The influence of fluorine terminal group and flexible spacers on properties of the liquid crystal dimers

Two series of symmetric LC dimers with the same rigid group and different fluorine terminal group (F and F 3 C) have been synthesised by varying the length of flexible spacers, termed 1 F series (1 F-4, 1 F-6, 1 F-8) and 3 F series (3 F-4, 3 F-6, 3 F-8). Chemical structures and LC properties of the...

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Bibliographic Details
Published inLiquid crystals Vol. 49; no. 3; pp. 380 - 391
Main Authors Gao, Yuan-Yuan, Wan, Xin-yi, Feng, Ze-long, Fang, Lu-xin, Chen, Xin-shi, Jia, Ying-Gang, Tian, Mei
Format Journal Article
LanguageEnglish
Published Abingdon Taylor & Francis 19.02.2022
Taylor & Francis Ltd
Subjects
Calorimetry
Differential scanning calorimetry
Dimers
flexible spacer
fluorinated liquid crystal
Fluorine
Fourier transforms
Infrared spectroscopy
Light microscopy
Liquid crystal
Liquid crystals
Melting
NMR
Nuclear magnetic resonance
Optical microscopy
Rigidity
Spacers
symmetric liquid crystal dimers
Thermogravimetric analysis
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Summary:Two series of symmetric LC dimers with the same rigid group and different fluorine terminal group (F and F 3 C) have been synthesised by varying the length of flexible spacers, termed 1 F series (1 F-4, 1 F-6, 1 F-8) and 3 F series (3 F-4, 3 F-6, 3 F-8). Chemical structures and LC properties of the six symmetric LC dimers were characterised by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance hydrogen spectrometer ( 1 H NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and polarised optical microscopy (POM). The 1 F series dimers only show nematic phase. While for 3 F series, smectic phase appeared, and with the increase of flexible spacers, the smectic phase is dominant. For the formation of smectic phase of 3 F series, the larger intermolecular transverse force coming from CF 3 may be the driving force, and the long flexible spacer makes it possible. The melting temperatures of the 1 F series and 3 F series gradually decrease as the length of the flexible spacer increases, respectively, indicating that molecular rigidity has a greater influence on the melting temperatures. The melting temperatures of the 3 F series dimers decrease faster, which may attribute to the influence of CF 3 on the conformation of the dimers.
ISSN:0267-8292
1366-5855
DOI:10.1080/02678292.2021.1970837