JPH10245549A - Electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electroluminescent element producing a high-luminance high-efficient emission and having a low emission initiation voltage and excellent durability by sandwiching an organic thin layer containing at least an organic luminescent layer comprising a distyryl compound between a hole injection electrode and an electron injection electrode. SOLUTION: An organic thin layer containing at least an organic luminescent layer (e.g. one prepared by vapor-depositing a 50nm thin film of a compound of formula I on a glass substrate coated with indium tin oxide) comprising a distyryl compound represented by formula I [wherein Ar1 and Ar2 are each a divalent (substituted) aromatic hydrocarbon group; R1 is an alkyl, an aralkyl or a (substituted)aryl; Ar3 is an alkyl, an aralkyl, an alkenyl, an alkoxyl, an aryloxy, a thioalkyl, an arylthio, a (substituted) aryl or a heterocyclic group; and Ar4 and Ar5 are each a (subsituted) alkyl, aralkyl, aryl or heterocyclic group, or may be combined with each other to form a ring] (e.g. a compound of formula II) is sandwiched between a hole injection electrode and an electron injection electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device having at least an organic thin film layer composed of an organic light emitting layer between a hole injection electrode and an electron injection electrode.

[0002]

2. Description of the Related Art In recent years, with the diversification of information equipment, the need for a flat display element which consumes less power than a cathode ray tube (CRT) (CRT) and which is thinner has increased. Liquid crystal, plasma display (PD) as such a flat display element
In particular, a self-luminous electroluminescent element with a clear display and a wide viewing angle has recently been receiving attention. here,
The electroluminescent device can be roughly classified into an inorganic electroluminescent device and an organic electroluminescent device depending on the constituent materials, and the inorganic electroluminescent device has already been put to practical use and commercially available as a product.

However, the driving voltage of the above-mentioned inorganic electroluminescent element is so-called collision excitation light emission in which accelerated electrons collide with the light emission center and emit light when a high electric field is applied. It is necessary to drive. For this reason, there has been a problem that the cost of peripheral devices is increased. In addition, there is also a problem that a full-color display cannot be performed because there is no luminous body that emits blue light.

On the other hand, in an organic electroluminescent device, charges (holes and electrons) injected from an electrode recombine in a luminous body to generate excitons, which excite molecules of a luminescent material. It is possible to drive at a low voltage because of so-called injection type light emission. Moreover, since it is an organic compound, the molecular structure of the light emitting material can be easily changed,
Any luminescent color can be obtained. Therefore, the organic electroluminescent device is very promising as a future display device.

Here, the organic electroluminescent device is a device having two layers of a hole transport layer and an electron transporting light emitting layer, Tang and VanSly.
proposed by ke (CWTang and SAVanSlyk
e; Appl. Phys. Lett., 51 (1987) 913). The structure of the device was an anode formed on a glass substrate, a hole transporting layer, an electron transporting light emitting layer, and a cathode.

In the above device, the hole transport layer functions to inject holes from the anode to the electron transporting light emitting layer, and also prevents the electrons injected from the cathode from escaping to the anode without recombination with the holes. It also serves to prevent electrons and to confine electrons in the electron-transporting light-emitting layer. For this reason, the recombination effect of electrons and holes occurs more efficiently than the conventional device having a single-layer structure due to the effect of confining electrons by the hole transport layer,
Driving voltage can be greatly reduced.

Saito et al. Have shown that in a device having a two-layer structure, not only an electron transport layer but also a hole transport layer can serve as a light emitting layer (C. Adachi, T. Tsutsui and S. Saito;
Appl. Phys. Lett., 55 (1989) 1489).

As an improvement of the two-layer structure, Saito et al. Proposed an organic electroluminescent device having a three-layer structure in which an organic light-emitting layer was sandwiched between a hole transport layer and an electron transport layer (C. Adachi, S. Tokito, T.Tsut
sui and S. Saito; Jpn. J. Appl. Phys., 27 (1988) L269).
It consists of an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode formed on a glass substrate.The hole transport layer functions to confine electrons in the light emitting layer, and the electron transport layer traps holes. The luminous efficiency was further improved due to the function of confining in the light emitting layer.

[0009]

As described above, improvements have been made from the layer structure in order to improve the luminous efficiency of the organic electroluminescent device, but it is still necessary to increase the luminance and efficiency of the luminescence. It is the current situation. Further, in order for the organic electroluminescent device to emit light for a long time, it is necessary to emit light at a lower voltage and a lower current density.

In view of the above, an object of the present invention is to provide an electroluminescent device which emits light with high luminance and high efficiency.

[0011]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that an organic thin film layer comprising at least an organic light emitting layer is provided between a hole injection electrode and an electron injection electrode. The present inventors have found that it is effective to use a distyryl compound represented by the following general formula [I] in an organic light emitting layer in an electroluminescent device having the same, and have accomplished the present invention:

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In the above formula, Ar ₁ and Ar ₂ each independently represent a divalent aromatic hydrocarbon group, for example, a phenylene group, and may have a substituent. The substituent may be an alkyl group such as a methyl group, a propyl group or a butyl group, or an alkoxy group such as a methoxy group, an ethoxy group or a butoxy group. Preferable is a phenylene group, which may have a substituent such as a methyl group or a methoxy group.

R ₁ represents an alkyl group such as a methyl group, a propyl group or a butyl group, an aralkyl group such as a benzyl group, or an aryl group such as a phenyl group. The aryl group may have a substituent. Examples of the substituent include an alkyl group such as a methyl group, a propyl group or a butyl group, an alkoxy group such as a methoxy group, an ethoxy group or a butoxy group, an aryl group such as a phenyl group, and a halogen atom such as a chlorine atom. Good. Desirable R ₁ is a phenyl group, a benzyl group, or a phenyl group having a substituent such as a methyl group or a methoxy group. Particularly preferred is a phenyl group having a substituent such as a methyl group or a methoxy group.

Ar ₃ is an alkyl group such as a methyl group, a propyl group or a butyl group; a cycloalkyl group such as a cyclohexyl group; an aralkyl group such as a benzyl group; an alkenyl group such as ethenyl, propenyl, butenyl, pentenyl and 2-metallate butenyl , A methoxy group, an alkoxy group such as an ethoxy group or a butoxy group, an aryloxy group such as phenyloxy, thiomethyl, thioethyl, thiopropyl,
A thioalkyl group such as thiobutyl and thiopentyl; an arylthio group such as phenylthio; an aryl group such as phenyl, naphthyl or anthryl; or a heterocyclic group such as carbazole, thiophene or furan. The aryl group may have a substituent. Examples of the substituent include an alkyl group such as a methyl group, a propyl group or a butyl group, an alkoxy group such as a methoxy group, an ethoxy group or a butoxy group, an aryl group such as a phenyl group, and a halogen atom such as a chlorine atom. May be. Preferred Ar ₃ is a phenyl group, a tolyl group, a thienyl group, an anthryl group, a pyrenyl group, a cyclohexyl group,
A phenylthio group or a furyl group is particularly preferable, and a phenyl group, a tolyl group, a thienyl group, an anthryl group, and a pyrenyl group are particularly preferable.

Ar ₄ and Ar ₅ each independently represent an alkyl group such as a methyl group, a propyl group or a butyl group;
Represents an aralkyl group such as a benzyl group, an aryl group such as phenyl or naphthyl, or a heterocyclic group such as furan or thiophene, and Ar ₄ and Ar ₅ are a ring together with a carbon atom together with a ring, for example,

Embedded image May be formed.

These groups may have a substituent.
The substituent may be an alkyl group such as a methyl group, a propyl group or a butyl group, an aryl group such as a phenyl group, or a halogen atom such as a chlorine atom. Preferred Ar ₄ and Ar ₅ are each a phenyl group, a tolyl group, a furyl group, a diphenyl group, or

Embedded image It is. Particularly preferred are a phenyl group, a tolyl group and a diphenyl group.

Specific examples of the distyryl compound used in the present invention include, but are not limited to, the following.

[0018]

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[0019]

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[0020]

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[0021]

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[0022]

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[0023]

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[0024]

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[0025]

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[0026]

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The electroluminescent device of the present invention may comprise at least an organic light emitting layer between the electrodes and, depending on the case, a hole injection / transport layer or an electron injection / transport layer.

FIGS. 1 to 4 schematically show possible configurations of the electroluminescent device of the present invention. In FIG. 1, (1) denotes an anode, on which a hole injection / transport layer (2), an organic light emitting layer (3), and a cathode (4) are sequentially laminated. The organic light emitting layer contains a distyryl compound represented by the above general formula [I].

In FIG. 2, (1) is a hole injection electrode (anode), on which a hole injection transport layer (2), an organic light emitting layer (3), an electron injection transport layer (5) and This shows a configuration in which electron injection electrodes (cathodes) (4) are sequentially stacked. The organic light emitting layer (3) contains a distyryl compound represented by the above general formula [I].

In FIG. 3, (1) is a hole injection electrode, on which an organic light emitting layer (3), an electron injection transport layer (5) and an electron injection electrode (4) are sequentially laminated. Is shown. The organic light emitting layer contains a distyryl compound represented by the above general formula [I].

In FIG. 4, (1) denotes a hole injection electrode, on which an organic light emitting layer (3) and an electron injection electrode (4) are sequentially laminated. The organic light emitting layer contains an organic light emitting material (6) and a charge transport material (7), and a distyryl compound represented by the above general formula [I] is used as the organic light emitting material.

A hole injection electrode (1) and an electron injection electrode (2)
And an organic light-emitting layer (3) emits light by applying a voltage between both electrodes.

The specific distyryl compound represented by the general formula [I] is a good blue-yellow luminescent material. This is considered to be because the quantum yield of fluorescence of the specific distyryl compound in a solid was high.

The substance used as the hole injection electrode (1) of the electroluminescent device is a conductive substance and preferably has a work function larger than 4 eV, and may be carbon, aluminum, vanadium, iron, cobalt, nickel, Copper, zinc, tungsten, silver, tin, gold and their alloys, tin oxide,
A conductive metal compound such as indium oxide, antimony oxide, zinc oxide, or zirconium oxide is used.

The material forming the electron injection electrode (4) is preferably a metal having a work function smaller than 4 eV, such as magnesium, calcium, titanium, yttrium lithium, gadolinium, ytterbium, ruthenium,
Manganese and their alloys are used.

In the electroluminescent device, at least the hole injection anode (1) or the electron injection electrode (4) needs to be a transparent electrode so that light emission can be seen. At this time, if the electron injection electrode is a transparent electrode, the transparent electrode is likely to be oxidized and deteriorated and the transparency is easily impaired. Therefore, it is preferable that the hole injection electrode be a transparent electrode.

When forming a transparent electrode, on a transparent substrate,
Using a conductive material as described above, a device such as vapor deposition, sputtering, or a method such as a sol-gel method or a method of dispersing and applying in a resin or the like is used to secure desired translucency and conductivity. I just need.

The transparent substrate has an appropriate strength and is not adversely affected by heat due to vapor deposition or the like during the manufacture of the electroluminescent device.
The material is not particularly limited as long as it is transparent. For example, a glass substrate and a transparent resin such as polyethylene, polypropylene, polyethersulfone, and polyetheretherketone may be used. As a transparent electrode formed on a glass substrate, IT
Commercial products such as O and NESA are known, but these may be used.

The fabrication of an electroluminescent device having the structure shown in FIG. 2 using the above-mentioned electrodes will be described as an example. First, a hole injection transport layer (2) is formed on the hole injection electrode (1). The hole injecting and transporting layer (2) may be formed by evaporating a hole transporting material or by dip coating or spin coating a solution in which the hole transporting material is dissolved or a solution in which a suitable resin is dissolved. May be.

The thickness is usually 1 to 500 nm when formed by the vapor deposition method, and 5 to 500 nm when formed by the coating method.
The thickness may be about 1000 nm. As the film thickness is larger, the applied voltage for emitting light needs to be higher, and the luminous efficiency is poor and the electroluminescent element is likely to be deteriorated. When the film thickness is small, the luminous efficiency is improved, but the breakdown is easy and the life of the electroluminescent element is shortened.

As the hole transporting material used for the hole injecting and transporting layer, known materials can be used. For example, N, N'-
Diphenyl-N, N'-bis (3-methylphenyl)-
1,1′-diphenyl-4,4′-diamine, N, N ′
-Diphenyl-N, N'-bis (4-methylphenyl)
-1,1'-bis (3-methylphenyl) -4,4'-
Diamine, N, N'-diphenyl-N, N'-bis (4
-Methylphenyl) -1,1'-diphenyl-4,4 '
-Diamine, N, N'-diphenyl-N, N'-bis (1-naphthyl) -1,1'-diphenyl-4,4'-
Diamine, N, N'-diphenyl-N, N'-bis (2
-Naphthyl) -1,1'-diphenyl-4,4'-diamine, N, N'-tetra (4-methylphenyl) -1,
1'-diphenyl-4,4'-diamine, N, N'-tetra (4-methylphenyl) -1,1'-bis (3-methylphenyl) -4,4'-diamine, N, N'- Diphenyl-N, N'-bis (3-methylphenyl) -1,
1'-bis (3-methylphenyl) -4,4'-diamine, N, N'-bis (N-carbazolyl) -1,1'-
Diphenyl-4,4′-diamine, 4,4 ′, 4 ″ -tris (N-carbazolyl) triphenylamine, N,
N ′, N ″ -triphenyl-N, N ′, N ″ -tris (3-methylphenyl) -1,3,5-tri (4-aminophenyl) benzene, 4,4 ′, 4 ″ -tris [ N,
N ′, N ″ -triphenyl-N, N ′, N ″ -tris (3-methylphenyl)] triphenylamine. These may be used as a mixture of two or more.

Next, an organic light emitting layer (3) is formed on the hole injection / transport layer (2). In the organic light emitting layer, the above general formula [I]
A distyryl compound represented by the formula:

The organic light-emitting layer may have a single-layer structure of a distyryl compound, or may have a multi-layer structure in order to adjust characteristics such as emission color and emission intensity. Further, two or more kinds of light-emitting substances may be mixed or the light-emitting layer may be doped.

The organic light emitting layer (3) may be formed by vapor deposition of a distyryl compound, or by dip coating or spin coating a solution in which the luminescent substance is dissolved or a solution in which a suitable resin is dissolved. Is also good.

In the case of forming by a vapor deposition method, the thickness is usually 1 to 500 nm, and in the case of forming by a coating method, it is 5 to 500 nm.
The thickness may be about 1000 nm. As the film thickness is larger, the applied voltage for emitting light needs to be higher, and the luminous efficiency is poor and the electroluminescent element is likely to be deteriorated. When the film thickness is small, the luminous efficiency is improved, but the breakdown is easy and the life of the electroluminescent element is shortened.

An electron injection / transport layer (5) is formed on the organic light emitting layer (3). As the electron injecting and transporting material used in the electron injecting and transporting layer, known materials can be used. For example, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4 -Oxadiazole, 2-
(1-Naphthyl) -5- (4-tert-butylphenyl)
-1,3,4-oxadiazole, 1,4-bis {2-
[5- (4-tert-butylphenyl) -1,3,4-oxadiazolyl] {benzene, 1,3-bis} 2- [5
-(4-tert-butylphenyl) -1,3,4-oxadiazolyl] {benzene, 4,4′-bis} 2- [5-
(4-tert-butylphenyl) -1,3,4-oxadiazolyl] biphenyl, 2- (4-biphenylyl)
-5- (4-tert-butylphenyl) -1,3,4-thiodiazole, 2- (1-naphthyl) -5- (4-tert
-Butylphenyl) -1,3,4-thiodiazole,
1,4-bis {2- [5- (4-tert-butylphenyl) -1,3,4-thiodiazolyl]} benzene,
3-bis {2- [5- (4-tert-butylphenyl)-
1,3,4-thiodiazolyl]｝ benzene, 4,4′-
Bis {2- [5- (4-tert-butylphenyl) -1,
3,4-thiodiazolyl] biphenyl, 3- (4-biphenylyl) -4-phenyl-5- (4-tert-butylphenyl) -1,2,4-triazole, 3- (1-
Naphthyl) -4-phenyl-5- (4-tert-butylphenyl) -1,2,4-triazole, 1,4-bis {3- [4-phenyl-5- (4-tert-butylphenyl)- 1,2,4-triazolyl]｝ benzene, 1,3
-Bis {3- [4-phenyl-5- (4-tert-butylphenyl) -1,3,4-oxadiazolyl]} benzene, 4,4′-bis {2- [4-phenyl-5- (4 −
tert-butylphenyl) -1,3,4-oxadiazolyl] {biphenyl, 1,3,5-tris} 2- [5-
(4-tert-butylphenyl) -1,3,4-oxadiazolyl] @benzene. These may be used as a mixture of two or more.

The electron injecting and transporting layer may be formed by vapor deposition of an electron transporting material, or may be formed by dip coating or spin coating a solution in which the electron transporting material is dissolved or a solution in which a suitable resin is dissolved.

When formed by the vapor deposition method, the thickness is usually 1 to 500 nm, and when formed by the coating method, the thickness is 5 to 500 nm.
The thickness may be about 1000 nm.

When the film thickness is large, it is necessary to increase the applied voltage for causing light emission, which tends to cause deterioration of the electroluminescent element. Further, when the film thickness is small, the luminous efficiency is improved, but the breakdown is easy, and the life of the electroluminescent element is shortened.

Next, the above-described electron injection electrode is formed on the electron injection transport layer.

As described above, the hole injecting and transporting layer (2), the light emitting layer (3), the electron injecting and transporting layer (5), and the electron injecting electrode (4) are sequentially laminated on the hole injecting electrode (1). Although the case of forming the light emitting element has been described, the light emitting layer (3), the electron injection transport layer (5) and the electron injection electrode (4) are sequentially laminated on the hole injection electrode (1), or the electron injection electrode ( 4) On top of it, an electron injection / transport layer (5) and an organic photosensitive layer (3)
In addition, a hole injection electrode (1) is sequentially stacked, a hole injection transport layer (2), a light emitting layer (3), and an electron injection electrode (4) are sequentially stacked on the anode (1). Of course, the electron injection / transport layer (5), the light emitting layer (3), the hole injection / transport layer (2), and the hole injection electrode (1) may be sequentially stacked on the injection electrode (4).

A pair of transparent electrodes, ie, an electron injection electrode and a hole injection electrode, is connected to an appropriate lead wire (8) such as a nichrome wire, a gold wire, a copper wire, a platinum wire, etc. Light is emitted by applying an appropriate voltage (Vs) to both electrodes.

The electroluminescent device of the present invention can be applied to various display devices or display devices.

Hereinafter, the present invention will be described by way of examples.

Example 1 Compound (4) was vapor-deposited as an organic light emitting layer on a glass substrate coated with indium tin oxide to form a thin film having a thickness of 50 nm. As an electron injecting and transporting layer thereon, 1,3-bis {2- [5- (4-tert-butylphenyl) -1,3,3].
[4-oxadiazolyl]} benzene was deposited to form a thin film having a thickness of 50 nm. Next, magnesium was deposited as an electron injection electrode to form a thin film having a thickness of 200 nm. Thus, an electroluminescent device was manufactured.

Examples 2 to 4 In Example 1, instead of using the compound (4),
An electroluminescent device was produced in exactly the same manner as in Example 1, except that Compounds (7), (9) and (11) were used.

Example 5 A thin film having a thickness of 50 nm was formed as an organic luminescent layer on a glass substrate coated with indium tin oxide by vapor deposition of compound (12). On top of that, as an electron injection / transport layer, 3- (4
-Biphenylyl) -4-phenyl-5- (4-tert-
A thin film was formed by vapor deposition of (butylphenyl) -1,2,4-triazole so as to have a thickness of 50 nm. Next, magnesium was deposited by evaporation as an electron injection electrode.
A thin film was formed so as to have a thickness of 0 nm. Thus, an electroluminescent device was manufactured.

Examples 6 to 8 Electroluminescence was carried out in the same manner as in Example 4 except that Compound (12) was replaced with Compounds (14), (16) and (22). An element was manufactured.

Example 9 N, N′-diphenyl-N, N′-bis (4-methylphenyl) -1,1′-bis (N, N′-diphenyl-N, N′-bis (4-methylphenyl) was used as a hole injecting and transporting layer on a substrate of indium tin oxide coated glass. 3-methylphenyl) -4,4'-diamine is deposited and has a thickness of 30 n.
m was formed. A compound (27) was deposited thereon to form a thin film having a thickness of 20 nm as an organic light emitting layer. Next, 1,3-bis {2- [4-phenyl-5- (4-tert-butylphenyl) -1,2,4-triazolyl]} benzene is deposited as an electron injection / transport layer and has a thickness of 30 nm. A thin film was formed such that Next, as an electron injection electrode, a thin film having a thickness of 200 nm was formed by vapor deposition of Mg and Ag at an atomic ratio of 10: 1. Thus, an electroluminescent device was manufactured.

Examples 10 to 12 Electroluminescence was performed in the same manner as in Example 10 except that Compound (27) was replaced with Compounds (36), (41) and (44). An element was manufactured.

Evaluation The voltage at which light emission was started when the DC voltage was gradually applied to the electroluminescent elements obtained in Examples 1 to 12 and the glass electrode was used as an anode, the maximum light emission luminance and the voltage at that time were measured. did. Further, the device obtained in Example 1 was continuously illuminated at an initial 5 V in an inert gas atmosphere of nitrogen gas, and the half-life (time until the luminance was halved) of the emission luminance was measured. there were. The results are summarized in Table 1.

[0062]

[Table 1]

As can be seen from Table 1, the electroluminescent device of the present invention started to emit light at a low potential and exhibited good emission luminance. Further, the electric field generating element of the present invention has a small output reduction,
Stable luminescence with a long lifetime was observed.

The electric field generating element of the present invention achieves improvement of luminous efficiency, luminous luminance and long life, and also uses a luminescent substance, a luminescent auxiliary material, a charge transport material, a sensitizer, a resin, It is not limited to the electrode material and the like and the element manufacturing method.

[0065]

According to the present invention, the organic light emitting layer has the above general formula
By containing the distyryl compound represented by [I], it is possible to obtain an electroluminescent device having high light intensity, low luminescence starting voltage and excellent durability.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a configuration example of an electroluminescent device of the present invention.

FIG. 2 is a schematic cross-sectional view of one configuration example of the electroluminescent device of the present invention.

FIG. 3 is a schematic cross-sectional view of one configuration example of the electroluminescent device of the present invention.

FIG. 4 is a schematic cross-sectional view of one configuration example of the electroluminescent device of the present invention.

[Explanation of symbols]

 1: hole injection electrode 2: hole injection transport layer 3: organic light emitting layer 4: electron injection electrode 5: electron injection transport layer 6: organic light emitting material 7: charge transport material 8: lead wire

Claims (1)

[Claims] 1. An electroluminescent device comprising an organic thin film layer including at least an organic light emitting layer between a hole injection electrode and an electron injection electrode, wherein the organic light emitting layer comprises a distyryl compound represented by the following general formula [I]. Element: (Wherein, Ar ₁ and Ar ₂ each independently represent a divalent aromatic hydrocarbon group which may have a substituent; R ₁
Represents an alkyl group, an aralkyl group or an aryl group which may have a substituent; Ar ₃ represents an alkyl group, an aralkyl group, an alkenyl group, an alkoxy group, an aryloxy group,
Represents a thioalkyl group, an arylthio group, or an aryl group which may have a substituent, or a heterocyclic group; Ar ₄ and Ar ₅ each independently may have a substituent;
Represents an alkyl group, an aralkyl group, an aryl group, or a heterocyclic group; Ar ₄ and Ar ₅ may form a ring together).