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)-3 H -imidazo[4,5- b ]pyridin-2-ylidene]-based pincer chelate, which are derived from PX n ·H 3 (PF 6 ) 2 , where n = 1-4, and a cyclometalating chelate given from 9-[6-[5-(trifluoromethyl)-2λ 2 -pyrazol-3-yl]pyridin-2-yl]-9 H -carbazole [(PzpyCz)H 2 ], were successfully synthesized 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 CIE xy of (0.144, 0.157) and was subjected to only ∼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 ν-DABNA as a terminal emitter, giving both an improved EQE of 26.17% and CIE xy of (0.116, 0.144), confirming efficient Förster resonance energy transfer in this hyperdevice.