Recent knowledge of the details of molecular transistors provides the basis for investigating the electrochemistry of single molecules. Exploration of the harlequin patterns of the Coulomb blockade diamonds of molecules is a path for obtaining knowledge of the redox chemistry of single molecules. A combined QM/ MM method is used to calculate the properties of a paraphenylenevinylene oligomer, OPV5, in a gold junction. Subsequent construction of the Coulomb blockade diamonds is performed based on a simplified theoretical description of the experimental set-up. The theoretical investigations provide knowledge about the actual molecular structure and orientation between the two electrodes. Moreover, the study reflects the strength of the fast, and simple, QM/MM approach, by producing results that are comparable to what is measured experi- mentally. The single molecule redox chemistry of the OPV5 molecule is discussed based on the calculations, and compared to experiment. The study show evident resemblance to experiment. Furthermore, it reveals chemical changes of OPV5 when OPV5 is exposed to high voltages.