The oxidation/reduction properties of the thiol-substituted carotenoid, 7'-apo-7'-(4-mercaptomethylphenyl)-beta-carotene (AMC), on gold and glassy carbon electrodes were investigated. Similarities of the first and second oxidation potentials of AMC when the glassy carbon electrode is used are attributed to stabilization of the dication in the presence of CH2Cl2. This does not occur for AMC tethered to gold, where the second oxidation potential is higher than the first by 145 mV. Self-assembled monolayers between AMC and the gold electrode causes the first oxidation potential to be lower by 90 mV than that on glassy carbon electrode. These phenomena are examined with density functional theory (DFT) calculations, which show that the ionization potential for the AMC-transition metal complex is lower than that of AMC. DFT calculations also show that the LUMO of the carotenoid-transition metal complex is independent of the chain length of the carotenoid but is related to the transition metal. Upon reduction at -1.185 V versus SCE the C-S bond of self-assembled AMC is cleaved.