Benzoxazole compound and organic electroluminescent element using same

Abstract

Provided is an organic electroluminescent (EL) element in which a compound having a high refractive index at a wavelength of 450-750 nm and a low extinction coefficient is used in a coating layer, wherein the light extraction efficiency of the organic EL element is improved. An organic EL element having a positive electrode, a hole transport layer, a light-emitting layer, an electron transport layer, a negative electrode, and a coating layer in this order, the coating layer containing a benzoxazole compound represented by general formula (1) (in the formula, A represents a benzoxazole ring or the like, B and C represent a phenyl group, a naphthyl group, a phenanthroline group, an oxazolopyridyl group or the like, D represents a hydrogen atom, an aryl group or the like, and L1-L3 represent a single bond, a divalent aryl group or the like).

Description

TECHNICAL FIELD

[0001] The present application relates to a self-emitting electronic element suitable for various display devices, and particularly to a benzoxazole compound suitable for an organic electroluminescent element (hereinafter referred to as "organic EL element"), and an organic EL element, an electronic device, and an electronic element each using the compound. BACKGROUND

[0002] An organic EL element is brighter than a liquid crystal element and has excellent visual recognition, and can perform vivid display, and thus active researches have been conducted thereon. In 1987, C. W. Tang et al. of Eastman Kodak Company developed a layered structure element in which each material assumes various functions, and thus an organic EL element using an organic material became a practical element. Since then, many improvements have been made for practical use of the organic EL element, and a light-emitting element of a bottom emission structure in which an anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode are sequentially provided on a substrate by further subdividing the functions of the layers of the layered structure, and a light-emitting element of a top emission structure in which light is extracted from the top have been designed, and thus high efficiency and durability can be achieved (see Non-Patent Literature 1).

[0003] In recent years, a light-emitting element of a top emission structure in which a metal having a high work function is used for an anode and light is extracted from the top has been used. In a light-emitting element of a bottom emission structure in which light is extracted from the bottom of a pixel circuit, the area of a light-emitting portion is limited, and in contrast to this, in a light-emitting element of a top emission structure, light is extracted from the top and the pixel circuit is not shielded, and thus the light-emitting portion can be widened. On the other hand, in a light-emitting element of a top emission structure, in the case where light emitted from a light-emitting layer is incident on another film at an angle of equal to or more than a certain angle, total reflection occurs at the interface between the light-emitting layer and the other film, and only a part of the emitted light can be used. For this reason, in order to increase the light extraction efficiency, a light-emitting element provided with a high-refractive-index cover layer on the outside of a low-refractive-index LiF / Al / Ag, Ca / Mg, or LiF / MgAg or the like semi-transparent electrode (cathode) has been proposed (see Non-Patent Literatures 2 and 3).

[0004] Patent Literature 1: International Publication No. 2014 / 009310

[0005] Patent Literature 2: International Publication No. 2018 / 008718 Patent Literature 3: International Publication No. 2013 / 179536 Non-Patent Literature 1: Preprints of the 9th Symposium on Application Physics, 2001, p. 55-61 Non-Patent Literature 2: Appl. Phys. Lett., 2001, Vol. 78, No. 4, p. 544-546 Non-Patent Document 3: Appl. Phys. Let., 2003, Vol. 82, No. 3, p. 466-468 Non-Patent Document 4: Tetrahedron, 2002, Vol. 58, p. 9633-9695 Non-Patent Document 5: J. Org. chem., 2006, Vol. 71, p. 1802-1808 Non-Patent Document 6: Appl. Phys. Let., 2011, Vol. 98, No. 8, 083302 SUMMARY In the past, in order to form a cover layer, a metal mask having high fineness was used. However, in use under high temperature conditions, the metal mask is strained by heat, and there is a problem that positioning accuracy is reduced. Therefore, in Non-Patent Document 3, ZnSe (melting point: 1100°C or higher) used for a cover layer can not be evaporated to a correct position by a metal mask having high fineness, and adversely affects a light emitting element. Furthermore, even if film formation is performed based on a sputtering method, a light emitting element is adversely affected, and therefore an inorganic substance is not suitable as a material constituting a cover layer.

[0006] In addition, in Non-Patent Document 2, as a material constituting a cover layer for adjusting a refractive index, use of tris(8-hydroxyquinoline)aluminum (Alq3) is proposed. However, Alq3 is a general material as a green light emitting material or an electron transporting material, and it shows weak absorption near 450 nm which is close to the light emitting wavelength of a blue light emitting material. Therefore, when Alq3 is used for a blue light emitting element, there is a problem that color purity and light extraction efficiency are reduced.

[0007] As described above, in order to improve element characteristics of an organic EL element, and in order to improve light extraction efficiency, a material having a high refractive index, a low extinction coefficient, and excellent stability of a thin film, film formability, and durability, which can be used for a cover layer, is required.

[0008] An object of the present application is to provide a compound having a high refractive index and a low extinction coefficient in the range of wavelengths of 450 nm to 750 nm, which is suitable as a material for a cover layer of an organic EL element. In addition, an object of the present application is to provide an organic EL element in which light extraction efficiency is improved compared to the past.

[0009] The present inventors and others have intensively conducted optimization of molecular design focusing on the fact that a benzoxazole compound has excellent stability of a thin film and durability, in order to achieve the above object. As a result, a material having a high refractive index and a low extinction coefficient in the range of wavelengths of 450 nm to 750 nm was developed, and thus the present application was completed. That is, the present application includes the following configurations.

[0010] 1) An organic electroluminescent element comprising, in the stated order, an anode, a hole-transporting layer, a light-emitting layer, an electron-transporting layer, a cathode, and a capping layer, wherein the capping layer contains a benzoxazole compound represented by the following general formula (1), [Chem. 1]

[0011] wherein A represents a benzoxazole ring or a benzothiazole ring, B and C independently of each other represent a substituted or unsubstituted phenyl group, a naphthyl group, a quinolyl group, a quinoxalyl group, a quinazolyl group, a phenanthrolinyl group, a benzoxazolyl group, a benzothiazolyl group, a benzofuranyl group, a benzothiophenyl group, or an oxazolopyridyl group, D represents a hydrogen atom or a substituted or unsubstituted aryl group or heteroaryl group, L1to L3independently of each other represent a single bond or an unsubstituted divalent aryl group or divalent heteroaryl group.

[0012] 2) The organic electroluminescent element according to 1), wherein in the general formula (1), L2, L3, and L1are bonded to the 2-position, the 4-position, and the 6-position of the benzoxazole ring or the benzothiazole ring represented by A, respectively.

[0013] 3) The organic electroluminescent element according to 1) or 2), wherein L1to L3in the general formula (1) are independently of each other a single bond or an unsubstituted phenylene group, biphenylene group, or naphthylene group.

[0014] 4) The organic electroluminescent element according to any one of 1) to 3), wherein in the general formula (1), the aryl group or heteroaryl group represented by D is selected from the group consisting of a phenyl group, a biphenyl group, a naphthyl group, a furanyl group, a quinolyl group, a benzoxazolyl group, a benzothiazolyl group, an oxazolopyridyl group, a quinoxalyl group, a quinazolyl group, and a phenanthrolinyl group.

[0015] 5) The organic electroluminescent element according to any one of 1) to 4), wherein D in the general formula (1) is a hydrogen atom, a cyanophenyl group, or an unsubstituted phenyl group, biphenyl group, naphthyl group, furanyl group, quinolyl group, benzoxazolyl group, benzothiazolyl group, oxazolopyridyl group, quinoxalyl group, quinazolyl group, or phenanthrolinyl group.

[0016] 6) The organic electroluminescent element according to any one of 1) to 5), wherein in the general formula (1), at least one of B and C is a group selected from the group consisting of an unsubstituted phenyl group, naphthyl group, quinolyl group, quinazolyl group, phenanthrolinyl group, benzoxazolyl group, benzothiazolyl group, and oxazolopyridyl group.

[0017] 7) The organic electroluminescence element according to any one of 1) to 6), wherein When the cover layer is formed to a thickness of 30 nm to 120 nm, the refractive index of the formed film in a range of wavelengths of 450 nm to 750 nm is 1.70 or greater.

[0018] 8) The organic electroluminescence element according to any one of 1) to 7), wherein The cover layer is a stacked layer or a mixed layer containing two or more compounds including the benzoxazole compound represented by the general formula (1).

[0019] 9) A benzoxazole compound represented by the following general formula (2): [Chemical Formula 2]

[0020] In the formula, A represents a benzoxazole ring or a benzothiazole ring, B and C independently of each other represent a substituted or unsubstituted phenyl group, a naphthyl group, a quinolyl group, a quinoxalyl group, a quinazolyl group, a phenanthrolinyl group, a benzoxazolyl group, a benzothiazolyl group, a benzofuranyl group, a benzothiophenyl group, or an oxazolopyridyl group, D represents a hydrogen atom or a substituted or unsubstituted phenyl group, a biphenyl group, a naphthyl group, a furanyl group, a quinolyl group, a quinoxalyl group, a quinazolyl group, a phenanthrolinyl group, a benzoxazolyl group, a benzothiazolyl group, a benzofuranyl group, a benzothiophenyl group, or an oxazolopyridyl group, L1 to L3 independently of each other represent a single bond or an unsubstituted phenylene group, a biphenylene group, or a naphthylene group, L2, L3, and L1 are respectively bonded to the 2-position, the 4-position, and the 6-position of the benzoxazole ring or the benzothiazole ring represented by A, The benzoxazole compound satisfies any one of the following requirements 1 or 2: Requirement 1: At least one of B, C, and D includes a structure selected from the group consisting of a quinazoline, a phenanthrolinyl group, and an oxazolopyridyl group, wherein In the case where one or both of B, C, and D is a substituted or unsubstituted phenanthrolinyl group and neither one nor both of B, C, and D is a group selected from a substituted or unsubstituted quinazolyl group and an oxazolopyridyl group other than the phenanthrolinyl group, at least one selected from L1, L2, and L3 bonded to the phenanthrolinyl group is an unsubstituted phenylene group, a biphenylene group, or a naphthylene group, In the case where B, C, and D are substituted or unsubstituted phenanthrolinyl groups, at least one selected from L1, L2, and L3 bonded to the phenanthrolinyl group is an unsubstituted phenylene group, a biphenylene group, or a naphthylene group; Condition 2: B, C, and D do not include a structure selected from the group consisting of quinazoline, phenanthroline, and oxazolopyridine, L3 is a single bond, and D is a hydrogen atom.

[0021] 10) The benzoxazole compound according to 9), wherein In the general formula (2), at least one of B and C is a group selected from the group consisting of a substituted or unsubstituted phenyl group, a naphthyl group, a quinolyl group, a quinazolyl group, a phenanthrolinyl group, a benzoxazolyl group, a benzothiazolyl group, a benzofuranyl group, and an oxazolopyridyl group.

[0022] 11) An electronic device or an electronic component having a pair of electrodes and at least one organic layer, wherein The organic layer contains the benzoxazole compound according to 9) or 10).

[0023] The benzoxazole compound according to the present application has a high refractive index, a low extinction coefficient, can be deposited, is stable in a thin film state, and has high heat resistance in the wavelength range of 450 nm to 750 nm. Therefore, by providing a cover layer containing the compound on the outside of an electrode of an organic EL element, light extraction efficiency can be further improved than in the past. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a view showing specific examples of the benzoxazole compound represented by the general formula (1).

[0025] Figure 2 is a view showing specific examples of the benzoxazole compound represented by the general formula (1).

[0026] Figure 3 is a view showing specific examples of the benzoxazole compound represented by the general formula (1).

[0027] Figure 4 is a view showing specific examples of the benzoxazole compound represented by the general formula (1).

[0028] Figure 5 is a view showing specific examples of the benzoxazole compound represented by the general formula (1).

[0029] Figure 6 is a view showing specific examples of the benzoxazole compound represented by the general formula (1).

[0030] Figure 7 is a view showing specific examples of the benzoxazole compound represented by the general formula (1).

[0031] Figure 8 is a view showing specific examples of the benzoxazole compound represented by the general formula (1).

[0032] Figure 9This is a diagram showing specific examples of benzoxazole compounds represented by general formula (1).

[0033] Figure 10 This is a diagram illustrating an example of the structure of the organic EL element of the present invention. Detailed Implementation

[0034] <Organic EL Components> The organic EL element of the present invention comprises at least an anode, a hole transport layer, a light-emitting layer, an electron transport layer, a cathode, and a capping layer in sequence.

[0035] As a structure for organic EL elements, for example, when it is a top-emitting structure, examples include... Figure 10 The diagram shows a structure on a glass substrate 1 in which an anode 2, a hole transport layer 4, a light-emitting layer 5, an electron transport layer 6, a cathode 8, and a capping layer 9 are sequentially stacked. Other examples include structures with a hole injection layer 3 between the anode 2 and the hole transport layer 4; structures with an electron blocking layer (not shown) between the hole transport layer 4 and the light-emitting layer 5; structures with a hole blocking layer (not shown) between the light-emitting layer 5 and the electron transport layer 6; and structures with an electron injection layer 7 between the electron transport layer 6 and the cathode 8. In other words, as long as the organic EL element of the present invention has at least an anode, a hole transport layer, a light-emitting layer, an electron transport layer, a cathode, and a capping layer in sequence, the presence of other layers between these layers is not excluded. Furthermore, in these multilayer structures, a single organic layer can perform multiple functions. For example, it can be configured to have both a hole injection layer and a hole transport layer, both a hole transport layer and an electron blocking layer, both a hole blocking layer and an electron transport layer, and / or both an electron transport layer and an electron injection layer. Alternatively, it is possible to configure the device by stacking two or more organic layers with the same function. Specifically, examples include a configuration with two hole transport layers, a configuration with two light-emitting layers, a configuration with two electron transport layers, and / or a configuration with two capping layers. The layers constituting an organic EL element will be described below.

[0036] [Overlay] In the organic EL element of the present invention, the capping layer contains at least a benzoxazole compound represented by the following general formula (1).

[0037] [Chemical Formula 3]

[0038] In general formula (1), A represents a benzoxazole ring or a benzothiazole ring and is bonded to L1, L2, and L3 on the carbon atoms constituting the ring. For example, preferably as shown in the figure below. Figure 1As in compound (1), L2, L3, and L1 are bonded at positions 2, 4, and 6 of the benzoxazole or benzothiazole ring represented by A, respectively. Preferably, A is a benzoxazole ring.

[0039] B and C independently represent groups selected from the following substituted or unsubstituted groups: phenyl, naphthyl, quinolinyl, quinoxolinyl, quinazolinyl, phenanthrololinyl, benzoxazolyl, benzothiazolyl, benzofuranyl, benzothiophene, or oxazolopyridyl. Oxazolopyridyl can be either oxazolo[4,5-b]pyridyl or oxazolo[5,4-b]pyridyl.

[0040] Specifically, the following atoms or groups can be listed as "substituents" that the aforementioned substituted or unsubstituted groups represented by B and C may have.

[0041] Deuterium atom; halogen atoms such as fluorine, chlorine, bromine, and iodine; cyano; nitro; silyl groups such as trimethylsilyl and triphenylsilyl; straight-chain or branched alkyl groups with 1 to 6 carbon atoms such as methyl, ethyl, and propyl; straight-chain or branched alkyloxy groups with 1 to 6 carbon atoms such as methyloxy, ethyloxy, and propyloxy; alkenyl groups such as vinyl and allyl; aryloxy groups such as phenyloxy and tolyloxy; arylalkyloxy groups such as benzyloxy and phenethyloxy; phenyl and biphenyl. Aryl groups with 6 to 30 carbon atoms or heteroaryl groups with 2 to 20 carbon atoms, including terphenyl, naphthyl, anthraceneyl, phenanthryl, fluorenyl, spirodifluorenyl, indyl, pyrene, perylene, fluoranthyl, triphenylene, pyridyl, thiophene, furanyl, pyrroloyl, quinolinyl, isoquinolinyl, benzofuranyl, benzothiophene, indolyl, carbazoyl, benzoxazolyl, benzothiazoyl, quinoxolinyl, quinoxolinyl, quinoxolinyl, benzimidazolyl, pyrazolyl, dibenzofuranyl, dibenzothiophene, carbazoyl, phenanthroloylyl, etc. These substituents may further have the substituents exemplified above. Furthermore, these substituents and the benzene ring substituted by the substituent, or multiple substituents substituted on the same benzene ring, can form a ring through single bonds, substituted or unsubstituted methylene groups, oxygen atoms, or sulfur atoms.

[0042] Among the substituted or unsubstituted phenyl groups represented by B and C, cyano groups are preferred among the substituents exemplified above as possible substituents for the phenyl group. That is, when B and / or C are substituted phenyl groups, the substituted phenyl group is preferably a cyanophenyl group, more preferably a 3-cyanophenyl group or a 4-cyanophenyl group.

[0043] In the substituted or unsubstituted naphthyl group, the naphthyl group is preferably a 2-naphthyl group. That is, the substituted or unsubstituted naphthyl group is preferably a substituted or unsubstituted 2-naphthyl group. In the substituted or unsubstituted quinolinyl group, the quinolinyl group is preferably a 2-quinolinyl group or a 3-quinolinyl group. In the substituted or unsubstituted quinoxalinyl group, the quinoxalinyl group is preferably a 2-quinoxalinyl group or a 6-quinoxalinyl group. In the substituted or unsubstituted quinazolinyl group, the quinazolinyl group is preferably a 2-quinazolinyl group or a 6-quinazolinyl group. In the substituted or unsubstituted phenanthrolinyl group, the phenanthrolinyl group is preferably a [1,10]phenanthrolinyl group, more preferably a 2-[1,10]phenanthrolinyl group. In the substituted or unsubstituted benzoxazolyl group, the benzoxazolyl group is preferably a 2-benzoxazolyl group or a 6-benzoxazolyl group, more preferably a 2-benzoxazolyl group. In the substituted or unsubstituted benzothiazolyl group, as the benzothiazolyl group, a 2-benzothiazolyl group or a 6-benzothiazolyl group is preferred, more preferably a 2-benzothiazolyl group. In the substituted or unsubstituted benzofuranyl group, the benzofuranyl group is preferably a 2-benzofuranyl group. In the substituted or unsubstituted benzothiophenyl group, the benzothiophenyl group is preferably a 2-benzothiophenyl group. In the substituted or unsubstituted oxazolopyridinyl group, the oxazolopyridinyl group is preferably an oxazolo[5,4-b]pyridinyl group, more preferably a 2-oxazolo[5,4-b]pyridinyl group or a 5-oxazolo[5,4-b]pyridinyl group, further preferably a 2-oxazolo[5,4-b]pyridinyl group.

[0044] B and C are preferably each independently selected from, for example, a substituted or unsubstituted group of phenyl, 2-naphthyl, 2-quinolinyl, 3-quinolinyl, 2-quinoxalinyl, 6-quinoxalinyl, 2-quinazolinyl, 6-quinazolinyl, 2-[1,10]phenanthrolinyl, 2-benzoxazolyl, 6-benzoxazolyl, 2-benzothiazolyl, 6-benzothiazolyl, 2-benzofuranyl, 2-benzothiophenyl, 2-oxazolo[5,4-b]pyridinyl, or 5-oxazolo[5,4-b]pyridinyl. In addition, B and C are more preferably each independently selected from, for example, a substituted or unsubstituted group of phenyl, 2-naphthyl, 2-quinolinyl, 3-quinolinyl, 2-quinoxalinyl, 6-quinoxalinyl, 2-quinazolinyl, 6-quinazolinyl, 2-[1,10]phenanthrolinyl, 2-benzoxazolyl, 2-benzothiazolyl, 2-benzofuranyl, 2-benzothiophenyl, or 2-oxazolo[5,4-b]pyridinyl.

[0045] In addition, at least one of B and C is preferably selected from an unsubstituted group of phenyl, naphthyl, quinolinyl, quinazolinyl, phenanthrolinyl, benzoxazolyl, benzothiazolyl, or oxazolopyridinyl; more preferably from an unsubstituted group of phenyl, naphthyl, quinolinyl, quinazolinyl, phenanthrolinyl, benzothiazolyl, or oxazolopyridinyl; further preferably from an unsubstituted group of phenyl, naphthyl, quinazolinyl, phenanthrolinyl, or oxazolopyridinyl.

[0046] In general formula (1), D represents a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group. Specifically, the "aryl" or "heteroaryl" in "substituted or unsubstituted aryl" or "substituted or unsubstituted heteroaryl" can be selected from phenyl, biphenyl, terphenyl, naphthyl, anthracene, phenanthryl, fluorenyl, spirodifluorenyl, indene, pyrene, perylene, fluoranyl, triphenylene, pyridyl, pyrimidinyl, triazine, thiophene, furanyl, pyrroleyl, quinolinyl, and isoquinoline. The aryl group consisting of 6 to 30 carbon atoms or 2 to 20 carbon atoms is classified as benzo[4,5-b]pyridyl, indolyl, carbazolyl, benzo[oxazolyl], benzo[thiazolyl], oxazol[pyridyl], oxazol[pyrazinyl], quinoxolinyl, quinazolinyl, benzimidazolyl, pyrazolyl, dibenzo[oxazolyl], dibenzo[thiazolyl], naphthidyl, phenanthrolinel, acridinel, and carbazolyl. Oxazol[pyridyl] can be either oxazol[4,5-b]pyridyl or oxazol[5,4-b]pyridyl.

[0047] As for the "substituents" that can be present in the substituted or unsubstituted aryl or heteroaryl group represented by D, examples can be the same groups that are exemplified as the "substituents" that can be present in the groups represented by B and C above. The substituents can also be in the same manner. The substituted or unsubstituted aryl or heteroaryl group represented by D is preferably cyanophenyl (a phenyl group having a cyano group as a substituent) or an unsubstituted aryl or heteroaryl group.

[0048] Furthermore, the substituted or unsubstituted aryl or heteroaryl group represented by D is preferably selected from the group consisting of substituted or unsubstituted phenyl, biphenyl, naphthyl, furanyl, quinolinyl, benzoxazolyl, benzothiazolyl, oxazolopyridyl, quinoxalinyl, quinazololyl, and phenanthrolinel, more preferably from the group consisting of free cyanophenyl (phenyl with a cyano group as a substituent) and unsubstituted phenyl, biphenyl, naphthyl, furanyl, quinolinyl, benzoxazolyl, benzothiazolyl, oxazolopyridyl, quinoxalinyl, quinazololyl, and phenanthrolinel. That is, D is preferably a hydrogen atom or selected from the group consisting of substituted or unsubstituted phenyl, biphenyl, naphthyl, furanyl, quinolinyl, benzoxazolyl, benzothiazolyl, oxazolopyridyl, quinoxalinyl, quinazololyl, or phenanthrolinel. In addition, D is more preferably a hydrogen atom, cyanophenyl or selected from the following unsubstituted groups: phenyl, biphenyl, naphthyl, furanyl, quinolinyl, benzoxazolyl, benzothiazolyl, oxazolopyridyl, quinoxolinyl, quinazolyl or phenanthrolinel.

[0049] L1to L3independently of one another represent a single bond or an unsubstituted 2-valent aryl group or an unsubstituted 2-valent heteroaryl group. As the "2-valent aryl group" or "2-valent heteroaryl group" in the "unsubstituted 2-valent aryl group" or "unsubstituted 2-valent heteroaryl group", a 2-valent group obtained by removing one hydrogen atom from the "aryl group" or "heteroaryl group" represented by D described above can be mentioned, for example, a 2-valent group obtained by removing one hydrogen atom from the specific groups exemplified above can be mentioned. The "2-valent aryl group" is preferably phenylene, biphenylene or naphthylene.

[0050] L1to L3independently of one another are preferably a single bond or an unsubstituted phenylene group, unsubstituted biphenylene group or unsubstituted naphthylene group, more preferably a single bond, unsubstituted 1,3-phenylene group or 1,4-phenylene group, unsubstituted 4,4'-biphenylene group, unsubstituted 2,6-naphthylene group or unsubstituted 2,7-naphthylene group. In addition, L1and L3are preferably the same bond or group, more preferably L1and L3are both a single bond or a phenylene group (preferably 1,3-phenylene group or 1,4-phenylene group).

[0051] Among the benzoxazole compounds represented by the above general formula (1) which are applied to the cover layer of the organic EL element of the present application, the benzoxazole compounds represented by the following general formula (2) are novel compounds having a more characteristic structure. That is, the benzoxazole compounds represented by the above general formula (1) can be the benzoxazole compounds represented by the following general formula (2).

[0052] [Chemical Formula 4]

[0053] In general formula (2), A represents a benzoxazole ring or a benzothiazole ring and is bonded to L1, L2and L3on a carbon atom constituting the ring. A is preferably a benzoxazole ring. B and C independently of one another represent a group selected from the following groups which are substituted or unsubstituted: phenyl group, naphthyl group, quinolyl group, quinoxalyl group, quinazolyl group, phenanthrolinyl group, benzoxazolyl group, benzothiazolyl group, benzofuranyl group, benzothienyl group or oxazolopyridyl group. D represents a hydrogen atom or a group selected from the following groups which are substituted or unsubstituted: phenyl group, biphenyl group, naphthyl group, furanyl group, quinolyl group, quinoxalyl group, quinazolyl group, phenanthrolinyl group, benzoxazolyl group, benzothiazolyl group, benzofuranyl group, benzothienyl group or oxazolopyridyl group. L1to L3independently of one another represent a single bond or an unsubstituted phenylene group, biphenylene group or naphthylene group. In general formula (2), L2, L3and L1are bonded to the 2-position, 4-position and 6-position of the benzoxazole ring or benzothiazole ring represented by A, respectively.

[0054] Note that in general formula (2), either of the following requirements 1 or 2 is satisfied.

[0055] Condition 1: At least one of B, C, and D includes a structure selected from the group consisting of quinazoline, phenanthroline, and oxazolopyridine. Where one or both of B, C, and D is a substituted or unsubstituted phenanthroline group and neither one nor both of B, C, and D which is the phenanthroline group is a group selected from a substituted or unsubstituted quinazoline group and an oxazolopyridine group, at least one selected from L1, L2, and L3 which is bonded to the phenanthroline group is an unsubstituted phenylene group, biphenylene group, or naphthylene group (i.e., other than a single bond), and where B, C, and D are all substituted or unsubstituted phenanthroline groups, at least one selected from L1, L2, and L3 which is bonded to the phenanthroline group is an unsubstituted phenylene group, biphenylene group, or naphthylene group (i.e., other than a single bond); Condition 2: B, C, and D do not include a structure selected from the group consisting of quinazoline, phenanthroline, and oxazolopyridine, L3 is a single bond, and D is a hydrogen atom.

[0056] That is, in Condition 1, where at least one of B, C, and D includes a structure selected from the group consisting of quinazoline, phenanthroline, and oxazolopyridine, (1) a case where at least one of B, C, and D is a phenanthroline group, the remaining arbitrary B, C, and D are neither of a quinazoline group and an oxazolopyridine group, and at least one selected from L1, L2, and L3 which is bonded to the phenanthroline group is a single bond is excluded. Note that (2) when B, C, and D are all substituted or unsubstituted phenanthroline groups, a case where L1-B, L2-C, and L3-D are all single bond-phenanthroline groups is excluded, and at least one of L1, L2, and L3 needs to be a phenylene group, biphenylene group, or naphthylene group other than a single bond.

[0057] Here, L1, L2, and L3 which are bonded to a structure selected from the group consisting of the quinazoline and phenanthroline are preferably other than a single bond. That is, where at least one of B, C, and D is a quinazoline or phenanthroline structure, L1, L2, and L3 which are bonded to the any structure are preferably independently of each other an unsubstituted phenylene group, biphenylene group, or naphthylene group. Further, in General Formula (2), at least one of B, C, and D particularly preferably includes an oxazolopyridine structure. At this time, L1, L2, and L3 which are bonded to the oxazolopyridine structure can be a single bond. The oxazolopyridine can be either oxazolo[4,5-b]pyridine or oxazolo[5,4-b]pyridine, but is preferably oxazolo[5,4-b]pyridine.

[0058] In General Formula (2), at least one of B and C is preferably a group selected from the group consisting of a substituted or unsubstituted phenyl group, a naphthyl group, a quinolyl group, a quinazolyl group, a phenanthrolinyl group, a benzoxazolyl group, a benzothiazolyl group, a benzofuranyl group, and an oxazolopyridyl group. Further, at least one of B and C is more preferably a group selected from the group consisting of an unsubstituted phenyl group, a naphthyl group (preferably a 2-naphthyl group), a quinolyl group (preferably a 2-quinolyl group or a 3-quinolyl group), a quinazolyl group (preferably a 2-quinazolyl group or a 6-quinazolyl group), a phenanthrolinyl group (preferably a 2- [1, 10] phenanthrolinyl group), a benzoxazolyl group (preferably a 2-benzoxazolyl group or a 6-benzoxazolyl group), a benzothiazolyl group (preferably a 2-benzothiazolyl group or a 6-benzothiazolyl group), a benzofuranyl group (preferably a 2-benzofuranyl group), and an oxazolopyridyl group (preferably a 2-oxazolo[5, 4-b]pyridyl group or a 5-oxazolo[5, 4-b]pyridyl group, more preferably a 2-oxazolo[5, 4-b]pyridyl group). Still further, at least one of B and C is further preferably a group selected from the group consisting of an unsubstituted phenyl group, a naphthyl group, a quinolyl group, a quinazolyl group, a phenanthrolinyl group, a benzothiazolyl group, and an oxazolopyridyl group. Note that the details of A to D and L1to L3in General Formula (2) can be appropriately referred to the above description of General Formula (1).

[0059] The benzoxazole compound represented by General Formula (1) or (2) can be synthesized according to a known method, for example, as shown below. Further, the compound can be synthesized by a known coupling reaction using a palladium catalyst or the like (for example, refer to Patent Document 2, Non-Patent Documents 4 and 5).

[0060] [Chemical Formula 5]

[0061] Specific examples of the preferred compounds among the benzoxazole compounds represented by General Formula (1) or (2) are shown in Table 1 below. Figures 1-9 The present application is not limited to these compounds.

[0062] The purification method of the above benzoxazole compound is not particularly limited, and the compound can be purified by a known method for purifying an organic compound, such as column chromatography-based purification, adsorption purification based on silica gel, activated carbon, or activated clay, recrystallization purification based on a solvent, crystallization purification, sublimation purification, or the like. The compound can be identified by, for example, NMR analysis.

[0063] As the physical property values of the above benzoxazole compound, the melting point, the glass transition temperature (Tg), the refractive index, and the extinction coefficient are preferably measured. The melting point is an index of the evaporation property, and the glass transition temperature is an index of the stability of the thin film state. Further, the refractive index and the extinction coefficient are indices related to the improvement of the light extraction efficiency.

[0064] As to the melting point and the glass transition temperature, the powder can be measured by a high-sensitivity differential scanning calorimeter (for example, DSC3100SA manufactured by Bruker AXS). As to the refractive index and the extinction coefficient, an 80-nm thin film formed on a silicon substrate can be measured by a spectrometer (for example, F10-RT-UV manufactured by FILMETRICS).

[0065] In the present application, the cover layer contains a benzoxazole compound represented by the above general formula (1), and a benzoxazole compound represented by general formula (2) is more suitable among the benzoxazole compounds represented by general formula (1). Further, the cover layer can be a stacked layer or a mixed layer containing two or more kinds of compounds including the benzoxazole compound represented by the above general formula (1). As the compounds other than the benzoxazole compound represented by the above general formula (1), for example, phthalic acid derivatives (see Patent Document 3) and the like can be given. Of course, two or more kinds of the benzoxazole compounds represented by the above general formula (1) can be contained. They can be used by being formed into a film alone, or by being mixed and formed into a single layer. Alternatively, a stacked structure of layers each of which is formed into a film alone, a stacked structure of layers each of which is formed into a film by being mixed, or a stacked structure of layers each of which is formed into a film alone and layers each of which is formed into a film by being mixed can be formed. These materials can be formed into a film by a publicly known method such as an evaporation method, a spin coating method, and an inkjet method.

[0066] In the present application, when the cover layer containing the benzoxazole compound represented by the above general formula (1) or (2) is formed into a film having a thickness of 30 nm to 120 nm, the refractive index of the formed film in the range of wavelengths of 450 nm to 700 nm is preferably 1.70 or more. The above refractive index is more preferably 1.85 or more, and further preferably 1.90 or more.

[0067] [Other layers] As the material of the other layers, a publicly known material can be appropriately selected and used. As the substrate, there is no particular limitation, and a glass substrate, a plastic substrate, or the like can be used. As the material of the anode, an electrode material having a large work function such as ITO or gold can be used.

[0068] As materials for hole injection layers, arylamine compounds with a structure in which two or more triphenylamine structures are linked by single bonds or divalent groups without heteroatoms can be used. Examples include starburst-type triphenylamine derivatives, various triphenylamine tetramers, porphyrin compounds represented by copper phthalocyanine, and acceptor heterocyclic compounds such as hexacyanoazatriphenylene, as well as coating-type polymers. These can be used as individual films or mixed with other materials to form monolayers. Alternatively, they can be fabricated into stacked structures of individually formed layers, stacked structures of mixed-formed layers, or stacked structures of individually formed layers and mixed-formed layers. These materials can be formed using known methods such as vapor deposition, spin coating, and inkjet printing.

[0069] Materials suitable for hole transport layers include benzidine derivatives such as N,N'-diphenyl-N,N'-di(m-tolyl)benzidine (TPD), N,N'-diphenyl-N,N'-di(α-naphthyl)benzidine, and N,N,N',N'-tetraphenylbenzidine, as well as 1,1-bis[4-(di-4-tolylamino)phenyl]cyclohexane. Particularly preferred are arylamine compounds having a structure in which two triphenylamine structures are linked by single bonds or divalent groups without heteroatoms, such as N,N,N',N'-tetraphenylbenzidine. Furthermore, arylamine compounds having a structure in which three or more triphenylamine structures are linked by single bonds or divalent groups without heteroatoms, such as various triphenylamine trimers and tetramers, are preferred. These can be used alone or mixed with other materials to form a monolayer. Alternatively, it can be fabricated into a stacked structure of individually formed layers, a stacked structure of mixed-film layers, or a stacked structure of individually formed layers and mixed-film layers. Furthermore, coating-type polymers such as poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) can be used as materials for the hole injection layer and hole transport layer. These materials can be formed using known methods such as vapor deposition, spin coating, and inkjet printing.

[0070] In addition, as materials for hole injection layers and hole transport layers, products obtained by P-doping of materials commonly used in these layers with dopants such as tri(bromophenyl)amine antimony hexachloride and axial alkene derivatives (e.g., see Patent Document 1) and polymeric compounds having a benzidine derivative structure such as TPD as part of their structure can be used.

[0071] The organic EL element of the present application can have an electron-blocking layer. As a material for the electron-blocking layer, a compound having an electron-blocking effect such as a carbazole derivative such as 4,4',4"-tris(N-carbazolyl)triphenylamine (TCTA), 9,9-bis[4-(carbazol-9-yl)phenyl]fluorene, 1,3-bis(carbazol-9-yl)benzene (mCP), and 2,2-bis(4-carbazol-9-yl-phenyl)adamantane, and a compound having a triphenylsilyl group and a triarylamine structure represented by 9-[4-(carbazol-9-yl)phenyl]-9-[4-(triphenylsilyl)phenyl]-9H-fluorene can be used. They can be used as a single layer formed by being deposited alone or as a single layer formed by being mixed with other materials. Alternatively, a laminated structure of layers each formed by being deposited alone, a laminated structure of layers each formed by being mixed, or a laminated structure of layers each formed by being deposited alone and layers each formed by being mixed can be formed. These materials can be deposited by a publicly known method such as an evaporation method, a spin coating method, and an inkjet method.

[0072] As a material for the light-emitting layer, a metal complex of an 8-hydroxyquinoline derivative such as Alq3, various metal complexes, an anthracene derivative, a distyrylbenzene derivative, a pyrene derivative, an oxazole derivative, and a poly-p-phenylenevinylene derivative, or the like can be used. In addition, the light-emitting layer can be configured to include a host material and a dopant material. As the host material, an anthracene derivative is preferably used. In addition, as the host material, a heterocyclic compound having an indole ring as a partial structure of a condensed ring, a heterocyclic compound having a carbazole ring as a partial structure of a condensed ring, a carbazole derivative, a thiazole derivative, a benzimidazole derivative, a polydialkylfluorene derivative, or the like can be used. As the dopant material, quinacridone, coumarin, rubrene, perylene, pyrene, and a derivative thereof, a benzopyran derivative, a rhodamine derivative, an aminostyryl derivative, or the like can be used. As the dopant material, a green light-emitting material is preferably used. They can be used as a single layer formed by being deposited alone or as a single layer formed by being mixed with other materials. Alternatively, a laminated structure of layers each formed by being deposited alone, a laminated structure of layers each formed by being mixed, or a laminated structure of layers each formed by being deposited alone and layers each formed by being mixed can be formed.

[0073] Further, as the dopant material, a phosphorescent emitter can also be used. As the phosphorescent emitter, a metal complex of iridium, platinum, or the like can be used. Specifically, a green phosphorescent emitter such as Ir(ppy)3, a blue phosphorescent emitter such as FIrpic, FIr6, and a red phosphorescent emitter such as Btp2Ir(acac) can be given. Among them, a green phosphorescent emitter is preferably used. When a phosphorescent emitter is used as the dopant material, as the host material, a hole-injection and hole-transporting host material such as a carbazole derivative of 4,4'-di(N-carbazolyl)biphenyl, TCTA, and mCP, an electron-transporting host material such as p-bis(triphenylsilyl)benzene and 2,2',2"-(1,3,5-phenylene)-tris(1-phenyl-1H-benzimidazole) can be used. As for doping of the phosphorescent emitter into the host material, in order to avoid concentration quenching, co-evaporation is preferably performed in a range of 1 to 30% by mass with respect to the entire light-emitting layer.

[0074] Further, as the dopant material, a phosphorescent emitter can also be used. As the phosphorescent emitter, a metal complex of iridium, platinum, or the like can be used. Specifically, a green phosphorescent emitter such as Ir(ppy)3, a blue phosphorescent emitter such as FIrpic, FIr6, and a red phosphorescent emitter such as Btp2Ir(acac) can be given. Among them, a green phosphorescent emitter is preferably used. When a phosphorescent emitter is used as the dopant material, as the host material, a hole-injection and hole-transporting host material such as a carbazole derivative of 4,4'-di(N-carbazolyl)biphenyl, TCTA, and mCP, an electron-transporting host material such as p-bis(triphenylsilyl)benzene and 2,2',2"-(1,3,5-phenylene)-tris(1-phenyl-1H-benzimidazole) can be used. As for doping of the phosphorescent emitter into the host material, in order to avoid concentration quenching, co-evaporation is preferably performed in a range of 1 to 30% by mass with respect to the entire light-emitting layer.

[0075] The organic EL element of the present application can have a hole-blocking layer. As the material of the hole-blocking layer, a phenanthroline derivative such as bathocuproin, a metal complex of an 8-hydroxyquinoline derivative such as bis(2-methyl-8-hydroxyquinolinate)-4-phenylphenol aluminum (III) (BAlq), various rare earth complexes, a triazole derivative, a triazine derivative, a pyrimidine derivative, an oxadiazole derivative, a benzoxazole derivative, and the like, which have a hole-blocking action, can be used. These materials can be used as the material of the electron-transporting layer. They can be used as a single layer formed by a single film formation or as a single layer formed by mixing with other materials. Alternatively, a laminated structure of layers each formed by a single film formation, a laminated structure of layers each formed by mixing, or a laminated structure of layers each formed by a single film formation and layers each formed by mixing can be used. These materials can be formed by a publicly known method such as an evaporation method, a spin coating method, and an inkjet method.

[0076] As the material of the electron transport layer, metal complexes of 8-hydroxyquinoline derivatives such as Alq3 and BAlq, various metal complexes, triazole derivatives, triazine derivatives, pyrimidine derivatives, oxadiazole derivatives, pyridine derivatives, benzimidazole derivatives, benzoxazole derivatives, thiadiazole derivatives, anthracene derivatives, carbodiimide derivatives, quinoxaline derivatives, pyridoindole derivatives, phenanthroline derivatives, and silafluorene derivatives, etc. can be used. They can be used as a single layer or as a mixed layer with other materials. Alternatively, a stacked structure of layers each of which is formed of a single layer, a stacked structure of layers each of which is formed of a mixed layer, or a stacked structure of layers each of which is formed of a single layer and a mixed layer can be formed. These materials can be formed by a publicly known method such as an evaporation method, a spin coating method, and an inkjet method.

[0077] As the material of the electron injection layer, alkali metal salts such as lithium fluoride and cesium fluoride, alkaline earth metal salts such as magnesium fluoride, metal complexes of 8-hydroxyquinoline derivatives such as lithium 8-hydroxyquinolate, metal oxides such as aluminum oxide, and metals such as ytterbium (Yb), samarium (Sm), calcium (Ca), strontium (Sr), and cesium (Cs) can be used. Note that the electron injection layer can be omitted by the preferred selection of the electron transport layer and the cathode.

[0078] Further, as the material of the electron transport layer and the electron injection layer, a product obtained by N-doping a metal such as cesium to a material usually used for these layers can be used.

[0079] As the material of the cathode, a metal having a low work function such as aluminum, an alloy having a lower work function such as a magnesium-silver alloy, a magnesium-calcium alloy, a magnesium-indium alloy, and an aluminum-magnesium alloy, and ITO and IZO, etc. can be used.

[0080] The total thickness of the films of the respective layers of the organic EL element is preferably 200 nm to 750 nm, more preferably 350 nm to 600 nm. Further, the thickness of the cover layer is preferably, for example, 30 nm to 120 nm, more preferably 40 nm to 80 nm. When the thickness of the cover layer is in the above range, a more favorable light extraction efficiency can be obtained. Note that the thickness of the cover layer can be appropriately changed depending on the kind of the light-emitting material used for the light-emitting element, the thickness of each layer other than the cover layer, and the like.

[0081] Note that the organic EL element of the top emission structure is described above, but the present application is not limited thereto, and can be similarly applied to an organic EL element of a bottom emission structure, an organic EL element of a double emission structure which emits light from both the top and the bottom. In any case, the electrode located in the direction in which light is extracted from the light-emitting element to the outside is preferably transparent or semi-transparent.

[0082] The physical properties of compounds suitable for capping layers of organic EL elements include: (1) high refractive index, (2) low extinction coefficient, (3) vapor deposition capability, (4) film stability, and (5) high glass transition temperature. Furthermore, the physical properties of organic EL elements include: (1) high light extraction efficiency, (2) suppression of color purity reduction, (3) time-invariant light transmission, and (4) long lifetime. The benzozazole compounds of the present invention, represented by general formula (1) or (2), possess the characteristics of high refractive index, low extinction coefficient, vapor deposition capability, film stability, and high glass transition temperature. Therefore, by using such benzozazole compounds as capping layers, organic EL elements with high light extraction efficiency, suppression of color purity reduction, time-invariant light transmission, and long lifetime can be provided.

[0083] <Electronic devices or electronic components> The electronic device or electronic component of the present invention has a pair of electrodes and at least one organic layer containing a benzoxazole compound represented by the above general formula (1) or (2). It should be noted that at least one organic layer is preferably disposed on the outside of one electrode, and the organic layer disposed on the outside of the electrode more preferably contains a benzoxazole compound represented by the above general formula (1) or (2).

[0084] Example The embodiments of the present invention will be specifically described below, but the present invention is not limited to the following embodiments without departing from its spirit.

[0085] [Example 1: Synthesis of compound (4)] 8.8 g of 2-(4-chlorophenyl)-4,6-bis(naphthyl-2-yl)benzoxazole, 6.7 g of 3-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborhexacyclopentan-2-yl)phenyl]quinoline, 0.5 g of tris(dibenzylacetone)dipalladium(O), 0.5 g of tricyclohexylphosphine, and 7.8 g of tripotassium phosphate were added to a reaction vessel and refluxed with a 1,4-dioxane / H₂O mixed solvent for one night. After the resulting mixture was allowed to cool naturally, MeOH was added, and the precipitated solid was filtered to obtain the crude product. The crude product was purified by recrystallization with monochlorobenzene to obtain a pale yellow powder of 4,6-bis(naphthyl-2-yl)-2-{4'-(quinolin-3-yl)[1,1'-biphenyl]-4-yl}-benzoxazole (compound (4)): 5.0 g (yield: 42.0%).

[0086] [Chemical Formula 6]

[0087] The structure of the obtained pale yellow powder was identified using NMR.1 H-NMR (DMSO-d6) detected the following 30 hydrogen signals.

[0088] δ (ppm) = 9.37 (1H), 8.83 (1H), 8.77 (1H), 8.52 (1H), 8.45 (1H), 8.42 (2H), 8.30 (2H), 8.19-7.99 (15H), 7.81 (1H), 7.68 (1H), 7.60 (4H).

[0089] [Example 2: Synthesis of Compound (12)] To a reaction vessel were charged 2-(4-chlorophenyl)-4,6-di(quinolin-3-yl)benzoxazole: 11.3 g, 2-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]naphthalene: 6.4 g, tris(dibenzylideneacetone)dipalladium(0): 0.6 g, tricyclohexylphosphine: 0.7 g, and potassium phosphate tribasic: 9.9 g, and stirred at reflux in a 1,4-dioxane / H2O mixed solvent overnight. After the resulting mixture was allowed to cool naturally, MeOH was added, and the precipitated solid was filtered to obtain a crude product. The obtained crude product was recrystallized using monochlorobenzene, thereby obtaining a light yellow powder of 2-{4'-(naphthalen-2-yl)[1,1'-biphenyl]-4-yl}-4,6-di(quinolin-3-yl)-benzoxazole (Compound (12)): 6.3 g (yield: 41.3%).

[0090] The obtained light yellow powder was identified for structure using NMR. Using 1 H-NMR (DMSO-d6) detected the following 29 hydrogen signals.

[0091] δ (ppm) = 9.84 (1H), 9.54 (1H), 9.24 (1H), 8.96 (1H), 8.47 (2H), 8.42 (2H), 8.21 (1H), 8.23-7.92 (14H), 7.88 (1H), 7.83 (1H), 7.72 (2H), 7.57 (2H).

[0092] [Example 3: Synthesis of Compound (32)] To a reaction vessel were charged 4,6-dibromo-2-(naphthalen-2-yl)-benzoxazole: 8.0 g, 2-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]benzothiazole: 14.1 g, tetrakis(triphenylphosphine)palladium(0): 0.9 g, and potassium carbonate: 11.0 g, and stirred at reflux for one night in a mixed solvent of toluene / EtOH / H2O. After the resulting mixture was allowed to cool naturally, MeOH was added, and the precipitated solid was filtered to obtain a crude product. The crude product was recrystallized using monochlorobenzene to obtain a yellowish powder of 4,6-bis(4-benzothiazol-2-yl-phenyl)-2-(naphthalen-2-yl)-benzoxazole (compound (32)): 8.7 g (yield: 66.0%).

[0093] The structure of the resulting yellowish powder was identified using NMR. The following 25 hydrogen signals were detected by1H-NMR (DMSO-d6). 1 The following 25 hydrogen signals were detected by1H-NMR (DMSO-d6).

[0094] δ (ppm) = 8.93 (1H), 8.51 (2H), 8.39 (1H), 8.37 (1H), 8.34 (2H), 8.30-8.06 (12H), 7.70 (2H), 7.61 (2H), 7.52 (2H).

[0095] [Example 4: Synthesis of compound (33)] To a reaction vessel were charged 4,6-dibromo-2-(naphthalen-2-yl)-benzoxazole: 8.0 g, 2-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]benzothiazole: 14.1 g, tetrakis(triphenylphosphine)palladium(0): 0.9 g, and potassium carbonate: 11.0 g, and stirred at reflux for one night in a mixed solvent of toluene / EtOH / H2O. After the resulting mixture was allowed to cool naturally, MeOH was added, and the precipitated solid was filtered to obtain a crude product. The crude product was recrystallized using monochlorobenzene to obtain a yellowish powder of 4,6-bis(4-benzothiazol-2-yl-phenyl)-2-(naphthalen-2-yl)-benzoxazole (compound (32)): 8.7 g (yield: 66.0%).

[0096] The structure of the resulting yellowish powder was identified using NMR. The following 25 hydrogen signals were detected by1H-NMR (DMSO-d6). 1 The following 23 hydrogen signals were detected by1H-NMR (THF-d8).

[0097] δ (ppm) = 8.96 (1H), 8.58 (4H), 8.49 (3H), 8.38 (2H), 8.24 (2H), 8.21-8.10 (6H), 8.02 (1H), 7.65 (2H), 7.45 (2H).

[0098] [Example 5: Synthesis of compound (58)] 5.0 g of 4,6-dibromo-2-([1,1'-biphenyl]-4-yl)benzoxazole, 9.2 g of 2-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborphane-2-yl)phenyl]benzothiazole, 0.9 g of tetra(triphenylphosphine)palladium(O), and 11.0 g of potassium carbonate were added to a reaction vessel and refluxed with a toluene / EtOH / H2O mixed solvent for one night. After the resulting mixture was allowed to cool naturally, MeOH was added, and the precipitated solid was filtered to obtain the crude product. The crude product was purified by recrystallization with monochlorobenzene to obtain 8.9 g of pale yellow powder of 2-([1,1'-biphenyl]-4-yl)-4,6-bis(4-benzothiazol-2-yl-phenyl)-benzoxazole (compound (58)) (yield: 99.2%).

[0099] The structure of the obtained pale yellow powder was identified using NMR. 1 H-NMR (DMSO-d6) detected the signals of the following 27 hydrogen atoms.

[0100] δ (ppm) = 8.50 (2H), 8.39 (2H), 8.33 (3H), 8.26 (2H), 8.23-8.10 (7H), 8.00 (2H), 7.83 (2H), 7.64-7.44 (7H).

[0101] [Example 6: Synthesis of compound (74)] 2.5 g of 4,6-dibromo-2-phenyl-benzoxazole, 4.9 g of 3-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborphane-2-yl)phenyl]quinoline, 0.4 g of tetra(triphenylphosphine)palladium(O), and 2.9 g of potassium carbonate were added to a reaction vessel and refluxed and stirred overnight in a toluene / EtOH / H2O mixed solvent. After the resulting mixture was naturally cooled, MeOH / H2O was added, and the precipitated solid was filtered to obtain a crude product. The crude product was purified by recrystallization using monochlorobenzene to obtain 2.8 g of a white powder of 2-phenyl-4,6-bis(4-quinoline-3-yl-phenyl)-benzoxazole (compound (74)) (yield: 65.7%).

[0102] The structure of the obtained white powder was identified using NMR.1 H-NMR (CDC13) detected the following 27 hydrogen signals.

[0103] δ (ppm) = 9.30 (2H), 8.42 (2H), 8.38 (2H), 8.33 (2H), 8.18 (2H), 7.96-7.88 (10H), 7.76 (2H), 7.62 (2H), 7.58-7.57 (3H).

[0104] [Example 7: Synthesis of Compound (86)] Into a reaction vessel were put 4,6-dibromo-2-phenyl-benzoxazole: 5.0 g, 2-[4-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)phenyl]oxazolo[5,4-b]pyridine: 10.0 g, tetrakis(triphenylphosphine)palladium(0): 0.8 g, and potassium carbonate: 5.9 g, and stirred at reflux for one night in a mixed solvent of toluene / EtOH / H20. After the resulting mixture was naturally cooled, H20 was added, and the precipitated solid was filtered to obtain a crude product. The obtained crude product was purified by recrystallization using 1,2-dichlorobenzene, whereby white powder of 2-phenyl-4,6-bis(4-oxazolo[4,5-b]pyridin-2-yl-phenyl)-benzoxazole (Compound (86)) was obtained: 5.5 g (yield: 66.5%).

[0105] The obtained white powder was identified for structure using NMR. By 1 H-NMR (CDC13) detected the following 21 hydrogen signals.

[0106] δ (ppm) = 8.50 (2H), 8.45 (2H), 8.40-8.36 (6H), 8.12 (2H), 7.95-7.92 (4H), 7.59-7.58 (3H), 7.41-7.37 (2H).

[0107] [Example 8: Synthesis of Compound (119)] To a reaction vessel was charged 3'-(2-([1,1'-biphenyl]-4-yl)-6-chlorobenzo[b]oxazol-4-yl)-[1,1'-biphenyl]-4-carbonitrile: 9.0 g, 2-{4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl}oxazolo[5,4-b]pyridine: 6.6 g, tris(dibenzylideneacetone)dipalladium(0): 0.5 g, tricyclohexylphosphine: 0.6 g, and potassium phosphate tribasic: 7.9 g, and stirred at reflux in a 1,4-dioxane / H2O mixed solvent overnight. After the resulting mixture was allowed to cool naturally, H2O was added, and the precipitated solid was filtered to obtain a crude product. The crude product was recrystallized using 1,2-dichlorobenzene to obtain yellow powder of 3'-(2-([1,1'-biphenyl]-4-yl)-6-(4-(oxazolo[4,5-b]pyridin-2-yl)phenyl)benzo[b]oxazol-4-yl)-[1,1'-biphenyl]-4-carbonitrile (compound (119)): 7.1 g (yield: 59.3%).

[0108] The structure of the resulting yellow powder was identified using NMR. 1 The following signals of 26 hydrogens were detected by1H-NMR (CDCI3).

[0109] δ (ppm) = 8.43 (2H), 8.39 (4H), 8.15 (1H), 8.10 (1H), 7.92-7.88 (4H), 7.85 (2H), 7.79 (4H), 7.70-7.68 (4H), 7.50 (2H), 7.44-7.37 (2H).

[0110] The melting point and glass transition temperature (Tg) of the compounds obtained in Examples 1 to 8 were measured using a high-sensitivity differential scanning calorimeter (manufactured by Bruker AXS, trade name: DSC3100SA). The measurement results are shown in Table 1.

[0111] [Table 1]

[0112] As shown in Table 1, it was found that the benzoxazole compound of the present application could be vapor-deposited even if the melting point was high, and had no glass transition temperature or had a glass transition temperature of 100°C or higher. This result indicates that the thin film state of the benzoxazole compound of the present application is stable and has excellent durability.

[0113] Using the compounds obtained in Examples 1 to 8 and a compound (CPL-1) of the following structure (for example, refer to Patent Document 2) as comparative compounds, an evaporation film having a film thickness of 80 nm was formed on a silicon substrate. The refractive index n and the extinction coefficient k at a wavelength of 450 nm and 750 nm were measured for the formed evaporation film using a spectrometer (FILMETRICS Co., Ltd., product name: F10-RT-UV). The measurement results are summarized in Table 2.

[0114] [Chemical Formula 7]

[0115] [Table 2]

[0116] As shown in Table 2, the benzoxazole compounds of the present application have a value of the refractive index and the extinction coefficient which is equal to or higher than those of Alq3 and the compound (CPL-1) as comparative compounds between a wavelength of 450 nm and 750 nm. That is, by using the benzoxazole compounds of the present application as a material for the cover layer, an improvement in light extraction efficiency in the organic EL element can be expected.

[0117] [Example 9] A reflective ITO electrode as a transparent anode 2 was formed on a glass substrate 1 in advance, and a hole injection layer 3, a hole transport layer 4, a light emitting layer 5, an electron transport layer 6, an electron injection layer 7, a cathode 8, and a cover layer 9 were sequentially evaporated thereon, thereby producing an organic EL element having Figure 10 The organic EL element was produced.

[0118] Specifically, for the glass substrate 1 on which ITO of 50 nm in thickness, silver alloy of 100 nm in thickness, and ITO of 5 nm in thickness were sequentially deposited, after ultrasonic cleaning in isopropanol for 20 minutes, drying was performed on a hot plate heated to 250°C for 10 minutes. Thereafter, UV ozone treatment was performed for 2 minutes, and the resultant ITO-equipped glass substrate was installed in a vacuum deposition machine, and reduced to 0.001 Pa or less. Next, the electron acceptor (Acceptor-1) and the compound (HTM-1) of the following structure were binary-deposited at a deposition rate ratio of Acceptor-1 : (HTM-1) = 3 : 97 in a manner to cover the transparent anode 2, whereby a hole injection layer 3 of 10 nm in thickness was formed. The compound (HTM-1) was deposited on the hole injection layer 3 as a hole transport layer 4 in a manner to be 140 nm in thickness. The compound (EMD-1) and the compound (EMH-1) of the following structure were binary-deposited on the hole transport layer 4 at a deposition rate ratio of (EMD-1) : (EMH-1) = 5 : 95, whereby a light-emitting layer 5 of 20 nm in thickness was formed. The compound (ETM-1) and the compound (ETM-2) of the following structure were binary-deposited on the light-emitting layer 5 at a deposition rate ratio of (ETM-1) : (ETM-2) = 50 : 50, whereby an electron transport layer 6 of 30 nm in thickness was formed. Lithium fluoride was deposited on the electron transport layer 6 as an electron injection layer 7 in a manner to be 1 nm in thickness. Magnesium-silver alloy was deposited on the electron injection layer 7 as a cathode 8 in a manner to be 12 nm in thickness. Finally, the compound (4) obtained in Example 1 was deposited as a cover layer 9 in a manner to be 60 nm in thickness.

[0119] [Chem. 8]

[0120] [Chem. 9]

[0121] [Examples 10 to 16] As the cover layer 9, the compounds obtained in Examples 2 to 8 were used instead of the compound (4), and otherwise, an organic EL element relating to Examples 10 to 16 was produced by the same method as in Example 9.

[0122] [Comparative Example 1] As the cover layer 9, Alq3 was used instead of the compound (4), and otherwise, an organic EL element was produced by the same method as in Example 9.

[0123] [Comparative Example 2] As the cover layer 9, compound (CPL-1) was used instead of compound (4), and an organic EL element was produced in the same manner as in Example 9, except for this.

[0124] The organic EL elements produced in the Examples and Comparative Examples were evaluated for light emission characteristics (current density: 10 mA / cm 2 ). In addition, the element life was measured using the organic EL elements produced in the Examples and Comparative Examples. The results are summarized in Table 3. Note that, in the present application, the element life is represented by the time until the luminance decays to 95% of the initial luminance (100%) when constant current driving at 10 mA / cm 2 2

[0125] [Table 3]

[0126] As shown in Table 3, the driving voltage at a current density of 10 mA / cm 2 was roughly the same in the elements relating to Comparative Examples 1 and 2 and the elements relating to Examples 9 to 16. On the other hand, with respect to luminance, emission efficiency, power efficiency, and element life, a significant improvement was observed in the elements relating to all of the Examples, as compared with the elements relating to the Comparative Examples. This result indicates that the benzoxazole compound of the present application is a material suitable for use in a cover layer, and that the light extraction efficiency of an organic EL element can be greatly improved by increasing the refractive index of the material used in the cover layer.

[0127] The above-described preferred embodiments of the present application have been shown and described in detail, but it should be understood that the present application is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the gist or scope of the appended claims.

[0128] (Industrial Applicability) The benzoxazole compound of the present application has a high refractive index, can greatly improve the light extraction efficiency, is stable in a thin film state, and is thus suitable as a compound for use in a cover layer of an organic EL element. In addition, an organic EL element produced using the benzoxazole compound of the present application can achieve high efficiency. Furthermore, the benzoxazole compound of the present application, which does not exhibit absorption in the respective wavelength regions of blue, green, and red, is particularly suitable in cases where it is desired to display an image that is excellent in color purity, clear, and bright. The benzoxazole compound of the present application can be expected to be used, for example, in household electric appliances and lighting.

[0129] Explanation of Reference Signs 1 glass substrate 2 anode 3 hole injection layer 4 hole transport layer 5 light-emitting layer 6 electron-transporting layer 7 electron-injecting layer 8 cathode 9 capping layer

Claims

1. An organic electroluminescent device, comprising, in sequence, an anode, a hole transport layer, a light-emitting layer, an electron transport layer, a cathode, and a capping layer, wherein, The coating layer contains a benzoazole compound represented by the following general formula (1), [Chemical Formula 1] In the formula, A represents the benzoxazole ring or the benzothiazole ring. B and C independently represent substituted or unsubstituted phenyl, naphthyl, quinolinyl, quinoxalinyl, quinazolinyl, phenanthrolinel, benzoxazolyl, benzothiazolyl, benzofuranyl, benzothiophene, or oxazolopyridyl. D represents a hydrogen atom or a substituted or unsubstituted aryl or heteroaryl group. L1 to L3 represent single bonds or unsubstituted divalent aryl or divalent heteroaryl groups independently.

2. The organic electroluminescent element according to claim 1, wherein, In the general formula (1), L2, L3 and L1 are bonded to the 2, 4 and 6 positions of the benzoxazole ring or benzothiazole ring represented by A, respectively.

3. The organic electroluminescent element according to claim 1, wherein, In the general formula (1), L1 to L3 are independently single bonds or unsubstituted phenylene, biphenylene, or naphthylene.

4. The organic electroluminescent element according to claim 1, wherein, In the general formula (1), the aryl or heteroaryl group represented by D is selected from the group consisting of phenyl, biphenyl, naphthyl, furanyl, quinolinyl, benzoxazolyl, benzothiazolyl, oxazolopyridyl, quinoxalinyl, quinazolyl and phenanthrolinel.

5. The organic electroluminescent element according to claim 4, wherein, In the general formula (1), D is a hydrogen atom, cyanophenyl or an unsubstituted phenyl, biphenyl, naphthyl, furanyl, quinolinyl, benzoxazolyl, benzothiazolyl, oxazolopyridyl, quinoxolinyl, quinazolyl or phenanthrolinel.

6. The organic electroluminescent element according to claim 1, wherein, In the general formula (1), at least one of B and C is a group selected from the group consisting of unsubstituted phenyl, naphthyl, quinolinyl, quinazolinyl, phenanthrolinyl, benzoxazolyl, benzothiazolyl and oxazolopyridyl.

7. The organic electroluminescent element according to claim 1, wherein, When the coating layer is formed to a thickness of 30 nm to 120 nm, the resulting film has a refractive index of 1.70 or higher in the wavelength range of 450 nm to 750 nm.

8. The organic electroluminescent element according to any one of claims 1 to 7, wherein, The covering layer is a stack or mixture of two or more compounds containing a benzoxazole compound represented by the general formula (1).

9. A benzoazole compound represented by the following general formula (2): [Chemical Formula 2] In the formula, A represents the benzoxazole ring or the benzothiazole ring. B and C independently represent substituted or unsubstituted phenyl, naphthyl, quinolinyl, quinoxalinyl, quinazolinyl, phenanthrolinel, benzoxazolyl, benzothiazolyl, benzofuranyl, benzothiophene, or oxazolopyridyl. D represents a hydrogen atom or a substituted or unsubstituted phenyl, biphenyl, naphthyl, furanyl, quinolinyl, quinoxalinyl, quinoxalinyl, quinazolinyl, phenanthrolinel, benzoxazolyl, benzothiazolyl, benzofuranyl, benzothiophene, or oxazolopyridyl. L1 to L3 independently represent single bonds or unsubstituted phenylene, biphenylene, or naphthylene groups. L2, L3, and L1 are bonded to positions 2, 4, and 6 of the benzoxazole or benzothiazole ring represented by A, respectively. The benzoazole compound satisfies either requirement 1 or requirement 2 below: Requirement 1: At least one of B, C, and D contains a structure selected from the group consisting of quinazoline, phenanthroline, and oxazolopyridine, wherein... If one or both of B, C, and D are substituted or unsubstituted phenanthroline groups, and if none of B, C, and D are substituted phenanthroline groups, or if neither of B, C, and D are substituted quinazolinyl or oxazolopyridyl groups, then at least one of L1, L2, and L3 bonded to the phenanthroline group is an unsubstituted phenylene, biphenylene, or naphthylene group. When B, C, and D are all substituted or unsubstituted phenanthroline groups, at least one of L1, L2, and L3 bonded to the phenanthroline group is an unsubstituted phenylene, biphenylene, or naphthylene. Requirement 2: B, C and D do not contain any structures selected from the group consisting of quinazoline, phenanthroline and oxazolopyridine, L3 is a single bond and D is a hydrogen atom.

10. The benzoazole compound according to claim 9, wherein, In the general formula (2), at least one of B and C is a group selected from the group consisting of substituted or unsubstituted phenyl, naphthyl, quinolinyl, quinazolinyl, phenanthrolinyl, benzoxazolyl, benzothiazolyl, benzofuranyl and oxazolopyridyl.

11. An electronic device or electronic component having a pair of electrodes and at least one organic layer, wherein, The organic layer contains the benzo[a]azole compound as described in claim 9 or 10.

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