Fluorination effect on electrochemistry of dibutyl viologen in aqueous solution

We have synthesized a perfluoro analog of dibutyl viologen by replacing the side –(CH2)2-CH2CH3 groups with –(CH2)2-C2F5 groups. The effect of fluorination on the aqueous solution electrochemistry was investigated using experimental voltammetric measurements and DFT computations. The formal potential of one-electron transfer redox couple, viologen radical monocation/dication, became 128 mV less negative upon fluorination, and the diffusion coefficient of the oxidized form was lowered by ca. 12%. Calculations indicated that the shift of the formal potential is largely caused by strong electron-withdrawing nature of the perfluorinated groups despite a separation of (CH2)2 from the viologen core. The effect is counter balanced by an opposite but smaller effect from the change of solvation free energy due to perfluorination. This perfluoro viologen is water-soluble in both oxidation states and is expected to be used as a redox probe at electrified oil-water and fluorous phase-water interfaces