Dinuclear Pt II Complexes with Strong Blue Phosphorescence for Operationally Stable Organic Light‐Emitting Diodes with EQE up to 23 % at 1000 cd m −2

Here we describe the synthesis and characterization of a new class of dinuclear Pt II complexes with blue phosphorescence. Bulky N ‐heterocyclic carbene and tethered bridging ligands were employed to suppress photo‐induced structural changes and to improve thermal stability of the complexes. These complexes show mixed 3 IL/ 3 MLCT blue emission (≈460 nm) with emission quantum yields of up to 0.95, emission lifetimes of as low as 1.3 μs and radiative decay rate constants of up to 7.3×10 5 s −1 in 4 wt % doped PMMA films; the latter is attributed to a 1 MLCT excited state having high metal character (resulting in a large SOC) and a large transition dipole moment, based on DFT calculations. Phosphor‐sensitized blue hyper‐OLEDs with Commission Internationale de L'Eclairage (CIE) coordinates of (0.13, 0.12) showed a maximum EQE of 23.4 % with a full‐width‐at‐half‐maximum of 18 nm and a LT 50 >250 h at an L 0 of 1000 cd m −2 .