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

The synthesis and photophysical properties of several fullerene–phthalocyanine–porphyrin triads (1–3) and pentads (4–6) 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).