It is interesting to compare the electronic properties of the various structures, all consisting of different coupling motifs of the same precursor unit. As reference we thus take the precursor unit. Scanning tunneling spectroscopy measurements on the as-deposited molecules, however, are hindered by their limited stability. Whereas well-defined resonances associated with the occupied states can be observed (Fig. ), at positive bias values of around +2 V there is always a sudden jump in the conductance associated with a chemical transformation of the molecules; in particular, with their debromination. The unoccupied molecular orbitals of m1 are expected to be around those energies and the instability may be actually promoted by the population of the LUMO level upon tunneling. In any case, a proper characterization of the unoccupied orbitals is thus hindered. However, such instability is no longer present in debrominated monomer molecules. In this case we can also observe a clear resonance from the HOMO level, although shifted by about 0.29 eV towards the Fermi level to an energy of -1.34 eV (Fig. ). Halogenation of molecules is a commonly applied method to increase their ionization potential and electron affinity. We thus associate the observed shift with the disappearance of the halogen's effect as its bond to the molecule is broken. An advantage of this is that the LUMO resonance can now be nicely resolved as well, with its maximum at an energy of 2.05 eV, resulting in a HOMO-LUMO gap of 3.39 eV (Fig. ).