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, C-2'] 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 614nm 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 3.38mA= cm(2) and 1.11mA/cm(2).