Carotenoids: Nature's unique pigments for light and energy processing

Covalently linked carotenoid-porphyrin (C-P) dyads that mimic the photochemistry of carotenoids in photosynthetic membranes have been synthesized. Singlet energy transfer (C to P), triplet energy transfer (P to C), and quenching of P* by electron transfer from C to P*, have been observed and the structural requirements for these processes defined. A monolayer system has been developed in which a carotenoid bearing a terminal amino group is photoelectrochemically active. This demonstrates that carotenoid pigments could act as blue light photoreceptor pigments. A carotenoporphyrin for use as an imaging agent for tumor tissue detection has been synthesized and tested in vivo. This compound incorportates carotenoid photoprotection against singlet oxygen and is therefore not phototoxic.