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Conductance of Well-Defined Porphyrin Self-Assembled Molecular Wires up to 14 nm in Length

Ferreira, Q. ; Bragança, A. ; Alcácer, L. ; Morgado, J.

Journal of Physical Chemistry C Vol. 118, Nº 3, pp. 7229 - 7234, March, 2014.

ISSN (print): 1932-7447
ISSN (online): 1932-7455

Scimago Journal Ranking: 2,03 (in 2014)

Digital Object Identifier: 10.1021/jp501122n

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We show that molecular wires up to 14 nm in length composed by zinc-porphyrins bridged by bipyridines stand efficient electrical transport. Self-assembled molecular wires were prepared step-by-step, alternating up to 13 units of zinc-octaethylporphyrin with axially coordinated 4,4′-bipyridine, on highly oriented pyrolytic graphite (HOPG). A combination of molecular resolution imaging and scanning tunneling spectroscopy allowed us to follow molecules self-assembly in real time during wire fabrication and to measure wires current, respectively. A statistical analysis of hundreds of current–voltage curves was carried out to determine the conductance of individual porphyrin/bipyridine wires. From the conductance dependence on the wires length an ultra low attenuation factor (β = 0.015 ± 0.006 Å–1) was obtained for shorter wires, with a transition in conduction regime occurring at ca. 6.5 nm long wires.