Considering Tab. 5, we find that Cz-BDT-SO 2 shows similar characteristics to Cz-AQ only that the absorption and emission energies are strongly red-shifted and that the singlet-triplet gap is slightly raised. Cz-BDT-SO 2 may, therefore, be considered a TADF candidate assuming that its ∆E ST is still sufficiently low. Cz-BDF, on the other hand, has very similar characteristics to Cz-BDT in all of the values considered in Tab. 5. It is, thus, expected to exhibit a low photoluminescence quantum yield similarly to Cz-BDT.