Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan.
Chemistry. 2011 Jan 24;17(4):1193-200. doi: 10.1002/chem.201002132. Epub 2010 Nov 30.
The synthesis and brakelike performance of a new molecular system (1) consisting of a pentiptycene rotor and a 2-methyleneindanone brake are reported. The rotation kinetics of the rotor was probed by both variable-temperature (1)H and (13)C NMR spectroscopy and DFT calculations, and the switching between the brake-on and brake-off states was conducted by a combination of photochemical and electrochemical isomerization. Because of the greater steric hindrance between the rotor and the brake units in the Z form ((Z)-1) than in the E form ((E)-1), rotation of the rotor is slowed down 500-fold at room temperature (298 K) on going from (E)-1 to (Z)-1, corresponding to the brake-off and brake-on states, respectively. The (E)-1→(Z)-1 photoisomerization in acetonitrile is efficient and reaches an (E)-1/(Z)-1 ratio of 11:89 in the photostationary state upon excitation at 290 nm, attributable to a much larger isomerization quantum efficiency for (E)-1 versus (Z)-1. An efficient (Z)-1→(E)-1 isomerization (96%) was also achieved by electrochemical treatment through the radical anionic intermediates. Consequently, the reversibility of the E-Z switching of 1 is as high as 85%. The repeated E-Z switching of 1 with alternating photochemical and electrochemical treatments is also demonstrated.
报道了一种新型分子体系（1）的合成及其刹车性能，该体系由五并苯转子和 2-亚甲基茚满酮刹车组成。通过变温（1）H 和（13）C NMR 光谱和 DFT 计算研究了转子的旋转动力学，通过光化学和电化学异构化的组合实现了刹车开/关状态之间的切换。由于在 Z 构象（（Z）-1）中转子与刹车单元之间的空间位阻大于在 E 构象（（E）-1）中，因此转子的旋转在室温（298 K）下从（E）-1 到（Z）-1 时减慢了 500 倍，分别对应于刹车开和刹车关状态。在乙腈中的（E）-1→（Z）-1 光异构化效率很高，在 290nm 激发下达到光稳定态时的（E）-1/（Z）-1 比例为 11:89，这归因于（E）-1 相对于（Z）-1 的异构化量子效率要大得多。通过自由基阴离子中间体的电化学处理也实现了高效的（Z）-1→（E）-1 异构化（96%）。因此，1 的 E-Z 开关的可逆性高达 85%。还证明了通过交替的光化学和电化学处理对 1 进行重复的 E-Z 切换。
