Excitation energy transfer in carotenoid-chlorophyll protein complexes probed by femtosecond fluorescence decays

An energy transfer pathway in a carotenoid-chlorophyll alpha protein complex of dinoflagellates was studied by the femtosecond up-conversion method. The energy levels of the S-2 state of peridinin and their lifetime were essentially identical in methanol and in the complex. The S-1 lifetime of peridinin in solvents was more than 30-fold longer than in the complex. These results account for an observed transfer efficiency (higher than 85%) and indicate that an energy transfer occurs between the S-1 states of peridinin and chlorophyll alpha after a rapid internal conversion. This pathway is unique in photosynthetic organisms.