Basic auxochromes. Auxochrome vs chromophore. Auxochrome is a Greek word arising from two word roots; ‘auxo’ meaning “to increase” and. This lesson explains the parts of a molecule responsible for color: chromophores and auxochromes. Chromophores and auxochromes are. In , Witt proposed that dye molecules contain two groups; the chromophore and the auxochrome. The chromophore is a group of atoms which control the.

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Simple molecular excitation, such as in a neon tube, may cause the appearance of colour. Chromophores with double covalent bond appear to be colored as a result of the heightened state of the electrons. Hence the molecule appears coloured. Auxochromes are classified as either positively charged or negatively charged. If the energy incorporated is changed, automatically the wavelength of the radiation it absorbs will also change and the compound will appear colored.

However, only one of these effectively applies to dye molecules, since dye molecules are almost chro,ophore exception organic conjugated systems.


An auxochrome is a functional group of atoms attached to the chromophore which modifies the ability of the chromophore to absorb light, altering the wavelength or intensity of the absorption.

Please help improve this article by adding citations to reliable sources. If an auxochrome is present in the meta position of the chromophore, then there is no change in the color. The highly conjugated pi-bonding system of the macrocycle ring absorbs visible light. So how can a dye molecule’s hue be altered? Conjugated organic molecules absorb specific wavelengths of electro-magnetic radiation.


The superposition of these determines how broad an absorption band is 2. There is no need to resubmit your comment. At that auxkchrome, Witt suggested that the auxochrome was a salt-forming group, which helped to improve the colour of the dye. Chromophores also alter the energy in the delocalized systems. The chromophore is the part of the molecule where the energy difference between two different molecular orbitals falls within the range of the visible spectrum and hence absorbs some particular colours from visible light.

The presence of an auxochrome in the chromogen molecule is essential to make a dye. G—M List of colors: From Wikipedia, the free encyclopedia. Unsourced material may be challenged and removed.

Auxochrome increases chromophote color of any organic substance. June Learn how and when to remove this template message. If a light source is deficient in any colour band, the light appears to be coloured in the complementary colour.

It must be auxovhrome that the system shown znd is symmetrical, so the chromophore and auxochrome are interchangeable here, but this is not always the case.

By using this site, you agree to the Terms of Use and Privacy Policy. Woodward-Fieser rules can be used to approximate ultraviolet -visible maximum absorption wavelength in organic compounds with conjugated pi-bond systems. By using this site, you agree to the Terms of Use and Privacy Policy. Color model additive subtractive Color mixing Primary color Secondary color Tertiary color intermediate Quaternary color Quinary color Aggressive color auxxochrome Receding color cool Pastel colors Color gradient.


An auxochrome is a functional group of atoms with one or more lone pairs of electrons when attached to a chromophore, alters both the wavelength and quxochrome of absorption. In biological molecules that serve to capture or detect light energy, the chromophore is the moiety that causes a conformational change of the molecule when hit by light. For example, phenolphthalein is a pH indicator whose structure changes as pH changes as shown in aand following table:.

The different colours of white light Everyone is familiar with rainbows- see the top picture for a well known example! Colour in crystalline solids arises from band theory- the blurring of many orbitals through-out the solid.


Examples of such compounds include bilirubin and urobilinwhich exhibit a yellow color. These are responsible for the absorption of different radiations with different wavelengths based on the energy of the electron.

The electromagnetic spectrum has a very wide variation in wavelengths but the human eye visualizes only short wavelength radiation. The chromophore is a group of atoms which control the colour of the dye.

chemistry of dyes

Principles of Organic Chemistry. Transition metal complexes are coloured due to the distortion of the chrmoophore d-electron shell caused by ligands surrounding the metal ion. Retrieved from ” https: