Electroluminescence of iridium(III) complexes containing F or CF3 substituents

Electron withdrawing groups F or CF3 were attached to 6-methyl-4-diphenylquinoline (medpq) ligand. The effect of this substitution on photophysical and electroluminescent properties of four phosphorescent iridium(III) complexes containing the two upgraded medpq ligands and 2-(2-pyridyl) benzimidazole or 2-(1H-tetrazol-5-yl) pyridine ligand was comparatively investigated. All complexes emitted strong phosphorescence with absolute quantum efficiency of deoxygenated toluene solutions higher than 50% and the lifetime of 1.068-1.88 microseconds observed for neat films at 77 K. The orange phosphorescence of CF3-substituted complexes was slight shifted to higher energy region in comparison to that of the corresponding F-containing complexes. The ionization potentials detected by photoelectron emission spectroscopy for solid-state samples of the complexes were practically the same (5.91-6.04 eV). Exploiting the same device structure, phosphorescent organic light-emitting diodes (PhOLEDs) containing a CF3 -substituted complex exhibited maximum external quantum efficiency of 10.33% in contrast to 5.36% observed for PhOLEDs based on a F-containing complex.