Auxochrome

According to theory, the dye is a dye according to Witt typically of a coloring group ( chromophore ), and one or more auxochromic, ie, color-enhancing groups.

Auxochromes (from Greek auxanein "grow" and chroma " color" ) are functional groups in dye molecules that shift the absorption maximum of an existing coloring group ( chromophore ) in the longer wavelength region of the spectrum. This occurs, a visible color change, here we speak of the bathochromic effect. The absorption maximum of the chromophore alone is often in the UV range and is not visible to the human eye.

The effect of Auxochromes is caused by their action as electron donors. These lead to the conjugated system of the chromophore to the electron density and thus support their delocalization, thus lower energy for excitation, ie longer-wavelength light is needed. Examples of auxochromes are functional groups having free electron pairs, such as -OH,- NH 2,- OR or- NR 2, causing a corresponding change in color over a M effect with the double bond system of the chromophore. Alkyl groups which act only over a I effect as electron donors, are among the auxochromes, although their effect is weaker.

Can be enhanced by the bathochromic effect antiauxochromes. These are functional substituent having an electron-withdrawing effect, or -M - I effect. They are coupled together with auxochrome to the chromophore and reinforce the delocalization of the electrons. Since the donor effect of the Auxochromes is usually stronger, antiauxochromes act not impede supportive to the bathochromic effect. Examples of groups are antiauxochromes the carbonyl or nitro group.

Hypsochromic are functional substituents that have only one - I effect. These substituents lead as a single functional group to a blue shift of the chromophore. The absorption maximum of an existing chromophore is shifted here in the shorter wavelength region of the light spectrum. Hypsochromic groups are used less frequently targeted and play a minor role, since the absorption spectrum as previously mentioned mostly in the UV range and must be shifted into the visible region.