Methylene blue when kept in miliQ water for overnight becomes faint, bluish color disappears slowly. We thought may be because of some reduction process it happens so. But the color doesn't come back even after adding oxidant(ferricyanide). Does anybody know the reason for this? Is there a tendency of this dye to degrade(lose conjugation)?
Isn't it due to oxidation with oxygen? That the principle of a well-known demonstration experiment employing redox properties of MB (e.g.: http://en.wikipedia.org/wiki/Blue_bottle_%28chemical_reaction%29 ). The other reason may be formation of dimers and higher oligomers of MB, that is known to occur especially at higher concentrations ( http://pubs.acs.org/doi/abs/10.1021/jp050439j ) however all these aggregates are also coloured, so this perhaps does not apply to your faint of blue colour. However I have two suggestion for you: 1) try to keep the same MB solution without oxygen (bubble it with nitrogen/argon or degas it); 2) try to add reducing agent to the fainted solution. (And moral is, no, MB is not stable as many other fluorescent dyes are not)
thanks peter....but MB is colored in oxidized form...classic Blue bottle experiment says MB turns blue when the reduced MB mixed with oxygen. And the aggregation happens in frozen form as the above article says. Thanks again for your suggestions, it helps.
It may be because these dyes are sensitive to degradation in the presence of visible light which leads to the fading of color. However, this phenomenon is more pronounced with red colored dyes, but it occurs with blue colored dyes also.
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