Supramolecular assembly of self-labeled amphicalixarenes

The synthesis and precise supramolecular organization of new amphicalixarene 4 bearing four rodlike aligned fluorescent terephthalic benzamide moieties in the upper rim is reported. The aggregation of 4 was monitored by a combination of fluorescence, conductometry, and cryo-TEM measurements at different pH values and revealed significant structural differences. Most interestingly, we found that exactly 12 molecules of 4 assemble to form a spherical and structurally persistent micelle at pH 7, which coexists with rodlike micelles. In contrast to other examples of structurally defined micelles reported previously, this new type of self-labeled amphiphile serves as a fluorescence reporter with the terephthalic units additionally providing an extended cavity structure in the hydrophilic part, which facilitates the inclusion of guest molecules. In addition to the observed formation of well-defined micelles, the other highly important finding from this study is the fact that guest molecules directly influence the micellar organization because they can interact with both the free amphiphiles below the critical micelle concentration (cmc) or the micellar aggregate itself. These two types of interactions are especially pronounced in the case of the cationic pyrene derivative 10, which binds electrostatically with the amphiphile 4. In addition, a very unique membrane structure exhibiting a regular hexagonal pattern of 5 nm pores is formed by 4 at pH 4.