title: Switchable antenna: a star-shaped ruthenium/osmium tetranuclear complex with azobis(bipyridine) bridging ligands.
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 azobpy(2-) 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.
authors.affiliation: The College of Science and Technology, Nihon University, 1-8-14 Kanda Surugadai, Chiyoda-ku, Tokyo 101-8308, Japan. otsuki@chem.cst.nihon-u.ac.jp
authors.forename: Joe
authors.initials: J
authors.lastname: Otsuki
authors.forename: Arata
authors.initials: A
authors.lastname: Imai
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Sato
authors.forename: Dong-Mei
authors.initials: DM
authors.lastname: Li
authors.forename: Mayumi
authors.initials: M
authors.lastname: Hosoda
authors.forename: Masao
authors.initials: M
authors.lastname: Owa
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Akasaka
authors.forename: Isao
authors.initials: I
authors.lastname: Yoshikawa
authors.forename: Koji
authors.initials: K
authors.lastname: Araki
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Suenobu
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D008024:Ligands; D049449:Luminescence; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D009992:Osmium / Q000737:chemistry*; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D013997:Time Factors
chemical_list: D001391:Azo Compounds; D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D009992:Osmium; D012428:Ruthenium