Auxochrome

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Auxochrome - this is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. Example: -OH , - NH2 , Aldehydes.

An auxochrome is a functional group of atoms with nonbonded electrons which, when attached to a chromophore, alters both the wavelength and intensity of absorption. If these groups are in direct conjugation with the pi-system of the chromophore, they may increase the wavelength at which the light is absorbed and as a result intensify the absorption. A feature of these auxochromes is the presence of at least one lone pair of electrons which can be viewed as extending the conjugated system by resonance.