EXCITED-STATE ENERGY RELAXATION IN THE FMO COMPLEXES OF THE GREEN BACTERIUM PROSTHECOCHLORIS-AESTUARII AT LOW-TEMPERATURES

Energy transfer processes at 10 K in the water-soluble bacteriochlorop hyll a-protein complex (FMO complex) from the green bacterium Prosthec ochloris aestuarii have been studied by femtosecond one- and two-color pump-probe measurements. Decay-associated spectra have been obtained for different excitation wavelengths. From these we conclude that ener gy relaxation occurs via a stepwise, cascading process down the Q(y) m anifold of energy states in the FMO complex. Observed time constants f or these steps are 500 fs and 1.7, 5.5, and 30 ps and are correlated w ith the position in the Q(y) manifold, becoming shorter with increasin g energy. Anisotropy decay functions at different wavelengths exhibit two major components: one of similar to 100 fs and one of similar to 1 ps.