Self-Assembly of the Chiral Donor-Acceptor Molecule DCzDCN on Cu(100).

Donor-acceptor (D-A) structured molecules are essential components of organic electronics. The respective molecular structures of these molecules and their synthesis are primarily determined by the intended area of application. Typically, D-A molecules promote charge separation and transport in organic photovoltaics or organic field-effect transistors. D-A molecules showing a larger twist angle between D and A units are, e.g., essential for the development of high internal quantum efficiency in organic light-emitting diodes. A prototypical molecule of this D-A type is DCzDCN (5-(4,6-diphenyl-1,3,5-triazine-2-yl)benzene-1,3-dinitrile). In most cases, these molecules are only investigated regarding their electronic and structural interaction in bulk aggregates but not in ultrathin films supported by a metallic substrate. Here, we present growth and electronic structure studies of DCzDCN on a Cu(100) surface. We used a complementary approach through the use of scanning tunneling microscopy/spectroscopy (STM and STS), ultraviolet/inverse photoemission spectroscopy (UPS and IPES), and single-molecule density functional theory (DFT) calculations. This method combination enabled us to investigate the adsorption geometry (STM) and the local electronic states near the Fermi energy (EF) of a single adsorbed molecule (using STS) and to compare these data with the integral overall electronic structure of the DCzDCN/Cu(100) interface (using UPS/IPES). The orientation of the molecules with the donor part toward the substrate results in a chiral resolution at the interface due to the molecular as well as the substrate symmetry and additional strong molecular electrostatic forces induced by the charge distribution of the twisted dicarbonitrile part. Thus, the formation of various bulk-unlike homochiral structures and the appearance of hybrid interface states modify the molecular electronic properties of the DCzDCN/Cu(100) system, e.g., the transport gap by -1.3 eV compared to that of a single DCzDCN molecule. This may be useful not only for optoelectronic applications but also in organic spintronics.

Cobalt Catalysts for [2+2+2] Cycloaddition Reactions: Isolated Precatalysts and in†situ Generated Catalysts.

[2+2+2] Cycloaddition reactions belong to the not even large class of reactions, which can be catalyzed or mediated by a significant number of different transition metals. Cobalt complexes belong to the catalysts that paved the way for the extensive use and profound mechanistic knowledge on this particular transformation. Beside the established role, cyclopentadienyl (Cp) cobalt complexes inherit in synthetic applications of the cyclotrimerization reaction, modification of the precatalysts opened up novel reactivities and versatility for such catalytic initiators. At the same time the development of in situ generated cobalt catalysts allowed the conversion of novel substrates as well as novel reaction modes to be realized. In this personal account recent developments will be presented and the possibilities of catalysts containing cobalt atoms in different oxidation states be discussed.

Analysis of saccharides in beverages by HPLC with direct UV detection.

The present study demonstrates the suitability of direct UV detection for saccharide analysis in HPLC. Under highly alkaline conditions, the non-UV absorbing saccharides are converted by a photo-initiated chemical reaction in the detection cell into malonenolate, which can be detected at 266 nm. A straightforward method for such direct UV detection of saccharides after their separation by anion-exchange chromatography was developed and successfully applied to several beverage samples. Investigation and optimization of the influencing factors using design of experiment resulted in a baseline separation of glucose, fructose, and sucrose within 6 min and LOD values below 0.2 mg L(-1). In addition, a fast, simple and cost-effective flow injection method was developed to estimate the total saccharide concentration. The results of this method applied to beverage samples are in good agreement with the chromatographic method as well as to the saccharide concentration stated by the manufacturer. Finally, a comparison of different commercially available UV detectors and detector cells revealed that sensitive detection requires the use of recently introduced flow cells with extended path length.

Photoionization cross-section weighted DFT simulations as promising tool for the investigation of the electronic structure of open shell metal-phthalocyanines.

The valence band structure of different metal-phthalocyanines was investigated by comparing ultraviolet photoelectron spectra at different excitation energies with simulated spectra that take the different photoionization cross-sections at these energies into account. The Kohn-Sham eigenvalue spectra, derived from density functional theory calculations, using hybrid exchange-correlation functionals, were weighted with the photoionization coefficients in accordance with the used excitation energy. By applying these techniques, the differences in the photoelectron spectra using He I and He II radiation can be reproduced and investigated. It will be shown that the 3d-orbitals of the used metal central atom of these molecules have a major influence. The changes at different excitation energies were studied for Fe, Co, and Cu central atoms to describe the chemical tailoring effects.