What is ADP

This chapter introduces the theory of optical spectra and excitation energy transfer of light harvesting complexes in photosynthesis. The light energy absorbed by protein bound pigments in these complexes is transferred via an exciton mechanism to the photosynthetic reaction center where it drives the photochemical reactions. The protein holds the pigments in optimal orientation for excitation energy transfer and creates an energy sink by shifting the local transition energies of the pigments. In this way, the excitation energy is directed with high efficiency (close to 100 %) to the reaction center. In the present chapter, this energy transfer is studied theoretically. Based on crystal structure data, the excitonic couplings are calculated taking into account also the polarizability of the protein. The local transition energies are obtained by two independent methods and are used to predict the orientation of the FMO protein relative to the reaction center.