Ultrafast dynamics within the B820 subunit from the core (LH-1) antenna complex of Rs. rubrum

Femtosecond transient dynamics within the dimeric subunit of a bacterial light-harvesting complex have been investigated using magic angle and polarized pump-probe spectroscopy. Oscillations of 170 cm−1 and ≈ 20 cm−1, 50 cm−1 and 115 cm−1 are observed in the isotropic signal, and of ≈ 500 cm−1 in the anisotropy; the Stokes shift and dephasing of the dimer exciton levels occurs on a sub-50 fs timescale. The re-assembled aggregate exhibits ultrafast spectral evolution and biphasic anisotropy decay. Collectively, the results support a view of energy migration within LH-1 complexes as proceeding by strongly scattered excitation transfer between states of the dimeric subunits.