Benchmarking Charge-Transfer Excited States in TADF Emitters: ∆DFT outperforms TD-DFT for Emission Energies

20 May 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Charge-transfer excited states are crucial to modern electronics, particularly organic light-emitting diodes (OLEDs) based on thermally-activated delayed fluorescence (TADF). However, accurately modeling CT states remains challenging, even with modern implementations of (time-dependent) density functional theory [(TD-)DFT], especially in a dielectric environment. To identify short-comings and improve the methodology, we previously established the STGABS27 benchmark set with highly accurate experimental references for the adiabatic energy gap between the lowest singlet and triplet excited states (∆EST). Here, we diversify this set to the STGABS27-EMS benchmark by including experimental emission energies (Eem) and use this new set to (re)-evaluate various DFT-based approaches. Surprisingly, these tests demonstrate that a state-specific (un)restricted open-shell Kohn-Sham (U/ROKS) DFT coupled with a polarizable continuum model for perturbative state-specific non-equilibrium solvation (ptSS-PCM) provides exceptional accuracy for predicting Eem over a wide range of density functionals. In contrast, the main workhorse of the field, Tamm-Dancoff-approximated TD-DFT (TDA-DFT) paired with the same ptSS-PCM, is distinctly less accurate and strongly functional dependent. More importantly, while TDA-DFT requires the choice of two very different density functionals for good performance on either ∆EST or Eem, the time-independent U/ROKS/PCM approaches deliver excellent accuracy for both quantities with a wide variety of functionals.


Thermally-activated delayed fluorescence
Charge-transfer excited states
Excited-state solvation

Supplementary materials

Supporting Information
Detailed description of the computational workflow, methods, and used programs; complete plots of the emission energies for all used methods; investigation of basis set effects; definition of the used statistical measures


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.