Poster: "Light harvesting and photoprotective functions of carotenoids in compact artificial photosynthetic antenna designs"

KODIS, GERDENIS; PALACIOS, RODRIGO E.; HERRERO, CHRISTIAN; MARIÑO-OCHOA, ERNESTO; KENNIS, JOHN T. M.; GUST, DEVENS; MOORE, THOMAS A.; MOORE, ANA L.

Bad Honnef, Germany

Simposio; WE-Heraeus-Seminar “Excited State Processes of Carotenoids in Photosynthesis”.; 2003

Wilhelm und Else Heraeus-Stiftung

In photosynthesis, carotenoid polyenes act as antennas, as switches to limit the accumulation of excess excitation energy, as electron conductors connecting redox centers, and as photoprotective agents. Modeling these functions in synthetic systems can contribute to our understanding of the natural processes, and to the design of solar energy conversion systems. However, it has proven challenging due to the unusual photophysical properties of carotenoids. The traditional view of the low‐lying excited electronic states of carotenoids involves two singlet states, S1 (2Ag‐) and S2 (1Bu+), of which only the latter can be populated from the ground state S0 (1Ag‐) by the absorption of one photon. Theoretical calculations [1] predict additional singlet excited states for carotenoids of 1Bu‐ and 3Ag‐ symmetry, lying between the S2 and S1 excited states. Recently, new excited states have been identified experimentally; features observed in transient absorption spectra have been assigned to the so‐called S* [2,3] and Sx [4,5,6] excited singlet states. The assignment of these states to the theoretical ones is uncertain. In the presence of excitation energy acceptors such as the chlorophyll molecules in the light‐harvesting complexes, singlet excitation energy transfer competes with internal conversion and can occur from S2,both S2 and S1, and/or the new states; the overall efficiency can vary from as low as 35% to more than 90%. In this study, selected synthetic model systems designed to address some of these issues have been studied using ultrafast spectroscopic techniques.