Abstract
We have measured sub-microsecond time-resolved absorption spectra of the mixtures of various carotenoids and bacteriochlorophyll a (BChl a), by pumping at Qy. These carotenoids have different number of conjugated double bonds (n = 9-13). We have also measured the LH2 antenna complexes which contains different carotenoids (n = 9-11), isolated from 4 kinds of the purple photosynthetic bacteria. As the result, in the solutions, not only the triplet-energy transfer from BChl a to carotenoid, but also the "back" triplet-energy transfer from carotenoid to BChl a were observed. On the other hand, in the LH2 complexes, only the signal of the triplet carotenoid is observed, but no signal of triplet BChl appeared. This shows extremely efficient triplet-energy transfer in LH2. In each case, carotenoids having a longer conjugated chain dissipated the triplet energy more efficiently.
