Non-symmetric chiral nematic liquid crystal dimers containing trifluoromethyl and 1,2-propanediol

A series of non-symmetric liquid crystal (LC) dimers with the same chiral core 1,2-propanediol (PD) have been synthesised, termed as ABBA-PD-TFBA, PBBA-PD-TFBA, ABA-PD-TFBA, PBA-PD-TFBA and AA-PD-TFBA, respectively, in which one of the two mesogenic groups, the fluorinated mesogenic unit, was kept f...

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Bibliographic Details
Published in:Liquid crystals 2018-09, Vol.45 (12), p.1734-1745
Main Authors: Dong, Liang, Xu, Zhi-xin, Tao, He-zhong, Chen, Xin-shi, Hu, Jian-she, Yao, Dan-shu, Tian, Mei
Format: Article
Language:English
Subjects:
1,2-propanediol
Calorimetry
Chemical bonds
chiral nematic phase
Cholesteric liquid crystals
Differential scanning calorimetry
Dimers
fluorinated liquid crystal
Fluorination
Microscopy
Nematic crystals
NMR
Non-symmetric liquid crystal dimer
Nuclear magnetic resonance
Optical activity
Optical microscopy
Organic chemistry
Rigidity
Thermal properties
Thermodynamic properties
Thermogravimetric analysis
X-ray diffraction
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Summary:A series of non-symmetric liquid crystal (LC) dimers with the same chiral core 1,2-propanediol (PD) have been synthesised, termed as ABBA-PD-TFBA, PBBA-PD-TFBA, ABA-PD-TFBA, PBA-PD-TFBA and AA-PD-TFBA, respectively, in which one of the two mesogenic groups, the fluorinated mesogenic unit, was kept fix and the other arm was different. The intermediate compounds and LC dimers were characterised by FTIR, 1 H NMR, differential scanning calorimetry, thermogravimetric analysis, polarised optical microscopy and X-ray diffractometer (XRD). The results of the measurements indicated that ABBA-PD-TFBA, PBBA-PD-TFBA and ABA-PD-TFBA displayed optical activity and enantiotropic chiral nematic phase, and PBA-PD-TFBA was an enantiotropic nematic LC while AA-PD-TFBA was a monotropic LC, displaying both nematic phase and smectic A phase on cooling. The results indicated that PD was able to induce the chiral nematic phase, nevertheless, the rigidity of the mesogenic arm, the flexibility of the terminal group and even the type of the terminal chemical bond played an important effect on the thermal properties of the dimers, and even on the formation of the chiral nematic phase. It is also worth noting that C=C at the terminal helped to stabilise the LC phase.
ISSN:0267-8292
1366-5855
DOI:10.1080/02678292.2018.1469171