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

Abstract

AbstractHigh‐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 as Ir1, Ir2, Ir3, and Ir4, 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 on Ir3 or Ir4 show 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 in Ir3‐doped OLEDs, representing the state‐of‐the‐art EL performance in the iridium complex‐based NIR‐OLEDs. This work demonstrates that administrating π–π conjugation effects of core–shell structure in C^N ligand is a new avenue to obtain high‐efficiency NIR‐emitting iridium(III) complexes.