Fluorenone imidazolium salts as novel de Vries materials
Résumé
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 derivativesImR(On,Ym)Xwhich consist of a rigid central fluorenone core containing an alkoxy or thioether side chain and connectedviaa 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 spacingdby small-angle X-ray scattering (SAXS) and of optical tilt angles by POM demonstrate that ILCsImR(On,Ym)Xundergo SmA-SmC phase transitions with maximum layer contraction values between 0.4% and 2.1%. The lowest reduction factorRof 0.2 at the reduced temperatureT-T-AC= -10 K was calculated forIm(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.
Domaines
Chimie
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