Molecular recognition abilities of a new class of water-soluble cyclophanes capable of encompassing a neutral cavity

We developed a new class of water-soluble cyclophanes, pyrenophanes, capable of encompassing a neutral cavity, in which the hydrophobic area is constructed by aligning two flat polynuclear aromatic rings parallel at an appropriate space that could interpose just one layer of aromatic plane. The height, depth, and width of the cavity in an open conformation of the pyrenophane are 0.46, 0.95, and 1.31 nm, respectively, i.e., the area of this cavity is so large that even porphirin compounds might be incorporated. In the fluorescence spectra, the pyrenophanes showed only excimer-emission, reflecting the existence of two proximal pyrene rings. Treatment of the pyrenophanes with anionic and cationic aromatic compounds revealed the formation of complexes in the UV and fluorescence spectra, suggesting that the binding affinities of the pyrenophanes for aromatic compounds were mainly governed by hydrophobic and/or π-stacking interactions. The macrocyclic structures of the pyrenophanes were found to be indispensable for the complexation.