ULTRAFAST DYNAMICS OF LIGHT HARVESTING COMPLEXES

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The determination of ultrafast anisotropy changes can be of great value in determining how energy flows between different cofactors in an assembly. The techniques of anisotropy measurement have been significantly refined in order that coherent and orientational aspects of energy transfer can be determined with high accuracy. 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 ~ 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.