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Hunting for smectic C in calamitic azobenzene ionic liquid crystals with different cationic head groups
Author(s) -
Kapernaum Nadia,
Wuckert Eugen,
Frey Wolfgang,
Marino Sebastian,
Wahl Manuel,
Giesselmann Frank,
Laschat Sabine
Publication year - 2018
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3779
Subject(s) - azobenzene , mesogen , liquid crystal , chemistry , crystallography , phase (matter) , cationic polymerization , stereochemistry , molecule , organic chemistry , materials science , liquid crystalline , optoelectronics
Abstract 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.