Toward the saturated red phosphorescence for OLED: New iridium complexes of 2,3-bis(4-fluorophenyl)quinoxaline derivatives

For development of an optimized red dopant in the organic light emitting devices (OLEDs), new iridium complexes containing 2,3-dpqx derivatives as a ligand were prepared. The ligands were prepared according to Friedlander reaction. The complexes, Ir(2,3-dpqx-F2)2(acac) (2,3-dpqx-F2 = 2,3-bis(4-fluorophenyl)-quinoxaline; acac = acetylacetonate) and Ir(6-Me-2,3-dpqx-F2)2(acac) (6-Me-2,3-dpqx-F2 = 2,3-bis(4-fluorophenyl)-6-methylquinoxaline) were synthesized from the two-step reactions of IrCl3·xH2O with the corresponding ligand and characterized by 1H NMR, mass spectrometry and elemental analysis. Ir(2,3-dpqx-F2)2(acac) and Ir(6-Me-2,3-dpqx-F2)2(acac) exhibited the luminescence peaks at 632 and 630 nm, respectively. Their UV-spectra showed the strong 3MLCT transition due to the strong coupling between the 5d orbital of the iridium center and the highest occupied molecular orbitals (HOMOs) of the ligands. The organic light emitting devices employing these compounds as the dopant were prepared and their electroluminescence was investigated. Both of the complexes exhibited the phosphorescence close to the saturated red emission at the CIE coordinate of x = 0.68, y = 0.31.