Boosting Efficiency of Near-Infrared Emitting Iridium(III) Phosphors by Administrating Their π-π Conjugation Effect of Core-Shell Structure in Solution-Processed OLEDs

High-efficiency near-infrared (NIR) phosphorescent emitter is still a great challenge in solution processable organic light-emitting diodes (OLEDs). Herein, four novel NIR-emitting iridium(III) complexes with core-shell structure, named asIr1,Ir2,Ir3, andIr4, are rationally designed and synthesized, in which the highly rigid dibenzo[a,c] phenazine (DBPz) moiety is used as coordinated core and the flexible hexyl-thienyl or 4-(N,N-diphenylamino)phenyl as peripheral shell anchored in 3, 6-, or 11, 12-positions of DBPz. The influence of the core-shell structure on molecular aggregation, photophysical properties, and electroluminescent (EL) performance is systematically investigated. It is found that core-shell structure and substituted positions of shells have great influences on properties of iridium(III) complexes. Intense NIR emissions at 710-740 nm are observed with luminescent quantum yields of 18-30% in these complexes. Solution-processed NIR-OLEDs based onIr3orIr4show better electroluminescent properties. The maximum external quantum efficiency of 13.72% with a radiance of 26 996 mW Sr(-1)m(-2)(@708 nm) is obtained inIr3-doped OLEDs, representing the state-of-the-art EL performance in the iridium complex-based NIR-OLEDs. This work demonstrates that administrating pi-pi conjugation effects of core-shell structure in (CN)-N-<^> ligand is a new avenue to obtain high-efficiency NIR-emitting iridium(III) complexes.