Donor-σ-Acceptor Molecules for Green Thermally Activated Delayed Fluorescence by Spatially Approaching Spiro Conformation.

By separating donor/acceptor with a σ linker while keeping them in contact through space interactions, new oxygen-bridged triphenylamine/fluorene-based donor-σ-acceptor (D-σ-A) type thermally activated delayed fluorescence (TADF) emitters are developed. X-ray structural analyses and time-dependent density functional theory reveal that tilted configuration of spiro skeleton, extended delocalization of the highest occupied molecular orbital (HOMO), and lowest triplet state of charge transfer property (3CT) play key roles in the TADF mechanism. OLEDs fabricated with these D-σ-A emitters achieved good external quantum efficiency of 20.4% and long operating durability of 18000 h at 100 cd m-2.