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. A donor-donor′-acceptor molecule exhibited two thermally activated delayed fluorescence (TADF). TADF1 was detected with lifetime of nanosecond order, and was attributed to fast ISC1/RISC1 processes between the charge-transfer state 1CT and a degenerate locally excited triplet state 3LE. A second TADF weakly contributed to the emission as a decay component originating from 3CT, in the microsecond range.