Tomoo Sato

Photochemical formation of colloidal metals

Colloidal silver and gold have been formed by irradiation of AgClO4 and HAuCl4 solutions with 253.7 nm light in the presence of protective agents such as sodium dodecylsulphate, sodium alginate and colloidal silica. Absorption maxima of colloidal silver and gold have been observed at 390–420 and 540–560 nm, respectively. Colloidal metals have been purified by dialysis and their amounts analysed quantitatively. The quantum yields of metal deposition are 0.053–0.15 for colloidal silver and 0.030–0.039 for colloidal gold. The quantum yield is increased several times by the use of protective agents, with the exception of a AgClO4–sodium alginate solution.

Photochemical formation of colloidal silver: peptizing action of acetone ketyl radical

When an aqueous AgClO4–sodium dodecylsulphate (SDS)–isopropyl alcohol (Pri OH) solution was photolysed with 253.7 nm light, a sharp and intense absorption band of colloidal silver (λ= 390–400 nm) appeared after a relatively long induction period. In contrast, the sharp colloidal absorption rapidly developed when an AgClO4–SDS–acetone [(CH3)2CO] solution was irradiated under the same conditions. It has been shown by chemical analysis and TEM characterization of the reduced silver that some of the colloidal silver agglomerates formed as a result of photolysis were peptized to fine silver particles during irradiation. Acetone ketyl radical formed by excitation of (CH3)2CO with 253.7 nm light seems to have an ability to peptize colloidal agglomerate in the solution phase (peptizing action). A novel ‘photo-acetone method’ available for preparation of fine metal particles has been proposed and applied to obtain colloidal gold, copper and platinum.

Photochemical formation of silver metal films from silver salt of natural high molecular carboxylic acid

Thin films of silver salt of alginic acid, a typical high molecular carboxylic acid in nature, were photolyzed by 253.7 nm light. On irradiating with a 15‐W sterilization lamp in air at relative humidity of more than 70%, the silver alginate films first became yellow‐brown colored due to formation of photolytic colloidal silver particles. When irradiation was continued, the irradiated surface of the films finally changed into clear silver mirror. The morphology of these films was observed by means of a high‐resolution scanning electron microscope. Colloidal silver particles (10–50 nm diam) formed by a short‐time irradiation were sparsely distributed at the film surface. As a result of prolonged irradiation for ∼180 min, film surface was covered with aggregated colloidal silver. The x‐ray diffraction study of the irradiated films revealed sharp diffraction lines, indicating that the colloidal silver was in a highly crystalline state. A preliminary observation of a microtomed cross section of the film showe...

Nonlinear optical properties of silver sols prepared by photoreduction method

Abstract The third-order nonlinear susceptibility ( χ (3) of silver sol prepared by a photochemical method was measured by the degenerate four-wave mixing method. The χ (3) of the silver sol of brown-green color was larger than that of yellow-brown color. The photo-induced aggregation of silver particles affects the χ (3) of the sol. It has been found that the χ (3) of the silver sol is proportional to the intensity of surface-enhanced raman scattering from carboxylate ions adsorbed on the silver particle. The increase of χ (3) by the enhanced local electric field due to surface plasmon resonance is proposed.

Structure and photoelectrochemical properties of ITO electrodes modified with self-assembled monolayers of meso, meso-linked porphyrin oligomers

A systematic series of ITO electrodes modified chemically with self-assembled monolayers (SAMs) of meso, meso-linked porphyrin oligomers have been designed to provide valuable insight into the development of artificial photosynthetic devices. Photoelectrochemical measurements were carried out in an argon-saturated 0.1 M Na2SO4 aqueous solution containing methyl viologen (MV2+) as an electron acceptor or triethanolamine (TEA) as a sacrificial electron donor in a three electrode system including the modified ITO electrodes. The action spectrum of porphyrin oligomer SAMs exhibits photocurrent generation in a wide wavelength region, demonstrating the enhancement of light-harvesting properties in the visible region. The relative integrated value of the action spectrum as well as the quantum yield of photocurrent generation of the porphyrin oligomer SAMs increases with increasing the number of the porphyrins. These results clearly show that our strategy is highly promising for improving light energy conversion efficiency.

Hydrogen bonding effect on photocurrent generation in porphyrin–fullerene photoelectrochemical devices

A hydrogen bonding effect on photocurrent generation has been evaluated successfully in a mixed film of porphyrin and fullerene with hydrogen bonding on an ITO electrode, which exhibits efficient cathodic photocurrent generation as compared to the reference system without hydrogen bonding.

Photochemical deposition of noble metal ultrafine particles onto liposomes

Composite particles consisting of liposomes loaded with silver or gold ultrafine particles have been prepared by UV irradiation (λ=253.7 nm) of AgClO 4 or NaAuCl 4 aqueous solutions in the presence of l-α-dimyristoyl phosphatidylcholine liposomes. The diameter of the metal particles was <5–7 nm. The absorption peak of the composite particles was observed at λ=380–390 (silver) or 540 nm (gold). The absorption spectra of the liposome/silver composite particles were broad and weak. The quantum yield of photoreduction of silver ions increased in the presence of liposomes. The usefulness of the liposome as a matrix for loading and stabilizing the noble-metal ultrafine particles has been demonstrated.

Photoelectric response of black lipid membranes incorporating an amphiphilic azobenzene derivative

Abstract The planar bilayer lipid membrane (BLM) of egg lecithin containing amphiphilic azobenzene 8A5 (approx. 10 mol%) was fabricated. Electrical properties of the BLM were examined to clarify the mechanism of the recently observed novel photoelectric response; transient photocurrent and the change of AC impedance by alternate irradiation with UV and visible light. It has been concluded that the photoelectric response is caused by the change of membrane capacitance due to cis-trans isomerization of 8A5.

Preparation and luminescence properties of the J aggregate of cyanine dyes in phospholipid Langmuir- Blodgett films

Abstract The J aggregate of two cyanine dyes—dye I (5,6,5′,6′-dibenzo-1,1′-diethyl-2,2′- cyanine chloride) and dye II (5,5′-dichloro-3,3′-diethyl-9-phenyl-thiacarbocyanine chloride)—can be incorporated into acidic-phospholipid-containing Langmuir- Blodgett (LB) films. Dipalmitoyl-phosphatidylcholine (DPPC) and dipalmitoyl- phosphatidic acid (DPPA) were used for preparation of the LB films. An observation that J aggregation was difficult in the absence of negatively charged lipid species (DPPA) in the membrane reconfirms the importance of electrostatic interaction between negative charge at the matrix molecules and positive charge at the chromophore. The luminescence properties of the J aggregate in the more elaborate LB films with dye I and dye II aggregates at the same lipid surface were examined and interpreted in terms of excitation energy transfer from dye I to dye II aggregates.

Excitation energy transfer between J-aggregates of cyanine dyes in Langmuir-Blodgett films and liposomes

Abstract LB films and liposomes incorporating J-aggregates of two kinds of cyanine dyes at the same membrane surface have been prepared. Four cyanine dyes, 1,1′-diethyl-2,2′-cyanine chloride or iodide (dye-I), 5,6,5′,6′-dibenzo-1,1′-diethyl-2,2′-cyanine chloride (dye-II), 5,5′-dichloro-3,3′-diethyl-9-phenylthiacarbocyanine chloride (dye-III), 3,3′-dimethyl-9-phenyl-4,5,4′,5′-naphthothiacarbocyanine chloride (dye-IV) were employed. In the case of a couple of dye-II:dye-III aggregates, quenching of resonance fluorescence of dye-II aggregate and sensitization of resonance fluorescence of dye-III aggregate, due to excitation energy transfer, were observed. The energy transfer also occurs in the dye-I:dye-III, dye-I:dye-IV, dye-II:dye-IV aggregates. In these cases, quinocyanine dye (dye-I, dye-II) aggregates and thiacarbocyanine dye (dye-III, dye-IV) aggregates act as the energy donor and acceptor, respectively.