Exploiting trifluoromethyl substituents for tuning orbital character of singlet and triplet states to increase the rate of thermally activated delayed fluorescence

Jonathan S Ward,Martin R Bryce,Andrew Danos,Mark A Fox,Andrei S Batsanov,Andrew P Monkman,Patrycja Stachelek

doi:10.1039/d0qm00429d

Abstract

Highlights

This work shows that trifluoromethyl (CF3) substituents can be used to increase the rate of thermally activated delayed fluorescence (TADF) in conjugated organic molecules by tuning the excitonic character of the singlet and triplet excited states
Starting from the well-characterized blue TADF emitter 2,7-bis(9,9-dimethylacridin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DDMA-TXO2) 1, (Fig. 1), the motivation was to explore the effect on photophysical properties that arise from tuning the donor and acceptor abilities of the sub-units using systematic CF3 substitution.[64,65]
organic light-emitting diodes (OLEDs) using compounds 2 and 4 in various hosts (Section S5, Electronic supplementary information (ESI)†) were found to be unstable, with brightness dropping below half its initial value within seconds at constant voltage driving

Summary

Introduction

This work shows that trifluoromethyl (CF3) substituents can be used to increase the rate of thermally activated delayed fluorescence (TADF) in conjugated organic molecules by tuning the excitonic character of the singlet and triplet excited states. Trifluoromethyl (CF3) is a strongly inductive electron-withdrawing group which makes it a useful substituent for emission colour tuning via donor and acceptor strength manipulation in D–A–D CT emitters. This shift in reduction is quite substantial considering that the CF3 groups on the acceptor in [2,3,4] are on an sp[3] hybridized bridge which is not in direct conjugation with the p-system, and highlights the strongly s-withdrawing effect of the CF3 substituent.

Results

Conclusion