Abstract

Abstract

A series of MD simulations were conducted towards the selective deposition of organic luminescent molecules 3(5)-(9-anthryl) pyrazole (ANP) and perylene onto different densely packed organosilane self-assembled monolayers (SAMs). Our simulations indicated that the packing density of alkyl chains on SAM may directly control the site-selective deposition of organic molecules. Additionally we propose a possible mechanism for this phenomenon, which can also explain the experimental findings of the selective deposition of organic molecules onto template structures, made of l-α-dipalmitoyl-phosphatidylcholine (DPPC) in alternating liquid expanded (LE) and liquid condensed (LC) states.

Abstract

A new strategy for realizing patterned surfaces with different emission colors is demonstrated. This approach relies on the gas-phase deposition of dye molecules onto solid substrates that are prepatterned by nanoimprint lithography (see figure). Only a single molecular species is involved. Thus, the observed color change and corresponding spectral shift in the emission properties depends on the substrate used and can be tuned by surface engineering.

Brushing the surface: Structured polymer brushes are readily prepared by site-selective immobilization of initiators in a self-assembly process by Langmuir–Blodgett lithography with subsequent polymerization. The AFM images show a DPPC/alkoxy amine LB film before and after surface-initiated controlled nitroxide-mediated radical polymerization. Large surface areas (several cm²) can readily be structured with this method.

Strukturierte Polymerbürsten lassen sich leicht durch ortsselektive Immobilisierung von Polymerinitiatoren mit Langmuir-Blodgett-Lithographie und anschließender Polymerisation herstellen. Die Kraftmikroskopiebilder zeigen einen Dipalmitoylphosphatidylcholin/Alkoxyamin-Film vor und nach der kontrollierten Nitroxid-vermittelten Polymerisation. Die Methode ermöglicht die Strukturierung großer Flächen (mehrere cm²).

The low-cost, large-scale fabrication of high-density conducting-polymer nanostructures is desirable for a variety of applications. We report the realization of high-density conducting-polymer nanostructures through a combination of nanoimprint lithography, a copolymer strategy, and a lift-off process. Atomic force microscopy and optical measurements reveal that the quality of the prepared structures is rather good, and a resolution of 100 nm is achieved. Electrical measurements show that the conducting-polymer nanowires are conductive and indicate great anisotropy in the parallel and perpendicular directions. Moreover, by further connecting them with larger electrodes, these nanowire arrays function as nanosensors.

Two asymmetric, luminescent, bimetallic ruthenium trisbipyridine complexes with the general formula [Ru(bpy)₃-ph₄-Ru(bpy) L₂](PF₆)₄ (bpy = 2,2′-bipyridine, ph = phenyl, L = 4,4′-di-n-undecyl-2,2′-bipyridine (1); 4,4′-di-non-1-enyl-2,2′-bipyridine (2)) have been synthesized and characterized. The introduction of two 4,4′-dialkyl-2,2′-bipyridine ligands on one of the ruthenium centers does not influence the electronic structure of the overall complexes to a large extent. Owing to the hydrophobic and hydrophilic nature of the two terminal metal complexes, the compounds 1 and 2 are expected to form Langmuir monolayers at the air/water interface. The film-forming properties of the amphiphilic complexes have been investigated by measuring surface-pressure–molecular-area (π–A) isotherms and recording Brewster-angle microscopy images. Complexes 1 and 2 were shown to form monolayer films at the air/water interface, which have subsequently been transferred to solid substrates using the Langmuir–Blodgett (LB) technique. The homogeneity of the resulting LB films has been investigated using atomic force microscopy and has been compared with that of LB films of the reference compound [Ru(bpy)₃-ph₄-Ru(bpy)₃](PF₆)₄ (3), which lacks the alkyl chains. The presence of the hydrocarbon chains on one side of the rigid bimetallic complexes was shown to be a prerequisite for the formation of homogeneous monolayers, as with 3 only multilayer formation was obtained. Confocal laser scanning microscopy measurements proved that the LB films of complexes 1 and 2 display a homogeneous red emission upon photoexcitation. Such important results represent the first step towards the fabrication of mono- or few-molecular-layer electroluminescent devices.

A series of unsaturated long-chain-bridged diferrocenes Fc-(CH₂)_n-CHCH-(CH₂)_n-Fc (4 a–e) was synthesized by means of olefin metathesis. Subsequent catalytic hydrogenation furnished the saturated α,ω-bis-ferrrocenyl oligoethylene products Fc-(CH₂)_m-Fc (5). Members of both series formed highly ordered laminar structures at the highly oriented pyrolytic graphite (HOPG) solid/liquid interface or on the Ag(110) surface, which were characterized by STM. Details of the structural features of these ordered physisorbed surface assemblies of 4 and 5 were analyzed by comparison with DFT calculations on model systems and with the characteristic packing modes of these systems in the crystal.

Self-organized luminescent stripe patterns (see Figure) with submicrometer-scale lateral dimensions are obtained by transferring dye/phosphatidylcholine mixed monolayers onto a solid substrate by means of Langmuir–Blodgett deposition. The regular luminescent stripe formation can be interpreted as a substrate-induced microphase separation and a periodic oscillation of the meniscus at the three-phase contact line.

Fabrication of a nanosensor consisting exclusively of polymers with sensing performance superior to a microscale sensor is reported. The device is fabricated by a copolymer strategy combined with a lift-off process, which is capable of patterning a variety of conducting polymer species down to the nanometer scale (see Figure).

Three general paths for patterning semiconductor nanoparticles stabilized with a short chain stabilizer via microcontact printing (μCP) are presented. The interface between the nanoparticles and surfaces has to be carefully designed to realize a successful direct or indirect printing. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Regularly striped patterns of various dimensions and directions can emerge from the Langmuir–Blodgett transfer of phospholipids onto hydrophilic substrates under the appropriate conditions (see optical micrographs; bar=5 μm). The authors quantitatively measure the dependence of the pattern dimensions on the transfer velocity and the surface pressure. A mechanism for pattern formation, based on the local curvature of the monolayer-covered liquid–vapour interface in the vicinity of the three-phase contact line, is presented.

Planely positioned! Surface-mediated adsorption or chemical reactions is strongly influenced by the geometric availability of adsorption sites. Here, the authors investigate this influence on linearly arranged, chemically active template layers consisting of lipid modified amino acid derivatives (see picture) to study and control the effect of the steric hindrance due to the molecular arrangement on HOPG surfaces.