Syntheses, Photophysics, and Application of Iridium(III) Phosphorescent Emitters for Highly Efficient, Long‐Life Organic Light‐Emitting Diodes

Rational design and synthesis of Ir ^III complexes (1-3) bearing two cyclometalated ligands (C^N) and one 2- (diphenylphosphino)phenolate chelate (P^O) as well as the corresponding IrIII derivatives (4-6) with only one (C^N) ligand and two P^O chelates are reported, where (C^NH)=phenylpyridine (ppyH), 1-phenylisoquinoline (piqH), and 4-phenylquinazoline (nazoH). Single crystal X-ray diffraction studies of 3 reveal a distorted octahedral coordination geometry, in which two nazo ligands adopt an eclipsed configuration, with the third P^O ligand located trans to the phenyl group of both nazo ligands, confirming the general skeletal pattern for 1-3. In sharp contrast, complex 4 reveals a trans-disposition for the PPh ₂ groups, along with the phenolate groups residing opposite the unique cyclometalated ppy ligand, which is the representative structure for 4-6. These Ir ^III complexes exhibit green-to-red photoluminescence with moderate to high quantum efficiencies in the degassed luid state and bright emission in the solid state. For 1-6, the resolved emission spectroscopy and relaxation dynamics are well rationalized by the computational approach. OLEDs fabricated using 12 wt.% of 3 doped in CBP and with BCP as hole blocking material, give bright electroluminescence with _max= 628 nm and CIE _xy coordinates (0.65, 0.34). The turn-on voltage is 3.2 V, while the current efficiency and the power efficiency reach 11.2 cd A ^-11 and 4.5 lm W ^-1 at 20 mA cm ^-2. The maximum efficiency reaches 14.7 cd A ^-1and 6.8 lm W ^-1 upon switching to TPBI as hole blocking material. For evaluating evice lifespan, the tested device incorporating CuPc as a passivation layer, 3 doped in CTP as an emitting layer, and Alq as hole blocking material, shows a remarkably long lifetime up to 36000 h at an initial luminance of 500 cd m ^-2.