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.

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: May 24, 2019
• 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
• Public URL: https://durham-repository.worktribe.com/output/1296400