Isomeric modulation of thermally activated delayed fluorescence in dibenzo[ a, c ]phenazine-based (deep) red emitters

Brebels, Sonny; Cardeynaels, Tom; Jackers, Louis; Kuila, Suman; Penxten, Huguette; Salthouse, Rebecca J; Danos, Andrew; Monkman, Andrew P; Champagne, Benoît R.; Maes, Wouter

Abstract

A series of four emissive regio-isomers are synthesized based on the dibenzo[a, c]phenazine-11,12-dicarbonitrile (DBPzCN) acceptor scaffold and a triphenylamine (TPA) donor. Density functional theory is utilized to compare the relative differences in molecular conformation, excited state distributions, and orbital interactions. Steady-state and time-resolved emission spectroscopy reveal strongly contrasting emissive properties and triplet harvesting of the four materials. In zeonex host emission maxima range widely, with differences of over 100 nm. Additionally, isomers 3-TPA-DBPzCN and 4-TPA-DBPzCN show photoluminescence quantum yields (PLQYs) of 46 and 62%, while 1-TPA-DBPzCN and 2-TPA-DBPzCN instead show values <1 and 24%, respectively. Relevant to thermally activated delayed fluorescence (TADF), very small singlet–triplet energy gaps are observed for isomers 2-TPA-DBPzCN and 4-TPA-DBPzCN, with corresponding reverse intersystem crossing (rISC) rates of 0.6 and 1.6 × 105 s−1, respectively. Unique in possessing both fast rISC and a relatively high PLQY, the unconventional 4-TPA-DBPzCN regio-isomer turns out to be an efficient TADF emitter, highlighting the important role of donor–acceptor substitution position in the design of efficient TADF materials targeting specific wavelength ranges.

Citation

Brebels, S., Cardeynaels, T., Jackers, L., Kuila, S., Penxten, H., Salthouse, R. J., Danos, A., Monkman, A. P., Champagne, B. R., & Maes, W. (2024). Isomeric modulation of thermally activated delayed fluorescence in dibenzo[ a, c ]phenazine-based (deep) red emitters. Journal of Materials Chemistry C Materials for optical and electronic devices, 12(25), 9255-9265. https://doi.org/10.1039/d4tc01214c

• Journal Article Type: Article
• Acceptance Date: May 28, 2024
• Online Publication Date: May 29, 2024
• Publication Date: Jul 7, 2024
• Deposit Date: Jun 5, 2024
• Publicly Available Date: Jun 5, 2024
• Journal: Journal of Materials Chemistry C
• Print ISSN: 2050-7526
• Electronic ISSN: 2050-7534
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 12
• Issue: 25
• Pages: 9255-9265
• DOI: https://doi.org/10.1039/d4tc01214c
• Public URL: https://durham-repository.worktribe.com/output/2473539