Photoinduced electron transfer in a carbon nanohorn-C₆₀ conjugate

A nanohybrid combining two allotropic forms of carbon, namely carbon nanohorns (CNH) and C₆₀, has been obtained from a C₆₀ derivative bearing a benzocrown ether subunit (crown-C₆₀) and a CNH functionalized with NH₃⁺ groups (CNH-sp-NH ₃⁺F^-) through ammonium-crown ether interactions. The resulting CNH-C₆₀ nanohybrid has been characterized by Raman and XPS spectroscopies, thermogravimetric analysis (TGA) and high-resolution transmission electron microscopy (HR-TEM). The photophysical properties of the CNH-C₆₀ conjugate have been investigated in benzonitrile. Femtosecond laser flash photolysis measurements revealed the occurrence of an efficient electron transfer from the singlet excited state of the C₆₀ moiety to the CNH with a rate constant of 6.5 × 10 ¹⁰ s^-1 to produce a radical ion pair, which decayed by charge recombination with a lifetime of 1.0 ns to afford the triplet excited state of CNH-sp-NH₃⁺F^- and crown-C ₆₀. The two carbon nanoforms play therefore complementary roles in the CNH-C₆₀ conjugate, the CNH acting as an electron donor and C ₆₀ as an electron acceptor.