Upon the intrinsic optical properties of oligo(p-phenyleneethynylene)s (OPEs). Synthesis of OPE3 for experimental gas-phase absorption studies

A new oligo(p-phenyleneethynylene) (OPE3) was synthesized by step-wise Pd-catalyzed cross-coupling reactions. The molecule incorporates an amine functionality, which allows for transfer of the protonated molecule to the gas phase by electrospray ionization leaving the OPE entity neutral. This method has allowed for the first experimental gas-phase absorption spectrum of an OPE3 by action spectroscopy, employing an electrostatic ion storage ring in combination with a laser system. The studies reveal the effect of having a positive charge in proximity to the conjugated backbone of OPE3 in the absence of any interfering solvent molecules. In addition, ionization energies and electron affinities of OPE2-OPE17 were calculated at the density functional theory (DFT) level.     

State preparation and dynamics of ultracold atoms in higher lattice orbitals

We report on the realization of a multiorbital system with ultracold atoms in the excited bands of a 3D optical lattice by selectively controlling the band population along a given lattice direction. The lifetime of the atoms in the excited band is found to be considerably longer (10-100 times) than the characteristic time scale for intersite tunneling, thus opening the path for orbital selective many-body physics with ultracold atoms. Upon exciting the atoms from an initial lowest band Mott-insulating state to higher lying bands, we observe the dynamical emergence of coherence in 1D (and 2D), compatible with Bose-Einstein condensation to a nonzero momentum state.     

Controlled self-organization of atom vacancies in monatomic gallium layers

Ga adsorption on the Si(112) surface results in the formation of pseudomorphic Ga atom chains. Compressive strain in these atom chains is relieved via creation of adatom vacancies and their self-organization into meandering vacancy lines. The average spacing between these line defects can be controlled, within limits, by adjusting the chemical potential mu of the Ga adatoms. We derive a lattice model that quantitatively connects density functional theory (DFT) calculations for perfectly ordered structures with the fluctuating disorder seen in experiment and the experimental control parameter mu. This hybrid approach of lattice modeling and DFT can be applied to other examples of line defects in heteroepitaxy.     

LNA (locked nucleic acid) and analogs as triplex-forming oligonucleotides

The triplex-forming abilities of some conformationally restricted nucleotide analogs are disclosed and compared herein. 2'-Amino-LNA monomers proved to be less stabilising to triplexes than LNA monomers when incorporated into a triplex-forming third strand. N2'-functionalisation of 2'-amino-LNA monomers with a glycyl unit induced the formation of exceptionally stable triplexes. Nucleotide analogs containing a C2',C3'-oxymethylene linker (E-type furanose conformation) or a C2',C4'-propylene linker (N-type furanose conformation) had no significant effect on triplex stability proving that conformational restriction per se is insufficient to stabilise triplexes.     

Photoswitching Behavior of a Cyclohexene‐Bridged versus a Cyclopentene‐Bridged Dithienylethene System

Photoswitching is an intriguing way of incorporating functionality into molecules or their subunits. Dithienylethene switches are particularly promising, but have so far mostly been studied with five‐membered ring (cyclopentenyl) backbones. We aim at comparing the switching properties of backbones with five and six carbon atoms in the ring. A major advantage is that cyclohexenyl rings offer new options for chiral functionalization. A slight change in the reaction conditions of a McMurry ring closure reaction leads to the formation of dithienyl derivatives with a cyclohexene backbone in reasonable yield. Density functional theory calculations were carried out, demonstrating the similarity of both compounds. Experimental results confirm the theoretical outcomes.     

Factoring of positive definite functions: A counterexample based on an extension theorem

No abstract. December 24, 1999     

Fluoride bridges as structure-directing motifs in 3d-4f cluster chemistry

The use of kinetically robust chromium(III) fluorido complexes as synthons for mixed 3d-4f clusters is reported. The tendency toward linear {Cr(III)-F-Ln(III)} units dictates the cluster topology. Specifically, we show that reaction of cis-[Cr(III)F(2)(NN)(2)]NO(3) (NN = 1,10-phenanthroline ("phen") or 2,2'-bipyridine ("bpy")) with Ln(NO(3))(3)·xH(2)O produces isostructural series of molecular {Ln(2)Cr(2)} squares (1-9) with linear fluoride bridges. In a parallel fashion, fac-[Cr(III)F(3)L], where L = N,N',N″-trimethyl-1,4,7-triazacyclononane ("Me(3)tacn"), reacts with Nd(NO(3))(3)·6H(2)O to form a fluoride-centered penta-nuclear complex and fac-[Cr(III)F(3)L'], with L' = 1,1,1-tris-((methylamino)methylethane) ("Me(3)tame"), reacts with [Ln(hfac)(3)(H(2)O)(2)] (hfacH = 1,1,1,5,5,5-hexafluoroacetylacetone) to yield an isostructural series of {Ln(3)Cr(2)} (10-14) trigonal bipyramids with no central ligand. The formation of the latter is accompanied by a partial solvolysis of the Cr(III) precursor but without formation of insoluble LnF(3). The magnetic properties of the gadolinium containing clusters allow quantification of fluoride-mediated, antiferromagnetic Gd-Cr exchange interactions of magnitude between 0.14 cm(-1) and 0.71 cm(-1) (? = J(12)?(1)·?(2) formalism) and vanishingly small J(Gd-Gd) of 0.06(0) cm(-1). The large spin and small anisotropy together with weak exchange interactions in the {Gd(3)Cr(2)} (11) cluster give rise to a very large magneto-caloric effect of -ΔS(m) = 28.7 J kg(-1) K(-1) (μ(0)H = 90 to 0 kOe).     

Hydrothermal synthesis and humidity sensing property of ZnO nanostructures and ZnO-In(OH)3 nanocomposites

Prism- and raspberry-like ZnO nanoparticles and ZnO-In(OH)(3) nanocomposites were prepared by template free hydrothermal method. XRD investigations and microscopic studies showed that pill-like In(OH)(3) particles with body-centered cubic crystal structure formed on the surface of ZnO nanoparticles resulting in increased specific surface area. TEM-EDX mapping images demonstrated that not only nanocomposite formation took place in the course of the synthesis, but zinc ions were also built into the crystal lattice of the In(OH)(3). However, only undoped In(OH)(3) was found on the surface of the pill-like particle aggregates by XPS analyses. The raspberry- and prism-like ZnO particles exhibit strong visible emission with a maximum at 585 and 595 nm, respectively, whose intensity significantly increase due to nanocomposite formation. Photoelectric investigations revealed that photocurrent intensity decreased with increasing indium ion concentration during UV light excitation, which was explained by increase in visible fluorescence emission. QCM measurements showed that morphology of ZnO and concentration of In(OH)(3) had an influence on the water vapor sensing properties.     

High-order time-integration applied to p-version finite elements within finite strain thermo-viscoelasticity

In this essay a fully coupled, monolithic thermo-mechanical coupled simulation using high-order finite elements based on hierarchical shape-functions in combination with a high-order time-integration scheme using diagonally-implicit Runge-Kutta schemes is presented. The constitutive model is based on a finite strain thermo-viscoelasticity relation of overstress-type. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)