EXCITATION TRANSFER DYNAMICS AND SPECTROSCOPIC PROPERTIES OF THE LIGHT-HARVESTING BCHL A COMPLEX OF PROSTECOCHLORIS-AESTUARII

We studied the efficiency of energy transfer in the water-soluble BChl a complex of Prostecochloris aestuarii using singlet triplet annihilation. At 77 K the presence of one triplet state per trimer (21 BChl a molecules) is sufficient to quench the fluorescence of the trimer completely. At 4 K the efficiency of quenching by triplets is reduced, a mechanism for energy transfer between subunits is proposed to explain this observation. Laser-flash induced (polarized) triplet-singlet difference spectra clearly show that all Q(y) absorption bands of the complex are coupled by (strong) exciton interactions. The polarized T-S difference spectrum indicates that the 825 nm band of the trimer is split into three transitions, two degenerate transitions which are oriented in the plane of the trimer, and one slightly red-shifted transition, which is oriented parallel to the trimer C3 axes.