AUXOCHROME  Auxochrome is defined as any group, which does not itself act as a chromophore but whose presence brings about a shift of the absorption band towards the red end of the spectrum (longer wavelength)  Chromophore + Auxochrome = newer chromophore  Auxochrome is a colour enhancing group.

An auxochrome is a functional group of atoms with one or more line pairs of electrons when attached to a chromophore, alters both the wavelengths and intensity of absorption. Examples:- Hydroxyl group (-OH), Amino group (-NH2), Aldehyde group (-CH2) and the methyl marcaptan group (-SCH3).

Bathochromic shift (from Greek βαθύς bathys, “deep”; and χρῶμα chrōma, “color”; hence less common alternate spelling “bathychromic”) is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a longer wavelength (lower frequency).

Molecules that absorb light are called chromophores. There are two major types of choromphores: electronic transitions. vibrational transitions.

A compound containing only a chromophore may be coloured material but not a dye. For example azo benzene is red coloured but not a dye.

Chromophore is an unsaturated group that absorbs light and reflects it at specific angle to give the hue, e.g., azo, keto, nitro, nitroso, thio, ethylene etc; From: Fundamentals and Practices in Colouration of Textiles, 2014.

Chromophores having both π- electrons and n (non-bonding) electrons undergo two types of transitions. i.e., π-π* and n-π*, for examples: – carbonyls, nitriles, azo compounds and nitro compounds etc.

In the visible range, the main chromophores of human skin are hemoglobin and melanin. Hemoglobin is found in the microvascular network of the dermis, typically 50–500 μm below the skin surface. In contrast, melanin is located in the epidermis, which occupies the top 50–100 μm.

An auxochrome is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. The presence of an auxochrome in the chromogen molecule is essential to make a dye.

The benzene ring as an optically active chromophore—II☆ The optical rotatory dispersion (ORD) of several open chain compounds contaning the benzene chromophore at the asymmetric center has been measured in the UV spectral region.

The Benzene Ring as an Optically Active Chromophore.

auxochromes

Answer. D. Solution. -NH2 group is not a chromophore but is an auxochrome.