Efficient Blue Electrophosphorescence and Hyperphosphorescence Generated by Bis-tridentate Iridium(III) Complexes

Four blue-emissive iridium(III) complexes bearing a 3,3'-(1,3-phenylene)bis[1-isopropyl-6-(trifluoromethyl)-3H-imidazo[4,5-b]pyridin-2-ylidene]-based pincer chelate, which are derived from PXn.H-3(PF6)(2), where n = 1-4, and a cyclometalating chelate given from 9-[6-[5-(trifluoromethyl)-2 lambda(2)-pyrazol-3-yl]-pyridin-2-yI]-9H-carbazole [(PzpyCz)H-2], were successfully syn- thesized and employed as both an emissive dopant and a sensitizer in the fabrication of organic light-emitting diode (OLED) devices. These functional chelates around a Ir-III atom occupied two mutually orthogonal coordination arrangements and adopted the so-called bis-tridentate architectures. Theoretical studies confirmed the dominance of the electronic transition by the pincer chelates, while the dianionic PzpyCz chelate was only acting as a spectator group. Phosphorescent OLED devices with [Ir(PX3)(PzpyCz)] (B3) as the dopant gave a maximum external quantum efficiency (EQE) of 21.93% and CIExy of (0.144, 0.157) and was subjected to only similar to 10% of roll-off in efficiency at a high current density of 1000 cd m(-2). Blue-emissive narrow-band hyperphosphorescence was also obtained using B3 as an assistant sensitizer and nu-DABNA as a terminal emitter, giving both an improved EQE of 26.17% and CIExy of (0.116, 0.144), confirming efficient Forster resonance energy transfer in this hyperdevice.