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

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.