Marcel Mayor*, a, Michael Büschelb, Jörg Daubb, Katharina M. Frommc, Jean-Marie Lehnd, Heiko B. Webera, Joachim Reicherta, Detlef Beckmanna
aForschungszentrum Karlsruhe, Institute for Nanotechnology,
Karlsruhe D-76021 GERMANY bInstitut für Organische Chemie, Universität Regensburg cDép. de Chim. Minérale, Analytique et Appliquée, Uni. Genève dISIS, Université Louis Pasteur, Strasbourg
Molecular electronic, understood as constructing electronic circuits based on single molecules, strongly depends on the electron transport properties of the individual molecular structure. Currently great interest is focused on a modular building set of molecular structural motives, with well defined electronical properties. With two different approaches we contribute to the understanding of the molecular structure/electron transport relationship. a) By connecting reducible subunits, the electron transport properties of the bridging structures were studied in solution. b) Two gold electrodes were connected with a single molecule to study its current/voltage features.
A series of molecular motives was introduced as bridging structure between reducible pentakis(thiophenyl)benzene subunits. This allowed to study the electron transport properties of the bridging structures by conventional electrochemical techniques in solution. The bridging structures consist of para-divinylbenzene, bis-hydrazone and diacetylene. The diacetylene bridge turned out to be the best conducting connector, and its potential was further studied with longer, linear molecules  and with cyclic molecules  based on this structural motive.
In the second approach, the electron transport properties of individual molecules were observed directly. Therefore, a whole series of molecular rods of about 2 nm length and with thiol functions on each end was envisaged. First members, consisting of acetylene connected aromatic systems, are already synthesized. In a mechanically controlled break junction their current/voltage characteristics were studied. Internal properties of single molecules, like their symmetry, were observed for the first time by this technique.
Both methods contribute to the understanding of the electron transport in molecular structures and thereby provide insight into the physical properties of molecular building blocks for molecular electronic.
M. Mayor, M. B¸schel, K. M. Fromm, J. M. Lehn, J. Daub, Chem. Eur. J., 6, 1266-1272 (2001).
M. Mayor, J.-M. Lehn, K. M. Fromm, D. Fenske, Angew. Chem. Int. Ed. Engl., 36, 2370-2372 (1997).
M. Mayor, J.-M. Lehn, J. Am. Chem. Soc., 121, 11231-11232 (1999).
J. Reichert, R. Ochs, D. Beckmann, H. B. Weber, M. Mayor, H. von Löhneysen, submitted to Phys. Rev. Lett., cond-mat/0106219
Dr. Marcel Mayor
Forschungszentrum Karlsruhe GmbH, Institut für Nanotechnologie
Postfach 3640, Karlsruhe D-76021 GERMANY
phone: (+49)7247 82 6392
fax: (+49)7247 82 6369