Sub-Microsecond TADF Emission in D-D′-A Emitters

A new series of donor-donor′-acceptor molecules (D-D′-A design) is introduced. Due to different molecular configurations of the emitters, multiple triplet states were detected and happen to drive one thermally activated delayed fluorescence (TADF) with very short lifetime of the order of nanoseconds. A longer TADF component of microsecond order was also observed, thus showing an interesting case of dual upconversion. These results reveal how TADF becomes efficient enough to overwhelm the prompt fluorescence with the assistance of vibrational and rotational motions.