Two‐Component Fibers/Gels and Vesicles Formed from Hetero‐Double‐Helices of Pseudoenantiomeric Ethynylhelicene Oligomers with Branched Side Chains

A methodology for the formation of fibers/gels and vesicles by molecular assembly and for controlling their properties is presented. Two‐component systems of pentamer (P)‐ 5 and tetramer (M)‐ 4 pseudoenantiomeric ethynylhelicenes with decyloxycarbonyl (D) and 4‐methyl‐2‐(2‐methylpropyl)‐1‐pentyloxycarbonyl (bD) side‐chains have been examined. Distinct aggregates were formed by changing the solvent for the three combinations of (P)‐bD‐ 5 /(M)‐bD‐ 4 , (P)‐D‐ 5 /(M)‐bD‐ 4 , and (P)‐D‐ 5 /(M)‐D‐ 4 . In toluene, (P)‐bD‐ 5 /(M)‐bD‐ 4 , (P)‐D‐ 5 /(M)‐bD‐ 4 , and (P)‐D‐ 5 /(M)‐D‐ 4 all formed gels and fibrous assemblies were observed by AFM. The minimum gel‐forming concentration (MGC) decreased in the order (P)‐bD‐ 5 /(M)‐bD‐ 4 >(P)‐D‐ 5 /(M)‐bD‐ 4 >(P)‐D‐ 5 /(M)‐D‐ 4 . In diethyl ether, vesicular formation was observed by dynamic light scattering (DLS), AFM, and TEM, and the size of the vesicles decreased in the order (P)‐bD‐ 5 /(M)‐bD‐ 4 >(P)‐D ‐ 5 /(M)‐bD‐ 4 >(P)‐D ‐ 5 /(M)‐D ‐ 4 . Both fiber/gel and vesicle formation were accompanied by enhanced CDs and redshifted UV/Vis absorption bands with a change in color to deep yellow. These are novel two‐component oligomeric systems that form assemblies of fibers/gels or vesicles depending on the solvent, and the structures and properties of the assemblies can be fine‐tuned by changing the combination of oligomers. In m‐difluorobenzene, a homogeneous solution was obtained with (P)‐D‐ 5 /(M)‐bD‐ 4 , which again exhibits enhanced CDs and redshifted UV/Vis absorptions. Vapor pressure osmometry analysis showed the formation of a bimolecular heteroaggregate. The study has indicated that pseudoenantiomeric oligomers form hetero‐double‐helices that hierarchically assemble to form fibers/gels and vesicles.