Switchable antenna: A star-shaped ruthenium/osmium tetranuclear complex with azobis(bipyridine) bridging ligands

Joe Otsuki, Arata Imai, Katsuhiko Sato, Dong Mei Li, Mayumi Hosoda, Masao Owa, Tetsuo Akasaka, Isao Yoshikawa, Koji Araki, Tomoyoshi Suenobu, Shunichi Fukuzumi

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20 Scopus citations


A star-shaped Ru/Os tetranuclear complex, in which a central Os unit is linked to three peripheral Ru units by 4,4″-azobis(2,2′-bipyridine) (azobpy) bridging ligands, was prepared to examine the unique photodynamics regulated by its redox state. The Ru/Os tetranuclear complex exhibits Ru-based luminescence at 77 K, whereas the three-electron reduction (one for each azobpy) of the Ru/Os complex results in luminescence from the Os unit. The photoexcited state of the Ru/Os complex rapidly decays into low energy metal-to-ligand charge-transfer states, in which the excited electron is localized in the azobpy ligand in the form of azobpy. Upon the one-electron reduction of the azobpy ligands, the above-mentioned low-energy states become unavailable to the photoexcited complex. As a result, an energy transfer from the Ru-based excited state to the Os-based excited state becomes possible. Ultrafast transient absorption measurements revealed that the energy transfer process consists of two steps; intramolecular electron transfer from the terminal bipyridine ligand (bpy.-) to form azobpy2- followed by a metal-to-metal electron transfer. Thus, the Ru/Os tetranuclear complex collects light energy into the central Os unit depending on the redox state of the bridging ligands, qualifying as a switchable antenna.

Original languageEnglish
Pages (from-to)2709-2718
Number of pages10
JournalChemistry - A European Journal
Issue number9
StatePublished - 17 Mar 2008


  • Bridging ligands
  • Electron transfer
  • Photochemistry
  • Redox chemistry
  • Time-resolved spectroscopy


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