Shinsuke Takagi - Academia.edu (original) (raw)

Papers by Shinsuke Takagi

Research paper thumbnail of Inorganic Nanosheets and Nanosheet-Based Materials

Nanostructure Science and Technology, 2017

Research paper thumbnail of Preparation of Uniformly Dispersed Non-Aggregated Gold Nanoparticles on the Clay Surface

Research paper thumbnail of Photochemical Electron Transfer Reactions in Clay-porphyrin Complexes

Research paper thumbnail of Anisotropic energy transfer in a clay–porphyrin layered system with environment-responsiveness

Physical Chemistry Chemical Physics, 2020

The adsorption orientation behavior of tetrakis(1-methylpyridinium-3-yl)porphyrin (m-TMPyP) and p... more The adsorption orientation behavior of tetrakis(1-methylpyridinium-3-yl)porphyrin (m-TMPyP) and p-TMPyP on the clay monolayer prepared by the Langmuir Blodgett (LB) technique was investigated using the absorption and dichroic spectra obtained on a waveguide.

Research paper thumbnail of Which types of clay minerals fix cesium ions effectively? the “cavity-charge matching effect”

Physical Chemistry Chemical Physics, 2019

Cs+ mediated interlocking for the strong capturing “cavity-charge matching effect”.

Research paper thumbnail of Highly Selective Photochemical Epoxidation of Cyclohexene Sensitized by Ru(II) Porphyrin–Clay Hybrid Catalyst

Research paper thumbnail of “Surface-Fixation Induced Emission” of Porphyrazine Dye by a Complexation with Inorganic Nanosheets

The Journal of Physical Chemistry C, 2014

ABSTRACT This paper proposes a unique phenomenon of the strong enhancement in the fluorescence qu... more ABSTRACT This paper proposes a unique phenomenon of the strong enhancement in the fluorescence quantum yield (phi(f)) and the excited lifetime (tau) of tetra-cationic porphyrazine dye (Pz) upon a complexation with inorganic nanosheets. Although Pz does not strongly fluoresce in a bulk solution ((phi(f) = 0.01, tau = 0.1 ns), phi(f) and tau increased up to 19 and 34 times by an intercalation into stacked clay nanosheets. Steady-sate and time-resolved fluorescence measurements revealed that this strong enhancement in phi(f) and tau is derived from the suppression of nonradiative deactivation pathways of Pz by a complexation with day nanosheets. We here name this phenomenon a "Surface-Fixation Induced Emission (S-FIE)". S-FIE can be predicted easier than aggregation-induced emission (AIE) due to its clear mechanism depending on the flat solid surface, and we can thus simply design the photophysically enhanced system. Since photophysical characteristics of organic molecules directly influence the efficiency of objective reactions such as energy or electron transfers and photocatalysis, this study is beneficial to propose a novel strategy to create efficient photochemical reaction systems and photodevices.

Research paper thumbnail of Unique fluorescence behavior of dyes on the clay minerals surface: Surface Fixation Induced Emission (S-FIE)

Journal of Photochemistry and Photobiology A: Chemistry, 2017

We have been investigating complexes composed of nano-sheet with anionic charges such as clay nan... more We have been investigating complexes composed of nano-sheet with anionic charges such as clay nanosheets and molecules such as cationic organic dyes. Photochemical properties of organic dyes are much affected by the complex formation with nano-sheet in many cases. Especially, a strong fluorescence enhancement behavior of dyes was frequently observed on the nano-sheet surface. Based on the mechanism, we name this unique effect "S-Fixation Induced Emission (S-FIE)". The examples for fluorescence enhancement are shown and the mechanism is discussed in detail.

Research paper thumbnail of Photochemical Chlorination and Oxygenation Reaction of Cyclohexene Sensitized by Ga(III) Porphyrin–Clay Minerals System with High Durability and Usability

Bulletin of the Chemical Society of Japan, 2015

Photochemical chlorination and oxygenation reaction of cyclohexene sensitized by gallium(III) por... more Photochemical chlorination and oxygenation reaction of cyclohexene sensitized by gallium(III) porphyrinclay hybrid compound was investigated. Gallium(III) porphyrin did not aggregate on the clay surface, and thus, maintained photoactivity for the photochemical reaction. Gallium(III) porphyrin without clay decomposed immediately in the photochemical reaction. On the other hand, gallium(III) porphyrin adsorbed on clay was more stable than that without clay during the photochemical reaction and the altered porphyrin on clay still had photocatalytic ability along with original porphyrin. It was suggested that gallium(III) porphyrin was protected by clay surface during the photochemical reaction. In addition, the efficiency for the photochemical chlorination and oxygenation reaction was kept even at high porphyrin adsorption densities on clay. These findings are beneficial to construct efficient and durable photochemical reaction systems.

Research paper thumbnail of Microstructures of the Porphyrin/Viologen Monolayer on the Clay Surface: Segregation or Integration?

The Journal of Physical Chemistry C, 2014

Microstructures of the porphyrin/viologen monolayer on an anionic clay surface (synthetic saponit... more Microstructures of the porphyrin/viologen monolayer on an anionic clay surface (synthetic saponite) were investigated by the observation of photochemical behavior of porphyrin. Fluorescence behaviors of porphyrin−viologen− clay complexes were observed by steady state and time-resolved fluorescence spectroscopy. Although fluorescence of porphyrin was effectively quenched by coadsorbed viologen on the clay surface, a part of the fluorescence of porphyrin was not quenched and remained even at high loading level of viologen. According to time-resolved fluorescence measurement, the decay profile of excited singlet porphyrin can be analyzed by two-or three-component fitting for porphyrin−viologen−clay complexes. These results indicate that porphyrin and viologen adsorb with island (segregation) structure on the clay surface. The size of the island formed by porphyrin was quantitatively estimated for two kinds of porphyrins. It turned out that the porphyrin molecular structure affects the size of the island. It has been believed that electron transfer on a clay surface is inefficient due to segregation of dyes between clay sheets (A. J. Bard et al., J. Phys. Chem. 1984, 88, 5519). Our results indicate that segregation behavior sensitively depends on the structure of the dye, and it is possible to construct an efficient electron transfer system on the clay surface.

Research paper thumbnail of Unique photochemical behavior of novel tetracationic pyrene derivative on the clay surface

Tetrahedron Letters, 2012

Research paper thumbnail of Visible light induced oxygenation of cyclohexene with activation of water sensitized by dihydroxy coordinated tetraphenyloprphyrinatotin(IV)

Research on Chemical Intermediates, 2000

Visible light irradiation of a reaction mixture containing dihydroxy coordinated tetraphenylporph... more Visible light irradiation of a reaction mixture containing dihydroxy coordinated tetraphenylporphyrinatotin(IV), cyclohexene and potassium hexachloroplatinate induced oxygenation of the cyclohexene under degassed conditions. In the reaction system, a water molecule served as the oxygen donor. Cyclohex-2-enol, 1,2-dichlorocyclohexane and 2-chlorocyclohexanol were the major oxidation products and the quantum yield was around 0.1. An experiment using H218O revealed that an 18O atom was quantitatively incorporated into the oxygenated products. The reaction was initially induced by an electron transfer from an excited triplet porphyrin to potassium hexachloroplatinate producing a cation radical of the porphyrin. Metal-oxo type complexes formed through deprotonation of the hydroxy group of the porphyrin cation radical were key reactive intermediates reacting with cyclohexene. Two kinds of the metal-oxo type complex reactive intermediate were kinetically demonstrated to be involved in the reaction system, producing different oxidation products from cyclohexene.

Research paper thumbnail of An artificial muscle model unit based on inorganic nanosheet sliding by photochemical reaction

Nanoscale, 2013

From the viewpoint of developing photoresponsive supramolecular systems in microenvironments to e... more From the viewpoint of developing photoresponsive supramolecular systems in microenvironments to exhibit more sophisticated photo-functions even at the macroscopic level, inorganic/organic hybrid compounds based on clay or niobate nanosheets as the microenvironments were prepared, characterized, and examined for their photoreactions. We show here a novel type of artificial muscle model unit having much similarity with that in natural muscle fibrils. Upon photoirradiation, the organic/inorganic hybrid nanosheets reversibly slide horizontally on a giant scale, and the interlayer spaces in the layered hybrid structure shrink and expand vertically. In particular, our layered hybrid molecular system exhibits a macroscopic morphological change on a giant scale (~1500 nm) compared with the molecular size of ~1 nm, based on a reversible sliding mechanism.

Research paper thumbnail of Highly Efficient and Selective Epoxidation of Alkenes by Photochemical Oxygenation Sensitized by a Ruthenium(II) Porphyrin with Water as Both Electron and Oxygen Donor

Journal of the American Chemical Society, 2003

Visible light irradiation of a reaction mixture of carbonyl-coordinated tetra(2,4,6-trimethyl)phe... more Visible light irradiation of a reaction mixture of carbonyl-coordinated tetra(2,4,6-trimethyl)phenylporphyrinatoruthenium(II) (Ru II TMP(CO)) as a photosensitizer, hexachloroplatinate(IV) as an electron acceptor, and an alkene in alkaline aqueous acetonitrile induces selective epoxidation of the alkene with high quantum yield (Φ) 0.6, selectivity) 94.4% for cyclohexene and Φ) 0.4, selectivity) 99.7% for norbornene) under degassed conditions. The oxygen atom of the epoxide was confirmed to come from a water molecule by an experiment with H 2 18 O. cis-Stilbene was converted into its epoxide, cis-stilbeneoxide, without forming trans-stilbeneoxide. trans-Stilbene, however, did not exhibit any reactivity. Under neutral conditions, an efficient buildup of the cation radical of Ru II TMP(CO) was observed at the early stage of the photoreaction, while an addition of hydroxide ion caused a rapid reaction with the cation radical to promote the reaction with reversion to the starting Ru II TMP(CO). A possible involvement of a higher oxidized state of Ru such as Ru IV , Ru V , Ru VI through a dismutation of the Ru III species was excluded by an experiment with Ru VI TMP(O)2. Decarbonylation of the Ru complex was also proven to be invalid. A reaction mechanism involving an electron transfer from the excited triplet state of Ru II TMP(CO) to hexachloroplatinate(IV) and subsequent formation of OH-coordinated Ru III species, leading to an oxo-ruthenium complex as the key intermediate of the photochemical epoxidation, was postulated.

Research paper thumbnail of Visible light-induced reduction of carbon dioxide sensitized by a porphyrin–rhenium dyad metal complex on p-type semiconducting NiO as the reduction terminal end of an artificial photosynthetic system

Journal of Catalysis, 2014

Visible light-induced, two-electron reduction of carbon dioxide to carbon monoxide, catalyzed by ... more Visible light-induced, two-electron reduction of carbon dioxide to carbon monoxide, catalyzed by a newly synthesized metal complex dyad composed of a zinc porphyrin as a light-harvesting sensitizer and a rhenium bipyridyl complex as a catalytic moiety for the reduction, was attained for the first time on the p-type semiconductor NiO without any sacrificial electron donor. The fluorescence of the dyad adsorbed on the NiO nanoparticles (20-30 nm diameter) was efficiently quenched with a very short lifetime (29 ps) compared with the intrinsic value of 1.6 ns in DMF. The radical anion of the zinc porphyrin was actually formed upon excitation of 5,10,15,20-tetra(4-carboxy)phenylporphyrinatozinc (ZnTCPP) (5) on NiO by fast electron injection from NiO to the excited ZnTCPP with a lifetime of $180 ns, corresponding to the charge recombination with the hole on NiO. An electrochemical cell composed of the dyad-adsorbed NiO particle layers on an FTO cathode and platinum as a counter electrode in CO 2-saturated DMF solution showed a constant cathodic photocurrent upon visible light irradiation (k = 420 nm) accompanied by the formation of the two-electron-reduced product (CO). The photoreduction was further enhanced by a factor of 5.5 in a system prepared by co-adsorbing ZnTCPP (5) as a light-and electron-harvesting moiety and the dyad ZnDMCPP-Re(bpy)(NHAc) (1) as a catalytic moiety on NiO, as a promising example of the design of a CO 2 photoreduction system as the reduction terminal end of an artificial photosynthetic system.

Research paper thumbnail of Adsorption and stacking behaviour of zwitterionic porphyrin on the clay surface

Clay Minerals, 2012

AB ST R ACT : Zwitterionic porphyrin (tetrakis {4-(2-carboxyethyl)pyridinio}porphyrin (TPyCP)) wi... more AB ST R ACT : Zwitterionic porphyrin (tetrakis {4-(2-carboxyethyl)pyridinio}porphyrin (TPyCP)) with four pyridinium and carboxyl groups in the molecule was synthesized. The adsorption behaviour of TPyCP on the montmorillonite clay surface was examined in an aqueous colloidal solution. While the adsorption maximum l max of TPyCP was 424 nm in water, it shifted to longer wavelengths on complex formation with clay. The l max on the exfoliated clay surface was 450 nm, and that in the stacked clay sheets was 471 nm, respectively. Under alkaline conditions ([NaOH] = 2610 À4 M), the stacking behaviour of the clay was completely suppressed. It emerged that anionic parts in the porphyrin molecule can suppress the stacking of clay sheets. Judging from the quantitative analysis, the maximum adsorption amount of TPyCP was 100% vs. cation exchange capacity (CEC) of the clay. As the adsorption density of TPyCP increased, l max shifted slightly to longer wavelengths due to the interactions between adjacent porphyrins. When the loading level of TPyCP was 200% vs. CEC, the stacking of TPyCP was indicated. The average stacking layer number was calculated to be 1.48. On the other hand, it is known that tetra cationic porphyrins without anionic parts do not form such stacking structures. Thus, it seems that zwitterionic porphyrin has the potential to form a three dimensional structure through electrostatic interactions between porphyrins on the clay surface.

Research paper thumbnail of Efficient Oxygenation of Alkene through Reductive Quenching of Excited Sb(V)tetraphenylporphyrin by Triphenylphosphine

Research paper thumbnail of Effects of Axial Ligands on the Formation of a Layered Structure in Mono- and Di-Cationic Charged Tetraphenylporphyrinatoantimony(V)/Synthetic Clay Composites

Bulletin of the Chemical Society of Japan, 2005

Novel metalloporphyrin-clay composites were prepared from a synthetic clay (Sumecton SA: SSA) and... more Novel metalloporphyrin-clay composites were prepared from a synthetic clay (Sumecton SA: SSA) and cationic tetraphenylporphyrinatoantimony(V) bromide (SbTPP, 1-4) having various axial ligands. Both the crystal structure for SbTPP-SSA composites and the adsorption behaviors of SbTPP into SSA sheets are investigated regarding the relation to the structure of an axial ligand at SbTPP by measuring the X-ray diffraction (XRD), IR, UV-vis, and fluorescence spectroscopy. The XRD analysis revealed that powdered SbTPP-SSA composites could take a layered structure for 1, and an amorphous structure for 2, respectively. The IR spectrum of naked SSA showed a broad absorption band around 3000-3600 cm - 1 , which can probably be assigned as some adsorbed water molecules onto SSA. The intensity of the broad absorption band became weaker with an increase of the loading level (%LL), which was defined as a ratio of the concentration of the cationic sites of 1-4 to the concentration of anionic sites of SSA. The band completely disappeared at 100%LL in both 2-SSA and 4-SSA composites with the amorphous structure, whereas the band remained even at 100%LL in both 1-SSA and 3-SSA composites with the layered structure. Information about an aggregation state of 1-4 into SSA was obtained by measuring both the UV-vis absorption spectra of 1-4 in an aqueous colloidal clay solution and the fluorescence spectra of SbTPP-SSA composites in the solid state by using a confocal laser scanning fluorescence microscope. Each spectral data indicated that the ammonium cationic part on an axial ligand of 1 only led to effective non-aggregated adsorption onto SSA sheets, while 2-4 were located with the aggregated state on SSA sheets. These results also support that an axial ligand structure can control not only the formation of the crystal structure, but also the adsorption behaviors with aggregation or non-aggregation onto SSA sheets.

Research paper thumbnail of Controlling the Microadsorption Structure of Porphyrin Dye Assembly on Clay Surfaces Using the “Size-Matching Rule” for Constructing an Efficient Energy Transfer System

ACS Applied Materials & Interfaces, 2012

The microadsorption structure of two kinds of porphyrin molecules on an anionic clay surface was ... more The microadsorption structure of two kinds of porphyrin molecules on an anionic clay surface was investigated by photochemical energy transfer reaction. Three procedures were examined for the preparation of the clay/porphyrin complexes: (i) coadsorption (CA) method, (ii) sequential adsorption (SA) method, and (iii) independent adsorption (IA) method as described in the text. Efficient and moderate energy transfer reactions were observed in the CA and SA complexes, respectively. On the contrary, the energy transfer did not occur in the IA complex. These results indicate that the microadsorption structure of the two kinds of porphyrin on the clay mineral surface resulting from the sample preparation methods, affects the energy transfer efficiency. As a result, it was revealed that (i) the adsorbed porphyrins can move on the clay mineral surface but cannot move from one clay surface to another clay sheet, and (ii) the integration structure of two kinds of porphyrin is more stable than the segregation structure in the present system. This unusual structure originated from an extremely strong electrostatic interaction between the porphyrin and the clay mineral as a result of a "sizematching rule". These unique strongly fixed dye assemblies on the clay mineral surface, in which the aggregation and segregation of dyes are suppressed, is very promising and attractive for constructing efficient photochemical reaction systems.

Research paper thumbnail of What Lowers the Efficiency of an Energy Transfer Reaction Between Porphyrin Dyes on Clay SURFACE?(TMC2010)

Clay Science, 2011

Excited energy transfer reaction from tetrakis(1-methylpyridinium-2-yl) porphyrin (o-TMPyP) to te... more Excited energy transfer reaction from tetrakis(1-methylpyridinium-2-yl) porphyrin (o-TMPyP) to tetrakis(I-methyLpyridinium-4-yl) porphyrin (p-TMPyP) on an anionic clay surface was investigated. The energy transfer eMciency and quenching eMciency due to an e]ectron transfer were quantitatively estimated. Both the energy transfer eMciency and quenching eficiency increased as the dye loadings incrcased. By a comparison with the results ofother porphyrin combination systems, it was found that the major factor for lowcring the energy transfer eMciency was the selflquenchjng of the donor porphyrin on the clay surface. Since the selequenching was effectivcly suppressed by the strong adsorption ofporphyrin on the clay surface due to the Size-Matcbing Effect, relatively erncient energy transfer was achieved. For constructing an efficient energy transfer system, such as an artificial light-harvesting system, a suppression of the selequenching of dyes on the clay surface shouldbeimportant.

Research paper thumbnail of Inorganic Nanosheets and Nanosheet-Based Materials

Nanostructure Science and Technology, 2017

Research paper thumbnail of Preparation of Uniformly Dispersed Non-Aggregated Gold Nanoparticles on the Clay Surface

Research paper thumbnail of Photochemical Electron Transfer Reactions in Clay-porphyrin Complexes

Research paper thumbnail of Anisotropic energy transfer in a clay–porphyrin layered system with environment-responsiveness

Physical Chemistry Chemical Physics, 2020

The adsorption orientation behavior of tetrakis(1-methylpyridinium-3-yl)porphyrin (m-TMPyP) and p... more The adsorption orientation behavior of tetrakis(1-methylpyridinium-3-yl)porphyrin (m-TMPyP) and p-TMPyP on the clay monolayer prepared by the Langmuir Blodgett (LB) technique was investigated using the absorption and dichroic spectra obtained on a waveguide.

Research paper thumbnail of Which types of clay minerals fix cesium ions effectively? the “cavity-charge matching effect”

Physical Chemistry Chemical Physics, 2019

Cs+ mediated interlocking for the strong capturing “cavity-charge matching effect”.

Research paper thumbnail of Highly Selective Photochemical Epoxidation of Cyclohexene Sensitized by Ru(II) Porphyrin–Clay Hybrid Catalyst

Research paper thumbnail of “Surface-Fixation Induced Emission” of Porphyrazine Dye by a Complexation with Inorganic Nanosheets

The Journal of Physical Chemistry C, 2014

ABSTRACT This paper proposes a unique phenomenon of the strong enhancement in the fluorescence qu... more ABSTRACT This paper proposes a unique phenomenon of the strong enhancement in the fluorescence quantum yield (phi(f)) and the excited lifetime (tau) of tetra-cationic porphyrazine dye (Pz) upon a complexation with inorganic nanosheets. Although Pz does not strongly fluoresce in a bulk solution ((phi(f) = 0.01, tau = 0.1 ns), phi(f) and tau increased up to 19 and 34 times by an intercalation into stacked clay nanosheets. Steady-sate and time-resolved fluorescence measurements revealed that this strong enhancement in phi(f) and tau is derived from the suppression of nonradiative deactivation pathways of Pz by a complexation with day nanosheets. We here name this phenomenon a "Surface-Fixation Induced Emission (S-FIE)". S-FIE can be predicted easier than aggregation-induced emission (AIE) due to its clear mechanism depending on the flat solid surface, and we can thus simply design the photophysically enhanced system. Since photophysical characteristics of organic molecules directly influence the efficiency of objective reactions such as energy or electron transfers and photocatalysis, this study is beneficial to propose a novel strategy to create efficient photochemical reaction systems and photodevices.

Research paper thumbnail of Unique fluorescence behavior of dyes on the clay minerals surface: Surface Fixation Induced Emission (S-FIE)

Journal of Photochemistry and Photobiology A: Chemistry, 2017

We have been investigating complexes composed of nano-sheet with anionic charges such as clay nan... more We have been investigating complexes composed of nano-sheet with anionic charges such as clay nanosheets and molecules such as cationic organic dyes. Photochemical properties of organic dyes are much affected by the complex formation with nano-sheet in many cases. Especially, a strong fluorescence enhancement behavior of dyes was frequently observed on the nano-sheet surface. Based on the mechanism, we name this unique effect "S-Fixation Induced Emission (S-FIE)". The examples for fluorescence enhancement are shown and the mechanism is discussed in detail.

Research paper thumbnail of Photochemical Chlorination and Oxygenation Reaction of Cyclohexene Sensitized by Ga(III) Porphyrin–Clay Minerals System with High Durability and Usability

Bulletin of the Chemical Society of Japan, 2015

Photochemical chlorination and oxygenation reaction of cyclohexene sensitized by gallium(III) por... more Photochemical chlorination and oxygenation reaction of cyclohexene sensitized by gallium(III) porphyrinclay hybrid compound was investigated. Gallium(III) porphyrin did not aggregate on the clay surface, and thus, maintained photoactivity for the photochemical reaction. Gallium(III) porphyrin without clay decomposed immediately in the photochemical reaction. On the other hand, gallium(III) porphyrin adsorbed on clay was more stable than that without clay during the photochemical reaction and the altered porphyrin on clay still had photocatalytic ability along with original porphyrin. It was suggested that gallium(III) porphyrin was protected by clay surface during the photochemical reaction. In addition, the efficiency for the photochemical chlorination and oxygenation reaction was kept even at high porphyrin adsorption densities on clay. These findings are beneficial to construct efficient and durable photochemical reaction systems.

Research paper thumbnail of Microstructures of the Porphyrin/Viologen Monolayer on the Clay Surface: Segregation or Integration?

The Journal of Physical Chemistry C, 2014

Microstructures of the porphyrin/viologen monolayer on an anionic clay surface (synthetic saponit... more Microstructures of the porphyrin/viologen monolayer on an anionic clay surface (synthetic saponite) were investigated by the observation of photochemical behavior of porphyrin. Fluorescence behaviors of porphyrin−viologen− clay complexes were observed by steady state and time-resolved fluorescence spectroscopy. Although fluorescence of porphyrin was effectively quenched by coadsorbed viologen on the clay surface, a part of the fluorescence of porphyrin was not quenched and remained even at high loading level of viologen. According to time-resolved fluorescence measurement, the decay profile of excited singlet porphyrin can be analyzed by two-or three-component fitting for porphyrin−viologen−clay complexes. These results indicate that porphyrin and viologen adsorb with island (segregation) structure on the clay surface. The size of the island formed by porphyrin was quantitatively estimated for two kinds of porphyrins. It turned out that the porphyrin molecular structure affects the size of the island. It has been believed that electron transfer on a clay surface is inefficient due to segregation of dyes between clay sheets (A. J. Bard et al., J. Phys. Chem. 1984, 88, 5519). Our results indicate that segregation behavior sensitively depends on the structure of the dye, and it is possible to construct an efficient electron transfer system on the clay surface.

Research paper thumbnail of Unique photochemical behavior of novel tetracationic pyrene derivative on the clay surface

Tetrahedron Letters, 2012

Research paper thumbnail of Visible light induced oxygenation of cyclohexene with activation of water sensitized by dihydroxy coordinated tetraphenyloprphyrinatotin(IV)

Research on Chemical Intermediates, 2000

Visible light irradiation of a reaction mixture containing dihydroxy coordinated tetraphenylporph... more Visible light irradiation of a reaction mixture containing dihydroxy coordinated tetraphenylporphyrinatotin(IV), cyclohexene and potassium hexachloroplatinate induced oxygenation of the cyclohexene under degassed conditions. In the reaction system, a water molecule served as the oxygen donor. Cyclohex-2-enol, 1,2-dichlorocyclohexane and 2-chlorocyclohexanol were the major oxidation products and the quantum yield was around 0.1. An experiment using H218O revealed that an 18O atom was quantitatively incorporated into the oxygenated products. The reaction was initially induced by an electron transfer from an excited triplet porphyrin to potassium hexachloroplatinate producing a cation radical of the porphyrin. Metal-oxo type complexes formed through deprotonation of the hydroxy group of the porphyrin cation radical were key reactive intermediates reacting with cyclohexene. Two kinds of the metal-oxo type complex reactive intermediate were kinetically demonstrated to be involved in the reaction system, producing different oxidation products from cyclohexene.

Research paper thumbnail of An artificial muscle model unit based on inorganic nanosheet sliding by photochemical reaction

Nanoscale, 2013

From the viewpoint of developing photoresponsive supramolecular systems in microenvironments to e... more From the viewpoint of developing photoresponsive supramolecular systems in microenvironments to exhibit more sophisticated photo-functions even at the macroscopic level, inorganic/organic hybrid compounds based on clay or niobate nanosheets as the microenvironments were prepared, characterized, and examined for their photoreactions. We show here a novel type of artificial muscle model unit having much similarity with that in natural muscle fibrils. Upon photoirradiation, the organic/inorganic hybrid nanosheets reversibly slide horizontally on a giant scale, and the interlayer spaces in the layered hybrid structure shrink and expand vertically. In particular, our layered hybrid molecular system exhibits a macroscopic morphological change on a giant scale (~1500 nm) compared with the molecular size of ~1 nm, based on a reversible sliding mechanism.

Research paper thumbnail of Highly Efficient and Selective Epoxidation of Alkenes by Photochemical Oxygenation Sensitized by a Ruthenium(II) Porphyrin with Water as Both Electron and Oxygen Donor

Journal of the American Chemical Society, 2003

Visible light irradiation of a reaction mixture of carbonyl-coordinated tetra(2,4,6-trimethyl)phe... more Visible light irradiation of a reaction mixture of carbonyl-coordinated tetra(2,4,6-trimethyl)phenylporphyrinatoruthenium(II) (Ru II TMP(CO)) as a photosensitizer, hexachloroplatinate(IV) as an electron acceptor, and an alkene in alkaline aqueous acetonitrile induces selective epoxidation of the alkene with high quantum yield (Φ) 0.6, selectivity) 94.4% for cyclohexene and Φ) 0.4, selectivity) 99.7% for norbornene) under degassed conditions. The oxygen atom of the epoxide was confirmed to come from a water molecule by an experiment with H 2 18 O. cis-Stilbene was converted into its epoxide, cis-stilbeneoxide, without forming trans-stilbeneoxide. trans-Stilbene, however, did not exhibit any reactivity. Under neutral conditions, an efficient buildup of the cation radical of Ru II TMP(CO) was observed at the early stage of the photoreaction, while an addition of hydroxide ion caused a rapid reaction with the cation radical to promote the reaction with reversion to the starting Ru II TMP(CO). A possible involvement of a higher oxidized state of Ru such as Ru IV , Ru V , Ru VI through a dismutation of the Ru III species was excluded by an experiment with Ru VI TMP(O)2. Decarbonylation of the Ru complex was also proven to be invalid. A reaction mechanism involving an electron transfer from the excited triplet state of Ru II TMP(CO) to hexachloroplatinate(IV) and subsequent formation of OH-coordinated Ru III species, leading to an oxo-ruthenium complex as the key intermediate of the photochemical epoxidation, was postulated.

Research paper thumbnail of Visible light-induced reduction of carbon dioxide sensitized by a porphyrin–rhenium dyad metal complex on p-type semiconducting NiO as the reduction terminal end of an artificial photosynthetic system

Journal of Catalysis, 2014

Visible light-induced, two-electron reduction of carbon dioxide to carbon monoxide, catalyzed by ... more Visible light-induced, two-electron reduction of carbon dioxide to carbon monoxide, catalyzed by a newly synthesized metal complex dyad composed of a zinc porphyrin as a light-harvesting sensitizer and a rhenium bipyridyl complex as a catalytic moiety for the reduction, was attained for the first time on the p-type semiconductor NiO without any sacrificial electron donor. The fluorescence of the dyad adsorbed on the NiO nanoparticles (20-30 nm diameter) was efficiently quenched with a very short lifetime (29 ps) compared with the intrinsic value of 1.6 ns in DMF. The radical anion of the zinc porphyrin was actually formed upon excitation of 5,10,15,20-tetra(4-carboxy)phenylporphyrinatozinc (ZnTCPP) (5) on NiO by fast electron injection from NiO to the excited ZnTCPP with a lifetime of $180 ns, corresponding to the charge recombination with the hole on NiO. An electrochemical cell composed of the dyad-adsorbed NiO particle layers on an FTO cathode and platinum as a counter electrode in CO 2-saturated DMF solution showed a constant cathodic photocurrent upon visible light irradiation (k = 420 nm) accompanied by the formation of the two-electron-reduced product (CO). The photoreduction was further enhanced by a factor of 5.5 in a system prepared by co-adsorbing ZnTCPP (5) as a light-and electron-harvesting moiety and the dyad ZnDMCPP-Re(bpy)(NHAc) (1) as a catalytic moiety on NiO, as a promising example of the design of a CO 2 photoreduction system as the reduction terminal end of an artificial photosynthetic system.

Research paper thumbnail of Adsorption and stacking behaviour of zwitterionic porphyrin on the clay surface

Clay Minerals, 2012

AB ST R ACT : Zwitterionic porphyrin (tetrakis {4-(2-carboxyethyl)pyridinio}porphyrin (TPyCP)) wi... more AB ST R ACT : Zwitterionic porphyrin (tetrakis {4-(2-carboxyethyl)pyridinio}porphyrin (TPyCP)) with four pyridinium and carboxyl groups in the molecule was synthesized. The adsorption behaviour of TPyCP on the montmorillonite clay surface was examined in an aqueous colloidal solution. While the adsorption maximum l max of TPyCP was 424 nm in water, it shifted to longer wavelengths on complex formation with clay. The l max on the exfoliated clay surface was 450 nm, and that in the stacked clay sheets was 471 nm, respectively. Under alkaline conditions ([NaOH] = 2610 À4 M), the stacking behaviour of the clay was completely suppressed. It emerged that anionic parts in the porphyrin molecule can suppress the stacking of clay sheets. Judging from the quantitative analysis, the maximum adsorption amount of TPyCP was 100% vs. cation exchange capacity (CEC) of the clay. As the adsorption density of TPyCP increased, l max shifted slightly to longer wavelengths due to the interactions between adjacent porphyrins. When the loading level of TPyCP was 200% vs. CEC, the stacking of TPyCP was indicated. The average stacking layer number was calculated to be 1.48. On the other hand, it is known that tetra cationic porphyrins without anionic parts do not form such stacking structures. Thus, it seems that zwitterionic porphyrin has the potential to form a three dimensional structure through electrostatic interactions between porphyrins on the clay surface.

Research paper thumbnail of Efficient Oxygenation of Alkene through Reductive Quenching of Excited Sb(V)tetraphenylporphyrin by Triphenylphosphine

Research paper thumbnail of Effects of Axial Ligands on the Formation of a Layered Structure in Mono- and Di-Cationic Charged Tetraphenylporphyrinatoantimony(V)/Synthetic Clay Composites

Bulletin of the Chemical Society of Japan, 2005

Novel metalloporphyrin-clay composites were prepared from a synthetic clay (Sumecton SA: SSA) and... more Novel metalloporphyrin-clay composites were prepared from a synthetic clay (Sumecton SA: SSA) and cationic tetraphenylporphyrinatoantimony(V) bromide (SbTPP, 1-4) having various axial ligands. Both the crystal structure for SbTPP-SSA composites and the adsorption behaviors of SbTPP into SSA sheets are investigated regarding the relation to the structure of an axial ligand at SbTPP by measuring the X-ray diffraction (XRD), IR, UV-vis, and fluorescence spectroscopy. The XRD analysis revealed that powdered SbTPP-SSA composites could take a layered structure for 1, and an amorphous structure for 2, respectively. The IR spectrum of naked SSA showed a broad absorption band around 3000-3600 cm - 1 , which can probably be assigned as some adsorbed water molecules onto SSA. The intensity of the broad absorption band became weaker with an increase of the loading level (%LL), which was defined as a ratio of the concentration of the cationic sites of 1-4 to the concentration of anionic sites of SSA. The band completely disappeared at 100%LL in both 2-SSA and 4-SSA composites with the amorphous structure, whereas the band remained even at 100%LL in both 1-SSA and 3-SSA composites with the layered structure. Information about an aggregation state of 1-4 into SSA was obtained by measuring both the UV-vis absorption spectra of 1-4 in an aqueous colloidal clay solution and the fluorescence spectra of SbTPP-SSA composites in the solid state by using a confocal laser scanning fluorescence microscope. Each spectral data indicated that the ammonium cationic part on an axial ligand of 1 only led to effective non-aggregated adsorption onto SSA sheets, while 2-4 were located with the aggregated state on SSA sheets. These results also support that an axial ligand structure can control not only the formation of the crystal structure, but also the adsorption behaviors with aggregation or non-aggregation onto SSA sheets.

Research paper thumbnail of Controlling the Microadsorption Structure of Porphyrin Dye Assembly on Clay Surfaces Using the “Size-Matching Rule” for Constructing an Efficient Energy Transfer System

ACS Applied Materials & Interfaces, 2012

The microadsorption structure of two kinds of porphyrin molecules on an anionic clay surface was ... more The microadsorption structure of two kinds of porphyrin molecules on an anionic clay surface was investigated by photochemical energy transfer reaction. Three procedures were examined for the preparation of the clay/porphyrin complexes: (i) coadsorption (CA) method, (ii) sequential adsorption (SA) method, and (iii) independent adsorption (IA) method as described in the text. Efficient and moderate energy transfer reactions were observed in the CA and SA complexes, respectively. On the contrary, the energy transfer did not occur in the IA complex. These results indicate that the microadsorption structure of the two kinds of porphyrin on the clay mineral surface resulting from the sample preparation methods, affects the energy transfer efficiency. As a result, it was revealed that (i) the adsorbed porphyrins can move on the clay mineral surface but cannot move from one clay surface to another clay sheet, and (ii) the integration structure of two kinds of porphyrin is more stable than the segregation structure in the present system. This unusual structure originated from an extremely strong electrostatic interaction between the porphyrin and the clay mineral as a result of a "sizematching rule". These unique strongly fixed dye assemblies on the clay mineral surface, in which the aggregation and segregation of dyes are suppressed, is very promising and attractive for constructing efficient photochemical reaction systems.

Research paper thumbnail of What Lowers the Efficiency of an Energy Transfer Reaction Between Porphyrin Dyes on Clay SURFACE?(TMC2010)

Clay Science, 2011

Excited energy transfer reaction from tetrakis(1-methylpyridinium-2-yl) porphyrin (o-TMPyP) to te... more Excited energy transfer reaction from tetrakis(1-methylpyridinium-2-yl) porphyrin (o-TMPyP) to tetrakis(I-methyLpyridinium-4-yl) porphyrin (p-TMPyP) on an anionic clay surface was investigated. The energy transfer eMciency and quenching eMciency due to an e]ectron transfer were quantitatively estimated. Both the energy transfer eMciency and quenching eficiency increased as the dye loadings incrcased. By a comparison with the results ofother porphyrin combination systems, it was found that the major factor for lowcring the energy transfer eMciency was the selflquenchjng of the donor porphyrin on the clay surface. Since the selequenching was effectivcly suppressed by the strong adsorption ofporphyrin on the clay surface due to the Size-Matcbing Effect, relatively erncient energy transfer was achieved. For constructing an efficient energy transfer system, such as an artificial light-harvesting system, a suppression of the selequenching of dyes on the clay surface shouldbeimportant.