New Pyridylimidazole-Based Near-Infrared Iridophosphors: Synthesis, Photophysical Properties, and Electroluminescence Application

A pair of highly efficient near-infrared (NIR) phosphorescent iridium(III) complexes ( NIR-Ir1 and NIR-Ir2 ) based on pyridylimidazole derivatives are rationally designed. 1-(Benzo[ b ]thiophen-2-yl)isoquinoline is selected as the cyclomedtalating ligand for complexes, which determines the  near-infrared  phosphorescence. 2-(1 H -imidazol-2-yl)pyridine and 2-(pyridin-2-yl)-1 H -benzo[ d ]imidazole serve as the ancillary ligands, which aims to finely adjust the photophysical properties of these two NIR iridophosphors. At room temperature, both complexes exhibit intense near-infrared phosphorescence and the emission spectra well overlap with each other (685 nm with 750 nm as the shoulder for NIR-Ir1 and NIR-Ir2 ), high photoluminescence quantum yield (0.10 for NIR-Ir1 , 0.13 for NIR-Ir2 ) in dichloromethane. The pyridylimidazole-type ancillary ligands incorporated into the complexes enable the effective NIR phosphorescence and the robust chemical stability for NIR organic light-emitting diodes (OLEDs). The preliminary results show that the maximum luminescence and external quantum efficiency for the OLEDs based on new NIR complexes with electroluminescence peaked at around 690 nm are 1,464 cd/m 2 and 1.48 %, respectively.