Study of the Photoinduced Supramolecular Chirality in Columnar Liquid Crystals by Infrared and VCD Spectroscopies

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• 作者：Juan Ram贸n Avil茅s Moreno ; Juan Jes煤s L贸pez Gonz谩lez ; Francisco Partal Ure帽a ; Francisco Vera ; M. Blanca Ros ; Teresa Sierra
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：April 26, 2012
• 年：2012
• 卷：116
• 期：16
• 页码：5090-5096
• 全文大小：384K
• 年卷期：v.116,no.16(April 26, 2012)
• ISSN：1520-5207

文摘

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, Col_r and Col_h, 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 Col_r 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.