5,5‘-Bis(methylthio)-2,2‘-bithiophene: A Potential Cathode Electroactive Material for Energy Storage Devices

Abstract

We present a study of the electrochemical properties of a set of oligothiophenes including 2,5-bis(methylthio)thiophene (BMTT), its derivatives, and 5,5‘-bis(methylthio)-2,2‘-bithiophene (BMTbT). BMTbT, which possesses an α-coupled bithiophene capped with methylthio groups, exhibited two one-electron reversible processes at 3.8 and 4.0 V vs Li/Li+, respectively, while BMTT exhibited only one reversible process. The chemically and electrochemically reversible processes of BMTbT derive from the stabilization of the monocation and dication by the methylthio groups at the 2,5-positions and by the extension of the conjugated resonance structure (i.e., from mono- to bithiophene). Compared to other substituents at the 2,5-positions such as methoxy, methyl, sulfinylmethyl, t-butylthio, and pyrrolidine groups, we found that methylthio groups uniquely stabilize the oxidized species more effectively, giving rise to the chemically reversible redox couples. Furthermore, the stabilizing effect of the methylthio groups ...