In situ-XAS and catalytic study of acrolein hydrogenation over silver catalyst: Control of intramolecular selectivity by the pressure

The gas phase hydrogenation of acrolein over 7.5% Ag/SiO2 has been studied in a broad pressure range from 7.5 mbar to 20 bar. Higher pressures favour the formation of allyl alcohol (selectivities up to 42%), whereas at low pressures propionaldehyde is by far the main product. In situ-XAS has been performed at 7.5 mbar in order to gain insight into the interaction of acrolein with Ag(1 1 1). Hydrogenated propionaldehyde-like surface species could be detected which orientated parallel to the surface. The observed intermediate correlates perfectly with the online catalytic data

Controlling spins in adsorbed molecules by a chemical switch

The development of chemical systems with switchable molecular spins could lead to the architecture of materials with controllable magnetic or spintronic properties. Here, we present conclusive evidence that the spin of an organometallic molecule coupled to a ferromagnetic substrate can be switched between magnetic off and on states by a chemical stimulus. This is achieved by nitric oxide (NO) functioning as an axial ligand of cobalt(II)tetraphenylporphyrin (CoTPP) ferromagnetically coupled to nickel thin-film (Ni(001)). On NO addition, the coordination sphere of Co2+ is modified and a NO–CoTPP nitrosyl complex is formed, which corresponds to an off state of the Co spin. Thermal dissociation of NO from the nitrosyl complex restores the on state of the Co spin. The NO-induced reversible off–on switching of surface-adsorbed molecular spins observed here is attributed to a spin trans effect

Surface state engineering of molecule-molecule interactions

Engineering the electronic structure of organics through interface manipulation, particularly the interface dipole and the barriers to charge carrier injection, is of essential importance to improved organic devices. This requires the meticulous fabrication of desired organic structures by precisely controlling the interactions between molecules. The well-known principles of organic coordination chemistry cannot be applied without proper consideration of extra molecular hybridization, charge transer and dipole formation at the interfaces. Here we identify the interplay between energy level alignment, charge transfer, surface dipole and charge pillow effect and show how these effects collectively determine the net force between adsorbed porphyrin 2H-TPP on Cu(111). We show that the forces between supported porphyrins can be altered by controlling the amount of charge transferred across the interface accurately through the relative alignment of molecular electronic levels with respect to the Shockley surface state of the metal substrate, and hence govern the self-assembly of the molecules

Multimorphism in molecular monolayers: Pentacene on Cu(110)

The architecture of the contacting interface between organic molecular semiconductors and metallic or insulating substrates determines its cooperative properties such as the charge injection and the charge-carrier mobility of organic thin-film devices. This paper contributes a systematic approach to reveal the evolution of the different structural phases of pentacene on Cu(110) while using the same growth conditions. Complementary measurement techniques such as scanning tunneling microscopy and low-energy electron diffraction together with ab initio calculations are applied to reveal the complex multiphase behavior of this system at room temperature. For coverages between 0.2 and 1 monolayer (ML) a complex multiphase behavior comprising five different phases is observed, which is associated to the interplay of molecule/molecule and molecule/substrate interactions. Multimorphism critically depends on the thermodynamics and kinetics determined by the growth parameters as well as the system itself and arises from shallow energy minima for structural rearrangements. In consequence, the multimorphism affects the interface structure and therefore the interface properties

Exchange interaction between a ferromagnetic substrate and adsorbed metallo-porphyrin molecules

Exchange coupling between a magnetized thin film cobalt on mica substrate and adsorbed manganese(III)-tetraphenyl-porphyrin chloride (MnTPPCl) molecules is studied by X-ray magnetic circular dichroism. In the regime of a submonolayer coverage of MnTPPCl a clear circular dichroism is observed at the Mn LIII,II-edge, which is reverted with opposite grazing incidence with respect to the spin moments in the cobalt film. This result shows that the two species are ferromagnetically coupled to each other. Further evidence for the role of exchange interaction as the primary cause of the induced magnetism in MnTPPCl is observed on hysteresis loops of Co and MnTPPCl