Strong quenching of dye fluorescence in monomeric perylene orange/TMDC hybrid structures.

Hybrid structures with an interface between two different materials with properly aligned energy levels facilitate photo-induced charge separation to be exploited in optoelectronic applications. Particularly, the combination of 2D transition metal dichalcogenides (TMDCs) and dye molecules offers strong light-matter interaction, tailorable band level alignments, and high fluorescence quantum yields. In this work, we aim at the charge or energy transfer-related quenching of the fluorescence of the dye perylene orange (PO) when isolated molecules are brought onto monolayer TMDCs thermal vapor deposition.

Pulsed Electrical Stimulation Affects Osteoblast Adhesion and Calcium Ion Signaling.

An extensive research field in regenerative medicine is electrical stimulation (ES) and its impact on tissue and cells. The mechanism of action of ES, particularly the role of electrical parameters like intensity, frequency, and duration of the electric field, is not yet fully understood. Human MG-63 osteoblasts were electrically stimulated for 10 min with a commercially available multi-channel system (IonOptix).

The nanomorphology of cell surfaces of adhered osteoblasts.

The functionality of living cells is inherently linked to subunits with dimensions ranging from several micrometers down to the nanometer scale. The cell surface plays a particularly important role. Electric signaling, including information processing, takes place at the membrane, as well as adhesion and contact.

UV-Polymerized Vinylimidazolium Ionic Liquids for Permselective Membranes.

Ionic liquids are highly charged compounds with increasing applications in material science. A universal approach to synthesize free-standing, vinylalkylimidazolium bromide-containing membranes with an adjustable thickness is presented. By the variation of alkyl side chains, membrane characteristics such as flux and mechanical properties can be adjusted.

Role of redox-active axial ligands of metal porphyrins adsorbed at solid-liquid interfaces in a liquid-STM setup.

In a liquid-STM setup environment, the redox behavior of manganese porphyrins was studied at various solid-liquid interfaces. In the presence of a solution of Mn(III)Cl porphyrins in 1-phenyloctane, which was placed at a conductive surface, large and constant additional currents relative to a set tunneling current were observed, which varied with the magnitude of the applied bias voltage. These currents occurred regardless of the type of surface (HOPG or Au(111)) or tip material (PtIr, Au or W).

Self-Assembly of Covalently Linked Porphyrin Dimers at the Solid-Liquid Interface.

The synthesis and surface self-assembly behavior of two types of metal-porphyrin dimers is described. The first dimer type consists of two porphyrins linked via a rigid conjugated spacer, and the second type has an alkyne linker, which allows rotation of the porphyrin moieties with respect to each other. The conjugated dimers were equipped with two copper or two manganese centers, while the flexible dimers allowed a modular built-up that also made the incorporation of two different metal centers possible.

Nanostructuring of self-assembled porphyrin networks at a solid/liquid interface: local manipulation under global control.

Molecules of (5,10,15,20-tetraundecylporphyrinato)-copper(II) [(TUP)Cu] can self-assemble into four different polymorphs at the interface between highly oriented pyrolytic graphite and 1-octanoic acid. Scanning tunneling microscopy (STM) reveals that it is possible to combine the global control over monolayer structure, provided by the composition and concentration of the supernatant solution, with local control, from nanomanipulation by the STM tip. In the initially formed monolayer, with a polymorph composition governed by the concentration of (TUP)Cu in the supernatant solution, the exchange of molecules physisorbed at the solid/liquid interface with those in the liquid is very limited.

Detection of different oxidation states of individual manganese porphyrins during their reaction with oxygen at a solid/liquid interface.

Manganese porphyrins have been extensively investigated as model systems for the natural enzyme cytochrome P450 and as synthetic oxidation catalysts. Here, we report single-molecule studies of the multistep reaction of manganese porphyrins with molecular oxygen at a solid/liquid interface, using a scanning tunnelling microscope (STM) under environmental control. The high lateral resolution of the STM, in combination with its sensitivity to subtle differences in the electronic properties of molecules, allowed the detection of at least four distinct reaction species.

Polymorphism in porphyrin monolayers: the relation between adsorption configuration and molecular conformation.

Self-assembled monolayers of meso-5,10,15,20-tetrakis(undecyl)porphyrin copper(II) on a graphite/1-octanoic acid interface have been studied by Scanning Tunnelling Microscopy. Four distinct polymorphs were observed, varying in their unit cell size. Arrays of unit cells of the various polymorphs seamlessly connect to each other via shared unit cell vectors.

Extremely strong self-assembly of a bimetallic salen complex visualized at the single-molecule level.

A bis-Zn(salphen) structure shows extremely strong self-assembly both in solution as well as at the solid-liquid interface as evidenced by scanning tunneling microscopy, competitive UV-vis and fluorescence titrations, dynamic light scattering, and transmission electron microscopy. Density functional theory analysis on the Zn(2) complex rationalizes the very high stability of the self-assembled structures provoked by unusual oligomeric (Zn-O)(n) coordination motifs within the assembly. This coordination mode is strikingly different when compared with mononuclear Zn(salphen) analogues that form dimeric structures having a typical Zn(2)O(2) central unit.

Little exchange at the liquid/solid interface: defect-mediated equilibration of physisorbed porphyrin monolayers.

The transition from low to high density 2D surface structures of copper porphyrins at a liquid/solid interface requires specific defects at which nearly all exchange of physisorbed molecules with those dissolved in the supernatant occurs.

Controlled templating of porphyrins by a molecular command layer.

The copper porphyrin (5,10,15,20-tetraundecylporphyrinato)copper(II) can be templated in a well-defined arrangement using p-(hexadecyloxycarbonyl)phenylacetylene as a command layer on graphite. The bicomponent system was characterized at the submolecular level at a solid/liquid interface by scanning tunneling microscopy (STM). It is proposed that the layer of copper porphyrins is templated on top of the command layer in a hierarchical fashion, via a combination of intermolecular π-π stacking and van der Waals interactions.

Axial ligand control over monolayer and bilayer formation of metal-salophens at the liquid-solid interface.

Nickel salophens exclusively form monolayers at a liquid-solid interface, while in contrast zinc salophens mainly self-assemble into bilayers via axial ligand self-coordination which can be disrupted by the addition of pyridine axial ligands.

Molecular friction as a tool to identify functionalized alkanethiols.

By using the nanografting method, well-defined nanoscale patches of alkanethiols were constructed in a self-assembled monolayer (SAM) matrix on an atomically flat gold (Au(111)) surface. A series of nanografted patches, composed of alkanethiols with different end groups (-CH(3), -CF(3), -OH, -SH, -COOH, and -NH(2)), were analyzed in detail by a combination of atomic force microscopy (AFM) height and quantitative lateral friction measurements. By constructing a series of nanografted patches of methyl-terminated thiols with various chain lengths, it was shown that the absolute friction of the nanografted patches was always smaller than that of the surrounding SAM matrix, demonstrating that, because of the spatially confined self-assembly during nanografting, SAMs show less defects.

The effect of underlying octadecylamine monolayer on the DNA conformation on the graphite surface.

DNA was immobilized on highly oriented pyrolytic graphite (HOPG) surfaces modified in octadecylamine (ODA) vapor. ODA molecules, deposited from the vapor phase onto HOPG form a nanostructured surface, which was utilized as a template for DNA adsorption. Peculiarities of double- and single-stranded DNA adsorption on these surfaces were investigated with atomic force microscopy (AFM) both in air, liquid and under different salt conditions.

Scanning tunnelling spectroscopy on arrays of CdSe quantum dots: response of wave functions to local electric fields.

We use scanning tunnelling microscopy (STM) to controllably contact individual CdSe quantum dots (QDs) in a multilayer array to study electrical contacts to a model QD solid. The probability of electron injection into the QD array depends strongly on the symmetry of the QD wave functions and their response to the local electric field. Quantitative spectroscopy of the QD energy levels is possible if the potential distribution in the STM tip-QD array-substrate system is taken into account.

Theoretical study of the stable radicals galvinoxyl, azagalvinoxyl and wurster's blue perchlorate in the solid state.

Calculations on crystalline organic radicals were performed to establish the ground states of these materials. These calculations show that the radicals may interact, depending on their orientation in the crystal structure. For galvinxoyl, a second structure is proposed which is similar to that of azagalvinoxyl, in which the radicals form pairs.

Supramolecular porphyrin polymers in solution and at the solid-liquid interface.

We have investigated in detail the self-assembly of a chiral porphyrin trimer in different solvents and correlated this behavior to the aggregation of the molecule at a solid-liquid interface. In n-hexane and cyclohexane, CD spectroscopy and dynamic and static light scattering studies showed that the porphyrin trimer self-assembles already at micromolar concentrations into long, chiral supramolecular polymers, which precipitate as fibers when the solution is drop-cast onto a mica surface. In contrast, in chloroform, the compound is molecularly dissolved up to concentrations of 0.

Distinct kinetic and mechanical properties govern ALCAM-mediated interactions as shown by single-molecule force spectroscopy.

The activated leukocyte cell adhesion molecule (ALCAM) mediates dynamic homotypic and heterotypic cellular interactions. Whereas homotypic ALCAM-ALCAM interactions have been implicated in the development and maintenance of tissue architecture and tumor progression, heterotypic ALCAM-CD6 interactions act to initiate and stabilize T-cell-dendritic-cell interactions affecting T-cell activation. The ability to resist the forces acting on the individual bonds during these highly dynamic cellular contacts is thought to be crucial for the (patho)physiology of ALCAM-mediated cell adhesion.

Nonspecific protein adsorption at the single molecule level studied by atomic force microscopy.

Liquid tapping atomic force microscopy was used to study the nonspecific adsorption of horse spleen ferritin at a bare gold surface at single molecule resolution. The majority of ferritin molecules adsorbed irreversible on gold surfaces in accordance with the random sequential adsorption (RSA) mechanism frequently used to describe irreversible adsorption processes. However, the time-resolved data also reveal events that go beyond the RSA model, i.

Giant porphyrin disks: control of their self-assembly at liquid-solid interfaces through metal-ligand interactions.

The synthesis and self-assembly behaviour of porphyrin dodecamers 1H(2) and Zn-1, which consist of twelve porphyrins that are covalently attached to a central aromatic core, is described. According to STM, 1D and 2D NMR studies, and molecular modelling calculations, the porphyrin dodecamers have a yo-yo-shaped structure. Their large pi surface, in combination with their disk-like shape, allows them to form self-assembled structures, which in the case of Zn-1 can be tuned by adding bidentate ligands.

Can scanning tunnelling spectroscopy measure the density of states of semiconductor quantum dots?

Molecules, supramolecular structures and semiconductor nanocrystals are increasingly used as the active components in prototype opto-electrical devices with miniaturized dimensions and novel functions. Therefore, there is a strong need to measure the electronic structure of such single, individual nano-objects. Here, we explore the potential of scanning tunnelling spectroscopy to obtain quantitative information on the energy levels and Coulomb interactions of semiconductor quantum dots.