Photophysical and electrochemical properties of blue phosphorescent iridium(III) complexes

A series of 2-difluorophenyl-4-methoxypyridine ligands were synthesized and successfully used to prepare iridium complexes including bis[2-(2',3'-difluorophenyl)-4-methoxypyridinato-N,C-2']iridium(III) [5-(2'-pyridyl)tetrazolate] (5a1), bis[2-(2',4'-difluorophenyl)-4-methoxypyridinato-N,C-2']iridium(III) [5-(2'-pyridyl)tetrazolate] (5a2), bis[2-(2',5'-difluorophenyl)-4-methoxypyridinato-N,C-2']iridium(III) [5-(2'-pyridyl)tetrazolate] (5a3), bis[2-(3',4'-difluorophenyl)-4-methoxypyridinato-N,C-2']iridium(III) [5-(2'-pyridyl)tetrazolate] (5a4), and bis[2-(3',5'-difluorophenyl)-4-methoxypyridinato-N,C-2']iridium(III) [5-(2'-pyridyl)tetrazolate] (5a5). Interestingly, 5a4 exhibits 2'-coordinated and 6'-coordinated isomers. The coordination behavior of this ligand with iridium metal differed depending on the repulsion energy and the delocalization energy effects of the iridium complexes. X-ray structural analysis technique was successfully applied to interpret the different coordination behavior of 5a4. In addition, introducing the methoxy group to the well-known ligand (2-difluorophenylpyridine) successfully expanded the band gap of iridium complexes and made 5a2 exhibit the bluest emission at 452 nm. To the best of our knowledge, this is one of the bluest OLEDs based on a 2-difluorophenylpyridine-iridium coordination emitter.