Hunting for smectic C in calamitic azobenzene ionic liquid crystals with different cationic head groups

The tilted smectic C phase is a rather uncommon phase in ionic liquid crystals (ILCs), whereas the orthogonal smectic A phase is the most common phase in ILCs. We now present 2 new groups of mesogens with an azobenzene core that exhibit smectic C as well as smectic A phases. Their phase sequences an...

Full description

Saved in:
Bibliographic Details
Published in:Journal of physical organic chemistry 2018-03, Vol.31 (3), p.n/a
Main Authors: Kapernaum, Nadia, Wuckert, Eugen, Frey, Wolfgang, Marino, Sebastian, Wahl, Manuel, Giesselmann, Frank, Laschat, Sabine
Format: Article
Language:English
Subjects:
amidinium
Aromaticity
de Vries material
guanidinium
Hunting
imidazolium
ionic liquid crystals
Ionic liquids
Ions
Liquid crystals
Order parameters
Phases
smectic C
Temperature dependence
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The tilted smectic C phase is a rather uncommon phase in ionic liquid crystals (ILCs), whereas the orthogonal smectic A phase is the most common phase in ILCs. We now present 2 new groups of mesogens with an azobenzene core that exhibit smectic C as well as smectic A phases. Their phase sequences and tilt angles were studied by polarizing microscopy, and their temperature‐dependent layer spacings and orientational order parameters were investigated by X‐ray diffraction. We present 1 new amidinium azobenzene mesogen that forms enantiotropic smectic C and A phases and another amidinium as well as 2 new guanidinium azobenzene mesogens that exhibit monotropic smectic C and enantiotropic smectic A phases. With this study, we show that azobenzene is indeed an SmC‐promoting group in ILCs. Comparing these results with our earlier results on azobenzenes with an N‐methylimidazolium head group (N Kapernaum et al, ChemPhysChem 2016, 17, 4116‐4123), we show that the aromaticity of the imidazolium head group plays an important role in the formation of smectic C phases. Novel amidinium and guanidinium ionic liquid crystals exhibit a smectic C phase, a common liquid crystal phase that is however very rarely found in ionic materials. Investigations of the phase transition from smectic A into the tilted smectic C phase together with earlier results provide new insights into the formation of smectic C phases in ionic liquid crystals. Enhancement of nanosegregation caused by an aromatic ionic end group can stabilize smectic C phases.
ISSN:0894-3230
1099-1395
DOI:10.1002/poc.3779