Cationic Iridium Complexes with Phenylpyridine and Strong Ancillary Ligands

We report the theoretical studies of cationic Ir(III) complexes with phenylpyridine and phosphines, [trans-Ir(dfMeppy)(2)(PPh2Me)(2)](+) and [cis-Ir(dfMeppy)(2) (PPh2Me)(2)](+). To gain insight into the factors responsible for the emission color change and the different quantum yields, we perform DFT and TDDFT calculations on the ground and excited states of these complexes, including solvation effects on the calculation of the excited states. [Trans-Ir(dfMeppy)(2)(PPh2Me)(2)](+) produces the PL emission at 450 and 475 nm, whereas [cis-Ir(dfMeppy)(2)(PPh2Me)(2)](+) produces the PL emission at 442 and 470 nm, respectively. The computational study allows us to reveal that the position of the PPh2Me ancillary ligands alter the MLCT energy mainly by changing the HOMO energy level. The HOMO energy level of the cis-isomer may be lowered by a high trans effect of the strong-field ancillary ligand, which causes a significant blue shifted emission. It is also likely that the strong-field ancillary ligand PPh2Me increases the MLCT characteristics of the cis-isomer by lowering the t(2g) energy level of 5d-orbitals of the metal. We discuss how the ancillary ligand PPh2Me influences both the emission peak and the MLCT transition efficiency.