Photo-induced dynamics of molecular systems

Life is intimately connected with the light from the sun, and many properties of living matter are tuned to its spectrum. Many biological functions, be it for harnessing the sun's power or for protection from its harmful rays, rely on interaction of specific molecules with ultraviolet (UV), visible or infrared (IR) light. In this chapter, we will develop a theoretical description of this interaction, which forms the basis both of our current understanding of photo-induced processes and the design of experimental methods used to investigate their details.

Among the biologically relevant photo-induced processes, photosynthesis probably occupies the most prominent place. Essentially all of the energy that is used by the biosphere is a result of photosynthesis, and the prospect of connecting humanity to the same energy source has recently motivated many interdisciplinary research lines. Insight about the design and function of natural photosynthetic systems is likely to play an important role in future research. Within the limited scope of this chapter it is therefore reasonable to limit ourselves to photosynthesis motivated molecular systems. Much of the theory presented in the following sections applies even beyond photosynthesis, e.g. in experiments on molecules related to vision, DNA photo-protection, or in IR spectroscopy of molecular vibrations. However, one has to keep in mind that approximations and models applicable in one field might not work well in another. In this chapter we will introduce and discuss concepts that, together with a good knowledge of a particular physical problem, should enable the reader to develop a theory in order to understand certain important classes of spectroscopic experiments on biomolecules.