EXCITON DYNAMICS IN THE LIGHT-HARVESTING COMPLEXES OF RHODOBACTER-SPHAEROIDES

We have used almost-equal-to 40 fs pulses from a Ti: Sa laser to inves tigate the ultrafast energy transfer and relaxation dynamics in the LH 1 and LH2 light-harvesting pigment-proteins of photosynthetic purple b acteria. Our results reveal a new feature, not earlier observed in lig ht-harvesting pigments, ultrafast relaxation characterized by a time c onstant of approximately 20 fs, which we interpret as interexciton sta te relaxation. The experimental results are compared with computer sim ulations of transient excited state absorption from the excited states of an excitonic aggregate.