Synthesis of efficient blue phosphorescent heteroleptic Ir(III) complexes containing 4-alkoxy- or 4-alkylaminopicolinates as ancillary ligands

Abstract

New blue phosphorescent iridium(III) complexes containing 2-phenylpyridine derivatives as the main ligands and 4-substituted picolinates as the ancillary ligands were synthesized and their photophysical properties were investigated. In addition, the structures of three of the iridium(III) complexes were determined by X-ray crystallography. The photophysical data show that the introduction of electron-donating long-alkoxy or dialkylamino chain (–OCH2CH2OCH2CH3, –OC5H11, –OC6H13, –OC7H13, –N(C3H7)2, or –N(C4H9)2) on the 4-position of picolinate improved the phosphorescence quantum efficiencies (Φp=0.57–0.77) of synthesized iridium(III) complexes with the maximum emission range of 461–464nm at 298K in ethanol solution. Interestingly, the substitution of the methyl group at the 4-position of the pyridine ring of the 2-phenylpyridine main ligands in the complexes with a more strongly electron-donating methoxy or dimethylamino group results in a significant bathochromic shift (69nm) rather than a hypsochromic shift of the phosphorescence emission maxima. Density field theory (DFT) calculations were performed to gain deeper understanding of these emission behaviors. The thermally most stable Ir7 among the synthesized blue phosphorescent iridium(III) complexes was tested as an emitting material in a simple OLED device.