New sky-blue and bluish–green emitting Ir(III) complexes containing an azoline ancillary ligand for highly efficient PhOLEDs

Abstract

Two Ir(III) complexes containing the chromophoric ancillary ligands 2-(4,5-dihydrooxazol-2-yl)phenol and 2-(1-ethyl-4,5-dihydro-1H-imidazol-2-yl)phenol, and a highly functionalized phenylpyridine derivative, 3-(4-(tert-butyl)pyridin-2-yl)-2,6-difluorobenzonitrile, as a cyclometalating ligand were designed and synthesized. The oxazoline/imidazoline heterocycle of the ancillary ligand has the effect of enhancing the metal to ligand charge transfer transition nature of the emitting excited state and the fluorine and cyano substituents on the ligand have enriched the intersystem crossings, as indicated by the experimental photoluminescence analysis. As a result, the oxazoline and imidazoline containing complexes exhibited high photoluminescence quantum yields of about >90% with bright sky-blue emission at 480 nm and bluish–green light at 495 nm, respectively, along with excellent thermal/morphological stability about 400 °C and good solubility, that make them suitable for both wet- and dry-processes. In particular, the phosphorescent OLEDs fabricated by a dry-process showed the maximum EQEs of 21.9% and 19.7% for the oxazoline and imidazoline containing complexes, respectively.