Maximizing TADF via Conformational Optimization

06 August 2021, Version 2
This content is a preprint and has not undergone peer review at the time of posting.


e investigate a new strategy to enhance thermally activated delayed fluorescence (TADF) in organic light-emitting diodes (OLEDs). Given that the TADF rate of a molecule depends on its conformation, we hypothesize that there exists a conformation that maximizes the TADF rate. In order to test this idea, we use time-dependent density functional theory (TDDFT) to simulate the TADF rates of several TADF emitters, while shifting their geometries towards higher TADF rates in a select subspace of internal coordinates. We find that geometric changes in this subspace can increase the TADF rate up to three orders of magnitude with respect to the minimum energy conformation, and the simulated TADF rate can even be brought into the submicrosecond timescales under the right conditions. Furthermore, the TADF rate enhancement can be maintained with a conformational energy that might be within the reach of modern synthetic chemistry. Analyzing the maximum TADF conformation, we extract a number of structural motifs that might provide a useful handle on the TADF rate of a donor-acceptor (DA) system. The incorporation of conformational engineering into the TADF technology could usher in a new paradigm of OLEDs.


thermally activated delayed fluorescence
organic light-emitting diode
geometry optimization
time-dependent density functional theory
donor-acceptor system

Supplementary materials

Supplementary Information: Maximizing TADF via Conformational Optimization
Our version of the Nelder-Mead simplex method; calculation of the RISC rate and evaluation of its effects on the TADF rate; recalculation of the electronic structures using PBE0, M06-2X, LRC-ω*PBE, M06-2X/IEF-PCM and LRC-ω*PBE/IEF-PCM; geometries of Cz2BP, AcMPM, and SprioACTRZ at the TADF maximum with various energy penalties, and after the relaxation of DOFs that had been fixed in the TADF rate maximization; dominant NTO pairs of DCzTrz, Cz2BP, AcMPM, and SprioACTRZ in the S_1 and T_1 states; Z-matrices thereof.


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