| Abstract
| - Novel molecular electron donor−acceptor (DA) dyads, composed of a phytochlorin donor and a[60]fullerene acceptor, have been photochemically characterized. In these dyads, a pyrrolidine spacer grouplinks the chlorin and the C60 moieties covalently, forming a rigid dyad with a short and almost constant D−Adistance. The photochemical behavior of the metal-free dyads and the corresponding Zn complexes was studiedby means of fluorescence and absorption spectroscopies with femto- and picosecond time resolutions in polarbenzonitrile and nonpolar toluene solutions. In consistence with the previous studies on porphyrin−fullerenedyads, the novel chlorin−fullerene dyads underwent a fast intramolecular photoinduced electron transfer in abenzonitrile solution. The recombination rates of the charge-transfer (CT) states were 4.8 × 1010 s-1 for theZn dyads and ca. 1.5 × 1010 s-1 for the metal-free compounds. The CT state was preceded by at least threeintermediate states in the time domain from 200 fs to 100 ps. Two of the states were identified as singletexcited states of either the phytochlorin or the fullerene moiety. The third state was attributed to an intramolecularexciplex, which was transformed to the CT state. In the frame of this model, the formation rate constant of theCT state was estimated to be 1.6 × 1011 s-1 for the Zn dyads and 0.5 × 1011 s-1 for the metal-free compounds.The formation of the exciplex was also observed in nonpolar solvents, e.g., toluene. In contrast to the behaviorin polar solvents, the exciplex relaxed in toluene directly to the ground state, without the formation of the CTstate. The lifetime of the exciplex was 140 ps for the Zn dyads and 1−2 ns for the metal-free compounds intoluene.
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