Exciton dynamics in LH1 and LH2 of Rhodopseudomonas acidophila and Rhodobium marinum probed with accumulated photon echo and pump-probe measurements

Exciton dynamics in the B850 and B875 bands of isolated complexes of Rhodop seudomonas acidophila (strain 10 050 and 7050) and in the B875 band of isol ated complexes of Rhodobium marinum were investigated by means of accumulat ed photon echo and pump-probe techniques at different temperatures and wave lengths. For all three systems, the optical dephasing time T-2 was found to be very similar: at 4.2 K, T-2 is 116 and 106 ps for the B850 and B875 ban ds of Rhodopseudomonas acidophila, respectively, and 93 ps for the B875 ban d of Rhodobium marinum. The rapid dephasing, which displays glassy characte r, is a consequence of the strong pigment-protein interactions that arise t hrough the rather short distances in these complexes. The observed dephasin g time at the red edge of the B850 band of Rhodopseudomonas acidophila at 4 .2 K reveals the existence of spectral diffusion in this system. From the w avelength dependence of the pump-probe signal in the B875 LH1 band of Rhodo pseudomonas acidophila at 3 K it is concluded that energy transfer between energetically inequivalent LH1 rings occurs on a time scale of several tens picoseconds, while energy trapping takes place in about 250 ps.