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The Taming of the Shrew: Using Mild Heavy‐Atom Effect for Constraining Molecular Vibrations in a Triphenylamine Donor–Acceptor System for Enhanced Photo‐ and Electroluminescence

Year: 2026
Type: article
Abstract: ABSTRACT Achieving efficient triplet harvesting remains a key challenge in the development of all‐organic red and near‐infrared (NIR) thermally activated delayed fluorescence (TADF) emitters. In this study, we demonstrate how strategic ortho‐chlorine substitution in a triphenylamine ( TPA )‐based Donor–Acceptor (D‐A) system significantly improves reverse intersystem crossing (rISC) efficiency by simultaneously reducing the singlet‐triplet energy gap (Δ E ST ) and enhancing spin‐orbit coupling (SOC). Through combined spectroscopic and theoretical analysis, we reveal that chlorine‐induced molecular distortion of two side phenyl rings of TPA and increased rigidity lead to lower reorganization energies, while collectively these factors facilitate an over 20‐fold enhancement in rISC rates. Notably, the modified emitter ( diClDa‐CNBPz ) exhibits higher photoluminescence quantum yield, reduced sensitivity to external media, and optimized triplet harvesting via both 3 CT‐ 1 CT and 3 LE‐ 1 CT pathways. The latter is responsible for the enhanced SOC owing to a heavy‐atom effect. When incorporated into OLEDs, diClDa‐CNBPz achieves twice the external quantum efficiency and a fourfold reduction in efficiency roll‐off compared to the unsubstituted counterpart. Additionally, its application in NIR hyperfluorescent OLEDs further underscores the benefits of enhanced triplet harvesting. These findings highlight halogen substitution as a powerful tool for fine‐tuning TADF materials, paving the way for next‐generation high‐performance optoelectronic devices.
DOI: 10.1002/adom.71346
Authors: Michał Mońka, Daria Grzywacz, Patryk Kamiński, Piotr Pander, Andrew P. Monkman, Illia E. Serdiuk
Language: English
Open Access status: green
OpenAlex ID: W4413858965
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