Showing papers by "Hiroshi Nishihara published in 2010"
TL;DR: This review examines the main available pathways to improve the photosynthetic H2 production and finds that e− and H+ recombine and form molecular hydrogen, which has a great potential for clean and cheap sources—water and solar energy.
Abstract: Among various technologies for hydrogen production, the use of oxygenic natural photosynthesis has a great potential as can use clean and cheap sources—water and solar energy. In oxygenic photosynthetic microorganisms electrons and protons produced from water and redirected by the photosynthetic electron-transport chain via ferredoxin to the hydrogen-producing enzymes hydrogenase or nitrogenase. By these enzymes, e− and H+ recombine and form molecular hydrogen. Hydrogenase activity can be very high but is extremely sensitive to the photosynthetically evolved O2 that leads to reduced and unstable H2 production. However, presently, several approaches are developed to improve the energetic efficiency to generate H2. This review examines the main available pathways to improve the photosynthetic H2 production.
117 citations
TL;DR: A variety of dibenzosiloles and -germoles as well as dithiophenosilole (VII) are prepared, better tolerating the functional groups as the methods applied so far.
Abstract: A variety of dibenzosiloles and -germoles as well as dithiophenosilole (VII) are prepared, better tolerating the functional groups as the methods applied so far.
104 citations
TL;DR: Surface junction effects on the electron conduction of p-phenylene-bridged bis(terpyridine)iron oligomers terminated with a ferrocene moiety were quantitatively analyzed by employing three different surface-anchoring terp Pyridine ligands.
Abstract: Surface junction effects on the electron conduction of p-phenylene-bridged bis(terpyridine)iron oligomers terminated with a ferrocene moiety were quantitatively analyzed by employing three different surface-anchoring terpyridine ligands. The dependence of the electron-transfer rate constant for oxidation of the ferrocene moiety, ket, on the distance between the electrode surface and the ferrocene moiety, x, showed that the attenuation factor, βd, which indicates the degree of reduction of ket with x, was ∼0.018 in all cases. However, the absolute ket value depended strongly on both electronic and steric factors of the surface-anchoring ligand.
89 citations
TL;DR: A new convertible copper(I) complex using 2-pyridyl-4-methylpyrimidine and diphosphine as ligands exhibited mechanical bistability based on the inversion motion of the pyrimidine ring, leading to dual luminescence behavior.
Abstract: We developed a new convertible copper(I) complex using 2-pyridyl-4-methylpyrimidine and diphosphine as ligands. This complex exhibited mechanical bistability based on the inversion motion of the pyrimidine ring, leading to dual luminescence behavior. The inversion dynamics was strongly dependent on temperature and solvent. Variable-temperature 1H NMR spectra revealed that the two isomers interconverted in solution via ring inversion, and the motion was frozen below 200 K. The complex exhibited characteristic CT absorption and emission bands in solution. Emission lifetime measurements demonstrated that the emission could be deconvoluted into two components. The fast and slow components were assigned to the two isomers, the excited states of which were characterized by different structural relaxation process and/or additional solvent coordination properties. The emission properties of the two isomers differed not only in lifetime and wavelength but also in heat sensitivity. The molar ratio of the two isomer...
74 citations
TL;DR: Water-soluble luminescent AuNPs of 1.3 ± 0.3 nm in diameter with a large Stokes shift were facilely synthesized by a new molten matrix sputtering (MMS) method.
47 citations
TL;DR: Utilizing the redox property of ferrocenes, electrochemically control the encapsulation and release of ferroenes into the DPA in a manner similar to redox-responsive proteins such as ferritin, pointing the way toward the use of such systems in material science.
Abstract: Dendritic polyphenylazomethines (DPA) could encapsulate ferroceniums by complexation of the electron-donating skeleton of the DPA imines. Upon addition of ferroceniums to a series of dendritic polyphenylazomethines (DPAGX, where X is the generation number, X = 1−4), the UV−vis spectra showed changes in a manner similar to that observed for the complexation of metal ions with DPAGX. Stepwise shifts in the isosbestic point were consistently observed with the number of imine groups in the first and second layers of the generation-4 dendrimer (DPAG4). DPAG2 and DPAG3 were also found to trap 6 equiv of ferroceniums. To investigate the complexation, UV−vis spectroscopy, 57Fe Mossbauer spectroscopy, electrospray ionization-mass spectroscopy (ESI-MS), cyclic voltammetry (CV), and fluorescence spectroscopy were performed. We confirmed that neutral ferrocenes cannot complex with the imine group while ferroceniums can. Utilizing the redox property of ferrocenes, we were able to electrochemically control the encapsul...
46 citations
TL;DR: A convenient procedure has been developed by integrated palladium-catalyzed cross-coupling of aromatic iodides with the corresponding Group 14 hydrides in the presence of a base, and the desired arylated products were obtained in synthetically useful yields.
Abstract: A convenient procedure has been developed for the preparation of Group 14 compounds by integrated palladium-catalyzed cross-coupling of aromatic iodides with the corresponding Group 14 hydrides in the presence of a base. The reaction conditions can be applied to the cross-coupling of tertiary, secondary, and primary Group 14 compounds. In most cases, the desired arylated products were obtained in synthetically useful yields. Even in the case of aryl iodides containing OH, NH 2 , CN, or CO 2 R groups, the reactions proceeded with good to high yields with tolerance of these reactive functional groups. A possible application of this method is the unique synthesis of a fungicidal diarylmethyl(1H-1,2,4-triazol-1-ylmethyl)silane derivative.
46 citations
TL;DR: Photosensing performance of a system composed of photosystem I, vitamin K(1) (VK(1))-like molecular wire, and gold nanoparticles (AuNPs) in an aqueous solution was increased considerably by the addition of double surfactants, hexylamine and dodecylbenzenesulfonate.
44 citations
TL;DR: The obtained condensed-ring compounds show unique optical, electrochemical, and magnetic properties due to the extremely narrow HOMO-LUMO gap, and the dication shows paramagnetic behavior with two spins centered on two triarylamine moieties through valence tautomerization with the pentacyclic backbone.
Abstract: Protonation-induced intramolecular cyclization reactions of new donor (D)−acceptor (A) and D−A−D conjugated molecules 1-triarylaminoethynylanthraquinone (1-AmAq) and 1,5-bis(triarylaminoethynyl)anthraquinone (1,5-Am2Aq), respectively, were achieved. The former undergoes monoprotonation with bis(trifluoromethanesulfone)imide acid (TFSIH) to give pyrylium salt [1-AmPyl]TFSI, whereas the latter undergoes a novel double proton cyclization reaction to yield 1,5-bis(triarylamino)dipyrylium salt [1,5-Am2Pyl2](TFSI)2 with a new pentacyclic backbone. This divalent cationic salt can be reduced to give the neutral species 2,8-bis(triarylamino)benzo[de]isochromeno[1,8-gh]chromene ([1,5-Am2Pyl2]0), which maintains the planar pentacyclic backbone. The obtained condensed-ring compounds show unique optical, electrochemical, and magnetic properties due to the extremely narrow HOMO−LUMO gap. In particular, the dication [1,5-Am2Pyl2]2+ shows paramagnetic behavior with two spins centered on two triarylamine moieties through ...
39 citations
TL;DR: The treatment of aryl iodides with tris(trimethylsilyl)silane in the presence of Pd(P(tBu)(3))(2) and the Hünig base leads to the formation of hypersilylated aromatic products in good to excellent yields without cleavage of weak Si-Si bonds under mild conditions.
35 citations
TL;DR: A new metalladithiolene containing a 2,2,6,6-tetramethyl-1-piperidinyl Noxide (TEMPO) radical moiety, (tempodt)Pt, is developed, and it is revealed that this complex has a quite unique electronic structure, in which the energy level of the singly occupied molecular orbital (SOMO; resulting from the TEMPO radical) is lower than that of the highest occupied molecular
Abstract: In recent decades, it has been demonstrated that the appropriate control of the electronic structure of a metalladithiolene moiety in several planar metalladithiolenes is a promising way to realize desired physical and/or chemical properties. We have recently developed a new metalladithiolene containing a 2,2,6,6-tetramethyl-1-piperidinyl Noxide (TEMPO) radical moiety, (tempodt)Pt, and have revealed that this complex has a quite unique electronic structure, in which the energy level of the singly occupied molecular orbital (SOMO; resulting from the TEMPO radical) is lower than that of the highest occupied molecular orbital (HOMO; centered on the p-conjugated dithiolene moiety). One-electron (1e ) oxidation of the complex led to the generation of a p radical on the HOMO. Next, we focused on the application of this unique electronic structure to the development of new chemical phenomena, by employing planar metalladithiolenes, [M(dithiolene)2] n (M = Au, Ni; n = 0, 1, 2). These complexes are well known to have interesting electronic structures in which their HOMOs (SOMOs) delocalize over p-conjugated dithiolene ligands, and they are easily oxidized to produce ligand-based p-radical species. From this perspective, we designed novel planar metalladithiolenes [M(tempodt)2] n 1 (1a : M = Au, n = 1; 1b : M = Ni, n = 2). These compounds are composed of a planar p-conjugated dithiolene moiety and two TEMPO radical moieties. Because of a strong donating ability of this type of p-conjugated dithiolene skeleton, a SOMO–HOMO converted electronic structure similar to (tempodt)Pt was expected for compound 1. It was also expected that a p radical would be produced on the p-conjugated skeleton upon 1e oxidation, and that the resulting multispin species would show peculiar chemical reactivity and/or physical properties. Herein, a particular intramolecular cyclization by radical coupling through 1 according to this scenario is reported. The complexes 1 a, 2a, and 2b were newly synthesized by reaction of tempodtR2 with NaAuCl4 or NiCl2 in the presence of Bu4NOH in THF/MeOH (see the Supporting Information). In the case of M = Au, 1a and the reduced side products were initially formed as purple precipitates, followed by precipitation of the green solid 2 a, whereas compound 2b formed as a dark green precipitate when M = Ni. Note that a [Ni(dithiolene)2] 2 dianion species generated in situ is spontaneously oxidized to afford the [Ni(dithiolene)2] ion. This difference in behavior was attributed to differences in donating ability: the Ni-containing p-conjugated skeleton was much more easily oxidized than the Au-containing one (Supporting Information, Figure S1). The molecular structure of 1a, analyzed by single-crystal XRD, is shown in Figure 1a. The Au atom was located at the
01 Mar 2010
TL;DR: The main function of the photosynthetic process is to capture solar energy and to store it in the form of chemical fuels as discussed by the authors, which is the potential to produce hydrogen as both use clean and cheap sources water and solar energy.
Abstract: The main function of the photosynthetic process is to capture solar energy and to store it in the form of chemical fuels. Many fuel forms such as coal, oil and gas have been intensively used and are becoming limited. Hydrogen could become an important clean fuel for the future. Among different technologies for hydrogen production, oxygenic natural and artificial photosynthesis using direct photochemistry in synthetic complexes have a great 3 Biomimetics, Learning from Nature 50 potential to produce hydrogen as both use clean and cheap sources water and solar energy. Photosynthetic organisms capture sunlight very efficiently and convert it into organic molecules. Artificial photosynthesis is one way to produce hydrogen from water using sunlight by employing biomimetic complexes. However, splitting of water into protons and oxygen is energetically demanding and chemically difficult. In oxygenic photosynthetic microorganisms water is splitted into electrons and protons during primary photosynthetic processes. The electrons and protons are redirected through the photosynthetic electron transport chain to the hydrogen-producing enzymes-hydrogenase or nitrogenase. By these enzymes, eand H+ recombine and form gaseous hydrogen. Biohydrogen activity of hydrogenase can be very high but it is extremely sensitive to photosynthetic O2. At the moment, the efficiency of biohydrogen production is low. However, theoretical expectations suggest that the rates of photon conversion efficiency for H2 bioproduction can be high enough (> 10%). Our review examines the main pathways of H2 photoproduction using photosynthetic organisms and biomimetic photosynthetic systems and focuses on developing new technologies based on the effective principles of photosynthesis.
TL;DR: Slipped cofacial porphyrin dimer 1(2) with di-p-anisylamino groups on the meso-positions shows characteristic photo- and electroproperties making it suitable as a photosynthetic special pair model: more intense and red-shifted absorptivities in the visible region, and electronic communication between the two porphyrs in mixed-valent cation radical 1( 2)(+), which is quantified with an IVCT band analysis
TL;DR: In this article, a new 4-hydroxyazobenzene-appended bipyridine complex of copper, [Cu(oAB-2OH)2]BF4, was synthesized, which exhibits a reversible acid-base responsive redox-active photoisomerization react.
Abstract: We report the synthesis of a new 4-hydroxyazobenzene-appended bipyridine complex of copper, [Cu(oAB-2OH)2]BF4, which exhibits a reversible acid–base responsive redox-active photoisomerization react...
TL;DR: Two thioacetyl-terminated ferrocene-anthraquinone donor-acceptor molecules with different π-electron conjugative units have been synthesized via a series of Stille and Sonagashira reactions, indicating that these complexes are sensitive to external perturbation of protonation, leading the structural change to an expansion of ρ-conjugated system by cyclocondensation reaction.
Abstract: Two thioacetyl-terminated ferrocene-anthraquinone donor-acceptor molecules with different π-electron conjugative units have been synthesized via a series of Stille and Sonagashira reactions. Their photochemical and electrochemical properties before and after addition of an organic acid are investigated, indicating that these complexes are sensitive to external perturbation of protonation, leading the structural change to an expansion of π-conjugated system by cyclocondensation reaction and promoting intramolecular electron transfer from donor to acceptor. They would be good candidates for studies of novel SAMs, and the properties triggered by protonation-induced intramolecular electron transfer will make the SAMs be useful in designing new functional molecular devices.
TL;DR: A variety of dibenzosiloles and -germoles as well as dithiophenosilole (VII) are prepared, better tolerating the functional groups as the methods applied so far as mentioned in this paper.
Abstract: A variety of dibenzosiloles and -germoles as well as dithiophenosilole (VII) are prepared, better tolerating the functional groups as the methods applied so far.
Patent•
12 Mar 2010TL;DR: In this article, a compound having absorbing and luminescence wavelengths at relatively longer wavelength side of the visible area, and having thermal stability, which acts as a dye and/or a luminecence material and has practical utility therefor, and a production method thereof.
Abstract: The present invention provides a compound having absorbing and luminescence wavelengths at relatively longer wavelength side of the visible area, and having thermal stability, which acts as a dye and/or a luminescence material and has practical utility therefor, and a production method thereof. The above subject of the present invention can be solved by a compound represented by general formula I: R 1 —X—R 2 , wherein R 1 and R 2 each independently represents, for example, an N,N-diaryl-4-aminophenyl group, and X is one condensed ring group selected from the group consisting of following formulae X-1 to X-3:
TL;DR: The pitting potential Epit and the repassivation potential Erep were measured for a previously passivated iron electrode in an aerated Cl−-containing borate buffer solution (pH 8.49) with and without various inhibitors using potentiodynamic polarization measurements.
Abstract: The pitting potential Epit and the repassivation potential Erep were measured for a previously passivated iron electrode in an aerated Cl−-containing borate buffer solution (pH 8.49) with and without various inhibitors using potentiodynamic polarization measurements. The values of Epit and Erep were discussed based on the hard and soft acids and bases (HSAB) principle. Iodide and bromide ions and 1,3-di-n-butyl-2-thiourea, which are classified as soft bases, shifted Erep in the positive direction, indicating inhibition of the pit growth process. Electron-probe micro-analyses showed that these soft base inhibitors were adsorbed on the surface of iron substrate acting as a soft acid within a pit. However, inhibition effects of these inhibitors on Epit were not observed. Organic anion inhibitors of hard bases, which have been reported to suppress pit formation by repair of defects or pores in the passive film with precipitates of complexes or salts formed by the hard acid-hard base reactions, were ineffective for Erep because the hard base inhibitors prefer not to bind to the iron substrate surface within the pit.
TL;DR: The history of organic electronic conductors for half century is shortly reviewed and some recent topics on the synthesis of conducting polymers are presented as mentioned in this paper, which is one of the most fascinating materials of its high EL ability.
Abstract: The history of organic electronic conductors for half century is shortly reviewed and some recent topics on the synthesis of conducting polymers are presented. Organic conductors can be roughly divided into two categories, crystalline and polymeric materials, of which chemistry and physics have advanced markedly and a variety of examples have appeared. The crystalline materials involve superconducting low-dimensional charge-transfer salts and M3C60 (M is an alkali metal), and the polymeric conductors are mostly made of linearly π-conjugated organic polymers. One of the recent topics given is synthesis of poly (phenylene vinylene) that is one of the most fascinating materials of its high EL ability. Other topics described are synthesis of new class of conducting polymers, π-conjugated donor-acceptor copolymers and π-conjugated polymers involving transition metal complexes. The history clearly indicates that the role of synthetic chemists is still important for finding a breakthrough to open a new era of organic conducting materials.