Noritsugu Kometani

Synthesis and Spectroscopic Studies of Composite Gold Nanorods with a Double-Shell Structure Composed of Spacer and Cyanine Dye J-Aggregate Layers

The composite gold nanorods (Au NRs) having a double-shell structure composed of Au NR (core), spacer layer (inner shell), and J-aggregate (JA) layer (outer shell) have been synthesized to examine the spectroscopic properties of the hybrid system in which the localized surface plasmon is coupled with the molecular exciton of JA. The spacer layer consisting of N,N,N-trimethyl(11-mercaptoundecyl)ammonium chloride plays a significant role in the formation of JA shell for several kinds of cyanine dyes. The absorption spectra of composite NRs are characterized by a distinct dip near the J-band when the plasmon energy of Au core is close to the exciton energy of JA shell, whereas a normal J-band peak appears when two energies are widely different from each other. The gradual change from the dip type to peak type absorption was observed when the plasmon energy was modulated by varying the aspect ratio of Au NR. Furthermore, composite NRs with thicker spacer layers have been fabricated by inserting the multilayer shell of polyelectrolytes between TMA and JA layers. They exhibited an alteration of the spectral line shape from the dip type to peak type with increase in the thickness of spacer layer. These observations have been interpreted in terms of the strength of the exciton-plasmon coupling, which is sensitive to the configuration of composite NRs as well as the relative difference between plasmon and exciton energies.

Tuning of the spectroscopic properties of composite nanoparticles by the insertion of a spacer layer: effect of exciton-plasmon coupling.

Composite nanoparticles (NPs) having a double-shell structure, Au core, spacer layer (inner shell), and J-aggregate (JA) layer (outer shell) (Au/spacer/JA) have been synthesized. The spacer layer composed of N,N,N-trimethyl(11-mercaptoundecyl)ammonium chloride played an important role in promoting the J-aggregation of anionic cyanine dyes on the surface, as evidenced by the successful formation of the JA layers with four kinds of anionic cyanine dyes. It was found that the presence of a spacer layer causes a significant change in the line shape of the absorption spectrum, particularly near the J-band; there is the appearance of a peak type absorption for the composite NPs with the double-shell structure, while there is a dip type absorption for the ones without the spacer layer. The change from the peak type absorption to the dip type absorption in the Au/spacer/JA NPs occurs when the size of the Au core is varied from 5 to 15 nm. These observations would indicate that the strength of exciton-plasmon coupling between the Au core and the JA layer is enhanced with the increase in the core size or the decrease in the separation between the Au core and the JA shell. The photoluminescence arising from the JA can be detected for the composite NPs with the double-shell structure, showing that the quenching by the Au core is effectively suppressed by the spacer layer.

Laser flash photolysis study of the photochemical formation of colloidal Ag nanoparticles in the presence of benzophenone

Sensitized photoreduction of Ag+ ions and subsequent formation of colloidal Ag nanoparticles take place when an aqueous solution of a mixture of AgClO4, sodium dodecylsulfate (SDS) and benzophenone (BP) is irradiated with near-UV light. In this study, the mechanism and kinetics of the reaction have been studied by means of nanosecond laser flash photolysis, time-resolved emission spectroscopy and also steady-state photolysis. Benzophenone ketyl radial (BPK) is formed by the hydrogen abstraction reaction of the benzophenone triplet (BPT) from SDS, which reduces Ag+ ions. It is found that the yield of colloidal Ag nanoparticle formation decreases remarkably with increasing concentration of Ag+ ions, indicating the efficient quenching process of BPT by Ag+ ions. Rate constants for the oxidation of BPK as well as the quenching of BPT by Ag+ ions in SDS micellar solution are considerably larger than those expected in the bulk solution, reflecting that Ag+ ions and BP molecules are concentrated in the SDS micelles. The rate of colloidal Ag nanoparticle formation, VAg, and BP photobleach, VBP, under steady-state irradiation with near-UV light (λ = 365 nm) were evaluated and the dependence of VAg and VBP on the concentration of Ag+ ions is interpreted quantitatively in terms of rate constants estimated by laser flash photolysis.

Solvation dynamics in a microemulsion in near-critical propane

Abstract Solvation dynamics of coumarin 343 (C343) is studied in AOT microemulsion in near-critical propane. It is observed that the solvation dynamics for a water pool of w 0 =15 at 10 MPa pressure is described by bimodal behavior having a short component of 215 ps (47%) and a long component of 14 ns (53%). These components are similar to those detected for other probes in microemulsions at 0.1 MPa pressure. This indicates that the water pool is unaffected by pressure. The slow dynamics is ascribed to the restricted mobility of the water molecules confined within the pool.

Excited-state dynamics of the mixed J-aggregate of two kinds of cyanine dyes in layer-by-layer alternate assemblies

Abstract Layer-by-layer alternate assemblies, which incorporate two kinds of cyanine dyes in the form of mixed J-aggregates, were fabricated by means of the alternate adsorption method. The excited-state dynamics of the mixed J-aggregates were examined by steady-state fluorescence spectroscopy and picosecond lifetime measurements. In these assemblies, the behavior of excitation energy transfer between the donor and acceptor J-aggregates obeyed Stern–Volmer kinetics in the low concentration region of the acceptor molecules. It was found that both the fluorescence lifetime and quantum yield of the acceptor aggregates decrease with increasing concentration of the acceptor molecules, which indicates that fluorescence self-quenching occurred in the acceptor aggregates.

Degradation of Chlorobenzene by the Hybrid Process of Supercritical Water Oxidation and TiO2 Photocatalysis

A novel hybrid process of hydrothermal or supercritical water oxidation and TiO2 photocatalysis was developed to examine the degradation of chlorobenzene as a model of the oxidative decomposition of organic pollutants. Aqueous solutions of chlorobenzene containing H2O2 as the oxidizing agent and/or colloidal TiO2 nanoparticles as catalyst, were fed into the reactor with the temperature and the pressure controlled to be T = 25–400°C and P = 30 MPa, respectively. Chlorobenzene was considerably decomposed in the presence of H2O2 under hydrothermal conditions for T ≧ 300°C. It appeared that photocatalytic decomposition of chlorobenzene takes place at all temperatures by colloidal TiO2 nanoparticles under irradiation with near-UV light. We have realized the synergic decomposition of chlorobenzene by the coexistence of H2O2 and TiO2 in which maximum conversion is more than 80% under irradiation at T = 200°C.

In Situ Observations of Thermoreversible Gelation and Phase Separation of Agarose and Methylcellulose Solutions under High Pressure.

Thermoreversible sol-gel transitions of agarose and methylcellulose (MC) aqueous solutions on isobaric cooling or heating under high pressure up to 400 MPa have been investigated by in situ observations of optical transmittance and falling-ball experiments. For agarose, which undergoes the gelation on cooling, the application of pressure caused a gradual rise in the cloud-point temperature over the whole pressure range examined, which is almost consistent with the pressure dependence of gelling temperature estimated by falling-ball experiments, suggesting that agarose gel is stabilized by compression and that the gelation occurs nearly in parallel with phase separation under ambient and high-pressure conditions. For MC, which undergoes the gelation on heating, the cloud-point temperature showed a slight rise with an initial elevation of pressure up to ∼150 MPa, whereas it showed a marked depression above 200 MPa. In contrast, the gelling temperature of MC, which is nearly identical to the cloud-point temperature at ambient pressure, showed a monotonous rise with increasing pressure up to 350 MPa, which means that MC undergoes phase separation prior to gelation on heating under high pressure above 200 MPa. Similar results were obtained for the melting process of MC gel on cooling. The unique behavior of the sol-gel transition of MC under high pressure has been interpreted in terms of the destruction of hydrophobic hydration by compression.

High-pressure study of solvation properties of room-temperature ionic liquids

The solvation properties of some room-temperature ionic liquids consisting of imidazolium cations and various anions were examined by means of the high-pressure spectroscopy with solvatochromic probes. We measured the pressure dependence of Kamlet-Taft solvatochromic parameters (π*, β) and microviscosity (η). It was found that π* and β were not so sensitive to the types of imidazolium cations and polyatomic anions, but the type of monoatomic anions. The pressure dependence of microviscosity was found to obey the empirical power-law equation.

Photocatalytic Degradation of Chlorobenzene by in High-Temperature and High-Pressure Water

A fluidized-bed-type flow reactor available for the photocatalytic treatment of the suspension of model soil under high-temperature, high-pressure conditions was designed. An aqueous suspension containing hydrogen peroxide () as an oxidizer and inorganic oxides as a model soil, titania (), silica (), or kaoline () was continuously fed into the reactor with the temperature and the pressure controlled to be and  = 30 MPa, respectively. The degradation of chlorobenzene (CB) in water was chosen as a model oxidation reaction. It appeared that most of the model soils are not so harmful to the SCWO treatment of CB in solutions. When the suspension containing was irradiated with near-UV light, the promotion of the degradation caused by photocatalytic actions of was observed at all temperatures. Persistence of the photocatalytic activity in the oxidation reaction in high-temperature, high-pressure water would open up a possibility of the development of the hybrid process based on the combination of SCWO process and photocatalysis for the treatment of environmental pollutants in soil and water, which are difficult to handle by conventional SCWO process or catalytic SCWO process alone.

Ab initio calculation of the torsional potential for 2-alkenylanthracene in the ground and excited states

Abstract Torsional potentials between the anthracene ring and alkene planes for two 2-alkenylanthracene derivatives both in the ground- and excited-states were calculated using ab inito method as a function of dihedral angle. Molecular geometries were optimized at the restricted Hartree–Fock level in the ground-state, whereas in the excited-state at the level of configuration interaction with single excitation. In the ground-state it is s- trans conformation that is more stable and more planar. While in the excited-state both are planar and the potential shape is more like symmetrical for 2-vinylanthracence, although somewhat distorted for 2-(2 ′ propenyl) anthracene. Stabilization energies, barrier energies, and barrier top frequencies of both ground- and excited-states were determind