Sky‐Blue Emitters With Four Fluorene Arms Exhibiting High Hole Mobilities and Thermally Activated Delayed Fluorescence for Efficient Organic Light Emitting Diodes and Detection of Nitroaromatic Explosive Compounds

ABSTRACT New donor–acceptor–donor type emitters, N,N,N',N'‐tetrafluoren‐2‐yl‐4,4'‐diaminobenzophenone (FABP) and its ethyl‐containing counterpart (EFABP) are reported as thermally activated delayed fluorescent (TADF) emitters. The study of photophysical properties of both the compounds reveal the coexistence of multiple emissive states, whose relative contributions are redistributed by thermal treatment. The constrained dihedral angle calculations demonstrate that conformational flexibility strongly modifies the excited state landscape, providing a plausible explanation for the experimentally observed distribution of emissive states. The emission of FABP exhibits higher sensitivity toward picric acid, whereas EFABP shows photoluminescence quantum yield of up to 44% when molecularly dispersed in an inert polymer matrix. Its vacuum deposited film exhibits high hole mobility reaching 10 −3 cm 2 V −1 s −1 at high electric fields. EFABP also shows superior selectivity for nitroaromatic explosive detection. Furthermore, EFABP serves as an efficient sky‐blue emitter for OLED, delivering a low turn‐on voltage and maximum external quantum efficiency of 16.6%.