Single-molecule spectroscopy on photosystem I pigment-protein complexes

Photophysical properties of low-energy antenna chlorophylls were probed in individual Photosystem I complexes from the cyanobacterium Synechococcus el ongatus. Temperature activated fluorescence quenching unravels energy trans fer pathways within the red-most pigment pool and to the reaction center. L ow-temperature spectroscopy indicates that two subgroups of pigments which are present in the red antenna pool differ not only by their spectral posit ion but also by the strength of electron-phonon coupling. Possible dimeric nature of the strongly phonon coupled red-most state is discussed in contex t of hole-burning data (Ratsep, M.; Johnson, T, W.; Chitnis, P. R.; Small, G. J. J. Phys. Chen. B 2000, 104, 836).