On the fluorescence and photoreduction of methyl viologens

Abstract

The fluorescence of methyl viologen (MV²⁺) has been reinvestigated. The green emission has been attributed to impurities whose formation from MV²⁺ can be induced thermally or photochemically. One of the green fluorescent compounds has been found to act as an efficient photosensitizer for the reduction of MV²⁺ to MV⁺. In contrast to MV²⁺, the 1,1′,2,2′,6,6′-hexamethyl-4,4′-bipyridinium dication was found to be fluorescent. The fluorescence properties of 2,2′,6,6′-tetramethyl-4,4′-bipyridine and its protonated cations are also reported. The values of ^*pK_a(S₁) of a 4,4′-bipyridine have been obtained for the first time.