Viologen 4,4 -Dipyridyl

Viologen (4,4 -dipyridyl dihydrochloride) [27926-72-3] M 229.1, m >300 . Purified by pptn on adding excess of acetone to a concentrated solution in aqueous MeOH. It has also been recrystd several times from MeOH and dried at 70° under vacuum for 24h [Prasad et al. 5 Am Chem Soc 108 5135 7986], and recrystd three times from MeOH/isopropanol [Stramel and Thomas J Chem Soc, Faraday Trans 82 799 1986]. 

For instance, inclusion of l,T-dimethyl-4,4 -dipyridyl cation-radical (the cation-radical of methyl viologen) into a cavity of sulfocalixarenes prevents the disadvantageous n dimerization. This is important for more effective use of viologens as components of electrochromic displays and electric condnctors (Gno et al. 2007, references therein). 

Fig. 6. Summary of the standard oxidation-reduction potentials of several dyes and the experimentally determined rate constants for their reduction by P430 . [DP, dipyridyls, preceded by the redox-potential values M(B)V, methyl (benzyl) viologens ST. safranine T MB, methylene blue]. Figure source Ke (1973) The primary electron acceptor of photosystem I. BiochimBiophysActa301 29.

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