Advanced Materials

On pg. 66, Paul Braun and co-workers report the use of direct laser writing to pattern porous 3D structures from photo-responsive colloidal building blocks. Upon 2-photon exposure, the colloids become highly attractive, enabling localized control of aggregation behavior. 3D structures composed of porous walls are harvested by writing into a colloidal sediment of these particles, followed by rinsing away unexposed colloidal species. Applications may include microfluidics, and studies of porous media, cellular growth and signaling, and colloidal physics. Cover art by Steven Eisenmann of the Beckman Institute VMIL.

The inside cover, drawn by Irene Wang, illustrates that electrical atomic force microscopy techniques can play an integral part in the research and development of organic electronic materials. On p. 19 Pingree, Reid, and Ginger highlight the use of scanning probe microscopy techniques in examining heterogeneities, defects, and various transport properties including injection, trapping, and generation/recombination in organic lightemitting diodes, thin-film transistors, and solar cells.

Reversible immobilization onto the surface of highly porous polymers through co-assembly of stimuli-responsive polymers is reported on p. 55 by Neil Cameron and co-workers. Elastin-based side-chain polymers (EBPs) are prepared by RAFT polymerization and attached to the surface of PEG-based emulsion-templated porous polymers. By careful choice of EBP molecular weight and experimental conditions, pH-controlled reversible co-assembly of a complementary EBP from solution is demonstrated.

2009 marks the 200th anniversary of the birth of Charles Darwin, and as Advanced Materials commences weekly publication, we take a look back over some important changes in science, publishing, and the journal itself, to see how well scientists, journals, and editors have adapted to changes in their environment.

Organic and conjugated-polymer electronics are being developed for light-emitting diodes (LEDs), thin-film transistors (TFTs), and solar cells (organic photovoltaic/ OPV). We highlight how scanning-probe techniques, such as electrostatic force microscopy (EFM), conductive atomic force microscopy (c-AFM), and scanning Kelvin probe microscopy (SKPM), are applied to probe local electronic properties, and the effects of nanoscale film morphology in these devices.

Thin films of single-walled carbon nanotubes (SWNTs) can serve as active materials for various electronic and sensor systems, ranging from flexible, transparent circuits to chemical detectors to radio frequency analog devices. The image shows a flexible SWNT thin film digital logic circuit wrapped around a cylindrical support (background) and electrical characteristics of a representative transistor (foreground). This review describes progress in this emerging field.

Reversible immobilization onto the surface of highly porous polymers through the co-assembly of stimuli-responsive polymers is explored (see figure). Elastin-based side-chain polymers (EBPs) are prepared by RAFT and attached to the surface of PEG-based emulsion-templated porous polymers, leading to a responsive surface capable of pH-controlled reversible immobilization.

High aspect ratio cylindrical droplets of carbon-nanotube solutions present interesting hydrodynamic flow patterns during evaporation, where particles are aligned and positioned. The flow inside droplets with diameters <1000 nm positions all the nanotubes along the droplet centerline with 95% precision, while droplets with diameters >3µm align the nanotubes along the droplet edges during evaporation.

3D patterning of colloidal structures is enabled by the phototriggered aggregation of photoresponsive colloids. We use direct laser writing to locally control aggregation behavior of photoresponsive colloids via a 2-photon absorption process. 3D structures composed of porous walls are harvested after rinsing away unexposed colloidal species. Aggregation is fully reversible with sufficient agitation.

A recent report of ferromagnetism appearing in silicon after etching in hot KOH (Kopnov et al., Adv. Mater.2007, 19, 925) is shown to be due to iron from the pyrex glassware, which precipitates on the silicon surface in the form of well-separated ferromagnetic nanoparticles. The reaction is explained in terms of the Pourbaix diagram.

Hydroxyapatite/silk biocompatible composites with unprecedented mechanical strength and toughness areproduced in a new process with theintegrated mineralization of macroporous silk fibroin scaffolds. Thebiomimetic bone-like composites areabsorbable and load-bearing with compressive strength, modulus, andtoughness comparable to the mechanical tolerances of cancellous bone.

Poly(phenylenevinylene)-based organic light-emitting diodes (OLEDs) are fabricated using air-stable metal oxides as electrodes, producing very efficient and bright electroluminescent devices. Efficiencies of 8 cd A⁻¹ and luminances above 20000 cd m⁻² are obtained, comparable to the values reported for classic OLED structures using reactive metals as cathodes.

A π-conjugated, cyclododeca-2,7-fluorene macrocycle is synthesized as a new model compound for polyfluorenes. The structure formation is demonstrated by ¹H NMR spectroscopy, MALDI-TOF, and STM measurements, and the optical properties of this monodisperse cycle are investigated using UV-vis and fluorescence spectroscopy.

A new class of triblock oligopeptides, containing arginine for DNA binding, histidine for intracellular buffering, and hydrophobic residues for enhanced cellular uptake has been designed, with each block offering unique functionalities essential for efficient gene delivery. Together, these materials demonstrate strong DNA binding ability, low cytotoxicity, and significantly higher in vivo gene-transfection efficiency compared to the PEI standard.

Single-carbon-atomic-resolution detection of odorant molecules has been demonstrated using a human olfactory receptor-based bioelectric nose. Furthermore, since the human olfactory receptor is a G-protein-coupled receptor (GPCR), these sensor systems may be a new powerful platform for the development of new drugs and fragrances.

Metal-organic frameworks containing an organic fluorophore such as stilbene dicarboxylate emit prompt visible light when they interact with ionizing radiation (e.g., high-energy protons or alpha particles). A completely new class of scintillation materials is created by this development, with the potential to rationally tailor properties for specific radiation detection applications.

The detailed interactions between hydrated bromine ions and a number of graphene-like surfaces are elucidated for the first time. A common edge site that exhibits preferential binding of bromide is observed for all materials. The local structure around the hydrated bromide in this interaction region is that of the ion binding to a zigzag, convex site on the graphene sheet edge, consistent with predictions of a recent theoretical model.

A dilute fluorene copolymer produces enhanced optical amplification. High gain with 1000 times optical amplification and a long lifetime is achieve in only 1mm of the material, and exciton–exciton annihilation is suppressed.

A series of NIR organic chromophores with donor–π–acceptor–π–donor structure are synthesized. Good thermal stability and strong photoluminescence in solid state render them suitable for application in light-emitting diodes. Exclusive near-infrared emission at 1080 nm with external quantum efficiency of 0.28% is obtained from the nondoped OLEDs. The longest electroluminescence wavelength is 1220 nm.