Chromophore

Leaves change color in the fall because their chromophores (chlorophyll molecules) break down and stop absorbing red and blue light.[1]

A chromophore is a molecule which absorbs light at a particular wavelength and reflects 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 (or in informal contexts, the spectrum under scrutiny). 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.

Healthy plants are perceived as green because chlorophyll absorbs mainly the blue and red wavelengths but green light, reflected by plant structures like cell walls, is less absorbed.[2]
The eleven conjugated double bonds that form the chromophore of the β-carotene molecule are highlighted in red.
  1. ^ Kräutler, Bernhard (26 February 2016). "Breakdown of Chlorophyll in Higher Plants—Phyllobilins as Abundant, Yet Hardly Visible Signs of Ripening, Senescence, and Cell Death". Angew. Chem. Int. Ed. 4882 (55): 4882–4907. doi:10.1002/anie.201508928. PMC 4950323. PMID 26919572.
  2. ^ Virtanen, Olli; Constantinidou, Emanuella; Tyystjärvi, Esa (2020). "Chlorophyll does not reflect green light – how to correct a misconception". Journal of Biological Education. 56 (5): 1–8. doi:10.1080/00219266.2020.1858930.