Three-Charge (0, -1, -2) Ligand-Based Binuclear and Mononuclear Deep-Red Phosphorescent Iridium Complexes Bearing Benzo[ d ]oxazole-2-Thiol Ligand.

A new class of three-charge (0, -1, -2) ligand-based binuclear and mononuclear iridium complexes bearing benzo[ d ]oxazole-2-thiol ligand have been synthesized. Notably, the binuclear complexes ( IrIr1 and IrIr2 ) can be generated at low temperatures by reacting the iridium complex precursors ( 2a and 2b ) with equal amounts of the benzo[ d ]oxazole-2-thiol ligands, while the corresponding mononuclear complexes ( Ir1 and Ir2 ) are formed at high temperatures. X-ray diffraction analysis shows that the benzo[ d ]oxazole-2-thiol ligand plays an unusual and interesting bridging role in binuclear complexes and induces rich intermolecular and intramolecular interactions, while in mononuclear complexes, it forms an interesting four-membered ring coordination. More importantly, all complexes experienced efficient deep-red emission in the 628-674 nm range, and the mononuclear complexes have higher luminescent efficiency and longer excited state lifetime than the binuclear complexes. As a result, organic light-emitting diode devices incorporating two mononuclear complexes ( Ir1 and Ir2 ) as guest material of the light-emitting layer can obtain good maximum external quantum efficiency (3.5% and 5.5%) in the deep-red region (629 and 632 nm) with CIE coordinates (0.61, 0.33) and (0.62, 0.34), along with a low turn-on voltage (2.8 V).