Since, by definition, dyes are aromatic compounds their structure includes aryl rings which have delocalised electron systems. These are responsible for the absorption of electromagnetic radiation of varying wavelengths, depending on the energy of the electron clouds. For this reason, chromophores do not make dyes coloured in the sense that they confer on them the ability to absorb radiation. Rather, chromophores function by altering the energy in the delocalised electron cloud of the dye, and this alteration results in the compound absorbing radiation from within the visible range instead of outside it. Our eyes detect that absorption, and respond to the lack of a complete range of wavelengths by seeing colour.
Chromophores are atomic configurations which can alter the energy in delocalised systems.
They are composed of atoms joined in a sequence composed of alternating single and double bonds. Double bonds in organic compounds can be of two types. If the atoms with double bonds are not adjacent, they are termed isolated double bonds, and exist independently of other double bonds in the same molecule. If adjacent atoms have double bonds they are termed conjugated double bonds and the bonds interact with each other. Chromophore configurations often exist as multiple units, having conjugated double bonds, and are more effective when they do so.