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

Lookup NU author(s): Dr Thomas Northey, Professor Thomas Penfold



This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).


Intense, simultaneous, room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) is observed in a series of donor-acceptordonor (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.

Publication metadata

Author(s): Huang R, Avó J, Northey T, Chaning-Pearce E, dosSantos PL, Ward JS, Data P, Etherington MK, Fox MA, Penfold TJ, Berberan-Santos MN, Lima JC, Bryce MR, Dias FB

Publication type: Article

Publication status: Published

Journal: Journal of Materials Chemistry C

Year: 2017

Online publication date: 23/05/2017

Acceptance date: 23/05/2017

Date deposited: 24/05/2017

ISSN (print): 2050-7526

ISSN (electronic): 2050-7534

Publisher: Royal Society of Chemistry


DOI: 10.1039/C7TC01958K


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