PREPARATION AND PHOTOPHYSICAL STUDIES OF PORPHYRIN-C60 DYADS |
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Authors: | Paul A. Liddell John P. Sumida Alisdair N. Macpherson Lori Noss Gilbert R. Seely Kristine N. Clark Ana L. Moore Thomas A. Moore Devens Gust |
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Affiliation: | Department of Chemistry and Biochemistry, Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, AZ 85287–1604. |
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Abstract: | Abstract Porphyrin-C60 dyads in which the two chromophores are linked by a bicyclic bridge have been synthesized using the Diels-Alder reaction. The porphyin singlet lifetimes of both the zinc (Pzn-C60) and free base (P-C60) dyads, determined by time-resolved fluorescence measurements, are ≦17 ps in toluene. This substantial quenching is due to singlet-singlet energy transfer to C60 The lifetime of Pzn-1C60 is -5 ps in toluene, whereas the singlet lifetime of an appropriate C60 model compound is 1.2 ns. This quenching is attributed to electron transfer to yield Pznbull;+-C60bull;-. In toluene, P-1C60 is unquenched; the lack of electron transfer is due to unfavorable thermodynamics. In this solvent, a transient state with an absorption maximum at 700 ran and a lifetime of-10 μs was detected using transient absorption methods. This state was quenched by oxygen, and is assigned to the C60 triplet. In the more polar benzonitrile, P-1C60 underoes photoinduced electron transfer to give P•+-C60bull;-. The electron transfer rate constant is −2 × 1011 s−1. |
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