LAUSR

Molecular design strategies to develop highly efficient and long wavelength thermally activated delayed fluorescent (TADF) emitter are crucial because the inherent limitation of the energy gap law degrades the efficiency of the red or orange TADF emitters. In order to resolve the low efficiency issue, we designed and synthesized two TADF emitters,4,4'-(6-(9,9-dimethylacridin-10(9H)-yl)-7-fluoroquinoxaline-2,3-diyl)dibenzonitrile (FDQCNAc) and 11-(9,9-dimethylacridin-10(9H)-yl)-12-fluorodibenzo[a,c]phenazine-3,6-dicarbonitrile (FBPCNAc), by utilizing fluorine and peripheral cyano substituted quinoxaline and phenazine acceptors of 4,4'-(6-fluoroquinoxaline-2,3-diyl)dibenzonitrile (FDQCN) and 11-fluorodibenzo[a,c]phenazine-3,6-dicarbonitrile (FBPCN), respectively. Fluorine atom at the ortho-position of the acridine donor acts as an auxiliary acceptor to minimize singlet-triplet energy gap (ΔEST) below 0.1 eV and promote reverse intersystem crossing (RISC) process. Organic light emitting device (OLED) fabricated with the FDQCNAc and FBPCNAc emitters demonstrated high external quantum efficiency (EQE) of 27.6 and 25.4 % in the yellow-red TADF OLEDs, respectively. In particular, the combination of the F auxiliary acceptor unit and rigidified FBPCN acceptor enabled red-shifted emission by about 56 nm without much sacrifice of the EQE in the red region.