Novel glass-forming liquid crystals. III Helical sense and twisting power in chiral nematic systems

Abstract

Based on nematic and chiral precursors comprising of acetylenic, phenyl, naphthyl and terminal cyan0 groups in conjugation and cyclohexane as the central core, a series of novel nematic and chiral nematic glass-forming liquid crystals with a T . 3 6 0°C were synthesized for an investigation of handedness and helical twisting power, HTP, as functions of chemical structure.Three chiral building blocks with a single asymmetric carbon Centre were employed: (S)-( -)-1-phenylethanol, (9-( -)-u-methyl-2-naphthalenemethanol, and (S)-( -)-1-phenylethylamine, were all found to yield a left-handed cholesteric mesophase. With reference to (5')-( -)-1-phenylethanol, the HTP value was found to be nearly doubled in the presence of a strong anchoring plane furnished by a naphthyl group surrounding the asymmetric carbon centre, but reduced by one third in the presence of intermolecular hydrogen bonding through the amide group. All these observations were properly accounted for by a molecular interaction model of a steric nature while allowing for hydrogen bonding. Consistent with previous observations on naturally occurring ( -)-cholesterol, ( + )-estrone was found to give a left-handed cholesteric mesophase and an HTP value a quarter of that of (8-( -)-1-phenylethanol under otherwise identical structural settings, both remaining unaccounted for from a molecular point of view. The cyclohexane ring to which chiral as well as nematic precursors are attached was found to improve miscibility with cyclohexane-based nematic hosts and to elevate the T . of the blends with an improved morphological stability but a very modest increase in HTP, all in comparison to c h i d precursors as the dopant. The optical elements prepared on a single glass substrate and between a pair of substrates using the presently reported materials showed broad selective wavelength reflection bands with a monodomain feature characterized by pronounced side band oscillations.

Short wavelength light reflecting films from side‐chain liquid crystal homopolymers with chiral spacers

“…These optical properties result from the helical arrangement of chiral molecules in the nematic state that induce a twist in the director of adjacent molecules thereby forming a supermolecular helicoidal structure with pitch P corresponding to a 2p twist of the nematic director [2]. Low molar mass glass forming chiral nematics are rare and tend to be limited by the tendency to crystallise over time causing light scattering from grain boundaries [3]. After the discovery of the spacer concept [4,5] side chain liquid crystal polymers (SCLCPs) can be synthesised which combine the well developed chemistry and physical properties of low molar mass liquid crystals with those of conventional polymers.…”

Molecular Dynamics and Kinetics of Isothermal Cold Crystallization in the Chiral Smectogenic 3F7FPhH6 Glassformer

“…For a few of the mentioned fluorinated smectogens, the glass transition of the SmC * A phase was reported, even for slow cooling (1 K/min or at an even lower rate, enough to avoid crystallization) [12][13][14][15][16][17][18]. It allows for the obtainment of glass with anisotropic properties, whose practical application was already proposed both for smectic and nematic glassformers [19][20][21][22][23]. In this study, we report results regarding the vitrification of the SmC *…”

Vitrified Chiral−Nematic Liquid Crystalline Films for Selective Reflection and Circular Polarization

“…Vitrifiable chiral−nematic liquid crystals consist of a volume-excluding central core to which nematogenic and chiral pendants are chemically bonded . Although all three structural elements are crystalline as separate entities, the hybrid system readily forms macroscopically ordered glass on cooling without residual crystallinity or a tendency toward spontaneous crystallization .…”

“…One unique feature of VLCs is that the molecular order can be frozen in the solid state, thereby rendering device robustness. In particular, both right- and left-handed materials were made available using a pair of enantiomers as the chiral building block . In the present study, nematic and left-handed chiral−nematic VLCs were synthesized based on a cyclohexane core with methoxybiphenylbenzoate and ( S )−(−)-1-phenylethylamine pendants.…”