White Light Emission Using Heteroleptic Tris-Cyclometalated Iridium (III) Complexes

The synthesis and photophysical study of efficient phosphorescent heteroleptic tris-cyclometalated iridium (III) complexes for white organic light-emitting devices (WOLEDs) are reported. In order to obtain a large broad band, we designed and prepared Ir(dfppy)2(pq) and Ir(pq)2(dfppy), where dfppy and pq are 2-(2,4-difluorophenyl) pyridine and 2-phenylquinoline, respectively. The emission wavelengths and the lifetimes of Ir(dfppy)2acac and Ir(pq)2acac (acac = acetyl acetonate) were reported as 469 nm and 596 nm, and 1.6 μs and 2.0 μs, respectively. A reasonably similar phosphorescent lifetime is crucial for white light emission materials. The luminescence mechanism is determined by using the decay times of two different cyclometalated (CˆN) ligands. As similar phosphorescent lifetimes are possible for luminescence in two ligands at the same time, the emission wavelengths of Ir complexes have large broad peaks, leading a white color. Our experimental results provide evidence that the absorption of Ir complexes occurs at each ligand upon excitation. Thus, the excitation energy causes blue and orange colors to be emitted in each ligand of the complex. To realize this idea, we synthesized an iridium complex having two different ligand structures and theoretically calculated the complex by using a computational method.