High-Energy Charge-Separated States by Reductive Electron Transfer Followed by Electron Shift in the Tetraphenylethylene-Aluminum(III) Porphyrin-Fullerene Triad

A high-potential supramolecular triad (TPE-AlPor <- Im-C-60) composed of aluminum(III) porphyrin (AlPor), fullerene (C-60), and tetraphenylethylene (TPE) has been constructed. The fullerene and tetraphenylethylene units are bound axially to opposite faces of the porphyrin plane via coordination and covalent bonds, respectively. The ground and excited-state properties of the triad and reference dyads are studied using steady-state and time-resolved spectroscopic techniques. The transient data show that photoexcitation results in charge separation from tetraphenylethylene to the excited singlet state of the porphyrin ((1)AlPor*), generating a high-energy (2.14 eV) charge separated state, (TPE)(center dot+)-(AlPor)(center dot-), in toluene. A subsequent electron migration from the AlPor(-center dot) to fullerene generates a second high-energy (1.78 eV) charge-separated state (TPE)(center dot+)-AlPor <- Im-(C-60)(center dot-). The lifetime of the charge separation is about 25 ns. The high energy stored in the form of charge-separated states along with their reasonable lifetimes makes these donor-acceptor systems potential electron-transporting catalysts to carry out energy-demanding photochemical reactions, especially in artificial photosynthesis for conversion of solar energy into chemical energy.