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

Research output: Contribution to journalArticlepeer-review

20 Scopus citations

Abstract

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
Volume14
Issue number9
DOIs
StatePublished - 17 Mar 2008

Keywords

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

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