Molecular Design of Thermally Activated Delayed-Fluorescent Emitters Using 2,2'-Bipyrimidine as the Acceptor in Donor-Acceptor Structures.

Donor-acceptor-donor (D-A-D)-type thermally activated delayed fluorescence (TADF) emitters 5,5'-bis{4-[9,9-dimethylacridin-10(9H)-yl]phenyl}-2,2'-bipyrimidine (Ac-bpm) and 5,5'-bis[4-(10H-phenoxazin-10-yl)phenyl]-2,2'-bipyrimidine (Px-bpm), based on the 2,2'-bipyrimidine accepting unit, were developed and their TADF devices were fabricated. The orthogonal geometry between the donor unit and the 2,2'-bipyrimidine accepting core facilitated a HOMO/LUMO spatial separation, thus realizing thermally activated delayed fluorescence. The exhibited electroluminescence ranged from green to yellow, depending on the donor unit, with maximum external quantum efficiencies of up to 17.1 %.