Phosphorescent organic light-emitting devices (PhOLEDs) based on heteroleptic bis-cyclometalated complexes using acetylacetonate as the ancillary ligand

•Four neutral iridium complexes have been tested as emitters.•The four complexes vary by their respective cyclometalated ligands.•UV–vis absorption and photoluminescence spectroscopy of complexes are investigated.•The substitution pattern determined the electroluminescence performances. A series of four heteroleptic iridium (III) complexes comprising acetylacetonate as the ancillary ligand is synthesized and tested as phosphorescent dopants in OLEDs. It was found that the substitution pattern of the cyclometalated ligand strongly influences the device performance. Notably, reduced device performances were observed for the fluorinated complexes as a result of poor exciton confinement in the guest molecules.