EXCITONS AND EXCITATION TRANSFER IN THE PHOTOSYNTHETIC UNIT OF PURPLEBACTERIA

Photosynthetic purple bacteria employ an antenna system to absorb sunl ight and transfer electronic excitation to a centrally located protein , the photosynthetic reaction center. The antenna system employs for t his purpose a hierarchy of circular bacteriochlorophyll aggregates. Fo r the case of a particular light harvesting protein with known structu re, one-and two-exciton spectra of its circular bacteriochlorophyll ag gregate are determined by means of an effective Hamiltonian descriptio n. A detailed geometric model for the complete antenna system of the p urple bacterium Rhodobacter sphaeroides is provided by molecular model ling and its bacteriochlorophyll aggregates are investigated, employin g also an effective Hamiltonian. Transfer times within the complete an tenna system and from the antennae to the reaction center are calculat ed. (C) 1998 Elsevier Science B.V. All rights reserved.