  We present a comprehensive study of the properties of the off-resonant
conductance spectrum in oligomer nanojunctions between graphitic electrodes. By
employing first-principle-based methods and the Landauer approach of quantum
transport, we identify how the electronic structure of the molecular junction
components is reflected in electron transport across such systems. For
virtually all energies within the conduction gap of the corresponding idealised
polymer chain, we show that: a) the inverse decay length of the tunnelling
conductance is intrinsically defined by the complex-band structure of the
molecular wire despite ultrashort oligomer lengths of few monomer units, and b)
the contact conductance crucially depends on both the local density of states
on the metal side and the realised interfacial contact.
