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Nikolai Severin

Publications and source records attributed to Nikolai Severin.

9 recordsLinked to original sources
PubMed2006

Adsorption of polyelectrolyte molecules to a nanostructured monolayer of amphiphiles.

We investigate the conformation of atactic poly(sodium 4-styrene sulfonate) (PSS) molecules both in water-ethanol solutions and adsorbed to a template provided by a nanostructured monolayer of flat-lying octadecylamines on graphite. The conformations of the PSS molecules in these solutions undergo two conformational transitions, a re-entry transition at 40 vol % and a coil-globule conformational transition at 80 vol % ethanol. On the surface the conformations are characterized by two different length scales: on a short length scale they are defined by the template, whereas the large-scale structures reflect the conformations in solution. We conclude that the conformational transitions are discontinuous on the level of single molecules and appear continuous in the ensemble.

Adsorption↗
PubMed2004

Tuning intermolecular interactions in a rodlike polymer assembled at surfaces and in solution.

The isolation of single polyelectrolyte chains of water-soluble poly(isocyanodipeptide)s (PICs) bearing carboxylic acid terminated side chains occurring both at surfaces and in solution was accomplished by reducing the intermolecular interactions through complexation with cations or positively charged surfactants. Scanning force microscopy and viscosity analyses revealed that this method allows to tune the conformation of the macromolecule, which is of importance for tailoring the physicochemical properties of the material. This is particularly significant for the use of these polymer chains as seed for biomineralization processes.

Carboxylic Acids↗
PubMed2004

A hexa-peri-hexabenzocoronene cyclophane: an addition to the toolbox for molecular electronics.

Cyclophanes with the largest-to-date polycyclic aromatic hydrocarbon (hexa-peri-hexabenzocoronene, HBC) to be entrained in such a structural motif are reported. The two disks are covalently captured by intermolecular ring-closing olefin metathesis of dienes in good yield. DSC, optical microscopy, and WAXD show the new cyclophanes to self-assemble to thermotropic columnar liquid crystal mesophases similar to monomeric analogues. Solution spectroscopic studies reveal that the two disks within a single unit lie face-to-face, with a small average lateral offset. Self-assembly into two-dimensional crystals at a solid-liquid interface was visualized by STM, and the electrical properties of single molecules were assessed by scanning tunneling spectroscopy revealing a diode-like behavior which is similar to that previously reported for single HBC disks, laying the groundwork for future electrical interrogations of dynamic molecular complexes.

Journal Article↗
PubMed2002

Epitaxial composite layers of electron donors and acceptors from very large polycyclic aromatic hydrocarbons.

Large polycyclic aromatic hydrocarbons (PAHs) can be considered as nanographenes, whose electron donating or accepting properties are controlled by their size and shape as well as functionalities in their periphery. Epitaxial thin films of them are targets for optoelectronic applications; however, large PAHs are increasingly difficult to process. Here we show that epitaxial layers of very large unsubstituted PAHs (C(42)H(18) and C(132)H(34)), as well as a mixed layer of C(42)H(18) with an electron acceptor, can be obtained by self-assembly from solution. The C(132)H(34) is by far the largest nanographene that up to now has been processed into ordered thin films; due to its size it cannot be sublimed in a vacuum. Scanning tunneling microscopy (STM) studies reveal that the interaction with the substrate induces a strong perturbation of the electronic structure of the pure donor in the first epitaxial monolayer. In a second epitaxial layer with a donor acceptor stoichiometry of 2:1 the molecules are unperturbed.

Journal Article↗
PubMed2002

Cyclodextrin-threaded conjugated polyrotaxanes as insulated molecular wires with reduced interstrand interactions.

Control of intermolecular interactions is crucial to the exploitation of molecular semiconductors for both organic electronics and the viable manipulation and incorporation of single molecules into nano-engineered devices. Here we explore the properties of a class of materials that are engineered at a supramolecular level by threading a conjugated macromolecule, such as poly(para-phenylene), poly(4,4'-diphenylene vinylene) or polyfluorene through alpha- or beta-cyclodextrin rings, so as to reduce intermolecular interactions and solid-state packing effects that red-shift and partially quench the luminescence. Our approach preserves the fundamental semiconducting properties of the conjugated wires, and is effective at both increasing the photoluminescence efficiency and blue-shifting the emission of the conjugated cores, in the solid state, while still allowing charge-transport. We used the polymers to prepare single-layer light-emitting diodes with Ca and Al cathodes, and observed blue and green emission. The reduced tendency for polymer chains to aggregate allows solution-processing of individual polyrotaxane wires onto substrates, as revealed by scanning force microscopy.

Cyclodextrins↗