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.

Author: Malashicage Takinos
Country: Bhutan
Language: English (Spanish)
Genre: Politics
Published (Last): 7 September 2007
Pages: 242
PDF File Size: 8.55 Mb
ePub File Size: 20.75 Mb
ISBN: 469-5-77446-620-9
Downloads: 36460
Price: Free* [*Free Regsitration Required]
Uploader: Faezahn

Hue Dichromatism Colorfulness chroma and saturation Tints and shades Lightness tone and value Grayscale. Woodward-Fieser rules can be used to approximate ultraviolet -visible maximum absorption wavelength in organic compounds with conjugated pi-bond systems. The presence of an auxochrome in the chromogen molecule is essential to make a dye. By using this site, you agree to the Terms of Use and Privacy Policy.

The highly conjugated pi-bonding system of the macrocycle ring absorbs visible light. The two groups are connected by a conjugated system 2. A molecule exhibits colour because it absorbs colours only of certain frequencies and reflects or transmits others. Electrolytic dissociation of the auxochrome group helps in binding and it is due to this reason a basic substance takes an acidic dye. Auxochromes are a bunch of atoms that when combined with an appropriate chromophore heighten or enhance the color.

Auxochromes are classified as either positively charged or negatively charged. The hue of a dye depends on the wavelength it absorbs.

Chromophore – Wikipedia

This change in structure affects a chromophore in the pH indicator molecule. Conjugated organic molecules absorb specific wavelengths of electro-magnetic radiation. An auxochrome is known as a compound that produces a bathochromic shiftalso known as red xnd because it increases the wavelength of absorption, therefore moving closer to infrared light.

To convert basic dyes to acidic dyes, the negatively charged sulphonic groups are often used. Normally, auxochromes which intensify the colour are chosen. Amino groups are examples of positively charged whereas carboxyl, hydroxyl and sulphonic groups are examples of negatively charged auxochromes. For example, phenolphthalein is a pH indicator whose structure changes as pH changes as shown in the following table:.

  IEC 60909 1 PDF

Various factors in a chromophore’s structure go into determining at what wavelength region in a spectrum the chromophore will absorb. Colour in crystalline solids arises from band theory- the blurring of many orbitals through-out the solid. 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. They are used together to make dyes.

However, if an auxochrome is present in the fhromophore position to the chromophore, it does not affect the color.

chemistry of dyes

A bathochromic shift may anc caused by increasing the electron-withdrawing power of the chromophore X or Yincreasing the electron-donating power of the auxochrome Y or X and by increasing the length of the conjugated system connecting the two 2. The different colours of white light Everyone is familiar with rainbows- see the top picture for a well known example!

Linguistic relativity and the color naming debate Blue—green distinction in language Color history Color in Chinese culture Traditional colors of Japan Human skin color. An auxochrome is a functional group of atoms attached to the chromophore which auxochrom the ability of the chromophore to absorb light, altering the wavelength or intensity of the absorption.

The first four mechanisms all rely on some form of energy transfer to move either molecules or electrons from their ground state into some excited state.

They are capable of absorbing and emitting light of various frequencies.

The position of the chromophore and auxochrome also has an effect. It can be calculated using the Beer-Lambert Law. At that time, Witt suggested that the auxochrome was a salt-forming group, which helped chrompphore improve the colour of the dye. This is a property of pH indicatorswhose molecular structure changes upon certain changes in the surrounding pH.


These are responsible for the absorption of different radiations with different wavelengths based on the energy of the electron. If the energy incorporated is changed, automatically the wavelength of the radiation it absorbs will also change and the compound will appear colored. They themselves fail to produce the colour; but when present along with the chromophores in an organic compound intensifies the colour of the chromogen.

A structural change which causes the absorption band to longer wavelengths i. This page was last edited on 30 Marchat Views Read Edit View history. Color space Color model additive subtractive Color mixing Primary color Secondary color Tertiary color intermediate Quaternary color Quinary color Aggressive color warm Receding color cool Pastel colors Color gradient.

User assumes all risk of use, damage, or injury. Academic Press, New York. Auxochromes are molecules chromophor are attached to non ionizing compounds yet retain their ability to ionize and affect the ability of absorbing light when attached to a chromophore. Chromophores with double covalent bond appear to be colored as a result of the heightened state of the electrons.


Chromophores are represented as nitrogen, carbon, oxygen and sulphur which usually have single or double bonds. The reverse shift, towards shorter wavelengths is known as a hypsochromic effect 2. The electromagnetic spectrum has a very wide variation in wavelengths but the human eye visualizes only short wavelength radiation.

Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state. G—M List of colors: This page was last edited on 30 Septemberat This article needs additional citations for verification.

This article was written by admin