Fluorenone imidazolium salts as novel de Vries materials

In ionic liquid crystals (ILCs) tilted mesophases such as SmC required for electro-optic devices are quite rare. We report a design concept that induced the SmC phase and enabled de Vries-like behaviour in ILCs. For this purpose, we synthesized and characterized a library of ILC derivatives ImR(On,Y...

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Bibliographic Details
Published in:RSC advances 2020-06, Vol.1 (4), p.23999-2416
Main Authors: Bader, Korinna, Müller, Carsten, Molard, Yann, Baro, Angelika, Ehni, Philipp, Knelles, Jakob, Laschat, Sabine
Format: Article
Language:English
Subjects:
Chemical Sciences
Chemistry
Electron density
Emission analysis
Ionic liquids
Liquid crystals
Mathematical analysis
Optical microscopy
Optical properties
Phase transitions
Small angle X ray scattering
Temperature dependence
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Summary:In ionic liquid crystals (ILCs) tilted mesophases such as SmC required for electro-optic devices are quite rare. We report a design concept that induced the SmC phase and enabled de Vries-like behaviour in ILCs. For this purpose, we synthesized and characterized a library of ILC derivatives ImR(On,Ym)X which consist of a rigid central fluorenone core containing an alkoxy or thioether side chain and connected via a flexible spacer to an imidazolium head group. The mesomorphic properties were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD). Temperature-dependent measurements of smectic layer spacing d by small-angle X-ray scattering (SAXS) and of optical tilt angles by POM demonstrate that ILCs ImR(On,Ym)X undergo SmA-SmC phase transitions with maximum layer contraction values between 0.4% and 2.1%. The lowest reduction factor R of 0.2 at the reduced temperature T − T AC = −10 K was calculated for Im(O12,S14)Br . Electron density calculations indicated a bilayer structure. Furthermore, temperature dependent emission studies show that self-assembling has a strong influence on the emission intensity of these ILCs. ILCs consisting of cationic head group-spacer-fluorenone central core-side chain show de Vries-like behaviour.
ISSN:2046-2069
2046-2069
DOI:10.1039/d0ra04650g