Deep-red phosphorescent iridium(III) complexes containing 1-(benzo[b] thiophen-2-yl) isoquinoline ligand: synthesis, photophysical and electrochemical properties and DFT calculations.

Four new bis-cyclometalated iridium(III) complexes, [Ir(btq) 2phen] [PF6] (3a), [Ir(btq) 2bpy] [PF6] (3b), [Ir(btq) 2dtbipy] [PF6] (3c) and [Ir(btq) 2pic] (3d) (btq = 1-(benzo[b] thiophen-2-yl) isoquinoline, phen = 1,10-phenanthroline, bpy = 2,2'-bipyridine, dtbipy = 4,4'-di-tert-butyl-2,2'-bipyridine, pic = picolinic acid) have been synthesized and fully characterized. The crystal structure of 3a has been determined by X-ray analysis. The photophysical and electrochemical properties of these new complexes 3a - 3d have been studied. The photoluminescence spectra of all Ir(III) complexes exhibit deep-red emission maxima at 682, 682, 683 and 698 nm, respectively. The most representative molecular orbital energy-level diagrams and the lowest energy electronic transitions of 3a - 3d have been calculated with density functional theory (DFT) and time-dependent DFT (TD - DFT). The results show that the pic ancillary ligand of complex 3d influences the absorption and emission energies with a further red-shift relative to other three complexes 3a - 3c.