Blue-emitting iridium complexes with substituted 1,2,4-triazole ligands: synthesis, photophysics, and devices

Neutral heteroleptic mononuclear iridium(III) complexes with (2,4-difluoro)phenylpyridine and different pyridine-1,2,4-triazole ligands were synthesized and fully characterized. We investigated the effects of substituents in the 5-position of the triazole ring on the photophysical and electrochemical behavior. Increasing the electron-withdrawing capabilities generally leads to a lowering of the HOMO level with a consequent slight widening of the HOMO-LUMO gap and a blue shift in emission. The complexes reported exhibit high emission quantum yields and long luminescent lifetimes, typical of iridium(III) complexes, and most of them show reversible redox processes in solution. Also, many of the complexes reported here have been obtained as single crystals suitable for X-ray crystallography. Two of the complexes were further tested as phosphorescent dyes in OLED devices and showed high external quantum efficiencies (~7%) and color points better than the "standard" for blue iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2']picolinate (FIrpic). We also report the full electrochemical investigation of FIrpic in different solvents.