Molecular Design Opening Multiple Charge Transfer Pathways in Oxygen‐Bridged Boron Emitters for High‐Efficiency Pure Violet Organic Light‐Emitting Diodes

ABSTRACT In this study, we designed and synthesized two novel oxygen‐bridged boron‐based thermally activated delayed fluorescence (TADF) emitters, 11‐(9H‐carbazol‐9‐yl)‐16‐phenyl‐12‐(3‐(triphenylsilyl)phenyl)‐16H‐5,9‐dioxa‐16‐aza‐13b‐boraindeno[1,2‐a]naphtho[1,2,3‐fg]anthracene (BOID‐Cz‐Si) and 9‐(12‐(3‐(triphenylsilyl)phenyl)‐5,9,16‐trioxa‐13b‐boraindeno[1,2‐a]naphtho[1,2,3‐fg]anthracen‐11‐yl)‐9H‐carbazole (BOBF‐Cz‐Si). These compounds produce fluorescent emission through short‐range and long‐range charge transfer (CT) within the polycyclic aromatic hydrocarbon framework along with additional long‐range CT between the donor and acceptor units of the emitter. Indole and benzofuran units were incorporated into the oxygen‐bridged boron core as electron‐donating moieties to modulate the long‐range CT and enhance the multiple resonance (MR)‐TADF properties. Furthermore, a bulky tetraphenylsilane group and an auxiliary carbazole unit were incorporated to suppress intermolecular interactions and enhance emission through long‐range CT. Both emitters exhibited pure violet emission (peaks near 400 nm) with narrow full width at half‐maximum values (approximately 25 nm) in the solution state and high photoluminescence quantum yields (up to 95%). Notably, the BOID‐Cz‐Si device showed a violet emission peak at 420 nm and a maximum external quantum efficiency of 22.7%, which is one of the highest efficiency values reported in the violet region. These results indicate the promising potential of hybridized oxygen‐bridged boron scaffolds, which combine short‐ and long‐range CT within the MR framework with rational donor engineering, as high‐efficiency, high‐color‐purity MR‐TADF emitters.