Synthesis and characterization of highly efficient blue Ir(III) complexes by tailoring β-diketonate ancillary ligand for highly efficient PhOLED applications

We synthesized two new heteroleptic blue-emitting Ir(III) complexes tBuCN-FIrmMes and tBuCN-FIrdMes by using systematically tailored ancillary ligands 1-mesitylbutane-1,3-dione (mMes) and 1,3-dimesitylpropane-1,3-dione (dMes), respectively. Near-unity photoluminescence quantum yield (PLQY: 96 ± 3%) was achieved for tBuCN-FIrmMes in doped films with short phosphorescence lifetime and high horizontal dipole ratio (Θ: 76%) than the di-mesityl complex, tBuCN-FIrdMes (PLQY: 75 ± 3%, Θ: 71%). Here, introduction of mMes reduces the singlet-triplet splitting energy (ΔE_ST), permanent dipole moment (μ), and the symmetry of tBuCN-FIrmMes as compared with tBuCN-FIrdMes, these parameters can highly affect the PLQY and Θ values. As a result, the blue phosphorescent organic light-emitting diode (PhOLED) of tBuCN-FIrmMes exhibits high external quantum efficiency (EQE) of ≥ 20% throughout a wide luminance range 1000–10000 cd/m² with a very low efficiency roll-off, which is crucial for solid-state lighting applications.