Synthesis and Characterization of Highly Efficient Solution-Processable Green Ir(III) Complexes with High Current Efficiency and Very Low Efficiency Roll-Off

Three new highly efficient green-emitting heteroleptic phosphorescent iridium(III) complexes are designed and synthesized for the fabrication of solution-processable phosphorescent organic light-emitting diodes (PHOLEDs). Their photophysical, thermal, and electroluminescent (EL) properties are systematically investigated. The Ir(III) complexes comprise an amide-bridged trifluoromethyl (CF₃)-substituted phenylpyridine unit as the main ligand and picolinic acid (pic) and tetraphenylimidodiphosphinate (tpip) as ancillary ligands. In addition, the 2-ethoxyethnol (EO₂) solubilizing group is attached to the 4-position of pic ancillary ligand via tandem reaction, which improved the absolute photoluminescence quantum yields (PLQYs) and EL performance. The high-performance solution-processable PHOLEDs based on the bis[5-methyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one](4-(2-ethoxyethoxy picolinate) iridium(III) (Ir1) complex exhibit a maximum external quantum efficiency (EQE) of 24.22% and a maximum current efficiency (CE) of 92.44 cd A⁻¹, with the latter being among the best reported CEs achieved though solution processing. In contrast, PHOLEDs with the bis[5-hexyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one] (tetraphenylimidodiphosphinato)iridium (Ir3) complex show extremely low efficiency roll-off, with an EQE_max of 19.40% and an EQE of 19.29% at 10 000 cd m⁻².