ENERGY-TRANSFER AND SPIN POLARIZATION OF THE CAROTENOID TRIPLET-STATEIN SYNTHETIC CAROTENOPORPHYRIN DYADS AND IN NATURAL ANTENNA COMPLEXES

A series of carotenoporphyrin dyads, in which the carotenoid is covale ntly linked to a tetraarylporphyrin at the ortho, meta or para positio n of one of the meso aromatic rings, has been studied using Time-Resol ved Electron Paramagnetic Resonance (TREPR) spectroscopy. In parallel, an investigation has been carried, on two different photosynthetic an tenna systems, the B800-B850 complex of R, acidophila and the LHCII co mplex of higher organisms. The initial spin polarization of the carote noid triplet-state, populated indirectly by laser excitation, has been detected. It has been demonstrated that the initial polarization is n ot a characteristic property of the carotenoid triplet-state, as previ ously stated, but depends on the donor-acceptor mutual orientation. Th e triplet energy transfer to the carotenoid from a chlorophyll or porp hyrin triplet state is discussed on the basis of the observed spin pol arization.