Efficient Prediction of Singlet–Triplet Gaps in Delayed Fluorescence Emitters Using Kohn–Sham Orbital Energies

Accurate prediction of singlet-triplet gaps (STGs) is crucial for designing inverted singlet-triplet (INVEST) and thermally activated delayed fluorescence (TADF) emitters, which are key to next-generation organic light-emitting diodes. However, the widely used time-dependent density functional theory (TDDFT) fails to reliably predict STGs with mainstream functional approximations, while more accurate wave function methods are computationally too expensive. In this work, we demonstrate that quasiparticle energy density functional theory (QE-DFT) provides a highly efficient and accurate alternative for predicting STGs, calculating them directly from Kohn-Sham orbital energy differences. Using the B3LYP functional, QE-DFT achieves a mean absolute error of 0.06 eV across diverse STG sets containing 233 INVEST and TADF molecules, significantly outperforming TDDFT with conventional functional approximations. Furthermore, its low computational cost makes QE-DFT especially suitable for high-throughput virtual screening. This work highlights QE-DFT as a promising tool for accelerating the discovery of new INVEST and TADF emitters.