Hunting for smectic C in calamitic azobenzene ionic liquid crystals with different cationic head groups. (18th October 2017)

• Record Type: Journal Article
• Authors: Kapernaum, Nadia; Wuckert, Eugen; Frey, Wolfgang; Marino, Sebastian; Wahl, Manuel; Giesselmann, Frank; Laschat, Sabine
• Is Part Of: Journal of physical organic chemistry. Volume 31:Number 3(2018)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-10-18
• Subjects: amidinium -- de Vries material -- guanidinium -- imidazolium -- ionic liquid crystals -- smectic C; Chemistry, Physical organic -- Periodicals; 547.1
• DOI: 10.1002/poc.3779
• Languages: English
• ISSNs: 0894-3230

Abstract

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. Abstract : 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.