Laterally substituted symmetric and nonsymmetric salicylideneimine-based bent-core mesogens

Sonja Findeisen-Tandel,H N Shreenivasa Murthy,Wolfgang Weissflog,Gerhard Pelzl,Ute Baumeister,Channabasaveshwar V Yelamaggad

doi:10.3762/bjoc.8.15

Sonja Findeisen-Tandel, H N Shreenivasa Murthy + Show 4 more

Open Access

https://doi.org/10.3762/bjoc.8.15

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Abstract

Bent-core mesogens have gained considerable importance due to their ability to form new mesophases with unusual properties. Relationships between the chemical structure of bent-core molecules and the type and physical properties of the formed mesophases are relatively unknown in detail and differ strongly from those known for calamitic liquid crystals. In this paper symmetric and nonsymmetric five-ring salicylideneaniline-based bent-core mesogens are presented, and the effect of lateral substituents attached at the outer phenyl rings (F, Cl, Br) or the central phenyl ring (CH3) on the liquid-crystalline behaviour and on the physical properties is studied. Corresponding benzylideneaniline-based compounds were additionally prepared in order to study the influence of the intramolecular hydrogen bond. The occurring mesophases were investigated by differential scanning calorimetry, polarising microscopy, X-ray diffraction and dielectric and electro-optical measurements. The paper reports on new findings with respect to the structure–property relationships of bent-core mesogens. On one hand, the disruptive effect of laterally substituted halogen atoms, F, Cl and Br, on the mesophase behaviour of three isomeric series was much lower than expected. On the other hand, an increase of the clearing temperature by 34 K was observed, caused by small lateral substituents. The electro-optical behaviour, especially the type of polar switching and corresponding molecular movements, is sensitive to variations in the molecular structure.

Highlights

For a long time there was a general perception that molecules capable of exhibiting liquid crystal (LC) phases have to be rodlike, so-called calamitic LCs
Relationships between the chemical structure of bent-core molecules and the type and physical properties of the formed mesophases are relatively unknown in detail and differ strongly from those known for calamitic liquid crystals
In 2007, we reported systematic investigations on the influence on the mesophase behaviour of lateral groups attached to the central phenyl ring of several homologous series [42]

Summary

Introduction

For a long time there was a general perception that molecules capable of exhibiting liquid crystal (LC) phases have to be rodlike, so-called calamitic LCs. New achiral four-ring molecules were reported by Deb et al, in which two substituted salicylideneaniline moieties are linked by an ester group (Scheme 1C) These compounds, which show a strong photoluminescence, exhibit typical banana phases B1 and B7 [31]. The observation of a B7 mesophase on the hexadecyloxy compound is surprising, because the central phenyl ring was not substituted by a nitro or cyano group as is the case for most of the other banana-shaped liquid crystals that form this phase type [40]. In continuation of our work on salicylideneaniline-based banana-shaped mesogens, we report a study of the effect of lateral substituents on the mesophase behaviour of symmetric and nonsymmetric five-ring bent-core mesogens. In order to focus the study on the effect of lateral substituents, the hydrocarbon chains at both terminal phenyl rings were fixed with dodecyloxy groups

Results and Discussion

95 I H 4b

Conclusion