Fluorenone imidazolium salts as novel de Vries materials

Abstract

ILCs consisting of cationic head group–spacer–fluorenone central core–side chain show de Vries-like behaviour.

Current Topics in Ionic Liquid Crystals

“…According to strategy (c) we aimed at ILC dyes as novel de Vries materials showing both SmA and SmC phases as well as emissive behaviour and thus connected fluorenone via flexible alkyl spacer to the imidazolium head group (Scheme 6). [133] Compound Im(O6,O8)OTf possessed only a SmA phase, but showed a green emission in CHCl 3 solution (λ em 532 nm), while the bulk emission (λ em 610 nm) significantly decreased in the SmA mesophase upon cooling from the isotropic phase.…”

“… Fluorenone imidazolium salt Im(S14,O12)Br reported by Laschat [133] and H‐bonded imidazolium salt 56 described by Kohmoto [192] …”

“…In comparison with other head groups imidazolium ILCs show a small contraction of the smectic layers at the SmA‐to‐SmC transition, which is indicative of de Vries behaviour. More recently, it was found by us that the replacement of the azobenzene core by a fluorenone core resulted in the lowest layer shrinkage known so far (Scheme 25, Im(S14,O12)Br ) [133] …”

Molecular design of viologens to exhibit low-order liquid-crystalline phases

“…Note that a de Vries material is an LC compound that exhibits a small interlayer shrinkage in the SmC phase. [25][26][27][28][29][30][31] The de Vries diffusion cone model explains that the layer shrinkage in the SmC phase is smaller because the molecules are tilted away from the normal of the layer in the SmA phase. 32 Please do not adjust margins Please do not adjust margins 33 As the temperature decreased from the SmA-SmC phase transition, the layer shrinkage ratio of de Vries materials first decreased and then increased above 1, which clearly indicates the de Vries property 34 .…”

First azulene liquid crystal with de Vries behavior and a SmA re-entrant phase

“…7 In a more general approach, a combination of a low orientational order parameter S 2 and very well-defined layers lead to the sought-after de Vries-like properties. Usually nano-segregating elements like perfluorated side chains, 8 carbosilane 5,9 units or ionic headgroups 10 were chosen to acquire the necessary degree of translational order. However, materials with ordinary alkyl chains and very low lc max have also been reported.…”