A group in a dye molecule that influences the colour due to the chromophore. Auxochromes are groups, such as –OH and –NH₂, containing lone pairs of electrons that can be delocalized along with the delocalized electrons of the chromophore. The auxochrome intensifies the colour of the dye. Formerly, the term was also used of such groups as –SO₂O⁻, which make the molecule soluble and affect its application.