Synthesis, thermal, dielectric and electro-optic properties of new series of fluorinated hydrogen-bonded liquid crystals

• Published in: Journal of molecular liquids 2022-12, Vol.367, p.120510, Article 120510
• Main Authors: Derbali, Mouna, Soltani, Taoufik, Guesmi, Ahlem, Ben Hamadi, Naoufel, Jeanneau, Erwann, Chevalier, Yves
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Dielectric spectroscopy; Hydrogen-bonded liquid crystal; Material chemistry; Nematic phase; Organic chemistry; Smectic phases
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2022.120510

[Display omitted] •4-Alkyloxy-2,3-difluorobenzoic acids self-associate as SmA and SmC hydrogen-bonded liquid crystals.•Mixtures of 4-alkoxy-2,3-difluorobenzoic acids and 4-octylloxybenzoic acid display nematic, SmA and SmC phases.•Order parameter, transition temperatures, threshold voltage and response time decrease with increasing alkoxy chain length. Two series of hydrogen-bonded liquid crystals (HBLC) were investigated: 4-alkoxy-2,3-difluorobenzoic acids (nOBAFF) with alkoxy chain lengths of n = 7–12 carbon atoms and mixtures of nOBAFF and 4-octyloxybenzoic acid (8OBA). Their phase behavior has been established using differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. At variance with non-fluorinated and monofluorinated homologues, the difluorinated nOBAFF compounds only form SmA and SmC liquid crystalline phases. An additional nematic phase is obtained upon mixing nOBAFF and 8OBA, showing the sequence: Isotropic liquid–Nematic–SmA–SmC–crystalline solid upon cooling from the isotropic phase. All the transition temperatures decrease with increasing alkoxy chain length of nOBAFF, which reveals a decrease of order parameter for longer chains. The dielectric and electro-optic behaviors of the nematic phase of nOBAFF/8OBA mixtures reveal a decrease of the threshold voltage and response time upon increasing the alkyl chain length of nOBAFF.