Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters

Etherington, Marc K.; Franchello, Flavio; Gibson, Jamie; Northey, Thomas; Santos, Jose; Ward, Jonathan S.; Higginbotham, Heather F.; Data, Przemyslaw; Kurowska, Aleksandra; Dos Santos, Paloma Lays; Graves, David R.; Batsanov, Andrei S.; Dias, Fernando B.; Bryce, Martin R.; Penfold, Thomas J.; Monkman, Andrew P.

Abstract

Regio- and conformational isomerization are fundamental in chemistry, with profound effects upon physical properties, however their role in excited state properties is less developed. Here two regioisomers of bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide, a donor–acceptor–donor (D–A–D) thermally-activated delayed fluorescence (TADF) emitter, are studied. 2,8-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide exhibits only one quasi-equatorial conformer on both donor sites, with charge-transfer (CT) emission close to the local triplet state leading to efficient TADF via spin-vibronic coupling. However, 3,7-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide displays both a quasi-equatorial CT state and a higher-energy quasi-axial CT state. No TADF is observed in the quasi-axial CT emission. These two CT states link directly to the two folded conformers of phenothiazine. The presence of the low-lying local triplet state of the axial conformer also means that this quasi-axial CT is an effective loss pathway both photophysically and in devices. Importantly, donors or acceptors with more than one conformer have negative repercussions for TADF in organic light-emitting diodes.

Citation

Etherington, M. K., Franchello, F., Gibson, J., Northey, T., Santos, J., Ward, J. S., …Monkman, A. P. (2017). Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters. Nature Communications, 8, Article 14987. https://doi.org/10.1038/ncomms14987

• Journal Article Type: Article
• Acceptance Date: Feb 19, 2017
• Online Publication Date: Apr 13, 2017
• Publication Date: Apr 13, 2017
• Deposit Date: Apr 13, 2017
• Publicly Available Date: Apr 18, 2017
• Journal: Nature Communications
• Publisher: Nature Research
• Peer Reviewed: Peer Reviewed
• Volume: 8
• Article Number: 14987
• DOI: https://doi.org/10.1038/ncomms14987
• Public URL: https://durham-repository.worktribe.com/output/1381105