Computational Design of Thermally Activated Delayed Fluorescence Materials: The Challenges Ahead

Abstract

Thermally activated delayed fluorescence (TADF) offers the premise for all-organic light emitting diodes with quantum efficiencies competing those of transition metal-based phosphorescent devices. While computational efforts have so far largely focused on gas-phase calculations of singlet and triplet excitation energies, the design of TADF materials requires multiple methodological developments targeting among others a quantitative description of electronic excitation energetics, fully accounting for environmental electrostatics and molecular conformational effects, the accurate assessment of the quantum-mechanical interactions that trigger the elementary electronic processes involved in TADF, as well as a robust picture for the dynamics of these fundamental processes. In this perspective, we describe some recent progress along those lines and highlight the main challenges ahead for modeling, which we hope will be useful to the whole TADF community.

Suppression of Concentration Quenching in Ortho‐Substituted Thermally Activated Delayed Fluorescence Emitters

“…V SOC is calculated to have a mean absolute value of ≈0.01 meV (i.e., ≈0.1 cm −1 ), which is on the lower end of the values reported for typical TADF molecules (0.02-0.10 meV). [61] In line with the results for other TADF molecules, [53] the V SOC values correlate approximately linearly with the ΔE ST values (V SOC ∝ ΔE ST , Figure 7a). This underlines that an increase in V SOC value comes at the expense of an increase in the barrier for the RISC transition.…”

“…As shown in Figure 4b, over 52% of the molecules possess a Δ E ST less than 0.05 eV, ensuring that a considerable ratio of oBFCzTrz monomers can potentially exhibit significant reverse intersystem crossing rates at room temperature. It is worth mentioning that the Δ E ST values are found to be positive for all the structures considered here; previous studies on TADF emitters have indicated that intermolecular interactions can sometimes alter the relative positions of the S 1 to T 1 states, leading to negative Δ E ST values in the case of a few of the emitters …”

“…It is worth mentioning that the ΔE ST values are found to be positive for all the structures considered here; previous studies on TADF emitters have indicated that intermolecular interactions can sometimes alter the relative positions of the S 1 to T 1 states, leading to negative ΔE ST values in the case of a few of the emitters. [52,53]…”

Computational Studies of Molecular Materials for Unconventional Energy Conversion: The Challenge of Light Emission by Thermally Activated Delayed Fluorescence

“…We are also aware of other technical requirements, such as: short excited-state lifetime to avoid non-radiative decay and thus maximize the photoluminescence quantum yields (PLQYs), appropriate color CIE coordinates and color purity, etc. However, in the following sections we focus on the basic aspects for the molecular modelling, at the molecular scale, related to energy conversion [10]. Molecules 2020, 25, x 3 of 11 Figure 2.…”

Molecular Orientation Effects in Organic Light‐Emitting Diodes

“…[114,115] For an in-depth discussion about the range of validity and the challenges of quantum chemical calculations in OLEDs, e. g., vertical transition energies and DE ST in TADF compounds, we invite interested readers to see another recent review. [116] In the aspect of modeling molecular orientation, we would like to point out that careful force-field parametrization is of particular importance, especially for nonbonded interactions.…”