High-efficiency long-wavelength NIR iridium complexes constructed by extending rigid coordination and optimizing peripheral donor position to break cocoon into butterfly
Xiang Chang, Kaiyu Lu, Songkun Zeng, Denghui Liu, Jingwei Huang, Bin Ma, Li Wang, Xiangqin Gan, Junting Yu, Yafei Wang, Shi‐Jian Su, Weiguo Zhu
Abstract
Due to the non-radiative decay of excited states, it is extremely complicated for iridium (III) complexes to simultaneously harvest high-efficiency and long-wavelength emission in the near-infrared (NIR) region based on the energy-gap law. In order to address this issue, we designed and synthesized two butterfly-type iridium(III) complexes of (PyPz-TPA) 2 Ir(acac) and (PyQl-TPA) 2 Ir(acac), in which pyrene-pyrazine (PyPz) and pyrene-quinoxaline (PyQl) are respectively used as the rigid C^N bidentate coordinated cocoons, peripherally with two triphenylamine (TPA) units at 4, 5-positions. Their photophysical, electrochemical and electroluminescent properties are primarily investigated. It is found that the (PyQl-TPA) 2 Ir(acac) presents stronger spin-orbital coupling effect, a smaller Δ E ST energy difference, and lower reorganization energy than (PyPz-TPA) 2 Ir(acac) by selecting rigid pyrene-quinoxaline coordination and optimizing peripheral TPA position. Furthermore, the (PyQl-TPA) 2 Ir(acac)-doped OLEDs exhibit a red-shifted NIR emission peaked at 784 nm with a record external quantum efficiency of 5.42% using CBP as host matrix by solution process, which is a rare representation to shrink the limitation of energy-gap law in NIR region for iridium(III) complexes. This study provides a feasible strategy to construct high-efficiency NIR-emitting iridium(III) complexes by an artfully motivated strategy of extending and breaking the C^N coordinate cocoon into butterfly.