Bis-oxazoline derivatives as ancillary ligands for bis-cyclometalated iridium complexes

Organometallic iridium complexes with two cyclometalated ligands (C N) and one bis-oxazoline derived ancil-lary ligand (L X), i.e. (C N)2Ir(L X), are reported. The C N ligands are 1-phenylpyrazoline (ppz), 2-(4,6-difluorophenyl)pyridine (F2ppy), 2-phenylpyridine (ppy), 1-phenylisoquinoline (piq). The box ligand is (4S-+)-phenyl-alpha-[(4S)-phenyloxazolidin-2-ylidene]-2-oxazoline-2-acetonitrile. The emission of these complexes span across the visible and into the near-ultraviolet region of the electromagnetic spectrum with moderate to high photoluminescence quantum yields (phi PL = 0.45-1.0). These complexes were found to emit from a metal-ligand to ligand charge transfer (ML'LCT) state and have lifetimes (1.3-2.1 mu s), radiative rates (105 s-1), and non -radiative rates (104-105 s-1) comparable to state-of-the-art iridium emitters. The (ppy)2Ir(BOX-CN) complexes were resolved into the Delta-and Lambda-diastereomers using differences in their solubility and additionally characterized by x-ray crystallography, stability, and chiroptic studies. The high phi PL of these isomers results in the best to date brightness for circularly polarized luminescence (CPL) from iridium complexes (7.0 M-1 cm-1), with dissym-metry factors of-0.57 x 10-3 and +1.9 x 10-3 for 3 Delta and 3 Lambda, respectively. The significant difference in CPL magnitude between 3 Delta and 3 Lambda likely arises from interligand interactions (edge-to-face arrangement versus strong 7C-7C interaction) for the pendant phenyl ring of the BOX-CN ligand which differ for the two isomers.

Automated summary

Organometallic iridium complexes with two cyclometalated ligands and one bis-oxazoline derived ancillary ligand were studied. These complexes have emission spanning across the visible and near-ultraviolet region, with moderate to high photoluminescence quantum yields. The (ppy)2Ir(BOX-CN) complexes were resolved into Delta- and Lambda-diastereomers based on solubility differences.