Effects of polaron hopping on the transport through DNA

For functionality of organic molecules it is of primary importance to understand how they can operate as current switches. On the way to this goal, we examine possible mechanisms of the reported experimentally ”conductance switching” behavior in alkyldithiol molecular wires modified with a viologen (bipyridinium) moiety, which oxidation state can be controlled by electrochemical gating [1,2]. Based on density functional theory calculations, we show that molecules under study behave as weakly coupled quantum dots, where the current is carried by a redox-active LUMO-(lowest unoccupied molecular) level [3]. We calculate how the conductance decays with increasing the wire length and thereby recover quantitatively the experimental tunneling exponent [4]. Our calculations imply, that the charging induced conformational change in the bipyridinium unit is not a main switching agent, rather than the phonon-assisted inelastic electron transport through the viologen redox-level explains the observed switching behavior [3].