Iridium(iii) complexes incorporating thieno[2,3-d]pyrimidine units for efficient orange-to-yellow electroluminescence with low efficiency roll-off

Abstract

In this study, two cyclometalated iridium(III) complexes, named (4tfptp)₂Ir(tpip) and (4tfptp)₂Ir(Stpip), with 4-(4-(trifluoromethyl)phenyl)thieno[2,3-d]pyrimidine (4tfptp) as the main ligand and bis(diphenylphosphoryl)amide (tpip) or bis(diphenylphorothioyl)amide (Stpip) as the ancillary ligand, were synthesized for organic light-emitting diodes (OLEDs). (4tfptp)₂Ir(Stpip) was obtained in a few minutes at room temperature due to the strong coordination ability of the sulfur atom and the Ir metal center. (4tfptp)₂Ir(tpip) and (4tfptp)₂Ir(Stpip) exhibit different emission peaks at 589 and 564 nm with photoluminescence quantum efficiencies (Φ_PL) of 35% and 52% in CH₂Cl₂ solutions, respectively, which may result from the different heteroatoms introduced into the ancillary ligands. Furthermore, the Φ_PL of (4tfptp)₂Ir(Stpip) in co-deposited films is improved greatly up to 90%. The OLEDs employing these complexes as emitters exhibit good performance. Particularly, the OLED based on the (4tfptp)₂Ir(Stpip) complex with Stpip as the ancillary ligand exhibits better performance with a maximum brightness of 38 560 cd m⁻², a maximum current efficiency of 86.3 cd A⁻¹, a maximum external quantum efficiency (EQE_max) of 24.7% and an EQE of 20.9% at a luminance of 10 000 cd m⁻², suggesting that these materials have potential applications in efficient OLEDs.