Redox flow batteries are promising energy storage technology, but they incorporate many integrated parts including electrolytes, electrode-electrolyte interfaces, and separators / membranes. Methods for monitoring deleterious events such as electrode deposition, membrane crossover, and overall battery health are needed. Self-reporting molecules are useful internal probes to diagnose and troubleshoot these events. Here, we report a series of fluorescent redox-active materials that function as such tools. 2,1,3-benzothiadiazole (BzNSN) is a known energy-rich molecule with a reduction potential of -1.58 vs. Ag/Ag<sup>+</sup>. Acetamide-containing BzNSN homologs were synthesized via commercially available materials and their electrochemical stability and spectroscopic properties were evaluated. Molecular design was crucial for radical anion stability. For example, an <i>N</i>-methylacetamide derivative was one of the most stable BzNSN radicals ever synthesized with an extremely long radical lifetime (ca. 130 hours) while the parent acetamide decayed 15 minutes after electrolysis. DFT studies were used to understand molecular conformation distinctions affecting stability. Absorption and fluorescence behavior as a function of electrolyte salt was measured to provide Stern-Volmer plots and determine salt-dependent quenching and aggregation behavior. Due to ease of synthesis, these materials could be extended to oligomer and polymer designs. Oligomer and polymer versions were designed to evaluate membrane crossover, pore blocking, and fluorescence quenching based on proximity effects. Specifically, a poly(carbonate) platform was chosen that could be easily derivatized through post-synthetic modification. Factors such as polymer length, redox tether length, and copolymer designs were considered and evaluated for redox stability.

From small molecules to polymers: Fluorescent benzothiadiazoles for advanced monitoring of flow battery components

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.