Photo-induced colour generation and colour erasing switched by the sol-gel phase transition

The controlled colour generation and colour erasing phenomena of alkylammonium polyoxomolybdate complexes were first observed in the trans-(1R,2R)-1,2-bis(undecylcarbonylamino)cyclohexane organogel system using the sol-gel phase transition.     

Periodically poled lithium niobate structures grown by the off-center Czochralski technique for backward and forward second harmonic generation

We report on the characterization of periodically poled lithium niobate structures grown by the off-center Czochralski technique with periods ranging between 2 and . The domains distribution along the crystal was inspected by a profilometer scan after etching the structures and carrying a suitable data processing. The second harmonic generation efficiency was predicted by numerically integrating the governing equations through to a recently proposed nonlinear bidirectional beam propagation method. The numerical analysis pointed out the feasibility of the backward second harmonic generation in the sample with the shortest domain period. The predicted second harmonic generation efficiency was finally corrected considering the phase shifts induced in the second harmonic wave by the presence of different sized domains.     

1,4‐Addition of Bis(iodozincio)methane to α,β‐Unsaturated Ketones: Chemical and Theoretical/Computational Studies

1,4‐Addition of bis(iodozincio)methane to simple α,β‐unsaturated ketones does not proceed well; the reaction is slightly endothermic according to DFT calculations. In the presence of chlorotrimethylsilane, the reaction proceeded efficiently to afford a silyl enol ether of β‐zinciomethyl ketone. The C? Zn bond of the silyl enol ether could be used in a cross‐coupling reaction to form another C? C bond in a one‐pot reaction. In contrast, 1,4‐addition of the dizinc reagent to enones carrying an acyloxy group proceeded very efficiently without any additive. In this case, the product was a 1,3‐diketone, which was generated in a novel tandem reaction. A theoretical/computational study indicates that the whole reaction pathway is exothermic, and that two zinc atoms of bis(iodozincio)methane accelerate each step cooperatively as effective Lewis acids.     

A molecular template designed by the modification of a helix-forming β-1,3-glucan polysaccharide to fabricate one-dimensional nanostructures

We report the development of a new templating molecule designed by the modification of a helix-forming β-1,3-glucan polysaccharide to the cationic semiartificial one and its application to the fabrication of one-dimensional (1D) gold nanostructures by simple photoirradiation. Transmission electron microscopy observation showed that Au(III) ions are primarily reduced to gold nanoparticles self-assembling into the 1D array with the aid of the cationic β-1,3-glucan polysaccharide, which gradually fuse into the 1D gold nanostructure with the tapelike structure. The gold nanotape structure could not be created by neutral β-1,3-glucan polysaccharides or random coil synthetic cationic polymers. These findings consistently support the view that Au(III) ions are reduced by unmodified OH groups to gold nanoparticles under the photoirradiation, which are wrapped in the helical structure of the cationic β-1,3-glucan polysaccharide and eventually fuse into gold nanotapes. One may regard, therefore, that this cationic β-1,3-glucan polysaccharide can act as an "all-in-one" template playing three roles of reduction, 1D arrangement, and fusion of gold nanoparticles. In addition, we found an interesting phenomenon that the obtained gold nanotapes coated with cationic β-1,3-glucan polysaccharides show unique surface-enhanced Raman scattering for anionic porphyrines organized on the surface of gold nanotapes through the electrostatic interaction.     

Silver and gold doping of SiO2 glass by solid-state field-assisted diffusion

In this work, a solid-state field-assisted diffusion technique is used to induce diffusion of silver or gold ions into a silica matrix. The obtained systems are characterized by secondary ion mass spectrometry and Rutherford backscattering spectrometry. The metal/glass interface chemistry plays an important role in the behavior of the metals and, especially for Ag, a proper time is required for the deposited film to first oxidize and then diffuse into the matrix, owing to the external electric field. Diffusion of Ag in silica is observed to be very sensitive to the applied field at relatively high temperatures, being stopped when a high field value is applied. This behavior may be attributed to the low availability of sites and the build-up of local electric fields within the glass. As for gold, a quite peculiar behavior of the current density during the process was recorded, indicating that its behavior is even more complex than one could expect. In general, the presented preliminary experimental observations demonstrate the potential of the technique.     

Iron doping of lithium niobate by thermal diffusion from thin film: study of the treatment effect

Thermal diffusion from thin film is one of the most widespread approaches to prepare iron doped regions in lithium niobate with limited size for photorefractive applications. In this work, we investigate the doping process with the aim of determining the best process conditions giving a doped region with the characteristics required for photorefractive applications. Six samples were prepared by changing the atmosphere employed in the diffusion treatment in order to obtain different combination of diffusion profiles and reduction degrees and also to check the effect of employing a wet atmosphere. The compositional, optical, and structural properties are then extensively characterized by combining Secondary ion Mass Spectrometry, UV, visible and IR spectrophotometry, High Resolution X-Rays Diffraction, and Micro-Raman Spectroscopy. Moreover, the sample topography was checked by Atomic Force Microscopy. An analysis of all our data shows that the best results are obtained performing a double step process, i.e. diffusion in oxidizing atmosphere and subsequent reduction at lower temperature in an hydrogen-containing atmosphere.     

Post-polymerization of preorganized assemblies for creating shape-controlled functional materials

Combination of supramolecular chemistry with molecular recognition has been successfully applied to creating large superstructures with a wide variety of morphologies. Control of shapes and patterns of ordered molecular assemblies in nano and micro scales has attracted considerable interest as promising bottom-up technology. It is known, however, that these molecular assembling superstructures are fragile, reflecting the characteristic of the non-covalent interaction, a driving force operating in these molecular systems. In fact, they easily collapse or change by small perturbation in the environmental conditions. Thus, over the last decade, researchers have been seeking possible methods for the immobilization these superstructures. This critical review focuses on recent advances in in situ post-modification under the influence of the molecular assemblies as templates and polymerization of ordered molecular assemblies such as organogel fibers and crystals to preserve their original superstructures and intensify their mechanical strength.