The self-assembly and redox-properties of two viologen derivatives, N-hexyl-N 0 -(6-thiohexyl)-4,4 0 -bipyridinium bromide (HS-6V6-H) and N,N 0 -bis(6-thiohexyl)-4,4 0 -bipyridinium bromide (HS-6V6-SH), immobilized on Au(111)-(1 Â 1) macro-electrodes were investigated by cyclic voltammetry, surface enhanced infrared spectroscopy (SEIRAS) and in situ scanning tunneling microscopy (STM). Depending on the assembly conditions one could distinguish three different types of adlayers for both viologens: a low coverage disordered and an ordered ''striped'' phase of flat oriented molecules as well as a high coverage monolayer composed of tilted viologen moieties. Both molecules, HS-6V6-H and HS-6V6-SH, were successfully immobilized on Au(poly) nano-electrodes, which gave a well-defined redox-response in the lower pA-current range. An in situ STM configuration was employed to explore electron transport properties of single molecule junctions Au(T)|HS-6V6-SH(HS-6V6-H)|Au(S). The observed sigmoidal potential dependence, measured at variable substrate potential E S and at constant bias voltage (E T À E S ), was attributed to electronic structure changes of the viologen moiety during the one-electron reduction/re-oxidation process V 21 2 V 1d . Tunneling experiments in asymmetric, STM-based junctions Au(T)-S-6V6-H|Au(S) revealed current (i T )-voltage (E T ) curves with a maximum located at the equilibrium potential of the redox-process V 21 2 V 1d . The experimental i T À E T characteristics of the HS-6V6-H-modified tunneling junction were tentatively attributed to a sequential two-step electron transfer mechanism.

Ti-substituted mesoporous SBA-15 (Ti-SBA-15) materials have been synthesized by using a new approach in which the hydrolysis of the silicon precursor (tetramethoxysilane, TMOS) is accelerated by fluoride. These materials were characterized by powder X-ray diffraction patterns (XRD), X-ray fluorescence spectroscopy (XRF), N 2 sorption isotherms, diffusereflectance UV-visible (UV-vis) and UV-Raman spectroscopy, 29 Si MAS NMR, and the catalytic epoxidation reaction of styrene. Experiments show that Ti-SBA-15 samples of high quality can be obtained under the following conditions: F/Si g 0.03 (molar ratio), pH e 1.0, aging temperature e 80°C, and Ti/Si e 0.01. It was found that the hydrolysis rate of TMOS was remarkably accelerated by fluoride, which was suggested to play the main role in the formation of Ti-SBA-15 materials of high quality. There is no stoichiometric incorporation of Ti, and the Ti contents that are obtained are quite low in the case of the approach that is proposed. The calcined Ti-SBA-15 materials show highly catalytic activity in the epoxidation of styrene.

The potential-induced adsorption and self-assembly of 1,3,5-benzene-tricarboxylic acid (TMA) was investigated at the electrified Au(111)/0.05 M H2SO4 interface by in-situ scanning tunneling microscopy (STM) and surface enhanced infrared reflection absorption spectroscopy (SEIRAS) in combination with electrochemical techniques. Depending on the applied electric field, TMA forms five distinctly different, highly ordered supramolecular adlayers on Au(111) surfaces. We have elucidated their real-space structures at the molecular scale. In the potential range -0.25 V < E < 0.20 V, planar-oriented TMA molecules form a hexagonal open-ring honeycomb structure, Ia, a hydrogen-bonded ribbon-type phase, Ib, and a herringbone-type phase, Ic, stabilized by directional hydrogen bonding and weak substrate-adsorbate interactions. Interfacial water molecules are being replaced. In 0.20 V < or = E < 0.40 V, e.g., around the potential of zero charge, and at slightly higher coverages, a close-packed physisorbed adlayer of hydrogen-bonded TMA dimers, II, was observed. Further increase of the electrode potential to positive charge densities causes an orientation change from planar to upright. An initially disordered phase, IIIa, transforms into an ordered, stripelike chemisorbed adlayer, IIIb, of perpendicularly oriented TMA molecules. One carboxylate group per molecule is bound to the electrode surface, while the two other protonated carboxyl groups are directed toward the electrolyte and act as structure-determining components of a hydrogen-bonded two-dimensional ladder-type network. Structural transitions between the various types of ordered molecular adlayers are attributed to (hole) nucleation and growth processes.

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Two-step redox reactions (Mn(ii) ions ⇌ ZnMn2O4 spinel ⇌ layered Zn-birnessite) during the charge–discharge process.

The conductance of molecular junctions formed of N,N′-bis(n-thioalkyl)-4,4′-bipyridinium bromides or alkanedithiols between a gold (Au) scanning tunnelling microscope tip and a Au(111)-(1 × 1) electrode has been studied at electrified solid/liquid interfaces. A statistical analysis based on large sets of individual current–distance traces was applied to obtain the electrical conductance of single junctions. The one-electron reduction of the viologen moiety from the dication V2+ to the radical cation state gives rise to a 50% increase of the junction conductance. Increasing the length of the alkyl spacer units leads to a tunnelling decay constant βCH2 = 5.9–6.1 nm−1. This value is significantly lower than βCH2 = 8.2 nm−1 estimated for molecular junctions of alkanedithiols. The difference is attributed to conformational changes within the two junctions. The contact conductance was estimated to 10 µS.

The nucleation process of iron-exchanged zeolite Fe-ZSM-5, from the assembly of distorted tetrahedrally coordinated iron species and silicate rings in the precursor to the final Fe-ZSM-5 crystals, as well as variations in the coordination environment of iron, were studied by UV resonance Raman spectroscopy and complementary techniques.The entire sequence of crystallization events of Fe-ZSM-5 was monitored by UV Raman spectroscopy in combination with HRTEM, UV/Vis spectroscopy, X-ray diffraction patterns, and periodic DFT calculations. Fe-ZSM-5 was synthesized by an organic-free method to avoid signal interference from the organic template in Raman spectra. Framework iron atoms with resonance Raman bands at 516, 1115, and 1165 cm(-1), and a Raman band at 1016 cm(-1) are detected for Fe-ZSM-5. In the early stage of Fe-ZSM-5 synthesis, the precursor contains iron atoms in distorted tetrahedral coordination and five- and six-membered silicate rings. Nucleation by aggregation of the precursor species was monitored by UV Raman spectroscopy based on the resonance Raman effect, and confirmed by periodic DFT calculations. Evolution of iron species on the surface and in the bulk phase was monitored by UV Raman spectroscopy with excitation at 244 and 325 nm, as well as HRTEM. Nucleation takes place first in the core of the amorphous particles, and crystalline nuclei with Fe-ZSM-5 structure are formed in the core by consuming the amorphous shell. Finally the amorphous particles are completely transformed into Fe-ZSM-5 crystals.

The adsorption and self-assembly of benzoic acid (BA), isophthalic acid (IA), and trimesic acid (TMA) on Au(111) single crystals and on Au(111-25 nm) quasi-single crystalline film electrodes have been investigated in 0.1 M HClO4 by combining in situ surface-enhanced infrared reflection absorption spectroscopy (SEIRAS) and scanning tunneling microscopy (STM) with cyclic voltammetry. All three acids are physisorbed on the electrode surface in a planar orientation at negative charge densities. Excursion to positive charge densities (or more positive potentials) causes an orientation change from planar to perpendicular. Chemisorbed structures are formed through the coordination of a deprotonated carboxyl group to the positively charged electrode surface. The three acid molecules assemble in different ordered patterns, which are controlled by pi-stacking (BA) or intermolecular hydrogen bonds between COOH groups (IA, TMA). A detailed analysis of the potential and time dependencies of the nu(C=O), nus(OCO), and nu(C-OH) vibration modes shows that the strength of lateral interactions increases upon chemisorption with an increasing number of COOH groups in the sequence of BA