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Photophysics of thermally activated delayed fluorescence molecules

Lookup NU author(s): Dr Thomas Penfold

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


Abstract

Thermally activated delayed fluorescence (TADF) has recently emerged as one of the most attractive methods for harvesting triplet states in metal-free organic materials for application in organic light emitting diodes (OLEDs). A large number of TADF molecules have been reported in the literature with the purpose of enhancing the efficiency of OLEDs by converting non-emissive triplet states into emissive singlet states. TADF emitters are able to harvest both singlets and triplet states through fluorescence (prompt and delayed), the latter due to the thermally activated reverse intersystem crossing mechanism that allows up-conversion of low energy triplet states to the emissive singlet level. This allows otherwise pure fluorescent OLEDs to overcome their intrinsic limit of 25% internal quantum efficiency (IQE), which is imposed by the 1:3 singlet–triplet ratio arising from the recombination of charges (electrons and holes). TADF based OLEDS with IQEs close to 100% are now routinely fabricated in the green spectral region. There is also significant progress for blue emitters. However, red emitters still show relatively low efficiencies. Despite the significant progress that has been made in recent years, still significant challenges persist to achieve full understanding of the TADF mechanism and improve the stability of these materials. These questions need to be solved in order to fully implement TADF in OLEDs and expand their application to other areas. To date, TADF has been exploited mainly in the field of OLEDs, but applications in other areas, such as sensing and fluorescence microscopies, are envisaged. In this review, the photophysics of TADF molecules is discussed, summarising current methods to characterise these materials and the current understanding of the TADF mechanism in various molecular systems.


Publication metadata

Author(s): Dias FB, Penfold TJ, Monkman AP

Publication type: Article

Publication status: Published

Journal: Methods and Applications in Fluorescence

Year: 2017

Volume: 5

Online publication date: 08/03/2017

Acceptance date: 13/12/2016

ISSN (electronic): 2050-6120

Publisher: Institute of Physics Publishing Ltd.

URL: https://doi.org/10.1088/2050-6120/aa537e

DOI: 10.1088/2050-6120/aa537e


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