Electron Transport Through Molecular Structures

Electron transport through molecular structures is investigated with three different concepts. Polythiophenyl substituted benzenes were studied as reducible substructures in molecular architectures. By linking two reducible substructures with different bridging motives the potential of the bridging structure as electronic connector was investigated. Diacetylene turned out to be the most promising bridging motive and was therefore further studied. Longer, linear rod-like structures consisting of up to four reducible substructures linked with diacetylenes in para position displayed delocalization of the reducing electron over the whole structure. Macrocycles consisting of four, six, eight and ten reducible substructures connected in meta position with diacetylenes accepted several reduction electrons at the same potential and displayed the behavior of molecular batteries. Molecular rods were immobilized with terminal sulfur functions between two gold electrodes of a mechanically controlled break junction. Electronic transport properties of single molecules were investigated in this setup. Comparison of the spatial symmetries of molecular rods based on organic π-systems and their current/voltage characteristics provided evidences that indeed electric currents through single molecules were observed. Incorporation of a trans-platinum(II) center in the π-system of the bridging rod yielded in an increased resistance of more than three orders of magnitude, giving to the investigated platinum complex the features of a single molecule insulator. A new concept of investigating electron mobility in nanoscale molecular cycles is presented together with the synthetic route to the required nanoscale object. The experiment addresses questions concerning the coherence of electron wave functions and the conjugation length in organic molecular structures.