Photoinduced Electron Transfer in Tetrathiafulvalene−Porphyrin−Fullerene Molecular Triads |
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Authors: | Paul A. Liddell,Gerdenis Kodis,Linda de la Garza,Jeffrey L. Bahr,Ana L. Moore,Thomas A. Moore,Devens Gust |
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Abstract: | The two molecular triads 1a and 1b consisting of a porphyrin (P) covalently linked to a fullerene (C60) electron acceptor and tetrathiafulvalene (TTF) electron‐donor moiety were synthesized, and their photochemical properties were determined by transient absorption and emission techniques. Excitation of the free‐base‐porphyrin moiety of the TTF−P2 H−C60 triad 1a in tetrahydro‐2‐methylfuran solution yields the porphyrin first excited singlet state TTF−1P2 H−C60, which undergoes photoinduced electron transfer with a time constant of 25 ps to give TTF−P2 H.+−C60.−. This intermediate charge‐separated state has a lifetime of 230 ps, decaying mainly by a charge‐shift reaction to yield a final state, TTF.+−P2 H−C60.−. The final state has a lifetime of 660 ns, is formed with an overall yield of 92%, and preserves ca. 1.0 eV of the 1.9 eV inherent in the porphyrin excited state. Similar behavior is observed for the zinc analog 1b . The TTF‐PZn.+−C60.− state is formed by ultrafast electron transfer from the porphyrinatozinc excited singlet state with a time constant of 1.5 ps. The final TTF.+−PZn−C60.− state is generated with a yield of 16%, and also has a lifetime of 660 ns. Although charge recombination to yield a triplet has been observed in related donor‐acceptor systems, the TTF.+−P−C60.− states recombine to the ground state, because the molecule lacks low‐energy triplet states. This structural feature leads to a longer lifetime for the final charge‐separated state, during which the stored energy could be harvested for solar‐energy conversion or molecular optoelectronic applications. |
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