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

By separating donor/acceptor with a sigma linker while keeping them in contact through space interactions, new oxygen-bridged triphenyl-amine/fluorene-based donor-sigma-acceptor (D-sigma-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 ((CT)-C-3) play key roles in the TADF mechanism. OLEDs fabricated with these D-sigma-A emitters achieved good external quantum efficiency of 20.4% and long operating durability of 18000 h at 100 cd m(-2).