Partition of carotenoid-to-bacteriochlorophyll singlet-energy transfer through two channels in the LH2 complex from Rhodobacter sphaeroides G1C

The excited-state dynamics of both carotenoid (Car) and bacteriochlorophyll (BChl) in the LH2 complex from Rhodobacter sphaeroides G1C were simultaneously probed by subpicosecond time-resolved absorption spectroscopy in the visible and near-infrared regions. By the use of a four excited-state model, where the 1B_u⁺ and 1B_u⁻ states were treated inclusively as the ‘1B_u' state, the time constant and the efficiency partition of Car-to-BChl singlet-energy transfer were determined to be 67–114 fs and 60–74% for the ‘1B_u' channel, and 1.39–1.42 ps and 24–38% for the 2A_g⁻ channel, when a time constant of 170–190 fs was assumed for the 1B_u-to-2A_g⁻ internal conversion.