# Patent

## Title
Light-emitting material and light-emitting device

## Abstract

There is provided a light-emitting material comprising a metal coordination compound having a partial structure represented by the following general formula (1).




The light-emitting material has high luminous efficiency and high stability and can be produced at a low cost.

## Background
This application claims priority from Japanese Patent Application No. 2003-196957 filed on Jul. 15, 2003, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting device using an organic compound. More specifically, the present invention relates to a light-emitting device that can provide stability and high efficiency by using a metal coordination compound as a light-emitting material.
2. Related Background Art
Applied studies have been vigorously conducted on organic EL elements as light-emitting devices having high-speed response and high efficiency (see, for example, Macromol. Symp. 125, 1-48 (1997)).
Copper complexes can be manufactured at relatively low costs because their raw materials are available at low costs. Sufficiently exploiting the performance of a copper complex enables a low-cost and high-performance organic EL element to be manufactured.
Organic EL elements using copper complexes are disclosed in Japanese Patent No. 2940514 and Advanced Materials 1999 11 No. 10 p. 852 Y. Ma et al. “High Luminescence Gold (1) and Copper (1) Complexes with Triplet Excited State for Use in Light-Emitting Diodes.” However, those EL elements have significantly low luminous efficiency and those publications describe insufficiently the efficiency of those elements. Therefore, it is hard to consider that the properties of the copper complexes are sufficiently exploited. The performance of those elements is not enough for use in displays, lighting, and so on.
Acta Crystallographica Section C C54, 1998, p. 1087 discloses a copper complex having a structure which is relatively similar to that of a compound of the present invention. However, this publication has no description relating to light emission. Moreover, the copper complex cannot be regarded as a light-emitting material because the copper complex emits no light or extremely weak light at room temperature.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a low-cost light-emitting material having high luminous efficiency and high stability.
That is, according to one aspect of the present invention, there is provided a light-emitting material which is a metal coordination compound having a partial structure represented by the following general formula (1):




(wherein:

Cu represents a copper ion;
a ligand A is a bidentate ligand having as its fundamental skeleton 2,2′-bipyridinyl which may have a condensed cyclic group or a substituent;
an atom P that coordinates with Cu is a phosphorus atom of a phosphine compound represented by PR1R2R3 (R1, R2, and R3 in PR1R2R3 each represent one of a straight-chain, branched, or cyclic alkyl group and an aromatic cyclic group that may have a substituent, and R1, R2, and R3 may be identical to or different from one another. A CH2 group in the alkyl group may be substituted by —O— or —NH—. An H atom may be substituted by an aromatic cyclic group or a halogen atom.);
an atom of X1 that coordinates with Cu is selected from the group consisting of a halogen atom, an oxygen atom, a sulfur atom, and a nitrogen atom; and
one of R1, R2, and R3 in PR1R2R3 may contain X1 to form a bidentate ligand).
According to another aspect of the present invention, there is provided a light-emitting device having a light-emitting layer containing the above light-emitting material.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A, 1B, 1C, and 1D are diagrams each showing an example of a light-emitting device according to an embodiment of the present invention;
FIG. 2 is a 1H-NMR chart of Exemplified Compound 326;
FIG. 3 is a 1H-NMR chart of Exemplified Compound 335; and
FIG. 4 shows emission spectra of Exemplified Compounds 101, 102, and 335.



DESCRIPTION OF THE PREFERRED EMBODIMENT
Hereinafter, an embodiment of the present invention is described in detail.
First, the characteristics of a metal coordination compound (copper complex) which is a light-emitting material of the present invention are described.
A metal coordination compound of the present invention has a structure in which a nitrogen atom in a ligand A having an aromatic diimine structure and a phosphorus atom in phosphine having a PR1R2R3 structure coordinate with monovalent Cu.
A copper ion to be used as a central metal of a copper complex is preferably a +1 valent ion. When the electron configuration of a copper atom is taken into consideration, +1 valent copper should contain 10 d electrons. In general, a transition metal having an even number of d electrons often exhibits good light-emitting property.
The ligand A is preferably selected from the following structural formulae:




(wherein: each of the above structural formulae has a basic structure and may have a condensed cyclic group or a substituent; the substituent is a halogen atom, a straight-chain, branched, or cyclic alkyl group, or an aromatic cyclic group that may have a substituent; a CH2 group in the alkyl group may be substituted by —O— or —NR— (R represents an alkyl group or an aromatic cyclic group that may be substituted.); and an H atom may be substituted by an aromatic cyclic group or a halogen atom).

The ligand A is more preferably represented by the following structural formula:




(wherein: R and R′ each represent a straight-chain, branched, or cyclic alkyl group or an aromatic cyclic group that may have a substituent, and R and R′ may be identical to or different from each other; a CH2 group in the alkyl group may be substituted by —O— or —NH—; an H atom may be substituted by an aromatic cyclic group or a halogen atom; and one of R and R′ may be a hydrogen atom).

Specific examples of the ligand A are shown below.



















Specific examples of a phosphine ligand (monodentate ligand) are shown below.
















The metal coordination compound of the present invention is desirably a neutral and nonionic compound having no counter ion in view of an element preparation process in order to use the compound for a light-emitting device. To achieve this, it is preferable that, because each of the ligand A and the phosphine ligand is a zero valent neutral ligand, X1 be a −1 valent monodentate ligand and the atom of X1 that coordinates with Cu be selected from the group consisting of a halogen atom, a nitrogen atom in an aromatic cyclic group that may have a substituent, an oxygen atom in —OR, and a sulfur atom in —SR(R in —OR or in —SR is a straight-chain, branched, or cyclic alkyl group or an aromatic cyclic group that may have a substituent. A CH2 group in the alkyl group may be substituted by —O— or —NH—. An H atom may be substituted by an aromatic cyclic group or a halogen atom.). Specific examples of X1 are shown below.







Also, −1 valent bidentate ligands as shown below obtained by adding anionic groups to phosphine are preferable.







The excited states of the copper coordination compounds having those structures can belong to metal-to-ligand-charge-transfer (MLCT) excited states, so that strong light emission can be obtained. To obtain those excited states, it is desirable that a copper ion easily emit an electron and the electron-acceptability of a ligand that accepts the electron be strong upon excitation. In the case of the copper coordination compound of the present invention, a ligand that accepts an electron is the ligand A having a diimine structure with a long conjugate length and a large electron affinity. For instance, as described above, each of phenanthroline, 2,2′-bipyridine, and derivatives thereof can be used for the ligand. In addition, it is sufficient to allow a ligand having high electron-donating property to coordinate with a Cu ion in order to make it easy for the Cu ion to emit an electron. The phosphine ligand used in the present invention has the property and promotes strong light emission.
To achieve high luminous efficiency, it is important to adopt a ligand structure that suppresses a structural change between a ground state and an excited state. The coordination structure of Cu (1) is a 4-coordination pseudo-tetrahedral structure. High luminous efficiency can be obtained when the structure is maintained in an excited state. For example, in the case where the ligand A is such that 2- and 9-positions of phenanthroline are substituted by two alkyl groups, the ligand has an effect of maintaining a pseudo-tetrahedral structure in a ground state even in an excited state, so that high light-emitting property can be obtained. In an excited state, a tetrahedral structure tends to be a planar structure. However, a structure close to a tetrahedral structure can be maintained by substituting the ligand with a bulky substituent.
In addition, the light-emitting material of the present invention emits extremely strong light in a solid state, in particular, a perfect powder state as compared to a generally used light-emitting material in spite of the fact that the luminous efficiency of the light-emitting material of the present invention in a solution is not high. Probably, this is mainly due to the following two reasons.
One reason is that the coordination structure of Cu (1) in a ground state is a 4-coordination pseudo-tetrahedral structure. When Cu (1) is brought into an excited state by exciting it, Cu (1) forms an MLCT excited state. Therefore, Cu is in a state close to a +2 valent state, so that a structure close to a planar structure is stable. At this time, the structure changes to a large extent between the ground state and the excited state, and the number of heat inactivation paths of energy increases, thereby resulting in weakened light emission. However, the structural change is suppressed because a molecular motion is inhibited in a solid. Therefore, strong light emission may be obtained.
The other reason is that an additional coordination structure is formed in a solution and a 5-coordination structure may be formed. A 5-coordination structure cannot provide strong light emission. Such a 5-coordination reaction is hardly obtained in a solid because a molecular motion is suppressed in the solid. Therefore, strong light emission can be obtained in a solid.
In addition, the Cu coordination compound of the present invention in a powder solid form has an emission lifetime in the range of 0.05 to 50 μsec.
Alumiquinolinol derivatives, coumarin derivatives, quinacridone derivatives, and the like which have been conventionally used can provide extremely strong light emission in solutions, and their strong light-emitting properties are maintained as they are even in solid dispersions. Those properties effectively act even in organic EL elements, so that the high luminous efficiency of the elements can be obtained.
However, in the Cu complex of the present invention, light emission in a solid is extremely strong as compared to that in a solution. The inventors of the present invention have focused on the property and have found that the Cu complex is useful in high-efficiency and stable light emission in an organic EL element.
The Cu coordination compound of the present invention is useful for a light-emitting material for an organic EL element. It is needless to say that the Cu coordination compound has high luminous efficiency. In addition, the Cu coordination compound is suitable for film formation according to an evaporation process and for spin coating for dispersion in a high molecular weight substance. The Cu coordination compound enables stable element preparation because the compound undergoes no damages such as decomposition in an element preparation process. In addition, the inventors have confirmed that the Cu coordination compound poses no problem for the light emission stability of an EL element upon conduction.
As shown in the following examples, the compound of the present invention was found to exhibit excellent performance in terms of stability in a conduction endurance test.
Specific examples of the metal coordination compound of the present invention are shown below.












TABLE 1







Exemplified

Phosphine




Compound No.
Ligand A
ligand
X1





















101
31
41
51



102
31
41
52



103
31
41
53



104
31
41
54



105
31
41
55



106
31
41
56



107
31
41
57



108
31
41
58



109
31
41
59



110
31
41
510



111
31
41
511



112
31
41
512



113
31
41
513



114
31
41
514



115
31
41
515



116
31
41
516



117
31
41
517



118
31
41
518



119
31
47
51



120
31
47
52



121
31
47
53



122
31
47
54



123
31
47
55



124
31
47
56



125
31
47
57



126
31
47
58



127
31
47
59



128
31
47
510



129
31
47
511



130
31
47
512



131
31
47
513



132
31
47
514



133
31
47
515



134
31
47
516



135
31
47
517



136
31
47
518



137
33
41
51



138
33
41
52



139
33
41
53



140
33
41
54






















TABLE 2







Exemplified

Phosphine




Compound No.
Ligand A
ligand
X1





















141
33
41
55



142
33
41
56



143
33
41
57



144
33
41
58



145
33
41
59



146
33
41
510



147
33
41
511



148
33
41
512



149
33
41
513



150
33
41
514



151
33
41
515



152
33
41
516



153
33
41
517



154
33
41
518



155
33
47
51



156
33
47
52



157
33
47
53



158
33
47
54



159
33
47
55



160
33
47
56



161
33
47
57



162
33
47
58



163
33
47
59



164
33
47
510



165
33
47
511



166
33
47
512



167
33
47
513



168
33
47
514



169
33
47
515



170
33
47
516



171
33
47
517



172
33
47
518



173
32
41
51



174
34
41
51



175
35
41
51



176
36
41
51



177
37
41
51



178
38
41
51



179
39
41
51



180
310
41
51






















TABLE 3







Exemplified

Phosphine




Compound No.
Ligand A
ligand
X1





















181
311
41
51



182
312
41
51



183
313
41
51



184
314
41
51



185
315
41
51



186
316
41
51



187
317
41
51



188
318
41
51



189
319
41
51



190
320
41
51



191
321
41
51



192
322
41
51



193
323
41
51



194
324
41
51



195
325
41
51



196
326
41
51



197
327
41
51



198
32
41
52



199
34
41
52



200
35
41
52



201
36
41
52



202
37
41
52



203
38
41
52



204
39
41
52



205
310
41
52



206
311
41
52



207
312
41
52



208
313
41
52



209
314
41
52



210
315
41
52



211
316
41
52



212
317
41
52



213
318
41
52



214
319
41
52



215
320
41
52



216
321
41
52



217
322
41
52



218
323
41
52



219
324
41
52



220
325
41
52






















TABLE 4







Exemplified

Phosphine




Compound No.
Ligand A
ligand
X1





















221
326
41
52



222
327
41
52



223
32
41
55



224
34
41
55



225
35
41
55



226
36
41
55



227
37
41
55



228
38
41
55



229
39
41
55



230
310
41
55



231
311
41
55



232
312
41
55



233
313
41
55



234
314
41
55



235
315
41
55



236
316
41
55



237
317
41
55



238
318
41
55



239
319
41
55



240
320
41
55



241
321
41
55



242
322
41
55



243
323
41
55



244
324
41
55



245
325
41
55



246
326
41
55



247
327
41
55



248
32
44
51



249
34
44
51



250
35
44
51



251
36
44
51



252
37
44
51



253
38
44
51



254
39
44
51



255
310
44
51



256
311
44
51



257
312
44
51



258
313
44
51



259
314
44
51



260
315
44
51






















TABLE 5







Exemplified

Phosphine




Compound No.
Ligand A
ligand
X1





















261
316
44
51



262
317
44
51



263
318
44
51



264
319
44
51



265
320
44
51



266
321
44
51



267
322
44
51



268
323
44
51



269
324
44
51



270
325
44
51



271
326
44
51



272
327
44
51



273
32
44
52



274
34
44
52



275
35
44
52



276
36
44
52



277
37
44
52



278
38
44
52



279
39
44
52



280
310
44
52



281
311
44
52



282
312
44
52



283
313
44
52



284
314
44
52



285
315
44
52



286
316
44
52



287
317
44
52



288
318
44
52



289
319
44
52



290
320
44
52



291
321
44
52



292
322
44
52



293
323
44
52



294
324
44
52



295
325
44
52



296
326
44
52



297
327
44
52



298
32
44
55



299
34
44
55



300
35
44
55






















TABLE 6







Exemplified

Phosphine




Compound No.
Ligand A
ligand
X1





















301
36
44
55



302
34
44
55



303
38
44
55



304
39
44
55



305
310
44
55



306
311
44
55



307
312
44
55



308
313
44
55



309
314
44
55



310
315
44
55



311
316
44
55



312
317
44
55



313
318
44
55



314
319
44
55



315
320
44
55



316
321
44
55



317
322
44
55



318
323
44
55



319
324
44
55



320
325
44
55



321
326
44
55



322
327
44
55



323
31
42
51



324
31
43
51



325
31
44
51



326
31
45
51



327
31
46
51



328
31
48
51



329
31
49
51



330
31
410
51



331
31
411
51



332
31
412
51



333
31
413
51



334
31
414
51



335
31
415
51



336
31
416
51



337
31
417
51



338
31
418
51



339
31
419
51



340
31
420
51






















TABLE 7







Exemplified

Phosphine




Compound No.
Ligand A
ligand
X1





















341
31
421
51



342
31
422
51



343
31
423
51



344
31
424
51



345
31
42
52



346
31
43
52



347
31
44
52



348
31
45
52



349
31
46
52



350
31
48
52



351
31
49
52



352
31
410
52



353
31
411
52



354
31
412
52



355
31
413
52



356
31
414
52



357
31
415
52



358
31
416
52



359
31
417
52



360
31
418
52



361
31
419
52



362
31
420
52



363
31
421
52



364
31
422
52



365
31
423
52



366
31
424
52



367
33
42
51



368
33
43
51



369
33
44
51



370
33
45
51



371
33
46
51



372
33
48
51



373
33
49
51



374
33
410
51



375
33
411
51



376
33
412
51



377
33
413
51



378
33
414
51



379
33
415
51



380
33
416
51






















TABLE 8







Exemplified

Phosphine




Compound No.
Ligand A
ligand
X1





















381
33
417
51



382
33
418
51



383
33
419
51



384
33
420
51



385
33
421
51



386
33
422
51



387
33
423
51



388
33
424
51



389
33
42
52



390
33
43
52



391
33
44
52



392
33
45
52



393
33
46
52



394
33
48
52



395
33
49
52



396
33
410
52



397
33
411
52



398
33
412
52



399
33
413
52



400
33
414
52



401
33
415
52



402
33
416
52



403
33
417
52



404
33
418
52



405
33
419
52



406
33
420
52



407
33
421
52



408
33
422
52



409
33
423
52



410
33
424
52



















TABLE 9







Phosphine


Example No.
Ligand A
ligand

















501
31
61


502
31
62


503
31
63


504
31
64


505
31
65


506
31
66


507
31
67


508
32
61


509
32
62


510
32
63


511
32
64


512
32
65


513
32
66


514
32
67


515
33
61


516
33
62


517
33
63


518
33
64


519
33
65


520
33
66


521
33
67


522
35
61


523
35
62


524
35
63


525
35
64


526
35
65


527
35
66


528
35
67


529
37
61


530
37
62


531
37
63


532
37
64


533
37
65


534
37
66


535
37
67


536
38
61


537
38
62


538
38
63


539
38
64


540
38
65


541
38
66


542
38
67









An example of a method of synthesizing a metal coordination compound of the present invention is shown below. In this example, 2,9-dimethylphenanthroline (31 shown before) is used for the ligand A. 2,9-Dimethylphenanthroline and CuX (X=I, Br, Cl) are allowed to react with each other by using toluene as a reaction solvent to confirm the formation of a red powder. Then, PR1R2R3 is added to the reaction mixture. Each of 41 to 424 shown before can be used for PR1R2R3. Phosphine ligands except those can also be used. After the addition of PR1R2R3, the reaction mixture is refluxed for 3 hours in a stream of nitrogen to precipitate a reactant. The reactant is filtered out and washed with toluene, resulting in a target product.




Next, a light-emitting device of the present invention is described. The light-emitting device of the present invention is characterized in that a light-emitting layer contains the above light-emitting material, and the light-emitting layer preferably contains 100% of the light-emitting material.
Next, the light-emitting device of the present invention is described with reference to FIGS. 1A to 1D.
In each figure, reference numeral 11 denotes a metal electrode; 12, a light-emitting layer; 13, a hole-transporting layer; 14, a transparent electrode; 15, another transparent electrode; 16, an electron-transporting layer; and 17, an exciton diffusion preventive layer.
FIGS. 1A to 1D each show a basic structure of an organic EL element of the present invention.
As shown in FIGS. 1A to 1D, an organic EL element is generally constructed by laminating the transparent electrode 14 and the metal electrode 11 on the transparent substrate 15 with one or multiple organic layers sandwiched between the transparent electrode 14 and the metal electrode 11.
In FIG. 1A, the organic layers comprise the light-emitting layer 12 and the hole-transporting layer 13. ITO or the like, which has a large work function, is used for the transparent electrode 14 to provide good property of injecting a hole from the transparent electrode 14 into the hole-transporting layer 13. A metallic material with a small work function such as aluminum, magnesium, or an alloy made from them is used for the metal electrode 11 to provide good property of injecting electrons into the organic layers. Those electrodes each have a thickness in the range of 50 to 200 nm.
An alumiquinolinol complex (a representative example thereof is Alq shown below) or the like, which has electron-transporting and light-emitting properties, is used for the light-emitting layer 12. In addition, a material having electron-donating property such as a triphenylamine derivative (a representative example thereof is α-NPD shown below) is used for the hole-transporting layer 13.
The element constructed as described above exhibits rectifying property. When an electric field is applied to the element to set the metal electrode 11 as a cathode and the transparent electrode 14 as an anode, an electron is injected from the metal electrode 11 into the light-emitting layer 12 and a hole is injected from the transparent electrode 14 into the light-emitting layer 12.
The injected hole and electron recombine with each other in the light-emitting layer 12 to generate an exciton, thereby leading to light emission. At this time, the hole-transporting layer 13 serves as an electron-blocking layer. As a result, the recombination efficiency at an interface between the light-emitting layer 12 and the hole-transporting layer 13 increases, resulting in increased luminous efficiency.
In FIG. 1B, the electron-transporting layer 16 is additionally provided between the metal electrode 11 and the light-emitting layer 12 of FIG. 1A. Light emission and electron/hole transporting functions are separated to establish a more effective carrier-blocking construction. As a result, the element can emit light efficiently. For example, an oxadiazole derivative or Alq, Bphen, or BCP shown below can be used for the electron-transporting layer 16.
In addition, as shown in FIG. 1C, the exciton diffusion preventive layer 17 can be provided such that an exciton to be generated in the light-emitting layer 12 is trapped in the light-emitting layer 12 to perform efficient light emission.
In addition, as shown in FIG. 1D, the element can be constructed by using only one organic layer. The element, which is often used in the application of a high molecular weight substance, can be used in vacuum evaporation of a low molecular weight substance.




The high-efficiency light-emitting device of the present invention can be applied to products that require energy savings and high intensity. Possible application examples thereof include: light sources for display devices, lighting units, and printers; and backlights for liquid crystal display devices. Possible display devices include a high-visibility and light-weight flat panel display that can provide energy savings. In addition, with regard to a light source for a printer, the light-emitting device of the present invention can replace a laser light source of a laser beam printer which has been widely used at present. Elements that can be addressed independently are arranged on an array to carry out desired exposure on a photosensitive drum, thereby forming an image. The use of the element of the present invention can remarkably reduce a device volume. With regard to lighting units and backlights, an energy savings effect can be expected from the present invention.
EXAMPLES 1 TO 10
Compounds listed in Table 10 were synthesized according to the formula (A). Their structures were identified through 1H-NMR (Bruker DPX-400 NMR) and elemental analysis (Vario EL CHNOS). FIGS. 2 and 3 show 1H-NMR charts of Exemplified Compounds 326 and 335, respectively. Elemental analyses of the compounds agreed well with the calculated values for their weight ratios of elements C, H, and N.
In addition, their light-emitting properties by photoexcitation were measured. Table 10 shows the results. Their emission spectra were measured by using an F4500 (manufactured by Hitachi Instruments Service Co., Ltd., having an excitation wavelength in the range of 380 to 450 nm). The measurement was performed while all the compounds were in powder states. Their luminescent colors ranged from yellowish orange to red.









TABLE 10







Light emission



Exemplified
spectrum peak


Example
Compound No.
λmax (nm)

















1
101
593


2
102
610


3
138
608


4
251
592


5
274
605


6
326
601


7
332
620


8
335
578


9
363
600


10
368
592









Strong light emission was obtained in each compound in a solid state. FIG. 4 shows the emission spectra of Exemplified Compounds 101, 102, and 335.
EXAMPLES 11 AND 12
In each example, an organic EL element was prepared by using Exemplified Compound 101 synthesized in Example 1 or Exemplified Compound 102 synthesized in Example 2 as a light-emitting material.
The element construction employed was one having only one organic layer as shown in FIG. 1D. ITO of 100 nm in thickness (corresponding to the transparent electrode 14) was patterned on a glass substrate (corresponding to the transparent substrate 15) to have an electrode area of 3 mm2.
An organic layer of 120 nm in thickness (corresponding to the light-emitting layer 12) was formed on the ITO substrate by spin-coating a solution containing the following compounds under a nitrogen atmosphere at 2,000 rpm for 20 seconds.

















Chlorobenzene:
10
g



Polyvinyl carbazole (having an average molecular
100
mg



weight of 9,600):



Exemplified Compound 101 or 102:
3.0
mg










After the film formation, the substrate was loaded into a vacuum evaporation chamber to form a cathode having the following construction (corresponding to the metal electrode 11).

    A metal electrode layer 1 (15 nm): AlLi alloy (containing 1.8 wt % of Li)
    A metal electrode layer 2 (100 nm): Al


Element properties were evaluated by applying a DC voltage to each element with the metal electrode 11 as a negative electrode and the transparent electrode 14 as a positive electrode.
The volt-ampere characteristics of the elements exhibited good rectifying properties. The emission spectra of the elements were measured by using a spectrum measuring instrument SR1 manufactured by Topcon Corporation. Their emission spectra were longer than those obtained in Examples 1 and 2 by about 10 nm. The luminous efficiency of each of the elements upon application of a voltage of 14 V was calculated to be 0.3 lm/W and 0.5 lm/W. The elements provided stable light emission even when they were made to emit light upon conduction for 50 hours.
EXAMPLES 13 AND 14
In each example, a single bit organic EL element shown in FIG. 1B having three organic layers consisting of the hole-transporting layer 13, the light-emitting layer 12, and the electron-transporting layer 16 was prepared by using Exemplified Compound 101 synthesized in Example 1 or Exemplified Compound 251 synthesized in Example 4. Then, the element properties were measured.
A no alkali glass substrate was used as the transparent electrode 15. Then, indium tin oxide (ITO) of 100 nm in thickness was formed as the transparent electrode 14 on the transparent substrate 15 according to a sputtering method, and was patterned into an electrode of 2 mm in diameter.




A high molecular weight film solution containing PEDOT and PSS represented by the above structural formulae was spin-coated on the transparent electrode 14 to form the hole-transporting layer 13 of 30 nm in thickness. A 1.0% chloroform solution of each of Exemplified Compounds 101 and 251 was spin-coated twice on the hole-transporting layer 13 and dried in an oven at 60° C. for 60 minutes to obtain the light-emitting layer 12 of 70 nm in thickness. The light-emitting layer 12 was formed only of a copper coordination compound. Furthermore, a compound represented by Bphen above was subjected to resistance heating evaporation at a degree of vacuum of 10−4 Pa to obtain an organic layer of 40 nm in thickness as the electron-transporting layer 16.
Potassium fluoride (KF) was arranged with a thickness of 5 nm on the electron-transporting layer 16 to serve as an under coating layer of the metal electrode 11. Furthermore, an aluminum (Al) film of 100 nm in thickness was evaporated as the metal electrode 11 to form a cathode layer, thereby preparing an organic EL element.
The properties of the organic EL elements were measured as follows. The volt-ampere characteristics of the elements were measured by using a micro-ammeter 4140B manufactured by Hewlett-Packard and the light-emitting intensity of each element was measured by using a BM7 manufactured by Topcon Corporation. Each element of the examples exhibited good rectifying property.
The present EL elements were observed to emit light upon application of a voltage of 15 V. Their light emission wavelength peaks were at 595 nm and 597 nm. Light emission wavelengths nearly the same as those of Examples 1 and 4 were observed. The luminous efficiency at this time was 0.8 lm/W. In other words, stable light emission was obtained.
EXAMPLE 15
An organic EL element was prepared in the same manner as in each of Examples 13 and 14 except that organic layers were formed according to a vacuum evaporation method. It should be noted that α-NPD shown as 61 to 67 was used as a material for the hole-transporting layer 13, Exemplified Compound 326 synthesized in Example 6 was used for the light-emitting layer 12, and Bphen used in each of Examples 13 and 14 was used for the electron-transporting layer 16. Each layer had a thickness of 40 nm.
Electrical optical properties of the element were measured in the same manner as in each of Examples 13 and 14. The light emission wavelength peak of the element was at 610 nm upon application of a voltage of 10 V. A light emission wavelength nearly the same as that of Example 6 was observed. The luminous efficiency at this time was 0.6 lm/W. In other words, stable light emission was obtained.
As described above by way of the embodiment and examples, the light-emitting material of the present invention provides high luminous efficiency and high stability, and is available at a low cost. Therefore, the light-emitting material of the present invention is useful for a light-emitting material for an organic EL element.

## Claims

1. A light-emitting device comprising a light-emitting layer containing a light-emitting material between a pair of electrodes, said light-emitting material comprising a metal coordination compound having a partial structure represented by a following general formula (1):




(wherein:
Cu represents a copper ion;
a ligand A is represented by a following structural formula:





(wherein: R and R′ each represent one of a straight-chain, branched, or cyclic alkyl group and an aromatic cyclic group that may have a substituent, and R and R′ may be identical to or different from each other; a CH2 group in the alkyl group may be substituted by one of —O— and —NH—; an H atom may be substituted by one of an aromatic cyclic group and a halogen atom; and one of R and R′ may be a hydrogen atom);
an atom P that coordinates with Cu is a phosphorus atom of a phosphine compound represented by PR1R2R3 (R1, R2, and R3 in PR1R2R3 each represent one of a straight-chain, branched, or cyclic alkyl group and an aromatic cyclic group that may have a substituent, and R1, R2, and R3 may be identical to or different from one another, a CH2 group in the alkyl group may be substituted by one of —O— and —NH—, a H atom may be substituted by one of an aromatic cyclic group and a halogen atom;
an atom of X1 that coordinates with Cu is selected from the group consisting of a halogen atom, an oxygen atom, a sulfur atom, and a nitrogen atom; and
one of R1, R2, and R3 in PR1R2R3 may contain X1 to form a bidentate ligand).

2. The light-emitting device according to claim 1, wherein the metal coordination compound comprises an electrically neutralized nonionic compound.

3. The light-emitting device according to claim 1, wherein X1 comprises −1 valent monodentate ligand and the atom of X1 that coordinates with Cu is selected from the group consisting of a halogen atom, a nitrogen atom in an aromatic cyclic group that may have a substituent, an oxygen atom in —OR, and a sulfur atom in —SR (R in one of —OR and —SR is one of a straight-chain, branched, or cyclic alkyl group and an aromatic cyclic group that may have a substituent, a CH2 group in the alkyl group may be substituted by one of —O— and —NH—, a H atom may be substituted by one of an aromatic cyclic group and a halogen atom).

4. The light-emitting device according to claim 1, wherein the copper ion comprises a +1 valent ion.

5. The light-emitting device according to claim 1, wherein the light-emitting material is present only in the light-emitting layer.