PHOTOSYNTHETIC LIGHT-HARVESTING

The peripheral light-harvesting complex of the photosynthetic bacteriu m Rhodopseudomonas acidophila (LH2) absorbs solar photons and transfer s 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 i s 1 nm or less and, as a consequence, the electronic interaction betwe en the pigments is strong (> 100 cm(-1)). Therefore, the excitation tr ansport in these photosynthetic light-harvesting systems can not be de scribed by a simple Forster type transfer mechanism, but new or other transfer mechanisms may be operative, for instance a mechanism in whic h the excitation is to some extent delocalized. Crucial parameters are the strength of the electronic coupling, the amount of energetic diso rder and/or heterogeneity and the nature and strength of the interacti ons of the pigments with the protein.