The Role of Ancillary Ligands in Iridium(III) Complexes for Blue OLEDs

Abstract

In this study, new deep blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other and two cis-ancillary ligands, such as Ir{(CF3)2Meppy}(PPh3)2(H)(Cl), [Ir{(CF3)2Meppy}(PPh3)2(H)(NCMe)]+ and Ir{(CF3)2Meppy} (PPh3)2(H)(CN), [(CF3)2Meppy = 2-(3′,5′-bis-trifluoromethylphenyl)-4-methylpyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. We investigate the strong field capabilities of ancillary ligands to gain insight into the factors responsible for the emission color change and the different luminescence efficiencies. This work represents a strategy for the design of deep blue phosphorescent iridium complexes. The electron-withdrawing trifluoromethyl group substituted on the phenyl ring, the electron-donating methyl group on the pyridyl ring and the cyano strong field ancillary ligand increase HOMO-LUMO gap to achieve the hypsochromic shift in emission color. As a result, the maximum emission spectrum of Ir{(CF3)2Meppy}(PPh3)2(H)(Cl), [Ir{(CF3)2Meppy}(PPh3)2(H)(NCMe)]+ and Ir{(CF3)2Meppy}(PPh3)2(H)(CN) were in the ranges of 436, 434 and 434 nm, respectively.