Design and Synthesis of Heteroleptic Iridium(III) Phosphors for Efficient Organic Light-Emitting Devices

The phosphorescent emitters are essential to realize energy-efficient display and lighting panels. The solution processability is of particular interest for large-scale and low-cost production. Here, we present a series of the heteroleptic iridium (Ir) complexes, Ir(ppy)₂L1, Ir(ppy)₂L2, and Ir(ppy)₂L3, using the new ancillary ligands, including 1-(2-chlorophenyl)-5-hydroxy-3-methyl-1H-pyrazole-4-carbaldehyde (L1), 5-hydroxy-3-methyl-1-(p-tolyl)-1H-pyrazole-4-carbaldehyde (L2), and 5-hydroxy-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde (L3). Their photophysical and electrochemical properties were systematically characterized, followed by comparing with those predicted by density functional theory simulations using hybrid functionals. Among the three phosphors synthesized, Ir(ppy)₂L1 exhibits the highest photoluminescence quantum yield (Φ_PL = 89%), with an exciton lifetime of 0.34 μs. By using 4,4'-bis(carbazole-9-yl)biphenyl as the host material, we demonstrate high current efficiencies of 64 and 40 cd A^-1 at 100 cd m^-2 in its vacuum-evaporated and solution-processed organic light-emitting devices, respectively, revealing the promise for large-area light sources.