Three types of charged ligand-based neutral phosphorescent iridium() complexes featuring -carborane: synthesis, structures, and solution processed organic light-emitting diode applications

In view of the fact that coordination configurations and special functional groups are both important for the optical properties of phosphorescent iridium complex materials, we have prepared a novel family of three types of charged ligand (0, −1, and −2) based neutral phosphorescent iridium( iii ) complexes ( Ir1-Ir4 ) featuring nido -carborane. Single crystal structures indicate that complexes ( Ir2 , Ir3 and Ir4 ) with nido -carborane as a functional group at different substitution sites all show a trans -C^C configuration between dianionic (−2) and monoanionic (−1) ligands, which are different from the trans -N^C configuration in complex Ir1 with nido -carborane as a coordination skeleton, which has an interesting Ir-B coordination bond. Notably, Ir2 , Ir3 and Ir4 all show obvious yellow light emission, while Ir1 does not emit light either in solution or in the solid state. DFT calculations demonstrate that complexes Ir2 , Ir3 and Ir4 exhibit an unusual ligand-to-metal charge transfer (LMCT) excited state character due to the strong electron-donating character of nido -carborane. Considering its better solubility and luminescence properties, Ir3 was successfully applied in solution-processed organic light-emitting diodes and an effective yellow emission was achieved. This work provides a new strategy for the investigation of three types of charged ligand (0, −1, and −2) based phosphorescent iridium complex materials by constructing new dianionic ligands with nido -carborane. A novel family of three types of charged ligand (0, −1, and −2) based neutral phosphorescent iridium( iii ) complexes featuring nido -carborane have been prepared and their structures and photophysical properties have been studied.