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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.; Santos, J.; Graves, D.; Data, P.; Nobuyasu, R.S.; Fox, M.A.; Batsanov, A.S.; Palmeira, T.; Berberan-Santos, M.N.; Bryce, M.R.; Monkman, A.P.

The Role of Local Triplet Excited States and D-A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices Thumbnail


Authors

J. Santos

D. Graves

P. Data

R.S. Nobuyasu

A.S. Batsanov

T. Palmeira

M.N. Berberan-Santos

M.R. Bryce



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.

Citation

Dias, F., Santos, J., Graves, D., Data, P., Nobuyasu, R., Fox, M., …Monkman, A. (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), Article 1600080. https://doi.org/10.1002/advs.201600080

Journal Article Type Article
Acceptance Date Jun 23, 2016
Online Publication Date Jul 18, 2016
Publication Date Dec 1, 2016
Deposit Date Mar 1, 2016
Publicly Available Date Jul 21, 2016
Journal Advanced Science
Publisher Wiley Open Access
Peer Reviewed Peer Reviewed
Volume 3
Issue 12
Article Number 1600080
DOI https://doi.org/10.1002/advs.201600080

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

Copyright Statement
Advance online version © 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.







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