Revealing the Effect of Pendant Identity on the Electrochemistry of Non-Conjugated Redox Active Polymers.

Abstract

Understanding charge transfer in redox-active non-conjugated polymers is key to unlocking their potential as alternative materials for energy storage. Many factors contribute to charge transfer, such as flexibility of the backbone, redox moiety type, and distance between neighboring redox sites. In a previous work, a series of spatially defined 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-containing polymers was reported, with varied spacer lengths between the redox sites. Herein, the synthesis and characterization of spatially defined polymers is reported with the same spacing of three different redox pendants (phenothiazine, phthalimide, and dopamine) and the corresponding electrochemical properties. By doing so, the effect of solution-polymer interactions (in both the charged and neutral states) is revealed. The apparent diffusion coefficient (D_app), the self-exchange rate constant (k_ex), and the polymer-solvent interactions (χ and A₂) of the phenothiazine, phthalimide, and TEMPO polymers are compared. The dopamine-based polymer exhibits limited solubility, preventing further characterization. D_app and k_ex correlate with χ, suggesting that solvent favorability enhances charge transfer in the solution state. These findings highlight the important role that polymer-solvent interactions play in the transfer of electrons, suggesting that a swollen polymer chain conformation promotes solution-state electron transfer and that solvent favorability promotes charge transfer.