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An auxochrome (Greek αὐξάνειν ''auxánein'': "to increase" and χρῶμα ''chrōma'': "colour") is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. They themselves fail to produce the colour; but when present along with the chromophores in an organic compound intensifies the colour of the chromogen. Examples include the hydroxyl group (-OH), the amino group (-NH2), the aldehyde group (-CHO), and the methyl mercaptan group (-SMe).〔Gronowitz, Salo JO. Arkiv För Kemi, 27, 239 (1958).〕 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. ==Effects on chromophore== It increases the color of any organic compound. For example, benzene does not display color as it does not have a chromophore; but nitrobenzene is pale yellow color because of the presence of a nitro group (-NO2) which acts as a chromophore. But Para-hydroxynitrobenzene exhibits a deep yellow color, in which -OH group acts as an auxochrome. Here the auxochrome (-OH) is conjugated with the chromophore -NO2. Similar behavior is seen in azobenzene which has a red color, but para-hydroxy azobenzene is dark red in color. The presence of an auxochrome in the chromogen molecule is essential to make a dye. However, if an auxochrome is present in the meta position to the chromophore, it does not affect the color. An auxochrome is known as a compound that produces a bathochromic shift, also known as red shift because it increases the wavelength of absorption, therefore moving closer to infrared light. Woodward-Fieser rules estimate the shift in wavelength of maximum absorption for several auxochromes attached to a conjugated system in an organic molecule. An auxochrome helps a dye to bind to the object that is to be colored. Electrolytic dissociation of the auxochrome group helps in binding and it is due to this reason a basic substance takes an acidic dye. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「auxochrome」の詳細全文を読む スポンサード リンク
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