Single-Molecule Spectroscopy on Photosystem I Pigment−Protein Complexes

Abstract

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