Design and Evaluation of a Boron Dipyrrin Electrophore for Redox Flow Batteries

A boron dipyrrin (BODIPY) dye was designed as a molecular single‐component electrophore for redox flow batteries. All positions of the BODIPY core were assessed on the basis of literature data, in particular cyclic voltammetry and density functional calculations, and a minimum required substitution pattern was designed to provide solubility, aggregation, radical cation and anion stabilities, a large potential window, and synthetic accessibility. In‐depth electrochemical and physical studies of this electrophore revealed suitable cathodic behavior and stability of the radical anion but rapid anodic decomposition of the radical cation. The three products that formed under the conditions of controlled oxidative electrolysis were isolated, and their structures were determined by spectroscopy and comparison with a synthetic model compound. From these structures, a benzylic radical reactivity, initiated by one‐electron oxidation, was concluded to play the major role in this unexpected decomposition. Radical behavior: A boron dipyrrin (BODIPY) derivative, rationally designed for application in a symmetric redox flow battery, shows unexpected reactions upon exhaustive oxidation. The side‐reactions for the electro‐oxidation of a BODIPY electrophore are discussed, and the value of exhaustive electrolysis experiments for the evaluation of redox‐active materials is highlighted.