Iridium(III) phosphors with rigid fused-heterocyclic chelating architecture for efficient deep-red/near-infrared emission in polymer light-emitting diodes
Deep-red/near-infrared (DR/NIR) OLEDs based on transition metal complexes have drawn much attention due to their potential applications in display, bioimaging and photodynamic therapy. In this article, two novel iridium(III) complexes, (DBPz-11,12-DO)2Ir(acac) and (PPz-11,12-DO)2Ir(acac), are primarily designed and synthesized using highly rigid fused-heterocyclic phenazine derivatives as ligands. By tuning benzo number in phenazine, the iridium complexes exhibit significantly different emission characteristics. Strong NIR emission at 732 nm with a quantum efficiency of 13% and a lifetime of 0.60 μs is observed in (PPz-11,12-DO)2Ir(acac) solution. In contrast, a remarkably blue-shifted DR emission at 685 nm with a quantum efficiency of 27% and a lifetime of 0.40 μs is exhibited in (DBPz-11,12-DO)2Ir(acac) solution. As a result, both iridium complexes exhibit high-efficiency DR/NIR electroluminescence in their doped polymer light-emitting devices. The (PPz-11,12-DO)2Ir(acac) devices show a maximum external quantum efficiency (EQE) of 4.14% with a radiance up to 20981 mW/Sr/m2, and the (DBPz-11,12-DO)2Ir(acac) devices give an increasing EQE of 7.04% with a radiance of 33671 mW/Sr/m2. Such a strategy of rigid fused-heterocyclic cyclometalated ligand has opened a new avenue for high-efficiency DR/NIR-emitting iridium complexes.