New Cruciform Structures: Toward Coordination Induced Single Molecule Switches

New cruciform structures 1−4 were synthesized to investigate a new single molecule switching mechanism arising from the interplay between the molecule and the electrode surface. These molecular cruxes consist of two rod-type substructures, namely an oligophenylenevinylene and an oligophenyleneethynyl. While the oligophenylenevinylene rods are functionalized with acetyl protected sulfur anchor groups, the oligophenyleneethynyl rods provide terminal pyridine units. The hypothesized switching mechanism should arise from the electrochemical potential dependent coordination of the pyridine unit to the electrode surface. The assembly of the oligophenylenevinylene substructure was based on a Wittig reaction whereas its perpendicular oligophenyleneethynyl rod was assembled by Sonogashira−Hagihara coupling reactions. Preliminary transport investigations with molecular cruciforms 2 and 4 in a mechanical controllable break junction in a liquid environment displayed the trapping of single molecules between two gold electrodes via the terminally sulfur functionalized oligophenylenevinylene rod

Electrical Conductance of Conjugated Oligomers at the Single Molecule Level

We determine and compare, at the single molecule level and under identical environmental conditions, the electrical conductance of four conjugated phenylene oligomers comprising terminal sulfur anchor groups with simple structural and conjugation variations. The comparison shows that the conductance of oligo(phenylene vinylene) (OPV) is slightly higher than that of oligo(phenylene ethynylene) (OPE). We find that solubilizing side groups do neither prevent the molecules from being anchored within a break junction nor noticeably influence the conductance value