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Delayed Blue Fluorescence via Upper-triplet State Crossing from C-C Bonded Donor-Acceptor Charge-Transfer Molecules with Azatriangulene cores

Ward, J.; Kukhta, N.; Dos Santos, P.; Congrave, D.; Batsanov, A.; Monkman, A.; Bryce, M.

Delayed Blue Fluorescence via Upper-triplet State Crossing from C-C Bonded Donor-Acceptor Charge-Transfer Molecules with Azatriangulene cores Thumbnail


Authors

J. Ward

N. Kukhta

P. Dos Santos

D. Congrave



Abstract

We report the synthesis and structural and photophysical characterization of two series of molecules with functionalized azatriangulene electron donor cores and three pendant electron acceptor units. The presented donor and acceptor units are joined by C–C bonds, instead of the usual C–heteroatom bonds often found in thermally activated delayed fluorescence (TADF) emitters. The effects of the donor–acceptor strength and donor–acceptor dihedral angle on the emission properties are assessed. The data establish that the singlet–triplet energy gap is >0.3 eV and that delayed emission is present in only specific host matrices, irrespective of host polarity. Specific host behavior is atypical of many TADF materials, and we suggest the delayed emission in this work does not occur by a conventional vibronically coupled TADF mechanism, as the ΔEST value is too large. Detailed photophysical analysis and supporting density functional theory calculations suggest that some presented azatriangulene molecules emit via an upper-triplet state crossing mechanism. This work highlights that several different mechanisms can be responsible for delayed emission, often with highly similar photophysics. Detailed photophysical analysis is required to establish which delayed emission mechanism is occurring. Our results also highlight a clear future direction toward vibronically coupled C–C bonded TADF materials.

Citation

Ward, J., Kukhta, N., Dos Santos, P., Congrave, D., Batsanov, A., Monkman, A., & Bryce, M. (2019). Delayed Blue Fluorescence via Upper-triplet State Crossing from C-C Bonded Donor-Acceptor Charge-Transfer Molecules with Azatriangulene cores. Chemistry of Materials, 31(17), 6684-6695. https://doi.org/10.1021/acs.chemmater.9b01184

Journal Article Type Article
Acceptance Date May 10, 2019
Online Publication Date May 22, 2019
Publication Date May 22, 2019
Deposit Date May 15, 2019
Publicly Available Date Mar 29, 2024
Journal Chemistry of Materials
Print ISSN 0897-4756
Electronic ISSN 1520-5002
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 31
Issue 17
Pages 6684-6695
DOI https://doi.org/10.1021/acs.chemmater.9b01184

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Publisher Licence URL
http://creativecommons.org/licenses/by/4.0/

Copyright Statement
Advance online version This is an open access article published under a Creative Commons Attribution (CC-BY)
License, which permits unrestricted use, distribution and reproduction in any medium,
provided the author and source are cited.






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