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Pure Appl. Chem., 2005, Vol. 77, No. 6, pp. 1001-1008

Bioinspired energy conversion

Rodrigo E. Palacios1, Stephanie L. Gould1, Christian Herrero1, Michael Hambourger1, Alicia Brune1, Gerdenis Kodis1, Paul A. Liddell1, John Kennis2, Alisdair N. Macpherson3, Devens Gust1, Thomas A. Moore1 and Ana L. Moore1

1 The Center for the Study of Early Events in Photosynthesis, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287, USA
2 Department of Biophysics, Division of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands
3 Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK

Abstract: Artificial photosynthetic antenna systems have been synthesized based on carotenoid polyenes and polymer-polyenes covalently attached to tetrapyrroles. Absorption of light in the blue/green region of the spectra excites the polyenes to their S2 state, and ultrafast singlet energy transfer to the tetrapyrroles occurs when the chromophores are in partial conjugation. The additional participation of other excited states of the polyene in the energy-transfer process is a requirement for perfect antenna function. Analogs of photosynthetic reaction centers consisting of tetrapyrrole chromophores covalently linked to electron acceptors and donors have been prepared. Excitation of these constructs results in a cascade of energy transfer/electron transfer which, in selected cases, forms a final charge-separated state characterized by a giant dipole moment (>150 D), a quantum yield approaching unity, a significant fraction of the photon energy stored as chemical potential, and a lifetime sufficient for reaction with secondary electron donors and acceptors. A new antenna-reaction center complex is described in which a carotenoid moiety is located in partial conjugation with the tetrapyrrole π-system allowing fast energy transfer (<100 fs) between the chromophores. In this assembly, the energy transduction process can be initiated by light absorbed by the polyene.