WO2010093176A2

WO2010093176A2 - Iridium complex and organic light-emitting diodes

Info

Publication number: WO2010093176A2
Application number: PCT/KR2010/000855
Authority: WO
Inventors: Ung-Chan Yoon; Eun-Ah Chae; Dae-Won Cho; Hea-Jung Park; Jung-Hei Choi
Original assignee: University Industry Cooperation Foundation of Pusan National University
Current assignee: University Industry Cooperation Foundation of Pusan National University
Priority date: 2009-02-13
Filing date: 2010-02-11
Publication date: 2010-08-19
Anticipated expiration: 2011-08-13
Also published as: WO2010093176A3; KR101066743B1; KR20100092572A

Abstract

An iridium complex compound represented by Chemical Formula I is disclosed [Chemical Formula I] The iridium complex compound represented by Chemical Formula I provides luminescent materials with superior blue light-emitting property and significantly improved quantum yield as compared to existing iridium complexes. The luminescent material may be employed in an electroluminescent layer of an organic light-emitting diode (OLED) and may be used in a display device.

Description

[DESCRIPTION]

[invention Title]

Iridium complex and organic light-emitting diodes

[Technical Field]

The present invention relates to an iridium complex and an organic light-emitting diode (OLED) comprising the same, and more particularly, to an iridium complex having superior blue light- emitting property and improved phosphorescence quantum yield as compared to existing iridium complexes and an OLED comprising the same .

[Background Art]

An organic light-emitting diode (OLED) is a display device using light-emitting organic materials. When an electric field is applied to the organic material, an electron and a hole are transported respectively from the cathode and the anode and they recombine in the organic material. The recombination causes an emission of radiation resulting from a drop in the energy level of the electron. This is also called organic electroluminescence. When compared with liquid crystal displays (LCDs), OLEDs provide a good viewing angle, consume less power and are capable of processing high-quality images because of remarkably improved response time. Thus, OLEDs are preferred as next-generation display devices.

Radiation emitted from an OLED may be either fluorescence or phosphorescence. Fluorescence refers to an emission of light occurring when an- organic molecule in the singlet excited state relaxes to the singlet ground state, whereas phosphorescence refers to an emission of light occurring when an organic molecule in the triplet excited state relaxes to the ground state. An organic compound doped in the OLED is formed via carbon-carbon covalent bonding or covalent bonding between carbon and other atom. In the organic molecule, a pair of atomic orbitals is combined to form a bonding molecular orbital and an anti-bonding molecular orbital. The band formed by interaction of a lot of bonding molecular orbitals is called the valence band, and the band formed by a lot of anti-bonding molecular orbitals is called the conduction band. The highest energy level of the valence band is called the highest occupied molecular orbital (HOMO), and the lowest energy level of the conduction band is called the lowest unoccupied molecular orbital (LUMO) . The energy difference between the HOMO and the LUMO is called the band gap. An electron and a hole injected to the LUMO and the HOMO of the organic electroluminescent layer of the OLED respectively are recombined to form an exciton. The electrical energy of the exciton is converted into light. The color of the light is determined by the band gap of the electroluminescent layer where the exciton is formed. During the procedure, singlet excitons with a total spin 0 and triplet excitons with a total spin 1 are produced at a proportion of about 1:3. According to the spin selection rule for electric dipole transition, a transition from the excited state to the ground state accompanying a change in total spin is very difficult to occur. Since the organic molecule in the ground state is in the singlet state, the singlet exciton may be effectively transited and relaxed to the ground state while emitting fluorescence. However, the triplet exciton can not be effectively transited and relaxed to the ground state because the spin quantum number has to be changed. Accordingly, when a fluorescent material is used as the electroluminescent layer or doped in the electroluminescent layer, the maximum internal quantum yield of an OLED is limited to ca . 25%. If the spin-orbital coupling can be enhanced significantly, a mixed state of singlet and triplet increases and the efficiency of intersystem crossing between singlet and triplet states increases greatly. As a result, the triplet exciton may efficiently relax to the singlet ground state while emitting phosphorescence. If all of the triplet excitons are able to be used to emit light, the internal quantum yield of the OLED can be improved to 100% in theory.

Phosphorescent OLEDs which are capable of improving the emission efficiency of the OLED remarkably were studied and developed by Professor S. R. Forrest at the Princeton University and Professor M. E. Thompson at the USC in 1999. In particular, since the spin-orbital coupling occurs in proportion to the fourth power of the atomic number, complexes of heavy atoms such as platinum (Pt) , iridium (Ir), europium (Eu) and terbium (Tb) have high efficiency of intersystem crossing and good phosphorescence efficiency. In the case of a platinum complex, the triplet exciton having the lowest energy is the ligand-centered (LC) exciton and has a generally longer lifetime. But, in the case of an iridium complex, the triplet exciton having the lowest energy is the metal-to-ligand charge transfer (MLCT) state. Therefore, the iridium complex forms stronger spin-orbital coupling than the platinum complex and, thereby, exhibits high phosphorescence efficiency while having a much shorter triplet exciton lifespan. In this regard, C. Adachi et al . developed an OLED having a maximum emission yield of 60 lm/W and a maximum internal quantum yield of about 87% by doping a green phosphorescent material bis (2- phenylpyridine ) iridium ( I II ) acetylacetonate [ (ppy ) ₂Ir ( acac ) ] having iridium as the central heavy metal atom into 3-phenyl-4- ( 1 ' - naphthyl ) -5-phenyl-l , 2 , 4 -triazole (TAZ) . And, Universal Display Corp.

(UDC) announced that they attained the high emission yield of 82 lm/W by doping the same green phosphorescence material into an electroluminescent layer and using a hole injection material developed by LG Chem.

Although the phosphorescent OLEDs emitting blue, green and red light were developed as described above, the development of the phosphorescent OLEDs having excellent emission yield, color coordinate and lifespan is still insufficient. As one example, a blue light-emitting phosphorescent material called FIrpic (iridium (III) bis[2,2',4'-difluorophenylpyridinato-N,C²']picolinate) and a red light-emitting phosphorescent material called Ir(btp)₂(acac) (iridium(III)bis(2-(2'-benzothienyl)pyridinato-

N, C^2') (acetylacetonate)) were developed recently. However, there is much to be improved in color purity, efficiency and solubility. US Patent No. 7,329,898 discloses that an iridium complex

containing phenylpyridine and heterocyclic ring ligands is capable of

emitting blue and white light, and exhibits low driving voltage as

well as excellent durability and high efficiency. US Patent

Application No. 2008-0217606 discloses an OLED employing an iridium

complex having triazole, imidazole or pyrazole group in an

electroluminescent layer. However, the electroluminescent materials

disclosed in the patents do not show sufficient efficiency and

brightness in the blue region.

[ Disclosure] [Technical Problem]

An object of the present invention is to provide a

phosphorescent iridium complex exhibiting good external quantum yield

and brightness property in the blue region.

Another object of the present invention is to provide an

electroluminescent material including the iridium complex.

Another object of the present invention is to provide an organic

light-emitting diode (OLED) wherein the electroluminescent material

including the iridium complex is injected into an electroluminescent l ayer .

Another object of the present invention is to provide a display

device employing the OLED including the iridium complex.

[Technical Solution]

To achieve the object of the present invention, the present invention provides an iridium complex represented by Chemical Formula I :

[Chemical Formula I]

Ra

wherein

E₁ represents an aromatic or heteroaromatic ring, which may be further condensed with an aromatic or non-aromatic ring and have one or more substituent ( s ) , the ring E₁ optionally having one or more substituent ( s ) which may selectively form a condensation structure with a ring including E₂ and being coordinated by Ir metal by means of sp²-hybridized carbon;

E₂ represents a nitrogen-containing aromatic ring, which may be further condensed with an aromatic or non-aromatic ring, the ring E₂ optionally having one or more substituent (s ) which may selectively form a condensation structure with a ring including E₁ and being coordinated by Ir metal by means of sp²-hybridized nitrogen;

Ri and R₂ independently represent N, NR₄ or CR₄; R₃ and R₄ independently represent the same or different electron- donating group selected from a group consisting of H, F, Cl, Br, straight or branched Ci_₂o alkyl, C_3-2O cyclic alkyl, straight or branched Ci-₂₀ alkoxy, straight or branched Ci_-2O dialkylamino, C₄-_I4 aryl, C_4-14 heteroaryl, C₄-_I4 aryl with one or more subst ituent ( s ) , C_4-14 heteroaryl with one or more substituent ( s ) ; and n represents an integer 2.

To achieve the another object of the present invention, the

present invention provides an electroluminescent material including

the iridium complex represented by Chemical Formula I.

To achieve the another object of the present invention, the

present invention provides an organic light-emitting diode (OLED)

including the electroluminescent material in an electroluminescent

layer .

[Advantageous Effects]

The iridium complex according to the present invention has

remarkably improved phosphorescence quantum yield and emission yield

in the blue region as compared with existing iridium complexes. The

electroluminescent material including the iridium complex may be

employed in an electroluminescent layer of an organic light-emitting

diode (OLED) and may be used to manufacture a display device. [Description of Drawings]

The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

Fig. 1 shows a cross-sectional view of a display device comprising the organic electroluminescent material of the present invention;

Fig. 2 shows absorption and emission spectra of iridium complex 1;

Fig. 3 shows absorption and emission spectra of iridium complex 2;

Fig. 4 shows absorption and emission spectra of iridium complex 3; Fig. 5 shows absorption and emission spectra of iridium complex

4;

Fig. 6 shows absorption and emission spectra of iridium complex 5;

Fig. 7 shows absorption and emission spectra of iridium complex 6; Figs. 8 to 10 show absorption and emission spectra of iridium

complexes 1 and 4, 2 and 5, and 3 and 6, respectively; and

Fig. 11 shows cyclic voltammograms of iridium complexes 1 to 6,

respectively .

[Best Mode]

Hereinafter, the embodiments of the present invention will be

described in detail with reference to accompanying drawings.

The present invention provides an iridium complex represented by

Chemical Formula I :

[Chemical Formula I]

wherein

E₁ represents an aromatic or heteroaromatic ring, which may be further condensed with an aromatic or non-aromatic ring and have one or more substituent (s ) , the ring E₁ optionally having one or more substituent ( s ) which may selectively form a condensation structure with a ring including E₂ and being coordinated by Ir metal by means of sp²-hybridized carbon; E₂ represents a nitrogen-containing aromatic ring, which may be further condensed with an aromatic or non-aromatic ring, the ring E₂ optionally having one or more substituent ( s ) which may selectively form a condensation structure with a ring including El and being coordinated by Ir metal by means of sp²-hybridized nitrogen; R₁ and R₂ independently represent N, NR₄ or CR₄;

R₃ and R₄ independently represent the same or different electron- donating group selected from ^'a group consisting of H, F, Cl, Br, straight or branched Ci_-20 alkyl, C₃-₂o cyclic alkyl, straight or branched Ci_₂o alkoxy, straight or branched Ci_-2O dialkylamino, C_4-I4 aryl, C₄-_I4 heteroaryl, C_4-I4 aryl with one or more subst ituent ( s ) , C_4-14 heteroaryl with one or more substituent (s) ; and n represents an integer 2.

The present invention also provides an electroluminescent

material comprising the iridium complex represented by Chemical

Formula I .

The present invention further provides an organic light-emitting

diode (OLED) comprising the electroluminescent material in an

electroluminescent layer.

Preferably, in Chemical Formula I, the ligand

is selected

from a phenylpyridine derivative ligand with at least one fluorine

atom substituted at the phenyl ring.

Preferably, the phenylpyridine ligand is selected from the

followings :

More preferably, the phenylpyridine ligand is selected from the followings :

Preferably, in Chemical Formula I, R₁ may be NR₄, R₂ may be CH and n may be 2, or R₁ may be CH, R₂ may be NR₄ and n may be 2 to form an imidazole ligand. In case both R₁ and R₂ are CH, a pyrrole ligand is obtained .

Preferably, the iridium complex may be selected from the f ol l owings :

The presence of the ancillary ligand having one or more electron-donating group (s) on the right side of the iridium complex improves the phosphorescence quantum yield (PQY) of the electroluminescent material. Preferably, an iridium complex having an imidazole derivative ligand exhibits better absorption and emission properties than one having a pyrrole derivative ligand. The iridium complex having an imidazole derivative or a pyrrole derivative may be used as an electroluminescent material. In general, the iridium complex according to the present invention may be synthesized easily from a reaction of a μ-chloro- bridged iridium dimer comprising two main phenyl pyridines ligands, and an ancillary ligand.

The iridium complex according to the present invention may be used as an electroluminescent material in an electroluminescent layer of an OLED. Also, the iridium complex according to the present invention may be used as a phosphorescent material to manufacture an OLED, and may be used as a phosphorescent dopant in a host layer under an appropriate condition. An appropriate host material is selected from those capable of electroluminescence when a voltage is applied to the device.

An OLED according to the present invention comprises, as illustrated in Fig. 1, a substrate 1; an anode 2; optionally a hole transport layer (HTL) 3; an electroluminescent layer (EML) 4 ; optionally a hole blocking layer (HBL) 5; an electron transport layer ( ETL ) 6 ; and a cathode 7 .

The present invention further provides a display device comprising the OLED.

[Mode for Invention!

The examples and experiments will now be described. The following examples and experiments are for illustrative purposes only and not intended to limit the scope of the present invention.

Example 1: Synthesis of imidazole carboxylic acid

1-1. Synthesis of N- (2, 2-dimethoxyethyl ) trichloroacetamidine (7) Trichloroacetonitrile (14.4 g, 100 mmol) in THF (25 mL ) was added to a 100 mL two-bulb flask. Then, aminoacetaldehyde dimethyl acetal(10.9 mL, 10.5 g, 100 mmol) was added dropwise at -35 to -40 ⁰C (under an argon atmosphere) . After removing the cooling bath, the reaction mixture was diluted with ethyl acetate when the temperature reached room temperature. The solution was washed with water and dried with anhydrous sodium sulfate. After removing the solvent under reduced pressure, an oil was obtained (90%) . 1H-NMR (CDCl₃, 300 M Hz) δ (ppm) = 3.42 (s, 6H), 3.47 (d, 2H, J = 5 . 4 H z ) , 4 . 54 ( t , I H , J = 5 . 4 H z ) .

1-2. Synthesis of 2-imidazole carboxylic acid (8)

N- ( 2 , 2-Dimethoxyethyl ) trichloroacetamidine (7, 2.00 g, 8.0 mmol) was added to trifluoroacetic acid (TFA, 2 mL) at 0 °C. The solution was kept for 24 hours at room temperature. After removing the solvent under reduced pressure, benzene was added to the residue.

The mixture was evaporated under reduced pressure and dried.

Water (5 mL) was added to the solution of 2- ( trichloromethyl ) imidazole in TFA prepared from N- (2,2- dimethoxyethyl ) trichloroacetamidine (7, 2.00 g) . The solution was heated for 1 hour at refluxing temperature. After removing the solvent under reduced pressure and adding benzene to the residue, the mixture was dried by distilling twice under reduced pressure. The solid residue was crystallized in 2-propanol-THF to obtain pure 2- imidazole carboxylic acid (yield: = 50%, m.p. = 162-164 ⁰C) . CCI₃CN + H₂NCH₂CH(OMe)₂ ; ; * CCI₃ TCNHCH₂CH(OMe)₂

8

Example 2: Synthesis of main liqands

The main ligand, 2- ( 2 ' , 4 ' -difluorophenyl ) -4-methylpyridine (9) and 2-(2',4'-difluoro-3- ( trifluoromethyl ) phenyl) -4-methylpyridine (11) were prepared by using Suzuki coupling reaction.

2-1. Synthesis of 2- ( 2 ' , 4 ' -difluorophenyl ) -4 -methylpyridine (9) 2 , 4 -Difluorophenylboric acid (2.5 g, 15.8 mmol) , 2-bromo-4- methylpyridine (2.2 g, 12.6 mmol), barium hydroxide (15 g, 47.4 mmol) and 1 , 4-dioxane : H₂O (3:1) were added to a 100 mL two-bulb flask equipped with a reflux condenser. Then, tetrakis (triphenylphosphine) palladium ( 0 ) (0.9 g, 0.8 mmol) was added to the flask. Then, N₂ gas was filled in the flask at vacuum. The reaction mixture stirred overnight at 110 ⁰C and cooled to room temperature. After removing the solvent, methylene chloride (50 mL) was added to the residue. Then, precipitate was removed using filter paper. The organic phase was washed with 1 M NaOH (2 * 50 mL ) and then with saturated aqueous NaCl solution (50 mL) , dried with anhydrous magnesium sulfate, and then concentrated. The mixture was purified by column chromatography using ethyl acetate and hexane as eluent (yield: 50% ) .

¹H-NMR (CDCl₃, 300M Hz) δ (ppm) = 2.41 (s, 3H) , 6.86-6.94 (m, IH) , 6.95-7.02 (m, IH) , 7.09 (d, IH, J = 5.1 Hz) , 7.55 (s, IH), 7.91- 7.99 (m, IH) , 8.02 (d, 2H, J = 4.8 Hz) .

2-2. Synthesis o_f 2-(2',4'-difluoro-3' -iodophenyl) -A- methylpyridine (10)

A 2 M lithium diisopropylamide (LDA) solution in heptane (16.4 mL) was added dropwise to a solution of 2- ( 2 ' , 4 ' -dif luorophenyl ) -4 - methylpyridine (9, 4.5 g, 21.9 mmol) in THF (50 mL) at -78 °C and stirred for 1 hour. Then, iodine (7.8 g, 30.7 mmol) dissolved in THF

(40 mL) was added to the solution. The mixture was stirred at -78 ⁰C for 3 hours and heated to room temperature. Then, after adding water

(300 ml), the solution was extracted twice with diethyl ether (300 mL x 2) . The ether solution was washed with water (300 mL) , saturated sodium thiosulfate (Na₂S₂O₃) aqueous solution (300 mL) and NaCl (300

HiL) . After drying the solution with sodium sulfate, the residue was evaporated under reduced pressure. The mixture was purified by column chromatography using ethyl acetate and hexane as eluent (yield: 46%) .

¹H-NMR (CDCl₃, 300M Hz) δ (ppm) = 2.40 (s, 3H), 6.97-7.03 (m, IH), 7.09 (d, IH, J = 5.1 Hz), 7.54 (s, IH), 7.89-8.55 (m, IH) .

2-3. Synthesis of 2- (2 ' , 4 ' -difluoro-3 ' - (trifluoromethyl) - phenyl ) -4 -methylpyridine (11)

Copper (I) iodide (2.6 g, 13.6 mmol) and spray-dried anhydrous potassium fluoride (0.79 g, 13.6. mmol) were added to a 100 mL two- bulb flask and heated mildly under reduced pressure using a burner until the color turned yellow. Then, after adding 2- (2 ' , 4 ' -difluoro- 3 ' -iodophenyl ) -4-methylpyridine (10, 3 g, 9.1 mmol) followed by purging with argon gas and addition of N-methylpyrrolidone (NMP), (trifluoromethyl ) trimethylsilane (2.7 mL, 18.2 mmol) was added to the flask. The reaction mixture was stirred at room temperature. The mixture was washed with 14% ammonia water (40 mL) and extracted three times with methylene chloride. The organic layer was washed with water (40 mL ) and aqueous NaCl solution (40 mL), dried with anhydrous magnesium sulfate, and then concentrated. The mixture was purified by column chromatography using ethyl acetate and hexane as eluent (yield: 25%) .

¹H-NMR (CDCl₃, 300M Hz) δ (ppm) = 2.40 (s, 3H), 7.07-7.17 (m, IH), 7.57 (s, IH), 8.11-8.21 (m, IH), 8.57 (d, IH, J = 5.1 Hz) .

Example 3

The cyclometalated iridium ( I II ) -μ-chloro-bridged dimers (12, 13) were synthesized by refluxing IrCl₃-IiH₂O with the main ligand (9) and (11) in a 3:1 mixture of 2-ethoxyethanol and water according to the method reported by Nonoyama .

3-1. Synthesis of [ (2- (2 ' , 4 '-difluorophenyl)-4- methylpyridine) ₂Ir (μ-Cl) ]₂ (12)

2- (2' , 4 ' -Difluorophenyl-4-methylpyridine (9, 0.55 g, 2.68 mmol),

IrCl₃-H₂O-HCl (Aldrich, 0.32 g, 0.89 mmol) and 2-ethoxyethanol : H₂O

(3:1) were added to a 100 mL two-bulb flask equipped with a reflux condenser. The flask was purged and filled with N₂ gas. Then, the reaction mixture was stirred at 140 ⁰C for 16 hours. After cooling to room temperature, the solvent was removed by evaporation. After washing with water and then with 3 times the volume of ethanol, the residue was filtered. The resulting solid was dried (yield: 74%) .

¹H-NMR (CDCl₃, 300M Hz) δ (ppm) = 2.67 (s, 12H), 5.32 (d, 4H, J = 4.8 Hz), 6.31(t, 10.2 Hz), 6.61 (d, 4H, J = 6 Hz), 8.10 (s, 4H), 8.91 (d, 4H, J = 6 Hz) .

3-2. Synthesis of [2- ( 2 ' , 4 ' -difluoro-3' - ( trifluoromethyl ) phenyl- 4-methylpyridine)^Ir(μ-Cl) ] ₂ (13) 2-(2',4'-Difluoro-3'-( trif luoromethyl ) phenyl-4-methylpyridine

(11, 0.55 g, 2.68 mmol), IrCl₃-H₂O-HCl (Aldrich, 0.32 g, 0.89 mmol) and 2-ethoxyethanol : H₂O (3:1) were added to a 100 mL two-bulb flask equipped with a reflux condenser. The flask was purged and filled with N₂ gas. Then, the reaction mixture was stirred at 140 ⁰C for 15 hours. After cooling to room temperature, the solvent was removed by evaporation. After washing with water (40 mL) and filtering, the residue was extracted with 3 times the volume of chloromethanol . The organic layer was washed with water (40 mL) and aqueous NaCl solution

(4OmL), dried with anhydrous magnesium sulfate, and then concentrated. The resulting solid residue was recrystallized using methylene chloride and π-hexane to obtain pure product (yield: 50% ) .

¹H-NMR (CDCl₃, 300M Hz) δ (ppm) = 2.69 (s, 12H) , 5.41 (d, 4H, J

= 10.8 Hz] 6.71 (d, 4H, J = 5.7 Hz) .21 (s, 4H) (d, 4H, J =

5.7 Hz) .

10 11

12

Example 4

Synthesis of iridium complexes (1~6!

Synthesis of the iridium complexes (1~6) was performed by refluxing pyrrole-2-carboxylic acid, imidazole-2-carboxylic acid (8) or imidazole-5-carboxlic acid in 2-ethoxyethanol in the presence of cyclometalated iridium ( III ) -μ-chloro-bridged dimer (12) or (13) .

13

4-1. Synthesis of iridium complex [ 2- ( 2 ' , 4 ' -difluorophenyl ) -4- methylpyridine) ] ₂Ir (pyrrole-2-carboxylate) (1) (yield:

¹H-NMR (CDCl₃, 300M Hz) δ (ppm) = 2.53 (d, 6H, J = 5.7 Hz), 5.7

(d, 2H, J = 10.8 Hz), 5.98 (q, IH, J = 1.8 Hz), 6.10 (t, IH, J = 1.5

Hz), 6.29-6.42 (m, 2H), 6.68 (d, IH, J = 3.6 Hz), 6.98 (dd, 2H, J = 6

Hz, 5.7 Hz), 7.30 (d, IH, J = 6 Hz), 8.04 (d, 2H, J = 6 Hz), 8.60 (d,

IH, J = 5.7 Hz), HRMS (FAB) (M+H⁺, 711.1122, Calcd 710.1)

4-2. Synthesis of iridium complex [2- (2 ', 4 ' -difluorophenyl ) -4 - methylpyridine] ₂Ir ( imidazole-2-carboxylate ) (2) (yield: 70%)

¹H-NMR (CDCl₃, 300M Hz) δ (ppm) = 2.54 (d, 6H, J = 3.6 Hz), 5.72

(dd, 2H, J = 9 Hz, 7 Hz), 6.30-6.42 (m, 2H), 6.51 (s, IH), 6.90 (dd,

2H, J = 6 Hz, 5.7 Hz) , 7.09 IH), 7.47 (d, IH, J = 6 Hz), 8.04 (d,

2H, J = 12.9 Hz), 8.46 (d, IH, J = 6 Hz), HRMS (FAB) (M+H⁺, 713.1147,

Calcd 711.6866) . 4-3. Synthesis of iridium complex [ 2- ( 2 ' , 4 ' -difluorophenyl ) -4- methylpyridine] ^Ir ( imidazole-5-carboxylate ) (3) (yield: 88%)

¹H-NMR (DMSO-d₆ , 300M Hz) : δ (ppm) = 2.53 (s, 6H), 5.58 (dd, 2H, J = 10.5, 9.0 Hz), 6.69 (t, 2H, J = 9.6, 12.0 Hz), 7.17 (d, IH, J = 6.0 Hz), 7.30 (d, 2H, J = 6.9 Hz), 7.56 (s, IH), 7.58 (d, IH, J = 5.7 Hz), 8.02 (d, 2H, J = 12.0 Hz), 8.41 (d, IH, J = 5.7 Hz), HRMS (FAB) (M+H⁺, 713.11, Calcd 712.11) .

4-4. Synthesis of iridium complex [ 2- ( 2 ' , 4 ' -dif luoro-3-

( trif luoromethyl ) phenyl- 4 -methylpyridine) ] ₂Ir (pyrrole-2-carboxylate)

(4) (yield: 80%)

¹H-NMR (CDCl₃, 300M Hz) δ (ppm) = 2.48 (s, 6H), 5.73 (t, 2H, J =

11.4, 11.1 Hz), 6.11 (d, IH, J = 1.8 Hz), 6.35 (s, IH), 6.47 (d, IH, J = 3 Hz), 6.85 (d, 2H, J = 5.4 Hz), 7.22 (d, IH, J = 5.7 Hz), 7.81

(t, 2H, J = 11.1, 6 Hz), 8.04 (s, IH), HRMS (FAB) (M+ H⁺ , 847.09,

Calcd 846.08) .

4-5. Synthesis of iridium complex [2- (2 ' , 4 ' -difluoro-3- (trifluoromethyl ) phenyl- 4 -methylpyridine) ] ₂Ir (imidazole-2- carboxylate) (5) (yield: 70%)

¹H-NMR (CDCl₃, 300M Hz) δ (ppm) = 2.54 (d, 6H, J = 5.1 Hz), 5.83

(dd, 2H, J = 11.1, 10.8 Hz), 6.57 (s, IH), 6.94 (d, IH, J = 5.7 Hz]

7.10 (t, 2H, J = 10.8, 6.6 Hz), 7.48 (d, IH, J = 6 Hz), 8.13 (d, 2H,

J = 11.4 Hz) , 8.46 (d, IH, J = 6 Hz), HRMS (FAB) (M+H⁺, 849.0892,

Calcd 848.08) .

4-6. Synthesis of iridium complex [ 2- ( 2 ' , 4 ' -difluoro-3-

( trif luoromethyl ) phenyl- 4 -methylpyridine ) ] ₂ Ir (imidazole-5-carboxylic acid) (6) (yield: 65%;

¹H-NMR (DMSO-d₆ , 300M Hz) δ (ppm) = 2.54 (d, 6H, J = 2.4 Hz)

5.86 (dd, 2H, J = IO 11.1 Hz), 7.25 (dd, 2H, J = 6, 5.7 Hz! 7.50

IH! 7.72 (t, 2H, J = 10.2, 6 Hz) ,20 (d, 2H, J = 9 Hz) , 8.47

(d, 2H, J = 6 Hz), HRMS (FAB) (M+H⁺, 849.0889, Calcd 848.08)

1. R₁ = CH ₁ R₂ = CH

2. R₁ = CH , R₂ = NH

3. R₁ = NH , R₂ = CH

Example 5: UV absorption and emission property

UV absorption and emission properties of iridium ( III ) complex 3 and iridium ( III ) complex 6 were measured in methanol solution.

Absorption and emission spectra of other materials, iridium complexes

2, 4, and 5 were measured in chloroform (2.7*1CT⁴ M) solution. The film for emission property measurement was prepared by spin coating I^{l Il} on a glass plate of the methanol or chloroform solution containing I^{l Il} the iridium complex and polymethyl methacrylate (PMMA) . The iridium(III) complexes showed strong absorption and emission properties. The absorption spectrum exhibited absorption bands in the region between 350 and 470 nm. The absorption spectrum in film state was similar to that in solution state or showed a very slight shift toward shorter wavelength by about 1-2 nm.

Tris ( 2-tolylpyridine ) iridium (Ir(tpy>₃), which was used as reference, exhibits strong phosphorescence bands and is reported to have a phosphorescence quantum yield of 0.45 (Φ = 0.45) . The material (Ir(tpy)₃) was used as reference for the measurement of phosphorescence quantum yield, and quantum yields (Φ) of iridium complexes 1-6 were obtained as shown in Table 1. The iridium complex with an imidazole derivative having one more N atom in the heterocycle as the ancillary ligand showed phosphorescence emission band in the shorter-wavelength blue region but decreased phosphorescence quantum yield (Φ = 0.1~ 0.2) as compared to the iridium complex with a pyrrole derivative (Φ = 0.3 and 0.5) as the ancillary ligand. The result is shown in Table 1.

Table 1

In Table 1, MLCT^a means the maximum UV absorption peak for transition to the singlet excited state, and MLCT^b means the maximum absorption peak for transition to the triplet excited state. Φ^c means the quantum yield obtained with the phosphorescence iridium complex

Ir(tpy)₃ as the reference. Δv (cm ) means the Stokes shift, i.e. the difference in frequency between the maximum absorption peak for transition to the triplet excited state and the maximum phosphorescence peak.

Example 7 : Measurement of HOMO and LUMP energy level

Electrochemical property of an electrochemical cell comprising a platinum electrode (diameter: 2 mm), a platinum wire counter electrode and an Ag/AgCl reference electrode was measured using CHI600 (CH Instruments Inc., USA) . For supporting electrolyte solution (scan rate: 50 mVs^"1), 0.1 M tetrabutylammonium perchlorate

(Bu₄NClO₄, TBAP) in dichloromethane (Aldrich, HPLC grade) was used.

Fig. 11 shows the cyclic voltammograms of the iridium complexes of the present invention. HOMO and LUMO measurement results for iridium complexes 1 to 6 are summarized in Table 2. As seen in Table

2, the HOMO levels for iridium complexes 1 to 6 are -5.55 eV, -5.61 eV, -5.57 eV, -5.71 eV, -5.8 eV and -5.65 eV, respectively, and the

LUMO levels are -2.72 eV, -2.73 eV, -2.68 eV, -2.81 eV, -2.85 eV and

-2.67 eV, respectively. The iridium complexes of the present invention showed band gap of 2.83~2.98 eV. Among the iridium complexes of the present invention, iridium complex 6 had the largest band gap (2.98 eV) between the HOMO and the LUMO and emission at the shortest wavelength in solution with a large quantum yield (Φ = 0.2) . Iridium complex 5 also exhibits emission at almost the same wavelength as the complex 6 in a film state (Φ = 0.2) . Importantly iridium complexes 5~6 which contain a imidazole carboxylate as an ancillary ligand exhibit their emissions at shorter wavelength in the blue color region (5:458nm 6:459nm) in their film states comprising to ones in solution state.

Table 2

As described above, the iridium complexes of the present

invention show emission in the blue region of 457 nm . This means

that they are appropriate to be used as efficient blue

phosphorescence compounds in an OLED. Further, they exhibit very

high phosphorescence quantum yield. This superior performance means

that the iridium complexes of the present invention are good

candidates for electroluminescent materials. An electroluminescent

material comprising the iridium complex may be used in an

electroluminescent layer of an OLED and may be used in a display

device .

The present application contains subject matter related to Korean Patent Application No. 10-2009-0011745, filed in the Korean Intellectual Property Office on February 13. 2009, the entire content of which is incorporated herein by reference.

While the present invention has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

[CLAIMS]

[Claim l]

An iridium complex compound represented by Chemical Formula I

[Chemical Formula I]

wherein

Ei represents an aromatic or heteroaromatic ring, which may be further condensed with an aromatic or non-aromatic ring and have one or more substituent ( s ) , the ring Ei optionally having one or more substituent ( s ) which may selectively form a condensation structure with a ring including E₂ and being coordinated by Ir metal by means of sp²-hybridi zed carbon;

E₂ represents a nitrogen-containing aromatic ring, which may be further condensed with an aromatic or non-aromatic ring, the ring E₂ optionally having one or more substituent (s ) which may selectively form a condensation structure with a ring including Ei and being coordinated by Ir metal by means of sp²-hybridized nitrogen; Ri and R₂ independently represent N, NR₄ or CR₄;

R₃ and R₄ independently represent the same or different electron- donating group selected from a group consisting of H, F, Cl, Br, straight or branched Ci-₂₀ alkyl, C_3-2O cyclic alkyl, straight or branched Ci_-20 alkoxy, straight or branched Ci-₂₀ dialkylamino, C₄-_I4 aryl,

C_4-I4 heteroaryl, C_4-14 aryl with one or more substituent (s ), C_4-14 heteroaryl with one or more substituent ( s ) ; and n represents an integer 2.

[Cl aim 2]

The iridium complex compound according to claim 1, wherein a

ligand of the

portion is selected from a phenylpyridine derivative ligand with one or more fluorine atom(s) substituted on the