Low lying carotenoid 'dark' singlet states in light-harvesting complexes revealed by multi-photon fluorescence excitation spectroscopy

摘要

Carotenoids serve important functions in photosynthetic organisms: as structural components of pigment-protein complexes, accessory light-harvesting pigments and photoprotective agents. Elucidation of the role(s) of the lowest excited singlet states of carotenoids, in particular, of the (optically "dark") state 2(A{sub}g){sup}-^s(S{sub}1) in light harvesting and excess energy dissipation is a field of intense current research interest. Two-photon absorption (TPA) of carotenoids detected by (bacterio)chlorophyll, (B)Chl, fluorescence (following excitation energy transfer, EET) can be used to localize the (optically "dark") 2(A{sub}g){sup}-^s(S{sub}1) state of relevant carotenoids in photosynthetic pigment-protein complexes (Fig. 1, cf. also [1]).