Abstract
Carotenoids are among the most investigated molecules in organic physics and chemistry [1]. They perform several vital functions in photosynthetic systems: (i) light harvesting, by absorbing energy in the blue-green region and transferring it to the chlorophylls with very high efficiency; (ii) photoprotection via quenching of the chlorophyll triplet states; (iii) singlet oxygen scavenging. In carotenoids both the ground state (S0) and the first excited state (S1) possess Ag character (according to the approximate C2h symmetry), while the second excited state (S2) possesses Bu symmetry. Therefore only the S0→S2 transition is optically allowed; however, after photoexcitation, an ultrafast internal conversion (IC) to S1 takes place. The dynamics of this process is important for the understanding of photosynthesis, because energy transfer from the carotenoids to the chlorophylls can take place either from S2 or from S1. The recent availability of sub-10-fs laser pulses in the visible has allowed to directly study IC in carotenoids with unprecedented time resolution [2].
© 2002 Optical Society of America
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