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 (Delta E-ST) values less than 0.1 eV. With their high PL quantum yield (Phi(PL)) and sufficient rate constant for RISC process (k(RISC)), organic light emitting diodes (OLEDs) employing AcCN and PxCN as emitters achieve a maximum external quantum efficiency (eta(ext)) of 20.6% and 15.5%, respectively, with green emissions.