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

• Iridium complexes (EHO-5CF3-ppy)2Ir(acac) (5) and (EHO-5CF3-ppy)2Ir(pic) (6).
• Trifluoromethyl and dendritic ethylhexyloxy groups were incorporated into ligands.
• EL devices ITO/PEDOT: PSS/PVK: PBD: 5 or 6 (2 and 8 wt% dopant)/TPBi/LiF/Al.
• Device for 5 (2 wt% dopant) emitted at 536 nm with maximum efficiency of 10.4 cd/A.
• Device for 6 (2 wt% dopant) peaked at 524 nm with maximum efficiency of 16.7 cd/A.

A novel cyclometallated ligand 2-(4-(2′-ethylhexyloxy)phenyl)-5-trifluoromethyl-pyridine (EHO-5CF3-ppy) was synthesized, and two solution-processable iridium complexes bis[2-(4-(2′-ethylhexyloxy)phenyl)-5-trifluoromethylpyridinto-C3, N] iridium (acetylacetonate) (EHO-5CF3-ppy)2Ir(acac) (5) and bis[2-(4-(2′-ethylhexyl-oxy)phenyl)-5-trifluoromethylpyridinto-C3, N] iridium (2-picolinic acid) (EHO-5CF3-ppy)2Ir(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.