Anharmonic magnetic deformation of self-assembled molecular nanocapsules

High magnetic fields were used to deform spherical nanocapsules, self-assembled from bola-amphiphilic sexithiophene molecules. At low fields the deformation -- measured through linear birefringence -- scales quadratically with the capsule radius and with the magnetic field strength. These data confirm a long standing theoretical prediction (W. Helfrich, Phys. Lett. {\bf 43A}, 409 (1973)), and permits the determination of the bending rigidity of the capsules as (2.6$\pm$0.8)$\times 10^{-21}$ J. At high fields, an enhanced rigidity is found which cannot be explained within the Helfrich model. We propose a complete form of the free energy functional that accounts for this behaviour, and allows discussion of the formation and stability of nanocapsules in solution.Comment: 4 pages, 3 figures, accepted in Phys. Rev. Let

Topological defects and shape of aromatic self-assembled vesicles

We show that the stacking of flat aromatic molecules on a curved surface results in topological defects. We consider, as an example, spherical vesicles, self-assembled from molecules with 5- and 6-thiophene cores. We predict that the symmetry of the molecules influences the number of topological defects and the resulting equilibrium shape.Comment: accepted as a Letter in the J. Phys. Chem.

A π-Extended Donor-Acceptor-Donor Triphenylene Twin linked via a Pyrazine-bridge

Beta-amino triphenylenes can be accessed via palladium catalyzed amination of the corresponding triflate using benzophe-none imine. Transformation of amine 6 to benzoyl amide 18 is also straightforward and its wide mesophase range demon-strates that the new linkage supports columnar liquid crystal formation. Amine 6 also undergoes clean aerobic oxidation to give a new twinned structure linked through an electron-poor pyrazine ring. The new discotic liquid crystal motif contains donor and acceptor fragments, and is more oval in shape rather than disk-like. It forms a wide range columnar mesophase. Absorption spectra are strong and broad; emission is also broad and occurs with a Stokes shift of ca. 0.7 eV, indicative of charge-transfer characte

High anisotropy of the field-effect transistor mobility in magnetically aligned discotic liquid-crystalline semiconductors

A magnetic field has been utilized for producing highly oriented films of a substituted hexabenzocoronene (HBC). Optical microscopy studies revealed large area HBC monodomains that covered the entire film, while wide-angle X-ray measurements showed that the HBC molecules are aligned with their planes along the applied field. On the basis of this method, solution-processed field-effect transistors (FET) have been constructed with charge carrier mobilities of up to 10-3 cm2/V·s, which are significantly enhanced with respect to the unaligned material. Exceptionally high mobility anisotropies of 25-75 for current flow parallel and perpendicular to the alignment direction have been measured as a function of the channel length. Atomic force microscopy performed on the FET structures reveals fibril superstructures that are oriented perpendicularly to the magnetic field direction, consisting of molecular columns with a slippage angle of 40° between the molecules. For channel lengths larger than 2.5 µm, the fibrils are smaller than the electrode spacing, which adversely affects the device performance

Uniaxial alignment of nanoconfined columnar mesophases.

By confining discotic phthalocyanines in a network of crisscrossed nanogrooves, we obtain a uniaxial alignment of the columnar mesophase. The alignment process is based on the anisotropy of interface tension between the mesophase and the nanogrooves' walls. Preferential mesophase alignment results from this nonhomogeneity combined with the anisotropy of the network cell dimensions. A simple model is proposed to explain the experimental observations.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Domain structure of the antiferromagnetic insulating state in Nd0.5Sr0.5MnO3

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Two-dimensional growth, anisotropic polaron transport, and magnetic phase segregation in epitaxial Nd0.52Sr0.48MnO3 films

Nd0.52Sr0.48MnO3 films have been fabricated by dc magnetron sputtering on single-crystal LaAlO3 (001) and SrTiO3 (011) substrates with additional annealing to relax the lattice strain. Although the Nd0.52Sr0.48MnO3 films were deposited simultaneously on different substrates at the same deposition rate, they differ in thickness by a factor of ? . The observed difference in thickness is explained by the two-dimensional (layer-by-layer) film growth, rather than by a difference in growth rate controlled by the crystalline orientation of the substrate. An analysis of optical and transport properties reveals that the observed anisotropy in the polaron motion is governed by a strong anisotropy in the trapping energy, rather than in polaron formation. It is shown that the deposited Nd0.52Sr0.48MnO3 films exhibit magnetic behavior typical of two-phase magnetic systems and should be regarded as an assembly of interacting magnetic clusters.Applied Science