A Light-Controlled Molecular Brake with Complete ON-OFF Rotation
A Light-Controlled Molecular Brake with Complete ON-OFF Rotation
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DOI：
10.1002/chem.200902123
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发表时间：
2010-01-01
影响因子：
4.3
通讯作者：
Tamaoki, Nobuyuki
中科院分区：
文献类型：
--
作者：
Basheer, Meethale C.;Oka, Yoshimi;Tamaoki, Nobuyuki
报道了一种基于环偶氮苯的光控分子机器，该分子机器由一个二氧萘旋转单元和一个由亚甲基间隔剂桥接的光异构二氧偶氮苯单元组成。在化合物1和2中，1,5-和2,6-二氧基萘部分分别通过不同的亚甲基间隔物（la和2中n=2； 1b中n=3）连接到对二氧基偶氮苯，而在3中1,5-二氧基萘部分通过双亚甲基间隔物连接到间二氧基偶氮苯。在1b和2中，萘环可以在室温下以反式和顺式自由旋转。从其核磁共振谱可以看出，通过光诱导偶氮苯的可逆反顺（E-Z）异构化或将系统保持在低温下，可以控制旋转速度。此外，我们首次展示了一种光控分子制动器，其中在化合物3的反式异构体中，由于其较小的空腔尺寸，萘部分通过环烷的旋转完全关闭。这种受限制的旋转使分子具有平面手性，相应的对映体可以用手性高效液相色谱拆分。然而，在顺式异构体中，由于其空腔尺寸的增加，萘部分的旋转呈现为ON，并且在实验中通过光诱导E-Z异构化使分离的对映体外消旋得到了证明。
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 la 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.