High efficiency photocurrent generation by two-dimensional mixed J-aggregates of cyanine dyes

Two-dimensional mixed J-aggregates of structurally and spectrally analogous anionic cyanine dyes, coadsorbed on a self-assembled monolayer of aminoalkanethiolate on Au(111), generated a high-efficiency (20-30% quantum efficiency) cathodic photocurrent and a significant photovoltaic effect in reversible Fe2+/Fe3+ redox solution.     

Adsorption of cyanine dyes on gold nanoparticles and formation of J-aggregates in the nanoparticle assembly

This paper describes the results of an investigation of the interparticle interactions and reactivities in the assembly of gold nanoparticles mediated by cyanine dyes. The combination of the positively charged indolenine cyanine dyes and the negatively charged gold nanoparticles is shown to form a J-aggregate bridged assembly of nanoparticles, in addition to hydrophobic interparticle and electrostatic dye-particle interactions. Such interparticle interactions and reactivities are studied by probing the absorption of J-aggregates and fluorescence from the dyes and the surface plasmon resonance absorption from the nanoparticles. The J-aggregation of the dyes adsorbed on the nanoparticles is shown to play an important role in the assembly of nanoparticles. The spectral evolution of the J-band of the dyes and the surface plasmon resonance band of the nanoparticles was found to be sensitive to the nature of the charge and the structure of the dyes. The fluorescence quenching for the dyes was shown to be quantitatively related to the surface coverage of the dyes on the nanocrystal surfaces. These findings have provided important information for assessing a two-step process involving a rapid adsorption of the dyes on the nanoparticles and a subsequent assembly of the nanoparticles involving a combination of interparticle J-aggregation and hydrophobic interactions of the adsorbed dyes. The results are discussed in terms of the structural effects of the dyes, and the interparticle molecular interactions and reactivities, which provide important physical and chemical insights into the design of dye-nanoparticle structured functional nanomaterials.     

Specifics of the formation of J-aggregates of cyanine dyes in solutions of AOT/water/hexane reverse micelles

The behavior of a cyanine dye (3,3′-di-(gamma-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt) was studied in AOT/water/hexane reverse micelles over a wide range of W at various concentrations of the dye, AOT, and reverse micelles. The processes occurring during the formation of the AOT/water/hexane micellar solution were studied in detail. It has been shown that, before the formation of the stable microemulsion, the dye aggregation processes occur by virtue of the interaction of the dye with the AOT anion. The amount of J-aggregates is proportional to the logarithm of the ratio of the amount of AOT molecules to the amount of dye molecules. The time behavior of J-aggregates after the formation of a micellar structure depends on the concentration of reverse micelles, thereby indicating an important role of intermicellar exchange.     

Formation of mixed J-aggregates of cyanine dyes stimulated by Eu<Superscript>+3</Superscript> cations

The block mechanism of the formation of J-aggregates from the dimers of various dyes in an aqueous solution under the action of the multiply charged Eu⁺³ cation was considered for the first time. It was shown that the structure and the position of the absorption maximum of the mixed J-aggregates are determined by the length of the dye chromophore moiety. It was concluded that the mixed J-aggregates are of interest as nanosized optical elements with varying optical and electronic properties depending on the structure of cyanines used.     

Chiral transformation of cyanine dye aggregates induced by small peptides

Three small peptides (K4, K5, and K6) with different length were designed to induce the transformation of the assembled state and the chirality of cyanine dye supramolecule. The absorption and circular dichroism (CD) results indicated that, the peptides tend to induce cyanine dye to H-aggregation, competed with Na(+) in PBS, which would induce dye to J-aggregation. Meanwhile, all three peptides could influence the chirality of both J-aggregates induced by Na(+) and H-aggregates, among which K6 could induce chiral reversion of J-aggregates. Furthermore, molecular modeling and energy calculation results have shown that the peptides with different chain length have different conformations. This might be the reason for cyanine dye to form the different chiral assembly induced by these oligo-peptide templates.     

Phenylcarbamate derivatives of cellulose and amylose immobilized onto silica gel as chiral stationary phases for high-performance liquid chromatography

Three polysaccharide phenylcarbamate derivatives [cellulose 2,3-bis(3,5-dimethylphenylcarbamate)-6-(3,5-dimethylphenylcarbamate)/(2-methacryloyloxyethylcarbamate), cellulose 2,3-bis(3,5-dichlorophenylcarbamate)-6-(3,5-dichlorophenylcarbamate)/(2-methacryloyloxyethylcarbamate), and amylose 2,3-bis(3, 5-dimethylphenylcarbamate)-6-(3,5-dimethylphenylcarbamate)/(2-methacryloyloxyethylcarbamate)] with vinyl groups were prepared and coated onto silica gel to immobilize them via radical copolymerization with 2,3-dimethylbutadiene. The copolymerization efficiently proceeded, and the coated polysaccharide derivatives were mostly immobilized on the surface of the silica gel. The immobilized polysaccharide derivatives showed high chiral recognition abilities similar to those of the corresponding coated polysaccharide derivatives. They could be used with an eluent containing chloroform, which dissolved the polysaccharide derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4704–4710, 2004     

Silver nanoparticle formation in microemulsions acting both as template and reducing agent

A novel method of making silver nanoparticles in water-in-oil microemulsions using the surfactants as both the reducing agent and as the structure-directing agent is presented. Since no external strong reducing agent is used the kinetics of the formation is slow, which makes it possible to study the silver nanoparticle formation in situ. The microemulsions used were based on either the nonionic surfactant Brij30 (C12E4), which reduces the silver ion to metallic silver and is thereby partly oxidized, or mixtures of Brij30 and AOT (sodium bis(2-ethylhexyl) sulfosuccinate, where the latter does not reduce the silver ions. The influences of silver ion and nonionic surfactant concentrations on the formation kinetics of the nanoparticles were followed in situ using UV-vis spectroscopy, and both parameters were found to have a big influence. The microemulsion droplet's size, size distribution, and shape were examined by small-angle X-ray scattering (SAXS), and the formed silver nanoparticles were studied using both transmission electron microscopy and SAXS. The SAXS measurements showed that the presence of silver nitrate does not affect the microemulsion systems noticeably and that the droplet's size and shape are retained during the particle formation. It is shown that the size and morphology of the particles do not directly follow the shape and size of the microemulsion droplets even though there is a relation between the droplet size and the radii of the formed particles.     

Studies of surface adsorbability of sodium carboxymethyl cellulose onto nylon 6 fiber byζ-potential method

Summary The surface adsorption behavior of a polyelectrolyte, sodium carboxymethyl cellulose (Na-CMC), onto Nylon 6 fiber was studied by measuring-potential of the fiber in acidic aqueous solutions (pH 3) of the polyelectrolyte. The amount of Na-CMC adsorbed per unit area of the fiber surface was calculated from the-potential. With the increase in the Na-CMC concentration, the sign of the-potential of the fiber rapidly changed from positive to negative and thereafter the negative values approached to the saturation values, and the amount of adsorption of the polyelectrolyte (expressed in g/cm²-fiber) increased also. These results may possibly be attributed mainly to the formation of the electrostatic bond between the fiber and the Na-CMC. The maximum amount of adsorption of the polyelectrolyte,A _s , decreased with the increase in the degree of polymerization. The slope,a, of theA _s vs. molecular weight,M, curve was equal to or less than zero. It was, therefore, suggested that the polyelectrolyte lay flat on the fiber surface with the same dimension as that in the solution.

---

Zusammenfassung Es wurde das Oberflächenadsorptions verhalten eines Polyelektrolyten (Natriumcarboxymethylcellulose (Na-CMC)) auf Nylon 6 Faser durch-Potential-Messungen in sauren wässerigen Lösungen (pH 3) des Polyelektrolyten untersucht. Die Menge von Na-CMC, die pro Flächeneinheit der Faseroberfläche adsorbiert wird, wurde aus den-Potentialen berechnet. Mit steigender Na-CMC-Konzentration änderte sich das Vorzeichen des-Potentials der Faser rasch von positiv zu negativ, und danach näherte sich der negative Wert einem Sättigungswert; auch die adsorbierte Menge des Polyelektrolyten (in g/cm² Faser) nahm zu. Die Ergebnisse sind wahrscheinlich auf die Ausbildung elektrostatischer Bindungen zwischen Faser und Na-CMC zurückzuführen. Die maximal adsorbierte Menge an PolyelektrolytA _s nahm mit steigendem Polymerisationsgrad ab. Die Steigung (a) derA _s vs. Molekulargewicht (M)-Kurve war gleich oder kleiner als Null. Daraus wird gefolgert, daß der Polyelektrolyt eben auf der Faseroberfläche aufliegt mit den gleichen Dimensionen wie in der Lösung.

---

---

With 7 figures and 2 tables

---

Presented at the 29th Annual Meeting of the Chemical Society of Japan, the Symposium of Interfacial Electrical Phenomena, Hiroshima, Oct. 1973.     

Nanotube foam prepared by gelatin gel as a template

It has been known that simply mixing single-walled carbon nanotubes (SWCNTs) in an aqueous solution of gelatin disperses SWCNTs well for a period of months. Gels made from the gelatin-SWCNT mixture are also stable and have a clear, black color. Scanning electron microscopy shows that gelatin molecules self-organize into a foamlike structure. All SWCNTs are embedded in the gelatin film that makes up the foam walls. Those SWCNTs belonging to one face of the foam cell cannot approach other faces to make van der Waals contact. Thus, the foam structure is associated with stabilization of the SWCNT dispersion. The gelatin can be removed thermally while maintaining the foam structure to give a sponge made of nanotube foams. This highly porous solid is electrically conducting and mechanically stable and can be used as a structural frame for composite materials.     

J-aggregates of diprotonated tetrakis(4-sulfonatophenyl)porphyrin induced by ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate

The J-aggregation behavior of diprotonated tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4(2-)) in aqueous solution in the presence of the hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) was investigated in detail using UV-vis absorption spectroscopy, fluorescence spectroscopy, resonance light scattering (RLS) spectroscopy, Raman spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. With the addition of bmimBF4, increasing peaks appeared at a wavelength of 490 nm in the absorption spectra to account for the formation of H 2TPPS4(2-) J-aggregates. In addition, the experimental results also showed decreased fluorescence emission, enhanced RLS signals, intensified Raman scattering peaks, and the disappearance of NMR signals to further indicate that porphyrin J-aggregates exist in the studied system. NMR shifts of bmimBF 4 toward high field occurred corresponding to H2, H4, and H5 in the cationic imidazolium ring (bmim+), suggesting that bmim+ enters the magnetic shielding domain of the anionic phenyl sulfonate ion owing to the association process between the "large" cation and anion. Additionally, the fact that the absorption spectral shifts occurred in the nonprotonated porphyrin TPPS4(4-) further indicates the existence of the ion association effect of bmim+, which functions as an important factor in porphyrin aggregation.     

The use of highly ordered vesicle gels as template for the formation of silica gels

A spontaneously forming gel of unilamellar vesicles based on sodium oleate (Na oleate) and 1-octanol as amphiphiles has been employed as a template in the formation of a silica gel formed by the hydrolysis of the inorganic precursor tetraethyl orthosilicate (TEOS). Up to about 10 wt % TEOS can be incorporated into this vesicle gel without phase separation and in a fully homogeneous formation process by simple mixing of the components. The process itself relies solely upon the self-organizing properties of this amphiphilic template system. The formation process was followed by means of time-resolved turbidity, rheology, and small-angle neutron scattering (SANS) experiments. It can be concluded that the presence of the precursor TEOS affects the kinetics of the process but the original vesicle gel structure is retained even up to highest TEOS content. The kinetic studies confirm that under the chosen conditions the vesicle formation proceeds much faster than the hydrolysis of TEOS and the subsequent formation of the silica gel. SANS displays in the low q-range an additional scattering due to the silica gel network, i.e., a hybrid material of an amphiphilic vesicle gel and an inorganic oxide gel is formed. Thus, this method is a very facile novel route of forming a highly ordered silica/vesicle gel by employing a self-organizing amphiphilic system as template and the formation of the silica network proceeds in a fully homogeneous fashion under kinetic control.     

Polysaccharides as a template for silicate generated by sol-gel processes

The polysaccharides, as established previously (Yu.A. Shchipunov, J. Colloid Interface Sci. 268 (2003) 68; Yu.A. Shchipunov, T.Yu. Karpenko, Langmuir 20 (2004) 3882), can manipulate the formation of hybrid silica nanocomposites by sol-gel processes. Here atomic force microscopy was applied to show whether carbohydrate macromolecules serve as a template for silicate. Mica was used as a substrate to adsorb polysaccharide. It was found that its surface is not neutral to the sol-gel processes, providing the silica precipitation. To hinder it, the mica was protected by a monomolecular film of arachidic acid with the help of a Langmuir-Blodgett technique. Hydrophobically modified cationic hydrohyethylcellulose was adsorbed from a diluted aqueous solution. It was demonstrated that the carbohydrate macromolecules located on the hydrophobic surface did promote silica precipitation, serving as a template.     

Double‐helical network in amylose as seen by slow calorimetry and FTIR

The phase content and crystallinity of initially amorphous amylose–water mixtures (70/30 W/W) have been changed by slow cycles of dissolution and recrystallization from T_max with 50 °C < T_max < 120 °C. Analysis of the treatment‐induced changes is made by X‐ray diffraction, FTIR, fast T‐ramp DSC and slow calorimetry. Our interest was to follow the relaxation of the network phase and its consequence on the growth of crystallinity. The DSC technique, which gives the temperature of disappearance of long‐range order, is unable to quantitatively follow the growth of crystallinity achieved by treating the samples. In highly interactive polymer–solvent systems, order is unmeltable in a fast T‐ramp due to strain developed during the ramp. In a 6 K/h T‐ramp, the order becomes meltable and grows from 21 J/g to 147 J/g when T_max increases. The other conclusion is that strain‐melting and the network phase, characterized first in polyolefins has a more prominent role in the characterization of H‐bonded polysaccharide–water mixtures. Correlation is achieved between the concentration of bands in the C O stretching region, the fraction of single and double helices, and the three endotherms found on the slow T‐ramp dissolution traces. FTIR spectra show that chains in the network cannot be disentangled by quenching but can be organized during a slow cooling. The B and V crystalline modifications are observed in the treated samples. Quenched treated amylose and enzyme‐resistant amylose seem to contain a comparable amount of double‐helical/strainable fraction. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1662–1677, 2000     

Interactions between colloidal particles induced by polymer brushes grafted onto the substrate

We investigate the interaction energy between two colloidal particles on or immersed in nonadsorbing polymer brushes grafted onto the substrate as a function of the separation of the particles by the use of a self-consistent-field theory calculation. Depending on the colloidal size and the penetration depth, we demonstrate the existence of a repulsive energy barrier of several kBT, which can be interpreted by separating the interaction energy into three parts: colloid-polymer interfacial energy, entropic contribution due to "depletion zone" overlap of colloidal particles, and entropic elastic energy of grafted chains by the compression of particles. The existence of a repulsive barrier which is of entirely entropic origin can lead to kinetic stabilization of the mixture rather than depletion flocculation or phase separation. Therefore, the present result may suggest an approach for controlling the self-assembling behavior of colloids for the formation of target structures, by tuning the colloidal interaction on the grafting substrate under appropriate selection of colloidal size, effective gravity (influencing the penetration depth), and brush coverage density.