Synthesis and characterization of ortho-phenylene ethynylene oligomers: A new scaffold for foldamer research

As a new frontier of foldamer research based on the synthesis and characterization of oligomers programmed to fold and self assemble into secondary structures continues to open, new scaffolds with a variety of dimensions are required. Presented here is the synthesis and characterization of a new ortho -Phenylene Ethynylene (o-PE) backbone scaffold. This scaffold has been synthesized using Sonogashira methods with a variety of building blocks containing pi-rich and pi-poor elements substituted with non polar and polar substituents. Solvent induced folding of these short oligomers into well defined helices was confirmed via 1D and 2D NMR methods. Utilizing the electron rich and electron poor phenylene building blocks, variations of these o-PE oligomers have been synthesized to determine the folded stability of pi-rich vs. pi-poor vs. pi-poor/rich systems. Variations in temperature offer a route, aside from solvent denaturation, to probe the stability of the folded structures. This is the first report of a highly detailed solution NMR characterization using 1-D and 2-D methods examining the folding of a PE backbone without hydrogen bonds, and the first for an oPE system in general.