Silicon-phthalocyanine-cored fullerene dendrimers: Synthesis and prolonged charge-separated states with dendrimer generations

Silicon-phthalocyanine-cored fullerodendrimers with up to eight fullerene substituents (SiPc-nC(60); n=2, 4, and 8) have been synthesized. Photo-physical properties of newly synthesized SiPc-nC(60), have been investigated by time-resolved fluorescence and transient absorption analysis with pulsed laser light. Laser photolysis measurements suggest the occurrence of a charge-separation process from (SiPc)-Si-1* to the C-60 subunits. The nanosecond transient absorption spectra in the near-IR region indicate that the lifetimes of the formed radical ion pairs are prolonged on the order of SiPc-8 C-60 > SiPc-4C(60)> SiPc-2C(60), which may be related to the electron migration among the C-60 subunits. The usefulness of SiPc-nC(60) as light-harvesting systems, evaluated as a ratio of the rates of charge recombination to those of charge separation, increases markedly with the dendrimer generation.