Advanced Level Organic Chemistry: UV and visible light absorption spectroscopy - azo dyes

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Doc Brown's Advanced Chemistry: PART 15.5 uv and visible light absorption spectroscopy - azo dyes

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses Spectroscopic methods of analysis and molecular structure determination

SPECTROSCOPY INDEXES  *  All Advanced Organic Chemistry Notes  *  [WEBSITE SEARCH BOX]

15.5.1 The origin of colour, the wavelengths of visible light, our perception!

15.5.2 uv-visible spectroscopy theory, spectrometer, examples of absorption & reflectance spectra explained

15.5.3 uv-visible absorption spectra - index of examples: uses, applications, more on the chemistry of colour

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The uv and visible absorption spectrum of azo dye compounds

simplified diagram of the visible light absorption spectra of a yellow, red and blue dye molecule azo dyestuff  

Dye A absorbs in the blue and will look yellow, λmax 410 nm.

Dye B absorbs in the blue-green-yellow and will look reddish purple?, λmax 510 nm

Dye C absorbs in the yellow-orange-green, will look violet-blue, λmax 590 nm

 

The four azo dye molecules below all contain the same chromophore, but the presence of other groups in the benzene ring will modify the colour of these azo dyes.

(i) (c) doc b , where C6H5-N=N-C6H4 is the chromophore, modified by the OH group, orange

(ii) (c) doc b , where C6H5-N=N-C6H4 is the chromophore, modified by the NH2 group, yellow

(iii) (c) doc b , where C6H4-N=N-C6H4 is the chromophore, modified by the OH group, colour?

(iv) (c) doc b , where C6H4-N=N-C6H4 is the chromophore, modified by the NH2 group, colour?

 

The uv and visible absorption spectrum of the dye disperse red 19 azo dye

Image adapted from https://www.semanticscholar.org/paper/Absorption-and-fluorescence-spectra-of-disperse-red-Jaggi-Giri/6e59de87899a3ca3b70cfe6c64ff1bfea6819d28

uv-visible absorption spectrum of disperse red 19 azo dye molecular structure example of aromatic spectra of azo dyestuffs

diagram image of the visualisation of the wavelengths of visible light in nanometres nm

The uv-visible absorption spectra of the azo dye disperse red 19 azo dye in dilute solution in ethanol.

It absorbs strongly in the blue-green region of the visible region, and appears red in solution.

The two peaks of maximum absorbance occur at 285 nm (ultraviolet) and 495 nm (blue-green visible light)

 

For more details of absorption spectra of dyes and pigments see:

The absorption spectra of selected aromatic compounds e.g. arenes and azo dyes

The absorption spectrum of chlorophyll

The absorption spectrum of haemoglobin

The absorption spectra of the photopigments in the human eye



Key words & phrases: interpreting the uv-visible absorption spectra of azo dyes, identifying the maximum absorption peaks in the uv-visible absorption spectra of azo dyes, explaining the uv-visible absorption spectra of azo dyes, how to use the visible absorption spectra of azo dyes to explain the different colours of azo dyes, applications of the uv-visible absorption spectra of azo dyes uv-visible light absorption spectrum of disperse red 19 azo dye, identifying the maximum absorption peaks in the uv-visible absorption spectrum of disperse red 19 azo dye, explaining the uv-visible absorption spectrum of disperse red 19 azo dye, how to use the visible absorption spectra of disperse red 19 azo dye to explain the colour of disperse red 19 azo dye, applications of the uv-visible absorption spectrum of disperse red 19 azo dye


Associated links

UV and visible spectroscopy index

SPECTROSCOPY INDEXES

INDEX of all AROMATIC COMPOUND chemistry revision notes

Chemical properties of phenylamine - derivatives including diazonium ions and azo dyes

All Advanced Organic Chemistry Notes

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