Electronic Effects of p-Phenyl Substituted Substituents on the Electrochemical Oxidative a-Thiophene Dimerization
As the concern for global climate change has increased throughout the years, research involving renewable and non-carbon emitting sources of energy, including wind and solar, has become increasingly important. An area of focus in this research is determining a method to store energy efficiently and for a long period of time, so it can be used when the energy cannot be used as readily, such as windless days or during the night. A promising system is using solar energy to drive a nonspontaneous a-thiophene dimerization reaction resulting in energy storage in the form of a carbon-carbon bond of the dimer. Carroll College researchers previously synthesized monomer structures of thiophene used in this research, which contained different substituents in the 2-position of the thiophene ring, including 4-ethoxycarbonylphenyl and 4-methoxyphenyl groups. With these two monomers, we employed electrochemistry and performed cyclic voltammetry (CV) experiments to determine potential values of oxidation and reduction correlating to the production and consumption of the potential dimer and finding the overall mechanism of the reaction. From the CV, the thiophene monomer with the 4-ethoxycarbonylphenyl substituted group showed an oxidation potential value at +1.0 V and the one with the 4-methoxyphenyl substituted group exhibited a less positive oxidation potential value of +0.7 V. We conclude that the slight shift in oxidation potential values was consistent with the 4-methoxyphenyl substituted thiophene being more electron-rich and, therefore, easier to oxidize than the 4-ethoxycarbonylphenyl substituted thiophene. Future studies will be directed at determining dimerization rate constants of the thiophene compounds for the purposes of performing a Hammett Analysis of the system.