Department of Physical and Analytical Chemistry, Experimental Sciences Faculty, University of Jaén , Campus Las Lagunillas, E-23071 Jaén, Spain.
J Phys Chem B. 2012 Apr 26;116(16):5090-6. doi: 10.1021/jp3017453. Epub 2012 Apr 18.
IR and VCD spectroscopies are employed to clarify the molecular origins of supramolecular chirality in azobenzene-containing columnar liquid crystals. The different columnar mesomorphic assemblies, Colr and Colh, of an achiral and a chiral propeller-like hydrogen-bonded complex, respectively, are used for this study. The mesomorphic behavior of the achiral complex is studied here for the first time, and the structural parameters of its Colr mesophase are determined by X-ray diffraction. Both complexes bear azobenzene units and this makes it possible to implement photoresponsive columnar architectures, the chirality of which can be induced and modulated by irradiation with 488 nm circularly polarized light (CPL). Thin films of the respective rectangular and hexagonal columnar phases of these complexes have been processed in order to study the IR absorption spectra and the vibrational circular dichroism responses upon irradiation with CPL. These studies allow confirming that the outer part of the columns, consisting on azobenzene groups, is mainly involved in the photoinduced supramolecular chirality, rather than the inner part of the columns where a melamine core is located. This supports a structural model based on the helical disposition of the azobenzene groups along the stacked propeller-like complexes.
采用红外和可见光圆二色光谱来阐明含偶氮苯的柱状液晶中超分子手性的分子起源。分别使用非手性和手性螺旋形氢键复合物的两种不同柱状中间相 Colr 和 Colh 进行这项研究。本研究首次研究了非手性复合物的中间相行为，并通过 X 射线衍射确定了其 Colr 中间相的结构参数。这两个复合物都含有偶氮苯单元，这使得有可能实现光响应的柱状结构，其手性可以通过用 488nm 圆偏振光（CPL）照射来诱导和调制。为了研究 CPL 照射时的红外吸收光谱和振动圆二色响应，已经处理了这些复合物各自的矩形和六边形柱状相的薄膜。这些研究证实，由偶氮苯基团组成的柱的外部主要参与光诱导超分子手性，而不是位于其中的三聚氰胺核心的柱的内部。这支持了一种基于螺旋排列的偶氮苯基团沿着堆叠的螺旋形复合物的结构模型。
