Efficient phosphorescent red iridium(III) complexes containing a four-membered Ir–S–C–S ring backbone and large hindered spacers for high-performance OLEDs

Two efficient red iridium(III) complexes, (4tfmpq)₂Ir(^tBudpdtc) and (4tfmpq)₂Ir(^tBuCzdtc), containing a unique four-membered ring Ir–S–C–S backbone with flexible dithiocarbamate derivatives (^tBudpdtc = N,N-bis(4-(tert-butyl)phenyl)dithiocarbamate and ^tBuCzdtc = N-3,6-di-tert-butyl-9H-carbazole dithiocarbamate) with large hindered spacers as ancillary ligands, respectively, and 4-(4-(trifluoromethyl)phenyl)quinazoline (4tfmpq) as the main ligand were synthesized at room temperature in 10 min and investigated in detail. Due to the electron-deficient 4tfmpq main ligand and two ancillary ligands with bulky electron-donating substituents, the photophysical properties of two complexes can be effectively regulated (λ_peak = 630 nm, Φ_P = 75.0% for (4tfmpq)₂Ir(^tBudpdtc), and 614 nm and 85.0% for (4tfmpq)₂Ir(^tBuCzdtc), respectively). Employing the two complexes as emitters, organic light emitting diodes (OLEDs) with double emissive layers exhibit superior performances with a maximum current efficiency of 34.72 cd A⁻¹, a maximum external quantum efficiency (EQE_max) of 26.66% with low efficiency roll-off and an EQE of 24.62% was still obtained at a practical luminance of 1000 cd m⁻². These results suggest that Ir(III) complexes with a four-membered ring Ir–S–C–S backbone containing flexible dithiocarbamate derivatives have potential application in OLEDs.