Chromophore
The part of a molecule responsible for absorbing light at a particular wavelength.
Unit
nm
In depth
Chromophores contain pi bonds or lone pairs whose electrons can be excited by ultraviolet or visible photons. Extending conjugation lowers the energy gap and shifts absorption to longer wavelengths, which is why highly conjugated compounds are strongly coloured.
Examples in the real world
The carbonyl group absorbing near 280 nm; the eleven conjugated double bonds making beta-carotene orange.