Modeling Molecular Emitters in Organic Light-Emitting Diodes with the Quantum Mechanical Bespoke Force Field

Abstract

Combined molecular dynamics (MD) and quantum mechanics (QM) simulation procedures have gained popularity in modeling the spectral properties of functional organic molecules. However, the potential energy surfaces used to propagate long-time scale dynamics in these simulations are typically described using general, transferable force fields designed for organic molecules in their electronic ground states. These force fields do not typically include spectroscopic data in their training, and importantly, there is no general protocol for including changes in geometry or intermolecular interactions with the environment that may occur upon electronic excitation. In this work, we show that parameters tailored for thermally activated delayed fluorescence (TADF) emitters used in organic light-emitting diodes (OLEDs), in both their ground and electronically excited states, can be readily derived from a small number of QM calculations using the QUBEKit (QUantum mechanical BEspoke toolKit) software and improve the overall accuracy of these simulations.

Fast and Accurate Determination of the Singlet–Triplet Gap in Donor–Acceptor and Multiresonance TADF Molecules by Using Hole–Hole Tamm–Dancoff Approximated Density Functional Theory

“…Consequently, the apparent larger MAE of the hh‐TDA approach for singlet excitation energy compared to TD‐DFT is not inherent to the method itself. Indeed, while the correspondence between the hh‐TDA/B3LYP MAE value of 0.66 eV for the D‐A compounds in Scheme 2 and the Stokes shift of ≈0.6 eV of PTZ‐DBTO2 [ 61,64 ] is simply fortuitous, this comparison gives a feeling of the error order being induced into the MAE values by considering the absorption onset energies of the DA compounds instead of their emission energies, error which has nothing to do with the performances of the hh‐TDA method. Nevertheless, the hh‐TDA/B3LYP approach exhibits the highest correlation of 0.84 for D‐A TADF.…”

“…These effects also manifest in the Stokes shift stemming from structural changes in the emitter, which, in the case of PTZ‐DBTO2 molecule, have been quantified by means of molecular dynamics simulation to be as large as 0.6 eV. [ 61 ]…”

“…which, in the case of PTZ-DBTO2 molecule, have been quantified by means of molecular dynamics simulation to be as large as 0.6 eV. [61] We focus first on the performances of the TD-DFT method for the first excited state of standard D-A TADF compounds as shown in Figure 2. In this frame, only the results using two tuned 𝜔functionals (LC-*𝜔PBEh+ and *𝜔B97X+) are given, as the other functionals are known to perform very poorly for ΔE ST .…”

Rapid predictions of the colour purity of luminescent organic molecules

“…Consequently, the smaller energy gap combined with the increased SOC leads to the increased importance of direct ISC in 15. This simplifies the mechanism for triplet harvesting and also removes the strong environment effects observed in D-A molecules [68][69][70][71][72][73][74][75] making it easier to develop high throughput design rules.…”

Dominant dimer emission provides colour stability for red thermally activated delayed fluorescence emitter

“…13 More recent follow-up modelling work by Yang et al showed that SSSE may still play a larger role than initially predicted but it remains a weak effect compared to standard solution polarity effects. 14 Etherington et al investigated the photophysics of 4CzIPN in more detail, looking at potential dimer formation that could lead to the shift of the CT emission. 15 Sublimation of pristine 4CzIPN led to the formation of several fractions, all of them crystal polymorphs with different emission properties in which the carbazole units of separate molecules were found to show partial or full face-to-face overlap to form dimer species.…”