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<sup>–2