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The iImportance of vibronic coupling for efficient reverse intersystem crossing in thermally activated delayed fluorescence molecules.

Gibson, J. and Monkman, A.P. and Penfold, T. (2016) 'The iImportance of vibronic coupling for efficient reverse intersystem crossing in thermally activated delayed fluorescence molecules.', ChemPhysChem., 17 (19). pp. 2956-2961.

Abstract

Factors influencing the rate of reverse intersystem crossing (krISC) in thermally activated delayed fluorescence (TADF) emitters are critical for improving the efficiency and performance of third-generation heavy-metal-free organic light-emitting diodes (OLEDs). However, present understanding of the TADF mechanism does not extend far beyond a thermal equilibrium between the lowest singlet and triplet states and consequently research has focused almost exclusively on the energy gap between these two states. Herein, we use a model spin-vibronic Hamiltonian to reveal the crucial role of non-Born-Oppenheimer effects in determining krISC. We demonstrate that vibronic (nonadiabatic) coupling between the lowest local excitation triplet (3LE) and lowest charge transfer triplet (3CT) opens the possibility for significant second-order coupling effects and increases krISC by about four orders of magnitude. Crucially, these simulations reveal the dynamical mechanism for highly efficient TADF and opens design routes that go beyond the Born-Oppenheimer approximation for the future development of high-performing systems.

Item Type:Article
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Available under License - Creative Commons Attribution.
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1002/cphc.201600662
Publisher statement:©2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Date accepted:No date available
Date deposited:21 April 2017
Date of first online publication:26 July 2016
Date first made open access:21 April 2017

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