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The role of local triplet excited states and d-a relative orientation in thermally activated delayed fluorescence : photophysics and devices.

Dias, F. B. and Santos, J. and Graves, D. and Data, P. and Nobuyasu, R.S. and Fox, M. A. and Batsanov, A.S. and Palmeira, T. and Berberan-Santos, M. N. and Bryce, M.R. and Monkman, A.P. (2016) 'The role of local triplet excited states and d-a relative orientation in thermally activated delayed fluorescence : photophysics and devices.', Advanced science., 3 (12). p. 1600080.

Abstract

Here, a comprehensive photophysical investigation of a the emitter molecule DPTZ-DBTO2, showing thermally activated delayed fluorescence (TADF), with near-orthogonal electron donor (D) and acceptor (A) units is reported. It is shown that DPTZ-DBTO2 has minimal singlet–triplet energy splitting due to its near-rigid molecular geometry. However, the electronic coupling between the local triplet (3LE) and the charge transfer states, singlet and triplet, (1CT, 3CT), and the effect of dynamic rocking of the D–A units about the orthogonal geometry are crucial for efficient TADF to be achieved. In solvents with low polarity, the guest emissive singlet 1CT state couples directly to the near-degenerate 3LE, efficiently harvesting the triplet states by a spin orbit coupling charge transfer mechanism (SOCT). However, in solvents with higher polarity the emissive CT state in DPTZ-DBTO2 shifts below (the static) 3LE, leading to decreased TADF efficiencies. The relatively large energy difference between the 1CT and 3LE states and the extremely low efficiency of the 1CT to 3CT hyperfine coupling is responsible for the reduction in TADF efficiency. Both the electronic coupling between 1CT and 3LE, and the (dynamic) orientation of the D–A units are thus critical elements that dictate reverse intersystem crossing processes and thus high efficiency in TADF.

Item Type:Article
Full text:(VoR) Version of Record
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Full text:(VoR) Version of Record
Available under License - Creative Commons Attribution.
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1002/advs.201600080
Publisher statement:© 2016 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 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:23 June 2016
Date deposited:21 July 2016
Date of first online publication:18 July 2016
Date first made open access:No date available

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