Electrochemical Energy Storage in Poly(dithieno[3,2-b:2′,3′-d]pyrrole) Bearing Pendant Nitroxide Radicals

The design and electrochemical synthesis of a conjugated radical polymer (CRP), poly­(dithieno­[3,2-b:2′,3′-d]­pyrrole) bearing pendant nitroxide radicals, is reported. Conjugated radical polymers potentially offer simultaneous conductivity and redox activity in the context of organic energy storage. One challenge is understanding the internal electron transfer that occurs in CRPs, which affects the electrochemical energy storage properties. The CRP here is purposefully designed to examine the case of when the conjugated backbone’s redox potential is less than that of the organic radical group. Cyclic voltammetry on the as-prepared CRP exhibits two well-resolved redox peaks at E pa1 = 3.15 V and E pa2 = 3.61 V vs Li/Li+, corresponding to the redox activities of the (dithieno­[3,2-b:2′,3′-d]­pyrrole) (DTP) backbone and nitroxide radical, respectively. Galvanostatic charge/discharge studies also reveal a two-step charge/discharge process. The lower oxidation potential of DTP contributes to a conductive pathway during the charge/discharge process. An internal electron transfer process occurs during the decay of the open circuit potential, as the final potential stabilizes around 3 V. This strategy emphasizes the effects on energy storage when the redox active polymer contains two moieties that are redox active at different potentials, thus impacting future CRP design.