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The Contributions of Molecular Vibrations and Higher Triplet Levels to the Intersystem Crossing Mechanism in Metal-Free Organic Emitters

Huang, Rongjuan; Avó, João; Northey, Thomas; Chaning-Pearce, E.; dos Santos, Paloma L.; Ward, Jonathan S.; Data, Przemyslaw; Etherington, Marc K.; Fox, Mark A.; Penfold, Thomas J.; Berberan-Santos, Mário N.; Lima, João C.; Bryce, Martin R.; Dias, Fernando B.

The Contributions of Molecular Vibrations and Higher Triplet Levels to the Intersystem Crossing Mechanism in Metal-Free Organic Emitters Thumbnail


Authors

Rongjuan Huang

João Avó

Thomas Northey

E. Chaning-Pearce

Paloma L. dos Santos

Jonathan S. Ward

Przemyslaw Data

Marc K. Etherington

Thomas J. Penfold

Mário N. Berberan-Santos

João C. Lima

Martin R. Bryce



Abstract

Intense, simultaneous, room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) is observed in a series of donor-acceptor-donor (D–A–D) molecules. This dual-luminescence is stronger in the “angular” isomers, compared to their “linear” regioisomers, which is consistent with an enhanced intersystem crossing (ISC) in the former. Herein, we demonstrate that the small energy gap between the triplet levels, T1-Tn, below the lowest singlet state, S1, in the “angular” regioisomers, enhances the coupling between S1 and T1 states and favors ISC and reverse ISC (rISC). This is consistent with a spin-vibronic mechanism. In the absence of this “triplet ladder”, due to the larger energy difference between T1 and Tn in the “linear” regioisomers, the ISC and rISC are not efficient. Remarkably the enhancement on the ISC rate in the “angular” regioisomers is accompanied by an increase on the rate of internal conversion (IC). These results highlight the contributions of higher triplet excited states and molecular vibronic coupling to harvest triplet states in organic compounds, and casts the TADF and RTP mechanisms into a common conceptual framework.

Citation

Huang, R., Avó, J., Northey, T., Chaning-Pearce, E., dos Santos, P. L., Ward, J. S., …Dias, F. B. (2017). The Contributions of Molecular Vibrations and Higher Triplet Levels to the Intersystem Crossing Mechanism in Metal-Free Organic Emitters. Journal of Materials Chemistry C Materials for optical and electronic devices, 5(25), 6269-6280. https://doi.org/10.1039/c7tc01958k

Journal Article Type Article
Acceptance Date May 23, 2017
Online Publication Date May 23, 2017
Publication Date Jul 7, 2017
Deposit Date May 8, 2017
Publicly Available Date May 30, 2017
Journal Journal of Materials Chemistry C Materials for optical and electronic devices
Print ISSN 2050-7526
Electronic ISSN 2050-7534
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 5
Issue 25
Pages 6269-6280
DOI https://doi.org/10.1039/c7tc01958k

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