View article

Femtosecond transient absorption measurements were performed on native and a series of reconstituted LH2 complexes from Rhodopseudomonas acidophila 10050 at room temperature. The reconstituted complexes contain chemically modified tetrapyrrole pigments in place of the native bacteriochlorophyll a-B800 molecules. The spectral characteristics of the modified pigments vary significantly, such that within the B800 binding sites the B800 Q_y absorption maximum can be shifted incrementally from 800 to 670nm. As the spectral overlap between the B800 and B850 Q_y bands decreases, the rate of energy transfer (as determined by the time-dependent bleaching of the B850 absorption band) also decreases; the measured time constants range from 0.9ps (bacteriochlorophyll a in the B800 sites, Q_y absorption maximum at 800nm) to 8.3ps (chlorophyll a in the B800 sites, Q_y absorption maximum at 670nm). This …