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Dedicated to P rofessor T. W. G oodw in on the occasion o f his 80th birthday C arotenoids, H igher Plants, L ight-H arvesting P igm ent-P rotein C om plex, P h otoprotection, Purple B acteria B esides the light-harvesting and pro tectin g role, caro ten o id s are also instrum ental as struc tural com ponents for the assem bly o f light-harvesting com plexes in p urple b acteria and green plants, as well as for the form ation o f p h otosystem II com plex. C aro ten o id s stabilize those pigm ent-protein com plexes, b u t have no effect on purple bacteria and photosystem I of plants.

Pathways of intramolecular conversion and intermolecular electronic excitation energy transfer (EET) in the photosynthetic apparatus of purple bacteria remain subject to debate. Here we experimentally tested the possibility of EET from the bacteriochlorophyll (BChl) Soret band to the singlet S level of carotenoids using femtosecond pump-probe measurements and steady-state fluorescence excitation and absorption measurements in the near-ultraviolet and visible spectral ranges. The efficiency of EET from the Soret band of BChl to S of the carotenoids in light-harvesting complex LH2 from the purple bacterium Ectothiorhodospira haloalkaliphila appeared not to exceed a few percent.