Mimicry of antenna and photo-protective carotenoid functions by a synthetic carotenoporphyrin

Carotenoid pigments, ubiquitous in photosynthetic membranes, are essential for the survival of green plants¹. Two facets of carotenoid function are recognized in photosynthetic membranes. First, carotenoids prevent the chlorophyll-photosensitized formation of highly destructive singlet oxygen by intercepting the chlorophyll triplet states^2-10 and may also scavenge additional singlet oxygen present^11,12. Second, carotenoids perform an antenna function by transferring the energy of absorbed light at the singlet excited state level to the chlorophyll system for the execution of photosynthetic work^13-16. Nevertheless, the mechanisms by which carotenoids perform these functions are poorly understood. We now report that a unique synthetic carotenoporphyrin I consisting of a carotenoid part covalently linked to a synthetic tetraarylporphyrin successfully mimics both the photophysical functions of carotenoids in photosynthesis. The explanation for this seems to be the close interaction of the carotenoid and porphyrin π-electron systems.