Advanced Functional Materials

Molecular recognition occurs at dynamic interfaces too! The cover shows a donor–acceptor–donor hydrogen-bond moiety, incorporated in a tailor-made monovalent molecular module (in blue), that is able to recognize both complementary monovalent (in red) and tetravalent (in green) molecular modules at interfaces. This finding, described by P. Samori and co-workers on page 1207, paves the way towards the formation of robust multicomponent 2D functional nanostructures with tunable size and geometries.

Noninvasive methods for diagnosis of organic devices are based on optical probes. At Politecnico di Milano, M. Celebrano et al. have developed a new method to optically map the electric field inside organic planar devices, as described on page 1180. Their technique involves the combination of electroreflectance spectroscopy with confocal microscopy to achieve high spatial resolution. The cover image shows an artistic impression of the optical probing of a CuPcF₁₆-based device.

Surfaces with light-switchable wettability can be fabricated by following four steps: i) deposition of SU-8 films onto SiO₂/Si substrates, ii) micropatterning of the SU-8 films by photolithography, iii) surface functionalization of the patterned substrates with surfactant-capped TiO₂ nanorods, and iv) UV irradiation that increases the TiO₂ hydroxylation. After irradiation, the surface reverts back to its native status when stored in the dark.

Oleic acid coated magnetic nanoparticles (MNs), a type of contrast agents in magnetic resonance imaging (MRI), are easily internalized by adipose-derived stem cells (ASCs; see image), which ensures the magnetic labeling of ASCs to facilitate subsequent MRI tracking.

A single step approach to tailored nanoparticle- bioconjugates, enabling the generation of gold nanoparticles by laser ablation and their in situ conjugation with any biomolecule bearing an electron donating function (e.g., thiolated oligonucleotides), is established. Their size is tailorable via process parameters. This rapid and universal method may provide biochemists with various nanoparticle-bioconjugates for screening the often unpredictable structure–function relationship.

A highly ordered bimolecular crystal forms when a fullerene molecule intercalates between the side-chains of a semi-crystalline polymer (see figure). This unexpected intercalation is observed in several polymer:fullerene blends and suggested for several others. Rational design of polymers for bulk heterojunction solar cells must consider this effect in order to push the efficiency higher.

An optical technique to monitor electric field distribution in organic based devices is reported. By monitoring the Stark shift of molecular transitions with confocal microscopy information on the field strength within the device channel is obtained with sub-micron spatial resolution. Large fluctuations across the interdigitated array associated to space charge accumulation are observed.

A sequence specific protein-DNA conjugate is engineered to function as a biomolecular platform to assemble inorganic nanoparticles on DNA scaffold using LacI-STB1 molecule as a linker. The LacI-STB1's ability to bind target inorganic nanoparticles is sculpted by tagging its C-terminus with specific inorganic-binding peptides. This approach may provide a generic platform for organizing desired nanoparticles in a controlled manner.

In the synthesis of carbon nanostructures, sulfur is shown to play a key role. It is demonstrated that sulfur not only acts on the catalyst but also affects the morphology and curvature of the material when incorporated into the carbon body. Analytical and microscopy results reveal five different covalent Y-junctions and even unique sea urchin-shaped nanostructures under different sulfur-assisted CVD synthesis conditions.

By adding small amounts of the non-solvent acetonitrile to solutions prior to film formation, the organization of the P3HT in precursor solutions is transformed from random-coil conformation to ordered aggregates. The ordering of the precursor in the solutions significantly improves the molecular ordering of the resulting P3HT thin film and enhances the field-effect mobility without post-treatment.

Functional surfaces can be developed using the self-assembly properties of properly designed molecular building blocks forming two dimensional nano structures with pre-programmed order at the supramolecular level. Hydrogen bonding can be successfully employed for this purpose taking advantage of its high directionality and selectivity. This approach allows for the growth of well-defined 2D nanostructures in a versatile way by varying the size and geometry of the molecular building blocks.

Electron microscopy studies are used to explore the morphology of thin poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate acid (PEDOT:PSS) films. The studies reveal the granular structure of the films. Energy dispersive X-ray analysis and atomic force microscopy scans then show that the films are composed of grains with a PEDOT-rich core dispersed in a PSS-rich matrix.

Nanoporous copper (NPC) with tunable nanopore size is developed as a promising surface enhanced Raman scattering (SERS) substrate. By tailoring nanopore sizes, the SERS effects of NPC can be dramatically improved and the maximum enhancements for both rhodamine 6G and crystal violet 10B molecules are observed at a nanopore size of 30–50 nm; the maximum enhancement is found to be ∼1.85 × 10⁵, comparable to that of nanoporous gold.

A method which enables the investigation of the buried interfaces without altering the properties of the polymer films is used to study vertical phase separation of spin-coated poly(3-hexylthiophene) (P3HT):fullerene derivative blends.

The physical properties of dye-sensitized films of TiO₂ nanoparticles change dramatically through exposure to UV and green light (see figure). After-irradiation films are denser (as shown by transmission electron microscopy and ellipsometry) and more hydrophobic (higher contact angle). Changes induced by visible- and UV-light result from the photodissociation of the organic capping layer (surfactant elimination).

A metal oxide functional interfacial layer prepared by mixing solution processable semiconducting metal oxides and salts is introduced for achieving high performance organic electronic devices, based on the understanding and tuning of the properties of nanointerfacial layers. The role of salts, as a source of Cs component, is found to modify the electronic property of the metal oxide. Polymer solar cells and polymer light emitting devices with this functional layer exhibited excellent characteristics.

Capillary driven self-assembly (CDSA) is a scalable method for site-selective self-assembly of colloidal crystals on topologically patterned substrates, such as wafers containing integrated optics components that are to be coupled with the crystals. In the figure, a 20 μm long crystalline silica opal (thickness 10 μm) is interposed between two ridge waveguides on a photonic chip.

The nanostructuring occurring in the AgPb₁₈SbTe₂₀ system is documented and it is shown to contain coherent or semi-coherent Ag-rich nano-inclusions, most in range of 2 to 30 nm embedded in an essentially PbTe matrix. The analysis of the nanostructuring supports the mechanism believed to be responsible for achieving a high thermoelectric figure-of-merit.

Three pyridine-containing triphenyl benzene derivatives with different nitrogen atom positions are developed as electron-transport layers and also hole/exciton-blocking layers for FIrpic-based blue phosphorescent organic light-emitting diodes. High efficiency and reduced efficiency roll-off are achieved due to improved electron injection and good confinement of both carriers and excitons within the emissive layer.

A stable, multifunctional, magnetic composite material containing magnetite, natural zeolite and silver nanoparticles (see figure) is successfully synthesized by sintering silica-coated magnetite with zeolite, ion exchange and thermal reduction of silver ions. This novel material captures elemental mercury from a gas stream and can be easily recovered from a complex multi-phase system using an external magnetic field.

The design, synthesis and characterization of thin films as a platform for studying the separate influences of physical and chemical cues of a matrix on the adhesion, growth and final phenotype of cells is demonstrated. Independent control of the physical and chemical properties of functionalized, swellable-hydrogel thin films is achieved.

Microwave irradiation can be used to initiate the growth of uniform carbon nanofibers on different substrates. Combined with electro-oxidative lithography, patterned arrays of nanofibers can be created and the selective absorption of microwave irradiation by the catalyst is demonstrated. The development of a safe and fast synthesis process has potential applications in the integration of carbon nanofibers into device frameworks.

Polyaniline entrapped in silver affects the conduction properties of the composite matrix. A correlation between material characteristics and the conduction is observed. This work adds to the diversity of applications demonstrated for the new field of entrapment of polymers within metal matrices.

Surface-bound nanofilaments are synthesized by nanomolding on a nanoporous template surface. The filaments carry molecularly imprinted binding sites for the specific recognition of small molecules or proteins. The wetting properties of the surfaces depend on the dimensions of the nanofilaments and on the polymer. They can be used as synthetic recognition layers in biosensors and biochips.