We report on the calculation of the I/V characteristic curve of a molecular species with an extended p system, which has been shown to behave as a single molecule diode. We have applied a computational method based on the Non-Equilibrium Green Function with a simplified treatment of the molecule-lead interaction that has been taken proportional to the projection of the orbitals onto specific terminal molecular fragments. We are able to fit the experimental data and to give an interpretation at the molecular level in terms of energy shift and mixing of the frontier orbitals around the Fermi level. (c) 2012 Elsevier B.V. All rights reserved.