Synthesis and Photophysical Properties of Blue Mono-Cyclometalated Ir(III) Complexes with Phenylpyidine Based Ligands and Phosphines

Abstract

New blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other such as Ir(dFOMeppy)(PPh3)2(H)(Cl), [Ir(dFOMeppy)(PPh3)2(H)(NCMe)]+ and Ir(dFOMeppy)(PPh3)2(H)(CN), [dFOMeppy=2-(2',4'-difluorophenyl)-4-methoxypyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. To achieve deep blue emission, the difluoro group substituted on the phenyl ring and the methoxy group substituted on the pyridyl ring increased HOMO-LUMO gap and achieved the hypsochromic shift. To gain insight into the factors responsible for the emission color change and the different luminescence efficiency, we investigate the electron-withdrawing capabilities of ancillary ligands using the DFT and TD-DFT calculations on the ground and excited states of the complexes. From these results, we discuss how the ancillary ligand influences the emission peak as well as the metal to ligand charge transfer (MLCT) transition efficiency. The maximum emission spectra of Ir(dFOMeppy)(PPh3)2(H)(Cl), [Ir(dFOMeppy)(PPh3)2(H)(NCMe)]+ and Ir(dFOMeppy)(PPh3)2(H)(CN) were in the ranges of 438, 433, 432nm, respectively.