TY - JOUR
T1 - Synthesis and structural, electrochemical, and optical properties of Ru(II) complexes with azobis(2,2′-bipyridine)s
AU - Otsuki, Joe
AU - Omokawa, Nobuyuki
AU - Yoshiba, Kenji
AU - Yoshikawa, Isao
AU - Akasaka, Tetsuo
AU - Suenobu, Tomoyoshi
AU - Takido, Toshio
AU - Araki, Koji
AU - Fukuzumi, Shunichi
PY - 2003/5/5
Y1 - 2003/5/5
N2 - Two new ditopic ligands, 5,5″-azobis(2,2′-bipyridine) (5,5″-azo) and 5,5″-azoxybis(2,2′-bipyridine) (5,5″-azoxy), were prepared by the reduction of nitro precursors. Mononuclear and dinuclear RU(II) complexes having one of these bridging ligands and 2,2′-bipyridine terminal ligands were also prepared, and their properties were compared with previously reported RU(II) complexes having 4,4″-azobis(2,2′-bipyridine) (4,4″-azo). The X-ray crystal structure showed that 5,5″-azo adopts the trans conformation and a planar rodlike shape. The X-ray crystal structure of [(bpy)2Ru(5,5″-azo)Ru(bpy)2] (PF6)4 (Ru(5,5″-azo)Ru) showed that the bridging ligand is in the trans conformation and nearly planar also in the complex and the metal-to-metal distance is 10.0 Å. The azo or azoxy ligand in these complexes exhibits reduction processes at less negative potentials than the terminal bpy's due to the low-lying π* level. The electronic absorption spectra for the complexes having 5,5″-azo or 5,5″-azoxy exhibit an extended low-energy metal-to-ligand charge-transfer absorption. The ligands, 5,5″-azo and 5,5″-azoxy, and the mononuclear complex, [(bpy)2Ru(5,5″-azo)]2+, isomerize reversibly upon light irradiation. The low-energy MLCT state sensitizes the isomerization of the azo moiety in this complex. While [(bpy)2Ru(4,4″-azo)Ru(bpy)2] (PF6)4 exhibits light switch properties, namely, significant electrochromism and a large luminescence enhancement, upon reduction, Ru(5,5″-azo)Ru does not show these properties. The radical anion formation upon reduction of these complexes has been confirmed by ESR spectroscopy.
AB - Two new ditopic ligands, 5,5″-azobis(2,2′-bipyridine) (5,5″-azo) and 5,5″-azoxybis(2,2′-bipyridine) (5,5″-azoxy), were prepared by the reduction of nitro precursors. Mononuclear and dinuclear RU(II) complexes having one of these bridging ligands and 2,2′-bipyridine terminal ligands were also prepared, and their properties were compared with previously reported RU(II) complexes having 4,4″-azobis(2,2′-bipyridine) (4,4″-azo). The X-ray crystal structure showed that 5,5″-azo adopts the trans conformation and a planar rodlike shape. The X-ray crystal structure of [(bpy)2Ru(5,5″-azo)Ru(bpy)2] (PF6)4 (Ru(5,5″-azo)Ru) showed that the bridging ligand is in the trans conformation and nearly planar also in the complex and the metal-to-metal distance is 10.0 Å. The azo or azoxy ligand in these complexes exhibits reduction processes at less negative potentials than the terminal bpy's due to the low-lying π* level. The electronic absorption spectra for the complexes having 5,5″-azo or 5,5″-azoxy exhibit an extended low-energy metal-to-ligand charge-transfer absorption. The ligands, 5,5″-azo and 5,5″-azoxy, and the mononuclear complex, [(bpy)2Ru(5,5″-azo)]2+, isomerize reversibly upon light irradiation. The low-energy MLCT state sensitizes the isomerization of the azo moiety in this complex. While [(bpy)2Ru(4,4″-azo)Ru(bpy)2] (PF6)4 exhibits light switch properties, namely, significant electrochromism and a large luminescence enhancement, upon reduction, Ru(5,5″-azo)Ru does not show these properties. The radical anion formation upon reduction of these complexes has been confirmed by ESR spectroscopy.
UR - http://www.scopus.com/inward/record.url?scp=0038299008&partnerID=8YFLogxK
U2 - 10.1021/ic026040g
DO - 10.1021/ic026040g
M3 - Article
AN - SCOPUS:0038299008
SN - 0020-1669
VL - 42
SP - 3057
EP - 3066
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 9
ER -