PHOSPHORS BASED ON CARBENE METAL COMPLEX

Abstract

This invention relates to an iridium metal complex. The iridium metal complex comprises no more than three 1,3-dihydro-2H-benzo[d]imidazol-2-ylidene based carbene cyclometalate ligands. The iridium metal complex provides a blue emission. This is useful for organic light emitting diode (OLED) components where blue emitters have trailed behind the advances of red and green emitters.

Claims

1. A metal complex according to formula (I): ##STR00028## wherein: M is a transition metal; n is selected from 1, 2 or 3; L.sup.1, L.sup.2, L.sup.3 and L.sup.4 each independently represent an optionally present monodentate ligand or two adjacent L.sup.1, L.sup.2, L.sup.3 and L.sup.4 may represent an optionally present bidentate ligand around the central transition-metal cation; A represents a C.sub.6-10 aryl ring or a 5 to 10 membered heteroaryl ring; two of A.sup.1, A.sup.2, A.sup.3 and A.sup.4 are C and are substituted by the strong electron withdrawing CF.sub.3 groups indicated in the formula and the remaining two of A.sup.1, A.sup.2, A.sup.3 and A.sup.4 may be independently selected from CH or N; R.sup.1 is selected from the group consisting of: C.sub.1-6 alkyl, C.sub.2-6 alkylether, C.sub.1-6 alkoxy, C.sub.1-6 fluoroalkyl, C.sub.2-6 alkenyl, C.sub.2-6 alkynyl, substituted or unsubstituted C.sub.3-8 cycloalkyl, substituted or unsubstituted C.sub.3-8 cycloalkenyl, substituted or unsubstituted 3 to 8 membered heterocycloalkyl, substituted or unsubstituted 3 to 8 membered heterocycloalkenyl, substituted or unsubstituted C.sub.6-10 aryl, substituted or unsubstituted C.sub.7-11 aralkyl, substituted or unsubstituted heteroaryl having 5 to 10 carbon atoms and/or heteroatoms, and substituted or unsubstituted heteroaralkyl having 6 to 11 carbon atoms and/or heteroatoms; and R.sup.2 is H, deuterium, cyano, fluorine, C.sub.1-6 alkyl, C.sub.1-6 alkoxy, C.sub.1-6 fluoroalkyl, substituted or unsubstituted C.sub.6-10 aryl, or substituted or unsubstituted heteroaryl having 5 to 10 carbon atoms and/or heteroatoms.

2. The metal complex of claim 1, wherein M is selected from iridium, rhodium, platinum, palladium, gold, osmium and ruthenium.

3. The metal complex of claim 1, wherein M is iridium.

4. The metal complex of claim 1, wherein A represents a phenyl ring or a pyridyl ring.

5. The metal complex of claim 1, wherein A.sup.1 and A.sup.3 are each independently selected from C or CH and A.sup.2 and A.sup.4 are each independently selected from C, CH or N, provided that two of A.sup.1, A.sup.2, A.sup.3 and/or A.sup.4 are C and they are substituted by the CF.sub.3 groups indicated in the formula.

6. The metal complex of claim 1, wherein the metal complex is a metal complex according to formula (IIIa) or (IIIb): ##STR00029## wherein A.sup.2 and A.sup.4 are each independently selected from C, CH or N, when A.sup.2 and/or A.sup.4 are C they are substituted by the CF.sub.3 groups indicated in the formula.

7. The metal complex of claim 1, wherein R.sub.1 is selected from the group consisting of: C.sub.1-6 alkyl, C.sub.2-6 alkylether, C.sub.1-6 alkoxy, C.sub.1-6 fluoroalkyl, substituted or unsubstituted C.sub.7-11 aralkyl, and substituted or unsubstituted C.sub.6-10 aryl.

8. The metal complex of claim 1, wherein R.sup.1 is selected from the group consisting of: methyl, ethyl, propyl, butyl (optionally tert-butyl).

9. The metal complex of claim 1, wherein R.sup.2 is H, deuterium, fluorine, methyl, trifluoromethyl, tert-butyl, phenyl, or benzyl.

10. The metal complex of claim 1, wherein the metal complex is selected from: ##STR00030## ##STR00031##

11. A metal complex of claim 1 for use in an organic light-emitting diode.

12. The metal complex of claim 11, wherein the metal complex is for use as an emitter in an organic light-emitting diode.

13. An organic light-emitting diode comprising a metal complex of any one of claims 1 to 10.

14. The organic light-emitting diode of claim 13, wherein the light emitting diode comprises: (a) an anode, (b) optionally a hole-injection layer, (c) optionally a hole-transporting layer, (d) optionally an electron/exciton-blocking layer, (e) a light-emitting layer between the anode and the cathode, wherein the light emitting layer comprises the metal complex, (f) optionally a hole/exciton-blocking layer, (g) optionally an electron-transporting layer, (h) optionally an electron-injection layer, (i) a cathode.

Description

DETAILED DESCRIPTION

[0043] The L.sup.1, L.sup.2, L.sup.3 and L.sup.4 groups are absent or present dependent on the value of the integer n and the number of co-ordinate sites on M. The number of co-ordinate sites may be affected by the inherent nature of M. For example, where M possesses a six co-ordination geometry (such as for iridium(III) and rhodium(III)) when n is 1, L.sup.1, L.sup.2, L.sup.3 and L.sup.4 are all present; when n is 2, two of L.sup.1, L.sup.2, L.sup.3 and L.sup.4 are absent and when n is 3 all of L.sup.1, L.sup.2, L.sup.3 and L.sup.4 are absent. Where M has a four co-ordination geometry (such as for platinum(II), palladium(II) and gold(III)) when n is 1 two of L.sup.1, L.sup.2, L.sup.3 and L.sup.4 are absent and when n is 2 all of L.sup.1, L.sup.2, L.sup.3 and L.sup.4 are absent.

[0044] In embodiments M is selected from Ir(III) and n is 1, 2 or 3; Rh(III) and n is 1, 2, or 3; or Pt(II), Pd(II) and Au(III) and n is 1 or 2.

[0045] In the case of metal complexes of the present invention the metal complex consists of a Iridium(III) metal centre chelated with three bidentate ligands, as represented in the formula provided herein. As will be known by the skilled person the ligands occupy an octahedral arrangement around the iridium(III) metal centre. The three ligands of the same type can occupy either the corners of one face of the octahedron (facial isomer (fac isomer)) or a meridian, i.e. two of the three ligand bonding points are in trans positions relative to one another (meridional isomer (mer isomer)).

[0046] The metal complex of the present invention may be either the mer- or fac- isomer of the compound. The metal complex may be predominantly or exclusively a single isomer or it may be a mixture of isomers. Where the metal complex is a mixture of isomers, it may be any mixture.

[0047] According to the present invention, the metal complexes of the present invention are employed in an OLED. More preferably, the cyclometalated Ir complexes of formula (I) are employed as an emitter material, preferably as an emitter material in the light-emitting layer of an OLED. Suitable OLEDs are known in the art.

[0048] The metal complex of the present invention or the mixture of emitter materials mentioned above may be comprised in the light-emitting layer of an OLED. The metal complex may be the light-emitting layer without further additional components or the metal complex may be comprised in the light-emitting layer with one or more further components. For example, a fluorescent dye may be present in the light-emitting layer of an OLED in order to alter the emission colour of the emitter material. However, the present invention may beneficially avoid the need to include a dye as it provides a blue emission. In addition, the light-emitting layer may further comprise one or more host (matrix) materials. This host material may be a polymer, for example poly(N-vinylcarbazole). The host material may, however, likewise be a small molecule with enlarged HOMO/LUMO energy gap and relatively greater triplet energy gap or tertiary aromatic amines, for example TCTA.

[0049] Suitable host materials are carbazole derivatives, for example 4,4′-bis (carbazol-9-yl)-2,2′-dimethylbiphenyl (CDBP), 4,4′-bis(carbazol-9-yl)biphenyl (CBP), 1,3-bis (N-carbazolyl)benzene (mCP), 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (mCBP), diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide (TSPO1), and 1-(4-(dibenzo[b,d]thiophen-4-yl)-2, 5-dimethylphenyl)-1H-phenanthro[9,10-d]imidazole (txl).

[0050] The layer sequence in the inventive OLED is preferably as follows: [0051] 1. anode (a) [0052] 2. hole-injection layer (optionally) (b) [0053] 3. hole-transporting layer (optionally) (c) [0054] 4. electron/exciton-blocking layer (optionally) (d) [0055] 5. light-emitting layer (e) [0056] 6. hole/exciton-blocking layer (optionally) (f) [0057] 7. electron-transporting layer (optionally) (g) [0058] 8. electron-injection layer (optionally) (h) [0059] 9. cathode (i)

[0060] Layer sequences different from the aforementioned construction are also possible, and are known to those skilled in the art.

[0061] In general, the different layers in the inventive OLED, if present, have the following thicknesses: [0062] anode (a): 50 to 500 nm, preferably 100 to 200 nm; [0063] hole-injection layer (optionally) (b): 1 to 50 nm, preferably 5 to 10 nm; [0064] hole-transporting layer (optionally) (c): 5 to 100 nm, preferably 10 to 80 nm; [0065] electron/exciton blocking layer (optionally) (d): 1 to 50 nm, preferably 5 to 10 nm; [0066] light-emitting layer (e): 1 to 100 nm, preferably 5 to 60 nm; [0067] hole/exciton-blocking layer (optionally) (f): 1 to 50 nm, preferably 5 to 10 nm; [0068] electron-transporting layer (optionally) (g): 5 to 100 nm, preferably 20 to 60 nm; [0069] electron-injection layer (optionally) (h): 1 to 20 nm, preferably 1 to 5 nm; [0070] cathode (i): 20 to 1000 nm, preferably 30 to 500 nm.

EXAMPLES

Synthesis of the Metal Complexes

[0071] Synthesis Example 1. Synthesis of Complex mer-/fac-Ir(dfpmb).sub.3.

[0072] a) Synthesis of 2-Bromo-3,5-bis(trifluoromethyl)aniline

##STR00011##

[0073] A solution of 3,5-bis(trifluoromethyl)aniline (11.46 g, 50 mmol) in 50 mL DCM was cooled to 0° C. followed by dropwise addition of a solution of N-bromosuccinimide (8.90 g, 50 mmol) in 340 mL of CH.sub.2CI.sub.2 while maintaining the temperature below 5° C. The reaction was monitored by TLC. After the reaction was completed, the reaction mixture was washed with a saturated aqueous solution of NaHCO.sub.3 (2×100 mL) and water (100 mL). The organic phase was dried over Na.sub.2SO.sub.4 and the solvent was evaporated under reduced pressure. The crude product was purified by column chromatography on silica gel using petroleum ether/DCM (4:1, v/v) as eluent to give off-white needles. Yield: 12.5 g (81.2%). .sup.1H NMR (300 MHz, CDCI.sub.3) δ 7.28 (d, J=1.6 Hz, 1 H), 7.14 (d, J=1.8 Hz, 1 H), 4.60 (s, 2 H).

[0074] b) Synthesis of 1-Phenyl-5,7-bis(trifluoromethyl)-1H-benzo[d]imidazole

##STR00012##

[0075] The mixture of 2-Bromo-3,5-bis(trifluoromethyl)aniline (3.08 g, 10 mmol), triethyl orthoformate (1.48 g, 1.66 mL, 10 mmol) and glacial acetic acid (30 mg, 29 pL, 0.5 mmol) was stirred for 4 hat 120° C., then cooled to R.T.. aniline (3.3 g, 10 mmol) was added and the resulting mixture was stirred for 12 hat 140° C. After cooled to R.T., DBU (1.52 g, 1.5 mL, 10 mmol), Cul (190 mg, 1.0 mmol) and DMSO (20 mL) were added and the reaction mixture was stirred overnight at 150° C. After the reaction was completed, ethyl acetate (50 mL) was added, to which the mixture was filtered through a Celite pad. The filtrate was washed with brine and water in sequence and dried over anhydrous Na.sub.2SO.sub.4 and, then, concentrated by rotatory evaporation. The crude product was purified by column chromatography using petroleum ether/ethyl acetate (4/1, v/v) as eluent to give a gray solid. Yield: 1.49 g (45.2%). .sup.1H NMR (400 MHz, CDCI.sub.3) δ 8.41 (s, 1 H), 8.16 (s, 1 H), 7.87 (s, 1 H), 7.57 (d, J=7.7 Hz, 3 H), 7.42 (d, J=6.3 Hz, 2 H).

[0076] c) Synthesis of 3-Methyl-1-phenyl-5,7-bis(trifluoromethyl)-1H-benzo[d]imidazol-3-ium trifluoromethanesulfonate

##STR00013##

[0077] Compound 1-Phenyl-5,7-bis(trifluoromethyl)-1H-benzo[d]imidazole (1.16 g, 3.5 mmol) was dissolved in anhydrous toluene (40 mL) at R.T. and, methyl trifluoromethanesulfonate (1.72 g, 1.19 mL, 10.5 mmol) was added dropwise and the reaction mixture was stirred for 4 h. The resulting precipitate was filtered off, washed with toluene, and dried overnight under vacuum to provide a colorless solid. Yield: 1.65 g (95.1%). .sup.1H NMR (300 MHz, DMSO) δ 10.35 (s, 1 H), 9.15 (s, 1 H), 8.43 (s, 1 H), 7.79-7.66 (m, 5 H), 4.28 (s, 3 H).

[0078] d) Synthesis of mer-/fac-Ir(dfpmb).sub.3

##STR00014##

[0079] Under N.sub.2 atmosphere, a mixture of 3-Methyl-1-phenyl-5,7-bis(trifluoromethyl)-1H-benzo[d]imidazol-3-ium trifluoromethanesulfonate (1.63 g, 3.3 mmol), Ir(tht).sub.3CI.sub.3 (563 mg, 1.0 mmol) and NaOAc (492 mg, 6.0 mmol) in 50 mL degassed ter.t.-butylbenzene was refluxed at 170° C. for 12 h to give a light-yellow suspension. After cooled to room temperature, the reaction mixture was filtered through a pad of celite and, then the filtrate was removed under reduced pressure. Light yellow mer-Ir(dfpmb).sub.3 and fac-Ir(dfpmb).sub.3 was obtained via flash chromatography using hexane/ethyl acetate (5/1, v/v) as eluent.

[0080] mer-Ir(dfpmb).sub.3, light yellow solid (553 mg, 45.3%). .sup.1H NMR (400 MHz, acetone-d.sub.6) δ 8.20 (s, 2 H), 8.13 (s, 1 H), 8.03 (s, 1 H), 7.97 (s, 1 H), 7.94 (s, 1 H), 7.64 (d, J=8.1 Hz, 1 H), 7.61-7.53 (m, 2 H), 6.95-6.79 (m, 5 H), 6.62 (tt, J=15.6, 7.6 Hz, 4 H), 3.72 (s, 3 H), 3.70 (s, 3 H), 3.57 (s, 3 H); .sup.19F NMR (376 MHz, acetone-d.sub.6) δ −53.00 (s, 3 F), −53.07 (s, 3 F), −53.21 (s, 3 F), −61.71 (s, 3 F), −61.73 (s, 3 F), −61.74 (s, 3 F).

[0081] fac-Ir(dfpmb).sub.3, light yellow solid (349 mg, 28.6%). .sup.1H NMR (400 MHz, acetone-d.sub.6) δ 8.15 (s, 3 H), 8.00 (s, 3 H), 7.64 (d, J=8.0 Hz, 3 H), 6.97-6.90 (m, 3 H), 6.61 (d, J=4.2 Hz, 6 H), 3.62 (s, 9 H); .sup.19F NMR (376 MHz, acetone-d.sub.6) δ −53.08 (s, 9 F), −61.74 (s, 9 F).

[0082] Synthesis Example 2. Synthesis of Complex mer-/fac-Ir(dfpmp).sub.3.

[0083] a) Synthesis of 2,6-bis(trifluoromethyl)-2,6-dihydroxytetrahydropyran-4-one

##STR00015##

[0084] The procedure was adapted from the previously reported literature (Angew. Chem. Int. Ed. 2011, 50, 10703-10707) to give the desired product as a white solid (24 g, 45%). .sup.1H NMR (300 MHz, acetone-d.sub.6) δ/ppm 7.41 (d, J=3 Hz, 2 H), 3.19 (d, J=15 Hz, 2 H), 2.76 (d, J=15 Hz, 2 H); .sup.19F NMR (376 MHz, acetone-d.sub.6) δ/ppm −86.23 (s, 6 F).

[0085] b) Synthesis of 2,6-bis(trifluoromethyl)pyridin-4-ol

##STR00016##

[0086] In a sealed tube, compound 2,6-bis(trifluoromethyl)-2,6-dihydroxytetrahydropyran-4-one (10 g, 37.3 mmol) was mixted with 50 mL of 25% aqueous ammonia and heated with stirring at a temperature of about 120° C. for 12 h. After cooling to room temperature, a large quanlity of white crystal was filtered. Dissolution of this white crystal in water was accomplised by the addition of sufficient of saturated NaOH solution. Subsequent acidification of the solution with 2 M HCI (aq.) and cooling at 0° C. gave white precipitate, which was filtered off and dried under vacuum to funish product as a white solid (7.6 g, 89%). .sup.1H NMR (400 MHz, acetone-d.sub.6) δ/ppm 11.07 (br, 1 H), 7.50 (s, 2 H); .sup.19F NMR (376 MHz, acetone-d.sub.6) δ/ppm −69.02 (s, 6 F).

[0087] c) Synthesis of 3-nitro-2,6-bis(trifluoromethyl)pyridin-4(1 H)-one

##STR00017##

[0088] Nitric acid (12.0 mL, 172.8 mmol, 65% aqueous solution) was added dropwise into 30 mL of CH.sub.3COOH in an ice bath. To this mixture, compound 2,6-bis(trifluoromethyl)pyridin-4-ol (5.0 g, 21.6 mmol) was added in portions with vigorous stirring. The resultant mixture was heated to 110° C. for 24 h. Half of the CH.sub.3COOH was removed by distillation in vacuo and the residue was poured onto ice water (100 mL), and then extracted with ethyl acetate (80 mL). The organic layer was washed with water and dried over anhydrous MgSO.sub.4. Thereafter, the solvent was removed in vacuo and the resulting crude product was further purified via silica gel column chromatography using hexane/ethyl acetate (5/1, v/v) as the eluent to afford 3 a light-yellow solid (4.8 g, 80%). .sup.1H NMR (400 MHz, DMSO-d.sub.6) δ/ppm 7.49 (s, 1 H), 5.98 (br, 1 H); .sup.19F NMR (376 MHz, DMSO-d.sub.6) δ/ppm −64.85 (s, 3 F), 67.49 (s, 3 F).

[0089] d) Synthesis of 4-chloro-3-nitro-2,6-bis(trifluoromethyl)pyridine

##STR00018##

[0090] Triethylamine (1.1 g, 10.9 mmol) was added dropwise into a mixture of 3-nitro-2, 6-bis(trifluoromethyl)pyridin-4(1 H)-one (3.0 g, 10.9 mmol) and POCI.sub.3 (5.0 mL, 54.5 mmol) at 0° C. The resulted white suspension was stirred and heated at 125° C. for 1 h forming a clear, colorless solution. Excess POCI.sub.3 was distilled off under vacuum and the residue was poured into a separatory funnel containing ethyl acetate (50 mL) and washed with ice water (100×3 mL) three times. The organic layer was dried over anhydrous Na.sub.2SO.sub.4, filtered and concentrated in vacuo to give target product as a light-yellow solid (2.6 g, 81%) .sup.1H NMR (400 MHz, CDCI.sub.3) δ/ppm 8.13 (s, 1 H); .sup.19F NMR (376 MHz, CDCI.sub.3) δ/ppm −65.36 (s, 3 F), 68.07 (s, 3 F).

[0091] e) Synthesis of 3-nitro-N-phenyl-2,6-bis(trifluoromethyl)pyridin-4-amine

##STR00019##

[0092] Compound 4-chloro-3-nitro-2,6-bis(trifluoromethyl)pyridine (2.6 g, 8.8 mmol), and aniline (0.8 g, 8.8 mmol) were reflux with 30 mL of 2-propanol for 1 h. Afterward, the reaction mixture was concentrated. The crude product was recrystallized from n-hexane to furnish product as a yellow crystal (2.7 g, 89%). .sup.1H NMR (400 MHz, CDCI.sub.3) δ/ppm 8.04 (s, 1 H), 7.53 (t, J=7.8 Hz, 2 H), 7.45 −7.38 (m, 2 H), 7.25 (m, 2 H); .sup.19F NMR (376 MHz, CDCI.sub.3) δ/ppm −64.82 (s, 3 F), 68.94 (s, 3 F).

[0093] f) Synthesis of N.sup.4-phenyl-2,6-bis(trifluoromethyl)pyridine-3,4-diamine

##STR00020##

[0094] At R.T., a solution of compound 3-nitro-N-phenyl-2,6-bis(trifluoromethyl)pyridin-4-amine (2.37 g, 6.8 mmol) dissolved in the mixture of tetrahydrofuran and methanol (20 mL, 1:1, v/v) was added slowly into the suspension of NH.sub.4CI (1.8 g, 34 mmol) and iron powder (1.9 g, 34 mmol) in water (20 mL), maintaining temperature around 25° C. Under vigorous stirring, the reaction mixture was heated at 50° C. for 8 h. After cooled to R.T., the mixture was filtered through celite. Solvents was removed under reduced pressure, and the residue dissolved in ethyl acetate and washed with distilled water (100 mL). The organic layer was separated and concentrated to dryness. The crude product was recrystallized from n-hexane to furnish target product as a white powder (2.1 g, 97%). .sup.1H NMR (400 MHz, CDCI.sub.3) δ/ppm 7.42 (dd, J=10.4, 5.2 Hz, 3 H), 7.20 (t, J =7.5 Hz, 1 H), 7.11 (d, J=7.6 Hz, 2 H), 5.81 (s, 1 H), 4.20 (s, 2 H). .sup.19F NMR (376 MHz, CDCI.sub.3) δ/ppm −65.11 (s, 3 F), 67.23 (s, 3 F).

[0095] g) Synthesis of 1-phenyl-4,6-bis(trifluoromethyl)-1H-imidazo[4,5-c]pyridine

##STR00021##

[0096] The compound N.sup.4-phenyl-2,6-bis(trifluoromethyl)pyridine-3,4-diamine (2.0 g, 6.2 mmol), and formic acid (15 mL) were stirred at 105° C. for 4 h until the color of the solution turned brown. Excess formic acid was removed in vacuo resulting a brown solid. This brown solid was dissolved in ethyl acetate and washed with dilute Na.sub.2CO.sub.3 solution (50 mL). The organic layer was dried over Na.sub.2SO.sub.4 and concentrated under reduced pressure. The crude product was purified from recrystallization using n-hexane to afford product as a white solid (1.5 g, 75%). .sup.1H NMR (400 MHz, CDCI.sub.3) δ/ppm 8.44 (s, 1H), 8.01 (s, 1H), 7.72-7.60 (m, 3 H), 7.51 (dd, J=5.3, 3.3 Hz, 2 H). .sup.19F NMR (376 MHz, CDCI.sub.3) δ/ppm −65.11 (s, 3 F), 66.31 (s, 3 F).

[0097] h) Synthesis of 3-methyl-1-phenyl-4,6-bis(trifluoromethyl)-1H-imidazo[4,5-c]pyridine-3-ium trifluoromethanesulfonate

##STR00022##

[0098] At R.T., 1-phenyl-4,6-bis(trifluoromethyl)-1H-imidazo[4,5-c]pyridine (0.5 g, 1.5 mmol) was dissolved in 30 mL toluene, methyl trifluoromethanesulfonate (0.2 mL, 1.8 mmol) was added dropwise and, then the reaction mixture was vigorously stirred for another 12 h. The resulted white precipitate was filtered and used for the next step without further purification (0.6 g, 80%). .sup.1H NM R (400 MHz, CDCI.sub.3) δ/ppm 10.52 (s, 1 H), 8.83 (s, 1 H), 8.01-7.94 (m, 2 H), 7.85-7.79 (m, 3 H), 4.58 (d, J=1.7 Hz, 3 H). .sup.19F NMR (376 MHz, CDCI.sub.3) δ/ppm −61.63 (d, J=1.7 Hz), −67.42 (s), −79.13 (s).

[0099] i) Synthesis of mer-/fac-Ir(dfpmp).sub.3

##STR00023##

[0100] Under N.sub.2 atmosphere, a mixture of compound 3-methyl-1-phenyl-4, 6-bis(trifluoromethyl)-1H-imidazo[4,5-c]pyridine-3-ium trifluoromethanesulfonate (0.3 g, 0.6 mmol), Ir(tht).sub.3CI.sub.3 (120 mg, 0.2 mmol) and NaOAc (49 mg, 0.6 mmol) in 20 mL degassed tert-butylbenzene was refluxed at 140° C. for 12 h to give a light-yellow suspension. After cooled to room temperature, the reaction mixture was filtered through a pad of celite and, then the filtrate was removed under reduced pressure. Light yellow mer-Ir(dfpmp).sub.3 and fac-Ir(dfpmp).sub.3 was obtained via flash chromatography using hexane/ethyl acetate (5/1, v/v) as eluent.

[0101] mer-Ir(dfpmp).sub.3, light yellow solid (147 mg, 60%). .sup.1H NMR (400 MHz, acetone-d.sub.6) δ/ppm 9.13 (s, 1 H), 9.10 (s, 1 H), 9.06 (s, 1 H), 8.22 (dd, J=8.0, 1.7 Hz, 2 H), 8.17 (d, J=8.0 Hz, 1 H), 7.12-7.01 (m, 3 H), 6.99 (dd, J=7.2, 1.3 Hz, 1 H), 6.81-6.67 (m, 5 H), 3.80 (d, J=1.8 Hz, 3 H), 3.72 (d, J=2.0 Hz, 3 H), 3.53 (d, J=2.0 Hz, 3 H). .sup.19F NMR (376 MHz, acetone-d.sub.6) δ/ppm −59.48 (d, J=2.0 Hz, 3 F), −59.56 (d, J=2.0 Hz, 3 F), −59.69 (d, J=1.8 Hz, 3 F), −66.73 (s, 9 F).

[0102] fac-Ir(dfpmp).sub.3, light yellow solid (61 mg, 25%). .sup.1H NMR (400 MHz, acetone-d.sub.6) δ/ppm 9.07 (s, 3 H), 8.22 (d, J=8.0 Hz, 3 H), 7.16-7.06 (m, 3 H), 6.70 (t, J=7.3 Hz, 3 H), 6.49 (dd, J=7.4, 1.1 Hz, 3 H), 3.85 (d, J=1.8 Hz, 9 H). .sup.19F NMR (376 MHz, acetone-d.sub.6) δ/ppm −59.59 (d, J=1.8 Hz), −66.71 (s).

[0103] N-heterocyclic carbene (NHC) based ligands have higher triplet energy, increased thermodynamic stability, and enlarged ligand field stabilization energy in comparison to the conventional N-heteroaromatic cyclometalate chelates. The following disclosure demonstrates that NHC-based Ir(III) metal complexes are excellent candidates for efficient and robust blue-emitting OLEDs.

##STR00024## ##STR00025## ##STR00026##

[0104] The photophysical properties of eight NHC-Ir(III) complexes of the present invention, shown above, were investigated. The photophysical properties were compared to two comparative compounds mer-Ir(pmb).sub.3 and fac-Ir(pmb).sub.3. The results of the experiments are shown in Table 1a and Table 1b.

##STR00027##

TABLE-US-00001 TABLE 1a Photophysical data of the representative tris-bidentate, NHC-based Ir(III) complexes and their parent compounds mer-Ir(pmb).sub.3 and fac-Ir(pmb).sub.3. λmax FWHM Φ τ.sub.obs τ.sub.rad (nm) (cm.sup.−1) (%) (μs) (μs) mer-Ir(pmb).sub.3 395 — 0.2 0.015 — fac-Ir(pmb).sub.3 389 — 4 0.22 — mer-Ir(dfpmb).sub.3 499 4345 41 0.68 1.66 fac-Ir(dfpmb).sub.3 466 3947 59 1.14 1.94 fac-Ir(3-bdfpmb).sub.3 478 3898 70 0.96 1.37 fac-Ir(4-bdfpmb).sub.3 474 3820 68 1.2 1.77 mer-Ir(dfpmp).sub.3 501 4623 43 0.32 0.74 fac-Ir(dfpmp).sub.3 443 4430 70 0.39 0.58 mer-Ir(3-bdfpmp).sub.3 512 4174 48 0.57 1.19 fac-Ir(3-bdfpmp).sub.3 462 3486 74 0.74 1.00

TABLE-US-00002 TABLE 1b Photophysical and electrochemical data of the representative tris-bidentate, NHC-based Ir(III) complexes and their parent compounds mer-Ir(pmb).sub.3 and fac-Ir(pmb).sub.3. k.sub.r k.sub.nr E.sub.HOMO E.sub.LUMO (10.sup.5 s.sup.−1) (10.sup.5 s.sup.1) (eV) (eV) mer-Ir(pmb).sub.3 1.3 665 −4.8 −1.4 fac-Ir(pmb).sub.3 1.8 44 −5.1 −1.8 mer-Ir(dfpmb).sub.3 6.03 8.68 −5.12 −2.48 fac-Ir(dfpmb).sub.3 5.16 3.58 −5.45 −2.49 fac-Ir(3-bdfpmb).sub.3 7.31 3.13 −5.33 −2.45 fac-Ir(4-bdfpmb).sub.3 5.65 2.66 −5.35− −2.44 mer-Ir(dfpmp).sub.3 13 17 −5.33 −2.73 fac-Ir(dfpmp).sub.3 18 7.6 −5.65 −2.75 mer-Ir(3-bdfpmp).sub.3 8.4 9.2 −5.26 −2.74 fac-Ir(3-bdfpmp).sub.3 10 3.5 −5.54 −2.75

[0105] Notes: All data for parent compounds are quoted according to the original reference. PL spectra, lifetime, and quantum yield of eight proposed complexes were recorded in doped PMMA thin film at RT (2 wt. %). The FMO energy levels of these compounds are calculated from the following equations: E.sub.HOMO=−(E.sub.ox.sup.onset+4.8) eV, E.sub.LUMO=−(E.sub.red.sup.onset+4.8) eV, where E.sub.ox.sup.onset and E.sub.red.sup.onset are measured in CH.sub.3CN solution and reported versus the Fc/Fc.sup.+ couple.

[0106] The results clearly demonstrate that the Ir(III) complexes of this invention exhibit a genuine blue emission, higher emission quantum yield, shorter radiative lifetime, and downward shifted LUMO energy levels than the parent compounds such as mer-Ir(pmb).sub.3 and fac-Ir(pmb).sub.3. These results may indicate a possible method of achieving efficient and robust blue phosphors and respective PHOLEDs.

[0107] The dual trifluoromethyl substituents at the benzimidazolylidene/pyridoimidazolylidene site of the present inventive bidentate NHC-based chelates may result in the downward shifting of both the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO), particular the latter, needed efficient blue emission and, finally, a considerably shortened radiative lifetime of approximately one microsecond or less. These characteristics are of particular importance as shorter the radiative lifetime, the less is the emission quenching that would occur at the higher driving voltages. In addition, the faster radiative decay may also improve the stability of the emitters due to the reduced residence time at the highly energized excited state manifolds. Furthermore, the downward shifted HOMO and LUMO levels are conducive to effective charge carrier transport and recombination when used in devices fabrication and, thereby, giving excellent device performances.