Elucidating the Nonradiative Deactivation Pathways in a Cationic Iridium Complex with 2,4-di(1H-pyrazol-1-yl)Pyridine as the Ancillary Ligand

Abstract

Deep insight into the nonradiative deactivation pathways in phosphorescent cationic iridium complexes is critically important for developing efficient blue-emitting complexes toward advanced applications. Here, we report the synthesis and photophysical and electrochemical characterizations of a blue-green-emitting cationic iridium complex [Ir(ppy)2(bipzpy)]PF6 (Hppy is 2-phenylpyridine, and bipzpy is 2,4-di(1H-pyrazol-1-yl)pyridine). The nonradiative deactivation pathways in [Ir(ppy)2(bipzpy)]PF6 have been elucidated through extensive density functional theory calculations. The calculations reveal that the higher-lying charge-transfer (CT) state in [Ir(ppy)2(bipzpy)]PF6, which arises from Ir/ppy → bipzpy transitions, favors nonradiative deactivation because of its large structural distortion compared to the ground state. Both the CT state and the dark metal-centered (3MC) state can be thermally accessed by the lowest-lying emitting triplet state at room temperature, with the former being much more easily ...