Synthesis and Mesomorphic and Electrical Investigations of New Furan Liquid Crystal Derivatives.

Laila A Al-Mutabagani,Sobhi M Gomha,Tariq Z Abolibda,Hoda A Ahmed,Latifah A Alshabanah,Mohamed Shaban

doi:10.3389/fchem.2021.711862

Abstract

New homologues set liquid crystalline materials, based on furfural derivatives, namely, (E)-4-((furan-2-ylmethylene)amino)phenyl 4-alkoxybenzoate (F n), were synthesized and investigated for their mesomorphic and optical characteristics. The prepared homologues series constitutes three derivatives that bear different terminal flexible alkyl chain lengths that vary between 6 and 12 carbons and attached to the phenyl ring linked to the ester group. A furfural moiety is introduced into the other terminal of the molecular structure. Mesomorphic characterizations of the prepared derivatives were measured using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Molecular structures were elucidated via elemental analyses, FTIR, and NMR spectroscopy. DSC and POM showed that all the synthesized furfural derivatives are purely nematogenic, exhibiting an enantiotropic nematic (N) mesophase, except for the longest chain derivative (F 12) that is dimorphic possessing a monotropic smectic A phase and an enantiotropic N mesophase. Results indicated that the incorporation of the heterocyclic furfural ring into the molecular skeleton affected both the mesophase range and stability of investigated homologue. Analysis of the optical properties revealed that the shortest chain compound (F 6) possesses two direct band gaps, at 2.73 and 3.64 eV, in addition to higher absorption than the higher homologues, F 10 and F 12. On the other hand, all the synthesized homologues (F n) showed Ohmic behaviors, with electric resistances in the GΩ range. The values of the electrical resistances are 103.71, 12.91, and 196.85 GΩ at 0.05 V for F 6, F 10, and F 12, respectively.

Highlights

Today, the higher cost and the lower conversion efficiency of solar energy limit its application
Phase transitions and optical characteristics of the investigated furfural group have been investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) measurements
New optical liquid crystalline homologues based on a furfural moiety named (E)-4-((furan-2-ylmethylene)amino)phenyl 4alkoxybenzoate (Fn) were synthesized

Summary

Introduction

The higher cost and the lower conversion efficiency of solar energy limit its application. Liquid crystalline (LC) semiconductors have been extensively investigated due to their pi-conjugated properties; large numbers of LC materials have been designed for solar cell applications (Frédéric et al, 2012; Funahashi, 2014; Paul, 2016; Hu et al, 2020). The addition of heteroatoms such as nitrogen, sulfur, or oxygen increases the species of the liquid crystals and greatly impacts the thermal and geometrical parameters of investigated materials (Frédéric et al, 2012; Han, 2013; Paul, 2016; Ghosh and Lehmann, 2017; Merlo et al, 2018; Yeap et al, 2018; Weng et al, 2019a; Weng et al, 2019b; Ren et al, 2019). Attachment of electronegative heteroatoms (S, N, and O) can significantly influence the bond angle as well as the delocalized resonance and the molecular geometry (Titov and Pavlyuchenko, 1980; Lehmann et al, 2005; Takase et al, 2007; Gomha and Riyadh, 2011; Gomha et al, 2016a; Gomha et al, 2016b; Gomha et al, 2020; Nafee et al, 2020; Sayed et al, 2020; Abu-Melha et al, 2021; Gomha et al, 2021a)

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