Blue Phosphorescent Mono-cyclometalated Iridium(III) Complexes

Abstract

New deep blue phosphorescent iridium(III) complexes comprised of one cyclometalate, two phosphines trans to each other and two cis-ancillary ligands, such as Ir(F2Meppy)(PPh2Me)2(H)(Cl), Ir(F2Meppy)(PPh2Me)2(H)(NCMe) , and Ir(F2Meppy)(PPh2Me)2(H)(CN), [F2Meppy = 2-(2’, 4’difluorophenyl)-4-methyl-pyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. We investigated the strong field effects of ancillary ligands to gain insight into the factors responsible for the emission color change and the different luminescence efficiency. Reducing the molecular weight of the phosphine ligand with PPh2Me leads to more efficient deep-blue organic light-emitting devices (OLED) by thermal processing instead of through solution processing. The electron-withdrawing difluoro group substituted on the phenyl ring, the electron-donating methyl group on the pyridyl ring, and the cyano strong field ancillary ligand increased the HOMO-LUMO gap and achieved a hypsochromic shift in the emission color. As a result, the maximum emission spectra of Ir(F2Meppy)(PPh2Me)2(H)(Cl), Ir(F2Meppy)(PPh2Me)2(H)(NCMe) , and Ir(F2Meppy)(PPh2Me)2-(H)(CN) were in the ranges of 440.5, 437, 436 nm, respectively.