Is Range Separation Always Necessary for Modelling TADF Emitters? A Benchmark Study of B3LYP on Dispersion-Corrected Geometries vs. Tuned ωB97X-D

Abstract

Thermally activated delayed fluorescence (TADF) emitters are commonly modeled using optimally tuned range-separated density functionals to capture their charge-transfer–dominated excited states. However, the necessity of such tuning remains an open question, particularly in view of its substantial computational cost. In this work, we present a systematic benchmark of density functional methods for predicting the ground- and excited-state properties of TADF molecules, based on a dataset of 26 experimentally reported emitters spanning diverse donor–acceptor architectures. We compare the performance of B3LYP augmented with Grimme’s D3 dispersion correction (B3LYP-D3) against optimally tuned ωB97X-D, M06-2X, and related variants. The assessment covers frontier orbital energies, singlet and triplet excitation energies, singlet–triplet gaps, radiative and non-radiative rate constants, and exciton charge-transfer descriptors. Within the computational protocol employed here, we find that B3LYP-D3 provides consistent predictions for several ground-state properties and yields singlet–triplet energy gaps and photophysical rate constants that are comparable to those obtained with optimally tuned functionals. While tuning the range-separation parameter can improve the description of certain excited-state energies, these gains are not systematic across the dataset and must be considered alongside the associated computational overhead. Taken together, the results indicate that, within the present workflow, dispersion-corrected B3LYP can provide performance comparable to more computationally demanding tuned range-separated functionals. This observation suggests that B3LYP-D3 may offer a computationally efficient option for exploratory calculations and preliminary screening of TADF emitters.