Supramolecular organization of foldable phenylene ethynylene oligomers

This review summarizes the supramolecular organization of foldable phenylene ethynylene (PE) oligomers and polymers. m-Phenylene ethynylenes (mPEs) have demonstrated the ability to undergo a cooperative, solvophobic collapse from a random conformation into a compact helical structure. The stability of this compact structure can be altered through modification of various nonspecific and specific interactions. A result of the solvophobic collapse of the mPE backbone is the formation of a solvophobic cavity where small-molecule guests may bind with some measure of specificity. Use of chiral guests or chiral moieties in the backbone or side chains can lead to a bias of the handedness of the helical form. Further supramolecular organization was observed in solution in the form of higher order aggregates and at the air-water interface. In the solid state it was found that mPE packing was dependent on the stability of the folded state. Application of these folding principles to imine-containing mPEs allowed for the biasing of combinatorial libraries toward the most stable folded state or host-guest complex, as well as the formation of high molecular weight polymers. Strategies for creating water-soluble mPEs are also explored. The theoretical groundwork for the emerging field of o-phenylene ethynylenes (oPEs) will also be discussed.