Department of Chemistry and Biochemistry
Arizona State University
PO Box 871604
Tempe, AZ 85287
One approach that Ana Moore's group had taken to artificial photosynthesis is mimicry of the steps used by photosynthetic organisms to convert solar energy into chemical potential. Analogs of photosynthetic reaction centers consisting of tetrapyrrole chromophores covalently linked to electron acceptors and donors are designed and synthesized in thier laboratory. Excitation of these artificial reaction centers results in a cascade of energy transfer/electron transfer processes 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. Reaction with secondary electron/hole transfer species, in some cases, occurs in solution, in membranes, or through interactions with conductive surfaces. Recent examples of artificial constructs include mimicry of light harvesting by carotenoid pigments. Antenna systems are being synthesized based on polymer polyenes covalently attached to tetrapyrroles. Absorption from the blue-green to the red has been observed. Conformational disorder is thought to limit the effective conjugation length of the polymer providing a distribution of shorter effective conjugation lengths. Thus, the spectrum of the polyene polymer covers the entire visible spectrum, making it a nearly ideal antenna for sunlight. New antenna reaction center complexes in which a carotenoid moiety is located in quasi-conjugation to the tetrapyrroles -system allowing fast energy transfer are being designed.