Synthesis and characterization of blue phosphorescent cyclometalated Ir(III) complexes containing 2-(imidazol-2-yl)pyridine as ancillary ligand

Four new blue phosphorescent iridium complexes containing 2-(fluoro substituted phenyl)pyridine as the cyclometalated ligands and 2-(imidazol-2-yl)pyridine as an ancillary ligand have been synthesized and characterized. The complexes have the general structure (C^N)2Ir(pym), where C^N are cyclometalating ligands (e.g., 2-(2,4-difluorophenyl)pyridine (24f2ppyH), 2-(3,4-difluorophenyl)pyridine (34f2ppyH), 2-(3,5-difluorophenyl)pyridine (35f2ppyH), and 2-(3,4,5-trifluorophenyl)pyridine (345f3ppyH)), pym is 2-(imidazol-2-yl)pyridine (pymH). The absorption, emission, and cyclic voltammetry of the complexes were systematically investigated. The (46f2ppy)2Ir(pym) has been characterized using X-ray crystallography and the electronic ground state calculated using B3LYP density functional theory. The highest occupied molecular orbital (HOMO) consists of a mixture of pym ligand (83.7%) and Ir orbitals (12.1%), while the lowest occupied molecular orbital (LUMO) is mostly on f2ppy ligands (93.4%). By replacing the ancillary ligand pic with pym can finely tune emission of the iridium complexes, showing blue luminescence at a wavelength of 467–491 nm at room temperature in CH2Cl2.