Flexible Backbone Effects on the Redox Properties of Perylenediimide-Based Polymers

Organic electrode materials are appealing candidates for a wide range of applications, including heterogeneous electrocatalysis and electrochemical energy storage. However, a narrow understanding of the structure-property relationships in these materials hinders the full realization of their potential. Herein, we investigate a family of insoluble perylenediimide (PDI) polymers to interrogate how backbone flexibility affects their thermodynamic and kinetic redox properties. We verify that the polymers generally access the highest percentage of redox-active groups with K⁺ ions (vs Na⁺ and Li⁺) due to its small solvation shell/energy and favorable soft-soft interactions with reduced PDI species. Through cyclic voltammetry, we show that increasing the polymer flexibility does not minimize barriers to ion-insertion processes but rather increases the level of diffusion-limited processes. Further, we propose that the condensation of imides to iminoimides can truncate the imide polymer chain growth for certain diamine monomers, leading to greater polymer solubilization and reduced cycling stability. Together, our results provide insight into how polymer flexibility, ion-electrode interactions, and polymerization side reactions dictate the redox properties of PDI polymers, paving the way for the development of next-generation organic electrode materials.