Synthesis and properties of helically-folded poly(arylenediethynylene)s

Aryl-based helical foldamers with diacetylene linkers are not only capable of providing physically large diameter cavities, but can also showcase a variety of properties, such as structural transformation, that the corresponding foldamers with simple acetylene linkers cannot achieve. Here, we have developed helical foldamers based on poly(arylene diethynylene)s (poly-ArDEs), in which each aryl group is connected by diacetylene linkers. The poly-ArDEs with naphthalene, pyrene and pyridine as a central aryl group each expressed unique properties. The foldamers incorporating naphthalene and pyrene stabilized the helical folding in a variety of solvents. In addition, the concentration-dependent emission by the pyrene polymer was completely different from that of the monomer due to its folded three-dimensional structure. The pyridine-based polymer showed unexpected solvent dependence and stimuli responsiveness, suggesting possible applications in sensing. These properties were elucidated in detail by UV-Vis absorption, fluorescence, and circular dichroism (CD) spectra, molecular dynamics calculations, and titration experiments.