Photoinduced Electron Transfer in Phytochlorin-(60)Fullerene Dyads

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 group links the chlorin and the C60 moieties covalently, forming a rigid dyad with a short and almost constant D−A distance. The photochemical behavior of the metal-free dyads and the corresponding Zn complexes was studied by means of fluorescence and absorption spectroscopies with femto- and picosecond time resolutions in polar benzonitrile and nonpolar toluene solutions. In consistence with the previous studies on porphyrin−fullerene dyads, the novel chlorin−fullerene dyads underwent a fast intramolecular photoinduced electron transfer in a benzonitrile solution. The recombination rates of the charge-transfer (CT) states were 4.8 × 1010 s-1 for the Zn dyads and ca. 1.5 × 1010 s-1 for the metal-free compounds. The CT state was preceded by at least three intermediate states in the time domain from 200 fs to 100 ps. ...