Abstract:
An organic EL device which contains an anode, a cathode, and at least one organic thin-file layer including a light emitting layer which contains a compound represented by the following general formula (1), (2) or (3):  
                         
 
     wherein Y represents an connecting aromatic group of the following general formula (4), (5) or (6):  
                         
 
     Ar 1  group represents a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group. X and Z represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted amino group, a substituted or unsubstituted alkoxy group a substituted or unsubstituted aryloxy group or a substituted or unsubstituted alkoxycarbonyl group; and Rx is one or more functional groups represented by a hydrogen atom, halogen atom, nitro group, cyano group, carboxyl group, or X. Two Rx groups may form a ring.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a luminescent material for an organic EL device having light-emitting properties.  
           [0003]    2. Description of the Related Art  
           [0004]    An organic electroluminescent device (organic EL device) is a light emitting device, containing a fluorescent material which emits light in response to the recombination of hole and electron injected from anode and cathode. For example, C. W. Tang et al. reported an organic EL device using a double-layered structure (Applied Physics Letters, 51,913 (1987)). This organic EL device, which has a tris (8-hydroxyquinolinol aluminum) in a light-emitting layer and a triphenyldiamine derivative in hole-transporting layer, greatly enhances the luminescence properties.  
           [0005]    To further improve luminescence efficiency, a method of doping a fluorescent dye had been utilized. For example, an organic EL device with a coumarin dye as the doping material (Applied Physics Letters, 65,3610 (1989)) has been used to greatly improve the luminescence efficiency. For improving the recombination efficiency of the injected hole and electron, multi-layered devices have been introduced. As a hole-transporting material, triphenylamine derivatives such as 4,4′,4″-tris(3-methylphenylphenylamino)-triphenylamine and aromatic diamine derivatives such as N,N′-diphenyl-N,N′ bis (3-methylphenyl)-[1,1′-biphenyl]-4,4′diamine are well known (see Japanese Patent Application Laid-Open Nos. 20771/1996, 40995/1996, 40997/1996, 53397/1996, 87122/1996). As an electron-transporting material, triazole derivatives and the like are also known.  
           [0006]    Examples of the blue light emissive material for organic EL device include condensed polycyclic aromatic compounds such as anthracene, pyrene and perylene (J. Chem. Phys., 44, 2902 (1996)), tetraphenylbutadiene-based compounds, distyrylbenzene-based compounds, stilbene-based compounds and polyphenyl-based compounds. (unexamined published Japanese patent application JP-A-61-37890, JP-A-1-245087, JP-A-2-247227, JP-A-2-247278, JP-A-2-209988, JP-A-3-33184, JP-A-3-84089, JP-A-3-231970, JP-A-4-117485, JP-A-4-275268, JP-A-5-17765, JP-A-140145, JP-A-3-47890, JP-A-3-33183, JP-A-5-247459 and JP-A-9-157642). However, these compounds have many problems involving durability, color purity, and luminescence efficiency.  
         SUMMARY OF THE INVENTION  
         [0007]    An object of the present invention is to provide a high performance material and to provide an organic EL device having blue luminescence. The organic EL device comprises an anode, cathode, and one or more organic thin film layers which contain, either singly or as a mixture, an indole compound represented by the following formula (1), (2) or (3):  
                         
 
           [0008]    wherein Y represents an extending aromatic group of the following general formula (4), (5) or (6):  
                         
 
           [0009]    wherein Ar 1  group represents a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group. X and Z represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted amino group, a substituted or unsubstituted alkoxy group a substituted or unsubstituted aryloxy group or a substituted or unsubstituted alkoxycarbonyl group; and Rx is one or more functional groups represented by a hydrogen atom, halogen atom, nitro group, cyano group, carboxyl group, or X. Two Rx groups may form a ring. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 illustrates a construction of an organic EL element of the present invention;  
         [0011]    [0011]FIG. 2 illustrates another construction of an organic EL element of the present invention;  
         [0012]    [0012]FIG. 3 illustrates yet another construction of an organic EL element of the present invention;  
         [0013]    [0013]FIG. 4 illustrates still another construction of an organic EL element of the present invention; and  
         [0014]    [0014]FIG. 5 illustrates yet still another construction of an organic EL element of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    The present invention will hereinafter be described specifically. The indole compound represented by the following formula (1), (2) or (3) to be used for the organic EL device. For the Z groups, a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group is a better choice. For the X groups, a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group is also a better choice. Some examples of X groups are shown below, but the present invention is not limited thereto:  
                         
 
         [0016]    wherein the Rx groups is the same with above.  
         [0017]    Y group means an extending aromatic group of the general formula (4), (5) or (6):  
                         
 
         [0018]    wherein the Ar 1  group represents a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group. In formula (4), it means that Ar 1  connecting with (1), (2) or (3) directly. In formula (5), it means that Ar 1  connecting with (1), (2) or (3) with a carbon-carbon double bond. In formula (6), it means that Ar 1  connecting with two unit of (1), (2) or (3) with two carbon-carbon double bonds. Some examples of Y groups are shown below, but the present invention is not limited thereto:  
                         
 
         [0019]    wherein Rx is the same with above. A represents an oxygen atom, nitrogen atom or a sulfur atom.  
         [0020]    Referring to the following reaction example, synthesis methods for the indole compound represented by the formula (1), (2) or (3) of the present invention will be described.  
         [0021]    First, 2-substituted indole compound can be prepared by various methods shown below in scheme (1).  
                         
 
         [0022]    Then, the Z group can be formed by the methods shown below in scheme (2).  
                         
 
         [0023]    As shown in scheme (3), an example of target indole compound can be prepared.  
                         
 
         [0024]    Examples of the indole compounds represented by the formulae (1), (2) or (3) to be used in the organic EL device of the present invention are shown below, but the present invention is not limited thereto.  
                         

                         

                         
 
         [0025]    The organic EL device according to the present invention has a multi-layered structure including a light emitting layer, hole transporting layer, and electron transporting layer. Methods of selecting hole transporting material and electron transporting material are well known. Examples of hole transporting materials are shown below and represented by formula (A) through formula (E). Examples of electron transporting materials are shown below and represented by formula (F) through formula (J). The anode material of the organic EL device used in this present invention is indium tin oxide (ITO), and the cathode material is aluminum or calcium or both.  
                         

                         
 
         [0026]    The present invention will hereafter be described in detail with reference to examples, but the present invention is not limited only to the following examples unless the spirit or scope of the invention is changed.  
       SYNTHESIS EXAMPLES  
     Example 1  
       [0027]    Synthesis of compound (1-1). A solution of dry THF containing 2-phenylindole (1 mmole) was added NaH (1.1 mmole) and MeI (1.2 mmole, dropwise), and the reaction mixture was stirred at 65 for 3 h. After cooling to room temperature, the reaction mixture was poured into water and extracted with ether. The extracts was dried (MgSO 4 ) and evaporated under reduced pressure to give yellow-orange solid. Further purification by column chromatography on silica gel with hexane as an eluent gave a pale yellow solid of 1-methyl-2-phenylindole (79% yield). The solid product (0.7 mmole) was dissolved in DMF (10 ml), a mixture of POCl 3  (0.09 mmole) and DMF (0.09 mmole) was added dropwise. After stirring at 75 for 1 h, the reaction mixture was added into saturate NaHCO 3  solution. The precipitated solid was collected by filtration and washed with ethanol to give a pale gray solid of 1-methyl-2-phenylindole-3-carboxaldehyde (85% yield). A dry DMF solution of the aldehyde (2 mmole) was added o-aminothiophenol (2.1 mmole) and Ac 2 O (0.5 ml) at room temperature. The mixture was stirred at 60 for 3 h. The reaction mixture was poured into stirred water and the precipitated solid was collected by filtration. The crude solid was washed with MeOH and recrystallized from benzene to afford compound 1-2 (38% yield).  1 H-NMR (CDCl 3 , TMS) (ppm)=3.6 (s, 3H, —CH 3  ), 7.3-7.8, 8.1, 8.9 (m, d, m, 13H, aromatic H).  
       Example 2  
       [0028]    Synthesis of compound (1-4). A solution of dry o-dichlorobenzene containing 2-phenylindole (1 mmole) was added K 2 CO 3  (1.5 mmole), 4-iodotoluene (1 mmole), copper powder (1.5 mmole) and 18-crown-6 (0.02 mmole) , the reaction mixture was stirred under argon at 185 overnight. After cooling to room temperature, the reaction mixture was washed with hexane. The solid mixture was dissolved in EA, the K 2 CO 3  and copper podwer was removed by filtration. EA solution was evaporated under reduced pressure to give brown-red crude solid. Further purification by column chromatography on silica gel with hexane as an eluent gave a pale yellow solid of 1,2-diphenylindole (75% yiled). The solid product (1 mmole) was dissolved in DMF (10 ml), a mixture of POCl 3  (1.2 mmole) and DMF (1.2 mmole) was added dropwise. After stirring at 75 for 1 h, the reaction mixture was added into saturate NaHCO 3  solution. The precipitated solid was collected by filtration and washed with ethanol to give a pale gray solid of 1,2-diphenylindole-3-carboxaldehyde (90% yield). A dry DMF solution of the aldehyde (2 mmole) was added o-aminothiophenol (2.1 mmole) and Ac 2 O (0.5 ml) at room temperature. The mixture was stirred at 60 for 3 h. The reaction mixture was poured into stirred water and the precipitated solid was collected by filtration. The crude solid was washed with MeOH and recrystallized from benzene to afford compound 1-4 (32% yield).  1 H-NMR (CDCl 3 , TMS) (ppm)=2.4 (s, 3H, Ar—CH 3 ), 7.1-7.6, 8.2 (m, d, 17H, aromatic H).  
       Example 3  
       [0029]    Synthesis of compound (1-10). A stirred mixture of 2-acetylfluorene (0.1 mmole), phenylhydrazine (0.11 mmole) and phosphoric acid (150 g) was heated to 150 for 30 mins. After cooling to room temperature, the reaction was poured into cooling water and extracted with ether. The extracts was dried (MgSO 4 ) and evaporated under reduced pressure to give yellow solid. The crude solid was recrystallized from EA to get pale yellow solid of 2-fluorene indole (35% yield). A solution of dry THF containing 2-fluorene indole (0.1 mmole) was added t-BuOK (0.11 mmole) and MeI (0.12 mmole, dropwise), and the reaction mixture was stirred at 65 for 3 h. After cooling to room temperature, the reaction mixture was poured into water and extracted with ether. The extracts was dried (MgSO 4 ) and evaporated under reduced pressure to give yellow solid. Further purification by washing with EA to get pale yellow solid of 1-methyl-2-fluorene indole (62% yield). The solid product (0.1 mmole) was dissolved in DMF (5 ml), a mixture of POCl 3  (0.12 mmole) and DMF (0.12 mmole) was added dropwise. After stirring at 75 for 1 h, the reaction mixture was added into saturate NaHCO 3  solution. The precipitated solid was collected by filtration and washed with ethanol to give a pale pink-yellow solid of 1-methyl-2 fluorene indole-3-carboxaldehyde (82% yield). A dry DMF solution of the aldehyde (2 mmole) was added diethyl benzylphosphonate (2.1 mmole) and t-BuOK (2.2 mmole) at room temperature. The mixture was stirred at 75 for 3 h. The reaction mixture was poured into stirred water and the precipitated solid was collected by filtration. The crude solid was washed with MeOH and recrystallized from benzene to afford compound 1-10 (58% yield).  1 H-NMR (CDCl 3 , TMS) (ppm)=3.8 (s, 3H, —CH 3  ), 4.0 (s, 2H, fluorine 2H), 7.1-7.9 (m, 18H, aromatic H, Ar—CH═CH—Ar).  
       Example 4  
       [0030]    Synthesis of compound (1-12). A solution of dry THF containing 2-phenylindole (1 mmole) was added NaH (1.1 mmole) and MeI (1.2 mmole, dropwise), and the reaction mixture was stirred at 65 for 3 h. After cooling to room temperature, the reaction mixture was poured into water and extracted with ether. The extracts was dried (MgSO 4 ) and evaporated under reduced pressure to give yellow-orange solid. Further purification by column chromatography on silica gel with hexane as an eluent gave a pale yellow solid of 1-methyl-2-phenylindole (79% yield). The solid product (0.7 mmole) was dissolved in DMF (10 ml), a mixture of POCl 3  (0.09 mmole) and DMF (0.09 mmole) was added dropwise. After stirring at 75 for 1 h, the reaction mixture was added into saturate NaHCO 3  solution. The precipitated solid was collected by filtration and washed with ethanol to give a pale gray solid of 1-methyl-2-phenylindole-3-carboxaldehyde (85% yield). A dry DMF solution of the aldehyde (2 mmole) was added 4-benzothiazolyl-diethyl benzylphosphonate (2.1 mmole) and t-BuOK (2.2 mmole) at room temperature. The mixture was stirred at 75 for 3 h. The reaction mixture was poured into stirred water and the precipitated solid was collected by filtration. The crude solid was washed with MeOH and recrystallized from benzene to afford compound 1-12 (63% yield).  1 H-NMR (CDCl 3 , TMS) (ppm)=3.6 (s, 3H, —CH 3 ), 6.9-7.7, 8.2 (m, d, 19H, aromatic H, Ar—CH═CH—Ar).  
         [0031]    The present invention regarding production of organic EL device is further discussed below. Examples of used glass substrates with ITO electrode having a surface resistance of 20 (/) as the anode, calcium and aluminum film as the cathode are illustrated.  
       DEVICE EXAMPLES  
     Example 1  
       [0032]    As the structure shown in FIG. 1, a 80 mg PVK (poyl-vinylcarbazole), 15 mg compound (H) and 3 mg compound (1-1) are dissolved in 10 ml 1,2-dichloroethane. An organic thin film is formed by spin coating on the anode  11  as an emitting layer  12 . An 1 nm of calcium layer  13  is formed by vacuum deposition on the organic layer  12  as the cathode  1 . Moreover, an aluminum cathode  14  is formed by vacuum deposition on the cathode  1  as the cathode  2 . When a dc voltage 21V is applied to the resulting device, a 130 cd/m 2  brightness light emission is obtained. In a similar manner as applied to example 1, example 2 through example 4 are fabricated and the results listed in Table 1 as follows:  
                       TABLE 1                       Example   Compound   Brightness (cd/m 2 )                   1   1-1    130       2   1-4    145       3   1-10   105       4   1-12   150                  
 
       Example 5  
       [0033]    As shown in FIG. 2, a 50 nm hole-transporting layer  22  is formed by vacuum deposition a compound (B) on the ITO  21 . Over the hole-transporting layer  22 , a 10 nm emitting layer  23  is formed by vacuum deposition a compound (1-1). Then, a 30 nm electron-transporting layer  24  is formed by vacuum deposition a compound (H) on the emitting layer  23 . Finally, a 200 nm aluminum cathode  25  is formed by vacuum deposition on the organic layer  24 . When a dc voltage of 15 V is applied to the resulting device, a 420 cd/m 2  brightness light emission is obtained. In a similar manner as applied to example 5, example 6 through example 8 are fabricated and the results listed in Table 2 as follows:  
                       TABLE 2                       Example   Compound   Brightness (cd/m 2 )                   5   1-1    420       6   1-4    450       7   1-10   310       8   1-12   560                  
 
       Example 9  
       [0034]    As shown in FIG. 2, a 50 nm hole-transporting layer  22  is formed by vacuum deposition a compound (B) on the ITO  21 . Over the hole-transporting layer  22 , a 10 nm emitting layer  23  is formed by vacuum deposition a compound (1-1). Then, a 30 nm electron-transporting layer  24  is formed by vacuum deposition a compound (J) on the emitting layer  23 . Finally, a 200 nm aluminum cathode  25  is formed by vacuum deposition on the organic layer  24 . When a dc voltage of 15 V is applied to the resulting device, a 1350 cd/m 2  brightness light emission is obtained. In a similar manner as applied to example 9, example 10 through example 12 are fabricated and the results listed in Table 3 as follows:  
                       TABLE 3                       Example   compound   Brightness (cd/m 2 )                    9   1-1    1350       10   1-4    1520       11   1-10   1020       12   1-12   1700                  
 
       Example 13  
       [0035]    As shown in FIG. 3, a 30 nm hole-transporting layer  32  is formed by vacuum deposition a compound (D) on the ITO  31  as the hole-transporting layer  1 . Over the hole-transporting layer  32 , a 40 nm of hole-transporting layer  33  is formed by vacuum deposition a compound (B) as the hole-transporting layer  2 . A 5 nm emitting layer  34  is formed by vacuum deposition a compound (1-1) on the hole-transporting layer  33 . Then, a 30 nm electron-transporting layer  35  is formed by vacuum deposition a compound (H) on the emitting layer  34 . Finally, a 200 nm aluminum cathode  36  is formed by vacuum deposition on the electron-transporting layer  35 . When a dc voltage of 15 V is applied to the resulting device, a 2100 cd/m 2  brightness light emission is obtained. In a similar manner as applied to example 13, example 14 through example 16 are fabricated and the results listed in Table 4 as follows:  
                       TABLE 4                       Example   compound   Brightness (cd/m 2 )                   13   1-1    2100       14   1-4    2250       15   1-10   1800       16   1-12   2800                  
 
       Example 17  
       [0036]    As shown in FIG. 4, a 30 nm hole-transporting layer  42  is formed by vacuum deposition a compound (D) on the ITO  41  as the hole-transporting layer  1 . Over the hole-transporting layer  42 , a 40 nm of hole-transporting layer  43  is formed by vacuum deposition a compound (B) as the hole-transporting layer  2 . A 5 nm emitting layer  44  is formed by a vacuum deposition a compound (1-1) on the hole-transporting layer  43 . Then, an 8 nm of hole blocking layer  45  is formed by vacuum deposition a compound (H) on the emitting layer  44 . Moreover, a 30 nm of electron-transporting layer  46  is formed by vacuum deposition a compound (I) on the hole blocking layer  45 . Finally, a 200 nm aluminum cathode  47  is formed by vacuum deposition on the electron-transporting layer  46 . When a dc voltage of 15 V is applied to the resulting device, a 2250 cd/m 2  brightness light emission is obtained. In the similar manner as applied to example 17, example 18 through example 20 are fabricated and the results listed in Table 5 as follows:  
                       TABLE 5                       Example   compound   Brightness (cd/m 2 )                   17   1-1    2250       18   1-4    2380       19   1-10   1750       20   1-12   3020                  
 
       Example 21  
       [0037]    As shown in FIG. 5, a 40 nm of hole-transporting layer  52  is formed by vacuum deposition a compound (B) on the ITO  51 . A 10 nm emitting layer  53  is formed by vacuum deposition a compound (1-1) on the hole-transporting layer  52 . A 30 nm of electron-transporting layer  54  is formed by vacuum deposition a compound (J) on the emitting layer  53  as the electron-transporting layer  1 . Then, a 0.8 nm of electron-transporting layer  55  is formed by vacuum deposition of LiF on the electron-transporting layer  54  as the electron-transporting layer  2 . Finally, a 200 nm aluminum cathode  56  is formed by vacuum deposition on the electron-injection layer  55 . When a dc voltage of 15 V is applied to the resulting device, a 2350 cd/m 2  brightness light emission is obtained. In the similar manner as applied to example 21, example 22 through example 24 are fabricated and the results listed in Table 6 as follows:  
                       TABLE 6                       Example   compound   Brightness (cd/m 2 )                   21   1-1    2350       22   1-4    2500       23   1-10   1850       24   1-12   2900