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.