Journal of Physical Chemistry B, Vol.113, No.34, 11720-11723, 2009
Two-Photon Excitation Spectroscopy of Carotenoid-Containing and Carotenoid-Depleted LH2 Complexes from Purple Bacteria
We applied two-photon fluorescence excitation spectroscopy to LH2 complex from purple bacteria Allochromatium minutissimum and Rhodobacter sphaeroides. Bacteriochlorophyll fluorescence was measured under two-photon excitation of the samples within the 1200-1500 rim region. Spectra were obtained for both carotenoid-containing and -depleted complexes of each bacterium to allow their direct comparison. The depletion of carotenoids did not alter the two-photon excitation spectra of either bacteria. The spectra featured a wide excitation band around 1350 nm (2 x 675 nm, 14 800 cm(-1)) which strongly resembled two-photon fluorescence excitation spectra of similar complexes published by other authors. We consider obtained experimental data to be evidence of direct two-photon excitation of bacteriochlorophyll excitonic states in this spectral region.