Photosynthetic light-harvesting

Abstract

The peripheral light-harvesting complex of the photosynthetic bacterium Rhodopseudomonas acidophila (LH2) absorbs solar photons and transfers the electronic excitation to the reaction center, to drive a charge separation. In LH2 the bacteriochlorophyll molecules are arranged in a highly symmetric ring and the average distance between the pigments is 1 nm or less and, as a consequence, the electronic interaction between the pigments is strong (> 100 cm-1). Therefore, the excitation transport in these photosynthetic light-harvesting systems can not be described by a simple Förster type transfer mechanism, but new or other transfer mechanisms may be operative, for instance a mechanism in which the excitation is to some extent delocalized. Crucial parameters are the strength of the electronic coupling, the amount of energetic disorder and/or heterogeneity and the nature and strength of the interactions of the pigments with the protein.