Iridium(III) Complexes with 6-Pentafluorophenyl-2,4-Diphenylquinolines for Red OLEDs

Abstract

Novel red electrophosphorescent devices were fabricated by doping perfluorophenyl substituted iridium(III) complex, bis[1-(6-Pentafluorophenyl-2,4-diphenyl)quinolinato-N,C2′] iridium(III) (acetylacetonate) [Ir(PF-dpq)2(acac)] for the application in organic light-emitting diodes (OLEDs). The maximum electroluminescent (EL) wavelengths of Ir(dpq)2(acac) and Ir(PF-dpq)2(acac) have shown at 614 nm and 620 nm, respectively. The device using Ir(PF-dpq)2(acac) showed red emission with 1931 CIE chromaticity coordinates (x = 0.640, y = 0.342) at 12 V. The perfluorophenyl substituent on the quinoline ring as electron withdrawing group decreased the lowest unoccupied molecular orbital (LOMO). As a result, the energy gap is reduced, leading to red-shift the emission wavelength. The ab initio calculation using the time-dependent density function theory (DFT) showed in agreement with the experimental results. However, the iridium complex of PF-dpq underwent a weak MLCT transition because of the weak coupling between the 5d-orbital of the iridium atom and HOMO of the substituted ligand. Thus, the luminous efficiency of the device using Ir(dpq)2(acac) and Ir(PF-dpq)2(acac) are 4.36 cd/A and 3.13 cd/A, respectively, at the current density of 3.38 mA/cm2 and 1.11 mA/cm2.