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Understanding the luminescent nature of organic radicals for efficient doublet emitters and pure-red light-emitting diodes

Abdurahman, A; Hele, TJH; Gu, Q; Zhang, J; Peng, Q; Zhang, M; Friend, RH; ... Evans, EW; + view all (2020) Understanding the luminescent nature of organic radicals for efficient doublet emitters and pure-red light-emitting diodes. Nature Materials , 19 (11) pp. 1224-1229. 10.1038/s41563-020-0705-9. Green open access

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Abstract

The doublet-spin nature of radical emitters is advantageous for applications in organic light-emitting diodes, as it avoids the formation of triplet excitons that limit the electroluminescence efficiency of non-radical emitters. However, radicals generally show low optical absorption and photoluminescence yields. Here we explain the poor optical properties of radicals based on alternant hydrocarbons, and establish design rules to increase the absorption and luminescence yields for donor–acceptor-type radicals. We show that non-alternant systems are necessary to lift the degeneracy of the lowest energy orbital excitations; moreover, intensity borrowing from an intense high-lying transition by the low-energy charge-transfer excitation enhances the oscillator strength of the emitter. We apply these rules to design tris(2,4,6-trichlorophenyl)methyl–pyridoindolyl derivatives with a high photoluminescence quantum yield (>90%). Organic light-emitting diodes based on these molecules showed a pure-red emission with an over 12% external quantum efficiency. These insights may be beneficial for the rational design and discovery of highly luminescent doublet emitters.

Type: Article
Title: Understanding the luminescent nature of organic radicals for efficient doublet emitters and pure-red light-emitting diodes
Open access status: An open access version is available from UCL Discovery
DOI: 10.1038/s41563-020-0705-9
Publisher version: https://doi.org/10.1038/s41563-020-0705-9
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher's terms and conditions.
Keywords: Lasers, LEDs and light sources, Organic LEDs
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10120026
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