Syntheses, Photoluminescence, and Electroluminescence of Iridium(III) Complexes with Fluorinated 2-Phenylpyridine as Main Ligands and Tertraphenylimidodiphosphinate as Ancillary Ligand

Three green-emitting heteroleptic iridium complexes with 2-(4,5,6-trifluorophenyl)pyridine, 2-(3,4,6-trifluorophenyl)pyridine, and 2-(3,4,5-trifluorophenyl)pyridine as main ligands and tetraphenylimidodiphosphinate (tpip) as the ancillary ligand were synthesized and characterized. The positions of the three fluorine atoms on the phenyl ring affect the emission properties of the complexes, and the application of Htpip as the ancillary ligand improves the electron mobility of the complexes to make it comparable to that of the popular electron transport material tris(8-hydroxyquinolinato)aluminium (Alq(3)) under the same electric fields. The organic light-emitting diodes (OLEDs) based on the above phosphorescent emitters {indium tin oxide (ITO)/1,1-bis[4-(di-p-tolyl-amino)phenyl]cyclohexane (TAPC), 30 nm/Ir complex (x wt.-%)/N,N-dicarbazolyl-3,5-benzene (mCP), 15 nm/1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBi), 45 nm/LiF (1 nm)/Al (100 nm)} exhibited good performances. The device doped with bis[2-(3,4,6-trifluorophenyl)pyridine](tetraphenylimidodiphosphinato)iridium [Ir(F(3,4,6)ppy)(2)(tpip)] (8 wt.-%) showed superior performance with a peak current efficiency ((c)) of 66.36 cdA(-1) and a peak external quantum efficiency ((ext), EQE) of 25.7% at 5.8 V, a maximum power efficiency ((p)) of 48.20 lmW(-1) at 4.4 V, and a maximum luminance (L-max) of 47627 cdm(-2) at 12.6 V. Notably, the electroluminescence (EL) efficiency roll-off effects at relatively high current density in all devices are very mild, which helps them to obtain high efficiency at brightness. The results suggest that the three complexes, [Ir(F(3,4,6)ppy)(2)(tpip)] especially, would have potential applications in OLEDs.