Mohamed M. S. Abdel-Mottaleb

Self-assembly of tetrathiafulvalene derivatives at a liquid/solid interface—compositional and constitutional influence on supramolecular ordering

The self-assembly of a series of tetrathiafulvalene (TTF) derivatives at the interface between non-volatile organic solutions and the graphite surface has been studied by scanning tunnelling microscopy (STM). The TTFs have been prepared such that they bear none, one, two (in different constitutions) or four alkyl chains of different lengths and different functional groups. The STM images reveal that the packing of the TTF cores can effectively be controlled by changing the substitution pattern on the heterocycle. Several structures are seen at the interphase—parquet-type packing, single and double core tapes, and even isolated molecules—all of which have the TTF core essentially coplanar with the surface. Molecular modelling has shown that several orientations of the molecules are practically equal in energy on the graphite, which explains the polymorphous packing of some of the molecules. Solvent effects also play a role in determining the 2D structures.

Dynamics in Physisorbed Monolayers of 5-Alkoxy-isophthalic Acid Derivatives at the Liquid/Solid Interface Investigated by Scanning Tunneling Microscopy

Monolayers of isophthalic acid derivatives at the liquid/solid interface have been studied with scanning tunneling microscopy (STM). We have investigated the dynamics related to the phenomenon of solvent co-deposition, which was previously observed by our research group when using octan-1-ol or undecan-1-ol as solvents for 5-alkoxy-isophthalic acid derivatives. This solvent co-deposition has now been visualized in real-time (two frames per second) for the first time. Dynamics of individual molecules were investigated in mixtures of semi-fluorinated molecules with video-STM. The specific contrast arising from fluorine atoms in STM images allows us to use this functionality as a probe to analyze the data obtained for the mixtures under investigation. Upon imaging the same region of a monolayer for a period of time we observed that non-fluorinated molecules progressively substitute the fluorinated molecules. These findings illustrate the metastable equilibrium that exists at the liquid/solid interface, between the physisorbed molecules and the supernatant solution.

Monolayer self-assembly at liquid-solid interfaces : chirality and electronic properties of molecules at surfaces

The spontaneous formation of supramolecular assemblies at the boundary between solids and liquids is a process which encompasses a variety of systems with diverse characteristics: chemisorbed systems in which very strong and weakly reversible bonds govern the assembly and physisorbed aggregates which are dynamic thanks to the weaker interactions between adsorbate and surface. Here we review the interest and advances in the study of chiral systems at the liquid–solid interface, and also the application of this configuration for the study of systems of interest in molecular electronics, self-assembled from the bottom up.

Adlayers and Low-Dimensional Assemblies of a TTF Derivative at a Liquid−Solid Interface

Scanning tunneling microscopy has been employed to investigate the ordering of a tetrathiafulvalene derivative at a liquid-solid interface at room temperature. Surprisingly, in addition to the observation of polymorphous two-dimensional pseudocrystals, lower-dimensional assemblies are observed. Scanning tunneling spectroscopy at the individual molecule level reveals rectifying behavior, independent of the molecular ordering.

STM at the Liquid/Solid and Air/Solid Interface: Exploring 2D Phase‐Behavior, Templating, and Tip‐Induced Reactivity

Forming controlled 2D patterns is an important goal. A very simply but efficient way of preparing ordered films of monolayer thickness is via physisorption at the liquid‐solid interface. In order to control the ordering of molecules in the 2D monolayer structure, directional non‐covalent modes of interaction such as hydrogen bonding and metal complexation, are of great help and importance. In this paper, we report on ways how to explore 2D phase‐behavior. For reports on templating and tip‐induced reactivity, we refer to ref. 7 and ref. 8.

Synthesis, separation, and isomer-dependent packing in two dimensions--detected by scanning tunnelling microscopy--of a TTF derivative.

The synthesis, isolation and STM imaging on graphite of the cis and trans isomers of a TTF reveal isomer-dependent packing, and constitutes a way to study the non-covalent interactions at play in these systems.