  We consider exciton- and light-induced current in molecular nanojunctions.
Using a model comprising a two two-level sites bridge connecting free electron
reservoirs we show that the exciton coupling between the sites of the molecular
bridge can markedly effect the source-drain current through a molecular
junction. In some cases when excited and unexcited states of the sites are
coupled differently to the leads, the contribution from electron-hole
excitations can exceed the Landauer elastic current and dominate the observed
conduction. We have proposed an optical control method using chirped pulses for
enhancing charge transfer in unbiased junctions where the bridging molecule is
characterized by a strong charge-transfer transition.
