Bipyridinium salts methyl viologen

Synonyms 1,r-Dimethyl-4,4 -bipyridinium 1,T-Dimethyl-4,4 -bipyridinium salt Dimethyl viologen Methyl viologen (2+)... 

Organic Molecules It can be seen from our earlier discussion that the presence of a transition metal ion is not always required for an electrochromic effect. Indeed, many organic molecules can yield colored products as a result of reversible reduction or oxidation. 4,4 -Bipyridinium salts are the best known example of such compounds. These compounds can be prepared, stored, and purchased in colorless dicationic form (bipm +). One electron reduction of the dication leads to the intensely colored radical cation (bipm+ ). Such radical cations exist in equilibrium with their dimers (bipm ). In the case of methyl viologen, the radical cation is blue and the dimer is red. By varying the substient group in the molecule, different colors can be obtained. 

This amplification phenomenon can be applied to sensor design and was first demonstrated by our group in 1995 [9,10]. In these studies, the sensing ability for a methyl viologen salt or JV,J T -dimethyl-4,4 -bipyridinium... 

Numerous papers dealing with the photoreduction of viologens have appeared. Rate constants for electron transfer between aromatic hydrocarbon triplets and bipyridinium and pyridinium salts have been measured. The results suggest that the process is both facile and efficient. All the rate constants necessary for the determination of the quantum yield of formation of the viologen cation-radical in the methyl viologen-Eosin-EDTA system are also now available. " The high activity of dihydroxytin(rv) uroporphyrin in the photoreduction of methyl viologen has been ascribed to the failure of a photochemi-cally inactive tt—tt complex to be formed between substrate and sensitizer. 

A number of electron acceptors have been identified for reaction (40) that can effectively mediate H2 evolution from water in the presence of Pt-group based redox catalysts. Typical examples are bipyridinium salts such as methyl viologen (MV " "), polypyridine complexes of Rh(III), Co(II) and cage complexes of Co(II). For this reason, the oxidative quenching of various transition metal polypyridine complexes, M(LL)3]" by these electron acceptors have been extensively studied ... 

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