PHOSPHORESCENT PtM2 (M=Cu,Ag,Au) COMPLEX AND ORGANIC LIGHT-EMITTING DIODE THEREOF

Abstract

An ionic phosphorescent metal complex has a formula of formula (I). R.sub.1 and R.sub.2 are the same or different, and are independently selected from alkyl, aryl and heteroaryl, wherein the alkyl, aryl and heteroaryl are optionally substituted with 1-5 of the following groups: halogen, alkyl, alkoxy, alkylthio, amino, alkylamino, dialkylamino, arylamino, diarylamino, haloalkyl, cyano, nitro, alkenyl, aryl and heteroaryl optionally substituted with 1-3 aryl groups; R.sub.3 is independently selected from halogen, alkyl, haloalkyl, alkoxy, alkylthio, amino, alkylamino, dialkylamino, cyano, nitro or alkenyl; M is Cu(I), Ag(I) or Au(I). The organic light-emitting diode prepared by using the phosphorescent metal complex of formula (I) as a dopant for an emissive layer is capable of achieving high-performance organic electroluminescence and is applicable to the fields of lighting and flat-panel display.

##STR00001##

Claims

1-10. (canceled)

11. A phosphorescent metal complex of formula (I) below: ##STR00007## wherein R.sub.1 and R.sub.2 are the same or different, and are independently selected from aryl, heteroaryl and heteroaryl aryl, wherein the aryl and heteroaryl are optionally substituted with 1-5 of the following groups: halogen, alkyl, alkoxy, alkylthio, amino, alkylamino, dialkylamino, arylamino, diarylamino, haloalkyl, cyano, nitro, alkenyl, alkynyl, aryl and heteroaryl optionally substituted with 1-3 aryl groups; R.sub.3 is the same or different, and is independently selected from halogen, alkyl, haloalkyl, alkoxy, alkylthio, amino, alkylamino, dialkylamino, cyano, nitro, alkenyl and alkynyl; M is Cu(I), Ag(I) or Au(I); A.sup.n− is an anionic group; wherein n is 1 or 2.

12. The phosphorescent metal complex according to claim 11, wherein A.sup.n− is ClO.sub.4.sup.−, PF.sub.6.sup.−, SbF.sub.6.sup.−, BF.sub.4.sup.−, SiF.sub.6.sup.2−, CF.sub.3SO.sub.3.sup.−, CF.sub.3CF.sub.2CF.sub.2CF.sub.2SO.sub.3.sup.− or dicyclohexyl succinate-2-sulfonate.

13. The phosphorescent metal complex according to claim 11, wherein R.sub.1 and R.sub.2 are independently selected from aryl and heteroaryl, wherein the aryl and heteroaryl are optionally substituted with 1-3 of the following groups: alkyl, alkoxy, halogen, haloalkyl, amino, arylamino, diarylamino, aryl, heteroaryl and heteroaryl substituted with one or two aryl groups.

14. The phosphorescent metal complex according to claim 11, wherein the aryl is phenyl, naphthyl, phenanthryl or anthryl; and the heteroaryl is thienyl, furanyl, dibenzothienyl, oxodibenzothienyl, carbazolyl, oxadiazolyl or triazinyl;

15. The phosphorescent metal complex according to claim 11, wherein R.sub.1 and R.sub.2 are independently selected from heteroaryl, aryl, alkoxyaryl, dialkoxyaryl, trialkoxyaryl, heteroaryl aryl, arylheteroarylaryl and diarylheteroarylaryl.

16. The phosphorescent metal complex according to claim 11, wherein R.sub.1 and R.sub.2 are independently selected from methoxyaryl, dimethoxyaryl, trimethoxyaryl, carbazolyl aryl, aryl oxadiazolyl aryl and diaryltriazinylaryl.

17. The phosphorescent metal complex according to claim 11, wherein R.sub.1 and R.sub.2 are independently selected from alkoxy-phenyl, dialkoxy-phenyl, trialkoxy-phenyl, heteroaryl-phenyl, diarylaminophenyl, arylheteroarylphenyl and diarylheteroarylphenyl.

18. The phosphorescent metal complex according to claim 11, wherein R.sub.1 and R.sub.2 are independently selected from phenyl, naphthyl, carbazolyl, 2-methoxy-phenyl, 3-methoxy-phenyl, 4-methoxy-phenyl, 2,4-dimethoxy-phenyl, 3,4,5-trimethoxy-phenyl, diphenylaminophenyl, carbazolylphenyl, dibenzothienyl, oxodibenzothienyl, phenyloxadiazolylphenyl and diphenyl-s-triazinylphenyl.

19. The phosphorescent metal complex according to claim 11, wherein R.sub.3 is independently selected from alkyl.

20. The phosphorescent metal complex according to claim 11, wherein R.sub.1 and R.sub.2 are the same.

21. The phosphorescent metal complex according to claim 11, wherein the complex is selected from the following complexes 1-6: ##STR00008##

22. A method for preparing the phosphorescent metal complex according to claim 11, comprising: dissolving PhP(CH.sub.2P(C.sub.6H.sub.4R.sub.3-2).sub.2).sub.2 and [M(tht).sub.2](A.sup.n−.sub.1/n) in a solvent, and then adding platinum-organic alkyne complex Pt(PPh.sub.3).sub.2(C≡CR.sub.1)(C≡CR.sub.2) to the resultant solution to give the phosphorescent complex, wherein the tht refers to tetrahydrothiophene; preferably, the solvent is a halohydrocarbon, such as dichloromethane.

23. An organic light-emitting diode comprising an emissive layer, wherein the emissive layer comprises the complex according to claim 11.

24. The organic light-emitting diode according to claim 13, wherein in the emissive layer comprises is 3 wt %-20 wt % of the phosphorescent metal complex based on a total weight of the emissive layer.

25. The organic light-emitting diode according to claim 13, wherein the organic light-emitting diode comprising an anode layer, a hole injection layer, a hole transport layer, an emissive layer, an electron transport layer, an electron injection layer and a cathode layer.

26. The organic light-emitting diode according to claim 15, wherein the anode layer is formed of indium tin oxide; the hole injection layer is formed of PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid)); the hole transport layer is formed of Poly-TPD (poly(bis(4-phenyl)(4-butylphenyl)amine)); the emissive layer comprises the phosphorescent metal complex according to claim 11, as well as TCTA (tris(4-(9-carbazole)phenyl)amine), mCP (1,3-bis(9-carbazolyl)benzene), CBP (4,4′-bis(9-carbazole)-1,1′-biphenyl) or 2,6-DCZPPY (2,6-bis(3-(9-carbazole)phenyl)pyridine) possessing hole transport properties and OXD-7 (1,3-bis(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene) possessing electron transport properties; the electron transport layer can be formed of BmPyPB (1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene), BmPyPB (3,3″,5,5″-tetra(3-pyridinyl)-1,1′:3′,1″-terphenyl), BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) or OXD-7; the electron injection layer is formed of LiF; the cathode layer is formed of Al.

27. The organic light-emitting diode according to claim 16, wherein the organic light-emitting diode has the following structure: ITO/PEDOT:PSS/Poly-TPD/mCP or TCTA:OXD-7:6 wt % of the complex according to claim 11 /BmPyPB/LiF/Al.

Description

DETAILED DESCRIPTION

[0056] In order to facilitate the understanding of the objects, technical scheme and technical effects of the present invention, the present invention is further described in detail below with reference to the drawing and examples.

[0057] In the following examples, dTolmp refers to PhP{CH.sub.2P(C.sub.6H.sub.4Me-2).sub.2}.sub.2, tht refers to tetrahydrothiophene.

[0058] TPA refers to diphenylaminophenyl, Carb refers to carbazolyl, BBF refers to

##STR00004##

OXD refers to

##STR00005##

and SQ refers to

##STR00006##

Example 1. Preparation of Complex [PtAu.SUB.2.(dTolmp).SUB.2.(C≡CC.SUB.6.H.SUB.3.(OMe).SUB.2.-2,4).SUB.2.](CF.SUB.3.SO.SUB.3.).SUB.2 .(1)

[0059] To a solution of [Au(tht).sub.2](CF.sub.3SO.sub.3) (0.1 mmol) in dichloromethane (20 mL) was added dTolmp (0.1 mmol). After being stirred for 30 min, the above solution was added with a solution of Pt(PPh.sub.3).sub.2(C≡CC.sub.6H.sub.3(OMe).sub.2-2,4).sub.2 (0.05 mmol) in dichloromethane (5 mL). The reaction system was stirred at room temperature for 4 h. The crude product was purified by silica gel column chromatography (eluent: CH.sub.2Cl.sub.2-MeCN (8:1)) to give a pure product in 83% yield. HRMS cald. for [M-2CF.sub.3SO.sub.3].sup.2+: 1018.2208, found: 1018.2207. .sup.3H NMR (CD.sub.2Cl.sub.2, ppm): 8.12-8.09 (m, 4H), 7.77-7.72 (m, 4H), 7.37-7.31 (m, 8H), 7.18-7.14 (m, 14H), 6.98-6.91 (m, 8H), 6.76-6.72 (t, 4H), 6.67-6.65 (d, 2H), 6.43-6.37 (m, 4H), 5.04-5.01 (m, 8H), 3.90, 3.86 (s, 12H), 2.22, 2.13 (s, 24H). .sup.31P NMR (CD.sub.2Cl.sub.2, ppm): 20.28 (m, 4P, J.sub.P-P=33.10 Hz), 8.24 (m, 2P, J.sub.Pt-P=2561 Hz, J.sub.P-P=32.54 Hz). Infrared spectrum (KBr, cm.sup.−1): 2104 (w), 1253 (m), 1148 (m), 1027 (s).

Example 2. Preparation of Complex [PtAg.SUB.2.(dTolmp).SUB.2.(C≡C-4-TPA).SUB.2.](ClO.SUB.4.).SUB.2 .(2)

[0060] To a solution of [Ag(tht)](ClO.sub.4) (0.1 mmol) in dichloromethane (20 mL) was added dTolmp (0.1 mmol). After being stirred for 30 min, the above solution was added with a solution of Pt(PPh.sub.3).sub.2(C≡C-4-TPA).sub.2 (0.05 mmol) in dichloromethane (5 mL). The reaction system was stirred at room temperature for 4 h. The crude product was purified by silica gel column chromatography (eluent: CH.sub.2Cl.sub.2-MeCN (8:1)) to give a pure product in 78% yield. HRMS cald. for [M-2ClO.sub.4].sup.2+: 1036.2117, found: 1036.2098. .sup.3H NMR (CD.sub.2Cl.sub.2, ppm): 8.12-7.90 (m, 7H), 7.65-7.58 (m, 4H), 7.46-6.94 (m, 44H), 6.88-6.58 (m, 12H), 6.39-6.25 (m, 3H), 6.66-6.62 (t, 2H), 6.59-6.56 (m, 3H), 6.43-6.41 (d, 1H), 6.22-6.16 (m, 3H), 4.73-4.04 (m, 8H), 2.16-2.01 (m, 24H). .sup.31P NMR (CD.sub.2Cl.sub.2, ppm): 12.94, 11.50 (m, 2P, J.sub.Pt-P=2442 Hz, J.sub.Pt-P=2407 Hz, J.sub.P-P=33.3 Hz), −12.25, −16.10, −19.32 (m, 4P, J.sub.Ag-P=522 Hz, J.sub.P-P=35.4 Hz). Infrared spectrum (KBr, cm.sup.−1): 2087 (w), 1100 (s).

Example 3. Preparation of Complex [PtAg.SUB.2.(dTolmp).SUB.2.(C≡C-4-Ph-9-Carb).SUB.2.](CF.SUB.3.SO.SUB.3.).SUB.2 .(3)

[0061] To a solution of [Ag(tht)](ClO.sub.4) (0.1 mmol) in dichloromethane (20 mL) was added dTolmp (0.1 mmol). After being stirred for 30 min, the above solution was added with a solution of Pt(PPh.sub.3).sub.2(C≡C-4-Ph-9-Carb).sub.2 (0.05 mmol) in dichloromethane (5 mL). The reaction system was stirred at room temperature for 4 h. The crude product was purified by silica gel column chromatography (eluent: CH.sub.2Cl.sub.2-MeCN (8:1)) to give a pure product in 80% yield. HRMS cald. for [M-2 CF.sub.3SC).sub.3].sup.2+: 1034.1960, found: 1034.1960. .sup.1H NMR (CD.sub.2Cl.sub.2, ppm): 8.26-8.17 (m, 11H), 7.83-7.71 (m, 4H), 7.58-7.32 (m, 24H), 7.29-7.05 (m, 18H), 7.00-6.93 (m, 4H), 6.87-6.73 (m, 4H), 6.56-6.54 (d, 1H), 4.98-4.27 (m, 8H), 2.31-2.12 (m, 24H). .sup.31P NMR (CD.sub.2Cl.sub.2, ppm): 12.93 and 12.03 (m, 2P, J.sub.Pt-P=2431 Hz, J.sub.Pt-P=2386 Hz, J.sub.P-P=33.2 Hz), −12.39, −16.31, −19.52 (m, 4P, J.sub.Ag-P=522 Hz, J.sub.P-P=43.5 Hz). Infrared spectrum (KBr, cm.sup.−1): 2096 (w), 1258 (m), 1150 (m), 1030 (s).

Example 4. Preparation of Complex [PtAg.SUB.2.(dTolmp).SUB.2.(C≡C-BBF).SUB.2.](ClO.SUB.4.).SUB.2 .(4)

[0062] To a solution of [Ag(tht)](ClO.sub.4) (0.1 mmol) in dichloromethane (20 mL) was added dTolmp (0.1 mmol). After being stirred for 30 min, the above solution was added with a solution of Pt(PPh.sub.3).sub.2(C≡C-BBF).sub.2 (0.05 mmol) in dichloromethane (5 mL). The reaction system was stirred at room temperature for 4 h. The crude product was purified by silica gel column chromatography (eluent: CH.sub.2Cl.sub.2-MeCN (8:1)) to give a pure product in 77% yield. HRMS cald. for [M-2ClO.sub.4].sup.2+: 1007.1154, found: 1007.1153. .sup.1H NMR (CD.sub.2Cl.sub.2, ppm): 8.21-8.07 (m, 7H), 7.91-7.80 (m, 4H), 7.76-7.59 (m, 12H), 7.50-7.36 (m, 7H), 7.30-7.04 (m, 17H), 6.95-6.74 (m, 8H), 6.17 (s, 1H), 4.88-4.16 (m, 8H), 2.27-2.05 (m, 24H). .sup.31P NMR (CD.sub.2Cl.sub.2, ppm): 12.20 (m, 2P, J.sub.Pt-P=2423 Hz, J.sub.P-P=36.4 Hz), −9.96, −13.16 −15.66, −18.74 (m, 4P, J.sub.Ag-P=522 Hz). Infrared spectrum (KBr, cm.sup.−1): 2098 (w), 1082 (m).

Example 5. Preparation of Complex [PtAg.SUB.2.(dTolmp).SUB.2.(C≡C-OXD).SUB.2.](ClO.SUB.4.).SUB.2 .(5)

[0063] To a solution of [Ag(tht)](ClO.sub.4) (0.1 mmol) in dichloromethane (20 mL) was added dTolmp (0.1 mmol). After being stirred for 30 min, the above solution was added with a solution of Pt(PPh.sub.3).sub.2(C≡C—OXD7).sub.2 (0.05 mmol) in dichloromethane (5 mL). The reaction system was stirred at room temperature for 4 h. The crude product was purified by silica gel column chromatography (eluent: CH.sub.2Cl.sub.2-MeCN (8:1)) to give a pure product in 80% yield. HRMS cald. for [M-2 ClO.sub.4].sup.2+: 1013.1705, found: 1013.1704. .sup.1H NMR (CD.sub.2Cl.sub.2, ppm): 8.21-8.05 (m, 11H), 7.95-7.89 (m, 3H), 7.73-7.51 (m, 14H), 7.45-7.39 (m, 5H), 7.26-6.97 (m, 18H), 6.89-6.87 (d, 2H), 6.82-6.67 (m, 5H), 4.88-4.16 (m, 8H), 2.13-2.03 (m, 24H). .sup.31P NMR (CD.sub.2Cl.sub.2, ppm): 12.41, 11.53 (m, 2P, J.sub.Pt-P=2427 Hz, J.sub.P-P=36.2 Hz), −11.44, −14.67, −16.23, −19.55 (m, 4P, J.sub.Ag-P=519 Hz). Infrared spectrum (KBr, cm-1): 2095 (w), 1080 (s).

Example 6. Preparation of Complex [PtAg.SUB.2.(dTolmp).SUB.2.(C≡C-SQ).SUB.2.](CF.SUB.3.SO.SUB.3.).SUB.2 .(6)

[0064] To a solution of [Ag(tht)](CF.sub.3SO.sub.3) (0.1 mmol) in dichloromethane (20 mL) was added dTolmp (0.1 mmol). After being stirred for 30 min, the above solution was added with a solution of Pt(PPh.sub.3).sub.2(C≡C-SQ).sub.2 (0.05 mmol) in dichloromethane (5 mL). The reaction system was stirred at room temperature for 4 h. The crude product was purified by silica gel column chromatography (eluent: CH.sub.2Cl.sub.2-MeCN (8:1)) to give a pure product in 82% yield. HRMS cald. for [M-2CF.sub.3SO.sub.3].sup.2+: 1100.2179, found: 1100.2168. .sup.3H NMR (CD.sub.2Cl.sub.2, ppm): 8.87-8.80 (m, 5H), 8.61-8.59 (m, 2H), 8.36-8.16 (m, 9H), 7.83-7.58 (m, 19H), 7.52-7.43 (m, 5H), 7.36-7.03 (m, 18H), 6.93-6.91 (d, 3H), 6.86-6.74 (m, 4H), 6.57-6.55 (d, 2H), 4.98-4.26 (m, 8H), 2.30-2.09 (m, 24H). .sup.31P NMR, (CD.sub.2Cl.sub.2, ppm): 12.57, 11.70 (m, 2P, J.sub.Pt-P=2424 Hz, J.sub.P-P=34.6 Hz), −11.95, −15.19, −16.36, −19.58 (m, 4P, J.sub.Ag-P=517 Hz). Infrared spectrum (KBr, cm.sup.−1): 2100 (w), 1030 (s), 1153 (s), 1257 (s).

Example 7. Measurement of Photoluminescence Performance

[0065] The excitation spectra, emission spectra, luminescence lifetimes and luminescence quantum yields of complexes 1-6 prepared in Examples 1-6 were measured on an Edinburgh FLS920 fluorescence spectrometer in solutions in deoxygenated dichloromethane, solid powders and films of 94 wt % of mCP:6 wt % of the complexes 1-6 of the present invention, wherein, the excitation spectra, emission spectra, luminescence lifetimes and luminescence quantum yields in solutions were measured in a cuvette containing 2×10.sup.−5 M solution in dichloromethane; the luminescence quantum yields of the solid powders were measured in an integrating sphere with a diameter of 142 mm; the luminescence quantum yields of the films of 94 wt % of mCP:6 wt % of the complexes 1-6 of the present invention prepared by spin coating with solutions in dichloromethane were measured in an integrating sphere with a diameter of 142 mm.

[0066] The complexes 1-6 exhibit strong phosphorescence in all the solutions, solids and films. For example:

[0067] The emission wavelengths, luminescence lifetimes and quantum yields of the complexes 1-6 in solutions in dichloromethane are 547 nm, 0.63 μs and 38.7% (1); 621 nm, 0.58 μs and 17.5% (2); 530 nm, 0.37 μs and 10.3% (3); 534 nm, 1.35 μs and 31.5% (4); 522 nm, 0.96 μs and 21.2% (5); and 517 nm, 0.95 μs and 19.4% (6), respectively;

[0068] the emission wavelengths, luminescence lifetimes and quantum yields of the complexes 1-6 in solid powders are 562 nm, 0.74 μs and 34.5% (1); 582 nm, 1.67 μs and 31.8% (2); 534 nm, 2.01 μs and 38.9% (3); 535 nm, 2.15 μs and 13.9% (4); 526 nm, 2.08 μs and 20.91 (5); and 522 nm, 2.56 μs and 11.2% (6), respectively;

[0069] the emission wavelengths, luminescence lifetimes and quantum yields of the complexes 1-6 in films of 94 wt % of mCP:6 wt % of the complexes of the present invention are 537 nm, 0.73 μs and 99.3% (1); 573 nm, 2.18 μs and 92.0% (2); 522 nm, 1.94 μs and 93.6% (3); 533 nm, 8.90 μs and 76.1% (4); 523 nm, 5.40 and 80.2 (5); and 515 nm, 4.07 μs and 90.6% (6), respectively.

Example 8. Preparation of Organic Light-Emitting Diode Device and Measurement of Electroluminescence Performance

[0070] The phosphorescent complexes 1-6 prepared in Examples 1-6 were doped at 6 wt % in a mixed host material of TCTA:OXD-7 or mCP:OXD-7 as the emissive layers to prepare organic light-emitting diodes, and the devices had the following structures: ITO/PEDOT:PSS (50 nm)/Poly-TPD (50 nm)/47 wt % of TCTA:47 wt % of OXD-7:6 wt % of the complex 1 or 2 (50 nm)/BmPyPB (50 nm)/LiF (1 nm)/Al (100 nm) and ITO/PEDOT:PSS (50 nm)/Poly-TPD (50 nm)/47 wt % of mCP:47 wt % of OXD-7:6 wt % of the complexes 3-6 of the present invention (50 nm)/BmPyPB (50 nm)/LiF (1 nm)/Al (100 nm).

[0071] The ITO substrate was cleaned with deionized water, acetone and isopropanol sequentially, and then treated with UV-ozone for 15 min. The ITO substrate was spin-coated with a filtered aqueous solution of PEDOT:PSS in a spin coater at 4800 rpm and dried at 130.sub.°° C. for 20 min to form a hole injection layer with a thickness of 40 nm; the PEDOT:PSS film was then spin-coated with a filtered 2 mg/mL Poly-TPD in a spin coater at 2800 rpm to form a hole transport layer with a thickness of 50 nm; the Poly-TPD film was then spin-coated with a filtered 5 mg/mL solution of 47 wt % of TCTA:47 wt % of OXD-7:6 wt % of the complex 1 or 2 of the present invention in dichloromethane and 5 mg/mL solution of 47 wt % of mCP:47 wt % of OXD-7:6 wt % of the complex 3, 4, 5, or 6 of the present invention in dichloromethane in a spin coater at 2000 rpm to form an emissive layer with a thickness of 50 nm. Subsequently, onto the ITO substrate were thermally evaporated in sequence BmPyPB to form an electron transport layer with a thickness of 50 nm, LiF to form an electron injection layer with a thickness of 1 nm and Al to form a cathode with a thickness of 100 nm, in a vacuum chamber with the vacuum degree being no less than 4×10.sup.−4 Pa.

[0072] The performance of the light-emitting diode device was measured in a dry air environment at room temperature. The electroluminescence performance parameters of Examples 1-6 including electroluminescence wavelength (λ.sub.EL), turn-on voltage (V.sub.on), maximum brightness (L.sub.max), maximum current efficiency (CE.sub.max), maximum power efficiency (PE.sub.max) and maximum external quantum efficiency (EQE.sub.max) are listed in Table 1.

TABLE-US-00001 TABLE 1 Performance of electroluminescence devices prepared by using the phosphorescent complexes 1-6 of the present invention.sup.a) λ.sub.EL V.sub.on.sup.b) L.sub.max.sup.c) CE.sub.max.sup.d) PE.sub.max.sup.e) EQE.sub.max.sup.f) FWHM.sup.g) Complex [nm] [V] [cd/m.sup.2] [cd/A] [lm/W] [%] [nm] 1 536 3.0 33041 96.2 65.0 26.4 60 2 579 3.8 6117 69.0 36.1 21.7 85 3 522 4.1 16849 63.4 33.2 17.6 67 4 532 3.8 6817 51.3 29.3 13.0 31 5 524 4.1 11865 69.5 42.8 18.2 37 6 517 3.8 12820 61.7 35.2 16.7 40 .sup.a)The emissive layer of the device prepared by using the complexes 1 or 2 is formed of TCTA (47 wt %): OXD-7 (47 wt %): the complex 1 or 2 (6 wt %); the emissive layer of the device prepared by using the complex 3, 4, 5 or 6 is formed of mCP (47 wt %): OXD-7 (47 wt %): the complex 3, 4, 5 or 6 (6 wt %). .sup.b)Turn-on voltage at a brightness of 1 cd/m.sup.2. .sup.c)Maximum brightness. .sup.d)Maximum current efficiency. .sup.e)Maximum power efficiency. .sup.f)Maximum external quantum efficiency. .sup.g)Full width at half maximum in electroluminescence spectrum.