Efficient deep red electroluminescence of iridium(iii) complexes with 2,3-diphenylquinoxaline derivatives and tetraphenylimidodiphosphinate

Abstract

Four novel iridium(III) complexes (Ir1–Ir4) containing 2,3-diphenylquinoxaline derivatives with or without fluoro-substituents at different positions (L1: 2,3-diphenylquinoxaline; L2: 6,7-difluoro-2,3-diphenylquinoxaline; L3: 2,3-bis(4-fluorophenyl)quinoxaline; L4: 6,7-difluoro-2,3-bis(4-fluorophenyl)quinoxaline) as the main ligands and tetraphenylimidodiphosphinate as an ancillary ligand were synthesized and thoroughly investigated. All the complexes emit deep red photoluminescence (PL) with high quantum yields (Ir1: λ_max: 662 nm, η_PL: 68.2%; Ir2: λ_max: 669 nm, η_PL: 60.4%; Ir3: λ_max: 639 nm, η_PL: 78.6%; Ir4: λ_max: 642 nm, η_PL: 98.3%). Organic light-emitting diodes (OLEDs) with single- or double-emitting layers (EMLs) were fabricated using these new emitters. The double-EML device using Ir4 with a structure of ITO (indium-tin-oxide)/MoO₃ (molybdenum oxide, 5 nm)/TAPC (di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, 30 nm)/TcTa (4,4′,4′′-tris(carbazol-9-yl)triphenylamine): Ir4 (2 wt%, 10 nm)/26DCzPPy (2,6-bis(3-(carbazol-9-yl)phenyl)pyridine): Ir4 (2 wt%, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) displays good electroluminescence (EL) performance with a maximum luminance, current efficiency, power efficiency and external quantum efficiency of up to 25 926 cd m⁻², 16.6 cd A⁻¹, 13.7 lm W⁻¹ and 19.9%, respectively, and the efficiency roll-off ratio is mild. The results demonstrated that the number and position of fluoro-substituents can affect both the PL and EL properties of the Ir(III) complexes, which are potential deep red phosphorescent materials for specific applications in OLEDs.