A family of diphenylethyne-lin
ked porphyrin dimers and trimers has been prepared via a buildingbloc
k approach for studies of energy-transfer processes. The dimers contain Mg and Zn porphyrins (MgZnU);the trimers contain an additional free base porphyrin (MgZnFbU). In both the dimers and trimers, sites ofattachment to the Mg porphyrin (at the meso- or
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-position) and diphenylethyne lin
ker (at the para- or meta-positions) were varied, producing four Mg porphyrin-Zn porphyrin arrangements with the following lin
kerconfigurations: meso-p/p-meso, meso-m/p-meso,
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-p/p-meso, and
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-m/p-meso. All four trimers employ ameso-p/p-meso Zn porphyrin-Fb porphyrin connection. The ground- and excited-state properties of theporphyrin dimers and trimers have been examined using static and time-resolved optical techniques. The rateof energy transfer from the photoexcited Zn porphyrin to the Mg porphyrin decreases according to the followingtrend: meso-p/p-meso (9 ps)
-1 >
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-p/p-meso (14 ps)
-1 > meso-m/p-meso (19 ps)
-1 >
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-m/p-meso (27 ps)
-1.In each compound, energy transfer between adjacent porphyrins occurs through a lin
ker-mediated through-bond process. The rate of energy transfer between Zn and Fb porphyrins is constant in each trimer ((24 ps)
-1).Energy transfer from the photoexcited Zn porphyrin branches to the adjacent Fb and Mg porphyrins, withnearly one-half to three-fourths proceeding to the Mg porphyrin (depending on the lin
ker). Energy transferfrom the excited Mg porphyrin to the nonadjacent Fb porphyrin occurs more slowly, with a rate that followsthe same trend in lin
ker architecture and porphyrin connection site: meso-p/p-meso (173 ps)
-1 >
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-p/p-meso(225 ps)
-1 > meso-m/p-meso (320 ps)
-1 >
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-m/p-meso (385 ps)
-1. The rate of transfer between nonadjacentMg and Fb porphyrins does not change significantly with temperature, indicating a superexchange mechanismutilizing orbitals/states on the intervening Zn porphyrin. Energy transfer between nonadjacent sites may proveuseful in directing energy flow in multiporphyrin arrays and related molecular photonic devices.