Abstract
We have isolated the Core (RC-LH1) complexes from purple photosynthetic bacteria, which contain carotenoids having different number of conjugated double bonds (n), Rhodobacter sphaeroides 2.4.1 (n = 10), Rhodopseudomonas acidophila (n = 11) and Rhodospirillum rubrum (n = 13), and measured their submicrosecond time-resolved absorption spectra exciting at the Qy absorption. The time-resolved spectra exhibited three components. A long-lived component was ascribed to the radical cation of bacteriochlorophyll a. The other two can be ascribed to triplet state of carotenoids, based on the typical spectral pattern of Tn ← T1 absorption. The transient absorption on the shorter-wavelength side shifted systematically depending on the conjugation length; their wavelengths corresponded to those of the carotenoid Tn ← T1 absorptions in the LH2 complexes. The transient absorption on longer wavelength may be due to T1 carotenoid in the reaction center.
