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

Abstract

Abstract Long live the OLED! Rational design and synthesis of Ir III complexes bearing two cyclometalated ligands (C N) and one 2‐(diphenylphosphino)phenolate chelate (P O) as well as the corresponding Ir III derivatives with only one (C N) ligand and two P O chelates are reported. According to the observed photophysical data, a P O ligand is found to be able to fine‐tune the light‐emitting electronic transition of these complexes. magnified image 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 Ir III 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 fluid 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 λ 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 −1 and 4.5 lm W −1 at 20 mA cm −2 . The maximum efficiency reaches 14.7 cd A −1 and 6.8 lm W −1 upon switching to TPBI as hole blocking material. For evaluating device lifespan, the tested device incorporating CuPc as a passivation layer, 3 doped in CTP as an emitting layer, and BAlq as hole blocking material, shows a remarkably long lifetime up to 36 000 h at an initial luminance of 500 cd m −2 .