  The possibility of using single molecule junctions as electron pumps for
energy conversion and storage is considered. It is argued that the small
dimensions of these systems enable to make use of unique intra-molecular
quantum coherences in order to pump electrons between two leads and to overcome
relaxation processes which tend to suppress the pumping efficiency. In
particular, we demonstrate that a selective transient excitation of one
chromophore in a bi-chromophoric donor-bridge-acceptor molecular junction model
yields currents which transfer charge (electron and holes) unevenly to the two
leads in the absence of a bias potential. The utility of this mechanism for
charge pumping in steady state conditions is proposed.
