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Subing Qu1 Zihao Ou1 Yavuz Savsatli1 Yu Cao1 E. Montoto1 Bo Li1 Brian Bailey1 Charles Schroeder1 Joaquin Rodriguez-Lopez1 Jeffrey Moore1 Qian Chen1 Paul Braun1

1, Univ of Illinois-Urbana-Champ, Urbana, Illinois, United States

Ethyl viologen-based nonconjugated redox active colloids (RAC) demonstrate efficient and reversible charge transport in aqueous and non-aqueous environments. They can be used as electrode materials in flow-battery setup to prevent crossover issues between anolytes and catholytes. RAC is also intriguing for the colloid science community as a novel type of colloid bearing intrinsic function (charge transport through electron hopping) at the molecular level. There is tremendous scientific value in direct visualization of contact-mediated electron and or energy transfer between these colloids, which will provide deep understanding of the unique dynamics as well as facilitate redox-state mapping in this system. Electrofluorochromism of RAC was discovered and exploited to serve the purpose. Via coupling a distinct fluorescent contrast with the respective redox states we successfully conducted in-situ imaging of intra- and inter-colloid electron hopping processes during electrochemical cycling. We captured an over 20μm electron diffusion in a RAC monolayer. Due to the percolation nature of RAC monolayer, inter-colloid charge transport diffusion coefficient DCT was facilely extracted and first-time reported. This system also displayed a sensitivity to fluorescence quenching, the photophysics of which was preliminarily investigated and ascribed to fast electron hopping among neighboring redox groups. By correlating charge input and fluorescence emission over time we developed a working curve which renders RAC a redox state meter in and of itself under optical microscopes.

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