Masa-aki Haga

Synthesis and protonation-deprotonation reactions of ruthenium(II) complexes containing 2, 2′-bibenzimidazole and related ligands

Abstract New ruthenium(II) complexes, [Ru(bpy)2L]n+ (bpy = 2, 2′-bipyridine; n = 1, L = 2-(o-hydroxy-phenyl)benzimidazole(OBzImH); n = 2, L = 2-(2-pyridyl)benzimidazole(PBzImH), 2-(2-pyridyl)imidazole(PImH), and 2, 2′-bibenzimidazole(BiBzImH2)), have been prepared. From the spectral and electrochemical measurements the metal-to-ligand charge transfer bands and oxidation potentials are rationalized in terms of the donor property of L, which increases in the order of bpy

Construction of highly ordered lamellar nanostructures through Langmuir-Blodgett deposition of molecularly thin titania nanosheets tens of micrometers wide and their excellent dielectric properties.

Exfoliated unilamellar titania nanosheets of Ti(0.87)O(2) with a lateral size of 10-30 microm were deposited layer-by-layer onto various substrates by Langmuir-Blodgett procedure to produce a highly ordered lamellar nanofilms. The nanosheets dispersed in an aqueous suspension containing quaternary ammonium ions as a supporting electrolyte floated spontaneously at the air/liquid interface, and they were successfully transferred onto the substrate after surface compression. Neat tiling of the nanosheets could be realized at an optimized surface pressure. The film thus obtained was exposed to UV light to turn the substrate surface hydrophilic, which was helpful for stable repetition of monolayer deposition. Layer-by-layer growth was confirmed by UV-visible absorption spectra, which showed progressive enhancement of an absorption band due to the nanosheet. Cross-sectional transmission electron microscopy images visualized the ultrathin film homogeneously deposited on the substrate surface and a lamellar fringe of the layer-by-layer assembled nanosheets was clearly resolved at a higher magnification. X-ray diffraction data on the films showed sharp basal reflections up to the seventh order, and Williamson-Hall analysis of the pattern indicated that the film was coherent across the total thickness with respect to X-ray and that the lattice strain was extremely small. In addition, the first basal reflection was accompanied by small satellite peaks, which are accounted for by the Laue interference function. All these features clearly indicate the formation of a highly ordered lamellar nanostructure of the titania nanosheets comparable to artificial lattice films produced via modern vapor-phase deposition processes. The obtained films showed superior dielectric and insulating properties as a reflection of the highly organized film nanoarchitecture.

Syntheses and Phosphorescent Properties of Blue Emissive Iridium Complexes with Tridentate Pyrazolyl Ligands

Novel neutral mixed-ligand Ir(N=C=N)(N=C)X complexes (N=C=N = 1,3-bis(3-methylpyrazolyl)benzene (bpzb), 1,5-dimethyl-2,4-bis(3-methylpyrazolyl)benzene (dmbpzb), and 1,5-difluoro-2,4-bis(3-methylpyrazolyl)benzene (dfbpzb); N=C = 2-phenyl pyridine (ppy); and X = Cl or CN) have been synthesized and characterized. An X-ray single-crystal structure of the complex Ir(dmbpzb)(ppy)Cl shows that the nitrogen atom in the ppy ligand occupied the trans position to the carbon atom in the tridentate N=C=N ligand of dmbpzb with the Ir-C bond length of 1.94(1) A, whereas the coordinating carbon atom occupied the trans position of chlorine. Electrochemical data show that the complexes exhibit an oxidation Ir(III/IV) process in the potential range of +0.5 approximately 0.9 V and two irreversible reductions at approximately -2.6 and -3.0 V against Fc (0)/Fc (+), respectively. All of the Ir(III) complexes do not emit phosphorescence at room temperature, although strong phosphorescence is exhibited at 77 K with the 0-0 transition centered at around 450 nm and lifetimes of 3-14 mus. DFT calculations indicate that the HOMOs are mainly localized on iridium 5dpi and chlorine ppi*, whereas the LUMOs are mainly from the ppy ligand pi* orbitals. The phosphorescence originates from a (3)LC state mixed with the (3)MLCT and (3)XLCT ones. Temperature-dependent lifetime measurements of Ir(dfbpzb)(ppy)Cl reveal the existence of a thermal deactivation process with a low activation energy (1720 cm (-1)) and very high frequency factor (2.3 x 10 (13) s (-1)). An unrestricted density functional theory indicates that the dd state, in which both the Ir-N (pyrazolyl) bond lengths increase considerably, exists almost at the same energy as that for the phosphorescent state. A thorough analysis based on the potential energy surfaces for the T 1 and S 0 states allows us to determine the reaction pathway responsible for this thermal deactivation. The calculated activation energies of 1600 approximately 1800 cm (-1) are in excellent agreement with the observed values.

Molecular design of a proton-induced molecular switch based on rod-shaped Ru dinuclear complexes with bis-tridentate 2,6-bis(benzimidazol-2-yl)pyridine derivatives

New dinuclear Ru complexes of bis-tridentate 2,6-bis(benzimidazol-2-yl)pyridine derivatives, [Ru2(terpy)2(H4Ln)]4+ (terpy = 2,2′:6′,2″-terpyridine, n = 0∼2), have been synthesized. The Ru complexes act as tetrabasic acids, in which N–H protons on benzimidazole moieties are responsible for a deprotonation site. Both the absorption spectra and oxidation potentials are strongly dependent on the solution pH, which leads to the basis of a proton-induced molecular switch. The dinuclear Ru complexes bridged by bis-tridentate bis{2,6-bis(benzimidazol-2-yl)pyridine} show a lower Ru(II/III) oxidation potential but almost similar MLCT absorption maxima, compared to the corresponding dinuclear Ru complexes with “back-to-back” bis-2,2′:6′,2″-terpyridine bridging ligands. These results indicate that the bis-tridentate bis{2,6-bis(benzimidazol-2-yl)pyridine} ligand has a stronger σ/π donor property and a weaker π-acceptor property than the bis-2,2′:6′,2″-terpyridine bridging ligand. The solubility of Ru complexes in solution is progressively decreased with increasing number of phenyl group in the bridging ligand, and therefore it becomes difficult to study the change of chemical properties for external stimuli such as pH change. Immobilization of complexes on a solid surface is one of the approaches to overcome their low solubility. The [Ru2(bpbbip)2(H4L0)]4+ complex with phosphonate groups (bpbbip = 2,6-bis(1-(4-diphosphonyl)butylbenzimidazol-2-yl)pyridine) was successfully immobilized on an ITO electrode and characterized by means of XPS, and cyclic voltammetry. The Ru complex monolayers exhibit a reversible Ru(II/III) oxidation at +0.80 V vs. Ag/AgCl in 0.1 M aqueous HClO4. The immobilized Ru complex monolayer is stable over the pH range 1 < pH < 10. The oxidation potential, E½, vs. pH plot reveals several lines, indicating that the proton-coupled oxidative reactions occur on the ITO surface. The phosphonate-immobilized Ru dinuclear complex monolayers exhibited a stable electrochromic response on an ITO electrode.

Bis(dioxolene)(bipyridine)ruthenium redox series

Preparation des complexes [Ru(bpy)(dioxolene) 2 ] u+ par electrolyse a potentiel controle des especes meres. Donnees IR, Raman, RMN, RPE

A practical one-pot synthesis of 2,3-disubstituted indoles from unactivated anilines

2-Substituted-3-methyl indoles are synthesized with good regioselectivity from readily available substrates and catalysts, i.e. the reaction of anilines with propargyl alcohols in the presence of 0.36–1 mol% Ru3(CO)12.

Fabrication and Placement of a Ring Structure of Nanoparticles by a Laser-Induced Micronanobubble on a Gold Surface

We have developed a new fabrication method for a ring structure of assembled nanoparticles on a gold surface by the use of continuous Nd:YAG laser light. A micronanobubble on a gold surface, created by laser local heating, acts as a template for the formation of the ring structure. Both Marangoni convection flow and capillary flow around the micronanobubble are responsible for the driving force to assemble nanoparticles such as CdSe Q-dots into the ring structure from the solution. Because a single micronanobubble was generated by the Nd:YAG laser focusing point, the precise positioning of the ring structure was feasible directly on the gold surface, which makes it possible to fabricate various patterns of rings such as arrays and letters and even a double-ring structure without any photomasks or any templates.

Memory Effects in Molecular Films of Free‐Standing Rod‐Shaped Ruthenium Complexes on an Electrode

There is significant interest in exploring new informationstorage systems for molecule-based devices as an alternative to silicon-based dynamic random access memory (DRAM). The operational principle of a DRAM is based on storing charge on a capacitive metal oxide layer by applying a voltage and reading the charge as a bias current. These devices, however, rely on silicon-based technology, in which photolithographic manufacturing is reaching the lower size limit. Accordingly, as is the case for the development of nanoscale technologies to overcome the fabrication limit of siliconbased devices, molecular electronic devices are an emerging research subject. The formation of molecular self-assembled monolayers (SAMs) on surfaces is a promising bottomup approach for the fabrication of molecule-based elements such as switches, memories, and logic gates. In molecular switches, the injection or exclusion of charges should be activated or controlled by external signals such as electrical or photonic stimuli, and the change of potential gradient should be electrically transduced and transmitted to external circuits. 12–16] In molecular memories, the charge storage in the molecular layers can be used as a memory bit. Recently, many attempts to construct molecular memory devices have been reported. For example, metalloporphyrins attached chemically onto an electrode stored charges by oxidation or reduction; that is, writing was achieved by oxidation of a porphyrin SAM, and reading was achieved by sensing a current under open-circuit potential after the oxidation. As an another example, the use of successive potential gradients in electron-transfer reactions within a polymer containing both quinone and viologen moieties or in bilayer films composed of two polymers, namely, [M(phen)2(vbpy)] 2+

Synthesis and electrochemical properties of binuclear molybdenum carbonyl complexes with bridging α,α′-diimine ligands

Abstract New binuclear molybdenum complexes with bridging ligands derived from 2-pyridinecarbaldehyde and the diamines such as hydrazine, p -phenylenediamine, p -xylylenediamine, and 4,4′-diaminobiphenyl were prepared, to elucidate the effect on the separated distance and π-conjugation between two metal centers. All the complexes exhibit the low lying metal-to-ligand charge transfer (MLCT) bands at ca . 500 nm. The cyclic voltammogram shows either a single broad two-electron wave, or two one-electron reduction waves, depending on the nature of the bridging ligand. The MLCT band and the reduction behavior are rationalized in terms of the interaction between LUMO orbitals of two molybdenum-α,α′-diimine moieties.

Glycine Crystallization in Solution by CW Laser-Induced Microbubble on Gold Thin Film Surface

We have developed a novel laser-induced crystallization method utilizing local heat-induced bubble/water interface. Continuous laser beam of 1064 nm is focused on a gold nanoparticles thin film surface covered with glycine supersaturated aqueous solution. Light absorption of the film due to localized plasmon resonance caused local heating at the focal position and produced a single thermal vapor microbubble, which generated thermal gradient followed by convection flow around the bubble and eventually induced glycine crystallization and growth. The crystallization mechanism is discussed by considering gathering and accumulating molecules around the bubble/water interface assisted by convection flow and temperature jump.