Synthesis and Photophysical Properties of Fullerene-Phthalocyanine-Porphyrin Triads and Pentads

The synthesis and photophysical properties of several fullerenephthalocyanineporphyrin triads (13) and pentads (46) are described. The three photoactive moieties were covalently connected in an one-step synthesis through 1,3-dipolar cycloaddition to C60 of the corresponding azomethine ylides generated in situ by condensation reaction of a substituted N-porphyrinylmethylglycine derivative and an appropriated formyl phthalocyanine or a diformyl phthalocyanine derivative, respectively. ZnP-C60-ZnPc (3), (ZnP)2-ZnPc-(C60)2 (6), and (H2P)2-ZnPc-(C60)2 (5) give rise upon excitation of their ZnP or H2P components to a sequence of energy and charge-transfer reactions with, however, fundamentally different outcomes. With (ZnP)2-ZnPc-(C60)2 (6) the major pathway is an highly exothermic charge transfer to afford (ZnP)(ZnP.+)-ZnPc-(C60.-)(C60). The lower singlet excited state energy of H2P (i.e., ca. 0.2 eV) and likewise its more anodic oxidation (i.e., ca. 0.2 V) renders the direct charge transfer in (H2P)2-ZnPc-(C60)2 (5) not competitive. Instead, a transduction of singlet excited state energy prevails to form the ZnPc singlet excited state. This triggers then an intramolecular charge transfer reaction to form exclusively (H2P)2-ZnPc.+-(C60.-)(C60). A similar sequence is found for ZnP-C60-ZnPc (3).