Self-organization of substituted azacrowns based on their discoid and amphiphilic nature

Abstract

Cyclame and hexacyclene derivatives, bearing four and six long-chain substituents respectively, were synthesized. They are discussed as monolayer-forming amphiphiles as well as liquid-crystalline-phase-forming thermotropic mesogens. The compounds investigated form ordered monolayers at the gas/water interface. In the monolayer the hydrophilic cyclic head group lies flat on the water surface, whereas the hydrophobic substituents are oriented perpendicularly with respect to the interface. Most derivatives fitted with aromatic substituents exhibit a solid condensed state exclusively. In contrast with this, solid condensed as well as expanded phases can be found when spreading the aliphatic-substituted compounds. In the latter case, the onset of the phase transition takes a bump-like shape, owing to kinetic reasons. A liquid-crystalline columnar order is only achieved with hexacyclenes bearing aromatic substituents, etherified with one alkyl chain. Besides this, the remaining derivatives melt from the crystalline state, transforming directly into the isotropic liquid, or show amorphous behaviour. Preliminary irradiating experiments in the columnar state of cinnamoyl-substituted hexacyclene Hex-7 were carried out in order to obtain polymeric tubes.