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Jablonski Diagrams

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The Interaction of Light with Biological Molecules

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Photochemistry

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).

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

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.

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This project was supported in part by the National Research Initiative Competitive Grants CAP project 2011-68002-30029 from the USDA National Institute of Food and Agriculture, adminstered by the University of California-Davis and by the National Science Foundation (NSF), Division of Undergraduate Education, National SMETE Digital Library Program, Award #0938034, administered by the University of Nebraska. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the USDA or NSF.