Synthesis and Characterization of a Series of Cholesterol-Based Liquid Crystalline Dimers with a Chiral (-)- Menthyl Terminal Group

Abstract

A novel series of cholesterol-based liquid crystalline (LC) dimers with a menthyl terminal group in the biphenyl base side have been synthesized. The chemical structures and LC properties of this series of compounds are characterized by FT-IR, 1 H-NMR, elemental analysis, hot-stage coupled polarizing microscopy and differential scanning calorimetry. All the dimers exhibit enantiotropic mesophases. These dimesogenic compounds with a short spacer are chiral nematic LCs, while with long spacers, they are SmA and chiral nematic LCs. Some of these LC dimers exhibit iridescent colors in their chial nematic (N * ) states.

1,2-Propanediol-linked chiral symmetric and non-symmetric liquid crystal dimers containing trifluoromethyl

“…LC dimers may be divided into two broad classes: symmetric [10,37,42] and nonsymmetric. [21,23,24,[29][30][31][32][33][34][35]42,43] In a symmetric LC dimer, the two mesogenic units are identical, whereas they are different in a non-symmetric dimer. The intercalated smectic phase was first observed in the study of LC dimers and, specifically, in non-symmetric dimers.…”

“…A wide range of chiral dimers, both symmetric [10,45] and non-symmetric, [11,24,43,45] have been reported in the literature. A key issue in the area of chiral LC dimers was to determine how the form chirality of the chiral phase would depend on the number of methylene groups in the flexible alkyl space.…”

“…A key issue in the area of chiral LC dimers was to determine how the form chirality of the chiral phase would depend on the number of methylene groups in the flexible alkyl space. [36,45] Cholesterol, [10,11,43,45] (S)-(-)-2-methyl-1-butanol [34,45] and (S)-(-)-2-methyl-1-enanthol [24] were usually used in chiral dimers. The bifunctional chiral reagents were seldom used in chiral trimers, [7,46] let alone in chiral dimers.…”

“…LC dimers have now attracted considerable research interest over a prolonged period, [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] not only because they can be used as models of thermotropic, semi-flexible main chain liquid crystalline, but also because of their quite different behaviours to conventional low-molar-mass LCs. LC dimers may be divided into two broad classes: symmetric [10,37,42] and nonsymmetric.…”

Liquid crystalline dimers containing a cholesteryl benzoate unit: smectic phase, chiral nematic phase and blue phase

“…As an important research direction in the field of liquid crystals, chirality 23,24 is introduced into molecules either by introducing chiral flexible spacers such as 1,2-propanediol 25 or by introducing chiral rigid groups such as cholesterol [26][27][28][29] and menthol, 30 etc. Cholesterol is easily obtained from nature, and its molecular structure is rigid with eight chiral cores.…”