Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

Abstract

SummaryThe addition of a chiral non-racemic dopant to a nematic liquid crystal (LC) has the effect of transferring the molecular chirality to the phase organization and a chiral nematic phase is formed. This molecular chirality amplification in the LC provides a unique possibility for investigating the relationship between molecular structure, intermolecular interactions, and mesoscale organization. It is known that axially chiral or helical-shaped molecules with reduced conformational disorder are good candidates for high helical twisting power derivatives. In particular, biaryl derivatives are known to be efficient chiral inducers in biaryl nematic mesophases. In this paper, we focus on a new series of helicene-like molecules of known absolute configuration. We have integrated cholesteric pitch measurements with geometry optimization by DFT calculations and analysis of the twisting ability by the Surface Chirality model to shed light on the structural features responsible for the analogies and differences exhibited by these derivatives. The investigation of these dopants with well-defined geometry, by virtue of the low conformational freedom, and the substituents variously distributed around the core, allows us to extend our knowledge of the molecular origin of the chirality amplification in liquid crystals and to confirm the simple relationship “molecular P-helicity” → “cholesteric P-handedness” for helical-shaped helicene-like derivatives.

A helical naphthopyran dopant for photoresponsive cholesteric liquid crystals

“…[6][7][8][9][10][11][12][13][14] Among the dopants for CLCs, helicene-like molecules are well known to provide amplified chirality transfer to the nematic host because of their intrinsic helical conformation. 15,16 However, photoisomerizable helicene derivatives are rather unexplored as photoresponsive dopants compared to photochemically reversible P-type molecules, such as diarylethenes and azobenzenes. [1][2][3][4][5][6] Recently, Frigoli et al reported on the novel photochromism of helical naphthopyrans overcoming fast thermal relaxation, 17,18 and we anticipated that its reversible conformational change could provide efficient superstructural manipulation of CLCs.…”

Mechanisms of Chiral Transfer in Optically Active Dopant – Nematic Liquid Crystal Systems

“…Вышеперечисленные возможности использования систем с индуцированными спиральными ЖК-фазами связаны с уникальным явлениемусилением молекулярной хиральности в анизотропных средах [29,30]. Это явление обеспечивает детектирование следов энантиомеров по их хиральной индукции, намного более чувствительное по сравнению с другими методами [31].…”

Chiral Dopants Derived from Ephedrine/Pseudoephedrine: Structure and Medium Effects on the Helical Twisting Power

“…Apart from the classical cholesterol ester, there is a huge number of appropriate compounds, such as derivatives of carbohydrates [1], 1,2-ethandiol [2], tartaric acid [3], bi-2-naphthol [4], helicene [5], or more recently phenyl-ethylamine alkaloids [6]. In comparison to the use of a single mesogenic substance with inherent chirality, mixtures prepared by doping offer considerably more possibilities to tune the materials properties (helical structure, phase range, optic and dielectric key figures).…”