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

ABSTRACT

Two visible light-harvesting perylenebisimide (PDI)-[60]fullerene (C60) systems, dyad P1 with one C60 unit and triad P2 with two C60 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 C60. Then, the high efficient intrinsic intersystem crossing of C60 eventually leads to the production of the triplet C60. 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 C60 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 C60 and even better than that of the commonly used triplet photosensitizer methylene blue (MB). The double C60 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.