Synthesis and Properties of Axially Symmetrical Rigid Visible Light-Harvesting Systems Containing [60]Fullerene and Perylenebisimide

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Two visible light-harvesting perylenebisimide (PDI)-[60]fullerene (C 60 ) systems, dyad P1 with one C 60 unit and triad P2 with two C 60 units, have been synthesized. Both systems are axially symmetrical with a rigid biphenyl linker, ensuring a relatively fixed spatial distance between the donor and acceptor, preventing through-space interaction, and enhancing energy transfer. Steady-state and transient spectroscopy, electrochemistry, as well as theoretical calculations have been used to investigate the electrochemical and photophysical properties of the two systems. Steady-state and time-resolved spectroscopy demonstrate that the excited state is featured by an efficient intramolecular energy transfer from PDI to C 60 . Then, the high efficient intrinsic intersystem crossing of C 60 eventually leads to the production of the triplet C 60 . The extensive visible light absorption of PDI in the range of 400–650 nm and the final localization of the excited energy at the triplet C 60 make these compounds ideal singlet oxygen inducers. Further investigation shows that the photooxidation capability for both compounds is significantly enhanced with respect to either PDI or C 60 and even better than that of the commonly used triplet photosensitizer methylene blue (MB). The double C 60 moieties in P2 display a better result, and the photooxidation efficiency of P2 increases 1.3- and 1.4-fold compared to that of P1 and MB, respectively. The combination of a light-harvesting unit with an intersystem crossing unit results in a highly efficient photooxidation system, which opens up a new way to triplet photosensitizer design.