Synthesis and Surface Behaviour of NDI Chromophores Mounted on a Tripodal Scaffold: Towards Self-Decoupled Chromophores for Single-Molecule Electroluminescence

This paper reports the efficient synthesis, absorption and emission spectra, and the electrochemical properties of a series of 2,6-disubstituted naphthalene-1,4,5,8-tetracarboxdiimide (NDI) tripodal molecules with thioacetate anchors for their surface investigations. Our studies showed that, in particular, the pyrrolidinyl group with its strong electron-donating properties enhanced the fluorescence of such core-substituted NDI chromophores and caused a significant bathochromic shift in the absorption spectrum with a correspondingly narrowed bandgap of 1.94 eV. Cyclic voltammetry showed the redox properties of NDIs to be influenced by core substituents. The strong electron-donating character of pyrrolidine substituents results in rather high HOMO and LUMO levels of -5.31 and -3.37 eV when compared with the parental unsubstituted NDI. UHV-STM measurements of a sub-monolayer of the rigid tripodal NDI chromophores spray deposited on Au(111) show that these molecules mainly tend to adsorb flat in a pairwise fashion on the surface and form unordered films. However, the STML experiments also revealed a few molecular clusters, which might consist of upright oriented molecules protruding from the molecular island and show electroluminescence photon spectra with high electroluminescence yields of up to 6×10⁻³. These results demonstrate the promising potential of the NDI tripodal chromophores for the fabrication of molecular devices profiting from optical features of the molecular layer.     

Molecular Graph Paper

We present a self-assembled template that consists of tetraphenylmethane derivatives and adopts a periodic lateral arrangement on a Au(111) surface with acetyl groups sticking out of the molecular film. By using the tip of a scanning tunneling microscope, these acetyl groups can be removed in a spatially controlled way without significantly affecting the remaining molecular assembly. The chemically modified molecules can be readily distinguished from the original ones such that information can be engraved in the molecular film. Both the modified nature of an individual molecule and the order of the molecular film are shown to persist at room temperature. The mesh size of this molecular graph paper can be tuned by varying the length of the molecular spacer so that writing and reading information on the nanoscale with variable letter sizes becomes possible.     

New neptunium(V) borates that exhibit the alexandrite effect

A new neptunium(V) borate, K[(NpO(2))B(10)O(14)(OH)(4)], was synthesized using boric acid as a reactive flux. The compound possesses a layered structure in which Np(V) resides in triangular holes, creating a hexagonal-bipyramidal environment around neptunium. This compound is unusual in that it exhibits the Alexandrite effect, a property that is typically restricted to neptunium(IV) compounds.     

Synthesis and Crystal Structure of the First Thallium Hydrous Nesosilicate Tl4SiO4·0.5H2O

Orange prismatic crystals of the first thallium hydrous nesosilicate Tl₄SiO₄·0.5H₂O have been obtained by evaporation from aqueous solution. There are three symmetrically independent Tl⁺ cations and five symmetrically independent oxygen atoms in the structure of Tl₄SiO₄·0.5H₂O. The O(4) and O(5) atoms belong to water molecules. Coordination polyhedra of the Tl⁺ cations are strongly distorted because of the stereoactive behavior of lone electron pairs. The structure of Tl₄SiO₄·0.5H₂O contains sheets of SiO₄ tetrahedra and Tl coordination polyhedra. The sheets have the composition [Tl₃SiO₄]^– and are parallel to [100]. Within the sheets, SiO₄ tetrahedra link to thallium polyhedra though common corners. The sheets are linked by dimers of face‐sharing Tl(3)O₅ polyhedra, thus providing interconnection of the sheets into a framework. The framework has large elliptical channels occupied by water molecules (OW2) and electron pairs of Tl⁺ cations.The comparison with some other M⁺ (M = K, Ag, Tl) silicates is given.     

Stray field interaction of stacked amorphous tapes

In this study, magnetic cores made of amorphous rectangular tape layers are investigated. The quality factor Q of the tape material decreases rapidly, however, when stacking at least two tape layers. The hysteresis loop becomes non-linear, and the coercivity increases. These effects are principally independent of the frequency and occur whether tape layers are insulated or not. The Kerr-microscopy was used to monitor local hysteresis loops by varying the distance of two tape layers. The magnetization direction of each magnetic domain is influenced by the anisotropy axis, the external magnetic field and the stray field of magnetic domains of the neighboring tape layers. We found that crossed easy axes (as the extreme case for inclined axes) of congruent domains retain the remagnetization and induce a plateau of the local loop. Summarizing local loops leads to the observed increase of coercivity and non-linearity of the inductively measured loop. A high Q-factor can be preserved if the easy axes of stacked tape layers are identical within the interaction range in the order of mm.     

PLLA Coating of Active Implants for Dual Drug Release

Cochlear implants, like other active implants, rely on precise and effective electrical stimulation of the target tissue but become encapsulated by different amounts of fibrous tissue. The current study aimed at the development of a dual drug release from a PLLA coating and from the bulk material to address short-term and long-lasting release of anti-inflammatory drugs. Inner-ear cytocompatibility of drugs was studied in vitro. A PLLA coating (containing diclofenac) of medical-grade silicone (containing 5% dexamethasone) was developed and release profiles were determined. The influence of different coating thicknesses (2.5, 5 and 10 µm) and loadings (10% and 20% diclofenac) on impedances of electrical contacts were measured with and without pulsatile electrical stimulation. Diclofenac can be applied to the inner ear at concentrations of or below 4 × 10⁻⁵ mol/L. Release of dexamethasone from the silicone is diminished by surface coating but not blocked. Addition of 20% diclofenac enhances the dexamethasone release again. All PLLA coatings serve as insulator. This can be overcome by using removable masking on the contacts during the coating process. Dual drug release with different kinetics can be realized by adding drug-loaded coatings to drug-loaded silicone arrays without compromising electrical stimulation.