Iridium(III) Blue Phosphors with Heteroleptic Carbene Cyclometalates: Isomerization, Emission Tuning, and OLED...

Ir(III) complexes are particularly noted for their excellent photophysical properties in giving blue OLED phosphors. In this study, two distinctive carbene pro-chelates LAH₂ ⁺ and LBH₂ ⁺ (or LCH₂ ⁺) were employed in preparation of heteroleptic Ir(III) complexes, to which LAH₂ ⁺ bears a cyano substituted benzoimidazolium along with N-mesityl appendage, while LBH₂ ⁺ (or LCH₂ ⁺) carries the symmetrical benzoimidazolium entity. Notably, the reversible equilibration at high temperature was observed for m, f-ct14 and m, f-ct15 with a single LA chelate. In contrast, only the mer-substituted m-ct16 was obtained upon employing two LA chelates. All Ir(III) complexes exhibited blue photoluminescence (Φ_PL $$ 78 %) with short radiative lifetimes (τ_rad $$ 1.05 μs) in solution. The Ph OLED device with m-ct16 afforded an external quantum efficiency (EQE) of 22.8 % at 5000 cd ⋅ m^-2. Moreover, the hyper-OLED based on m-ct16 and v-DABNA exhibited EQE₁₀₀₀ of 32.1 % (EQE recorded at 1000 cd ⋅ m^-2) and J₉₀ of 15.0 mA cm^-2 (current density at 90 % of max. EQE). Its suppressed efficiency roll-off (EQE of 32.1 % and 27.7 % at 1000 cd ⋅ m^-2 and 10000 cd ⋅ m^-2) demonstrated a milestone in fabrication of blue OLED devices.