Hideki Ohtsu

An Organic Hydride Transfer Reaction of a Ruthenium NAD Model Complex Leading to Carbon Dioxide Reduction

Ruthenium will fix it: CO(2) undergoes reduction to HCO(2)(-) when placed over a solution of a ruthenium complex bearing an NADH model ligand 1 (black in right structural formula). The organic hydride transfer is triggered by the addition of benzoate anion, which rapidly forms a complex with 1, a complex that is a stronger reductant than 1. A photocatalytic variant of the reaction using triethanolamine as a sacrificial reagent has also been developed.

Luminescence behaviour in acetonitrile and in the solid state of a series of lanthanide complexes with a single helical ligand

Luminescence mechanisms of EuIII, TbIII, GdIII and NdIII complexes with a hexadentate ligand (abbreviated to EuL, TbL, GdL, and NdL, respectively), which have two bipyridine moieties bridged by an ethylenediamine unit, have been examined. Our molecular design is that each complex forms a single helical polar structure based on the chelate ring to retain solubility in solutions. EuL and NdL show comparably bright emission from ff transitions both in acetonitrile solution and in the solid state. To understand the mechanism of the emission in detail, the energy level of the triplet (T) state of the ligand L has been estimated based on the phosphorescence measurements of GdL, because GdIII shows no ff emission. The donor level of the T state of L and the acceptor level of EuIII or NdIII can overlap, indicating that the excited photon localized on L has been used for the efficient ff emission, while not for ππ* emission. For TbL, the luminescence quantum yield is significantly dependent on temperature and the state: in the solid state of TbL, the quantum yield of ff emission is over 90% at 77 K, while no luminescence is observed at room temperature, and in solution TbL shows no emission. This observation suggests that the emissive f-level of TbIII and the energy donor level of the excited T state of L are in thermal equilibrium. The described lanthanide complexes are stable and retain their molecular structure even in solutions and show characteristic luminescence behaviour based on the energy relaxation process of each lanthanide ion. Furthermore the HoIII complex with L (HoL) has been prepared and its structure has been analyzed. HoL has a twisted arrangement of the bipyridine moiety surrounding HoIII due to the small ionic radius of HoIII.

Novel emission properties of melem caused by the heavy metal effect of lanthanides(III) in a LB film

A novel emissive molecular system is constructed by the intercalation of the fluorophore melem (triamino-tri-s-triazine) within a Langmuir-Blodgett (LB) film of stearic acid with the periodic arrangement of lanthanides (Ln(III)), mainly Pr(III) with supporting of Eu(III). From emission spectra, decay curves, quantum yields and XPS measurements, it is clarified that the external heavy metal effect of Pr(III) on melem is much stronger in the film than in the bulk solid state, resulting in producing an unusual triplet state of melem. The triplet state of melem in the LB film donates the excitation energy to Pr(III) in the LB film, which is completely different from the energy transfer pathway of Pr-melem complex in the solid state through the singlet state of melem.

Ultrafast Optical Responses in a One-Dimensional Mott Insulator of a Br-Bridged Ni Compound

We investigated the ultrafast optical responses of a one-dimensional (1D) Mott insulator by applying fs pump–probe absorption spectroscopy on a thin film sample of a Br-bridged Ni compound. Transie...

Photochemical Properties and Reactivity of a Ru Compound Containing an NAD/NADH-Functionalized 1,10-Phenanthroline Ligand

An NAD/NADH-functionalized ligand, benzo[b]pyrido[3,2-f][1,7]-phenanthroline (bpp), was newly synthesized. A Ru compound containing the bpp ligand, [Ru(bpp)(bpy)2](2+), underwent 2e(-) and 2H(+) reduction, generating the NADH form of the compound, [Ru(bppHH)(bpy)2](2+), in response to visible light irradiation in CH3CN/TEA/H2O (8/1/1). The UV-vis and fluorescent spectra of both [Ru(bpp)(bpy)2](2+) and [Ru(bppHH)(bpy)2](2+) resembled the spectra of [Ru(bpy)3](2+). Both complexes exhibited strong emission, with quantum yields of 0.086 and 0.031, respectively; values that are much higher than those obtained from the NAD/NADH-functionalized complexes [Ru(pbn)(bpy)2](2+) and [Ru(pbnHH)(bpy)2](2+) (pbn = (2-(2-pyridyl)benzo[b]-1.5-naphthyridine, pbnHH = hydrogenated form of pbn). The reduction potential of the bpp ligand in [Ru(bpp)(bpy)2](2+) (-1.28 V vs SCE) is much more negative than that of the pbn ligand in [Ru(pbn)(bpy)2](2+) (-0.74 V), although the oxidation potentials of bppHH and pbnHH are essentially equal (0.95 V). These results indicate that the electrochemical oxidation of the dihydropyridine moiety in the NADH-type ligand was independent of the π system, including the Ru polypyridyl framework. [Ru(bppHH)(bpy)2](2+) allowed the photoreduction of oxygen, generating H2O2 in 92% yield based on [Ru(bppHH)(bpy)2](2+). H2O2 production took place via singlet oxygen generated by the energy transfer from excited [Ru(bppHH)(bpy)2](2+) to triplet oxygen.

A NOVEL IMIDAZOLATE-BRIDGED COPPER-ZINC HETERODINUCLEAR COMPLEX AS A CU, ZN-SOD ACTIVE SITE MODEL

A novel imidazolate-bridged Cu(II)–Zn(II) heterodinuclear complex of an imidazole derivative containing two metal-binding groups has been synthesized, and its structure and properties have been clarified.

Construction of cis-Fused Hydrindane Skeleton with a Lactone Tether Utilizing Intramolecular Diels-Alder Reaction

Construction of cis-fused hydrindane skeleton with a lactone tether utilizing intramolecular Diels-Alder reaction Shuqing Yin, Kenji Takai, Daishiro Minato, Kenji Sugimoto, Hideki Ohtsu, Kiyoshi Tsuge, and Yuji Matsuya* Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan, Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.

Ultrafast optical responses in one-dimensional Mott insulators of halogen-bridged Ni compounds

Halogen-bridged nickel compounds have attracted much attention because they show large optical nonlinearity and photoinduced insulator-metal transition. We report a new fabrication method for thin film samples of the Ni compounds. Using these thin film samples, we have performed femtosecond pump-probe spectroscopy. Photomodulated absorption induced by resonant and nonresonant photoexcitation on charge-transfer band have revealed that excitons decay very fast with the time constant τ less than 2 picoseconds and charge carriers decay relatively slow with τ > 20 ps. The slower decay of the charge carriers is attributable to the formation of polarons and the resultant decrease of their mobility.