Advanced Functional Materials

A molecular system capable of organizing and dispersing upon exposure to different wavelengths of light is prepared by using an azobenzene derivative having three valyl moieties (see figure and cover). N-(L-valyl-L-valyl-L-valyl)azobenzene-4-carboxamide forms a β-sheet structure in this artificial assembly. Upon photoirradiation, the azobenzene moieties isomerize completely, and the reversibility of the structural organization through the flexibility of the β-sheet network is revealed.

The sensitivity of localized surface plasmon resonances with respect to changes in the refractive index of the surrounding medium is measured for regular gold nanodecahedra (see figure and inside cover), and compared to rigorous solutions of Maxwell's equations for bicones based upon the boundary element method. Excellent agreement between experimental and calculated spectra is found.

The sensitivity of localized surface plasmon resonances with respect to changes in the refractive index of the surrounding medium is measured for regular gold nanodecahedra (see figure and inside cover), and compared to rigorous solutions of Maxwell's equations for bicones based upon the boundary element method. Excellent agreement between experimental and calculated spectra is found.

Nanocontainers with surfaces modified with polyelectrolyte shells (see figure) are fabricated using a layer-by-layer method and are tested at various pHs for the release of benzotriazole. When immediate release is necessary, SiO₂-based or halloysite-based nanocontainers with a shell of weak polyelectrolytes are preferable. When continuous, gradual release is required, halloysite-based nanocontainers with a shell of one weak and one or two strong polyelectrolytes are preferable.

Monodisperse, spherical, nonaggregated pigment particles with a core/shell structure are produced using a facile sol–gel process. Spherical silica particles and Cr₂O₃, α-Fe₂O₃, ZnCo₂O₄, CuFeCrO₄, MgFe₂O₄, and CoAl₂O₄ pigments are used as cores and shells, respectively (see figure). The pigment particles have better dispersing properties than commercial products.

A versatile, template-confined, step-electrochemical growth technique is used in the facile fabrication of AgI/Ag heterojunction nanowires with ionic conductivity properties. Photoluminescence, Raman scattering, and ionic conductivity measurements reveal the structural evolution and interface-/defect-related migration of Ag⁺ ions.

Superparamagnetic hybrid nanoparticles are obtained; they consist of an inner iron oxide core coated by a silica shell (see figure) and are covalently coupled to a monoclonal antibody (anti-hCG). This has been verified by an immunochromatographic assay. These results point to the potential of the hybrid nanoparticles prepared for use as enhanced contrast agents in magnetic resonance imaging applications.

A variable optical attenuator is demonstrated that allows large optical contrasts in the near-IR with little color change in the visible region at low applied potentials. The attenuator consists of a flexible reflective display containing a dioxythiophene polymer film spray-cast from solution. The figure shows a schematic of the device and the attenuation for near-IR and visible light.

The unexpected and pronounced electrochemical activity of carbon- paper electrodes modified with TiO₂/nano-Pt composites for the reduction of trinitrotoluene (TNT) (see figure) leads to a completely new avenue for the manufacture of sensors for this explosive. In this electrochemical process, trinitroso-toluene and hydroxylamine derivatives are formed, which react with the ethylene glycol and ethanol of the background solution.

A series of novel semiconducting donor–acceptor block copolymers that contain substituted triphenylamines as donors and perylene diimide as the acceptor (see figure) are synthesized by means of nitroxide-mediated polymerization, and the influence of morphology and the highest occupied molecular orbital (HOMO) level of the donor on block-copolymer solar-cell characteristics is studied.

Large-area uniform arrays of single-crystalline CdS nanowires are obtained by a simple solution approach on Cd-foil substrates. The well-aligned nanowire arrays serve as laser cavities and exhibit bandgap lasing in the visible region, paving the way for applications in novel nano-optoelectronic devices. The figure displays room-temperature PL spectra showing bandgap emission from a CdS nanowire array excited by a Nd:YAG laser at various excitation power densities.

A molecular system capable of organizing and dispersing upon exposure to different wavelengths of light is prepared by using an azobenzene derivative having three valyl moieties (see figure and cover). N-(L-valyl-L- valyl-L-valyl)azobenzene-4-carboxamide forms a β-sheet structure in this artificial assembly. Upon photoirradiation, the azobenzene moieties isomerize completely, and the reversibility of the structural organization through the flexibility of the β-sheet network is revealed.

Switchable polymer/liquid crystal composite diffraction gratings (see figure) are prepared by multiphoton- induced photolithography. They are subsequently characterized by static and dynamic polarization-dependent multiphoton excited fluorescence microscopy. The data show that liquid-crystal orientation and field-induced reorientation dynamics are influenced by nanometer-scale polymer surface roughness.

Both polar and nonpolar guests of different sizes can be included in the novel porous magnet [Fe₃(HCOO)₆], which is the iron member of the [M₃(HCOO)₆] family (where M = Mn, Fe, Co, Ni, etc.). The compound can be prepared by using a mild solution- chemistry method and it displays permanent porosity and thermal stability, significant H₂ and N₂ adsorption, and guest-modulated 3D long-range magnetic ordering (see figure).

3D flowerlike platinum nanoparticle clusters (see figure) are electrodeposited onto multiwalled carbon nanotubes by using an all-electrochemical three-step protocol, involving a second step of a potential pulse sequence. The 3D fractal morphology thus produced provides significantly higher electrocatalytic activity and better stability for the oxidation of methanol than the 2D uniform nanoparticle dispersion achieved when using cyclic voltammetry as the second step.

Crystalline helical carbon nanotubes are synthesized selectively in large quantities by the pyrolysis of acetylene over iron nanoparticles. The resulting hollow nanotubes (see figure) are most commonly observed as symmetric pairs of helical structures with opposite helicities emanating from a carbon- encapsulated Fe₃C nanoparticle. The magnetic properties of these nanostructures are systematically studied, and they are also found to be excellent microwave absorbers.

A novel cruciform oligo(phenylene vinylene) chromophore has been designed and emits green–blue light with high photoluminescence (PL) efficiency both in solution and in the solid state, as shown in the figure. The cruciform shape impedes crystallization and allows amorphous films of the molecule to be produced by spin-coating. The high PL efficiency, strong two-photon-excited fluorescence, and good film-forming abilities make this molecule a promising candidate for use in solid-state optical devices.

A three-component system consisting of water, polyvinylpyrrolidone (PVP), and n-pentanol is shown to be an excellent initiator for the formation of Ag nanoprisms (see figure). The size and shape of these particles can be tuned by the respective amounts of water and PVP present. Using this simple one-step synthesis Ag nanoprism assemblies, Au and Pd nanoprisms, lamellar ZnO particles, and layered ZnO assemblies can also be prepared.

Visible light from an organic light-emitting transistor (OLET) under ambient conditions is achieved by the device structure presented here, which includes a heterojunction between the laterally arranged source and drain electrodes (see figure). The fabrication of such devices is simple and generally applicable, and as such, may be at the base of many light-emitting transistor applications.

Composite films, prepared by casting multiwalled carbon nanotubes (MWCNTs) wrapped with poly(4-vinylpyridine) (PVP) onto gold electrodes followed by electrochemical deposition of Prussian blue on the MWCNT/PVP matrix, show prominent electrocatalytic activity toward the reduction of hydrogen peroxide. Amperometric sensor manufactured from these films show them to be promising for the sensitive and fast detection of glucose (see figure).