  Redox-based electrical conduction in nonconjugated polymers has been explored
less than a decade, yet is already showing promise as a new concept for
electrical energy transport. Here using monolayers and sub-monolayers of
touching micron-sized redox active colloids (RAC) containing high densities of
ethyl-viologen (EV) side groups, intercolloid redox-based electron transport
was directly observed via fluorescence microscopy. This observation was enabled
by the discovery that these RAC exhibit a highly non-linear
electrofluorochromism which can be quantitatively coupled to the colloid redox
state. By evaluating the quasi-Fickian nature of the charge transfer (CT)
kinetics, the apparent CT diffusion coefficient DCT was extracted. Along with
addressing more fundamental questions regarding energy transport in colloidal
materials, this first real-time real-space imaging of energy transport within
monolayers of redox-active colloids may provide insights into energy transfer
in flow batteries, and enable design of new forms of conductive polymers for
applications including organic electronics.
