Feedstock-Derived Thiophene Radical Anions Exhibiting Redox Stability at Extreme Potentials.

Organic radicals that are both readily synthesized from commodity chemicals and stable at extreme redox potentials are rare, yet highly desirable for applications in energy storage and organic electronics. Herein, we report feedstock-derived thiophene radical anions bearing ester functionalities that undergo galvanostatic charge-discharge redox cycling at potentials below -2 V versus Fc/Fc (Fc = ferrocene). Systematic structural modification led to the identification of a derivative exhibiting exceptional redox stability, showing promise as a scalable and low-cost electrolyte for electron storage applications. Further, a crystalline thiophene radical anion was isolated and characterized using structural, spectroscopic, and computational methods. These studies revealed that the ester functionalities stabilize the reduced "quinoidal" thiophene electronic structure without the need for extended π-delocalization. Taken together, a new class of electron storage media is reported that combine redox stability at extreme potentials with straightforward synthesis, while offering rare insight into the structural and electronic features of stable thiophene radicals.