Solution processability endows polymer semiconductors with several intriguing prospects, from low-cost processing, such as inkjet printing, to the possibility of creating new materials by simply mixing solutions. Polymer blends have already been exploited in light-emitting diodes (LEDs) [1] and photovoltaic diodes, [2,3] as well as light-emitting electrochemical cells (LECs), [4] although the factors controlling their supramolecular structures [5] and properties are not fully understood. Most polymer blends undergo phase segregation. [6] This has been used to generate large-area heterojunctions, [2] but it can be detrimental where solid solutions are sought to increase photoluminescence (PL) efficiency, and where rough surface morphology is a problem. Here we use three supramolecular strategies to prepare a complex material that has none of these drawbacks and benefits from enhanced electroluminescence properties: firstly, ionic interactions favor mixing of a conjugated polyelectrolyte with poly(ethylene oxide), PEO, preventing phase segregation and boosting the PL efficiency; secondly, the PEO facilitates ion transport and allows fabrication of LEC-like devices which display a two orders-of-magnitude increase in the electroluminescence (EL) efficiency; thirdly, threading the conjugated polymer through cyclodextrins gives higher PL efficiencies at small PEO loadings, and increases the EL efficiency over the full range of PEO concentrations. Insulated molecular wires, IMWs, consisting of conjugated polymers threaded through cyclodextrin rings (b-CD-poly(paraphenylene) (b-CD-PPP), b-CD-poly(fluorene) (b-CD-PF), a-CD-poly(4,4′-diphenylene vinylene) (a-CD-PDV), and b-CD-poly(4,4′-diphenylene vinylene) (b-CD-PDV); Fig. 1) are versatile supramolecular architectures [7] that display a reduced degree of interchain interactions reflected in higher electroluminescence efficiency, blue-shifted absorption/emission, and reduced luminescence quenching and packing density, when compared to their uninsulated analogues (PPP, PDV, and PF). [8] In this paper we exploit their polyelectrolytic nature, and use the presence of lithium carboxylate and sulfonate substituents to drive the formation of supramolecular complexes with polymers featuring ion-coordination properties. This supramolecular assembly enables us to reduce the tendency of the different components to phase separate, to promote smooth surface morphologies, and to boost the PL and EL efficiency. The interaction of PEO with polyrotaxanes in aqueous solution was tested by fluorescence titration, using b-CD-PDV and PDV. This experiment revealed that both conjugated polymers bind PEO strongly even under extremely dilute conditions (1 ppm PEO by weight, ca. 1 × 10 -8 mol dm -3 of both components). The fluorescence spectra of PDV at a range of PEO concentrations are shown in Figure 2a, and the corresponding titration curve is plotted in Figure 2b (see Fig. S1 in the Supporting Information for analogous data for b-CD-PDV). The titration curves for b-CD-PDV and PDV fit remark...

A molecular wire consisting of a metal/molecule/metal junction can be regarded as the basic building block for future nanoelectronics applications. Alongside the great effort expended in the last ten years on the use of single molecules as electroactive components, [1][2][3] there is also a growing interest centered on the use of supramolecular architectures as electroactive species to bridge metallic electrodes.[4] The supramolecular approach can enhance the mechanical and electronic properties of the wire, which should improve the performance of electronic devices.[ [5][6][7][8][9][10] One major challenge in the study of charge transfer across organic molecules is achieving reproducible attachment between metallic electrodes. Although different electrode pairs have been employed, including break junctions, [3] lithographically tailored nanoelectrodes, [11] and a solid substrate and a conductive tip of an atomic force microscope [12][13][14] or a mercury drop, [15] new, scalable routes to the controlled incorporation of nanometer-scale objects in the gap between nanoelectrodes are required. The manipulation and alignment of an anisotropic object using dielectrophoretic forces in an electric field has been successfully accomplished with a variety of different structures including metal and semiconducting nanoparticles [11] and nanowires, [16] DNA molecules, [17] carbon nanotubes, [18,19] block copolymers, [20] ZnO-organic complexes, [21] and dendron rod-coil ribbons. [22] This has recently led, for example, to improved emission properties of single conjugated polymer molecules.[23] The possibility of applying this technique to supramolecularly engineered nanostructures is thus of major interest in view of their reversible self-assembling properties under external stimuli such as temperature and chemical environment. [24] We provide here the first direct quantitative determination of the electric-field-assisted alignment of single organic supramolecular fibers self-assembled at a surface. We have chosen a gel-forming functionalized 1,3,5-triamide cis,cis-cyclohexane derivative (cyclohexane trisamide gelator (CTG), Fig. 1a) that is known to self-assemble into supramolecular fibers in aqueous solution through the formation of hydrogen bonds. [25,26] Due to its wider applicability for electronic applications, we present here attempts to form similar fibers in an organic solvent. Fibers were deposited from solution onto two gold electrodes arranged in a source-drain geometry with micrometer-scale separation. During deposition, a DC voltage was applied between the two electrodes and the system was cooled below its sol-gel transition temperature (T sol-gel ).In the gel, the three intermolecular hydrogen bonds among the amide moieties of CTGs are both parallel to one another and perpendicular to the plane of the cyclohexane ring (see Fig. 1a inset), endowing strong, self-complementary, and uniaxial intermolecular interactions that are necessary to enforce quasi-1D self-assembly.[27] Since each hydrogen bond has a dipolar...

The advantages/limitations obtained by working in dynamic scanning force microscopy (DSFM) at different levels of tip/sample interaction forces (from the net attractive to the hard repulsive regime) are experimentally shown by imaging monolayers containing novel fibre-like supramolecular nanostructures wrapped up in spiral-like domains. The structures have been obtained by using the Langmuir–Blodgett technique and transferring onto mica monolayers of quercetin-3-O-palmitate molecules mixed with a fraction of about 25% of dimyristoylphosphatidylcholine. The measurements in the attractive regime allowed us to reveal morphological features of the supramolecular structures that cannot be demonstrated by the conventional repulsive regime. In particular, by attractive dynamic scanning force microscopy (DSFMA) the height of the fibre-like structures was a factor of two to three higher and peculiar nano-ruptures along the wrapped fibres have been observed. The influence of the tip/sample contact interaction was investigated by recording images in hard tapping and successively imaging the same region in DSFMA as well as by comparing the images in DSFMA with those obtained in negative lift mode force modulation microscopy, phase imaging and friction force microscopy.

Fiberlike supramolecular structures, almost monodisperse in diameter (14 ± 2 nm), were obtained in quercetin-3-O-palmitate (QP) Langmuir−Blodgett monolayers transferred on solid substrates by working at a relatively high subphase temperature (37 °C) and surface pressure (30 mN/m). The formation of QP fiberlike structures of similar diameter was also reached by exploiting phase separation processes occurring in mixed monolayers of dimyristoylphosphatidylcholine and QP at 10 °C. In the mixed films, the nanoscopic fibers were observed to curve and wrap up, leading to novel spirallike domains. The wrapping-up process was observed to be enhanced either by lowering the barrier compression speed at the air/water interface or by heating the solid support at the air/solid interface. The above phenomena were observed by scanning probe microscopy of the transferred monolayers. By employment of different operative modes including tapping, phase, friction, and the dynamic attractive regime, important insights on the phase separation as well as the mechanical properties of the nanostructures were found.

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Scanning force microscopy (SFM) is used to study the surface morphology of spin‐coated thin films of the ion‐transport polymer poly(ethylene oxide) (PEO) blended with either cyclodextrin (CD)‐threaded conjugated polyrotaxanes based on poly(4,4′‐diphenylene‐vinylene) (PDV), β‐CD–PDV, or their uninsulated PDV analogues. Both the polyrotaxanes and their blends with PEO are of interest as active materials in light‐emitting devices. The SFM analysis of the blended films supported on mica and on indium tin oxide (ITO) reveals in both cases a morphology that reflects the substrate topography on the (sub‐)micrometer scale and is characterized by an absence of the surface structure that is usually associated with phase segregation. This observation confirms a good miscibility of the two hydrophilic components, when deposited by using spin‐coating, as suggested by the luminescence data on devices and thin films. Clear evidence of phase segregation is instead found when blending PEO with a new organic‐soluble conjugated polymer such as a silylated poly(fluorene)‐alt‐poly(para‐phenylene) based polyrotaxane (THS–β‐CD–PF–PPP). The results obtained are relevant to the understanding of the factors influencing the interfacial and the intermolecular interactions with a view to optimizing the performance of light‐emitting diodes, and light‐emitting electrochemical cells based on supramolecularly engineered organic polymers.