What is responsible for colour in a dye?
Chemistry discussion, revision, exam and homework help.
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What is responsible for colour in a dye?In my book, it says the delocalised electron system is involved in colour in deyes. Then it says it's the chromophore involved in colours in dye on the next page.
Which one is it??
Also, what's the difference between an azo group and a chromophore? Both have N==N ? and why is the azo group and chromophore important? -
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Re: What is responsible for colour in a dye?A chromophore is just part of a molecule that is responsible for it's colour. Your book is describing the same thing on both pages.
A chromophore might include an azo group, but doesn't have to. Take beta-carotene for example.
The conjugated pi system in red accounts for the molecule's colour. You could call it a chromophore; but it doesn't have -N=N- in it. -
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Re: What is responsible for colour in a dye?The energy spacing between molecular orbitals is what determines the colour, as it is transitions between these levels that causes the absorbance of light.
The longer the delocalised system, the smaller the spacings. So long delocalised chains are usually needed to form chromophores (molecules that absorb visible light), particularly if they are to absorb red/orange light. e.g. the beta-carotene as above
