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.
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