Highly efficient electroluminescent materials based on fluorinated organometallic iridium compounds

Abstract

We report a class of highly efficient electroluminescent materials based on fluorinated iridium compounds. Using aluminum as the cathode, a device, using fac-tris[5-fluoro-2(5-trifluoromethyl-2-pyridinyl)phenyl-C,N]iridium (Ir-2h) as the luminescent layer, displayed intense electroluminescence at 525 nm with an efficiency of 20 cd/A and a maximum radiance of 4800 cd/m². Differing from the previously reported ${\mathrm{Ir(ppy)}}_{\mathrm{3}},$ Ir-2h can be used in the undiluted form without the use of a charge-transporting host. This indicates that Ir-2h by itself has good enough charge-transporting properties. Photoluminescence studies at room temperature and 77 K revealed that electroluminescence originates from the metal-to-ligand charge transfer state with a quantum yield of 0.56 for Ir-2h and 0.5 for ${\mathrm{Ir(ppy)}}_{\mathrm{3}}$ in toluene at room temperature. In the thin-film form, photoluminescence quantum yield of Ir-2h is a factor of 10 greater than that of ${\mathrm{Ir(ppy)}}_{\mathrm{3}}$ due to the larger self-quenching effect of ${\mathrm{Ir(ppy)}}_{\mathrm{3}}.$