Redox-responsive molecular helices with highly condensed π-clouds

Abstract

Helices have long attracted the attention of chemists, both for their inherent chiral structure and their potential for applications such as the separation of chiral compounds or the construction of molecular machines. As a result of steric forces, polymeric o-phenylenes adopt a tight helical conformation in which the densely packed phenylene units create a highly condensed π-cloud. Here, we show an oligomeric o-phenylene that undergoes a redox-responsive dynamic motion. In solution, the helices undergo a rapid inversion. During crystallization, however, a chiral symmetry-breaking phenomenon is observed in which each crystal contains only one enantiomeric form. Crystals of both handedness are obtained, but in a non-racemic mixture. Furthermore, in solution, the dynamic motion of the helical oligomer is dramatically suppressed by one-electron oxidation. X-ray crystallography of both the neutral and oxidized forms indicated that a hole, generated upon oxidation, is shared by the repeating o-phenylene units. This enables conformational locking of the helix, and represents a long-lasting chiroptical memory. Phenylene oligomers are shown to form left- and right-handed helices in solution, but a chiral symmetry-breaking process occurs on crystallization to give a non-racemic mixture of crystals that each contains only one enantiomer. One-electron oxidation of the oligomers suppresses the interconversion of the mirror-image helices in solution, locking-in one conformation and leading to chiral memory effects.

Cite this article

Ohta, E., Sato, H., Ando, S. et al. Redox-responsive molecular helices with highly condensed π-clouds. Nature Chem 3, 68–73 (2011). https://doi.org/10.1038/nchem.900

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