, zirconium, hafnium, silicon, titanium, or zinc, and among them, if it is a single metal oxide, it is preferable to include a metal oxide selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, and zinc oxide.

Examples of layers in which the single or two or more kinds of metal oxides are laminated and/or mixed include laminated and/or mixed combinations of metal oxides such as titanium oxide/zinc oxide, titanium oxide/magnesium oxide, titanium oxide/zirconium oxide, titanium oxide/aluminum oxide, titanium oxide/hafnium oxide, titanium oxide/silicon oxide, zinc oxide/magnesium oxide, zinc oxide/zirconium oxide, zinc oxide/hafnium oxide, zinc oxide/silicon oxide, calcium oxide/aluminum oxide, and laminated and/or mixed combinations of three kinds of metal oxides such as titanium oxide/zinc oxide/magnesium oxide, titanium oxide/zinc oxide/zirconium oxide, titanium oxide/zinc oxide/aluminum oxide, titanium oxide/zinc oxide/hafnium oxide, titanium oxide/zinc oxide/silicon oxide, indium oxide/gallium oxide/zinc oxide, and the like. Among these, IGZO, an oxide semiconductor that exhibits good characteristics as a special composition, and 12CaO7Al ₂ O ₃ , an electride, are also included.
In the present invention, those with a sheet resistance lower than 100 Ω/□ are classified as conductors, and those with a sheet resistance higher than 100 Ω/□ are classified as semiconductors or insulators. Therefore, thin films of ITO (tin-doped indium oxide), ATO (antimony-doped indium oxide), IZO (indium-doped zinc oxide), AZO (aluminum-doped zinc oxide), FTO (fluorine-doped indium oxide), etc., which are known as transparent electrodes, are highly conductive and do not fall under the category of semiconductors or insulators, and therefore do not correspond to one layer constituting the metal oxide layer 4 of the present invention.

The average thickness of the metal oxide layer 4 can be from 1 nm to several μm, but from the viewpoint of making an organic EL element that can be driven at a low voltage, it is preferably 1 to 1000 nm, and more preferably 2 to 100 nm. The average thickness of the metal oxide layer 4 can be measured by a stylus step gauge or spectroscopic ellipsometry.

The organic electroluminescent element of the present invention further preferably has an electron injection layer (metal oxide layer 4) made of a metal oxide between the cathode 3 and the light-emitting layer 6. The electron injection layer improves the speed and electron transport properties of the electron injection from the cathode 3 to the light-emitting layer 6, and by having the metal oxide layer 4 as an electron injection layer between the cathode 3 and the light-emitting layer 6, the storage stability of the organic EL element is improved and the driving stability is further improved.

1 contains the above-mentioned fused ring compound in the electron injection/transport layer 5 formed between the cathode 3 and the light-emitting layer 6. The electron injection/transport layer 5 is preferably formed by applying a solution containing the fused ring compound. When the electron injection/transport layer 5 is a layer made of the above-mentioned fused ring compound, the electron injection and electron transport properties of the electron injection/transport layer 5 are improved, the injection of holes from the anode and the injection of electrons from the cathode are balanced, the driving voltage of the organic EL element 1 is reduced, and the luminous efficiency is improved.
In FIG. 1 , the metal oxide layer 4 is laminated on the cathode 3, and further, the electron injection/transport layer 5 is laminated on the metal oxide layer 4. However, in the organic electroluminescence element of the present invention, the lamination order of the metal oxide layer 4 and the electron injection/transport layer 5 may be reversed.

In the organic electroluminescence device of the present invention, the electron injecting/transporting layer 5 (a layer made of a fused ring compound) preferably contains a reducing agent.
Here, the reducing agent acts as an n-dopant, and therefore, when the electron injection/transport layer 5 contains a reducing agent, electrons are sufficiently supplied from the cathode 3 to the light-emitting layer 6, so that the driving voltage of the organic EL element is reduced and the light-emitting efficiency is further improved.

The reducing agent is preferably an electron-donating compound, for example, 2,3-dihydrobenzo[d]imidazole compounds such as 1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazole, 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole, (4-(1,3-dimethyl-2,3-dihydro-1H-benzimidazol-2-yl)phenyl)dimethylamine (N-DMBI), 1,3,5-trimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole, and 3-methyl-2-phenyl-2,3-dihydrobenzo[d]thiazole. 2,3-dihydrobenzo[d]thiazole compounds such as 3-methyl-2-phenyl-2,3-dihydrobenzo[d]oxazole; triphenylmethane compounds such as leuco crystal violet (=tris(4-dimethylaminophenyl)methane), leucomalachite green (=bis(4-dimethylaminophenyl)phenylmethane), and triphenylmethane; dihydropyridine compounds such as 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate diethyl (Hantz ester), etc. can be used alone or in combination. Among these, 2,3-dihydrobenzo[d]imidazole compounds and dihydropyridine compounds are preferred, with (4-(1,3-dimethyl-2,3-dihydro-1H-benzimidazol-2-yl)phenyl)dimethylamine (N-DMBI) and 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate diethyl (Hantz ester) being particularly preferred.

The amount of the reducing agent is preferably 0.1 to 15% by mass relative to 100% by mass of the fused ring compound that forms the electron injection/transport layer 5. When the reducing agent is contained in such a ratio, the luminous efficiency of the organic EL element can be made sufficiently high. The amount of the reducing agent is more preferably 0.5 to 10% by mass relative to 100% by mass of the fused ring compound, and even more preferably 0.5 to 5% by mass.

In the organic electroluminescence element of the present invention, the electron injection/transport layer 5 (a layer made of a condensed ring compound) preferably contains a basic compound having an acid dissociation constant pKa of 1 or more. As the basic compound having an acid dissociation constant pKa of 1 or more, a tertiary amine, a phosphazene compound, a guanidine compound, a heterocyclic compound containing an amidine structure, a hydrocarbon compound having a ring structure, and a ketone compound are preferable. These compounds may be used alone or in combination of two or more.

The basic compound having an acid dissociation constant pKa of 1 or more has the ability to extract a proton (H ⁺ ) from a fused ring compound. The basic compound preferably has a pKa of 5 or more, more preferably 11 or more, and the higher the pKa, the higher the ability to extract a proton from a fused ring compound. As a result, the electron injection property of the electron injection/transport layer 5 is further improved. In addition, the basic compound is suitably coordinated to the defective portion of the inorganic compound, and therefore has the effect of preventing a reaction at the interface with oxygen or water entering from the outside, thereby enhancing the atmospheric stability of the element.
In the present invention, "pKa" usually means "acid dissociation constant in water", but if it cannot be measured in water, it means "acid dissociation constant in dimethyl sulfoxide (DMSO)", and if it cannot be measured even in DMSO, it means "acid dissociation constant in acetonitrile". Preferably, it means "acid dissociation constant in water".

The tertiary amine (tertiary amine derivative) may be a chain-like or cyclic amine compound, and if it is cyclic, it may be a heterocyclic amine compound, such as an aliphatic amine or an aromatic amine. The tertiary amine preferably has 1 to 4 amino groups, and more preferably has 1 or 2. The amine compound may also be a compound having an alkyl group, an alkylamino group, or an alkoxy group. Specific examples include (mono-, di-, and tri-)alkylamines; aromatic amines having 1 to 3 alkylamino groups; and aromatic amines having 1 to 3 alkoxy groups.

The tertiary amine is preferably one that does not contain a primary amine or a secondary amine.Specific examples of the tertiary amine include dialkylaminopyridines such as dimethylaminopyridine (DMAP) represented by the following general formula (4-1) or (4-2), amines having a structure represented by NR ¹ R ² R ³ such as triethylamine represented by the following general formula (4-3) (wherein R ¹ , R ² , and R ³ are the same or different and each represents a hydrocarbon group which may have a substituent), and acridine orange (AOB) represented by the following general formula (4-4).

The hydrocarbon group preferably has 1 to 30 carbon atoms, more preferably 1 to 8 carbon atoms, even more preferably 1 to 4 carbon atoms, and even more preferably 1 or 2 carbon atoms. When the hydrocarbon group has a substituent, it is preferable that the total number of carbon atoms including the substituent is the above number. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, and an alkynyl group, and an alkyl group is preferable. Examples of the substituent in the substituted hydrocarbon group include a halogen atom, a heterocyclic group, a cyano group, a hydroxyl group, an alkoxy group, an aryloxy group, and an amino group. As for dimethylaminopyridine, it is preferable that the position at which the dimethylamino group, which is an electron donating group, is bonded to the pyridine ring is the 2-position (2-DMAP) or the 4-position (4-DMAP). In particular, 4-dimethylaminopyridine, in which a dimethylamino group is bonded to the 4-position of the pyridine ring, is preferable because it has a high pKa and, moreover, when an organic thin film containing this is used as the electron injection/transport layer 5 of an organic EL device, a long life can be obtained.

As the tertiary amine, an alkoxypyridine derivative such as a methoxypyridine derivative can also be used. As the alkoxy group, an alkoxy group having 1 to 30 carbon atoms is preferable, an alkoxy group having 1 to 8 carbon atoms is more preferable, an alkoxy group having 1 to 4 carbon atoms is even more preferable, and an alkoxy group having 1 or 2 carbon atoms is even more preferable. The alkoxypyridine derivative also includes a compound having a structure in which one or more hydrogen atoms of an alkoxypyridine are substituted with a substituent. Examples of the substituent include the same as those of the substituent of the hydrocarbon group of the above-mentioned tertiary amine.
The methoxypyridine derivative is preferably 4-methoxypyridine (4-MeOP) represented by the following general formula (5-1) in which the methoxy group is bonded to the pyridine ring at the 4-position, or 3-methoxypyridine (3-MeOP) represented by the following general formula (5-2) in which the methoxy group is bonded to the pyridine ring at the 3-position. In particular, 4-methoxypyridine in which a methoxy group is bonded to the 4-position of the pyridine ring is preferred because of its high pKa.

As the tertiary amine, it is preferable to use one or more selected from heterocyclic aromatic amines having a dialkylamino group and/or an alkoxy group, and trialkylamines. From the viewpoint of improving electron injection properties and life, it is particularly preferable to use one or more selected from dialkylaminopyridines, trialkylamines, and alkoxypyridine derivatives.

In the heterocyclic compound containing an amidine structure, the amidine structure is ^a structure represented by ^R4 -C(= ^NR5 ) ^-NR6R7 (wherein ^R4 to ^R7 are the same or different and represent a hydrogen atom or a hydrocarbon group.) Examples of the heterocyclic compound containing an amidine structure include diazabicyclononene derivatives and diazabicycloundecene derivatives.

The diazabicyclononene derivatives include 1,5-diazabicyclo[4.3.0]nonene-5 (DBN) represented by the following general formula (6-1). DBN is preferable because it provides a long life when an organic thin film containing DBN is used as the electron injection/transport layer 5 of an organic EL device.
The diazabicycloundecene derivatives include 1,8-diazabicyclo[5.4.0]undecene-7 (DBU) represented by the following general formula (6-2).

The diazabicyclononene derivatives include compounds in which one or more of the hydrogen atoms of diazabicyclononene are substituted with a substituent, and the diazabicycloundecene derivatives include compounds in which one or more of the hydrogen atoms of diazabicycloundecene are substituted with a substituent. Examples of the substituent include the same ones as those of the hydrocarbon group of the tertiary amine described above.

The phosphazene compound (phosphazene base derivative) is, for example, a compound containing a structure represented by the following general formula (7).

In the above formula (7), R ⁸ represents a hydrogen atom or a hydrocarbon group, and R ⁹ to R ¹¹ represent a hydrogen atom, a hydrocarbon group, -NR'R'', where R' and R'' each independently represent a hydrogen atom or a hydrocarbon group, or a group represented by the following formula (8), and n represents a number from 1 to 5.

In the above formula (8), R ¹² to R ¹⁴ represent a hydrogen atom, a hydrocarbon group, or -NR'R" (wherein R' and R" each independently represent a hydrogen atom or a hydrocarbon group), and m represents a number from 1 to 5.

The hydrocarbon group in the above formulae (7) and (8) is preferably a group having 1 to 8 carbon atoms, more preferably a group having 1 to 4 carbon atoms. Moreover, the hydrocarbon group is preferably an alkyl group. As the above ^R11 , a tertiary butyl group is particularly preferable.

The phosphazene base derivative includes a compound represented by the following general formula (9).

The guanidine compound is a compound containing a structure represented by the following general formula (10).

In the above formula (10), R ¹⁵ to R ¹⁹ are the same or different and represent a hydrogen atom or a hydrocarbon group, and two or more of R ¹⁵ to R ¹⁹ may be bonded to form a cyclic structure.

The guanidine compound may be a guanidine cyclic derivative, etc. Examples of the guanidine cyclic derivative include 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) represented by the following formula (11-1) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) represented by the following formula (11-2).

The hydrocarbon compound having a ring structure is preferably a compound having a 5-membered or 6-membered ring as a ring structure, and is also preferably a compound having a ring structure in which a 5-membered ring and a 6-membered ring are condensed, or a ring structure in which multiple 6-membered rings are condensed. Examples of the 5-membered ring include a cyclopentane ring and a cyclopentadiene ring, and examples of the 6-membered ring include a benzene ring.
Preferred examples of hydrocarbon compounds having a ring structure include compounds having only a ring structure, compounds having a structure in which an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10, and more preferably 1 to 5 carbon atoms, is bonded to a ring structure, and compounds having a structure in which multiple ring structures are bonded directly or via a hydrocarbon linking group having 1 to 20 carbon atoms, preferably 1 to 10, and more preferably 1 to 5 carbon atoms. Specific examples of hydrocarbon compounds having a ring structure include compounds of the following formulae (12-1) to (12-14). In the formulae, Ph represents a phenyl group.

The ketone compound is preferably a ketone having 2 to 30 carbon atoms, and may have a cyclic structure. Specific examples include methyl ethyl ketone (MEK), acetone, diethyl ketone, methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MIPK), diisobutyl ketone (DIBK), 3,5,5-trimethylcyclohexanone, diacetone alcohol, cyclopentanone, cyclohexanone, etc.

The mass ratio of the fused ring compound to the basic compound having a pKa of 1 or more (fused ring compound:basic compound having a pKa of 1 or more) is preferably in the range of 1:0.01 to 1:10, and more preferably in the range of 1:0.5 to 1:5. If the mass ratio is in this range, the effects of the fused ring compound and the basic compound having a pKa of 1 or more are fully exerted, and the effect of improving the electron transport property and electron injection property is remarkable.

The electron injection/transport layer 5 may be formed by laminating the fused ring compound and a plurality of other materials. Examples of other materials that can be used include, in addition to the above-mentioned reducing agent and basic compound having an acid dissociation constant pKa of 1 or more, pyridine derivatives such as tris-1,3,5-(3'-(pyridin-3"-yl)phenyl)benzene (TmPyPhB), quinoline derivatives such as 2-(3-(9-carbazolyl)phenyl)quinoline (mCQ), pyrimidine derivatives such as 2-phenyl-4,6-bis(3,5-dipyridylphenyl)pyrimidine (BPyPPM), pyrazine derivatives, phenanthroline derivatives such as bathophenanthroline (BPhen), 2,4-bis(4-biphenyl)-6-(4'-(2-pyridinyl)-4-biphenyl)-[1,3 triazine derivatives such as 3-phenyl-4-(1'-naphthyl)-5-phenyl-1,2,4-triazole (TAZ), triazole derivatives such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl-1,3,4-oxadiazole) (PBD), imidazole derivatives such as 2,2',2"-(1,3,5-bentriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI), aromatic ring tetracarboxylic anhydrides such as naphthalene and perylene, bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (Zn(BTZ) ₂ ), various metal complexes represented by tris(8-hydroxyquinolinato)aluminum ( _Alq3 ), and organic silane derivatives represented by silole derivatives such as 2,5-bis(6'-(2',2"-bipyridyl))-1,1-dimethyl-3,4-diphenylsilole (PyPySPyPy).

The average thickness of the electron injection/transport layer 5 is preferably 5 to 100 nm. When the average thickness of the electron injection/transport layer 5 is 5 nm or more, the effect of blocking holes is large, and the driving stability of the organic EL element is further improved. When the average thickness of the electron injection/transport layer 5 is 100 nm or less, the driving voltage is low, which is preferable in practical use. The average thickness of the electron injection/transport layer 5 is more preferably 10 to 60 nm. In addition, in consideration of the continuous driving life of the organic EL element of the present invention, the average thickness of the electron injection/transport layer 5 is more preferably 10 to 30 nm. The average thickness of the electron injection/transport layer 5 can be measured by a stylus step gauge or spectroscopic ellipsometry.

In the organic EL element of the present invention, the material forming the light-emitting layer 6 may be a low molecular weight compound or a high molecular weight compound, or a mixture of these may be used.

Examples of polymeric materials for forming the light-emitting layer 6 include polyacetylene compounds such as trans-polyacetylene, cis-polyacetylene, poly(di-phenylacetylene) (PDPA), and poly(alkyl, phenylacetylene) (PAPA); poly(para-phenylenevinylene) (PPV), poly(2,5-dialkoxy-para-phenylenevinylene) (RO-PPV), cyano-substituted-poly(para-phenylenevinylene) (CN-PPV), poly(2 poly(2-methoxy,5-(2'-ethylhexoxy)-para-phenylenevinylene) (MEH-PPV) and other polyparaphenylenevinylene-based compounds; poly(3-alkylthiophene) (PAT) and poly(oxypropylene)triol (POPT) and other polythiophene-based compounds; poly(9,9-dialkylfluorene) (PDAF) and poly(dioctylfluorene) polyfluorene-based compounds such as α,ω-bis[N,N'-di(methylphenyl)aminophenyl]-poly[9,9-bis(2-ethylhexyl)fluorene-2,7-dyl] (PF2/6am4) and poly(9,9-dioctyl-2,7-divinylenefluorenyl-ortho-co(anthracene-9,10-diyl); poly(para-phenylene) (PPP), poly(1,5-dialkoxy-para- Examples of suitable compounds include polyparaphenylene compounds such as poly(N-vinylcarbazole) (PVK); polycarbazole compounds such as poly(methylphenylsilane) (PMPS), poly(naphthylphenylsilane) (PNPS), and poly(biphenylylphenylsilane) (PBPS); and boron compound-based polymeric materials described in JP-A Nos. 2011-184430 and 2012-151148.

Examples of the low molecular weight material forming the light emitting layer 6 include a metal complex functioning as a host, which will be described later, a phosphorescent material, and a thermally activated delayed fluorescent material. More specifically, examples of the low molecular weight material forming the light emitting layer 6 include tris(8-hydroxyquinoline)aluminum (Alq ₃ ), tris(4-methyl-8-quinolinolato)aluminum(III) (Almq ₃ ), 8-hydroxyquinoline zinc (Znq ₂ ), (1,10-phenanthroline)-tris-(4,4,4-trifluoro-1-(2-thienyl)-butane-1,3-dionate) europium(III) (Eu(TTA) _{3 )} . (phen)), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum (II) and other metal complexes; benzene-based compounds such as distyrylbenzene (DSB) and diaminodistyrylbenzene (DADSB); naphthalene-based compounds such as naphthalene and Nile Red; phenanthrene-based compounds such as phenanthrene; chrysene-based compounds such as chrysene and 6-nitrochrysene; perylene, N,N'-bis(2,5-di-t-butylphenyl)-3,4,9,10-perylene-di-carbo perylene compounds such as bis(styrylanthracene) and the like, coronene compounds such as coronene, anthracene compounds such as anthracene and bisstyrylanthracene, pyrene compounds such as pyrene, pyran compounds such as 4-(di-cyanomethylene)-2-methyl-6-(para-dimethylaminostyryl)-4H-pyran (DCM) and the like, acridine compounds such as acridine, stilbene compounds such as stilbene, 4,4'-bis[9-dicarbazolyl]-2,2'-biphenyl (CBP), 4,4'-bis(9-ethyl-3-carbazo carbazole compounds such as 2,5-dibenzoxazolethiophene; benzoxazole compounds such as benzoxazole; benzimidazole compounds such as benzimidazole; benzothiazole compounds such as 2,2'-(para-phenylenedivinylene)-bisbenzothiazole; butadiene compounds such as bistyryl(1,4-diphenyl-1,3-butadiene) and tetraphenylbutadiene; naphthalimide compounds such as naphthalimide; Examples of the compound include mide compounds, coumarin compounds such as coumarin, perinone compounds such as perinone, oxadiazole compounds such as oxadiazole, aldazine compounds, cyclopentadiene compounds such as 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (PPCP), quinacridone compounds such as quinacridone and quinacridone red, pyridine compounds such as pyrrolopyridine and thiadiazolopyridine, spiro compounds such as 2,2',7,7'-tetraphenyl-9,9'-spirobifluorene, metal or metal-free phthalocyanine compounds such as phthalocyanine (H ₂ Pc) and copper phthalocyanine, and boron compound materials described in JP-A-2009-155325 and JP-A-5660371. One or more of these compounds may be used.
Additionally, quantum dots and perovskite materials can also be used for the light emitting layer 6 .

The average thickness of the light-emitting layer 6 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 20 to 100 nm. The average thickness of the light-emitting layer 6 may be measured using a stylus step gauge, or may be measured using a quartz crystal thickness gauge during the deposition of the light-emitting layer 6.

As the material for the hole transport layer 7, any compound that can be usually used as a material for a hole transport layer can be used, and various p-type polymer materials and various p-type low molecular weight materials can be used alone or in combination.
Examples of p-type polymeric materials (organic polymers) include polyarylamines, fluorene-arylamine copolymers, fluorene-bithiophene copolymers, poly(N-vinylcarbazole), polyvinylpyrene, polyvinylanthracene, polythiophene, polyalkylthiophenes, polyhexylthiophene, poly(p-phenylenevinylene), polytinylenevinylene, pyrene formaldehyde resins, ethylcarbazole formaldehyde resins, and derivatives thereof.
These compounds can also be used in mixtures with other compounds, such as polythiophene-containing mixtures such as poly(3,4-ethylenedioxythiophene/styrenesulfonic acid) (PEDOT/PSS).

Examples of the p-type low molecular weight material include arylcycloalkane compounds such as 1,1-bis(4-di-para-triaminophenyl)cyclohexane and 1,1'-bis(4-di-para-tolylaminophenyl)-4-phenyl-cyclohexane, 4,4',4"-trimethyltriphenylamine, N,N,N',N'-tetraphenyl-1,1'-biphenyl-4,4'-diamine, N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD1), N,N'-diphenyl-N,N'-bis(4-methoxyphenyl)-1,1'-biphenyl-4,4'-diamine (TPD2), N,N,N',N'-tetrakis(4-methoxyphenyl)-1,1'-biphenyl-4,4'-diamine (TPD3), N,N'-di(1 arylamine compounds such as N,N,N',N'-tetraphenyl-para-phenylenediamine, N,N,N',N'-tetra(para-tolyl)-para-phenylenediamine, and N,N,N',N'-tetra(meta-tolyl)-meta-phenylenediamine (PDA); carbazole compounds such as carbazole, N-isopropylcarbazole, and N-phenylcarbazole; stilbene compounds such as stilbene and 4-di-para-tolylaminostilbene; oxazole compounds such as OxZ; triphenylmethane, 4,4',4"-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA) ), pyrazoline compounds such as 1-phenyl-3-(para-dimethylaminophenyl)pyrazoline, benzine (cyclohexadiene) compounds, triazole compounds such as triazole, imidazole compounds such as imidazole, oxadiazole compounds such as 1,3,4-oxadiazole and 2,5-di(4-dimethylaminophenyl)-1,3,4-oxadiazole, anthracene compounds such as anthracene and 9-(4-diethylaminostyryl)anthracene, fluorenone compounds such as fluorenone, 2,4,7-trinitro-9-fluorenone, and 2,7-bis(2-hydroxy-3-(2-chlorophenylcarbamoyl)-1-naphthylazo)fluorenone, aniline compounds such as polyaniline, silane compounds, 1,4 fluorene compounds such as fluorene; porphyrin compounds such as porphyrin and metal tetraphenylporphyrin; quinacridone compounds such as quinacridone; metallic or non-metallic phthalocyanine compounds such as phthalocyanine, copper phthalocyanine, tetra(t-butyl)copper phthalocyanine, and iron phthalocyanine; metallic or non-metallic naphthalocyanine compounds such as copper naphthalocyanine, vanadyl naphthalocyanine, and monochlorogallium naphthalocyanine; and benzidine compounds such as N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine and N,N,N',N'-tetraphenylbenzidine. These may be used alone or in combination.
Among these, arylamine compounds such as α-NPD and TPTE are preferred.

When the organic EL element of the present invention has a hole transport layer 7 as an independent layer, the average thickness of the hole transport layer 7 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 40 to 100 nm. The average thickness of the hole transport layer 7 can be measured by a quartz crystal film thickness meter in the case of a low molecular weight compound, and by a contact step gauge in the case of a high molecular weight compound.

The hole injection layer 8 is not particularly limited, and one or more metal oxides such as vanadium oxide (V ₂ O ₅ ), molybdenum oxide (MoO ₃ ), and ruthenium oxide (RuO ₂ ) can be used. Among these, vanadium oxide or molybdenum oxide is preferably used as the main component. When the hole injection layer 8 is mainly composed of vanadium oxide or molybdenum oxide, the hole injection layer 8 has a better function of injecting holes from the anode 9 and transporting them to the light emitting layer 6 or the hole transport layer 7. In addition, vanadium oxide or molybdenum oxide has a high hole transportability by itself, and therefore can suitably prevent the efficiency of hole injection from the anode 9 to the light emitting layer 6 or the hole transport layer 7 from decreasing. It is more preferable that the hole injection layer 8 is made of vanadium oxide and/or molybdenum oxide.

In addition, acceptor materials capable of promoting hole injection, such as 1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-hexacarbonitrile (HAT-CN), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ), and hexafluorotetracyanonaphthoquinodimethane (F6-TNAP), can also be used as the hole injection layer 8.

The average thickness of the hole injection layer 8 is not particularly limited, but is preferably 1 to 1000 nm, and more preferably 5 to 50 nm. The average thickness of the hole injection layer 8 can be measured during deposition using a quartz crystal thickness gauge.

In the organic EL element of the present invention, the method for forming all layers is not particularly limited, and examples of the method that can be used include gas phase film formation methods such as chemical vapor deposition (CVD) methods such as plasma CVD, thermal CVD, and laser CVD, dry plating methods such as vacuum deposition, sputtering, and ion plating, and thermal spraying methods, and liquid phase film formation methods such as wet plating methods such as electrolytic plating, immersion plating, and electroless plating, the sol-gel method, the MOD method, the spray pyrolysis method, and printing techniques such as a doctor blade method using a fine particle dispersion, a spin coating method, an inkjet method, and a screen printing method. An appropriate method can be selected and used depending on the material.
It is preferable to select these methods depending on the characteristics of the material of each layer, and the manufacturing method may differ for each layer.

The organic EL element of the present invention can change the emission color by appropriately selecting the material of the light-emitting layer 6, and the desired emission color can be obtained by using a color filter or the like in combination. Therefore, the organic EL element of the present invention can be suitably used in display devices and lighting devices.

<Display Device>
The display device of the present invention is characterized by comprising the organic electroluminescence element described above. The display device of the present invention comprises the organic EL element described above, which has a low driving voltage and excellent luminous efficiency, and therefore has a low driving voltage and excellent luminous efficiency. In addition to the organic electroluminescence element described above, the display device of the present invention can comprise other components that are generally used in display devices.

<Lighting equipment>
The lighting device of the present invention is characterized by comprising the organic electroluminescence element described above. The lighting device of the present invention has a low driving voltage and excellent luminous efficiency because it comprises the organic EL element described above, which has a low driving voltage and excellent luminous efficiency. The lighting device of the present invention can comprise other components commonly used in lighting devices in addition to the organic electroluminescence element described above.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

<NMR measurement method>
The AL400 manufactured by JEOL was used. The spectrometer was an AL-Series spectrometer, the probe was a TH5ATFG2 probe, and the solvent was _CDCl3 .

<Synthesis of fused ring compounds>
[1]benzothieno[3,2-b][1]benzothiophene (BTBT, 1.22 g, 5.07 mol, 1.0 eq.) represented by the following formula (13) and anhydrous tetrahydrofuran (THF, 15 mL) were added to a 50 mL reactor. At room temperature, n-BuLi (1.55 mol/L hexane solution) (3.27 mL, 5.07 mmol, 1.0 eq.) was added dropwise to this light yellow suspension over about 3 minutes, and the suspension was stirred at the same temperature for 30 minutes, cooled to 5°C in an ice bath, and iPrOBpin (1.03 g, 5.58 mmol, 1.1 eq.) was added. After stirring at the same temperature for 15 minutes, the cooling bath was removed and the suspension was warmed to room temperature to obtain suspension A.
[1]benzothieno[3,2-b][1]benzothiophene (BTBT, 1.29 g, 5.37 mol, 1.0 eq.) represented by the following formula (13) and anhydrous tetrahydrofuran (THF, 20 mL) were added to a 50 mL reactor. In an ice bath at about 8° C., n-BuLi (1.55 mol/L hexane solution) (3.27 mL, 5.07 mmol, 1.0 eq.) was added dropwise to this light yellow suspension over about 5 minutes, the cooling bath was removed, and the mixture was stirred at room temperature for 30 minutes, then cooled again to 5° C. in an ice bath, and iPrOBpin (1.3 g, 6.98 mmol, 1.3 eq.) was added. After stirring at the same temperature for 15 minutes, the cooling bath was removed and the mixture was warmed to room temperature to obtain suspension B.
This suspension B was combined with the above suspension A, and a 0.5N aqueous ammonium chloride solution (20 mL) was added. The mixture was extracted with ethyl acetate (50 mL) and toluene (50 mL), washed with city water and brine in that order, dried over anhydrous sodium sulfate, and concentrated to obtain a beige solid (3.91 g). This was purified by column purification (SiO ₂ = 60 g, toluene/heptane = 2/1 → 1/1) to obtain a light yellow powder (1.71 g). This was heated and refluxed with ethanol (20 mL) for 1 hour, cooled, filtered, and dried at 60°C under high vacuum to obtain a colorless powder of a compound represented by the following formula (14) (1.52 g, 4.15 mmol, 39%) and BTBT (0.31 g, recovered). The reaction scheme is shown below.

A 50 mL reactor was charged with the compound represented by the above formula (14) (0.48 g, 7.72 mmol, 1.0 eq.), 2-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine (0.254 g, 0.655 mmol, 1.2 eq.), palladium acetate (28 mg, 0.109 mmol, 0.02 eq.), S-Phos (0.112 g, 0.273 mmol, 0.5 eq.), sodium carbonate (0.174 g, 1.64 mmol, 3.0 eq.), toluene (3 mL), distilled water (3 mL), and ethanol (1.5 mL). The bath temperature of this suspension was raised to 95° C., and the suspension was stirred at the same temperature for 16 hours. To this suspension, 5% aqueous ammonium chloride solution (5 mL) and toluene (10 mL) were added, and the suspension was heated to about 50°C. Insoluble matter was filtered off, and the filtrate was separated into two layers. The aqueous layer was extracted with heated toluene (10 mL). The organic layers were combined, washed with city water and saturated saline, dried over anhydrous sodium sulfate, and concentrated to obtain a brown powder (0.41 g). This was dissolved in toluene (3 mL) at about 60°C, and then heptane (2 mL) was slowly added to the black solution. Immediately, column purification (SiO ₂ = 30 g, heated heptane/toluene = 2/1 → 1/1) was performed to obtain a colorless solid (0.25 g). This was again subjected to column purification (NH-SiO ₂ = 30 g, heated heptane/toluene = 2/1) to obtain a colorless solid (0.21 g). This was dispersed and washed with heated ethanol, filtered, and dried to obtain a fused ring compound (0.16 g, 0.292 mmol, 53%) represented by the following formula (15) in the form of a colorless powder. ^{The 1} H-NMR spectrum of the product is shown in Figure 2. The reaction scheme is shown below.

<Manufacture of Organic EL Element 1>
Organic EL element 1 was produced by the following method.

[Step 1]
A commercially available transparent glass substrate having an average thickness of 0.7 mm and a patterned electrode (cathode 3) made of ITO and having a thickness of 150 nm was prepared as the substrate 2. The substrate 2 having the cathode 3 was ultrasonically cleaned in acetone and isopropanol, and then UV ozone cleaning was performed for 20 minutes.

[Step 2]
On the ITO electrode (cathode 3) prepared in the above [Step 1], a zinc oxide (ZnO) layer with an average thickness of 10 nm was formed by sputtering using zinc metal as a target, oxygen as a reactive gas, and argon as a carrier gas. Then, the substrate was washed with isopropanol and acetone. Furthermore, the substrate was set on a spin coater, and a 1% by mass magnesium acetate solution (water/ethanol = 1/3) was spin-coated at 1600 rpm for 60 seconds, and annealed at 400 ° C. for 1 hour on a hot plate under atmospheric conditions. The substrate was then washed with water, and dried at 250 ° C. for 30 minutes on a hot plate under atmospheric conditions to form a metal oxide layer 4.

[Step 3]
Next, the electron injection/transport layer 5 was formed by the method described below.
The other layers are similar between Example 1 and Comparative Example 1, except for the electron injecting/transporting layer 5. The method of forming the electron injecting/transporting layer 5 in Example 1 and Comparative Example 1 will be described below.

Example 1
The fused ring compound (1 mass%) represented by the formula (15) synthesized as described above and 1,5-diazabicyclo[4.3.0]nonene-5 (DBN, 2 mass%) represented by the formula (6-1) were dissolved in cyclopentanone to obtain a mixed solution. Next, the cathode 3 and the substrate 2 on which the metal oxide layer 4 was formed, which were prepared in the above [Step 2], were placed on a spin coater. Then, while dropping the mixed solution onto the metal oxide layer 4, the substrate 2 was rotated at 3000 revolutions per minute for 30 seconds to form a coating film. Thereafter, an annealing treatment was performed at 120° C. for 2 hours using a hot plate under a nitrogen atmosphere to form an electron injection/transport layer 5. The average thickness of the obtained electron injection/transport layer 5 was 30 nm.

で表わされる縮合環化合物［東京化成工業（ＴＣＩ）製、２－デシル－７－フェニル［１］ベンゾチエノ［３，２－ｂ］［１］ベンゾチオフェン］（１質量％）と、上記式（６－１）で表わされる１，５－ジアザビシクロ［４．３．０］ノネン－５（ＤＢＮ、２質量％）をシクロペンタノンに溶解し、混合溶液を得た。次に、前記［工程２］で作製した陰極３および金属酸化物層４の形成されている基板２をスピンコーターに設置した。そして、混合溶液を金属酸化物層４上に滴下しながら、基板２を毎分３０００回転で３０秒間回転させて塗膜を形成した。その後、ホットプレートを用いて窒素雰囲気下で１２０℃、２時間のアニール処理を施し、電子注入・輸送層５を形成した。得られた電子注入・輸送層５の平均厚さは３０ｎｍであった。 (Comparative Example 1)
The following formula (16):

A fused ring compound represented by the formula (6-1) [manufactured by Tokyo Chemical Industry Co., Ltd. (TCI), 2-decyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene] (1 mass%) and 1,5-diazabicyclo[4.3.0]nonene-5 (DBN, 2 mass%) represented by the formula (6-1) were dissolved in cyclopentanone to obtain a mixed solution. Next, the substrate 2 on which the cathode 3 and metal oxide layer 4 formed in the above [Step 2] were formed was placed on a spin coater. Then, while dropping the mixed solution onto the metal oxide layer 4, the substrate 2 was rotated at 3000 revolutions per minute for 30 seconds to form a coating film. Thereafter, an annealing treatment was performed at 120° C. for 2 hours using a hot plate under a nitrogen atmosphere to form an electron injection/transport layer 5. The average thickness of the obtained electron injection/transport layer 5 was 30 nm.

[Step 4]
Next, the substrate 2 on which each layer up to the electron injection/transport layer 5 had been formed was fixed to a substrate holder of a vacuum deposition apparatus.
Also, bis[2-(2-benzothiazolyl)phenolato]zinc(II) (Zn(BTZ) ₂ ) represented by the following formula (17):
tris[1-phenylisoquinoline]iridium(III) (Ir(piq) ₃ ) represented by the following formula (18):
N,N'-di(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD) represented by the following formula (19),
N4,N4'-bis(dibenzo[b,d]thiophen-4-yl)-N4,N4'-diphenylbiphenyl-4,4'-diamine (DBTPB) represented by the following formula (20),
Al was placed in an alumina crucible and set in the deposition source.

Then, the pressure inside the vacuum deposition apparatus was reduced to about 1×10 ⁻⁵ Pa, and Zn(BTZ) ₂ was co-deposited as a host and Ir(piq) ₃ as a dopant to a thickness of 20 nm to form the light-emitting layer 6. At this time, the doping concentration of Ir(piq) ₃ was set to 6 mass % with respect to the entire light-emitting layer 6.
Next, on the substrate 2 on which the light-emitting layer 6 had been formed, DBTPB and α-NPD were evaporated to thicknesses of 10 nm and 30 nm, respectively, to form a hole-transporting layer 7 .
Furthermore, molybdenum trioxide (MoO3 ₎ was deposited by vacuum evaporation throughout to form a hole injection layer 8 having a thickness of 10 nm.

[Step 5]
Next, aluminum (anode 9) was evaporated to a film thickness of 100 nm on the substrate 2 on which the hole injection layer 8 had been formed, to obtain an organic EL element.

(Measurement of Light Emitting Characteristics of Organic EL Elements)
Voltage was applied to all the elements using a Keithley 2400 Source Meter, and the luminance was measured using a Konica Minolta LS-100. After that, the elements were continuously driven with an initial luminance of 1000 cd/ ^m2 , and the change in luminance over time was examined.

(Importance of Layer Made of Fused Ring Compound Having Triazine Structure in Inverted Structure Organic EL Device)
FIG. 3(a) shows the luminance-voltage characteristics of Example 1 and Comparative Example 1.
The fused ring compound represented by formula (15) and the fused ring compound represented by formula (16) both have high solubility in a solvent, and could form a good thin film in the coating step.
The main difference between the molecular structure of the fused ring compound represented by formula (15) and the molecular structure of the fused ring compound represented by formula (16) is whether or not the electron transport moiety has a triazine structure, and this difference is reflected in the device characteristics. That is, Example 1 formed from a fused ring compound (heteroacene compound) containing a triazine structure can be driven at a low voltage, whereas Comparative Example 1 has a high driving voltage.
Furthermore, a large difference was observed in the external quantum efficiency shown in Fig. 3(b) between Example 1 and Comparative Example 1. In Example 1, a maximum external quantum efficiency of about 11% was obtained, whereas the luminous efficiency was extremely low in Comparative Example 1. From this, it can be said that the fused ring compound containing a triazine structure is extremely effective in electron injection and transport.

The fused ring compound of the present invention can be used to form light-emitting elements such as organic EL elements.

1: Organic EL (electroluminescence) element 2: Substrate 3: Cathode 4: Metal oxide layer 5: Electron injection/transport layer 6: Light-emitting layer 7: Hole transport layer 8: Hole injection layer 9: Anode

Claims (7)

The following formula (1):

[At least one of R in formula (1) is represented by the following formula (2):

It is bonded to X in the
The ring A and the ring A′ in the formula (1) are fused to the adjacent ring at any position, and the ring A and the ring A′ in the formula (1) are represented by the following formula (1a-2) and formula (1a-3):

[0036]
R in formula (1) which is not bonded to X in formula (2) and R in formula (2) are independently hydrogen or a monovalent substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, and a substituted or unsubstituted aromatic 6-membered heterocyclic group having 3 to 30 carbon atoms, and adjacent substituents may be joined together to form a ring,
In the formula (1), n is 1 . An organic electroluminescence element having a cathode, a light-emitting layer, and an anode provided in this order on a substrate,
13. An organic electroluminescence device comprising a layer comprising the fused ring compound according to claim 1 between the cathode and the light-emitting layer. The organic electroluminescence element according to claim 2, wherein the layer made of the fused ring compound contains a reducing agent. 3. The organic electroluminescence device according to claim 2, wherein the layer made of the fused ring compound contains a basic compound having an acid dissociation constant pKa of 1 or more and capable of abstracting a proton from the fused ring compound . The organic electroluminescence element according to any one of claims 2 to 4, having an electron injection layer made of a metal oxide between the cathode and the light-emitting layer. A display device comprising an organic electroluminescence element according to any one of claims 2 to 5. A lighting device comprising an organic electroluminescence element according to any one of claims 2 to 5.

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