Synthesis, characterization and mesomorphic properties of non-symmetric hydrazine-based liquid crystal trimers
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Date
2014
Authors
Yit Peng, Goh
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Abstract
Four new series of non-symmetric hydrazine-based liquid crystal (LC) trimers, namely 1-[N-benzylideneoxy-N'-(4-decyloxybenzylidene)hydrazine] alkyloxy-3-[(4-(4'-decyloxyphenyl)methanimino)phenoxy]alkyloxybenzenes (ATCn), 1-[N-benzylideneoxy-N'-(4'-decyloxybenzylidene)hydrazine]pentyloxy-3-[(4''-(4'''-substitutedphenyl)methanimino)phenoxy]butyloxybenzenes (A5-X), 1-[4-(4'-(5-cholesteryloxy)carbonyl)butyloxy]-3-[N-benzylideneoxy-N'-(4-decyloxybenzylidene)hydrazine]alkyloxybenzenes (HZnCh5) and 1-[4-(4'-(10-cholesteryloxy)carbonyl)nonyloxy]-3-[N-benzylideneoxy-N'-(4-decyloxybenzylidene) hydrazine]alkyloxybenzenes (HZnCh10) have been synthesized and characterized. All trimers have resorcinol as the central core and differ in terms of mesogenic side arms and parity of the spacers. The molecular structures of these trimers were elucidated via CHN microanalysis, FT-IR, 1D- and 2D FT-NMR spectroscopy and their liquid crystalline properties were investigated using POM, DSC and XRD. All trimers are found to be monotropic or enantiotropic mesogens exhibiting mono- and/or polymorphism. The mesophases observed include blue phase (BP), nematic (N), chiral nematic (N*), twist grain boundary smectic A (TGBA*), smectic A (SmA), chiral smectic A (SmA*), smectic B (SmB) and smectic C (SmC) phases. A structure-property investigation revealed that the thermal behaviour and phase sequence of these trimers are strongly dependent on the molecular structures and parity of the spacers. Strong odd-even effects were also observed in the transitional
properties of ATCn, HZnCh5 and selected homologues of HZnCh10 upon varying the parity of the spacers.