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 freebase-porphyrin moiety of the TTF-P2H-C60 triad 1a in tetrahydro-2-methylfuran solution yields the porphyrin first excited singlet state TTF-1P2H-C60, which undergoes photoinduced electron transfer with a time constant of 25 ps to give TTF-P2H·+-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·+-P2H-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.
|Number of pages||19|
|Journal||Helvetica Chimica Acta|
|Publication status||Published - 2001|
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