Molecular design of highly effective thermally activated delayed fluorescence emitters based on ortho-substituted donor-acceptor-donor pyridinecarbonitrile derivatives and their application for high-performance OLEDs

In this work, we designed and investigated two TADF molecules, AcCN and PxCN, introducing donor moieties into the 3,5-position of 4-pyridinecarbonitrile acceptor core. These D‒A‒D type compounds exhibit effective utilization of triplet excitons through a reverse intersystem crossing (RISC) process with relatively small singlet-triplet energy splitting (ΔEST) values less than 0.1 eV. With their high PL quantum yield (ΦPL) and sufficient rate constant for RISC process (kRISC), organic light-emitting diodes (OLEDs) employing AcCN and PxCN as emitters achieve a maximum external quantum efficiency (ηext) of 20.6% and 15.5%, respectively, with green emissions.