Synthesis, mesomorphic properties and structural studies on 1,3,5-trisubstituted benzene-based star-shaped derivatives containing Schiff base ester as the peripheral arm
作者:Yew-Hong Ooi、Guan-Yeow Yeap、Daisuke Takeuchi
DOI:10.1016/j.molstruc.2013.08.015
日期:2013.11
Six new symmetrical three-armed star-shaped liquid crystals comprising phloroglucinol (1,3,5-trihydroxybenzene) as a core center and three Schiff base ester as the mesogenic arms have been synthesized. Their molecular structures were supported by spectroscopic techniques (FT-IR, H-1 NMR, C-13 NMR and two dimensional COSY, HMQC and HMBC). Each of the member differs in the length of the terminal alkyl chain (R-COO- where R = C8H17, C10H21, C12H25 C14H29, C16H33, C18H37). All the star-shaped mesogens are found to be monotropic smectogens with the short chain derivative (R = C8H17) exhibits only smectic A phase. While both the smectic A and smectic C phases are common for the derivatives with C10H21-C16H33 alkyl chain, the member with C18H37 shows only smectic C phase. Further investigation by X-ray diffraction confirms the smectic phase of the materials whereby two sharp reflections at 28.8 angstrom and 57.3 angstrom recorded via small angle in a ratio of 1:2 indicate unambiguously the presence of layered structure and a diffused scattering via the wide angle (4.5 angstrom) indicates a liquid-like order within the smectic layer. Increasing the length of terminal flexible chain has influenced remarkably the thermal and phase stability of the titled compounds. Besides, the liquid crystalline properties of all intermediary co-brominated Schiff base ester prior joining to the benzene core were also evaluated. (C) 2013 Elsevier B.V. All rights reserved.