Aqueous Assembly of Zwitterionic Daisy Chains

The synthesis and characterization of zwitterionic molecular [c2]‐ and [a2]‐daisy chains are described, relying on recognition of a positively charged cyclophane and a negatively charged oligo(phenylene‐ethynylene) (OPE) rod in aqueous medium. For this purpose, syntheses of an acetylene‐functionalized macrocyclic receptor and a water‐soluble OPE‐rod as the guest component are presented, from which a heteroditopic daisy chain monomer was prepared. This monomer aggregated strongly in water/methanol 4:1 and formed molecular daisy chains, which were isolated as interlocked species from a stoppering reaction at 1 mm concentration. The cyclic dimer [c2] was the main product with an isolated yield of 30 % and consisted of a mixture of diastereomers, as evidenced by 1H NMR spectroscopy

Six state molecular revolver mounted on a rigid platform

The rotation of entire molecules or large moieties happens at 100 ps time scales and the transition process itself is experimentally inaccessible to scanning probe techniques. However

Tuning the contact conductance of anchoring groups in single molecule junctions by molecular design

A tetraphenylmethane tripod functionalized with three thiol moieties in the para position can serve as a supporting platform for functional molecular electronic elements. A combined experimental scanning tunneling microscopy break junction technique with theoretical approaches based on density functional theory and non-equilibrium Green`s function formalism was used for detailed charge transport analysis to find configurations, geometries and charge transport pathways in the molecular junctions of single molecule oligo-

An electrically actuated molecular toggle switch

Molecular electronics is considered a promising approach for future nanoelectronic devices. In order that molecular junctions can be used as electrical switches or even memory devices, they need to be actuated between two distinct conductance states in a controlled and reproducible manner by external stimuli. Here we present a tripodal platform with a cantilever arm and a nitrile group at its end that is lifted from the surface. The formation of a coordinative bond between the nitrile nitrogen and the gold tip of a scanning tunnelling microscope can be controlled by both electrical and mechanical means, and leads to a hysteretic switching of the conductance of the junction by more than two orders of magnitude. This toggle switch can be actuated with high reproducibility so that the forces involved in the mechanical deformation of the molecular cantilever can be determined precisely with scanning tunnelling microscopy

Spatial and Lateral Control of Functionality by Rigid Molecular Platforms

Surface mounted molecular devices have received significant attention in the scientific community because of their unique ability to construct functional materials. The key involves the platform on which the molecular device works on solid substrates, such as in solid-liquid or solid-vacuum interfaces. Here, we outline the concept of rigid molecular platforms to immobilize active functionality atop flat surfaces in a controllable manner. Most of these (multipodal) platforms have at least three anchoring groups to control the spatial arrangement of the protruding functional moieties and form mechanically stable and electronically tuned contacts to the underlying substrate. Another approach is based on employing of flat aromatic scaffolds bearing perpendicular functionalities that form stable lateral assemblies on various surfaces. Emphasis is placed on the need for controllable assembly and separation of these tailor-made molecules that expose functionalities at the molecular scale. The discussions are focused on the different molecular designs realizing functional 3D architectures on surfaces, the role of various anchoring strategies to control the spatial arrangement, and structural considerations controlling physical features like the coupling to the surface or the available space for sterically demanding molecular operations

On reduction of the drug diflunisal in non-acqueous media

The electrochemical reduction of diflunisal was studied in dimethyl sulfoxide on static mercury drop electrode. Diflunisal yields one irreversible wave at -1.2 V (vs. Ag | AgCl | 1 M LiCl electrode) due to the reduction of the carboxylic functional group in the molecule. The electrochemical properties of the drug were compared with the ones of the chlorinated analogue. The study is based on cyclic voltammetry, tast polarography, and constant potential electrolysis. The experimental findings are supported by molecular orbital calculations. The mechanism of reduction of the carboxylic moiety was found to involve two electrons and two protons. The reduction pathway leads to formation of an aldehyde derivative

Oxidation mechanisms of Diflunisal on Glassy Carbon Electrode

The electrochemical oxidation of diflunisal in acetonitrile was studied on a glassy carbon electrode. Diflunisal yields one irreversible oxidation wave at 1.6 V (vs. Ag/AgCl/1M LiCl electrode). The oxidation mechanism depends on the basicity of the solvent. The study is based on cyclic voltammetry, electroanalytical methods and UV-Vis spectroelectrochemistry. The degradation products were determined by separation techniques (HPLC-DAD, GC-MS)

Degradable Fluorene- and Carbazole-Based Copolymers for Selective Extraction of Semiconducting Single-Walled Carbon Nanotubes

Among the solution-based purification methods of as-produced single-walled carbon nanotubes (SWCNTs), conjugated polymer sorting is one of the most promising approaches to obtain semiconducting SWCNTs (s-SWCNTs) with high purity. In order to meet the demand for pure polymer-free s-SWCNTs after polymer wrapping, we synthesized several degradable fluorene- and carbazole-based copolymers for selective extraction of s-SWCNTs. The copolymers are interlinked by imine bonds, and thus, the cleavage can be easily accomplished by acid treatment. The polymer/SWCNT complex dispersions were prepared with as-produced HiPco SWCNTs in toluene and characterized with absorption, photoluminescence excitation and emission mapping, and Raman spectroscopy. Among the synthesized polyimines, fluorene-carbazole copolymers show extremely high separation yield toward s-SWCNTs and high separation purity, while the fluoreneâEuro"fluorene and fluorene-p-phenylene copolymers show lower yield but higher selectivity to s-SWCNT with specific pairs of (n,m) indices. Quantitative removal of the polymer after acid-triggered degradation was confirmed by X-ray photoelectron spectroscopy. Moreover, the released dispersant-free s-SWCNTs can be further rewrapped by different polymers. Our results pave the way toward the use of dispersant-free semiconducting carbon nanotubes (CNTs) to develop the next generation of CNT devices

Assembly of [2]Rotaxanes in Water

Two [2]rotaxanes have been assembled in water from modular subunits through Cu-I-catalyzed azide-alkyne click chemistry. For this purpose, 2,6-disubstituted naphthalene axles with solubilizing oligo(ethylene glycol) (OEG) chains (n = 1-5) and propargyl terminal groups were synthesized and examined for their propensity to form inclusion complexes with a dicationic Diederich-type cyclophane host. The dependence of pseudorotaxane formation on the linkers between the naphthalene core and OEG chains, and in the case of ester linkers on different spacer lengths, was analyzed by titration experiments. In addition, the inclusion complexes of two [2]rotaxanes were trapped by using a water-soluble azide-functionalized stopper. Repetitive chromatography finally enabled the isolation of both mechanically interlocked [2]rotaxanes