Acceptor engineering for modulating circularly polarized luminescence and thermally activated delayed fluorescence properties

As the new type of organic photoelectric device, circularly polarized thermally activated delayed fluorescence (CP-TADF) organic light-emitting diodes (OLEDs) with the advantages of high exciton utilization and full color saturation show wide applications in 3D display, encrypted information storage and quantum computing. However, due to the conflict between high luminescence efficiency and large luminescence asymmetry factor (glum), the species of efficient CP-TADF molecules are limited. Herein, theoretical studies are performed by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods coupled with thermal vibration correlation function, the effects of different acceptors on circularly polarized luminescence (CPL) and TADF properties are investigated, inner mechanisms between basic molecular structures and luminescence properties are revealed. By calculating intersystem crossing rate, reverse intersystem crossing rate, radiative decay rate and non-radiative decay rate, we determine that the SPHCN molecule exhibited dominate TADF properties. Additionally, the electronic circular dichroism (ECD) spectrum and glum values are quantitatively calculated to measure the CPL properties. Based on our findings, we conclude that lengthening the acceptor unit is a feasible strategy for improving the luminescence properties of CP-TADF molecules. Our study provides a novel approach for understanding the molecular luminescence mechanism of CP-TADF, which could promote the development of CP-OLEDs.