A TADF Emitter Featuring Linearly Arranged Spiro‐Donor and Spiro‐Acceptor Groups: Efficient Nondoped and Doped Deep‐Blue OLEDs with CIE y <0.1

Reported herein is a molecular design strategy of deep‐blue emitters for resolving the lack of highly efficient deep‐blue organic light‐emitting diodes (OLEDs) featuring CIE y (Commission Internationale de l'Eclairage) color coordinates matching the display requirements (<0.1). The strategy is to combine weak spiro‐donor and spiro‐acceptor groups into a linear donor‐π‐acceptor type of thermally‐activated delayed fluorescence molecule through a sterically bulky π‐spacer. The strategy endows an emitter with deep‐blue emission, a narrower emission bandwidth (51 nm in toluene), a high photoluminescence quantum yield (0.95 in toluene), weak concentration quenching, and efficient triplet‐exciton utilization, which are all attractive characteristics for emitters of deep‐blue OLEDs with lower CIE y coordinates. Owing to the rational design, the emitter has realized not only highly efficient doped deep‐blue OLEDs with external quantum efficiencies (EQEs) up to 25.4 % and CIE y less than 0.1 but also so far the most efficient nondoped deep‐blue OLED (EQE up to 22.5 %) with CIE y less than 0.1.