| Abstract
| - The dramatic changes of the lifetimes of the charge-separated (CS) states were confirmed in zinc porphyrin(ZnP)−oligothiophene (nT)−fullerene (C60) linked triads (ZnP−nT−C60) with the solvent polarity. After theselective excitation of the ZnP moiety of ZnP−nT−C60, an energy transfer took place from the 1ZnP* moietyto the C60 moiety, generating ZnP−nT−C60*. In polar solvents, the CS process also took place directly viathe 1ZnP* moiety, generating ZnP•+−nT−C60•-, as well as the energy transfer to the C60 moiety. After thisenergy transfer, an indirect CS process took place from the 1C60* moiety. In the less polar solvent anisole, theradical cation (hole) of ZnP•+−nT−C60•- shifted to the nT moiety; thus, the nT moiety behaves as a cationtrapper, and the rates of the hole shift were evaluated to be in the order of 108 s-1; then, the final CS statesZnP−nT•+−C60•- were lasting for 6−7 μs. In the medium polar solvent o-dichlorobenzene (o-DCB), ZnP−nT•+−C60•- and ZnP•+−nT−C60•- were present as an equilibrium, because both states have almost the samethermodynamic stability. This equilibrium resulted in quite long lifetimes of the CS states (450−910 μs) ino-DCB. In the more polar benzonitrile, the generation of ZnP−nT•+−C60•- was confirmed with apparentshort lifetimes (0.6−0.8 μs), which can be explained by the fast hole shift to more stable ZnP•+−nT−C60•-followed by the faster charge recombination. It was revealed that the relation between the energy levels oftwo CS states, which strongly depend on the solvent polarity, causes dramatic changes of the lifetimes of theCS states in ZnP−nT−C60; that is, the most appropriate solvents for the long-lived CS state are intermediatelypolar solvents such as o-DCB. Compared with our previous data for H2P−nT−C60, in which H2P is free-baseporphyrin, the lifetimes of the CS states of ZnP−nT−C60 are ∼30 times longer than those in o-DCB.
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