852 nm near-infrared emission from iridium (III) complex based on an enlarging rigid coordinated core of Tribenzo[a,c]phenazine

Near-infrared (NIR) luminescent materials based on transition metal complexes have made great progress in recent years. However, there are few reports on pure NIR-emitting iridium complexes with rigid coordinated core and their organic light-emitting devices with an emission peak more than 800 nm. Herein, we designed and synthesized a NIR-emitting iridium (III) complex based on an enlarging rigid coordinated core of tribenzo[a,c] phenazine (TPz), namely (^tBuTPA-TPz)₂Ir(acac), in which di(tert-butyl) triphenylamine (^tBuTPA) is used as a peripheral shield and appended in TPz. The effect of the enlarging rigid coordinated core and peripheral shields on the emissive property was primarily studied. A significantly red-shifted photoluminescent emission peak from 710 nm to 860 nm was exhibited in this iridium complex by enlarging rigid coordinated core from dibenzo[a,c]phenazine to TPz in dichloromethane. Furthermore, a pure NIR electroluminescence peaked at 852 nm with a shoulder at 952 nm was observed in the (^tBuTPA-TPz)₂Ir(acac)-doped polymer light-emitting diodes. An increasing external quantum efficiency of 0.079% and radiant emittance of 879 mW Sr⁻¹m⁻² were obtained in the optimized devices. This study provides a feasible strategy to develop pure NIR-emitting iridium complexes with an emissive peak more than 800 nm by enlarging rigid coordinated core.