Toward an integral interpretation of the optical steady-state spectra of the FMO-complex of Prosthecochloris aestuarii.: 2.: Exciton simulations

We present a simultaneous simulation of various experimental steady-state spectra of the FMO-complex of green sulfur bacteria. The simulations are based on exciton calculations using a significantly lower dipolar interaction energy as compared to exciton calculations on the FMO-complex in the literature. Decrease of the interaction energy was suggested by comparing, our results obtained with linear-dichroic absorbance-detected magnetic resonance spectroscopy with exciton simulations using parameters taken from literature. By considering a single subunit only, we arrive at a minimal set of parameters, consisting of reduced interaction energies between the bacteriochlorophyll molecules, seven different site energies, and a common line width for all transitions of 80 cm(-1). With such a minimal set of parameters, we have achieved an unequalled match between the simulations and the experimental spectra, including the absorption, the linear dichroic, the circular dichroic, the triplet-minus-singlet, as well as the linear-dichroic triplet-minus-singlet spectra. We conclude that the structure in the various steady-state spectra is mainly determined by the variation in site energy and nearly all interaction energies are substantially less than the inhomogeneous width of the individual transitions within the Qy band of the FMO-complex.