Excited state dynamics in FMO antenna complexes from photosynthetic green sulfur bacteria: A kinetic model

We have simulated the excited stare dynamics of the FMO (Fenna-Matthews-Ols on) bacteriochlorophyll a-protein complexes of the green sulfur bacteria Ch lorobium (C.) tepidum and Prosthecochloris (P.) aestuarii at cryogenic temp erature in terms of an exciton model. The simulation is based on the electr onic structure, as described in previous publications (Louwe, R. J. W.; Vri eze, J.; Hoff, A. J.; Aartsma, T. J.; J. Phys. Chem. 1997, 101, 11280. Vult o, S. I. E.; de Baat, M. A.; Louwe, R. J. W.; Permentier, Ii. P.; Neef, T.; Miller, M.; van Amerongen, Ii.; Aartsma, T. J. J. Phys. Chem. 1998, 102, 9 577). Relaxation between exciton states is described by linear electron pho non coupling as a perturbation term in the Hamiltonian of the system. The s imulation was compared with experimental data obtained by pump-probe measur ements with various wavelengths of excitation. For C. tepidum, a quite good agreement was obtained between the calculated and measured dynamics. For P . aestuarii, the simulations are less satisfactory but they can be improved by including static disorder. We conclude that not only the steady-state o ptical spectra but also the excited-state dynamics in the FMO complex at lo w temperature can be described with a simple exciton model.