  Using a first principles approach, we study the electron transport properties
of two molecules of length 2.5nm which are the building blocks for a new class
of molecular wires containing fluorenone units. We show that the presence of
side groups attached to these units leads to Fano resonances close to the Fermi
energy. As a consequence electron transport through the molecule can be
controlled either by chemically modifying the side group, or by changing the
conformation of the side group. This sensitivity, which is not present in
Breit-Wigner resonances, opens up new possibilities for novel single-molecule
sensors.
