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Selective triplet exciton formation in a single molecule

Author

Listed:
  • Kensuke Kimura

    (Surface and Interface Science Laboratory, RIKEN
    The University of Tokyo)

  • Kuniyuki Miwa

    (Surface and Interface Science Laboratory, RIKEN
    University of California San Diego
    Northwestern University)

  • Hiroshi Imada

    (Surface and Interface Science Laboratory, RIKEN)

  • Miyabi Imai-Imada

    (Surface and Interface Science Laboratory, RIKEN
    The University of Tokyo)

  • Shota Kawahara

    (Surface and Interface Science Laboratory, RIKEN)

  • Jun Takeya

    (The University of Tokyo)

  • Maki Kawai

    (The University of Tokyo
    National Institutes of Natural Sciences)

  • Michael Galperin

    (University of California San Diego)

  • Yousoo Kim

    (Surface and Interface Science Laboratory, RIKEN)

Abstract

The formation of excitons in organic molecules by charge injection is an essential process in organic light-emitting diodes (OLEDs)1–7. According to a simple model based on spin statistics, the injected charges form spin-singlet (S1) excitons and spin-triplet (T1) excitons in a 1:3 ratio2–4. After the first report of a highly efficient OLED2 based on phosphorescence, which is produced by the decay of T1 excitons, more effective use of these excitons has been the primary strategy for increasing the energy efficiency of OLEDs. Another route to improving OLED energy efficiency is reduction of the operating voltage2–6. Because T1 excitons have lower energy than S1 excitons (owing to the exchange interaction), use of the energy difference could—in principle—enable exclusive production of T1 excitons at low OLED operating voltages. However, a way to achieve such selective and direct formation of these excitons has not yet been established. Here we report a single-molecule investigation of electroluminescence using a scanning tunnelling microscope8–20 and demonstrate a simple method of selective formation of T1 excitons that utilizes a charged molecule. A 3,4,9,10-perylenetetracarboxylicdianhydride (PTCDA) molecule21–25 adsorbed on a three-monolayer NaCl film atop Ag(111) shows both phosphorescence and fluorescence signals at high applied voltage. In contrast, only phosphorescence occurs at low applied voltage, indicating selective formation of T1 excitons without creating their S1 counterparts. The bias voltage dependence of the phosphorescence, combined with differential conductance measurements, reveals that spin-selective electron removal from a negatively charged PTCDA molecule is the dominant formation mechanism of T1 excitons in this system, which can be explained by considering the exchange interaction in the charged molecule. Our findings show that the electron transport process accompanying exciton formation can be controlled by manipulating an electron spin inside a molecule. We anticipate that designing a device taking into account the exchange interaction could realize an OLED with a lower operating voltage.

Suggested Citation

  • Kensuke Kimura & Kuniyuki Miwa & Hiroshi Imada & Miyabi Imai-Imada & Shota Kawahara & Jun Takeya & Maki Kawai & Michael Galperin & Yousoo Kim, 2019. "Selective triplet exciton formation in a single molecule," Nature, Nature, vol. 570(7760), pages 210-213, June.
  • Handle: RePEc:nat:nature:v:570:y:2019:i:7760:d:10.1038_s41586-019-1284-2
    DOI: 10.1038/s41586-019-1284-2
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    Citations

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    Cited by:

    1. Vibhuti Rai & Nico Balzer & Gabriel Derenbach & Christof Holzer & Marcel Mayor & Wulf Wulfhekel & Lukas Gerhard & Michal Valášek, 2023. "Hot luminescence from single-molecule chromophores electrically and mechanically self-decoupled by tripodal scaffolds," Nature Communications, Nature, vol. 14(1), pages 1-10, December.
    2. Francisco Tenopala-Carmona & Dirk Hertel & Sabina Hillebrandt & Andreas Mischok & Arko Graf & Philipp Weitkamp & Klaus Meerholz & Malte C. Gather, 2023. "Orientation distributions of vacuum-deposited organic emitters revealed by single-molecule microscopy," Nature Communications, Nature, vol. 14(1), pages 1-10, December.
    3. Jiří Doležal & Sofia Canola & Prokop Hapala & Rodrigo Cezar Campos Ferreira & Pablo Merino & Martin Švec, 2022. "Evidence of exciton-libron coupling in chirally adsorbed single molecules," Nature Communications, Nature, vol. 13(1), pages 1-8, December.
    4. Katharina Kaiser & Leonard-Alexander Lieske & Jascha Repp & Leo Gross, 2023. "Charge-state lifetimes of single molecules on few monolayers of NaCl," Nature Communications, Nature, vol. 14(1), pages 1-10, December.
    5. Yang Luo & Fan-Fang Kong & Xiao-Jun Tian & Yun-Jie Yu & Shi-Hao Jing & Chao Zhang & Gong Chen & Yang Zhang & Yao Zhang & Xiao-Guang Li & Zhen-Yu Zhang & Zhen-Chao Dong, 2024. "Anomalously bright single-molecule upconversion electroluminescence," Nature Communications, Nature, vol. 15(1), pages 1-8, December.

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