Abstract
Eenergy transfer in the B800 ring of the LH2 antenna of the purple bacteria Rhodopseudomonas (Rps.) acidophila and Rhodospirillum (Rs.) molischianum was studied at room temperature using three-pulse echo peak shift (3PEPS) and transient grating (TG) techniques. From the transient grating experiments, we found the B800 → B850 energy transfer rates to be 600−700 fs for both species. The anisotropy of the TG signal decays in about 1 ps for both species, which is ascribed to B800 → B800 energy transfer. The occurrence of B800 → B800 energy transfer was further substantiated by 3PEPS experiments. When measured over the whole B800 band, the initial peak shift of about 30 fs exhibited a fast <100 fs decay to about 10 fs due to the coupling to protein phonons, followed by a slow phase of about 1 ps, during which the peak shift decayed to 1−3 fs. Polarized 3PEPS experiments systematically resulted in smaller peak shift values for the third pulse polarized perpendicular to the first two than for the third pulse par...
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