Influence of hydrogen bond on the mesomorphic behaviour in urethane based liquid crystalline compounds: Experimental and computer simulation study

Burak Korkmaz, Sinem Agtas, Berkay Sütay, Erol Yildirim, Iskender Yilgor, Mine Yurtsever*, B. Filiz Senkal, Yesim Gursel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

We present a combined experimental and theoretical study on the novel hydrogen-bonded liquid crystalline complex (UR-LC11) exhibiting both nematic and smectic phases upon cooling. The complex was prepared by mixing 2-(2-methoxyethoxy)ethylbutyl carbamate (UR) as H-bond acceptor with calamitic mesogen 4′-((11-hydroxyundecyl)oxy)-[1,1′-biphenyl]-4‑carbonitrile (LC11) as H-bond donor. The complex was characterized by FTIR technique and its liquid crystalline properties were studied by differential scanning calorimetry (DSC) and polarized optical microscope (POM). The experimental IR spectra were compared with theoretically obtained IR spectra by Density Functional Theory (DFT) to suggest the structure of hydrogen-bonded liquid crystal (LC). The molecular dynamics (MD) simulations were performed to understand the impact of hydrogen bonding on the mesomorphic behaviour of the complex and the temperature dependency of the transitions between the mesophases. We determined that UR-LC11 is a stable H-bond acceptor/donor type complex and a single H-bond forms between the carbonyl oxygen atom of the amide moiety of UR and the hydrogen atom of the terminal hydroxyl group of the LC11. Although LC11 is present only in nematic liquid crystalline form, the new complex displayed both nematic and smectic phases during cooling. The reason for the two distinctive LC phases was explained by the presence of hydrogen bond interactions, which provides structural flexibility. Besides, H-bond maintains uniaxial rod shape of the molecule to promote self-assembly behaviour and induces positional ordering in the smectic phase. The enhancement in the self-assembly of the H-bonded chains in the complex is reflected in the increased ΔHfusion values. Due to the intermolecular π-π interactions of the phenyl rings and the formation of strong dipoles on the backbone, especially at the cyanobiphenyl end of the chains, the long-range directional order of the dipoles along their long axes are preserved at elevated temperatures and nematic to isotropic phase transition is observed at around 370 K both experimentally and theoretically.

Original languageEnglish
Article number114001
JournalJournal of Molecular Liquids
Volume317
DOIs
Publication statusPublished - 1 Nov 2020

Bibliographical note

Publisher Copyright:
© 2020 Elsevier B.V.

Funding

This work is a part of PhD project which is supported by the Scientific Research Project Center of the Istanbul Technical University (Project number: 42129 ). Computing resources used in this work were also provided by the National Center for High Performance Computing of Turkey (UHeM) under grant number 5004452017. We would like to thank Research Assistant Esra Su from Prof. O. Okay Lab. (ITU Chem. Dept.) for the DSC measurements. This work is a part of PhD project which is supported by the Scientific Research Project Center of the Istanbul Technical University (Project number: 42129). Computing resources used in this work were also provided by the National Center for High Performance Computing of Turkey (UHeM) under grant number 5004452017. We would like to thank Research Assistant Esra Su from Prof. O. Okay Lab. (ITU Chem. Dept.) for the DSC measurements.

FundersFunder number
National Center for High Performance Computing of Turkey
UHeM
Ulusal Yüksek Başarımlı Hesaplama Merkezi, Istanbul Teknik Üniversitesi5004452017
Istanbul Teknik Üniversitesi42129

    Keywords

    • Calamitic mesogen
    • DFT
    • Diethylene glycol monomethyl ether (DEGME)
    • Hydrogen bond
    • Liquid crystal
    • MD
    • Order parameter
    • Urethane compounds

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