Synthesis and study the liquid crystalline behaviors of double Schiff bases bearing ester linkage as a central core

ABSTRACT

Two series of 12 homologues, 4-(((4-substituentphenyl)imino)methyl)phenyl 4-((4-(alkoxy) benzylidene)amino)benzoate (D_n, X = –OCH₃ and E_n, X = –-Br), have been synthesised. The two series have different alkoxy terminal chains (OC_nH2_n+1, n = 3, 4, 6, 7, 9, 12) on one side of their structures while other side in the series (D_n and E_n) was substituted by methoxy and Bromo group, respectively. The structures of the synthesised derivatives have been identified using Fourier transform infrared spectrometry (FT-IR) and nuclear magnetic resonance for H and C (¹H-NMR, ¹³C-NMR) and the elemental analysis (CHN). The texture of liquid crystalline phases of the mesogens has been observed by optical polarised microscopy (OPM) while the details of the thermal transition of compounds were investigated by differential scanning calorimetry (DSC). The obtained liquid crystalline results showed that the derivatives of series (D_n) display a broad range of nematic mesophase (N) while the mesogens of (E_n) series appeared nematic and smectic mesophases. All the studied homologues show a wide range of liquid crystalline mesophases, the stability of mesomorphic behaviour of these compounds was dependent mainly on the length of terminal alkoxy chain (the number of carbon atoms) chain and the effect of substituent groups (OCH₃ and Br).

Graphical abstract

KEYWORDS:

• Liquid crystals
• Schiff bases
• mesomorphic properties
• ester linkage
• imine linkage

Acknowledgments

We are very thankful to all staff of the Chemistry department at Al-Iraqia and Mustansiriyah Universities for the collaboration to complete this study. Also, many thanks and respect to ASTF (Arab science of technology foundation) to provied the Chemistry Department with an polarized optical microscopy (POM) and hot-stage.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

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