Redox-Driven Folding, Unfolding, and Refolding of Bis(tetrathiafulvalene) Molecular Switch

We report redox-driven folding, unfolding, and refolding motions of a synthetic molecular system, in which two tetrathiafulvalene (TTF) units are tethered onto a conformationally rigid yet torsionally flexible π-conjugated backbone. Upon one-electron oxidation, this molecular switch undergoes swiveling motions from a fully relaxed and freely rotating Z-shaped conformation to a compact folded conformation stabilizing π-stacked radical species. Subsequent one-electron oxidation produces dicationic intermediates, which either engage in intimate π-π interactions or transition to an open structure. Further oxidation, however, brings the molecule back to the initial conformation to minimize the repulsion between doubly-charged TTF units. Intriguingly, the reaction coordinates of this redox-driven structural change have strong dependence on the environment, such as the solvent (THF vs CH₂Cl₂) and supporting electrolyte (PF₆^- vs B(C₆F₅)₄^-). With a proper design, factors that are typically considered as "secondary effects" could dictate the solution dynamics and reaction pathways of structural folding and unfolding, all driven by controlled delivery of electrons.