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Excited State Intramolecular Proton Transfer Dynamics for Triplet Harvesting in Organic Molecules

Lookup NU author(s): Dr Yang Cao, Dr Julien EngORCiD, Professor Thomas Penfold



This is the authors' accepted manuscript of an article that has been published in its final definitive form by American Chemical Society, 2019.

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Thermally activated delayed fluorescence (TADF) has shown great potential as a mechanism for harvesting low-lying triplet excited states in organic molecules and is therefore of great interest in the context of organic electronics, especially organic light emitting diodes (OLEDs). Herein we study the mechanism for triplet harvesting in triquinolonobenzene (TQB), which instead of relying upon the well-established donor-acceptor (D-A) scheme uses excited-state intramolecular proton transfer (ESIPT). We demonstrate that upon photoexcitation into the lowest singlet excited state the proton is transferred within 20 fs, suggesting it plays little role in triplet harvesting which occurs on the nano- to micro-second timescale. However, TQB exhibits multiple low-lying triplet states that are strongly coupled along this proton transfer coordinate. The majority of these states favour the structure prior to proton transfer (TQB-TA) and this means that the proton transfer dynamics (3TQB-TA->1TQB-TB) plays a crucial role in triplet harvesting. This mechanism yields an energy gap in good agreement with that reported experimentally and is consistent with previous photophysical characterisation. Finally, a discussion upon extending this understanding into a device context is also presented.

Publication metadata

Author(s): Cao Y, Eng J, Penfold TJ

Publication type: Article

Publication status: Published

Journal: Journal of Physical Chemistry A

Year: 2019

Volume: 123

Pages: 2640-2649

Print publication date: 04/04/2019

Online publication date: 08/03/2019

Acceptance date: 08/03/2019

Date deposited: 10/03/2019

ISSN (print): 1089-5639

ISSN (electronic): 1520-5215

Publisher: American Chemical Society


DOI: 10.1021/acs.jpca.9b00813


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