Redox behaviour of some asymmetrically substituted viologens and an alkyl bridged bis-viologen in non-aqueous solvents: a voltammetric and spectroscopic investigation

• DOI: 10.1007/s10008-014-2629-2
• Publication Date: 2014-10-13T05:29:10Z
• Authors: Monika Passon; Adrian Ruff; Paul Schuler; Bernd Speiser; Wolfgang Leis
• Keywords: 540; 01 natural sciences; 3. Good health; 0104 chemical sciences

A compound library of seven asymmetrically substituted viologens and, additionally, a bis-viologen is investigated by voltammetric and EPR- and UV–Vis spectroelectrochemical techniques as well as diffusion-ordered nuclear magnetic resonance (NMR) spectroscopy. In acetonitrile-based electrolytes, all compounds show a stepwise two electron chemically and electrochemically reversible reduction of the viologen moieties. In the case of the bis-viologen, peak potential difference data indicate a weak difference in the formal potentials of the two non-conjugated redox systems. Diffusion coefficients from cyclic voltammetric and pulse gradient spin echo NMR experiments are comparable for all mono-viologens while the size and saturation of the side chain in the mono-viologen compounds has only a minor influence on this transport property. The semi-quinone forms of the viologens are highly stable with respect to disproportionation and they are EPR active. For the mono-viologens, coupling constants for all hydrogen and nitrogen nuclei interacting with the unpaired electron were determined. The bis-viologen forms a bis(radical cation) as well as an EPR-silent (but UV-detectable) π-dimer. Furthermore, the effect of weakly coordinating anions on the different redox states is reported.