714 nm emission with 12.25% efficiency from iridium complexes with low iridium content by the strategy of rigid coordination core and amplifying shell

The development of near-infrared (NIR)-emitting phosphorescent emitters are still urgently needed for solution-processed organic light-emitting diodes (SP-OLEDs) with high efficiency, radiant emittance, and low cost. Herein, we designed and synthesized a new iridium complex, namely (^tBuTPA-DBPz)₂Ir(acac), with the rigid C^{^}N coordinated core of dibenzo[a,c] phenazine (DBPz) and an amplifying peripheral shell of 4,4 '-di(tert-butyl)-triphenylamine (^tBuTPA) attached at its 3,6-positions. The influence of the rigid DBPz core and big ^tBuTPA shell on the photophysical, electrochemical and electroluminescent properties of (^tBuTPA-DBPz)₂Ir(acac) was primarily studied in comparison with the archetype (DBPz)₂Ir(dpm). The NIR emission peaked at 714 nm with an outstanding external quantum efficiency of 12.25% and a recorded radiant emittance of 45 330 mW Sr^-1 m^-2 was observed in the (^tBuTPA-DBPz)₂Ir(acac)-doped devices at an optimized dopant ratio of 8 wt%. The EQE is 1.57 times that of (DBPz)₂Ir(dpm)-doped devices. Moreover, this NIR light-emitting device contains an Ir(III) content as low as 0.68 wt% and exhibits a bright NIR emission at 714 nm with outstanding efficiency and radiant emittance. Our results indicate that the NIR-emitting OLEDs with high efficiency, radiant emittance and low cost should be realized by developing core-shell type Ir(III) complexes with a rigid C^{^}N coordinate core and an amplifying shell.