Solution-processable phosphorescence based on iridium-cored small molecules with the trifluoromethyl group

Abstract A novel cyclometallated ligand 2-(4-(2′-ethylhexyloxy)phenyl)-5-trifluoromethyl-pyridine (EHO-5CF 3 -ppy) was synthesized, and two solution-processable iridium complexes bis[2-(4-(2′-ethylhexyloxy)phenyl)-5-trifluoromethylpyridinto-C 3 , N] iridium (acetylacetonate) (EHO-5CF 3 -ppy) 2 Ir(acac) ( 5 ) and bis[2-(4-(2′-ethylhexyl-oxy)phenyl)-5-trifluoromethylpyridinto-C 3 , N] iridium (2-picolinic acid) (EHO-5CF 3 -ppy) 2 Ir(pic) ( 6 ) were afforded. Trifluoromethyl and dendritic ethylhexyloxy group were incorporated into iridium ligands to tune luminescent color, to reduce luminescence quenching and to improve the solution-processable property. Photoluminescent spectra of 5 and 6 in tetrahydrofuran peaked at around 540 and 523 nm. Electrophosphorescent devices were fabricated using 5 and 6 as dopant emitters (2%), which exhibited electroluminescent (EL) peaks at 536 and 524 nm, and current efficiencies of 10.4 and 16.7 cd/A, respectively. With the concentration of iridium complexes increasing to 8%, the main EL peak showed a 4 nm of red shift and a distinct shoulder peak occurred at 583 nm for 5 or 560 nm for 6 , respectively. Maximum external quantum efficiencies of the devices at the concentration of 2% and 8% were 2.8% and 4.2% for 5 , 4.7% and 4.8% for 6 . These indicated that 5 and 6 were efficient solution-processable emitters.