Advanced Materials

The front cover shows an artist's impression of a conjugated polyfluorene polymer doped with perylene-diimide fluorophores. The blue luminescence of the fluorenes is transferred to the PDI moieties, allowing spectral tuning of the emission. This process is difficult to quantify due to the large structural freedom of the polymer chains. In their article on p. 1079, Johan Hofkens and co-workers describe how single-molecule imaging can tackle this complexity.

The inside cover displays a confocal image of electroluminescent polymeric nanofibers embedding dye-loaded zeolite L crystals obtained by electrospinning. Varun Vohra and co-workers show on p. 1146 that such nanofibers exhibit a two-step energy transfer (FRET) from the polymer to the dye molecule inside the zeolites. The stopcock molecule present at the channel entrances is the key to this two-step energy transfer.

The European Science Foundation (ESF) with its 34 year history in funding scientific networking activities that span across European borders has been the instigator of several programs within the field of materials science. The main results of these programs have made a real impact in the field, and are contributing to a new class of researchers that will be the leaders of the European Research Area.

The use of unconventional wet lithographies in the fabrication of small and regularly spaced nanostructures of soluble functional materials, including molecules oligomers, macromolecules, polymers, nanoparticles, clusters, and more generally, soft matter, is reviewed. This is important because most of the functional materials are synthesized in solution or are soluble.

Precise control over the self-assembly of functional supramolecular architectures on metallic substrates requires highly detailed information, which is more and more extensively accessed through the combined use of theory and experiments. We briefly report on recent developments in the study and selection of suitable building blocks and binding motifs.

The design of polyphenylene-based materials for electronic and opto-electronic applications is addressed in this Progress Report. The possibilities to achieve the desired function for electronics by controlling the complexity of organic molecules at the molecular and supramolecular level are particularly highlighted.

Revealing heterogeneity in macromolecular systems such as polymer matrices is difficult to achieve using traditional methods, but is highly suited to single-molecule imaging. In this Progress Report we discuss some approaches that can provide detailed information on the structure and dynamics of such systems. In particular, we focus on a recent technique, defocused wide-field imaging, which provides the position and orientation of a single molecule, and how this can be applied to explore phenomena such as polymer dynamics, nanoscale structuring, and energy transfer.

Thienothiophene semiconducting polymers can exhibit a planar backbone conformation, leading to highly crystalline structures, often with good orientation and inter-grain alignment. This thin-film microstructure is optimal in achieving high charge-carrier mobilities in organic field-effect transistors.

The sign of the monolayer-induced metal work function change is mainly determined by the relative polarizabilities of the head- and tail-groups of the molecules, while its magnitude can be finely tuned by adjusting the strength of depolarization in the SAM, which depends on the choice of length of the nonpolarizable spacer between the polar groups.

Blue-light-emitting poly(p-phenylene vinylene)s with fluorinated vinylene units are presented. It is demonstrated that self-aggregation governs the strength and polarization of the absorption spectra of thin films of these polymers. This indicates that self-assembly of the polymer chains in the films provides a means of tuning the electronic and optical properties of the π-conjugated systems.

A chemically amplified resist based on a hyperbranched polymer resin is demonstrated for the first time. The hyperbranched polymer is synthesized using the atom-transfer radical polymerization (ATRP) technique, and resists prepared from this hyperbranched polymer present good pattern profiles and line-edge roughness (3σ) values comparable to those of the reference (commercial) resist.

The templated self-assembly of water-soluble π-conjugated molecules bearing a diaminotriazine moiety H-bonding to a single-strand oligothymine template leads to defined structures. We study these assemblies with molecular modeling, circular dichroism spectroscopy, and scanning probe microscopy, to get a better understanding of the factors governing the supramolecular organization and structural order.

Supramolecular arrays composed of 1-D coordination networks on surfaces, with nanoscale control over both the geometry and the directionality, are achieved through the design and combination of organic tectons with metal complexes (CoCl₂) or metal centers (Pd(BF₄)₂). Scanning tunneling microscope at the solid/liquid interface allows the visualization of long and shape-persistent arrays, with either linear or zig-zag geometries.

Redispersible conductive core–shell nanoparticles with a polystyrene core and a polystyrene sulfonate shell loaded with polypyrrole (PPy) are constructed. The smooth conducting thin films assembled from the PPy core–shell nanoparticles show high transmittance in the visible range and adequate adhesion to the substrates. Performance of light-emitting devices with the conducting thin film as the hole injection layer is tested and compared with the one based on PEDOT/PSS.

A simple nonchemical functionalization method for transferring and patterning zeolite monolayers is described. Polarization experiments show that zeolite monolayers filled with two different dyes lead to different emission colors.

Electroluminescent polymeric nanofibers embedding dye-loaded zeolite L crystals are prepared. By exciting the polymer nanofiber, the energy is transferred to the fluorescent dyes inside the zeolite L channels through a two-step Förster resonant energy transfer process. This study opens new perspectives in the field of low-cost fabrication technology of flexible nanoscale OLEDs.

Aza boron-dipyrromethene dyes functionalized by extended donor-π-conjugated moieties present high potentialities for nonlinear applications in the telecommunication spectral range (1300–1500 nm). Their significant two-photon absorption cross-sections (σ₂ > 600 GM) over this entire spectral range, combined with their high stability and solubility, allow nonlinear transmission experiments.

Tris(bipyridyl)ruthenium(II) self-assembles with the oppositely charged conjugated-polyelectrolyte poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2, 7-diyl} in aqueous solution in the presence of the nonionic surfactant C₁₂E₅. Rapid energy transfer is observed from the singlet state of the polyelectrolyte to the metal complex, leading to emission from the triplet state of the ruthenium complex.

Polyfluorene nanowire Y-junctions synthesized by solution-assisted template wetting are shown to exhibit strongly polarized light emission from the branches and stems. It is demonstrated that the Y-junctions can be positioned, and branching angles may be adjusted, by micromanipulation. Nanowire junctions of this type could ultimately facilitate the incorporation of conjugated polymer materials into highly integrated electronic and photonic circuits and systems.

A double-gate device is used to demonstrate that a blended formulation of semiconducting small molecules and a polymer matrix can provide high electrical performance within thin-film field-effect transistors (OTFTs) with charge carrier mobilities of greater than 2 cm² V⁻¹ s⁻¹, good device-to-device uniformity, and the potential to fabricate devices from routine printing techniques.

Organic light-emitting field-effect transistors provide a deeper insight into the physics of ambipolar devices. Here, the source and drain contacts are altered to investigate the influence of injection barriers on the performance of ambipolar field-effect transistors. The experimental results are compared to a straightforward numerical model.

The conductivity through two self-assembled monolayers (SAMs) on gold based on the closed-and open-shell form of a polychlorotriphenylmethyl (PTM) derivative were investigated using 3D-mode conductive scanning force microscopy, and striking differences were observed, caused by their highly distinct electronic structure.

We used kinesin motor protein and its microtubule track to transport multi-walled carbon nanotubes (MWNTs) on engineered surfaces. Using a flow chamber, surface-adsorbed kinesins are shown to transport red-labeled microtubules loaded with green cargos of MWNTs. Our results establish a platform for assembling individually addressable MWNT nanostructures using microtubule templates.

Indenting viral capsids using AFM allows the determination of their material properties, which has widespread applicability in nanotechnology and medicine. Parameters such as the particle's Young's modulus and the threshold force for breaking are obtained from analyzing the force response upon indentation. The figure shows a bacteriophage capsid before and after breaking it in the course of a measurement.

The excellent charge transport properties of a thiophene-derived polymer, poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), in thin films are explained by the size and orientation of the crystalline domains, and the relative orientation of the polymer chains within these domains. The results are obtained by combining simulation techniques with X-ray diffraction and NEXAFS experiments.