Prediction of Intramolecular Charge-Transfer Excitation for Thermally Activated Delayed Fluorescence Molecules from a Descriptor-Tuned Density Functional

Abstract

The reliability of time-dependent density functional theory (TDDFT) for the calculation of the charge-transfer (CT) excitation energy depends on the proportion of the Hartree–Fock (HF) exchange (α) in a hybrid functional. Here, we develop a new descriptor-tuning methodology to determine the optimal α (OHF) in a hybrid PBE functional (PBEα). The conventional transition-density-based descriptors are shown to be inappropriate to measure the degree of CT for our approach because of the functional-dependence. A new functional-independent descriptor K, defined as the negative growth rate of the exciton binding energy upon α, is then developed and found to be highly correlated with the OHF in the PBEα. Applying the so-called K-OHF method, the lowest singlet excitation energy and singlet–triplet energy splitting of various reported thermally activated delayed fluorescence (TADF) materials are successfully reproduced with mean absolute deviations of 0.07 and 0.09 eV, respectively, compared to the carefully measure...