Unique Twisted Ribbons Generated by Self-Assembly of Oligo(p-phenylene ethylene) Bearing Dimeric Bile Acid Pendant Groups

A series of novel oligo)phenylene ethynylene) (OPE) derivatives bearing dimeric cholic acid (OPE1), deoxycholic acid (OPE2) and lithocholic acid (OPE3) was synthesized. The self-assembly behavior of these derivatives were systematically studied and compared in a THF/water solvent mixture. The addition of water to THF can induce the helical stacking of oligo(p-phenylene ethylene) bearing dimeric deoxycholic acid end groups, which leads to highly interesting twisted assemblies. Variation of the bile acid group led to nanostructures with drastically different morphologies. The application of spectroscopy in combination with X-ray diffraction techniques provided a reasonable view of the final self-assembled structures. The observed distinctive aggregate shapes and the preference in the type of molecular packing of these steroid-OPE conjugates are attributed to the subtle differences in their molecular features.