A series of red iridium(iii) complexes using flexible dithiocarbamate derivatives as ancillary ligands for highly efficient phosphorescent OLEDs

Abstract

Five red cyclometalated iridium(III) complexes containing the unique four-membered ring Ir–S–C–S backbone with different dithiocarbamate derivatives as ancillary ligands and 1-(4-(trifluoromethyl)phenyl)isoquinoline (4tfmpiq) as the main ligand were synthesized at room temperature within ten minutes. The emission color (λ_peak = 607–619 nm) and photoluminescence quantum efficiency (PLQY) (Φ_P = 36.6–63.0%) can be effectively tuned by introducing different electron – donating substituents such as diisopropylamine (dipdtc), diphenylamine (dpdtc), bis(4-(tert-butyl)phenyl)amine (^tBudpdtc), carbazole (Czdtc) and 3,6-di-tert-butyl-9H-carbazole (^tBuCzdtc) into the dithiocarbamate ancillary ligands. Employing (4tfmpiq)₂Ir(dipdtc) as the emitter, the organic light emitting diodes (OLEDs) with double emitting layers exhibit good performances with a maximum current efficiency (η_c,max) of 18.67 cd A⁻¹, an EQE_max of 20.69% and low efficiency roll-off with an EQE of 18.11% at the practical luminance of 1000 cd m⁻². The Commision Internationale de L’Eclairage coordinates of (0.660, 0.337) are quite close to the National Television System Comittee (NTSC) standard red emission. These results demonstrate that by introducing different electron – donating substituents into the dithiocarbamate ligands, the diversity of the S–C–S ligands is greatly enriched for red Ir(III) complexes and the corresponding OLEDs.