Enhanced Deep-Red Phosphorescence in Cyclometalated Iridium Complexes with Quinoline-Based Ancillary Ligands

Compounds with good photoluminescencequantum yields(phi(PL)) in the deep-red to near-infrared parts of thespectrumare desired for a variety of applications in optoelectronics, imaging,and sensing. However, in this region of the spectrum, quantum yieldsare usually modest, which is explained by the energy gap law and theinherently slower radiative decay rates for low-energy emitters accordingto the second-order perturbation theory. In this work, we outlinea new direction in deep-red luminescence, introducing a new suiteof bis-cyclometalated iridium complexes with efficient luminescencebeyond 650 nm. Seven new complexes are prepared using two differentcyclometalating ((CN)-N-boolean AND) ligands with four quinoline-derived ancillaryligands ((LX)-X-boolean AND). The chosen cyclometalating ligands are well-establishedto produce deep-red phosphorescence and include a metalated phenylring appended to a conjugated heterocycle. The ancillary ligands combinea rigid quinoline or benzoquinoline "L" donor with avariable anionic "X" donor comprised of an O-donor aryloxy or carboxylate or an N-donor amidate.These complexes phosphoresce in the deep-red region with wavelengthsbetween 650 and 700 nm and solution quantum yields between 0.018 and0.42.