Efficient red phosphorescent Ir() complexes based on rigid ligands with high external quantum efficiency and low efficiency roll-off

The rigid ligands in red phosphorescent Ir( iii ) complexes can suppress the vibration and rotation around metal ions to maximize the utilization of low energy singlet and triplet states, thus greatly reducing the probability of non-radiative decay. In this paper, the coordination groups (phenyl and quinolinyl) are fused by a cyclohexyl group to produce rigidified ligands (5,6-dihydro-benzo[ c ]acridine and 9-fluoro-5,6-dihydro-benzo[ c ]acridine). A bulky ancillary ligand (2,2,6,6-tetramethylheptane-3,5-dione) was applied for the synthesis of Ir( iii ) complexes ( Ir-DHBA and Ir-F-DHBA ) to minimize the intimate interactions between Ir( iii ) molecules and consequently to reduce triplet-triplet annihilation and triplet-polaron annihilation. When the two Ir( iii ) complexes were applied as dopants in organic light-emitting diode (OLED) devices, they both showed excellent electroluminescence (EL) performance. The device based on Ir-DHBA demonstrated a low efficiency roll-off with a maximum external quantum efficiency (EQE) of 26.0%, 25.3% EQE at a brightness of 1000 cd m −2 and 22.7% EQE at 10 000 cd m −2 . The device based on Ir-F-DHBA (at a doping ratio of 3%) with an exciplex as a co-host showed a maximum EQE of over 28% with Commission Internationale de l'Eclairage (CIE) coordinates of (0.61, 0.39) and an EL emission peak at 600 nm. Two highly efficient red phosphorescent Ir( iii ) complexes were prepared by the introduction of rigid cyclometalating ligands.