Chromophore, a group of atoms and electrons forming part of an organic molecule that causes it to be coloured.

Correlations between the structural features of chemical compounds and their colours have been sought since about 1870, when it was noted that quinones and aromatic azo and nitro compounds often are highly coloured and that the colours are diminished or destroyed when the compounds are hydrogenated. The ability of a compound to take up hydrogen, called unsaturation, is caused by the presence of electrons that are not strongly fixed in covalent bonds between particular pairs of atoms but occupy larger regions of space (molecular orbitals) that may be associated with several atoms. These electrons can absorb energy from light over a certain range of wavelengths in the visible region; transmission or reflection of the remainder of the light gives rise to the observed colour of the compound. Deep coloration results if several chromophores are closely joined in the same molecule or if another group, called an auxochrome, is present.

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...identification of compounds. They can serve as a fingerprint for a particular species in much the same manner as infrared spectra. Particular functional groups or molecular configurations (known as chromophores) tend to have strong absorptions that occur in certain regions of the visible-ultraviolet region. The precise frequency at which a particular chromophore absorbs depends significantly on...
The photopigments that absorb light all have a similar structure, which consists of a protein called an opsin and a small attached molecule known as the chromophore. The chromophore absorbs photons of light, using a mechanism that involves a change in its configuration. In vertebrate rods the chromophore is retinal, the aldehyde of vitamin A1. When retinal absorbs a photon, the...
Newton’s prism experiment.
All dyes and most pigments, whether natural or synthetic, are complex organic compounds whose molecular structures include a “colour-bearing” group known as a chromophore, usually a short conjugated system (a chain of atoms connected by alternating single and double bonds). The bonding electrons holding the molecule together can be viewed as belonging to the whole molecule. Simple...
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