Synthesis and thermal properties of liquid crystal trimers comprising cyanobiphenyl and salicylaldimine anisometric segments
作者:Channabasaveshwar V. Yelamaggad、V. Padmini Tamilenthi
DOI:10.1016/j.tet.2009.05.076
日期:2009.8
The synthesis and mesomorphism of a series of liquid crystal trimers made by covalently linking two cyanobiphenyl moieties with a central salicylaldimine core through two flexible spacers are reported. Nine different oxyalkyleneoxy spacers varying in the number of carbon atoms and thus, methylene units from 3 to 11 were used to understand structure-mesomorphic property correlations. The optical microscope and differential scanning calorimeter were employed to evaluate their phase transitional behavior. All the trimers exhibit an enantiotropic uniaxial nematic phase over a wide thermal range (>80 degrees C) while a homolog comprising an octamethylene (even-parity) spacer displays, additionally, a metastable smectic phase. The nematic-isotropic transition temperatures critically depend on the parity of the spacer with the values for the odd-parity spacer containing homologs being lower than those of the even members, a feature generally observed in oligomesogens. (C) 2009 Elsevier Ltd. All rights reserved.