Supramolecular π-stacked assemblies of bis(urea)-substituted thiophene derivatives and their electronic properties probed with scanning tunneling microscopy and scanning tunneling spectroscopy

In this contribution we investigated the two-dimensional (2D) supramolecular organization and electronic properties of two bis(urea)-substituted oligothiophene derivatives, containing two or three thiophene units (T2 and T3, respectively), at the solution/graphite interface with scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Because of the pi-stacking of the oligomers the observed zero conductance band gap in the I(V) curves of a ribbon is found to be considerably smaller than for an isolated oligothiophene molecule, indicating that there exists an effective conjugation in the pi-stacked ribbons on the surface.