TOWARD AN INTEGRAL INTERPRETATION OF THE OPTICAL STEADY-STATE SPECTRAOF THE FMO-COMPLEX OF PROSTHECOCHLORIS-AESTUARII - 1 - AN INVESTIGATION WITH LINEAR-DICHROIC ABSORBENCY-DETECTED MAGNETIC-RESONANCE

In this paper we present results of (linear-dichroic) absorbance-detec ted magnetic resonance experiments on the FMO-complex of Prosthecochlo ris aestuarii at 1.2 K. We have used these results as additional crite ria for testing exciton simulations of the optical spectra of this com plex. We find that the photo-excited triplet state is localized on a s ingle bacteriochlorophyll a chromophore of the complex associated with a S-1<--S-0 transition at similar to 825 nm in the Q(y)-absorption re gion (790-830 nm). The orientations of several optical transition mome nts in the Q(y)-absorption band relative to the triplet x-and y-axes o f the triplet-carrying molecule have been determined. Comparison of th e triplet-minus-singlet absorbance-difference spectra with simulations using parameter sets from the literature shows significant discrepanc ies, which can be traced to an overestimation of the dipolar interacti ons between the individual bacteriochlorophyll a molecules. Exciton si mulations based on considerably lower dipolar interactions, presented in an accompanying paper,:show considerable improvement of the fits to the relevant optical steady-state spectra.