Liquid crystal and photoluminescent properties of a series of symmetrical 1,2-bis(4-alkoxybenzylidene)hydrazines bearing long-tails of hydrocarbon chain

ABSTRACT

In this work, 1,2-bis[4-(n-alkoxy)benzylidene]hydrazine (n-alkoxy: O(CH₂)_nH, n = 11–18 or 20), a symmetrical series of azines (linear compounds with rod-like shape structure), were synthesised using a very simple two-step procedure as a part of our continuing effort in evaluating hydrophobic 1,2-disubstituted hydrazine compounds as photoluminescent liquid crystalline materials. The first step of the synthesis involved the alkylation of the OH group of 4-hydroxybenzaldehyde in basic medium using the Williamson method to obtain 4-alkoxybenzaldehydes. While the second step included the condensation reaction of hydrazine hydrate and appropriately 4-alkoxybenzaldehydes compounds (mole ratio 1:2, respectively) in acidic medium under ambient conditions. The prepared compounds were characterised and their structures elucidated depending upon infrared (IR), ultraviolet-visible (UV–Vis), nuclear magnetic resonance (¹HNMR, ¹³CNMR, DEPT NMR, 2D ¹H-¹H-COSY and 2D ¹H-¹³C- HSQC) and elemental analysis (CHN). Liquid crystalline behaviour and photoluminescent properties were studied using polarised light optical microscopy (POM), fluorescence emissions (FE), differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) techniques. The studies showed that all of these compounds are enantiotropic liquid crystalline materials exhibiting smectic (SmA and SmC) and nematic (droplet and thread) mesophases . The study also displayed that all of the prepared compounds are photoluminescent in the crystalline and liquid crystal states.

GRAPHICAL ABSTRACT

KEYWORDS:

• 12-disubstituted hydrazine
• liquid Crystal compounds
• photoluminescent materials
• azines

Acknowledgments

AJM Al-Karawi thanks Mustansiriya University/Iraq and Deutscher Akademischer Austauschdienst/Germany for support, and Prof Dr Wolfgang Bensch for assistance. H Terraschke thanks the German Research Foundation (DFG, Project TE 114711-1) for the financial support.

Disclosure statement

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

Supplementary material

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