Pattern Formation in organic monolayers

The thesis describes bottom-up approaches towards molecular patterning at the solid-liquid interface. The shape of the pattern depends on properties that can be influenced at the molecular level. The structures are visualized with the scanning tunneling microscope (STM).

Scanning tunnelling microscopy of a foldamer prototype at the liquid/solid interface: water/Au(111) versus 1-octanol/graphite

We report the design and synthesis of a catechol based foldamer containing amide functionalized alkyl chains, and its monolayer formation at the liquid/solid interface. By scanning tunnelling microscopy, both at the 1-octanol/graphite interface as well as at the water/Au(111) interface, the self-assembly has been investigated with submolecular resolution, demonstrating clear solvent dependent effects on the conformation of the ‘foldamer’ and its monolayer formation.

Metal ion complexation: A route to 2D templates?

The two-dimensional ordering of a number of 2,2'-bipyridine derivatives at the liquid/solid interface has been investigated by scanning tunneling microscopy. By appropriate functionalization of the bipyridine units, their intermolecular distance can be tuned, which has proved to be crucial for complexation with metal ions. The in situ addition of metal salts (Pd2+, Cu2+), leading to the formation of metal-bipyridine complexes, has a dramatic influence on the two-dimensional ordering of the molecules and suggests that these complexes could be used as templates

Supramolecular Control of Two-Dimensional Phase Behavior

We have used directed two-component self-assembly to "pattern" organic monolayers on the nanometer scale at the liquid/solid interface. The ability of the scanning tunneling microscope to investigate structural details in these adlayers was used to gain insight into the two-component two-dimensional phase behavior. The components are symmetrically alkylated bisurea derivatives (R1-urea-spacer-urea-R2; R1, R2=alkyl, spacer=alkyl or bisthiophene). The bisthiophene unit acts as a marker and its bisurea derivative (T2) is a component in all the mixtures investigated. By varying the position of the hydrogen-bond forming urea groups along the molecule and the length of the alkyl chains of the other components, the effect of 1) hydrogen bonding, 2) molecule length, 3) odd - even effects, and 4) shape complementarity on the two-dimensional phase behavior was investigated. Insight into the effect of these parameters leads to the control of the two-dimensional patterning: from randomly intermixed systems to phase separation.