Excitons in core LH1 antenna complexes of photosynthetic bacteria: Evidence for strong resonant coupling and off-diagonal disorder

The structure of the exciton manifold in the core bacteriochlorophyll antenna complexes from the purple photosynthetic bacterium Rhodobacter sphaeroides has been studied at 5 K using conventional and polarized fluorescence excitation spectroscopy supported with model simulations. Exciton bandwidths in the range of 2100-2200 cm−1, depending on sample integrity, have been determined in correlation with the largest mean coupling energy between the nearest-neighbor bacteriochlorophyll molecules close to 600 cm−1. These numbers are considerably bigger than those in any other native antenna complex known. Another noteworthy feature of these complexes is dominance of structural (off-diagonal) static disorder over the energetic (diagonal) disorder.