Anionic Fluorinated Zn-porphyrin Combined with Cationic Endohedral Li-fullerene for Long-Lived Photoinduced Charge Separation with Low Energy Loss

Abstract

Here we report an anionic meso-tetrakis(4-carboxymethylthio-2,3,5,6-tetrafluorophenyl) zinc porphyrin (ZnTF₄PPTC^4-) to form a supramolecular complex with a cationic lithium endohedral [60]fullerene (Li⁺@C₆₀). The supramolecular ZnTF₄PPTC^4-/Li⁺@C₆₀ complex formed by strong electrostatic attraction with a large binding constant generates a long-lived charge-separated (CS) state with low energy loss by photoinduced electron transfer from ZnTF₄PPTC^4- to Li⁺@C₆₀. The anionic fluorinated zinc porphyrin with high oxidation potential reduces the energy loss associated with the charge separation and enhances the energy level of the CS state. The energy level of the CS state determined by electrochemical measurements is at 0.94 eV, which is much higher than that of a similar supramolecular complex using an anionic meso-tetrakis(sulfonatophenyl) zinc porphyrin (ZnTPPS^4-) at 0.55 eV. Time-resolved transient absorption spectroscopy demonstrates that ZnTF₄PPTC^4-/Li⁺@C₆₀ generates a long-lived CS state with a lifetime of 0.29 ms in a binary solvent of acetonitrile and chlorobenzene. The lifetime of the CS state is comparable to that of ZnTPPS^4-/Li⁺@C₆₀ in benzonitrile.