@article{oai:nagasaki-u.repo.nii.ac.jp:00001457,
 author = {Sagara, Takamasa and Eguchi, Hitomi},
 journal = {Electrochimica Acta},
 month = {Feb},
 note = {Redox reactions of highly water-soluble bis-viologens were examined at Au electrodes using ultra-micro electrode steady state voltammetry and electroreflectance methods in addition to conventional voltammetry. A bulk UV-vis absorption spectral approach was also used. Alkane-1,n-diyl bis-viologens appeared as a class of prototypical electroactive molecule possessing two equivalent redox centers; they undergo two-consecutive one-electron transfer processes. When intramolecular dimerization takes place immediately after accepting the second electron to produce a form having two viologen radical cation (V•+) sites in one molecule, the second reduction potential may be more positive than the first one. This redox potential inversion is caused by strong tendency to form a stable intramolecular π−π stacking between the two V•+ sites. The redox potential inversion of a highly water-soluble bis-viologen with a butane-1,4-diyl linkage was quantitatively obtained to be 116 mV (E1 – E2 = -116 mV). In contrast, the bis-viologen with an ethane-1,2-diyl linkage exhibited no dimerization below 0.2 mM, and its second redox potential was found to at 63 mV more negative than the first (E1 – E2 = 63 mV), highlighting repulsive interaction. The value of E1 – E2 = -116 mV for the bis-viologen with a butane-1,4-diyl linkage corresponds to the attractive interaction energy in the redox process of 5.9 kBT of room temperature; this value is apparently the same as the dimerization Gibbs free energy of methyl viologen in water., Electrochimica Acta, 295, pp.215-223; 2019},
 pages = {215--223},
 title = {Revisiting aqueous redox process of alkyl-linked bis-viologen: Evaluation of redox potential inversion},
 volume = {295},
 year = {2019}
}