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首页> 外文期刊>Chemistry: A European journal >Supramolecular Chirality and Reversible Chiroptical Switching in New Chiral Liquid-Crystal Azopolymers
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Supramolecular Chirality and Reversible Chiroptical Switching in New Chiral Liquid-Crystal Azopolymers

机译：新型手性液晶聚合物中的超分子手性和可逆手性转换

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摘要

The synthesis of chiral liquid-crystalline polymers of well-controlled structure (linear and three-armed star-shaped) with distinct average chain lengths and low polydispersity was achieved by atom transfer radical polymerisation (ATRP) of a new optically active monomer (S)-4-[6-(2-methacryloyloxypropanoyloxy)hexyloxy)]-4'-ethoxyazobenzene [(S)-ML6A], containing the L-lactic residue of one absolute configuration in the side-chain. All the obtained polymeric samples, characterised by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarised optical microscopy (POM), exhibit a smectic A(1/2) (fully interdigitated) liquid-crystalline phase and high cleaning points, with transition temperatures dependent on the average polymerisation degree and the macromolecular structure. The chirality originated at the molecular level by the asymmetric functionality of the L-lactic acid residue provides the polymers, in the smectic phase, of highly homogeneous conformations with a prevailing chirality related to the presence of H-aggregates having conformational dissymmetry of one prevailing screw-sense. By irradiating with circularly polarised light (CPL). it is possible to photomodulate the chiroptical properties of these intrinsically chiral polymeric thin films. Upon irradiation with left-handed CPL (l-CPL), the circular dichroism (CD) spectra of the films show enhancement of ellipticity and a net inversion of sign. ne effect is reversible and the mirror image of the CD spectrum can be restored by pumping with right-handed CPL radiation (r-CPL). The results show the ability of l-CPL to invert the supramolecular chirality of the materials and demonstrate the essential role of azoaromatic aggregates.
机译：通过新型光学活性单体的原子转移自由基聚合（ATRP）合成具有良好平均链长和低多分散性的结构可控（线性和三臂星形）的手性液晶聚合物-4- [6-（2-（甲基丙烯酸丙烯酰氧基丙酰氧基）己氧基）]-4'-乙氧基偶氮苯[（S）-ML6A]，在侧链中含有一个绝对构型的L-乳酸残基。通过差示扫描量热法（DSC），X射线衍射（XRD）和偏振光学显微镜（POM）表征的所有获得的聚合物样品均表现出近晶A（1/2）（完全相互交叉）液晶相并具有高清洁度转变温度取决于平均聚合度和大分子结构。由L-乳酸残基的不对称官能度在分子水平上引发的手性为聚合物提供了近乎均相的构象，在近晶相中具有与具有一个主要螺杆的构象不对称性的H聚集体有关的主要手性。 -感。通过照射圆偏振光（CPL）。可以光调制这些本征手性聚合物薄膜的手性。在用左手CPL（1-CPL）辐照后，薄膜的圆二色性（CD）光谱显示出椭圆度的增强和符号的净反转。这种作用是可逆的，并且可以通过泵浦右旋CPL辐射（r-CPL）来恢复CD光谱的镜像。结果表明，I-CPL具有反转材料的超分子手性的能力，并证明了偶氮芳族聚集体的基本作用。

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