Alkylthio- and alkyl-substituted asymmetric diphenyldiacetylene-based liquid crystals: phase transitions, mesophase and single-crystal structures, and birefringence

Asymmetric diphenyldiacetylenes (DPDAs) bearing a fixed hexylthio group and different alkyl groups with carbon numbers (n) of 0-8 and 12 at each termini (or 4- and 4ʹ- positions), abbreviated as 6S-DPDA-n, were synthesised and their phase transition behaviour and birefringence were evaluated. It was...

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Bibliographic Details
Published in:Liquid crystals 2019-09, Vol.46 (11), p.1621-1630
Main Authors: Arakawa, Yuki, Inui, Satoyoshi, Igawa, Kazunobu, Tsuji, Hideto
Format: Article
Language:English
Subjects:
alkylthio group
Asymmetry
Birefringence
Crystal lattices
Crystal structure
Crystals
Density functional theory
Diphenyldiacetylene
Liquid crystals
Mesophase
Nematic crystals
Phase transitions
Single crystals
Substitutes
sulphur
Temperature
X ray analysis
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Summary:Asymmetric diphenyldiacetylenes (DPDAs) bearing a fixed hexylthio group and different alkyl groups with carbon numbers (n) of 0-8 and 12 at each termini (or 4- and 4ʹ- positions), abbreviated as 6S-DPDA-n, were synthesised and their phase transition behaviour and birefringence were evaluated. It was found that alkyl-unsubstituted and methyl-substituted analogues (6S-DPDA-0 and 6S-DPDA-1, respectively) do not show any mesophases, whereas 6S-DPDA-n (n ≥ 2) form enantiotropic liquid crystal phases. Wherein, the nematic (N) phase for 6S-DPDA-4 is supercooled to room temperature, and 6S-DPDA-12 forms not only N phase but also highly ordered mesophase under room temperature. In light of the fact that symmetrically alkylthio-possessing 6S-DPDA-S6, 6S-DPDA-0 and 6S-DPDA-1 are not mesogenic, the present results strongly suggest that an alkyl group opposite to an alkylthio group plays a vital role to induce mesophases. Single-crystal X-ray analysis revealed anti-parallel packed molecules in the lattice. 6S-DPDA-7 have higher birefringence than 7-DPDA-7 being the symmetric alkyl counterpart, over the entire range of each N phase, which is supported by the enhanced polarisabilities based on density functional theory calculation.
ISSN:0267-8292
1366-5855
DOI:10.1080/02678292.2019.1590744