Due to the large reduction of entropy caused by the complexation of cyclocarbons and C60 fullerene, the entropy penalty effect makes G°bind(gas) much more positive than Ebind. However, since all G°bind(gas) data in Fig. are still evidently negative, the formation of C60@Cn dimers must occur spontaneous in the gas phase, at least at room temperature. Furthermore, one can see that all G°bind(aq) are systematically more negative than G°bind(gas) by several kcal/mol, indicating that aqueous environment can facilitate the formation of the C60@Cn dimers. As is well known, the hydrophobic effect significantly promotes the aggregation of nonpolar substances in aqueous solution, thus this phenomenon also reflects the strong hydrophobic properties of the monomers. Fig. displays variation of G°bind(gas) with respect to temperature for C60@C18, C60@C34, and C60@C36. It can be clearly seen that the higher the temperature, the more positive the G°bind(gas) and the stronger the tendency for dissociation of the complexes, that is, the lower the possibility of forming complexes. The temperatures at which the G°bind(gas) equal to 0 corresponds to the critical temperature (T crit ) for formation of the dimers in the gas phase, which are labelled in Fig. . The T crit = 366 K of C60@C18 indicates that the dimer can remain stable to some extent above room temperature. As mentioned above, C34 has the strongest tendency of complexation with C60 fullerene compared with other cyclocarbons, and correspondingly, the T crit of C60@C34 of 605 K corresponds to the highest temperature that a cyclocarbon can form a dimer with C60 fullerene. The T crit of C60@C36 is calculated to be of 505 K, which is significantly lower than that of C60@C34, suggesting that cyclocarbons larger than C34 do not have a higher ability to bind C60 fullerene non-covalently from a thermodynamic point of view.