RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Nat Chem. 2011 Jan;3(1):68-73. doi: 10.1038/nchem.900. Epub 2010 Nov 14.
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.
螺旋结构一直以来都吸引着化学家的注意，这不仅是因为它们具有内在的手性结构，还因为它们具有潜在的应用价值，例如手性化合物的分离或分子机器的构建。由于空间位阻的影响，聚合的邻苯二酚会采用一种紧密的螺旋构象，其中堆积紧密的苯环单元形成了一个高度密集的π云。在这里，我们展示了一种具有氧化还原响应动态运动的低聚邻苯二酚。在溶液中，螺旋会发生快速反转。然而，在结晶过程中，观察到手性对称破缺现象，其中每个晶体只包含一种对映体形式。两种手性的晶体都可以得到，但它们是非外消旋混合物。此外，在溶液中，螺旋低聚物的动态运动被单电子氧化显著抑制。中性和氧化形式的 X 射线晶体学表明，在氧化过程中产生的空穴被重复的邻苯二酚单元共享。这使得螺旋的构象锁定成为可能，同时代表了一种持久的手性记忆。
