Multi‐Resonance Skeleton Engineering for Highly Efficient Blue OLEDs With High Color Purity and Visual Comfort

ABSTRACT Blue multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials necessitate high color purity along with visual comfort for their commercialization in organic light‐emitting diodes (OLEDs). Given that the slight adjustments in the MR‐TADF molecular structure commonly lead to significantly alter the emission spectrum, there is an urgent need to develop strategies for fine‐tuning spectral characteristics. Herein, an effective design strategy is proposed to develop blue MR‐TADF materials by integrating primary MR skeleton with auxiliary regulation unit, and through modulate the structure of auxiliary regulation unit, three MR‐TADF materials are designed and synthesized. The emission wavelengths of these emitters are gradually blue‐shifted from 466 to 458 nm accompanied by small full width at half‐maximum and negligible shoulder peak. The drastic changes in excited‐state dynamics of these emitters are recorded and the underlying mechanisms are systematically investigated and elucidated. High‐performance deep‐blue OLEDs are achieved based on CBN‐P, which provide an electroluminescence peak at 464 nm, Commission Internationale de L'Eclairage coordinates of (0.131, 0.088), a maximum external quantum efficiency ( η ext ) of 22.4%. Besides, the CBN‐A‐based blue OLEDs attain a maximum η ext of 30.2%, which is further augmented to 37.4% upon sensitization, representing one of the best blue MR‐TADF OLEDs reported so far.