  The ability to control the conductance of single molecules will have a major
impact in nanoscale electronics. Azobenzene, a molecule that changes
conformation as a result of a trans/cis transition when exposed to radiation,
could form the basis of a light-driven molecular switch. It is therefore
crucial to clarify the electrical transport characteristics of this molecule.
Here, we investigate theoretically charge transport in a system in which a
single azobenzene molecule is attached to two carbon nanotubes. In clear
contrast to gold electrodes, the nanotubes can act as true nanoscale electrodes
and we show that the low-energy conduction properties of the junction may be
dramatically modified by changing the topology of the contacts between the
nanotubes and the molecules, and/or the chirality of the nanotubes (that is,
zigzag or armchair). We propose experiments to demonstrate controlled
electrical switching with nanotube electrodes.
