Effect of functional group polarity on the encapsulation of C₆₀ derivatives in the inner space of carbon nanohorns

Encapsulation of C₆₀, its hydroxides (C₆₀(OH) _n, n = 10, 36, 44), and its hydride (C₆₀H₃₆) into inner space of carbon nanohorns (CNHs) from solutions or dispersions in various solvents by the nano-condensation method was attempted. The effect of the functional groups on the encapsulation was evaluated by transmission electron microscopy. C₆₀, C₆₀(OH)₁₀, and C ₆₀H₃₆ can be efficiently encapsulated inside CNHs using toluene, THF, and DMSO as solvents, whereas C₆₀(OH)₃₆ and C₆₀(OH)₄₄ are hardly encapsulated from any solution. Because the molecular size of C₆₀(OH)₁₀ is similar to that of C₆₀(OH)₃₆ and C₆₀(OH)₄₄, the difference in encapsulation is not caused by molecular size. The efficient encapsulation of C₆₀H₃₆ in CNHs suggests that molecules can be encapsulated in carbon nanomaterials even when the π-π interaction with the sp²-hybridized carbon walls is weak. These results suggest the polarity of the functional group of the C₆₀ derivatives as the main factor in determining whether they can be encapsulated in CNHs. C ₆₀(OH)₃₆ and C₆₀(OH)₄₄ contain many hydroxyl groups, thus these molecules self-aggregate and do not pass the holes of CNHs, resulting in poor encapsulation.