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首页> 外文期刊>Chemistry: A European journal >Induction of molecular chirality by circularly polarized light in cyclic azobenzene with a photoswitchable benzene rotor
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Induction of molecular chirality by circularly polarized light in cyclic azobenzene with a photoswitchable benzene rotor

机译：光开关苯转子在环状偶氮苯中通过圆偏振光诱导分子手性

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摘要

New phototriggered molecular machines based on cyclic azobenzene were synthesized in which a 2,5-dimethoxy, 2,5-dimethyl, 2,5-difluorine or unsubstituted-1,4-dioxybenzene rotating unit and a photoisomerizable 3,3′-dioxyazobenzene moiety are bridged together by fixed bismethylene spacers. Depending upon substitution on the benzene moiety and on the E/Z conformation of the azobenzene unit, these molecules suffer various degrees of restriction on the free rotation of the benzene rotor. The rotation of the substituted benzene rotor within the cyclic azobenzene cavity imparts planar chirality to the molecules. Cyclic azobenzene 1, with methoxy groups at both the 2- and 5-positions of the benzene rotor, was so conformationally restricted that free rotation of the rotor was prevented in both the E and Z isomers and the respective planar chiral enantiomers were resolved. In contrast, compound 2, with 2,5-dimethylbenzene as the rotor, demonstrated the property of a light-controlled molecular brake, whereby rotation of the 2,5-dimethylbenzene moiety is completely stopped in the E isomer (brake ON, rotation OFF), while the rotation is allowed in the Z isomer (brake OFF, rotation ON). The cyclic azobenzene 3, with fluorine substitution on the benzene rotor, was in the brake OFF state regardless of E/Z photoisomerization of the azobenzene moiety. More interestingly, for the first time, we demonstrated the induction of molecular chirality in a simple monocyclic azobenzene by circular-polarized light. The key characteristics of cyclic azobenzene 2, that is, stability of the chiral structure in the E isomer, fast racemization in the Z isomer, and the circular dichroism of enantiomers of both E and Z isomers, resulted in a simple reversible enantio-differentiating photoisomerization directly between the E enantiomers. Upon exposure to r- or l-circularly polarized light at 488 nm, partial enrichment of the (S)- or (R)-enantiomers of 2 was observed.
机译：合成了一种新的基于环偶氮苯的光触发分子机器，其中2,5-二甲氧基，2,5-二甲基，2,5-二氟或未取代的1,4-二氧苯旋转单元和可光异构的3,3'-二氧偶氮苯部分通过固定的亚甲基间隔基桥接在一起。取决于在苯部分上的取代和在偶氮苯单元的E / Z构象上，这些分子在苯转子的自由旋转上受到不同程度的限制。环状偶氮苯腔内取代苯转子的旋转使分子具有平面手性。环状偶氮苯1在苯转子的2-位和5-位均具有甲氧基，因此在构象上受到限制，以至于在E和Z异构体中均防止了转子的自由旋转，并且拆分了各自的平面手性对映体。相反，以2,5-二甲基苯为转子的化合物2表现出光控分子制动器的特性，由此2,5-二甲基苯部分的旋转在E异构体中完全停止（制动ON，旋转OFF） ），而在Z异构体中允许旋转（制动OFF，旋转ON）。不考虑偶氮苯部分的E / Z光异构化，在苯转子上具有氟取代的环状偶氮苯3处于制动关闭状态。更有趣的是，我们首次展示了圆偏振光在简单的单环偶氮苯中诱导的分子手性。环状偶氮苯2的关键特征，即E异构体的手性结构的稳定性，Z异构体的快速消旋作用以及E和Z异构体的对映异构体的圆二色性，导致了简单的可逆对映异构-光致异构化直接在E对映体之间。在暴露于488nm的r-或l-圆偏振光时，观察到部分富集2的（S）-或（R）-对映体。

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