A fluorophore is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds.

A chromophore is a molecule which absorbs light at a particular wavelength and emits color as a result. Chromophores are commonly referred to as colored molecules for this reason. The word is derived from Ancient Greek χρῶμᾰ (chroma) 'color', and -φόρος (phoros) 'carrier of'. Many molecules in nature are chromophores, including chlorophyll, the molecule responsible for the green colors of leaves. The color that is seen by our eyes is that of the light not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore indicates a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state. In biological molecules that serve to capture or detect light energy, the chromophore is the moiety that causes a conformational change in the molecule when hit by light.