Research Institute for Electronic Science, Hokkaido University, N20, W10, Sapporo, Hokkaido 001-0020, Japan.
Chemistry. 2010 Mar 15;16(11):3489-96. doi: 10.1002/chem.200902123.
A light-controlled molecular machine based on cyclic azobenzenophanes consisting of a dioxynaphthalene rotating unit and a photoisomerizable dioxyazobenzene unit bridged by methylene spacers is reported. In compounds 1 and 2, 1,5- and 2,6-dioxynaphthalene moieties, respectively, are linked to p-dioxyazobenzene by different methylene spacers (n=2 in 1a and 2; n=3 in 1b), whereas a 1,5-dioxynaphthalene moiety is bonded to m-dioxyazobenzene by bismethylene spacers in 3. In 1b and 2, the naphthalene ring can rotate freely in both the trans and cis states at room temperature. The rotation speed can be controlled either by photoinduced reversible trans-cis (E-Z) isomerization of the azobenzene or by keeping the system at low temperature, as is evident from its NMR spectra. Furthermore, for the first time, we demonstrate a light-controlled molecular brake, wherein the rotation of the naphthalene moiety through the cyclophane is completely OFF in the trans isomer of compound 3 due to its smaller cavity size. Such restricted rotation imparts planar chirality to the molecule, and the corresponding enantiomers could be resolved by chiral HPLC. However, the rotation of the naphthalene moiety is rendered ON in the cis isomer due to its increased cavity size, and it is manifested experimentally by the racemization of the separated enantiomers by photoinduced E-Z isomerization.
报道了一种基于环偶氮苯并环烷的光控分子机器，它由一个二氧萘旋转单元和一个可光致异构化的二氧偶氮苯单元组成，由亚甲基间隔基桥接。在化合物 1 和 2 中，1,5-和 2,6-二氧萘部分分别通过不同的亚甲基间隔基（n=2 在 1a 和 2 中；n=3 在 1b 中）与对二氧偶氮苯相连，而 1,5-二氧萘部分在 3 中通过双亚甲基间隔基与间二氧偶氮苯相连。在 1b 和 2 中，萘环在室温下可以在顺式和反式两种状态下自由旋转。旋转速度可以通过偶氮苯的光诱导可逆顺反（E-Z）异构化或通过将系统保持在低温来控制，这可以从其 NMR 光谱中明显看出。此外，我们首次展示了一种光控分子刹车，其中由于化合物 3 的环烷腔室较小，萘环部分通过环烷的旋转在反式异构体中完全关闭。这种受限的旋转赋予分子平面手性，并且可以通过手性 HPLC 分离对映异构体。然而，由于腔室尺寸增大，萘环部分在顺式异构体中的旋转变为开启，这通过光诱导 E-Z 异构化引起分离对映异构体的外消旋化来实验证明。
