Concept Of Chromophore-Auxochrome

Concept Of Chromophore-Auxochrome.To understand this concept we have to understand EMR. The region of 400-800nm in EMR is called a visible region. Due to this, we can see any OBJECT COLORFUL.

Question 2. What is the concept of chromophore and autochrome?

When this radiation is cast on an object, the present electron in the object absorbs radiation and moves from a lower energy level to a higher energy level.

Since the electron is unstable in the higher energy level, it returns to the lower energy level. When it comes from a higher to lower energy level, it emits the energy it had absorbed.

chromophore

Those isolated functional groups which show characteristic absorption in the ultraviolet region are called chromophores or chromophores. Or are often covalent unsaturated (double or triple ness) groups. They are responsible for the color.

For example:- all unsaturated group

–C≡N,>C=C<,>C=O,>C=S,–N=N,–NO2 etc.

Actually, those functional groups which have n–>π* and π—->π* transition are called Chromophores. There are two types of chromophore molecules.

Question 2. What is the concept of chromophore and autochrome?

One type of Chromophore has π-electrons in which π—->π* transition occurs. Example CH2=CH2, CH≡CH, etc.
The second type of Chromophore has both π- and n-(non-bonding) electrons. There can be two types of transitions. In these n–>π* and π—->π* transitions are possible. example -NO2,-N=N-,>C=O etc.

If any compound is colorful, some are visible green, some are visible blue, yellow, red, or any other color, then it is 100% sure that it will contain Chromophore.

But it is not necessary that all the Chromophore groups give color. It means that it is not necessary that all the compounds which are Chromophore give color.

Two conditions are necessary for Chromophore:- If either of the two is less then it will not be Chromophore.

1. chromophore must be present.

2. It is necessary to have a range of 400 to 800 nm (visible region).

autochrome

Question 2. What is the concept of chromophore and autochrome?

They do not have any color on their own, but when combined with a chromophore, they increase the color of the chromophore. An autochrome is a group of atoms attached to a chromophore that modify the chromophore’s ability to absorb light.

All n—->σ* transitions come under Auxochrome. Everything should be saturated. In this non-bonding means, there should be lone pair of electrons and there should be a sigma bond. Also, there should be conjugation in them. For example>-OH, -NH2, -Cl etc.

An autochrome is a functional group of atoms with one or more lone atoms attached to a chromophore, increasing both the wavelength and intensity of absorption.

n-electron ness group which does not show behavior like Chromophore itself, but when present with Chromophore. Then it shifts its Absorption band towards a longer Wavelength. (Red redshift), is called Auxochrome.

It also increases the intensity of the Absorption band. Like->-OH, -NH2, -Cl, etc. group. When Auxochrome combines with a Chromophore, it expands the Conjugation by sharing the lone pair.

Due to this extended conjugation, it changes into a new chromophore, which has a different maximum absorption and extinction coefficient.

For example, the absorption maximum of benzene is obtained at 255 nm (εmax = 204) while the maximum of aniline is obtained at 280 nm (εmax 1500).

Here the amino group (-NH2) is an Auxochrome.

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