On the localization and charge transfer character of the "special pair" triplet states for bacterial reaction centers

Within a simple excitonic model for the bacterial reaction center the zfs tensor of the special pair triplet state ³P is calculated. The orientation of the calculated spin axes is compared with experimental data for the reaction centers of Rps. viridis, Rb. sphaeroides and C. aurantiacus. It is shown that for these different reaction centers the experimentally observed spin axis orientations are consistent with the structure data for Rps. viridis. Our model calculations give information on the degree of delocalization and charge-transfer character of the triplet states and specific triplet-triplet excitation bands.