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Carbon nanotubes

Breaking Kasha's rule

Nature Photonics volume 4, pages 200–201 (2010)Cite this article

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The emission of visible light from a dye encapsulated within a carbon nanotube gives great hope and new opportunities for the design of nanoscale optoelectronic devices.

In optically functional molecules such as dyes, fluorescence (or phosphorescence) generally occurs from the excited state with the lowest energy. This is known as “Kasha's rule” — first formulated in 19501 by Michael Kasha — and is a general principle with only a few rare exceptions (for example, compounds such as azulene and cyclazine2). Now, according to recent research3 it seems that the dye α-sexithiophene, when encapsulated in a single-wall carbon nanotube (SWCNT), exhibits emission that also breaks this rule. The finding is significant because it suggests that organic-dye–nanotube hybrid light emitters can operate at higher photon energies than first thought, reaching to visible wavelengths. It also shows that nanotubes can help shield and protect sensitive light-emitting materials from the environment, improving their stability and offering new regimes of operation.

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Figure 1: Schematic of excited energy decay processes.

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Authors and Affiliations

  1. Kazuhiro Yanagi is at the Department of Physics, Tokyo Metropolitan University, Minami-Osawa, Hachioji, Tokyo, Japan,

    Kazuhiro Yanagi

  2. Hiromichi Kataura is at the Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan. h-kataura@aist.go.jp,

    Hiromichi Kataura

Authors
  1. Kazuhiro Yanagi
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  2. Hiromichi Kataura
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Yanagi, K., Kataura, H. Breaking Kasha's rule. Nature Photon 4, 200–201 (2010). https://doi.org/10.1038/nphoton.2010.77

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