[Zurück]

G. Kastlunger, X. Zhao, R. Stadler:
"Coherent tunneling and electron hopping in linear and branched molecules with multiple redox centers";
Poster: 13th European Conference on Molecular Electronics, Strassburg, Frankreich; 01.09.2015 - 05.09.2015.

For defining the conductance of single molecule junctions with a redox functionality in an electrochemical cell, two conceptually different electron transport mechanisms, namely coherent tunnelling and vibrationally induced hopping compete with each other, where implicit parameters of the setup such as the length of the molecule and the applied gate voltage decide which mechanism is the dominant one. Although coherent tunnelling is most efficiently described within Landauer theory, while the common theoretical treatment of electron hopping is based on Marcus theory, both theories are adequate for the processes they describe without introducing accuracy limiting approximations. For a direct comparison, however, it has to be ensured that the crucial quantities obtained from electronic structure calculations, i.e. the transmission function T(E)1, in Landauer theory, and the transfer integral2, the reorganisation energy and the driving force in Marcus theory, are derived from similar grounds3. In this contribution our framework is a single particle picture, where we perform density functional theory calculations for the conductance corresponding to both transport mechanisms for junctions with the central molecule containing one, two or three Ruthenium centers, respectively, and we extrapolate our results in order to define the critical length for the transition point of the two regimes (see Figure).
Branched molecules containing a redox active center in each of their two branches open up intriguing new possibilities which also depend on the electron transport regime in which the current flow occurs. If it is phase coherent electron tunnelling, wave like interference effects might be induced due to an asymmetry brought about by the use of different metals in both branches such as Osmium and Ruthenium and this might provide more flexibility in the related device design, in particular offering a route towards electrochemical switching. In the hopping regime on the other hand a local gating effect might be achieved, because the oxidation state of the metal in one branch is likely to have an influence on the electron transport through the other, thereby offering a route towards chemical sensors.

Projektleitung Robert Stadler:
Elektrochemische Interferenz