Chromophore

The chromophore is the part of a molecule responsible for its colour.

  • Things appear to have colour because they absorb some wavelengths of light and reflect others.
  • The chromophore is the region of a molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum.
  • A  molecular orbital describes the location and wave-like behaviour of an electron in a molecule.
  • Visible light that hits the chromophore can be absorbed by exciting an electron from its ground state into an excited state.

https://en.wikipedia.org/wiki/Chromophore