Effect of donor and acceptor position on light emitting performances of thermally activated delayed fluorescent emitters with two bicarbazole donors and two cyano acceptors

Positional effect of donors and acceptors in the thermally activated delayed fluorescent (TADF) emitters was examined using TADF emitters with two donors and two acceptors. The position of the donors and acceptors at the phenyl linker was regulated as ortho-, meta- and para- to study the positional effect of the donors and acceptors. The comparison of the three TADF emitters with the different substitution positions suggested that ortho- or meta- substitution of each donor or acceptor is a useful way of improving light-emitting performances of the TADF emitters. The TADF emitter with the two donors at meta- position achieved high quantum efficiency of 18.0% compared with 15.1% and 3.8% of other emitters. High photoluminescence quantum yield, high fluorescence rate constant, and high reverse intersystem crossing rate constant were the main factors for the high quantum efficiency of the meta- substituted emitter.