Self-Assembly of n-Shaped Rod–Coil Molecules into Thermoresponsive Nanoassemblies: Construction of Reversible Helical Nanofibers in Aqueous Environment

Abstract

Amphiphilic coil–rod–coil molecules 1 – 3, consisting of an n-shaped rod building block and poly(ethylene oxide) (PEO) with a degree of polymerization of 5 linked through a biphenyl unit as the coil segment, were synthesized. Molecule 1 self-assembles into lamellar and hexagonal perforated layer structures, in the crystalline and liquid crystalline phases, respectively. Remarkably, molecule 2 incorporating lateral methyl groups between the rod and coil segments spontaneously self-organizes into hexagonal perforated layer and oblique columnar structures. The additional incorporation of a lateral butyl group at the center of the rod segment of molecule 2 generates molecule 3, which assumes an exclusively oblique columnar structure in the solid state. In aqueous solutions, molecule 1 self-assembles into fibrous aggregates, whereas molecules 2 and 3 exhibit a self-organizing capacity to form helical fibers. Additionally, circular dichroism (CD) experiments and atomic force microscope (AFM) measurements of molecule 3 highlight a switch of the helical sense to the opposite handedness, depending on the temperature of the aqueous solution.