The energy in the excited singlet state electron may be used to carryout chemical reactions. The types of reactions stimulated by the absorption of light energy are diverse and include cis-trans isomerization such as found in vision, the production of Vitamin D, and the damaging of DNA by ultraviolet light. With regard to photosynthesis, the importance of light is that it enables reduction and oxidation reactions (Figure: Redox).

When a molecule absorbs the energy from a photon, the excited electron is a stronger reducing agent (potential electron donor) and an unpaired electron in the ground state is a stronger oxidizing agent (potential electron acceptor). The importance of redox in photosynthesis and the harnessing of energy will be examined in greater depth in Part II (Plant Pigments and Photosynthesis) of this course.

Redox: A molecule with an excited electron is a strong reductant, while one with electrons in the ground state are sharing oxidants.