What Happens When the Chlorophyll Molecule Absorbs Light?

When the chlorophyll molecule absorbs light, it is destabilized, and its relatively free-moving electrons are energized and donated to molecules which generate carbohydrates. This donation of energized electrons is the transformation of the absorbed light energy, which powers photosynthesis. The carbohydrate is generated with the energy from carbon dioxide and water and generates oxygen as a waste gas.

Chlorophyll is a complex molecule with a main group composed of a set of cyclic hydrocarbons surrounding a ring of nitrogen atoms. The nitrogen atoms themselves surround a single magnesium atom. The carbon rings around the nitrogen atoms alternate between single and double bonds, and electrons flow relatively freely from one part to another. In part due to this and in part due to the very low elecronegativity of magnesium, the molecule loses electrons very easily. The electron shed when chlorophyll absorbs light alters special molecules in leaves in a way that allows them to break apart carbon dioxide and water molecules and guide the creation of new bonds between their constituent elements.

Chlorophyll only absorbs red and blue wavelengths of light strongly, and thus, only these colors actually provide sufficient energy to power photosynthesis. Green light, meanwhile, is very strongly reflected by chlorophyll, such that the other pigments in leaves, such as red carotenoids, are totally obscured.