Efficient blue and bluish-green iridium phosphors: Fine-tuning emissions of FIrpic by halogen substitution on pyridine-containing ligands

Three new iridium compounds, 4-F-FIrpic, 4-Cl-FIrpic and 4-Br-FIrpic, were designed and synthesized by introducing the F, Cl and Br atoms to the 4-position of pyridine ring in the frame of sky-blue emitter, FIrpic. Adding F atom stabilizes the HOMO level of FIrpic but keeps the LUMO level of FIrpic almost unchanged, which consequently broadens the HOMO–LUMO gap of FIrpic and finely tunes the emission to 465 nm of 4-F-FIrpic from 470 nm of FIrpic. In contrast, introducing of Cl and Br atoms simultaneously lowers the HOMO and LUMO levels of FIrpic, which brings about the squeeze of HOMO–LUMO gap in FIrpic and makes the emissions of 4-Cl-FIrpic and 4-Br-FIrpic red-shift to 475 and 479 nm, respectively. The phosphorescent organic light-emitting devices using the three iridium compounds as dopants were fabricated with the following configuration: ITO/MoO₃/TAPC/TCTA:dopants/Tm/LiF/Al. The device based on 4-F-FIrpic showed a blue emission with the Commission Internationale de L’Eclairage coordinate of (0.15, 0.28), and revealed rather high efficiencies, with maximum current efficiency of 29 cd A⁻¹, power efficiency of 29 lm W⁻¹ and external quantum efficiency of 14.6%.