Apolar ortho-phenylene ethynylene oligomers: conformational ordering without intermolecular aggregation

This paper describes the characterization of solvent induced folding behavior for non-polar (NP) alkoxy substituted ortho-phenylene ethynylene (o-PE) oligomers. Oligomers of lengths up to nine units have been shown to adopt helical conformations in heptane by NMR and CD spectroscopy, while chloroform promotes extended conformations. Surprisingly, the molar ellipticity values found in heptane for these oligomers are very small compared to other literature values of meta-phenylene ethynylene (m-PE) folded systems; however, comparable molar ellipticity values were found for a closed macrocyclic o-PE suggesting the weak ellipticity is a molecular-feature rather than a quality of folding indicator.