Efficient charge separation in Li⁺@C₆₀ supramolecular complexes with electron donors

Lithium-ion-encapsulated fullerene (Li⁺@C₆₀) exhibits greatly enhanced reactivity in photoinduced electrontransfer reduction with electron donors compared with pristine C₆₀. The enhanced reactivity of Li⁺@C₆₀ results from the more positive one-electron reduction potential of Li⁺@C₆₀ (+0.14 V versus a standard calomel electrode (SCE)) than that of C₆₀ (-0.43 V versus SCE), whereas the reorganization energy of electron transfer of Li⁺@C₆₀ (1.01 eV) becomes larger than that of C₆₀ (0.73 eV) because of the change in electrostatic interactions of encapsulated Li⁺ upon electron transfer. Li⁺@C₆₀ can form strong supramolecular complexes with various anionic electron donors through electrostatic interactions. Li⁺@C₆₀ can also form strong supramolecular π complexes with various electron donors, such as cyclic porphyrin dimers, corannulene, and crown ether fused monopyrrolotetrathiafulvalenes. Photoinduced electron transfer from electron donors to Li⁺@C₆₀ afforded long-lived chargeseparated states of supramolecular complexes between electron donors and Li⁺@C₆₀. A photoelectrochemical solar cell composed of supramolecular nanoclusters of Li⁺@C₆₀ and zinc sulfonated meso-tetraphenylporphyrin exhibits significant enhancement in the photoelectrochemical performance than that of the reference system containing only a single component.