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%. (C) 2013 Elsevier B.V. All rights reserved.