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.

Scheme 1. Structures of the oEDOT derivative 1 and the mono-urea derivative 2.

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