LOW-TEMPERATURE ENERGY-TRANSFER IN FMO TRIMERS FROM THE GREEN PHOTOSYNTHETIC BACTERIUM CHLOROBIUM-TEPIDUM

The pump-probe kinetics of the slowest spectral equilibrations between inequivalent BChl a Q(y) states in FMO trimers from Chlorobium tepidu m are decelerated by nearly two orders of magnitude when the temperatu re is lowered from 300 K to 19 K. The pump-probe anisotropy decays are also markedly slower at 19 K than at 300 K. Singlet-singlet annihilat ion in FMO trimers is negligible at the laser powers used here. Howeve r, reduced temperatures greatly accentuate the probability of singlet- tripler annihilation, due to accumulation of metastable BChl a states under high laser repetition rates.