Interfacial electronic structure of vanadyl naphthalocyanine on highly ordered pyrolytic graphite

We present a core and valence region spectroscopic analysis of the interfacial electronic structure of thin films of vanadyl naphthalocyanine (VONc) deposited onto highly oriented pyrolytic graphite (HOPG). X-ray photoelectron spectroscopy indicates the predominantly ionic character of the vanadyl metal center coordinated by the heterocycle and affords the bandgap in the thin VONc films. Valence band photoelectron spectroscopy points to the existence of three different adsorption geometries of VONc on the HOPG surface. The distribution of the different geometries can be systematically influenced in a simple post-deposition processing step, with an immediate effect on the interfacial electronic environment. We find spectroscopic evidence in the valence levels that VONc grows on HOPG most likely in a 2D-gas fashion rather than by nucleation and growth of islands. These data allow us to predict accurately the interface dipole in the case of a broad class of dipolar organic semiconductors, based simply on molecular dipole moment, polarizability and molecular diameter. This ability provides an important step towards rational optimization of energy level alignment in organic electronics.     

Nonlinear effects in enantioselective chromatography: prediction of unusual elution profiles of enantiomers in non-racemic mixtures on an achiral stationary phase doped with small amounts of a chiral selector

Nonlinear effects caused by molecular association of enantiomers in non-racemic mixtures can cause unexpected effects in chiroptics, NMR spectroscopy, homogeneous catalysis, and chromatography. Herein we present a theoretical model to simulate and verify unusual elution orders of enantiomers on an achiral stationary phase doped with a small amount of a chiral selector or achiral columns coupled with columns doped with a chiral selector. Scenarios with strong, medium, and weak associations of enantiomers, different separation efficiencies typical for flash chromatography and liquid chromatography, and the influence of the enantioselectivity of the chiral selector on the complex equilibria have been investigated. The findings presented here are of importance for the validation of the determination of enantiomeric ratios in not fully separated elution zones as well as for the preparative separation of non-racemic enantiomeric mixtures on chiral stationary phases bonded to achiral matrices.     

Efficient Aerobic Wacker Oxidation of Styrenes Using Palladium Bis(isonitrile) Catalysts

The palladium‐catalyzed aerobic oxidation of alkenes and especially styrenes (Wacker oxidation) by using chiral pseudo C₂‐symmetrical bis(isonitrile) ligands in the absence of further cocatalysts gives rise to methyl ketones in a highly chemoselective manner. The palladium bis(isonitrile) catalyst was characterized by NMR spectroscopy and X‐ray structure analysis, revealing a dissymmetric coordination of palladium by the two isonitrile moieties.     

An Anionic Amido-Substituted Seven-Vertex Siliconoid Cluster

The silanide [Si₄{N(SiMe₃)Dipp}₃]⁻ ( 1 ) transforms into the anionic siliconoid cluster [Si₇{N(SiMe₃)Dipp}₃]⁻ ( 2 ) with four unsubstituted silicon atoms as a contact ion pair with [K([18]crown-6)] in C₆D₆ at room temperature within five weeks. Anion 2 was investigated by natural population analysis and visualization of intrinsic atomic orbitals. Magnetically induced current-density calculations of 2 revealed two distinct strong diatropic vortices that sum up in one direction and create a strongly shielded apical silicon atom in 2 .     

DTA/TGA/DSC and densification data for iron phosphate glasses having natural UO2.67 or surrogate Bi2O3 added

Journal of Thermal Analysis and Calorimetry - A new set of iron-uranium phosphate glasses containing (1–20) UO2.67. (10–20) Fe2O3. (55–68) P2O5 (mass/%) were melted adequately....     

Assignment of E/Z isomers in Schiff bases of 3-acyltetramic acids with ethylenediamine by 1H and 13C NMR spectroscopy

The reaction of ethylenediamine with an equivalent mixture of diversely substituted 3-acyltetramic acids leads to Z/Z, Z/E, E/Z and E/E isomers. The E/Z isomerisation is slow in the NMR time scale of the ¹H and ¹³C chemical shifts; therefore at room temperature and in deuterochloroform all isomers of the new synthesized asymmetric compounds N,N′-ethylene-(1-ethyl-5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic acid) a, N,N′-ethylene-(5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic acid) b and, N,N′-ethylene-(1,5,5-trimethyl-1′,5′,5′-trimethyl-3-acetyl-3′-formyl-tetramic acid) c could be found in the corresponding spectra. To assign the ¹³C NMR signals we used two-dimensional ¹³C-¹H one-bond (HMQC) and ¹³C-¹H multibond (HMBC) correlated spectroscopy and the empirical rule that CO signals involved in hydrogen bonds are shifted to a lower field. The relative stability of isomers depending on substitution pattern could be estimated from the composition of the equilibria. b crystallizes as Z/Z isomer from ethanolic solution. The X-ray structural analysis of b has shown two CH-O hydrogen bonds. Received: 31 May 1996 / Revised: 26 June 1996 / Accepted: 1 July 1996     

Post-polymerization modification of aromatic polyimides via Diels-Alder cycloaddition

We report a facile post-polymerization modification route to functionalized aromatic polyimides via Diels-Alder cycloaddition. Aromatic polyimides are important, versatile high-performance polymers; however, their structural diversity is restricted by the requirements of the step-growth polymerization. We prepared polyimides with alkynes in their main-chain as macromolecular dienophiles and quantitatively grafted tetraphenylcyclopentadienone based dienes. The resulting solution-processable, wholly aromatic polyimides show a considerable increase in surface area due to the induced conformational changes and bulky, rigid, and contorted molecular structures. The orthogonality of the reaction is exploited to insert functional groups, namely bromine and sulfonates, along the polymer backbone. In a further extension, the phenylene segments undergo cyclodehydrogenation to form nanographene segments within the polymer chains. The Diels-Alder cycloaddition onto polyimides is therefore demonstrated to be an effective, widely applicable route to tunable high-performance polymers with value-added functionality and thus considerable potential in a wide range of advanced materials.