  Using a first principles approach to electron transport, we calculate the
electrical and thermoelectrical transport properties of a series of molecular
wires containing benzo-difuran subunits. We demonstrate that the side groups
introduce Fano resonances, the energy of which is changing with the
electronegativity of selected atoms in it. We also study the relative effect of
single, double or triple bonds along the molecular backbone and find that
single bonds yield the highest thermopower, approximately 22$\mu$V/K at room
temperature, which is comparable with the highest measured values for
single-molecule thermopower reported to date.
