We have synthesized small silver clusters in aqueous microemulsion droplets in supercritical carbon dioxide (sc-CO
2) solutions with fluorinated surfactants; ammonium carboxylate perfluoropolyether, ...PFPE-1, PFPE-2 and PFPE-3. Irradiation of water-in-sc-CO
2 (w/c) microemulsions of PFPE-1 containing concentrated AgClO
4 solution within the water core (local concentration AgClO
4
=
5.0
M) at
P
=
36.3
MPa and
T
=
311
K with weak UV light resulted in the appearance of a broad absorption band in the
λ
=
320–400
nm range with a small peak around
λ
=
330
nm and a shoulder around
λ
=
370
nm in the UV–vis absorption spectra. Irradiation of the w/c microemulsions of PFPE-2 containing AgClO
4
=
5.0
M with intense UV light brought about the development of almost the same absorption band at the early stage. Then a single broad peak bearing the absorbance as large as about 3.0 around
λ
=
340
nm developed after prolonged irradiation. Those spectral features would demonstrate the formation of small Ag clusters, Ag
n
, due to photoreduction of Ag
+ ions inside of water core of the w/c microemulsions. Although the absorption spectrum gradually changed during dark storage at
P
=
30
MPa and
T
=
311
K, there was no indication of the surface plasmon band even after 20
h storage, indicating that the growth of colloidal Ag nanoparticles, Ag
c, by agglomeration of small Ag clusters does not proceed because microemulsions are separated each other in the sc-CO
2. These observations would suggest that the w/c microemulsion is an excellent “nanoreactor” to confine the reaction field on the nanometer scale.
The monolayer assemblies incorporating merocyanine J-aggregates, MC(S), MC(Se), 6-Me-MC(S), and their combinations have been fabricated by the Langmuir–Blodgett (LB) technique. At room temperature, ...absorption and fluorescence spectra of the monolayer assemblies: MC(S), MC(Se), 6-Me-MC(S), are characterized by a sharp J-band and resonance fluorescence. The monolayer assemblies incorporating two dyes: MC(S)/MC(Se), 6-Me-MC(S)/MC(S), 6-Me-MC(S)/MC(Se), bear a single absorption band and accompanying fluorescence band, which are assigned to the homogeneous aggregate of amalgamation type (HA-aggregate). Detailed spectroscopic measurements: absorption spectra in wide temperature range and the fluorescence decay curves, of the MC(S)/MC(Se) assembly have been carried out as a prototype of the HA-aggregate. The continuous shift of the absorption and fluorescence peak positions with increasing
x, from
x
=
0 (MC(S) assembly) to
x
=
1 (MC(Se) assembly), would indicate that the doping of MC(Se) molecules into the MC(S) J-aggregate does not induce serious structure change. An observation that the fluorescence lifetime of the MC(S)/MC(Se) assembly lies between those of the MC(S) assembly and the MC(Se) assembly implies that the inclusion of MC(Se) molecules does not result in the formation of defect states which may promote non-radiative decay of molecular excitons. The usefulness of the Urbach–Martienssen (UM) rule for the analysis of the low energy tail of absorption spectra of the MC(S)/MC(Se) assembly has been examined.
Langmuir-Blodgett (LB) films incorporating two kinds of unsymmetrical merocyanine dyes (MC (X)/MC (Y) X, Y=O, S, Se) have been fabricated by using octadecane (OD) and arachidic methyl ester (AME) as ...the matrix molecules; MC (X);MC (Y): 0D;AME = (1-x);x: 1: 1. Absorption spectra of the MC (X) assembies and the mixed assemblies (MC (X)/MC (Y)) have been measured in wide temperature range T=6.0-293 K. The relationship between the absorption coefficient of the low-energy tail of the aggregate band and incident photon energy has been analyzed in the framework of the Urbach-Martienssen (UM) rule. It has been found that the steepness parameter a versus T plot for each x is useful for the classification of the types of the mixed aggregate.
Two different types of the high-temperature high-pressure reactor systems with one-line or two-line flow paths have been developed to examine the hydrothermal syntheses of metal nanoparticles. For ...the two-line reactor system, two kinds of reaction solutions could be quickly mixed at the Y-shaped junction inside the reactor under high-temperature high-pressure conditions. The aqueous solutions containing 1.5mM silver nitrate, 30 wt% polyvinylpyrrolidone and three different kinds of reducing agents (trisodium citrate, ethanol or acetone) were reacted at T = 200-350°C and P = 40MPa by the one-line reactor system. The finest silver nanoparticles with average diameter of about 15nm were obtained when trisodium citrate was used as the reducing agent. The bimetallic nanoparticles composed of silver and platinum have been synthesized with the one-line reactor system by using the mixed solution of silver nitrate and dihydrogen hexachloroplatinate (IV) as the starting material. The optical absorption spectra of the obtained bimetallic nanoparticles in the aqueous solutions indicated the spontaneous formation of the platinum-core silver-shell structure. It was demonstrated that smaller Ag nanoparticles with narrower size distribution could be synthesized when the two-line reactor system was used instead of the one-line reactor system under nearly identical experimental conditions.
Current Topics in Photochemistry of Sensitizing Dyes YONEZAWA, Yoshiro; YAMAGUCHI, Atsushi; KOMETANI, Noritsugu
Journal of The Society of Photographic Science and Technology of Japan,
2003, Letnik:
66, Številka:
4
Journal Article
Odprti dostop
Current topics of the structure, spectroscopic properties, excitation dynamics and photochemistry of dye aggregates have been reviewed. Five typical cyanine dyes and merocyanine dyes have been taken ...up; those having long-alkyl chains: oxacyanine (S9) and thiacyanine (S11), merocyanine (MC), and those without long-alkyl chains: pseudoisocyanine (PIC), benzimidazolocarbocyanine (BIC, TDBC), meso-ethyl-thiacarbocyanine (TDC, THIATS). The J-aggregate (JA) of PIC was first reported by Jelley and Scheibe in 1936. Since then, JA of PIC, BIC, TDBC, TDC, THIATS in aqueous solutions, in lowtemperature glassy matrices, in adsorbed layers has been successfully prepared. Kuhn's group discovered the JA of S9, 511, MC in LB films, which open up the research field of photophysics, photochemistry and molecular architecture of organized molecular assemblies. Nowadays, the J-aggregate of many cyanine dyes without long-alkyl chains can be easily incorporated into organic thin films (LB films, SA films), and polymer films by LB technique, alternate adsorption technique, and spincoating method, which enhances the exploration of linear-and nonlinear optical materials composed of organic dyes. Rapid progress of new techniques; cryo-TEM, confocal fluorescence microscopy, SNOM and AFM has enabled us to visualize complex supramolecular structures of JA. Particularly, suprastructures of PIC and TDBC in aqueous solutions as visualized by cryo-TEM are striking. The application of ultrafast spectroscopy and non-linear spectroscopy to the JA in low-temperature glassy matrices combined with theoretical analysis has revealed special features as well as a common feature of the J-aggregate derived from different dyes. A beautiful ring structure of bacteriochlorophyll (BChl) molecules in the antenna system of photosynthetic bacteria has been mentioned in connection with the JA of organic dye molecules.
Spectroscopic Properties of Merocyanine J-aggregate in LB films Yamaguchi, Atsushi; Yoshida, Akihito; Kometani, Noritsugu ...
Journal of The Society of Photographic Science and Technology of Japan,
2004, Letnik:
67, Številka:
Suppliment2
Journal Article
Odprti dostop
Langmuir-Blodgett (LB) films incorporating unsymmetrical merocyanine dyes; MC (X), (X=0, S, Se), have been fabricated. The J-aggregates of MC (S) and MC (Se) are characterized by a sharp J-band and ...resonance fluorescence. MC (0) forms a non-fluorescent aggregate having a broad absorption band. We have examined the formation of mixed J-aggregates in the MC (X)/MC (Y) assemblies (X, Y=O, S, Se). It has been found that a homogeneous aggregate of amalgamation type (HA-aggregate) is formed in the MC (S)/MC (Se) assembly. The mixed J-aggregate in the MC (0)/ MC (S) and the MC (0)/ MC (Se) assemblies are classified into a mosaic (M-) or a separate (S-) aggregate. Despite of similar molecular structure of MC (O) with both MC (S) and MC (Se), the growth of the MC (0) aggregate with a help of the MC (S) or the MC (Se) J-aggregate as a template may hinder the homogeneous mixing of dye molecules.
Delocalization and energy transfer of the molecular exciton of the J-aggregate of oxacyanine dye, N, N'-dioctadecyl-oxacyanine perchlorate (S9) in LB films have been examined. Fluorescence lifetime ...of the S9 J-aggregate (S9 (J)) appears to be ca. 1 / 20 of the isolated S9 molecules (S9 (M)), which suggests that the coherent size of the J-aggregate, Ncohe, is about 22 at room temperature. Quenching of resonance fluorescence of S9 (J) by thiacyanine dye, N, N'-dioctadecyl-thiacyanine perchlorate (S11) obeys the Stern-Volmer relation with a Stern-Volmer constant of 1.2×103nm2 molecules-1 at room temperature, which is responsible to the incoherent size Ninco of about 2000. The rate constant of energy transfer kET amounts to 1.5×1013nm2 molecules-1s-1.
LB films incorporating the J-aggregate of cyanine dyes, N, N'-dioctadecyl-oxacyanine perchlorate (S9) and N, N'-dioctadecyl-thiacyanine perchlorate (S11), were prepared by using octadecane as the ...matrix molecule. Absorption spectra of the LB films were measured in wide temperature range. It is observed that the absorption tail of S9 and S1 1 J-band depends on temperature. For the low-energy tail of the J-band, the absorption coefficient at temperatures between 6.0K and 293 K obeys the Urbach-Martienssen rule. The low-energy absorption tail of the longer wavelength peak of the S9/S11 mixed aggregate is also expressed by Urbach-Martienssen rule. A0 and E0 values depend on molar mixing ratio Xof two dyes.
LB films incorporating the J-aggregate of cyanine dyes, N, N'-dioctadecyl-oxacyanine perchlorate (S9) and N, N'-dioctadecyl-thiacyanine perchlorate (S11), were prepared by using octadecane as the ...matrix molecule. Fluorescence spectra of the LB films were measured in wide temperature range. Fluorescence intensity and its peak position of S9 and S 11 depend on temperature. In low temperature fluorescence spectra of S9 and Sll J-aggregates, a broad peak appeared whose position is located at longer wavelength than that of resonance fluorescence. The increase of fluorescence intensity was observed at low temperatures. These effects were also observed for the S9 + S11 mixed aggregate.
We incorporated the alkyl chain substituted spiropyran derivatives, 1-methyl-3,3-dimethyl-6‘-nitrospiroindoline-2,2‘-2H1benzopyran (SP1), ...1-octadecyl-3,3-dimethyl-6‘-nitrospiroindoline-2,2‘-2H1benzopyran (SP18), and 1-octadecyl-3,3-dimethyl-6‘-nitro-8-docosanoyloxymethylspiroindoline-2,2‘-2H1benzopyran (SP1822) into the planar bilayer lipid membranes (BLM) of soybean lecithin for the first time, and the photoresponse of the BLM was monitored. When a dc voltage was applied across the BLM, the transmembrane current changed under alternate irradiation with ultraviolet light and visible light. Such a photoelectric response of the BLM seems to be caused by the change in the membrane conductivity due to photoisomerization of spiropyran.
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