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The photoreduction of CO2 catalyzed by [fac-Re(dmbpy)(CO)3Cl] was precisely investigated through operando measurements of X-ray absorption fine structure spectroscopy (XAFS) and laser-flash FT-IR transient spectroscopy. In the early stage of the photoreaction, Re0-species assigned as penta-coordinated complex, [Re0(dmbpy)(CO)3], appeared and a delayed rise of ReII-species, [ReII(dmbpy)(CO)3CO2] (3) / [ReII(dmbpy)(CO)3COOH]+ (3’), were observed in XAFS measurements. The valence state of Re-center in the catalytic cycle changed as ReI → Re0 → ReII to be a clear evidence of an oxidative addition of CO2 to the Re0 center. In the laser-flash induced FT-IR measurements, a rise and decay of 3 followed by a delayed rise and decay of 3’ was observed. The second electron transfer from the carbon radical of TEA to 3’ induced the formation of [ReI(dmbpy)(CO)4]+ through [ReI(dmbpy)COOH]. The rate determining step of the catalytic cycle was revealed to be the protonation process of forming 3’ from 3.

We have previously found reversible photo-induced expansion and contraction of organic/inorganic clay hybrids, and even sliding of niobate nano-sheets at the macroscopic level of organic/inorganic niobate hybrids, induced by the molecular photo-isomerization of the polyfluoroalkylated azobenzene derivative (C3F-Azo-C6H) intercalated within the interlayer, which is viewed as an artificial muscle model unit. Based on systematic investigations of the steady state photo-isomerization and transient behavior of the reaction, we comprehended that the phenomena is caused by trapping of excess energy liberated during the isomerization, as well as the relaxation processes upon excitation of azobenzene chromophores in the interlayers of the hybrid. In this paper, quantitative estimation of transient 'heat' trapped in various microenvironments has been studied by each co-intercalation of temperature sensing dye molecules - rhodamine B (RhB) or tris(bipyridine)ruthenium(ii) chloride (Rubpy) with C3F-Azo-C6H within clay (SSA) nano-layers. The amount of dye molecules co-intercalated was kept to trace amounts that did not alter the bi-layered structure of the hybrid. The temperature of the microenvironment surrounding the probe molecules was estimated from the emission lifetime analysis. The evidently reduced emission lifetimes in C3F-Azo-C6H/SSA and C3H-Azo-C6H/SSA hybrids in the film state, indicated the elevation of temperature of the microenvironment upon excitation of the chromophores, which demonstrated our previous hypothesis rationalizing that the high reactivity of isomerization in the hybrid film state is caused by heat trapping via multi-step dissipation of the excess energy. With the hybrid of a hydrocarbon analogue (C3H-Azo-C6H), a distinct difference in temperature gradient was found to show the crucial role of the perfluoroalkyl chain of the surfactant that traps the excess energy to retard its dissipation leading to three-dimensional morphological motion.

Artificial photosynthesis, which splits water into H2/O2 or reduces CO2 and N2 by visible light, catalyzed by molecular catalysts (MCs) with/without being coupled with a solar cell should serve as ...

A photo-responsive nanoscroll composed of niobate nanosheets and a polyfluoroalkyl azobenzene derivative (C3F-Azo-C6H) is one of the most interesting layered materials because the reversible winding and unwinding motion could be efficiently induced by photo-irradiations. Previously, we have studied a double-walled nanoscroll (DWNS) of niobate that could be synthesized by the intercalation of a cationic polyfluorinated surfactant only into the interlayer I of the layered niobate among the two interlayers, I and II. In this study, we have successfully synthesized another novel photo-responsive single-walled nanoscroll (SWNS) of niobate by a stepwise guest–guest ion-exchange method. All niobate nanosheets that were exfoliated at both interlayers I and II were efficiently converted to nanoscrolls by the intercalation of C3F-Azo-C6H. The synthetic yield has been quantitatively estimated. Though the photo-isomerization reaction of C3F-Azo-C6H was induced in the SWNS, its photo-reactivity was the lowest when compared with those of the nanosheet-stacked film and the DWNS. The photo-reactivity of C3F-Azo-C6H decreased in the order of DWNS > nanosheet-stacked film > SWNS. The different flexibility of the layered miroenvironment might influence the photo-reactivity of C3F-Azo-C6H in the niobate hybrid. The SWNS exhibited a reversible expansion and shrinkage of its interlayer spaces upon photo-irradiation, while the winding and unwinding motion was not observed, contrary to the DWNS. The direction of the expansion and shrinkage of the interlayer of the SWNS was opposite to those of the nanosheet-stacked film and the DWNS. Based on the experimental results, the tilt angle of C3F-Azo-C6H against the nanosheet surface and the matching structures of the top and bottom surfaces of the nanosheet could be the probable key factors that control the photo-reactivity of C3F-Azo-C6H in the layered microenvironment; the morphological changes of the nano hybrids was also discussed.

Recent development on alternative route to bypass the bottle-neck of water oxidation, two-electron oxidation of water catalyzed by earth-abundant metalloporphyrins to form hydrogen peroxide, has been briefly reviewed. The three pioneering reports by Fujishima (Honda-Fujishima effect), Meyer (chemical oxidation of water), and Lehn (photochemical reduction of CO2) triggered the extensive studies on artificial photosynthesis to have been forming the modern history of artificial photosynthesis. The current situation, especially for artificial photosynthesis by molecular catalysts, however, has faced with bottleneck subject of photon-flux-density problem of sun light radiation. In this review article, three milestones in the modern history of artificial photosynthesis, photon-flux-density problem as the bottleneck subject in water oxidation, crucial viewpoint of renewable energy factor (REF) in designing artificial photosynthesis even in fundamental stage of studies are explained. Several approaches to minimize the energy cost in REF for molecular catalysts such as utilization of earth-abundant elements and synthesis of molecular catalyst in water at ambient temperature were also introduced. Recent development of two-electron oxidation of water to form hydrogen peroxide, which would uncover the blind point of the bottleneck subject, would induce a game change in the methodologies of artificial photosynthesis.

Tetraphenylporphyrinatophosphorus(V) complexes (1) comprising two axially linked benzylidene imidazolone (Biz) moieties, which are chromophores of the green fluorescent protein, were prepared. In medical applications such as photodynamic therapy, the P-porphyrin part (Ptp) is expected to sensitize to generate singlet oxygen, whereas the Biz units act as fluorescent probes. The fluorescence spectra of 1 were analyzed under the excitations of Biz at 370 nm. Fluorescence stemming from the excited states of Biz and Ptp was observed at 460 and 610 nm, respectively. The intramolecular quenching of Biz in the excited singlet state by Ptp occurred, resulting in weak fluorescence from Biz. The introduction of a cyano group in the Biz units of 1 enhanced their fluorescence quantum yield up to 7.7 × 10−4. The fluorescence spectra of 1 under the excitations of Ptp at 550 nm were extremely similar to that of a reference compound of P-porphyrin without the Biz chromophore, dimethoxy(tetraphenylporphyrinato)phosphorus chloride. The physicochemical parameters of Ptp remained unaltered following the introduction of Biz on the axial positions of P-porphyrin.

Water soluble tin(IV)-porphyrins, trans-dihydroxy-5,10,15,20-tetra(N-methyl-4′-pyridiniumyl)porphyrinate tin (IV) (Sn(IV)TMPyP(OH)2) was successfully synthesized in high yield (90%) through one-pot process in water at room temperature by treating the parent free base (H2TMPyP) with Sn(II)Cl2. Re-investigation by the detailed kinetic analysis of the time dependent 1H NMR signals indicated that the tin(IV)-insertion reaction reversibly proceeded through three steps to start from free base dimer, [H2TMPyP]2, through Sn(II)TMPyP. New intermediate, an association complex between SnCl2 and H2TMPyP, which should be a precursor of Sn(II)TMPyP, was clearly observed in UV–vis and 1H NMR for the first time. Sn(II)TMPyP was also detected at around 500 nm in UV–vis spectroscopy, while it was silent against 1H NMR, which was supported by DFT calculation to indicate that Sn(II)TMPyP has a paramagnetic nature through substantial population on triplet spin states. To explore possible one-pot process for other porphyrins, such as neutral tetra-meso-substituted-tolylporphyrin (TTP), tetra-meso-substituted-mesitylporphyrin (TMP), and anionic tetra-meso-substituted-carboxyphenylporphyrin (TCPP), the reactions in water, binary-phase system of water/dichloromethane, and methanol were examined. The anionic TCPP suffered the tin(IV)-insertion at ambient temperature only in methanol with good yield (90%).

A series of four Tin(IV)porphyrins with different substituents on meso-phenyl groups, trans-dihydroxy-5,10,15,20-tetra(p-tolyl)porphyrinatetin(IV) (Sn(IV)TTP(OH)2), trans-dihydroxy-tetra(2,4,6-trimethyl)phenylporphyrinatetin(IV) (Sn(IV)TMP(OH)2), trans-dihydroxy-5,10,15,20-tetra(p-carboxyphenyl)porphyrinatetin(IV) (Sn(IV)TCPP), and trans-dihydroxy-5,10,15,20-tetra(N-methyl-4′-pyridiniumyl)porphyrinatetin(IV) (Sn(IV)TMPyP(OH)2) have been prepared and characterized focusing on their protolytic behavior of the axial ligands, hydroxy groups, both in the ground and excites states as well as their electrochemical oxidation behavior. The two axially ligating hydroxy groups on each Tin(IV)-porphyrins exhibit protonations and deprotpnations in five steps. The pKa value of each protolytic equilibrium in the ground states was spectrophotometrically determined, while fluorescence decay time profiles indicate that the protolytic processes are sufficiently slower than the intrinsic fluorescence decay rates to lead to non-protolysis in the excited states. The oxidation peak potentials were determined by cyclic voltammetric analysis. Pourbaix diagram of each protolytic species of Sn(IV)TMPyP in water indicated that the one-electron oxidation of fully deprotonated Sn(IV)TMPyP(O−)2 is not a proton-coupled process, while the doubly hydroxy coordinated species Sn(IV)TMPyP(OH)2 has a proton-coupled one. Tin(IV)-porphyrins exhibit efficient catalytic currents on the first oxidation wave in their cyclic voltammetry and the saturated catalytic currents were high enough in a wide range of pH to be promising as water oxidation catalysts. This is the first detailed study on Tin(IV)-porphyrins to examine water oxidation ability of the one-electron oxidized form against twenty kinds of species (five protolytic species for each of the four Tin(IV)-porphyrins).

We report here a new class of co-catalysts for hydrogen evolution on TiO2 particles upon photo-irradiation. TiO2 particles prepared by sol/gel method was allowed to graft metal ion by a simple treatment with metal salts (Pt (IV), Rh (III), Cu (II), Fe(III), Al (III) ions) in water. The metal ion surface-grafted particles of TiO2(sol/gel) exhibit excellent photochemical hydrogen evolution compared to Pt (0) cluster loaded particles of TiO2(sol/gel) under the UV light irradiation of λ > 290 nm. XPS analysis shows that the valence states of the metal ions grafted on the TiO2 particles are the same with the parent metal ion salts and no metal (0) clusters were detected. DFT calculation of the simple model of metal ion/TiO2 indicated that an injected electron mostly localized on the metal ion sites, but not on Ti sites, which rationalizes the metal ion serve as the hydrogen evolution sites. Earth abundant metal ions, Cu (II), Fe (III), and Al (III) thus can provide new class of hydrogen evolution sites for artificial photosynthetic systems. To explore the possibility of utilizing semiconductor as an electron relay in the future system of molecular-catalyst-sensitized water splitting into hydrogen and hydrogen peroxide, the stability of hydrogen peroxide on various TiO2 surfaces was examined. Hydrogen peroxide was found to be pretty stable on Rh (III), Fe (III), and Al (III) ions surface-grafted TiO2, while Pt (IV) and Cu (II) ion grafted one similarly caused decomposition of hydrogen peroxide as Pt (0) cluster loaded TiO2 (Pt(0)/TiO2).

The second most earth abundant atom incorporated meso-tetrapyridylporphyrinatesilicon(IV) (SiTPyP) as an electrochemical catalyst was newly synthesized. The two axially ligated water molecules on SiTPyP and the four meso-substituted pyridyl nitrogens suffer eight-step protonations and deprotonations. Our detailed pKa study indicated that the two axially ligated water molecules were fully deprotonated to exist as O−–Si–O− under the condition of pH > 2. Under basic conditions, SiTPyP(O−)2 exerted the two-electron oxidation of water to form hydrogen peroxide as the primary product in aqueous acetonitrile, which was initiated through a one-electron oxidation process on the electrode with faradaic yield of 84–92%.

The reaction mechanism of photochemical water oxidation catalyzed by Al(III)-porphyrins (AlTMPyP(OH)2) covalently adsorbed through one axial OH group coordination on the surface of TiO2 particle was investigated by time resolved nanosecond laser flash photolysis (NLFP). Three types of transient species with completely different absorption and decay characteristics were detected by means of NFLP、demonstrating that the photochemical production of H2O2 from water is initiated only by one-photon excitation of catalyst followed by stepwise two-electron conversion processes, providing a promising model for photochemical water oxidation. Upon laser flash excitation of AlTMPyP adsorbed on transparent TiO2 film leads to the formation of AlTMPyP(OH) radical cation through one-electron injection from the excited singlet state of catalyst to the conduction band of TiO2. The radical cation is subsequently deprotonated into AlTMPyP(O*), which further reacts with OH-/H2O to form a key intermediate, the radical anion of AlTMPyP(O-OH), having characteristic O-O bond at the axial position within a delay time of 2-3 µs. Thereafter the radical anion efficiently transfers second electron to TiO2 leading to the formation of AlTMPyP(O-OH) (~ 67 µs), which reacts further with OH-/H2O to liberate free hydrogen peroxide as an end-product with regeneration of the starting catalyst, AlTMPyP(OH), (~ 550 µs).

We report herein a new molecular catalyst for efficient water splitting, aluminum porphyrins (tetra-methylpyridiniumylporphyrinatealuminum: AlTMPyP), containing earth's most abundant metal as the central ion. One-electron oxidation of the aluminum porphyrin initiates the two-electron oxidation of water to form hydrogen peroxide as the primary reaction product with the lowest known overpotential (97 mV). The aluminum-peroxo complex was detected by a cold-spray ionization mass-spectrometry in high-resolution MS (HRMS) mode and the structure of the intermediate species was further confirmed using laser Raman spectroscopy, indicating the hydroperoxy complex of AlTMPyP to be the key intermediate in the reaction. The two-electron oxidation of water to form hydrogen peroxide was essentially quantitative, with a Faradaic efficiency of 99 %. The catalytic reaction was found to be highly efficient, with a turnover frequency up to ∼2×104 s-1 . A reaction mechanism is proposed involving oxygen-oxygen bond formation by the attack of a hydroxide ion on the oxyl-radical-like axial ligand oxygen atom in the one-electron-oxidized form of AlTMPyP(O- )2 , followed by a second electron transfer to the electrode.

Nano-layered hybrid compounds composed of a polyfluoroalkyl azobenzene surfactant (abbreviated as C3F-Azo-C6H) and layered inorganic nanosheets undergo three-dimensional morphological changes such as reversible shrinkage and expansion of interlayer spaces, and nanosheet sliding by photo-irradiation. Previously, we have investigated the photoreactivity of C3F-Azo-C6H/clay nano-layered hybrids in various microenvironments and found a remarkable enhancement in the photoreactivity for the cis-trans photo-isomerization reaction (Φcis-trans = 1.9). In this paper, nanosecond and microsecond dynamics of trans-C3F-Azo-C6H and its assembly in various microenvironments have been studied by laser flash photolysis to get deeper insight into the extraordinary reactivity of the molecular assembly in the nano-layered microenvironment. In solution, the molecular trans-C3F-Azo-C6H exhibited only a depletion of the trans-form of azobenzene upon the laser pulse excitation. On the other hand, in the case of the C3F-Azo-C6H/clay hybrid film, the depletion of the trans-form was drastically recovered in three steps on nano- and microsecond timescales. This indicates that the once reacted C3F-Azo-C6H molecule (cis-C3F-Azo-C6H) was reverted back to the trans-form after the laser pulse. It is considered that the excess energy provided by the photo-excitation, which is immediately dissipated to the surrounding media through the intermolecular vibrational modes in solution, is trapped in the nano-layered microenvironment to thermally revert the cis-form back to the trans-form. Conversely, in the case of cis-trans isomerization of the C3F-Azo-C6H/clay hybrid film upon photo-irradiation, the reactivity would be much enhanced by the additional contribution of the thermal excess energy efficiently trapped in the nano-layered microenvironment. As compared with the hydrocarbon analogue (C3H-Azo-C6H), the subsequent recovery was very much enhanced in the C3F-Azo-C6H/clay film. The polyfluoroalkyl part of the surfactant layer plays a key role in the retarded dissipation of the excess energy by photo-excitation, which might be coupled with the three-dimensional morphological motion with efficient isomerization reactions.

Photo-responsive nanoscrolls can be successfully fabricated by mixing a polyfluoroalkyl azobenzene derivative and a niobate nanosheet, which is exfoliated from potassium hexaniobate. In this study, we have found that the photo-responsive nanoscroll shows a morphological motion of winding and unwinding, which is basically due to the nanosheet sliding within the nanoscroll, by efficient photo-isomerization reactions of the intercalated azobenzene in addition to the interlayer distance change of the nanoscrolls. The relative nanosheet sliding of the nanoscroll is estimated to be ca. 280 nm from the AFM morphology analysis. The distance of the sliding motion is over 20 times that of the averaged nanosheet sliding in the azobenzene/niobate hybrid film reported previously. Photo-responsive nanoscrolls can be expected to be novel photo-activated actuators and artificial muscle model materials.

Aluminium(III)-tetramesitylporphyrin, with the Earth’s the most abundant metal and the third most abundant element as the Al(III) ion, induces the photochemical oxygenation of cyclohexene in deaerated aqueous acetonitrile to form the corresponding epoxide and alcohol with water as both electron and oxygen atom donor upon visible light irradiation. The Al(III) should be the most available and meaningful element to be utilized in the artificial photosynthetic unit. The excited triplet state of the water-coordinated porphyrin is responsible for the photochemical oxygenation.

Silicon as the second most abundant element on Earth was effectively utilized as the central atom in the porphyrin to induce photochemical oxygenation of alkenes as the first example of photocatalytic reaction through activation of water molecule in the presence of K2PtCl6 as an electron acceptor. Oxygen atom of water was confirmed to be incorporated in the oxygenated product by the photoreaction with H218O. The excited triplet state of silicon porphyrin was revealed to be responsible for the photochemical oxygenation. The one-electron oxidized silicon porphyrin was predicted by DFT calculation to have its spin population mostly on the axially ligated hydroxyl oxygen atom. The oxyl radical character of the axial ligand could rationalize the oxygenation reaction.

A new water-soluble silicon(IV)-tetra(4-carboxyphenyl)porphyrin (SiTCPP) with silicon(iv), the second most abundant element on Earth, in the center of porphyrin was synthesized. Fundamental properties including protolytic behaviour of axially coordinating hydroxy groups, and electrochemical behaviour were characterized. The properties were compared with those of silicon(IV)-tetra(2,4,6-trimethylphenyl)porphyrin (SiTMP) and silicon(IV)-tetra(4-trifluoromethylphenyl)porphyrin (SiTFMPP) and discussed in respect to the electron donating/withdrawing effect of the substituents. Two axially coordinating hydroxy groups of SiTCPP exhibit a four-step protolytic behaviour under the acidic conditions along with a single step protolysis of peripheral carboxyl groups. Though SiTCPP and SiTFMPP did not show any reactivity in the photochemical oxygenation of a substrate with K2PtCl6 as a sacrificial electron acceptor, the first oxidation wave in the electrochemical process of SiTCPP and SiTFMPP showed catalytic behaviour in aqueous acetonitrile solution at any pH condition, in contrast to SiTMP which has only a reversible oxidation wave under neutral and weakly acidic conditions. The criteria for the electrochemical oxidative activation of water and the photooxygenation of the substrate were obtained. The higher oxidation wave of Si-porphyrins than ∼0.86 volt vs. SHE is required for the electrochemical oxidation of water, while suitable protecting groups such as a methyl substituent is a requisite for the photochemical oxygenation with K2PtCl6 as a sacrificial electron acceptor.

Novel environment-benign one-pot syntheses of water-soluble porphyrins, trans-dihydroxy-5,10,15,20-tetra(N-methyl-4′-pyridiniumyl)porphyrinate tin(IV) (Sn(IV)TMPyP(OH)2) and water-insoluble trans-dihydroxy-5,10,15,20-tetra(4-pyridyl)porphyrinate tin(IV) (Sn(IV)TPyP(OH)2), were found to proceed in water as solvent at room temperature with high yield (90 and 93%).

Water-soluble cationic 5,10,15,20-tetra(N-methyl-4′-pyridiniumyl)porphyrinatoaluminum(III) (AlTMPyP) has been synthesized by novel one-pot reaction between the parent free-base porphyrin and trimet...

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 CO2-saturated DMF solution showed a constant cathodic photocurrent upon visible light irradiation (λ = 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 CO2 photoreduction system as the reduction terminal end of an artificial photosynthetic system.

Organic-inorganic hybrids composed of polyfluoroalkyl azobenzene surfactant (abbreviated as C3F-Azo-C6H) and inorganic layered compounds are able to undergo reversible three-dimensional morphology changes such as interlayer space changes and nanosheet sliding in a giant scale due to reversible trans-cis isomerization of the azobenzene moiety upon photo-irradiation. In this paper, we have systematically studied the relationship between the layered hybrid microstructures of C3F-Azo-C6H-clay and their photoreactivity for understanding the mechanism of the photo-induced morphology change. The photoreactivity was found to be very much affected by the surrounding microenvironments. As compared with it in solution, the cis-trans photo-isomerization in C3F-Azo-C6H-clay nano-layered film was substantially enhanced with the quantum yield exceeding unity (Φ = 1.9), while the trans-cis isomerization was rather retarded. The corresponding hydrocarbon analogue of the azobenzene surfactant (C3H-Azo-C6H) did not show such an enhancement. The enhancement was discussed in terms of a cooperative effect among adjacent azobenzene moieties along with polyfluoroalkyl chains and the inorganic clay nanosheet to prevent a dissipation of the excess energy being liberated during the photo-isomerization within the nano-layered microenvironment.

Water-soluble cationic 5,10,15,20-tetra(N-methyl-4′-pyridiniumyl)porphyrinatoaluminum(III) (AlTMPyP) has been synthesized by novel one-pot reaction between the parent free-base porphyrin and trimet...

The orientation of nanomaterials with an anisotropic nature such as nanoscrolls is very important for realizing their efficient and sophisticated functions in devices, including nanostructured electrodes in artificial photosynthetic cells. In this study, we successfully synthesized a nanoscroll by intercalation of a cationic polyfluorinated surfactant into the interlayer spaces of layered niobate and successfully controlled its orientation by applying an external magnetic field in water. The exfoliated niobate nanosheets were efficiently rolled-up to form nanoscrolls, which have a fine layered structure (d020 = 3.64 nm), by mixing with heptafluorobutanoylaminoethylhexadecyldimethylammonium bromide (C3F-S) in water, whereas the corresponding hydrocarbon analogue (C3H-S) did not form nanoscrolls. The synthetic yield for the purified and isolated nanoscrolls from the nanosheets was estimated to be 62% by weight. It was confirmed by atomic force microscopy (AFM) that most of the niobate nanosheets (98%) were converted to nanoscrolls. An external magnetic field was applied to the nanoscrolls to force them to align. After the magnetic treatment, the orientation of the nanoscrolls was investigated by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The non-uniform ring distribution of the SAXS patterns indicates that the nanoscrolls dispersed in water were aligned well on applying the magnetic field. The long axis of the nanoscroll was oriented in the direction of the applied field and long nanoscrolls were aligned more efficiently. When the intercalated C3F-S molecules were removed from the nanoscrolls by treating with an acid, the resultant nanoscrolls did not exhibit magnetic alignment, strongly suggesting that C3F-S plays an important role in the orientation control of the nanoscrolls by the magnetic field.

Visible-light-driven H(2) evolution based on Dye/TiO(2)/Pt hybrid photocatalysts was investigated for a series of (E)-3-(5'-{4-[bis(4-R(1)-phenyl)amino]phenyl}-4,4'-(R(2))(2)-2,2'-bithiophen-5-yl)-2-cyanoacrylic acid dyes. Efficiencies of hydrogen evolution from aqueous suspensions in the presence of ethylenediaminetetraacetic acid as electron donor under illumination at λ>420 nm were found to considerably depend on the hydrophilic character of R(1), varying in the order MOD (R(1)=CH(3)OCH(2), R(2)=H)≈MO4D (R(1)=R(2)=CH(3)OCH(2))>HD (R(1)=R(2)=H)>PD (R(1)=C(3)H(7), R(2)=H). In the case of MOD/TiO(2)/Pt, the apparent quantum yield for photocatalyzed H(2) generation at 436 nm was 0.27±0.03. Transient absorption measurements for MOD- or PD-grafted transparent films of TiO(2) nanoparticles dipped into water at pH 3 commonly revealed ultrafast formation (

The reaction mechanism of the highly efficient (phi = 0.60), selective photochemical epoxidation of alkenes sensitized by CO-coordinated tetra(2,4,6-trimethyl)phenylporphyrinatoruthenium(II) (Ru(II)TMP(CO)), with water acting both as an electron and oxygen atom donor, was investigated. The steady-state light irradiation of the reaction mixture indicated the formation of the Ru(II)TMP (CO) cation radical under neutral conditions, which was effectively trapped by an hydroxide ion to regenerate the starting sensitizer. By means of a laser flash photolysis experiment, the formation of the cation radical as the primary process from the triplet excited state of Ru(II)TMP(CO) was clearly observed. Four kinds of transients were detected in completely different ranges of the delay time: the excited triplet state of Ru(II)TMP(CO) [delay time region20 micros], the cation radical of Ru(II)TMP(CO)(CH3CN) [20-50 micros], the hydroxyl-coordinated Intermediate [I] [50-200 micros], and the cyclohexane-attached Intermediate [II] [200 micros-8 ms]. A reaction mechanism was revealed that involves RuTMP(CO) cation radical formation from the triplet excited state of the sensitizer, followed by attack of an hydroxide ion to form an hydroxyl-coordinated Ru-porphyrin (Intermediate [I]) and subsequent reaction with cyclohexene to form Intermediate [II]. The kinetics for each step of the successive processes was carefully analyzed and their rate constants were determined. The two-electron oxidation of water by one-photon irradiation, as revealed in the photochemical epoxidation, is proposed to be one of the more promising candidates to get through the bottleneck of water oxidation in artificial photosynthesis.

A polymer microassembly is formed by focusing a near-infrared (NIR) laser beam in a thin film of a polymer solution. We have investigated the mechanism of laser microdeposition of a polyfluorene assembly by measuring the surface deformation of the solution film and the morphology of the deposited assembly. It is clearly observed that a rupture is formed at the laser focus in the solution film by using laser interferometric imaging. The time necessary for the rupture formation and the volume of the deposited microassembly are analyzed as a function of laser power. Experimental results suggest that the solution surface deformation induced by local laser heating and optical trapping effects determined the volume of the laser microdeposition. By combining this method with multiple optical trapping, a polymer microassembly with a polygonal morphology is formed on the glass substrate.

We have demonstrated the laser deposition of polymer micro- and nanoassemblies from a solution onto a glass substrate. The size and shape of the deposited dot-like assembly can be controlled by the laser power (P) and the concentration of the solution (C). For an example, a nanoassembly of a π-conjugated polymer, whose width and height are 280 and 23 nm, respectively, is deposited at the conditions of C=1.0×10-5 mg/ml and P=700 mW. This laser deposition can be attributed to the optical trapping and the surface deformation of the solution layer using a focused laser beam. It is also demonstrated that the molecular orientation in the assembly can be aligned in the direction of the laser polarization. The present laser deposition is applicable to the micropatterning of various polymers dissolved in an organic solvent.

The thin film of poly[2-methoxy, 5-(2′-ethyl-hexyloxy- p -phenylene vinylene)] (MEH-PPV) was prepared on a glass plate by the spin coating of a chloroform solution. The mesoscopic structures and fluorescence dynamics of the MEH-PPV thin film in small domains were analyzed by AFM and picosecond time-resolved fluorescence SNOM. A wheel structure of MEH-PPV with a sub-μm to a few μm in diameter was found, the size of which was dependent on the position of the film. The formation mechanism of the MEH-PPV wheel and the position dependence of the wheel size were interpreted in terms of the two-dimensional (2D) gas bubble model. A good correlation between the shear-force topography and the fluorescence SNOM image was obtained. The fluorescence decay of the single-chain exciton was found to be much faster in the circumference of the wheel than in the surroundings or the inside of the wheel, which was probably due to the exciton migration among the polymers and trapping by the aggregate of MEH-PPV.

Hydrogen evolution coupled with the photochemical oxygenation of cyclohexene with water was observed in the system sensitized by Sn(IV)–porphyrin adsorbed on Pt loaded TiO2 nano-particles in aqueous acetonitrile solution upon visible light irradiation.

One of the most promising solutions to the current global problems of energy and the environment would be to develop a clean system for the chemical conversion of solar energy, for example, photochemical hydrogen evolution and carbon dioxide fixation. In both cases, the water molecule should be the electron source, as is the case with natural photosynthesis. The point of research in this area is to discover how the electrons of water can best be utilized. The oxidation of water can be approached through (a) one-electron (b) two-electron and (c) four-electron processes. In spite of remarkable progress of molecular catalysts, the visible light-induced oxidation of water to molecular oxygen via the four-electron process has been one of the bottle-necks in the field, mostly due to the photon-flux density problem of sunlight, with its intrinsically limited intensity. A photochemical method for the four-electron oxidation of water requires four photons to excite sensitizers and catalysts in a stepwise manner in order to reach the higher oxidized states. Under typical sunlight conditions, the time interval between the arrivals of photons to a single molecule is on the order of seconds, which is far longer than the usual timescale for the survival of the highly unstable oxidized states needed to elicit the catalytic activity. Alternative approaches thus are clearly required. In this context, we have been studying the one-electron initiated two-electron oxidation of water. The latest results on the oxidation of water catalyzed by earth-abundant metalloporphyrins will be reported.

A novel photoactivated artificial muscle model unit is reported. Here we show that organic/inorganic hybrid nanosheets reversibly slide horizontally on a giant scale and the interlayer spaces in the layered hybrid structure shrink and expand vertically by photoirradiation. The sliding movement of the system on a giant scale is the first example of an artificial muscle model unit having much similarity with that in natural muscle fibrils. In particular, our layered hybrid molecular system exhibits a macroscopic morphological change on a giant scale (∼1500 nm) relative to the molecular size of ∼1 nm by means of a reversible sliding mechanism.

We have demonstrated size-selective optical trapping and deposition of polymer and aromatic molecules from binary mixed solution. As a near-infrared laser beam is tightly focused in polystyrene and perylene mixed solution and dropped on a glass substrate, a molecular assembly is deposited at the laser focus and fixed on the substrate. The fluorescence spectrum of the deposited microassembly depends on the laser power; perylene monomer fluorescence is dominant in the case of high laser power, whereas excimer emission of perylene crystal is observed in the case of low laser power. This suggests that polystyrene molecules are preferentially deposited by focusing a higher laser power so that the ratio of polystyrene and perylene in the assembly can be controlled by laser power. This mechanism can be explained in view of the molecular size selectivity in optical trapping.

ZnOxSe1−x layers with x ≤ 1.35% were studied by photoreflectance at 80 K. Careful analysis of the PR spectra allowed the identification of the optical transitions from the valence band to the E− and E+ subbands originating from the band anticrossing interaction between the resonant oxygen level and the conduction band of the ZnSe host. In addition, it was possible to resolve a strain-induced splitting of the valence band into the heavy- and light-hole subbands. The strain changes from compressive to tensile with increasing oxygen concentration for these ZnOxSe1−x layers grown on a GaAs substrate.