FEMTOSECOND DYNAMICS OF CAROTENOID-TO-BACTERIOCHLOROPHYLL A ENERGY-TRANSFER IN THE LIGHT-HARVESTING ANTENNA COMPLEXES FROM THE PURPLE BACTERIUM CHROMATIUM-PURPURATUM
Po. Andersson et al., FEMTOSECOND DYNAMICS OF CAROTENOID-TO-BACTERIOCHLOROPHYLL A ENERGY-TRANSFER IN THE LIGHT-HARVESTING ANTENNA COMPLEXES FROM THE PURPLE BACTERIUM CHROMATIUM-PURPURATUM, Chemical physics, 210(1-2), 1996, pp. 195-217
The energy transfer from the carotenoid okenone to bacteriochlorophyll
a (Bchl a) in the light harvesting complex B800-830 and chromatophore
s of Chromatium purpuratum was studied by steady-state fluorescence an
d femtosecond transient absorption spectroscopy. By comparing the fluo
rescence excitation and the absorption spectra of the B800-830 antenna
complex the total energy transfer efficiency of the okenone-to-Bchl a
transfer was determined to 95 +/- 5%. A fast (< 200 fs) transfer from
(at least) one carotenoid was observed to the B830 chlorophylls. This
transfer was found by fs anisotropy measurements to be a transfer fro
m the okenone S-2 state to the Bchl a Q(x) state, probably caused by t
he dipole-dipole (Forster) mechanism. Later the low-lying okenone S-1
state, which has a lifetime of similar to 8 ps in solution, was observ
ed transferring energy to the B830 pool in similar to 3.8 ps, while a
second carotenoid transferred its energy also from the S, state to B80
0 in similar to 0.5 ps. The results are discussed in relation to the c
rystal structure of the B800-850 complex of Rhodopseudomonas acidophil
a [McDermott et al. Nature 374 (1995)].