To further understand the interaction between 2C-WP5A and trans/cis- G, we used isothermal titration calorimetry (ITC) to explore the thermodynamics of the host-guest inclusion complex (Fig. 3). The Ka values and thermodynamic parameters are listed in Table 1, and we are surprised to find that there was no obvious difference between the Ka-cis and the Ka-trans. The hydrophobic interaction is characterized by positive value of ΔH454748, which suggests that the hydrophobic interaction is the main force in the complexation. Meanwhile, 2C-WP5A and G immobilized their conformation during the complexation, resulted in a great negative entropy change which offset the positive entropy change aroused by solvent liberation49. This great unfavorable entropy make us easily understand why pillararene cannot bind with azobenzene in organic solution although its size is similar to α-cyclodextrin.